Illustrated Dictionary of
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Illustrated Dictionary
of Electronics
Eighth Edition
Stan Gibilisco
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DOI: 10.1036/0071389660
To Tony, Tim, and Samuel
from Uncle Stan
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Preface ix
Acknowledgments xi
Dictionary 1
Appendix A Schematic Symbols 773
Appendix B Tables and Data 787
Copyright © 2001 by The McGraw-Hill Companies, Inc.
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The Illustrated Dictionary of Electronics—8th Edition has been revised, clarified, and updated, reflecting technological advances of recent years. New definitions have been added in
the fields of wireless technology, robotics, and artificial intelligence. Every effort has been
made to be concise and accurate, without “talking down” to the reader.
Many definitions contain cross references (indicated in ALL CAPITALS); these provide
recommended additional information or allow comparison with related terms. Expressions of
special significance are printed in italics. Electronics abbreviations are included in the text;
the full terms are stated as definitions.
While an effort has been made to avoid superfluous mathematics, equations are sometimes necessary to completely and effectively define a term. Mathematics beyond the highschool level has not been used.
Appendix A contains the standard symbols used in electrical and electronic diagrams.
These symbols are used in illustrations throughout this dictionary. Appendix B contains the
following data tables:
Conversion between electrical systems
Greek alphabet
Mathematical functions and operations
Prefix multipliers
Resistor color code
Suggestions for future editions are welcome.
Stan Gibilisco
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Illustrations in this book were generated with CorelDRAW. Some clip art is courtesy of Corel
Corporation, 1600 Carling Avenue, Ottawa, Ontario, Canada K1Z 8R7.
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Illustrated Dictionary of
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1. Symbol for GAIN. 2. Symbol for AREA. 3. Symbol for AMPERE (SI unit for current).
Aⴚ Symbol for negative terminal of filament-voltage
source in a vacuum-tube circuit.
Aⴙ Symbol for positive terminal of filament-voltage
source in a vacuum-tube circuit.
a 1. Abbreviation of ATTO- (prefix). 2. Abbreviation
of AREA. 3. Abbreviation of ACCELERATION.
4. Abbreviation of ANODE. 5. Obsolete abbreviation of cgs prefix AB-.
aA 1. Abbreviation of attoampere. 2. Obsolete for
AAAS Abbreviation for American Association for the
Advancement of Science.
AAC Abbreviation of automatic aperture control
AAS Abbreviation of advanced antenna system
AASR Abbreviation of airport and airways surveillance radar.
AB Abbreviation of acquisition beacon (NASA).
A-B In sound and acoustics, the direct comparison
of two sources of sound by alternately turning on
one and the other.
ab- 1. Prefix that transforms the name of a practical electrical unit to that of the equivalent electromagnetic cgs unit (e.g., ABAMPERE, ABOHM,
ABVOLT). See individual entries of such cgs
units. 2. Abbreviation for ABSOLUTE.
abac A graphic device for the solution of electronics
problems. Also see ALIGNMENT CHART.
abampere The unit of current in the cgs electromagnetic system. One abampere equals 10
amperes and corresponds to 1 abcoulomb per
Abbe condenser 1. In microscopy, a special twopiece lens that has enhanced light-gathering
power. 2. A similar focusing device in an electromagnetic antenna.
abbreviated dialing In telephone systems, special
circuits requiring fewer-than-normal dialing operations to connect subscribers.
abc 1. Abbreviation of AUTOMATIC BASS COMPENSATION, a system for boosting the volume of
bass sounds at low amplifier gain. 2. Abbreviation of AUTOMATIC BIAS CONTROL. 3. Abbreviation of AUTOMATIC BRIGHTNESS CONTROL.
abcoulomb The unit of electrical quantity in the
cgs electromagnetic system. One abcoulomb
equals 10 coulombs and is the quantity of electricity that flows past any point in a circuit in one
second when the current is one abampere.
aberration 1. Distortion from perfect shape in a
lens or reflecting mirror or antenna dish. 2. A
small error in the determination of the direction
of a source of electromagnetic energy, on account
of the motion of the source and/or the detecting
apparatus. 3. A small displacement in the apparent positions of the stars from month to month on
account of the earth’s orbital motion.
ABETS Acronym for airborne beacon electronic test
set (NASA).
abfarad The unit of capacitance in the cgs electromagnetic system. One abfarad equals 109 farads
and is the capacitance across which a charge of
1 abcoulomb produces a potential of 1 abvolt.
abhenry The unit of inductance in the cgs electromagnetic system. One abhenry equals 10–9 henry
Copyright © 2001 by The McGraw-Hill Companies, Inc.
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abhenry • absolute error
and is the inductance across which a current
that changes at the rate of 1 abampere per second induces a potential of 1 abvolt.
ABL Abbreviation of Automated Biology Laboratory
abmho The obsolete unit of conductance and of
conductivity in the cgs electromagnetic system.
Replaced with ABSIEMENS.
abnormal dissipation Power dissipation higher or
lower than the customary level, usually an overload.
abnormal oscillation 1. Oscillation where none is
desired or expected, as in an amplifier. 2. Oscillation at two or more frequencies simultaneously
when single-frequency operation is expected.
3. Oscillation at an incorrect frequency. 4. Parasitic
abnormal propagation 1. The chance shifting of
the normal path of a radio wave, as by displacements in the ionosphere, so that reception is degraded. 2. Unintentional radiation of energy from
some point other than the transmitting antenna.
3. Propagation over a path or in a direction not
abnormal reflections Sharp, intense reflections at
frequencies higher than the critical frequency of
the ionosphere’s ionized layer.
abnormal termination The shutdown of a running
computer program or other process. Caused by
the detection of an error by the associated hardware that indicates that some ongoing series of
actions cannot be executed correctly.
abnormal triggering The false triggering or switching of a circuit or device, such as a flip-flop, by
some undesirable source instead of the true trigger
signal. Electrical noise pulses often cause abnormal triggering.
abohm The unit of resistance and of resistivity in
the cgs electromagnetic system. One abohm
equals 10–9 ohms and is the resistance across
which a steady current of 1 abampere produces a
potential difference of 1 abvolt.
abort To deliberately terminate an operation, experiment, process, or project before it has run its
normal course.
AB power pack 1. A portable dry-cell or wet-cell
array containing both A and B batteries in one
package. 2. An ac-operated unit in one package
for supplying A and B voltages to equipment normally operated from batteries.
abrasion machine An instrument for determining
the abrasive resistance of a wire or cable.
abrasion resistance A measure of the ability of a
wire or wire covering to resist mechanical damage.
ABS A basic programming abbreviation for the absolute value (of a number, variable, or expression).
abscissa 1. The independent variable in a function.
2. The axis (usually horizontal) on the graph of a
function that indicates the independent variable.
absence-of-ground searching selector A rotary
switch that searches for an ungrounded contact
in a dial telephone system.
absiemens The unit of conductance or conductivity in the cgs electromagnetic system. One
absiemens equals 109 siemens and is the
conductance through which a potential of 1 abvolt forces a current of 1 abampere.
absolute 1. A temperature scale in which zero represents the complete absence of heat. Units of measure are same as units on Celsius and Fahrenheit
scales. See ABSOLUTE SCALE. 2. Independent of
any arbitrarily assigned units of measure or value.
absolute accuracy The full-scale accuracy of a meter with respect to a primary (absolute) standard.
absolute address In a digital computer program,
the location of a word in memory, as opposed to
location of the word in the program.
absolute code A computer code in which the exact
address is given for storing or locating the reference operand.
absolute coding In computer practice, coding that
uses absolute addresses.
absolute constant A mathematical constant that
has the same value wherever it is used.
absolute delay The time elapsing between the
transmission of two synchronized signals from
the same station or from different stations, as in
radio, radar, or loran. By extension, the time interval between two such signals from any source,
as from a generator.
absolute digital position transducer A digital position transducer whose output signal indicates
absolute position. (See ENCODER.)
absolute efficiency The ratio Xx/Xs, where Xx is
the output of a given device, and Xs is the output
of an ideal device of the same kind under the
same operating conditions.
absolute encoder system A system that permits
the encoding of any function (linear, nonlinear,
continuous, step, and so on) and supplies a nonambiguous output.
absolute error The difference indicated by the approximate value of a quantity minus the actual
absolute error • absolute tolerance
value. This difference is positive when the approximate value is higher than the exact value,
and it is negative when the approximate value is
lower than the exact value. Compare RELATIVE
absolute gain Antenna gain for a given orientation
when the reference antenna is isolated in space
and has no main axis of propagation.
absolute humidity The mass of water vapor per
unit volume of air. Compare RELATIVE HUMIDITY.
absolute instruction A computer instruction that
states explicitly and causes the execution of a
specific operation.
absolute magnitude For a complex number quantity, the vector sum of the real and imaginary
components (i.e., the square root of the sum of
the squares of those components). Also see ABSOLUTE VALUE and IMPEDANCE.
absolute maximum rating The highest value a
quantity can have before malfunction or damage
absolute maximum supply voltage The highest
supply voltage that can be applied to a circuit
without permanently altering its characteristics.
absolute measurement of current Measurement
of a current directly in terms of defining quantities. 1. TANGENT GALVANOMETER method:
Current is proportional to the tangent of the angle of deflection of the needle of this instrument.
Deflection depends on torque, resulting from the
magnetic field produced by current in the galvanometer coil acting against the horizontal
component of the earth’s magnetic field.
2. ELECTRODYNAMOMETER method: With this
2-coil instrument, current is determined from
the observed deflection, the torque of the suspension fiber of the movable coil, and the coil dimensions.
absolute measurement of voltage Measurement
of a voltage directly in terms of defining quantities. 1. CALORIMETRIC method: A currentcarrying coil immersed in water raises the
temperature of the water. The difference of
potential that forces the current through the coil
then is determined in terms of the equivalent heat
energy. 2. Disk-electrometer method: In this
setup, a metal disk attached to one end of a
balance beam is attracted by a stationary disk
mounted below it, the voltage being applied to the
two disks. The other end of the beam carries a
pan into which accurate weights are placed. At
balance, the voltage is determined in terms of the
weight required to restore balance, the upper-disk
area, and the disk separation.
absolute minimum resistance The resistance between the wiper and the nearer terminal of a potentiometer, when the wiper is as close to that
terminal as physically possible. All potentiometers have two such specifications, one for each
end terminal.
absolute Peltier coefficient The product of the
absolute Seebeck coefficient and absolute temperature of a material.
absolute pitch A tone in a standard scale, determined according to the rate of vibration, independent of other tones in the range of pitch.
absolute pressure Pressure (force per unit area) of
a gas or liquid determined with respect to that of
a vacuum (taken as zero).
absolute-pressure transducer A transducer actuated by pressure from the outputs of two different
pressure sources, and whose own output is proportional to the difference between the two applied pressures.
absolute scale 1. A scale in which the zero value
indicates the lowest physically possible value that
a parameter can attain. 2. A standard scale
for measurement of a quantity. 3. A universally
agreed-upon scale for the determination of a variable quantity. 4. The Kelvin temperature scale.
5. The Rankine temperature scale.
absolute Seebeck coefficient The quotient, as an
integral from absolute zero to the given temperature, of the Thomson coefficient of a material divided by its absolute temperature.
absolute spectral response The frequency output
or response of a device in absolute power units
(such as milliwatts) as opposed to relative units
(such as decibels).
absolute system of units A system of units in
which the fundamental (ABSOLUTE) units are
those expressing length (l), mass (m), charge (q),
and time (t). All other physical units, including
practical ones, are then derived from these absolute units.
absolute temperature Temperature measured on
either the Kelvin or Rankine scales, where zero
represents the total absence of heat energy.
absolute temperature scale 1. The Kelvin temperature scale, in which the divisions are equal in
size to 1° Celsius, and the zero point is absolute
zero, the coldest possible temperature, approximately –273.16° Celsius. 2. The Rankine temperature scale, in which the divisions are equal in
size to 1° Fahrenheit, and the zero point is absolute zero or approximately –459.7° Fahrenheit.
absolute tolerance The value of a component as it
deviates from the specified or nominal value. It is
usually expressed as a percentage of the specified
absolute units • A-B test
absolute units Fundamental physical units (see
others are derived. See, for example, AMPERE,
absolute value The magnitude of a quantity without regard to sign or direction. The absolute value
of a is written |a|. The absolute value of a positive number is the number itself; thus, |10|
equals 10. The absolute value of a negative number is the number with its sign changed: |-10|
equals 10.
absolute-value circuit A circuit that produces a
unipolar signal in response to a bipolar input and
in proportion to the absolute value of the magnitude of the input.
absolute-value computer A computer in which
data is processed in its absolute form; i.e., every
variable maintains its full value. (Compare to
absolute-value device In computer practice, a device that delivers a constant-polarity output
signal equal in amplitude to that of the input
signal. Thus, the output signal always has the
same sign.
zero The
(459.7°F and 0 Kelvin). The coldest possible
temperature, representing the complete absence
of heat energy.
absorbed wave A radio wave that dissipates in the
ionosphere as a result of molecular agitation.
This effect is most pronounced at low and
medium frequencies.
absorptance The amount of radiant energy absorbed in a material; equal to 1 minus the transmittance.
absorption The taking up of one material or medium by another into itself, as by sucking or
soaking up. Also, the retention of one medium (or
a part of it) by another medium, through which
the first one attempts to pass. See, for example,
absorption band See ABSORPTION SPECTRUM.
absorption circuit A circuit that absorbs energy
from another circuit or from a signal source—especially a resonant circuit, such as a wavemeter
or wavetrap.
absorption current In a capacitor, the current resulting from absorption of energy by the dielectric
absorption dynamometer A power-measuring instrument in which a brake absorbs energy from a
revolving shaft or wheel.
absorption fading Fading of a radio wave, resulting from (usually) slow changes in the absorption
of the wave in the line of propagation.
absorption frequency meter See WAVEMETER.
absorption line See ABSORPTION SPECTRUM.
absorption loss 1. Transmission loss caused by
dissipation of electrical energy, or conversion of it
into heat or other forms of energy. 2. Loss of all or
part of a skywave because of absorption by the
ionosphere. Also called ionospheric absorption or
atmospheric absorption.
absorption marker A small blip introduced onto
an oscilloscope trace to indicate a frequency
point. It is so called because it is produced by the
action of a frequency-calibrated tuned trap, similar to an absorption wavemeter.
absorption modulation Amplitude modulation of a
transmitter or oscillator by means of an audiofrequency-actuated absorber circuit. In its simplest
form, the modulator consists of a few turns of wire
coupled to the transmitter tank coil and connected to a carbon microphone. The arrangement
absorbs energy from the transmitter at a varying
rate as the microphone changes its resistance in
accordance with the sound waves it receives.
absorption spectrum For electromagnetic waves, a
plot of absorption coefficient (of the medium of
propagation) versus frequency. Also called EMISSION SPECTRUM.
absorption trap See WAVETRAP.
absorption wavemeter A resonant-frequency indicating instrument that is inductively coupled to
the device under test.
absorptivity In audio and microwave technologies,
a measure of the energy absorbed by a given volume of material.
A-B test Comparison of two sounds by reproducing them in alternating succession.
abvolt • accentuation
abvolt The unit of potential difference in the cgs
electromagnetic system. One abvolt equals 10–8 V
and is the difference of potential between any two
points when 1 erg of work is required to move 1
abcoulomb of electricity between them.
abwatt The unit of power in the cgs electromagnetic
system. One abwatt equals 107 W and is the
power corresponding to 1 erg of work per second.
ac 1. Abbreviation of ALTERNATING CURRENT.
2. Abbreviation of ATTITUDE CONTROL. 3. Abbreviation of AERODYNAMIC CENTER. 4. A suffix meaning AUTOMATIC CALCULATOR or
a/c 1. Abbreviation of AIRCRAFT. 2. Abbreviation
Ac Symbol for ACTINIUM.
ACA Abbreviation of automatic circuit analyzer.
ac base current Symbol, IB(ac). The ac component of
base current in a bipolar transistor.
ac base resistance Symbol, RB (ac). The dynamic
base resistance in a bipolar transistor.
ac base voltage Symbol, VB(ac). The ac component
of base voltage in a bipolar transistor. It is the ac
input signal voltage in a common-emitter amplifier or emitter-follower amplifier.
ac bias In a tape recorder, the high-frequency current that passes through the recording head to
linearize operation.
acc 1. Abbreviation of AUTOMATIC CHROMINANCE CONTROL. 2. Abbreviation of AUTOMATIC COLOR COMPENSATION. 3. Abbreviation
ac cathode current Symbol, IK(ac). The ac component of cathode current in an electron tube.
ac cathode resistance Symbol, RK(ac). The dynamic
cathode resistance in an electron tube. RK(ac)
equals dVK/dIK for a constant value of VG.
ac cathode voltage Symbol, VK(ac). The ac component of cathode voltage in an electron tube. It is
the ac output signal voltage in cathode-follower
and grounded-grid amplifiers.
accelerated life test A test program that simulates the effects of time on devices or apparatus,
by artificially speeding up the aging process.
accelerated service test A service or bench test in
which equipment or a circuit is subjected to an
extreme condition in an attempt to simulate the
effects of average use over a long time.
accelerating conductor or relay A conductor or
relay that prompts the operation of a succeeding
device in a starting mode according to established
accelerating electrode In a cathode-ray tube or
klystron, the electrode to which the accelerating
voltage is applied.
accelerating time The elapsed time that starts
when voltage is applied to a motor, and ends
when the motor shaft reaches maximum speed.
accelerating voltage A positive high voltage applied
to the accelerating electrode of a cathode-ray tube
to increase the velocity of electrons in the beam.
acceleration at stall The angular acceleration of a
servomotor at stall, determined from the stall
torque and the moment of inertia of the motor’s
acceleration derivative Acceleration (a) expressed
as the second derivative of distance (s) with respect to time (t): a equals d 2s/dt 2.
potential See
acceleration switch A switch that operates automatically when the acceleration of a body to
which it is attached exceeds a predetermined rate
in a given direction.
acceleration time The time required by a computer to take in or deliver information after interpreting instructions. Compare ACCESS TIME.
acceleration torque During the accelerating period of a motor, the difference between the torque
demanded and the torque actually produced by
the motor.
acceleration voltage The potential between accelerating elements in a vacuum tube, the value of
which determines average electron velocity.
accelerometer A transducer whose output voltage
is proportional to the acceleration of the moving
body to which it is attached.
accentuation The emphasis of a desired band of
frequencies, usually in the audio-frequency spectrum.
accentuator • accuracy rating
RC(ac) equals dVC/dIC for a constant value of base
current IB (in a common-emitter circuit) or emitter current IE (in a common-base circuit).
ac collector voltage Symbol, VC(ac). The ac component of collector voltage in a bipolar transistor.
The ac output signal voltage in a common-emitter
or common-base amplifier.
accompanying audio channel The RF signal that
supplies television sound. Also called Cochannnel
sound frequency.
ac component In a complex wave (i.e., one containing both ac and dc), the alternating, fluctuating, or pulsating part of the combination.
accordion A printed-circuit connector contact with
a Z-shaped spring that allows high deflection
with low fatigue.
ac-coupled flip-flop A flip-flop that is operated by
the rise or fall of a clock pulse.
ac coupling Transformer coupling or capacitive
coupling, which transmit ac, but not dc. Compare
accentuator A circuit or device, such as a filter,
tone control, or equalizer, used to emphasize a
band of frequencies, usually in the audiofrequency spectrum. Also see ACCENTUATION.
acceptable-environmental-range test A test to
disclose the environmental conditions that equipment can endure while maintaining at least the
minimum desired reliability.
acceptable quality level Abbreviation, AQL. A percentage that represents an acceptable average of
defective components allowable for a process, or
the lowest quality that a supplier is permitted to
regularly present for acceptance.
acceptance sampling plan A probabilistic method
of sampling a quantity of units from a lot, and determining from the sample whether to accept the
lot, reject the lot, or perform another sampling.
acceptance test A test performed on incoming
equipment or on submitted samples to determine
if they meet tester’s or supplier’s specifications.
acceptor 1. Any device or circuit, such as a seriesresonant circuit, that provides relatively easy
transmission of a signal, in effect accepting the
signal. 2. A hole-rich impurity added to a semiconductor to make the latter p-type. It is so called
because its holes can accept electrons. Compare
acceptor circuit See ACCEPTOR, 1.
acceptor impurity See ACCEPTOR, 2.
access 1. To gain entrance to something, such as
the interior of the cabinet of a high-fidelity amplifier. 2. In a computer, the action of going to a specific memory location for the purpose of data
retrieval. 3. A port or opening into a piece of
equipment, placed there to make the equipment
easy to maintain and repair.
access arm A mechanical device that positions the
read/write mechanism in a computer storage unit.
access control register A register that is part of a
computer protection system that prevents interference between different software modules.
access method A method of transferring information or data from main storage to an input/output unit.
access right The access status given to computer
system users that indicates the method of access
permitted (e.g., read a file only or write to a file).
access time The time required by a computer to
begin delivering information after the memory or
storage has been interrogated.
accidental error An unintentional error committed by a person making measurements and
recording data.
accidental triggering The undesired chanceoperation of a flip-flop or other switching circuit
caused by a noise pulse or other extraneous signal.
ac collector current Symbol, IC(ac). The ac component of collector current in a bipolar transistor.
ac collector resistance Symbol, RC(ac). The dynamic collector resistance of a bipolar transistor.
accumulator 1. In a digital computer, a circuit or
register device that receives numbers, totals
them, and stores them. 2. Storage battery.
accuracy 1. Precision in the measurement of
quantities and in the statement of physical characteristics. 2. Degree of precision. Usually expressed, in terms of error, as a percentage of the
specified value (e.g., 10 V plus or minus 1%), as a
percentage of a range (e.g., 2% of full scale), or as
parts (e.g., 100 parts per million).
accuracy rating The maximum error in an instrument, given as a percentage of the full-scale
accw • ac magnetic bias
accw Abbreviation of ALTERNATING-CURRENT
ac/dc Abbreviation of ALTERNATING CURRENT/
DIRECT CURRENT. Pertains to equipment that
will operate from either ac utility power or a dc
power source. A notebook computer is a good example.
ac directional overcurrent relay A relay that
works on a specific value of alternating overcurrent that is rectified for a desired polarity.
ac drain current Symbol, ID(ac). The ac component
of drain current in a field-effect transistor.
ac drain resistance Symbol, RD(ac). The dynamic
drain resistance in a field-effect transistor; RD(ac)
equals dVD/dID for a constant value of gate voltage VG.
ac drain voltage Symbol, VD(ac). The ac component
of drain voltage in a field-effect transistor. The ac
output signal voltage in a common-source FET
ac dump The removal of all ac power from a system
or component.
ac emitter current Symbol, IE(ac). The ac component of emitter current in a bipolar transistor.
ac emitter resistance Symbol, RE(ac). The dynamic
emitter resistance of a bipolar transistor; RE(ac)
equals dVE/dIE for a constant value of base current IB (in an emitter-follower circuit) or collector
voltage VCC (in a common-base circuit).
ac emitter voltage Symbol, VE(ac). The ac component of emitter voltage in a bipolar transistor. The
ac input signal voltage in a common-base amplifier; the ac output signal voltage in an emitterfollower amplifier.
ac equipment An apparatus designed for operation from an ac power source only. Compare DC
ac erasing In tape recording, the technique of using an alternating magnetic field to erase material
already recorded on the tape.
ac erasing head Also called ac erase head. In tape
and wire recording, a head that carries alternating current to erase material already recorded on
the tape or wire. Also see AC ERASING.
acetate Cellulose acetate, a tough thermoplastic
material that is an acetic acid ester of cellulose. It
is used as a dielectric and in the manufacture of
photographic films.
acetate base 1. The cellulose acetate film that
served as the base for the magnetic oxide coating
in early recording tape. Most such tapes today
are of polyester base. 2. The cellulose acetate
substrate onto which certain photosensitive materials are deposited for lithographic reproduction. Also see ACETATE and ANCHORAGE.
acetate tape Recording tape consisting of a magnetic oxide coating on a cellulose acetate film.
ac gate voltage Symbol, VG(ac). The ac component
of gate voltage in a field-effect transistor. The ac
input signal voltage.
ac generator 1. A rotating electromagnetic machine that produces alternating current (e.g., a
dynamo or alternator). 2. An oscillator or combination of an oscillator and an output amplifier.
ac grid voltage Symbol, VG(ac). The ac component
of control grid voltage in an electron tube. The ac
input signal voltage in a common-cathode amplifier or cathode follower.
A channel The left channel of a two-channel stereo
achieved reliability A statement of reliability based
on the performance of mass-produced parts or
systems under similar environmental conditions.
achromatic 1. Without color. In a TV image, the
tones from black through gray to white. The term
occasionally refers to black-and-white television,
although MONOCHROMATIC is more often used
in this sense.
achromatic locus Also called achromatic region.
An area on a chromaticity diagram that contains
all points, representing acceptable reference
white standards.
achromatic scale A musical scale without accidentals.
ACIA Abbreviation of asynchronous communications interface adapter.
acicular Pertaining to the shape of magnetic particles on recording tape. Under magnification,
these particles look like thin rods.
acid A substance that dissociates in water solution
and forms hydrogen (H) ions (e.g., sulfuric acid).
Compare BASE, 2.
acid depolarizer Also called acidic depolarizer.
An acid, in addition to the electrolyte, used in
some primary cells to slow the process of polarization.
ac line A power line that delivers alternating current only.
ac line filter A filter designed to remove extraneous signals or electrical noise from an ac power
line, while causing virtually no reduction of the
power-line voltage or power.
ac line voltage The voltage commonly delivered
by the commercial power line to consumers. In
the United States, the two standards are 117 V
and 234 V (~ about 5 percent). The lower voltage
is used by most appliances; the higher voltage is
intended for appliances and equipment that
draws high power, such as electric ovens, cooking ranges, clothes dryers, and amateur-radio
amplifiers. In Europe, 220 V is the common
aclinic line Also called magnetic equator. An imaginary line drawn on a map of the world or of an
area that connects points of zero inclination (dip)
of the needle of a magnetic compass.
ACM Abbreviation for Association for Computing
ac magnetic bias See AC BIAS.
ac meter • acoustic feedback
ac meter A meter that is intended to work only on
alternating current or voltage. Such meters include iron-vane and rectifier types.
ac noise 1. Electromagnetic interference originating in the ac power lines. 2. Electrical noise of a
rapidly alternating or pulsating nature.
ac noise immunity In computer practice, the ability of a logic circuit to maintain its state, despite
excitation by ac noise.
acous Abbreviation for ACOUSTIC.
acoustic Pertaining to audible sound disturbances, usually in air (versus audio-frequency
currents or voltages).
acoustic absorption The assimilation of energy
from sound waves passing through or reflected by
a given medium.
acoustic absorption loss That portion of sound
energy lost (as by dissipation in the form of heat)
acoustic absorptivity The ratio of sound energy
absorbed by a material to sound energy striking
the surface of the material.
acoustic attenuation constant The real-number
component of the complex acoustical propagation
constant, expressed in nepers per unit distance.
acoustic burglar alarm An alarm that receives the
noise made by an intruder. The alarm device responds to the impulses from concealed microphones.
acoustic capacitance The acoustic equivalent of
electrical capacitance.
acoustic clarifier In a loudspeaker system, a set of
cones attached to the baffle that vibrate to absorb
and suppress sound energy during loud bursts.
acoustic communication Communications by
means of sound waves. This can be through the
atmosphere, or it can be through solids or liquids, such as a taut wire, a body of water, or the
acoustic compliance COMPLIANCE in acoustic
transducers, especially loudspeakers. It is equivalent to electrical capacitive reactance.
acoustic consonance An effect that occurs when
two objects are near each other but not in physical
contact, and both have identical or harmonically
related resonant frequencies. An example is shown
by two tuning forks with identical fundamental fre-
quencies. If one fork is struck and then brought
near the other, the second fork will begin vibrating.
If the second fork has a fundamental frequency
that is a harmonic of the frequency of the first fork,
the second fork will vibrate at its own resonant
acoustic coupling Data transfer via a sound link
between a telephone and a pickup/reproducer.
Was once common in computer terminals and
facsimile machines. This scheme has been largely
replaced by hard wiring and optical coupling.
acoustic damping The deadening or reduction of
the vibration of a body to eliminate (or cause to
die out quickly) sound waves arising from it.
acoustic delay line Any equivalent of a special
transmission line that introduces a useful time
delay between input and output signals. In one
form, it consists of a crystal block or bar with an
input transducer at one end and an output transducer at the other. An electrical input signal in
the first transducer sets up sound waves that
travel through the interior of the crystal; the
piezoelectric reaction of the crystal to sound vibrations sets up an output voltage in the second
transducer. The delay is caused by the time required for the acoustic energy to travel the length
of the crystal bar.
acoustic depth finder A direct-reading device for
determining the depth of a body of water, or for
locating underwater objects via sonic or ultrasonic waves transmitted downward and reflected
back to the instrument.
acoustic dispersion Variation of the velocity of
sound waves, depending on their frequency.
acoustic elasticity 1. In a loudspeaker enclosure,
the compressibility of air behind the vibrating
cone of the speaker. 2. In general, the compressibility of any medium through which sound
acoustic electric transducer A transducer, such
as a microphone or hydrophone, that converts
sound energy into electrical energy. Compare
acoustic feedback A usually undesirable effect
that occurs when sound waves from a loudspeaker (or other reproducer) reach a microphone
(or other input transducer) in the same system.
acoustic feedback • acoustic radiator
This can cause an amplifier to oscillate, with a resultant rumbling, howling, or whistling.
acoustic filter Any sound-absorbing or transmitting arrangement, or combination of the two, that
transmits sound waves of desired frequency while
attenuating or eliminating others.
response The
soundfrequency range as a function of sound intensity.
A means of describing the performance of an
acoustic device.
acoustic generator A device that produces sound
waves of a desired frequency and/or intensity.
Examples are electrical devices (headphones or
loudspeakers operated from a suitable oscillator,
buzzer, bell, or flame) and mechanical devices
(tuning forks, bells, string, or whistles).
acoustic grating A set of bars or slits that are parallel to one another and arranged a fixed distance
apart so that an interference pattern forms as
sound passes through. Used to determine the
wavelength of acoustic waves.
acoustic homing system 1. A system that uses a
sound signal for guidance purposes. 2. A guidance method in which a missile homes in on
noise generated by a target.
acoustic horn A tapered tube (round or rectangular, but generally funnel-shaped) that directs
sound and, to some extent, amplifies it. So called
to distinguish it from a microwave horn.
acoustic howl See ACOUSTIC FEEDBACK.
acoustician 1. A person skilled in acoustics (an
acoustics technician). 2. An AUDIOLOGIST.
acoustic impedance Unit, ACOUSTIC OHM. The
acoustic equivalent of electrical impedance. Like
the latter, acoustic impedance is the total opposition encountered by acoustic force. Also like electrical impedance, acoustic impedance has
resistive and reactive components: ACOUSTIC
acoustic inductance Also called inertance. The
acoustic equivalent of electrical inductance.
acoustic inertance See ACOUSTIC INDUCTANCE.
acoustic inhibition See AUDITORY INHIBITION.
acoustic intensity See SOUND INTENSITY.
acoustic interferometer An instrument that evaluates the frequency and velocity of sound waves
in a liquid or gas, in terms of a standing wave set
up by a transducer and reflector as the frequency
or transducer-to-reflector distance varies.
acoustic labyrinth A loudspeaker enclosure
whose internal partitions form a maze-like path
or “tube” lined with sound-absorbing material.
The tube effectively runs from the back of the
speaker down to where it terminates in a MOUTH
or PORT that opens at the front of the enclosure.
The labyrinth provides an extremely efficient reproduction system because of its excellent acoustic impedance-matching capability.
acoustic lens A system of barriers that refracts
sound waves the way that an optical lens does
with light waves.
acoustic line Baffles or other such structures
within a speaker that act as the mechanical equivalent of an electrical transmission line to enhance
the reproduction of very low bass frequencies.
acoustic load A device that serves simultaneously
as the output load of an amplifier and as a transducer of electrical energy into acoustic energy
(e.g., headphones or a loudspeaker).
acoustic memory In a computer, a volatile memory element employing an acoustic delay line, often incorporating quartz or mercury as the
transmission and delay element.
acoustic mirage A type of sound distortion in
which the listener experiences the illusion of two
sound sources when there is only one. The phenomenon is caused by the effect of a large temperature gradient in the air or water through
which the sound passes.
acoustic mode Crystal-lattice vibration without
producing an oscillating dipole.
acoustic noise Interferential (usually disagreeable)
sounds carried by the air (or other propagation
medium) to the ear or to an acoustic transducer.
This is in contrast to electrical noise, which consists of extraneous current or voltage impulses
and is inaudible until converted into sound.
acoustic ohm The unit of acoustic resistance, reactance, or impedance. One acoustic ohm equals
the volume velocity of 1 cm/s produced by a
sound pressure of 1 microbar (0.1 Pa). Also called
acoustical ohm.
acoustic phase constant The imaginary-number
component of the complex acoustic propagation
constant expressed in radians per second or radians per unit distance.
acoustic phase inverter A bass reflex loudspeaker
acoustic pressure 1. The acoustic equivalent of
electromotive force, expressed in dynes per
square centimeter; also called acoustical pressure. 2. Sound pressure level.
acoustic propagation The transmission of sound
waves, or subaudible or ultrasonic waves, as a
disturbance in a medium, rather than as an electric current or electromagnetic field.
acoustic radiator A device that emits sound
waves. Examples are the cone of a loudspeaker,
the diaphragm of a headphone, and the vibrating
reed of a buzzer.
acoustic radiometer • ac plate resistance
acoustic radiometer An instrument for measuring
the intensity of a sound wave (see SOUND INTENSITY) in terms of the unidirectional steadystate pressure exerted at a boundary as a result
of absorption or reflection of the wave.
acoustic reactance Unit, ACOUSTIC OHM. The
imaginary-number component of ACOUSTIC
IMPEDANCE. It can take the form of ACOUSTIC
acoustic reflectivity The ratio Fr/Fi, where Fr is
the rate of flow of sound energy reflected from a
surface and Fi is the rate of flow of sound energy
incident to the surface.
acoustic refraction The deflection of sound waves
being transferred obliquely between media that
transmit sound at different speeds.
acoustic regeneration See ACOUSTIC FEEDBACK.
acoustic resistance Unit, ACOUSTIC OHM. The
real-number component of ACOUSTIC IMPEDANCE. The opposing force that causes acoustic
energy to be dissipated in the form of heat. It is
attributed to molecular friction in the medium
through which sound passes. See ACOUSTIC
acoustic resonance In an enclosed chamber with
walls that reflect sound waves, resonance that occurs at certain wavelengths because the echoes
combine in and out of phase. Speaker enclosures
almost always have resonance at certain frequencies. This effect can be used to an advantage when
it is necessary to get good bass (low-frequency)
response from a relatively small speaker.
acoustic resonator 1. A chamber, such as a box,
cylinder, or pipe, in which an air column resonates
at a particular frequency. 2. A piezoelectric, magnetostrictive, or electrostrictive body that vibrates
at a resonant audio frequency that is governed by
the mechanical dimensions of the body when an
audio voltage at that frequency is applied.
acoustics 1. The physics of sound. The study and
applications of acoustic phenomena. 2. The qualities of an enclosure or sound chamber (room,
auditorium, or box) that describe how sound
waves behave in it.
acoustic scattering The spreading of a sound
wave in many directions as a result of diffraction,
reflection, or refraction.
acoustic suspension A loudspeaker design that
allows exceptional low-frequency reproduction
for a fairly small physical size. An airtight enclosure is used to increase the tension on the
speaker cone.
acoustic system 1. A coordinated array of acoustic components (e.g., acoustic filters, resonators,
etc.) that responds to sound energy in a predetermined manner. 2. An audio-frequency system in
which sound energy is converted into electrical
energy, processed, and then reconverted into
sound energy for a clearly defined purpose.
acoustic telegraph A telegraph that gives audible
signals, as opposed to visual signals or printed
acoustic transducer 1. Any device, such as headphones or a loudspeaker, for converting audiofrequency electrical signals into sound waves. 2.
Any device, such as a microphone, for converting
sound waves into alternating, pulsating, or fluctuating currents.
acoustic transmission The direct transmission of
sound energy without the intermediary of electric
acoustic transmission system A set of components designed to generate acoustic waves.
acoustic transmissivity Also called acoustic
transmitivity. The ratio et/ei, where et is the
sound energy transmitted by a medium, and ei is
the incident sound energy reaching the surface of
the medium. Acoustic transmissivity is proportional to the angle of incidence.
acoustic treatment Application of sound-absorbing materials to the interior of an enclosure or
room to control reverberation.
acoustic wave The traveling vibration, consisting
of molecular motion, via which sound is transmitted through a gas, liquid or solid. Usually
refers to sound waves in air.
acoustic wave filter See ACOUSTIC FILTER.
acoustoelectric effect The generation of a voltage
across the faces of a crystal by sound waves traveling longitudinally through the crystal.
acoustoelectronics A branch of electronics concerned with the interaction of sound energy and
electrical energy in devices, such as surface-wave
filters and amplifiers. In such devices, electrically
induced acoustic waves travel along the surface
of a piezoelectric chip and generate electrical energy. Also called praetersonics and microwave
ac plate current Symbol, IP(ac). The ac component
of plate current in a vacuum tube.
ac plate resistance Symbol, RP(ac). The dynamic
plate resistance of an electron tube. RP(ac) equals
dEP/dIP, where EP is the plate voltage and IP is the
plate current, for a constant value for grid voltage EG.
ac plate voltage • active chord mechanism
ac plate voltage Symbol, EP(ac). The ac component
of plate voltage in an electron tube. The ac output-signal voltage in a common-cathode amplifier.
ac power Symbol, Pac. Unit, watt (W). The power
acting in an ac circuit, Pac equals EI cos q, where
E is in volts, I in amperes, and q is the phase angle. Compare DC POWER. Also see POWER.
ac power supply A power unit that supplies ac
only (e.g., ac generator, vibrator-transformer, oscillator, or inverter). Compare DC POWER
acquisition 1. The gathering of data from transducers or a computer. 2. Locating the path of an
orbiting body for purposes of collecting telemetered data. 3. Orienting an antenna for optimum
pickup of telemetered data.
acquisition and tracking radar An airborne or
ground radar, which locks in on a strong signal
and tracks the body that reflects (or transmits)
the signal.
acquisition radar A radar that spots an oncoming
target and supplies position data regarding the
target to a fire-control or missile-guidance radar,
which then tracks the target.
acr 1. Abbreviation of AUDIO CASSETTE RECORDER. 2. Abbreviation of AUDIO CASSETTE
ac reclosing relay The controlling component in
an alternating-current circuit breaker. It causes
the breaker to reset after a specified period of
ac relay A relay designed to operate on alternating
current without chattering or vibrating.
ac resistance Pure resistance in an ac circuit. Unlike reactance and impedance, which are also
forms of opposition to the flow of current, ac resistance introduces no phase shift.
acronym A word formed from letters or syllables
taken from other applicable words of a multiword
term. Acronyms are convenient for naming new
devices and processes in electronics. Usually, a
term is considered an acronym only when it is
spelled in all-capital letters; once the term is accepted and popularized, it is written as a conventional word and is no longer thought of as an
acronym. For example, LASER was once an
acronym for light amplification by the stimulated
emission of radiation. By the popularization process, the acronym became a conventional word
from which other terms (such as the verb “lase”)
were derived.
acrylic resin A synthetic resin used as a dielectric
and in electronic encapsulations. It is made from
acrylic acid or one of its derivatives.
ACS Abbreviation of automatic control system.
ac source current Symbol, IS(ac). The ac component
of source current in a field-effect transistor.
ac source resistance Symbol, RS(ac). The dynamic
source resistance in a field-effect transistor; RS(ac)
equals dVS/dIS for a constant value of VG.
ac source voltage Symbol, VS(ac). The ac component of source voltage in a field-effect transistor.
The ac output-signal voltage in a source-follower
(grounded-drain) FET amplifier.
acss Abbreviation of analog computer subsystem.
ac time overcurrent relay A device with a certain
time characteristic, which breaks a circuit when
the current exceeds a certain level.
actinic rays Short-wavelength light rays in the violet and ultraviolet portion of the spectrum that
give conspicuous photochemical action.
actinism The property whereby radiant energy
(such as visible and ultraviolet light, X-rays, etc.)
causes chemical reactions.
actinium Symbol, Ac. A radioactive metallic element. Atomic number, 89. Atomic weight, 227.
actinodielectric Exhibiting a temporary rise in
electrical conductivity during exposure to light.
actinoelectric effect The property whereby certain materials (such as selenium, cadmium sulfide, germanium, and silicon) change their
electrical resistance or generate a voltage on exposure to light. Also see ACTINODIELECTRIC.
actinometer An instrument for measuring the direct heating power of the sun’s rays or the actinic
power of a light source.
action current A small transient current that
flows in a nerve in the human body as a result of
activate To start an operation, usually by applying
an appropriate enabling signal.
activation 1. Supplying electrolyte to a battery cell
to prepare the cell for operation. 2. Causing the
acceleration of a chemical reaction.
activation time In the activation of a battery cell
(see ACTIVATION, 1), the interval between addition of the electrolyte and attainment of full cell
activator A substance added to an accelerator (see
ACCELERATOR, 3) to speed the action of the accelerator.
active Pertaining to a circuit or device that requires a power supply for its operation. This differs from a passive circuit or device, which
operates with no external source of power.
active antenna An antenna that uses a small
whip, loop, or ferrite loopstick with a high-gain
amplifier for receiving at very-low, low, medium,
and high radio frequencies (approximately 9 kHz
to 30 MHz).
active area The forward-current-carrying portion
of the rectifying junction of a metallic rectifier.
active arm See ACTIVE LEG.
active balance In telephone repeater operation, the
sum of return currents at a terminal network balanced against the local circuit or drop resistance.
active chord mechanism Abbreviation, ACM. In
robots, an electromechanical gripper capable of
conforming to irregular objects. It has a structure
similar to the human spine, with numerous
small, rigid links connected by hinges.
active communications satellite • active repair time
active communications satellite A satellite containing receivers (which pick up beamed electromagnetic signals from a ground point and amplify
them) and transmitters (which send signals back
to the surface of the earth). Also called active
active component 1. A device capable of some dynamic function (such as amplification, oscillation, or signal control) that usually requires a
power supply for its operation. Examples include
bipolar transistors, field-effect transistors, and
integrated circuits. Compare PASSIVE COMPONENT. 2. In an ac circuit, a quantity that contains no reactance so that the current is in phase
with the voltage.
active component of current See ACTIVE CURRENT.
active computer A computer in an installation or
network that is processing data.
active control system A device or circuit that
compensates for irregularities in the operating
active current In an ac circuit, the current component that is in phase with the voltage. This is in
contrast to reactive current, which is not in phase
with the voltage, and is “inactive,” with respect to
power in the circuit. The active current is equal to
the average power divided by the effective voltage.
active decoder An automatic ground-station device that gives the number or letter designation of
a received radio beacon reply code.
active device 1. An electronic component, such as a
transistor that needs a power supply, and/or that
is capable of amplifying. 2. Broadly, any device (including electromechanical relays) that can switch
(or amplify) by application of low-level signals.
active electric network A network containing one
or more active devices or components, usually
amplifiers or generators, in addition to passive
devices or components.
active element The driven or RF-excited element
in a multielement antenna or antenna array.
active file A computer file in use (i.e., one that is
being updated or referred to).
active filter A bandpass, bandstop, highpass or
lowpass filter, consisting of resistors, capacitors,
and operational amplifiers, arranged to pass a desired frequency response. Commonly used at audio frequencies.
active infrared detection Detection of infrared
rays reflected from a target to which they were
active jamming Transmission or retransmission
of signals for the purpose of disrupting communications.
active junction A pn junction in a semiconductor
device that has been created by a diffusion process.
active leg An element within a transducer that
changes one or more of its electrical characteristics in response to the input signal of the transducer. Also called active arm.
active lines In a U.S. television picture, the lines
(approximately 488) that make up the picture.
The remaining 37 of the 525 available lines are
blanked and are called INACTIVE LINES.
active material 1. In a storage cell, the chemical
material in the plates that provides the electrical
action of the cell, as distinguished from the supporting material of the plates themselves. 2. A radioactive substance. 3. The phosphor coating of a
cathode-ray tube screen. 4. The material used to
coat an electron-tube cathode.
active mixer A signal mixer using one or more active components, such as transistors or integrated circuits. An active circuit provides
amplification, input-output isolation, and high
input impedance, in addition to the mixing action. Compare PASSIVE MIXER.
active modulator A modulator using one or more
active components, such as transistors or integrated circuits. An active circuit provides gain,
input-output isolation, and high input impedance, in addition to modulation. Compare PASSIVE MODULATOR.
active pressure The electromotive pressure that
produces a current in an ac circuit.
active pull-up An arrangement using a transistor
as a pull-up resistor replacement in an integrated
circuit, providing low output impedance and low
power consumption.
active RC network 1. A resistance-capacitance
(RC) circuit that contains active components
(transistors or integrated circuits), as well as passive components (capacitors and resistors). 2. An
RC network in which some or all of the resistors
and capacitors are simulated by the action of active components.
active repair time The time during which maintenance is done on a system and the system is out
of operation.
active satellite • adapter
active satellite See ACTIVE COMMUNICATIONS
active sensor In an electronic security system, a
transducer that generates an electromagnetic
field or acoustic-wave field, and detects changes
in the field resulting from the presence or movement of objects in the vicinity.
active substrate In an integrated circuit, a substrate consisting of single-crystal semiconductor
material into which the components are formed;
it acts as some or all of the components. This is in
contrast to a substrate consisting of a dielectric,
where the components are deposited on the surface.
active system A radio and/or radar system that
requires transmitting equipment to be carried in
a vehicle.
active tracking system A system in which a
transponder or responder on board a vehicle retransmits information to tracking equipment
(e.g., azusa, secor).
active transducer 1. A transducer that contains
an active device, such as a transistor or integrated circuit, for immediate amplification of the
sensed quantity. 2. A transducer that is itself an
active device.
active wire In the armature of a generator, a wire
experiencing induction and, therefore, is delivering voltage.
activity 1. Intensity of, as well as readiness for, oscillation in a piezoelectric crystal. 2. Radioactive
intensity. 3. Intensity of thermal agitation. 4.
Thermionic emission of electrons.
activity ratio The ratio of active to inactive records
in a computer file.
ac transducer A transducer that either requires an
ac supply voltage or delivers an ac output signal—even when operated from a dc supply.
ac transmission The use of an alternating voltage
to transfer power from one point to another, usually from generators to a distribution center, and
generally over a considerable distance.
actual ground The ground as “seen” by an antenna. The actual ground surface is not necessar-
ily in the same physical location as the true
ground surface (i.e., the earth itself ). An actual
ground can be an artificial ground plane, such as
that provided in some antenna structures. Actual
ground can also be modified by nearby rooftops,
buildings, guy wiring, and utility wiring.
actual height The highest altitude where radio
wave refraction actually occurs.
actual power Also called active or AVERAGE
POWER. Symbol, Pavg. In a resistive circuit under
sine-wave conditions, average power is the product of the rms voltage and the rms current. It is
also equal to half the product of the maximum
current and maximum voltage.
actuating device A device or component that operates electrical contacts to affect signal transmission.
actuating system 1. An automatic or manually
operated system that starts, modifies, or stops an
operation. 2. A system that supplies energy for
actuating time Also called actuation time. The
time interval between generation of a control signal, or the mechanical operation of a control device, and the resulting ACTUATION.
actuation 1. The starting, modification, or termination of an operation or process. 2. Activation of
a mechanical or electromechanical switching device.
actuator An electromechanical device that uses
electromagnetism to produce a longitudinal or rotary thrust for mechanical work. It is often the
end (load) device of a servosystem.
ACU Abbreviation of automatic calling unit.
ac voltage A voltage, the average value of which is
zero, that periodically changes its polarity. In one
cycle, an ac voltage starts at zero, rises to a maximum positive value, returns to zero, rises to a
maximum negative value, and finally returns to
zero. The number of such cycles per second is
termed the ac frequency.
ac voltmeter See AC METER.
acyclic machine Also called ACYCLIC GENERATOR. A dc generator in which voltage induced in
the active wires of the armature is always of the
same polarity.
A/D Abbreviation for ANALOG-TO-DIGITAL. See
Ada A microcomputer language designed primarily
for use in multi-computer systems, where each
small computer communicates with the others,
providing some of the advantages of a larger computer.
Adam A communications code word sometimes
used for phonetic verbalizing of the letter A. More
commonly, ALPHA is used.
adapter 1. A fitting used to change either the terminal scheme or the size of a jack, plug, or socket
to that of another. 2. A fitting used to provide a
transition from one type or style of conductor to
another (e.g., waveguide to coaxial line). 3. An
adapter • address generation
auxiliary system or unit used to extend the operation of another system (e.g., a citizens-band
adapter for a broadcast receiver).
adaptive communication A method of communication that adjusts itself according to the particular requirements of a given time.
adaptive suspension vehicle Abbreviation, ASV.
A specialized robot that moves on mechanical
legs, rather than on wheels. It generally has six
legs and resembles an insect. It is designed to
move over extremely irregular or rocky terrain,
and to carry a human passenger.
adaptivity The ability of a system to respond to its
environment by changing its performance characteristics.
Adcock antenna A directional antenna system
consisting of two vertical antennas, spaced in
such a way that the whole array behaves like a
loop antenna. Its members are connected and positioned so that it discriminates against horizontally polarized waves, and delivers output that is
proportional to the vector difference of signal voltages induced in the two vertical arms.
Adcock direction finder A radio direction-finding
system based on the directivity of the ADCOCK
Adcock radio range A radio range system with
four ADCOCK ANTENNAS situated at the corners
of a square, and a fifth antenna at the center of
the square.
add-and-subtract relay A stepping relay that can
be switched either uprange (add) or downrange
addend In a calculation, any number to be added
to another. Compare AUGEND.
addend register In a digital computer, the register
that stores the addend.
adder 1. In a digital computer, the device or circuit
that performs binary addition. A HALF ADDER is
a two-input circuit that can produce a sum output and a carry output, but it cannot accommodate a carry signal from another adder. A FULL
ADDER can accommodate a carry input, as well
as two binary signals to be added. Also see ANALOG ADDER. 2. A circuit in a color TV receiver
that amplifies the receiver primary matrix signal.
additive 1. The character or characters added to a
code to encipher it. 2. In a calculation, an item
that is to be added. 3. An ingredient, usually in a
small quantity, added to another material to improve the latter in quality or performance.
additive color A color formed by combining the
rays from two or three primary-colored lights
onto a single neutral surface. For example, by
projecting a red and a green beam onto a neutral
screen, a yellow additive color results.
additive primaries Primary colors that form other
colors in a mixing of light (see ADDITIVE COLOR),
but are not themselves formed by mixing other
additive primaries. For example, red, green, and
blue are the additive primaries used in color television. Through appropriate mixing, these colors
can be used to generate an unlimited variety of
other colors. Compare SUBTRACTIVE PRIMARIES, which form the color spectrum by mixing pigments rather than lights. In additive
systems, each superimposed primary color increases the total light output from the reflecting
(viewing) surface; in subtractive systems, each superimposed primary decreases the total reflectivity. Thus, equal combination of additive primaries
produces gray or white, and equal combination of
subtractive primaries produces gray or black.
addition record An extra data store created in a
computer during processing.
address 1. In computer operations, a usually numerical expression designating the location of
material within the memory or the destination of
such material. 2. The accurately stated location
of information within a computer; a data point
within a grid, matrix, or table; a station within a
network. 3. In computer operations, to select the
location of stored information.
address comparator A device that ensures that
the address being read is correct.
address computation In digital computer operations, the technique of producing or modifying
only the address part of an instruction.
address field In a computer, the part of the instruction that gives the address of a bit of data (or
a word) in the memory.
address generation The programmed generation
of numbers or symbols used to retrieve records
from a randomly stored direct-access file.
address indirect • adjusted decibels
address indirect An address that specifies a storage location that contains another address.
address memory The memory sections in a digital
computer that contain each individual register.
address modification In computer operations,
altering only the address portion of an instruction; if the command or instruction routine is
then repeated, the computer will go to the new
address part In a digital computer instruction, the
part of an expression that specifies the location.
Also called ADDRESS FIELD.
address register In a computer, a register in which
an address is stored.
add/subtract time In a computer, the time required to perform addition or subtraction, excluding the time required to get the quantities
from storage and to enter the sum or difference
into storage.
add time In computer operations, the time required to perform addition, excluding the time required to get the quantities from storage and to
enter the sum into storage.
a/d converter A device that changes an analog
quantity into a digital signal. See ANALOG-TODIGITAL CONVERSION.
adiabatic damping In an accelerator (see ACCELERATOR, 1), reduction of beam size as beam energy is increased.
adiabatic demagnetization A technique using a
magnetic field to keep a substance at a low temperature, sometimes within a fraction of a degree
of absolute zero.
adjacency A character-recognition condition in
which the spacing reference lines of two characters printed consecutively in line are closer than
adjacent- and alternate-channel selectivity The
selectivity of a receiver or radio-frequency (RF)
amplifier, with respect to adjacent-channel and
alternate-channel signals. That is, the extent to
which a desired signal is passed, and nearby unwanted signals are rejected.
adjacent audio channel See ADJACENT SOUND
adjacent channel The channel (frequency band)
immediately above or below the channel of interest.
adjacent-channel attenuation The reciprocal of
the selectivity ratio of a radio receiver. The selectivity ratio is the ratio of the sensitivity of a receiver (tuned to a given channel) to its sensitivity
in an adjacent channel or on a specified number
of channels removed from the original.
adjacent-channel interference In television or
radio reception, the interference from stations
on adjacent channels. A common form arises
from the picture signal in the next higher channel and the sound signal in the next lower
adjacent-channel selectivity The extent to which
a receiver or tuned circuit can receive on one
channel and reject signals from the nearest outlying channels.
adjacent sound channel In television, the radiofrequency (RF) channel containing the sound
modulation of the next lower channel.
adjacent video carrier In television, the radiofrequency (RF) carrier containing the picture
modulation of the next higher channel.
adjustable component Any circuit component
whose main electrical value can be varied at will
(e.g., a variable capacitor, inductor, resistor, or
adjustable instrument 1. An instrument whose
sensitivity, range, or response can be varied at
will (e.g., multirange meter or wideband generator). 2. An instrument that requires adjustment
or manipulation to measure a quantity (e.g.,
bridge, potentiometer, or attenuator).
adjustable motor tuning An arrangement that allows the motor tuning of a receiver to be confined
to a portion of the frequency spectrum.
adjustable resistor A wirewound resistor in which
the resistance wire is partially exposed to allow
varying the component’s value.
adjustable voltage divider A wirewound resistor
with terminals that slide on exposed resistance
wire to produce various voltage values.
adjusted circuit A circuit in which leads that are
normally connected to a circuit breaker are
shunted so that current can be measured under
short-circuit conditions without breaker tripping.
adjusted decibels Noise level (in decibels) above a
reference noise level (designated arbitrarily as
zero decibels) measured at any point in a system
with a noise meter that has previously been adjusted for zero (at reference), according to specifications.
admittance • affirmative
aeronautical fixed service station A station that
operates in the aeronautical fixed service.
aeronautical ground station A land station that
provides communication between aircraft and
ground stations.
aeronautical marker-beacon signal A distinctive
signal that designates a small area above a beacon
transmitting station for aircraft navigation.
aeronautical marker-beacon station A land station that transmits an aeronautical markerbeacon signal.
aeronautical mobile service A radio service consisting of communications between aircraft, and
between aircraft and ground stations.
aeronautical radio-beacon station An aeronautical radio-navigation land station that transmits
signals used by aircraft and other vehicles to determine their position.
aeronautical radionavigation services Services
provided by stations transmitting signals used in
the navigation of aircraft.
aeronautical radio service A service that encompasses aircraft-to-aircraft, aircraft-to-ground,
and ground-to-aircraft communications important to the operation of aircraft.
aeronautical station A station on land, and occasionally aboard ship, operating in the aeronautical mobile service.
Aeronautical Telecommunication Agency The
agency that administers the operation of stations
in the aeronautical radio service.
telecommunications Collectively,
all of the electronic and nonelectronic communications used in the aeronautical service.
aeronautical utility land station A ground station in an airport control tower that provides
communications having to do with the control of
aircraft and other vehicles on the ground.
aeronautical utility mobile station At an airport,
a mobile station that communicates with aeronautical utility land stations and with aircraft
and other vehicles on the ground.
aerophare See RADIO BEACON.
aerospace 1. The region encompassing the earth’s
atmosphere and extraterrestrial space. 2. Pertaining to transport and travel in the earth’s atmosphere and in outer space. This includes
aircraft, orbiting space vessels, and interplanetary spacecraft.
AES Abbreviation for Audio Engineering Society.
AEW Abbreviation of airborne (or aircraft) early
aF Abbreviation of ATTOFARAD.
AF Abbreviation of AUDIO FREQUENCY.
affirmative In voice communications, a word often
used for “yes”—especially when interference is
present or signals are weak.
admittance Symbol, Y. Unit, siemens (formerly
mho). The property denoting the comparative
ease with which an alternating current flows
through a circuit or device. Admittance is the reciprocal of impedance (Z ): Y = 1/Z.
adp 1. Abbreviation of AMMONIUM DIHYDROGEN
PHOSPHATE, a piezoelectric compound used for
sonar crystals. 2. Abbreviation of AUTOMATIC
adsorption Adhesion of a thin layer of molecules of
one substance to the surface of another without
absorption. An example is adsorption of water to
the surface of a dielectric. This term is often confused with ABSORPTION because the spellings of
the two words are almost identical. Compare ABSORPTION.
adu Abbreviation of automatic dialing unit.
advanced-class license An amateur-radio license
conveying all operating privileges, except for a few
small bands that are allocated to extra-class licensees. The second-highest class of amateur license.
advance information Data published prior to the
actual production or availability of a manufactured component, circuit, or system. Advance information is often only an approximate reflection
of the expected characteristics of a device.
advance wire A resistance wire used in thermocouples and precision applications. It is an alloy of
copper and nickel, which has high resistivity and
a negligible temperature coefficient of resistance.
aeolight A glow lamp using a cold cathode and a
mixture of inert gases. Because its illumination
can be regulated with an applied signal voltage, it
is sometimes used as a modulation indicator for
motion-picture sound recording.
aerial See ANTENNA.
aerial cable A wire or cable run through the air, using support structures, such as towers or poles.
aerodiscone antenna A miniature discone antenna designed for use on aircraft.
aerodynamics The science dealing with forces exerted by air and other gases in motion—especially
upon bodies (such as aircraft) moving through
these gases.
aerogram See RADIOGRAM.
aeromagnetic Pertaining to terrestrial magnetism,
as surveyed from a flying aircraft.
aeronautical advisory station A civil defense and
advisory communications station in service for
the use of private aircraft stations.
aeronautical broadcasting service The special
service that broadcasts information regarding air
navigation and meteorological data pertinent to
aircraft operation.
aeronautical broadcast station A station of the
aeronautical broadcasting service.
aeronautical fixed service A fixed radio service
that transmits information regarding air navigation and flight safety.
AFIPS • aircraft bonding
AFIPS Acronym for American Federation of Information Processing Societies.
afpc Abbreviation of automatic frequency/phase
afterglow The tendency of the phosphor of a cathode-ray-tube screen to glow for a certain time after the cathode-ray beam has passed. Also see
afterpulse An extraneous pulse in a multiplier
phototube (photomultiplier), induced by a preceding pulse.
a/g Abbreviation of AIR-TO-GROUND.
agent An active force, condition, mechanism, or
substance that produces or sustains an effect.
Thus, a sudden voltage rise is a triggering agent
in certain bistable circuits; arsenic is a doping
agent in semiconductor processing; the slow cooling of a heated metal to improve ductility is an
aging 1. An initial run of a component or circuit
over a certain period of time shortly after manufacture to stabilize its characteristics and performance. 2. The changing of electrical
characteristics or of chemical properties over a
protracted period of time.
agonic line An imaginary line connecting points on
the earth’s surface at which a magnetic needle
shows zero declination (i.e., points to true geographic north).
AGREE Acronym for Advisory Group on Reliability
of Electronics Equipment.
Ah Abbreviation of AMPERE-HOUR. Depending on
the standard used, the abbreviation can be amphr, a-h, a-hr, or A-h.
aH Abbreviation of ATTOHENRY.
aided tracking In radar and fire control, a system
in which manual correction of target tracking error automatically corrects the rate of movement
of the tracking mechanism.
AIEE Abbreviation for American Institute of Electrical Engineers, now consolidated with the IRE,
forming the IEEE.
AIP Abbreviation for American Institute of Physics.
air The mixture of gases that constitutes the
earth’s atmosphere and figures prominently in
the manufacture and operation of numerous
electronic devices. By volume, air contains about
21 percent oxygen, 78 percent nitrogen, and
lesser amounts of argon, carbon dioxide, helium,
hydrogen, krypton, neon, and xenon. It also contains varying amounts of water vapor, and in
smoggy areas, carbon monoxide and the oxides of
sulfur and nitrogen.
airborne intercept radar A type of short-range
radar used aboard fighter and interceptor aircraft
for tracking their targets.
airborne long-range input Equipment aboard aircraft, for the purpose of facilitating the use of
long-range missiles.
airborne noise See ACOUSTIC NOISE.
airborne radar platform Surveillance and altitude-finding radar used aboard aircraft.
air capacitor A capacitor in which air is the dielectric between two sets of conductive plates. Also
called air-dielectric capacitor.
aircarrier aircraft station On an aircraft, a radio
station that is involved in carrying people for hire
or in transporting cargo.
air cell A primary electrochemical cell in which the
positive electrode is depolarized by reduced oxygen in the air.
air cleaner See DUST PRECIPITATOR.
air column The open space inside an acoustic
chamber, pipe, or horn.
air-cooled component A component, such as a
power transistor, that is cooled by circulating air,
compared with one cooled by a circulating liquid,
such as water or oil.
air-cooled transistor A transistor (particularly a
power transistor) from which the heat of operation is drawn away, through radiation and convection, into the surrounding air. The transistor
is usually mounted on a heatsink or fitted with
air-cooled tube An electron tube from which heat
is drawn away, mainly via convection, into the
surrounding air. A device called a chimney can be
placed around the tube, through which air is
blown by a fan. Cool air enters through the bottom of the assembly, and hot air escapes from the
air-core inductor A coil of wire wound around a
hollow cylindrical form or in a loop, designed to
introduce inductive reactance into a circuit or
system. In practice, the maximum attainable inductance is approximately 1 mH. This type of inductor is used in some wireless transmitters,
receivers, and antenna networks. The component
can be designed for high current-carrying capacity by using heavy-gauge wire and a large winding
radius. The magnetic lines of flux extend considerably beyond the interior of the coil, especially
along the winding axis. This increases the likelihood of mutual inductance between the coil and
surrounding electrical components, devices, or
air-core transformer A transformer without a ferromagnetic core, so called because air is the only
material at the center of (and immediately surrounding) the transformer coils.
aircraft bonding The practice of solidly connecting, for electrical purposes, the metal parts of an
aircraft, including the engine.
aircraft flutter • airwaves
aircraft flutter Rapid, repetitive fading and intensifying of a received radio or television signal, resulting from reflections of the signal by passing
aircraft station A nonautomatic radio communications station installed on an aircraft.
air-dielectric coax A special type of COAXIAL CABLE designed to have minimum loss. The space
between inner and outer conductors is mostly
empty (i.e., air-filled). Some such cables are
sealed and filled with an inert gas. The inner conductor is held away from the inner wall of the
outer conductor by beads, washers, or a spiralwound filament of high-grade dielectric material,
such as polyethylene.
air environment Pertaining to communications
equipment aboard aircraft.
airflow The path or movement of air in, through, or
around an electronic device or piece of equipment—especially pertaining to an AIR-COOLED
air gap 1. A narrow space between two parts of a
magnetic circuit (e.g., the gap in the core of a filter choke). Often, this gap is filled with a nonmagnetic material, such as plastic, for
mechanical support. 2. The space between two or
more magnetically coupled or electrostatically
coupled components. 3. A device that gets its
name from the narrow gap between two small
metal balls, needle points, or blunt rod tips
therein. When an applied voltage is sufficiently
high, a spark discharges across the gap.
air/ground control radio station A station for
aeronautical telecommunications related to the
operation and control of local aircraft.
air-insulated line 1. An open-wire feeder or transmission line. Typically, the line consists of two
parallel wires held apart by separators (bars or
rods of high-grade dielectric material) situated at
wide intervals. 2. AIR-DIELECTRIC COAX.
air-moving device A mechanical device, such as a
specially designed fan or blower, used to facilitate
air cooling of electronic components.
airport beacon A radio or light beacon that marks
the location of an airport.
airport control station A station that provides
communications between an airport control
tower and aircraft in the vicinity.
airport surveillance radar An air-traffic-control
radar that scans the airspace within about 60
miles (approximately 100 kilometers) of an airport, and displays in the control tower the location of all aircraft below a certain altitude and all
obstructions in the vicinity.
air-position indicator An airborne computer system that, using airspeed, aircraft heading, and
elapsed time, furnishes a continuous indication
of the position of the aircraft. The indication is
affected by high-altitude winds. Compare
air-to-air communication Radio transmission
from one aircraft to another in flight. Compare AIR-TO-GROUND COMMUNICATION and
air-to-ground communication Radio transmission from an aircraft in flight to a station located
air-to-ground radio frequency The carrier frequency, or band of such frequencies, allocated for
transmissions from an aircraft to a ground station.
airwaves 1. Radio waves. The term is slang, but is
widely used. It probably came from the public’s
airwaves • aliasing noise
mistaken notion that radio signals are propagated by the air. 2. Skywaves.
Al Symbol for ALUMINUM.
alabamine See ASTATINE.
alacratized switch A mercury switch in which the
tendency of the mercury to stick to the parts has
been reduced.
alarm 1. An electronic security system. 2. A silent
and/or audible alert signal transmitted by an
electronic security system when an intrusion occurs. 3. A silent and/or audible signal that informs personnel of the occurrence of an
equipment malfunction.
alarm circuit A circuit that alerts personnel to a
system malfunction, a detected condition, or an
alarm condition 1. An intrusion or equipment
malfunction that triggers an alarm circuit. 2. The
operation of an alarm circuit that occurs in response to an intrusion or equipment malfunction.
alarm hold A device that keeps an alarm sounding
once it has been actuated.
alarm output The signal sent from an alarm circuit to a siren, buzzer, computer, or other external device to alert personnel to an ALARM
alarm relay A relay that is actuated by an alarm
A-law A form of companding law frequently used in
European electronics (the mu-law is more often
used in North America). A nonlinear transfer
characteristic in companding circuits. It can be
continuous, or can be a piecewise linear approximation of a continuous function.
A-law companded Companding by means of an 8bit binary code following the A-LAW, a specific
companding function.
albedo For an unpolished surface, the ratio of reflected light to incident light. It can vary from 0.0
to 1.0, or from 0 to 100 percent.
albedograph An instrument for measuring the
albedo of planets.
alerting device An audible alarm that includes a
self-contained solid-state audio oscillator. Powered from the ac line or a battery, the device produces a raucous noise when actuated.
Alexanderson antenna A very-low-frequency
(VLF) and low-frequency (LF) vertically polarized
antenna, designed to minimize ground losses in
structures of manageable height. It usually consists of several wires, each quarter-wave resonant with a loading coil, and all connected
together at the apex of a tower. The antenna is
fed between the ground and the base of one of
the wires.
Alford antenna A loop antenna, in a square configuration, with the corners bent toward the center
to lower the impedance at the current nodes.
algebraic adder In computer operations, an adder
that provides the algebraic sum, rather than the
arithmetic sum, of the entered quantities.
algebraic operation A form of electronic calculator
operation, in which the keystrokes proceed in an
intuitive sequence, following the way in which the
calculation is written down. Compare REVERSE
algebraic sum The sum of two or more quantities
with consideration of their signs. Compare
algorithm A step-by-step procedure for solving a
problem, (e.g., the procedure for finding the
square root of a number). It can be expressed in a
line-by-line instruction set or as a flowchart.
algorithmic language A computer language used
to describe a numeral or algebraic process.
alias A label that is an alternate term for items of
the same type; a label and several aliases can
identify the same data element in a computer
aliasing 1. In analog-to-digital (A/D) conversion, a
false output signal that results from a sampling
rate that is too slow. Ideally, the sampling rate is at
least twice the highest input signal frequency. 2.
Sawtooth-like irregularities, also called jaggies,
which are sometimes introduced into a bit-mapped
computer image when it is changed in size.
aliasing noise A form of signal distortion caused
by a signal with an excessive bandwidth.
align • alloy diode
align 1. To adjust (i.e., to preset) the circuits of an
electronic system, such as a receiver, transmitter, or test instrument, for predetermined response. 2. To arrange elements in a certain
precise orientation and spacing, relative to each
other, as in a Yagi antenna. 3. To orient antennas
so that they are in line of sight, with respect to
each other.
alignment The process of ensuring that equipment, components, or systems are adjusted, both
physically and electronically, for the most efficient possible performance.
alignment chart A line chart for the simple solution of electronic problems. It is so called because
its use involves aligning numerical values on various scales, the lines intersecting at the solution
on another scale. Also called nomograph.
alignment pin A pin or protruding key, usually in
the base of a removable or plug-in component, to
ensure that the latter will be inserted correctly
into a circuit. Often, the pin mates with a keyway,
notch, or slot.
alignment tool A specialized screwdriver or
wrench (usually nonmagnetic) used to adjust
padder or trimmer capacitors or inductor cores.
alive See LIVE.
alkali See BASE, 2.
alkali metals Metals whose hydroxides are bases
(alkalis). The group includes cesium, francium,
lithium, potassium, rubidium, and sodium.
alkaline battery 1. A battery composed of alkaline
cells and characterized by a relatively flat discharge curve under load.
alkaline cell A common non-rechargeable electrochemical cell that employs granular zinc for
the negative electrode, potassium hydroxide as
the electrolyte, and a device called a polarizer as
the positive electrode. Produces approximately
1.5 volts under no-load conditions. The geometry
of construction is similar to that of the zinc–
carbon cell, but it can deliver current effectively
at lower temperatures. Cells of this type have
shelf lives longer than zinc–carbon cells; they also
have greater energy-storage capacity per unit
volume, but they are more expensive than zinc–
carbon cells. They are used in calculators, transistor radios, and cassette tape and compact-disc
players. Compare ZINC–CARBON CELL.
alkaline-earth metals The elemental metals barium, calcium, strontium, and sometimes beryllium, magnesium, and radium, some of which are
used in vacuum tubes.
alkaline earths Substances that are oxides of the
alkaline-earth metals. Some of these materials
are used in vacuum tubes.
all-diffused A type of INTEGRATED CIRCUIT in
which both active and passive elements have
been fabricated by diffusion and related processes.
Allen screw A screw fitted with a six-sided (hexagonal) hole.
Allen wrench A tool used to tighten or loosen an
Allen screw. It is a hexagonal rod and is available
in various sizes.
alligator clip A spring-loaded clip with jagged
teeth, designed to be used for temporary electrical connections.
allocate 1. To assign (especially through legislation) operating frequencies or other facilities or
conditions needed for scientific or technical activity; see, for example, ALLOCATION OF FREQUENCIES. 2. In computer practice, to assign
locations in the memory or registers for routines
and subroutines.
allocated channel A frequency channel assigned
to an individual or group.
allocated-use circuit 1. A circuit in which one or
more channels have been authorized for the exclusive use of one or more services. 2. A communications link assigned to users needing it.
allocation of frequencies See RADIO SPECTRUM.
allocator A telephone system distributor associated with the finder control group relay assembly.
It reserves an inactive line-finder for another call.
allophone A variation in the sound of a phoneme,
depending on what comes before and/or after the
phoneme in the course of speech. Important in
speech recognition and synthesis. There are 128
different phoneme variations in the English language. See PHONEME.
alloter relay A telephone system line-finder relay
that reserves an inactive line-finder for the next
incoming call from the line.
allotropic Pertaining to a substance existing in
two forms.
alloy A metal that is a mixture of several other metals (e.g., brass from copper and zinc), or of a
metal and a nonmetal.
alloy deposition In semiconductor manufacture,
depositing an alloy on a substrate.
alloy-diffused transistor A transistor in which the
base is diffused and the emitter is alloyed. The
collector is provided by the semiconductor substrate into which alloying and diffusion are
affected. Compare ALLOY TRANSISTOR and
alloy diode A junction-type semiconductor diode
in which a suitable substance (such as p-type) is
alloyed into a chip of the opposite type (such as
alloy diode • alternating-charge characteristic
n-type) to form the junction. Also called alloyjunction diode.
alloy junction In a semiconductor device, a positive/negative (pn) junction formed by alloying a
suitable material (such as indium) with the semiconductor (silicon or germanium).
alloy transistor A transistor whose junctions are
created by alloying. Also see ALLOY JUNCTION.
all-pass filter Also called all-pass network. A filter
that (ideally) introduces a desired phase shift or
time delay, but has zero attenuation at all frequencies.
all-relay central office In telephone service, an
automatic central-office switchboard that uses
relay circuits to make line interconnections.
all-wave Pertaining to a wide operating-frequency
range. Few systems are literally all-wave. For example, a so-called “all-wave radio receiver” might
cover 500 kHz to 30 MHz only.
all-wave antenna An antenna that can be operated
over a wide frequency range with reasonable efficiency and preferably without needing readjustment. Examples are the DISCONE ANTENNA and
all-wave generator A signal generator that will
supply output over a wide range of frequencies.
all-wave receiver A radio receiver that can be
tuned over a very wide range of frequencies, such
as 10 kHz to 70 MHz.
allyl plastics Plastics, sometimes used as dielectrics
or for other purposes in electronics, based on
resins made by polymerization of monomers (such
as diallyl phthalate) that contain allyl groups.
alnico Coined from the words aluminum, nickel,
and cobalt. An alloy used in strong permanent
magnets, it contains the constituents noted plus
(sometimes) copper or titanium.
alpha 1. Symbol, α. The current gain of a commonbase-connected bipolar transistor. It is the ratio of
the differential of collector current to the differential of emitter current; α = dIC/dIE. For a junction
transistor, alpha is always less than unity, but
very close to it. 2. In voice communications, the
phonetic representation of the letter A.
alphabet The set of all characters in a natural language.
alphabetic coding In computer practice, an abbreviation system for coding information to be fed
into the computer. The coding contains letters,
words, and numbers.
alphabetic-numeric Also
alphabeticalnumerical and alphanumeric. In computer operations, pertaining to letters of the alphabet and
special characters, and to numerical digits.
alpha cutoff frequency Also called alpha cutoff. In
a bipolar transistor circuit, the frequency at
which the alpha (current gain) becomes 0.707
(70.7 percent) of its value at 1 kHz. A bipolar
transistor can have considerable gain at its alpha
cutoff. This specification denotes how rapidly a
transistor loses gain as the frequency increases,
an important consideration in the design of radiofrequency (RF) amplifiers. See ALPHA. Compare
alpha decay The decay of a substance in which the
nuclei of the atoms emit alpha particles, resulting
in a change of the atomic number and atomic
weight of the substance over a period of time.
alphanumeric See ALPHABETIC-NUMERIC.
alphanumeric code In computer operations or in
communications, a code composed of, or using,
both letters and numbers.
alphanumeric readout A type of digital readout
that displays both letters and numerals.
alpha particle A nuclear particle bearing a positive
charge. Consisting of two protons and two neutrons, it is given off by certain radioactive substances. Compare BETA RAYS and GAMMA RAYS.
alpha system An alphabetic code-signaling system.
alphatron An ionizing device in which the radiation source is an emitter of alpha particles.
alteration An inclusive-OR operation.
alternate channel In communications, a channel
situated two channels higher or lower than a
given channel. Compare ADJACENT CHANNEL.
interference Interference
caused by a transmitter operating in the channel beyond an adjacent channel. Compare
alternate digit inversion In multiplex equipment,
a method of switching the binary signals to the
opposite state, in accordance with A-law companding.
alternate frequency A frequency allocated as an
alternative to a main assigned frequency and
used under certain specified conditions.
alternate-mark inversion signal A signal that
conveys bits in which the successive signals are
of opposite polarity (positive, then negative, then
positive, etc.). They are equal in absolute value
alternate mode The technique of displaying several signals on an oscilloscope screen by rapidly
switching the signals in sequence at the end of
each sweep.
alternate routing A secondary, or backup, communications path, used when primary (normal)
routing is impossible.
alternating-charge characteristic In a nonlinear
capacitor, the relationship between the instanta-
alternating-charge characteristic • amateur extra-class license
neous charge and the instantaneous value of an
alternating voltage.
alternating current Abbreviation, ac. A current that
periodically reverses its direction of flow. In one cycle, an alternation starts at zero, rises to a maximum positive level, returns to zero, rises to a
maximum negative level, and again returns to zero.
The number of such cycles completed per second is
termed the ac frequency. Also see CURRENT.
alternating-current continuous wave An amplitude-modulated signal resulting from the operation of an oscillator or RF amplifier with raw ac
alternating current/direct current See AC/DC.
alternating-current erasing head See AC ERASING HEAD.
alternating-current pulse A short-duration ac
alternating-current transmission 1. The propagation of alternating currents along a length of
conductor—especially for power-transfer purposes. 2. A means of picture transmission in
which a given signal strength produces a constant value of brightness for a very short time.
alternating voltage Also called alternating-current
voltage. See AC VOLTAGE.
alternation In ac practice, a half cycle. In a complete
cycle, there are two alternations, one in the positive
direction and one in the negative direction.
alternative denial A NOT-AND operation.
alternator Any mechanically driven machine for
generating ac power. Sometimes specifically one
having a permanent-magnet rotor, such as a
altimeter station An airborne transmitter whose
signals are used to determine the altitude of aircraft.
altitude 1. The vertical distance of an object above
sea level. 2. The vertical distance of an object
above the earth’s surface. 3. The angle, measured
in degrees, with respect to the horizon, at which a
highly directional antenna is pointed.
altitude delay In a plan-position-indicating type of
radar, the sync delay introduced between transmission of the pulse and start of the trace on the
indicator screen to eliminate the altitude circle in
the display.
alumel An alloy used in the construction of one
type of THERMOCOUPLE. It is composed of
nickel (three parts) and aluminum (one part).
alumina An aluminum-oxide ceramic used in electron tube insulators and as a substrate in the
fabrication of thin-film circuits.
aluminum Symbol, Al. An elemental metal. Atomic
number, 13. Atomic weight, 26.98. Aluminum is
widely used in electronics, familiar instances being chassis, wire, shields, semiconductor doping,
and electrolytic-capacitor plates.
aluminum antimonide Formula, AlSb. A crystalline
compound useful as a semiconductor dopant.
aluminized screen A television picture-tube
screen with a thin layer of aluminum deposited
on its back to brighten the image and reduce ionspot formation.
Am Symbol for AMERICIUM.
A/m Abbreviation of ampere per meter: the SI unit
of magnetic field strength.
AM 1. Abbreviation of amplitude modulator. 2. Abbreviation of AMPLITUDE MODULATION.
amalgam An alloy of a metal and mercury. Loosely,
any combination of metals.
amateur 1. A nonprofessional, usually noncommercial devotee of any technology (i.e., a hobbyist). 2. A licensed radio operator legally
authorized to operate a station in the AMATEUR
amateur band Any band of radio frequencies assigned for noncommercial use by licensed radio
amateurs (see AMATEUR, 2). In the United
States, numerous such bands are above 1.8 MHz
(160 meters). Also see AMATEUR SERVICE and
amateur call letters Call letters assigned by a government licensing authority—especially to amateur stations. Call-letter combinations consist of
a letter prefix denoting the country in which the
station is situated, plus a number designating
the location within the country, and two or more
letters identifying the particular station. For example: W6ABC: W (or K) = United States, 6 = California, and ABC = identification of individual
licensee (issued alphabetically, except under special circumstances).
amateur callsign See AMATEUR CALL LETTERS.
amateur extra-class license The highest class of
amateur-radio operator license in the United
States. It conveys all operating privileges.
amateur radio • AM/FM tuner
amateur radio 1. A general term, referring to the
practice of operation, experimentation, and other
work in and related to the amateur service. 2. The
hardware that comprises an amateur radio station. 3. A radio receiver, transmitter, or transceiver
that is specifically designed for operation in the
amateur bands.
amateur radio operator Also called radio ham or
ham radio operator. An individual licensed to
transmit radio signals in the amateur service.
amateur service A two-way radio service, existing
purely for hobby purposes (i.e., without pecuniary interest).
amateur station A radio station licensed in the
amauroscope An electronic aid to the blind, in
which photocells in a pair of goggles receive light
images. Electric pulses proportional to the light
are impressed upon the visual receptors of the
brain through electrodes in contact with nerves
above each eye.
amber A yellow or brown fossil resin that is historically important in electronics. It is the first material reported to be capable of electrification by
rubbing (Thales, 600 BC). Also, the words electricity, electron, and electronics are derived from
the Greek name for amber, elektron.
ambience The acoustic characteristic of a room, in
terms of the total amount of sound reaching a listener from all directions.
ambient An adjective meaning “surrounding.” Often
used as a noun in place of the adjective-noun combination (thus, “10 degrees above ambient,” instead of “10 degrees above ambient temperature”).
ambient humidity The amount of moisture in the
air at the time of measurement or operations in
which dampness must be accounted for.
ambient level The amplitude of all interference
(acoustic noise, electrical noise, illumination,
etc.) emitted from sources other than that of a
signal of interest.
ambient light Also called ambient illumination.
Room light or outdoor light incident to a location
at the time of measurement or operations.
ambient-light filter In a television receiver, a filter
mounted in front of a picture-tube screen to minimize the amount of ambient light reaching the
ambient noise 1. In electrical measurements and
operation, background electrical noise. 2. In
acoustical measurements and operations, audible background noise.
ambient pressure Surrounding atmospheric pressure.
ambient temperature The temperature surrounding apparatus and equipment (e.g., room temperature).
ambient-temperature range 1. The range over
which ambient temperature varies at a given location. 2. The range of ambient temperature that
will cause no malfunction of, or damage to, a circuit or device.
ambiguity 1. Any unclear, illogical, or incorrect indication or result. 2. The seeking of a false null by
a servo. 3. In digital computer operations, an error resulting from improper design of logic.
ambiguous count In digital counters, a clearly incorrect count. See ACCIDENTAL TRIGGERING.
ambisonic reproduction A close approximation of
the actual directional characteristics of a sound in
a given environment. The reproduced sound almost exactly duplicates the sound in the actual
environment in which it was recorded.
American Morse code (Samuel F. B. Morse, 1791–
1872). Also called Railroad Morse. A telegraph
code, at one time used on wire telegraph lines in
the United States. It differs from the Continental
code, also called the International Morse Code,
which is used in radiotelegraphy. Compare CONTINENTAL CODE.
American National Standards Institute Acronym, ANSI. An industrial group in the United
States that encourages companies to manufacture devices and equipment in accordance with
certain standards. The objective is to minimize
hardware incompatibility problems.
American Radio Relay League A worldwide organization of amateur radio operators, headquartered in Newington, Connecticut. The official
publications are the monthly magazines, QST
and QEX. They also publish numerous books and
other educational materials.
American Standards Association Abbreviation,
ASA. At one time, the name of the national association in the U.S. devoted to the formation and dissemination of voluntary standards of dimensions,
performance, terminology, etc. See ANSI.
American wire gauge Abbreviation, AWG. Also
called Brown and Sharpe gauge or B & S gauge.
The standard American method of designating
wire sizes. Wire is listed according to gauge number from 0000 (460 mils diameter) to 40 (3.145
mils diameter).
americium Symbol, Am. A radioactive elemental
metal first produced artificially in the 1940s.
Atomic number, 95. Atomic weight, 243.
AM/FM receiver A radio set that can receive either
amplitude-modulated or frequency-modulated
signals. Usually, a band switch incorporates the
demodulation-selection circuitry so that as the
frequency range is changed, the appropriate detector is accessed.
AM/FM transmitter A radio transmitter whose
output signal can be frequency- or amplitudemodulated by a panel selector switch.
AM/FM tuner A compact radio receiver unit that
can handle either amplitude- or frequencymodulated signals, and delivers low-amplitude
output to a high-fidelity audio power amplifier.
Compare AM TUNER and FM TUNER.
AMI • Amperian whirl
.. .
. ...
. ..
.. ..
... .
American Wire Gauge (AWG) Diameters
A-minus Also, A-. The negative terminal of an A
battery, or pertaining to the part of a circuit connected to that terminal.
ammeter An instrument used to measure the
amount of current (in amperes) flowing in a circuit.
ammeter shunt A resistor connected in parallel with
an ammeter to increase its current range. Also see
ammeter-voltmeter method The determination of
resistance or power values from the measurement of voltage (E) and current (I ). For resistance,
R = E/I; for power, P = EI.
ammonium chloride Formula, NH4Cl. The electrolyte in the carbon-zinc type of primary cell.
Also called SAL AMMONIAC.
amortisseur winding 1. A winding that acts
against pulsation of the magnetic field in an electric motor. 2. A winding that acts to prevent oscillation in a synchronous motor.
amorphous substance A noncrystalline material.
amp 1. Slang for AMPERE. 2. Slang for AMPLIFIER—
especially in audio high-fidelity applications.
ampacity Current-carrying capacity expressed in
amperage The strength of an electric current (i.e.,
the number of amperes).
ampere (Andre Marie Ampere, 1775-1836). Abbreviations, A (preferred), a, amp. The SI base unit of
current intensity (I ). The ampere is the constant
current that, if maintained in two straight parallel
conductors of infinite length and of negligible circular cross section and placed 1 meter apart in a
vacuum, would produce between the conductors a
force of 2 × 10 –7 newton per meter. One ampere
flows through a 1-ohm resistance when a potential
of 1 volt is applied; thus I = E/R. Also see MICROAMPERE, MILLIAMPERE, NANOAMPERE,
ampere balance A device consisting of two conductors in which the force between them (caused
by current) is balanced against the gravitational
force exerted on an object in the gravitational
field of the earth. Used for the precise determination of current of large dimension, or of the size of
the ampere.
ampere-hour Abbreviations: Ah, amp-hr. The
quantity of electricity that passes through a circuit in one hour when the rate of flow is one ampere. Also see BATTERY CAPACITY.
ampere-hour meter An instrument for measuring
ampere-hours. It contains a small motor driven by
the current being measured and which moves a
point on an ampere-hour scale. The motor speed is
proportional to the current. The position of the
pointer is proportional to current and elapsed time.
Ampere’s law Current flowing in a wire generates
a magnetic flux that encircles the wire in the
clockwise direction when the current is moving
away from the observer.
ampere-turn Symbol, NI. A unit of magnetomotive
force equal to 1 ampere flowing in a single-turn
coil. The ampere-turns value for any coil is obtained by multiplying the current (in amperes) by
the number of turns in the coil.
Amperian whirl The stream of electrons in a
single-turn, current-conducting wire loop acting
as an elementary electromagnet.
amp-hr • amplify
Direction of
flux flow
of current
Ampere’s Law
amp-hr One style of abbreviating AMPERE-HOUR.
Also, Ah.
amplidyne A dynamo-like rotating dc machine
that can act as a power amplifier because the response of the output voltage to changes in field
excitation is quite rapid. Used in servo systems.
amplification 1. The process of increasing the
magnitude of a signal. This entails an input signal controlling a local power supply to produce a
larger output signal. Depending on the kind of input and output signals, amplification can be categorized as CURRENT, VOLTAGE, POWER, or
some combination of these. 2. The qualitative signal increase resulting from the process in 1. 3.
The quantitative signal increase (resulting from
the process in 1), expressed as a factor (such as
100) or in terms of decibels (dB). See AMPLIFICATION FACTOR and DECIBEL.
amplification factor 1. The ratio of the output
voltage, current, or power to the input voltage,
current, or power of an AMPLIFIER circuit. For
voltage or current, this ratio has meaning only
when the input and output impedances are iden-
tical. 2. The number of decibels by which an AMPLIFIER circuit increases the amplitude of a signal. For voltage or current, this figure has
meaning only when the input and output
impedances are identical. See DECIBEL. 3. The
ALPHA or BETA of a bipolar transistor. 4. In
the operation of an electron tube, the ratio of
the derivative (instantaneous rate of change) of
the plate voltage to the derivative of the grid voltage, for zero change in plate current.
amplified ALC Abbreviation, AALC. An automaticlevel-control (ALC) system that uses the amplification of the fed-back control signal. It is used in
RF power amplifiers, particularly single-sideband
(SSB) linear amplifiers, to prevent overmodulation and nonlinearity.
amplified back bias A declining voltage developed
across a fast-time-constant circuit in an amplifier
stage and fed back into a preceding stage.
amplifier Any device that increases the magnitude of an applied signal. It receives an input
signal and delivers a larger output signal that, in
addition to its increased amplitude, is a replica
amplifier diode Any semiconductor that can provide amplification in a suitable circuit or microwave system. See DIODE AMPLIFIER.
amplifier distortion A change in the waveform of a
signal, arising within an amplifier that is operated in compliance with specified conditions.
amplifier input 1. The terminals and section of an
amplifier that receive the signal to be amplified.
2. The signal to be amplified.
amplifier noise Collectively, all extraneous signals
present in the output of an amplifier when no
working signal is applied to the amplifier input
amplifier nonlinearity A condition in which the
amplifier output signal does not exhibit a linear
relationship to the corresponding input signal.
Some amplifiers are designed to operate in a linear manner at all times, but many amplifier types
need not function in this manner to be effective.
amplifier output 1. The terminals and section of
an amplifier that deliver the amplified signal for
external use. 2. The amplified signal.
amplifier power The power level of the output signal delivered by an amplifier (also called OUTPUT
POWER), or the extent to which the amplifier increases the power of the input signal (also called
amplifier response The performance of an amplifier throughout a specified frequency band. Factors usually included are gain, distortion,
amplitude versus frequency, and power output.
amplify To perform the functions of amplification
amplifying delay line • amplitude selection
munications and broadcasting. The modulatingsignal energy appears at sideband frequencies
above and below, and very close to, the carrier
frequency. These sideband signals carry all the
information. The extent of modulation is expressed as a percentage, from 0, which represents
an unmodulated carrier, to 100, which represents full modulation. In a signal modulated 100
percent, one-third of the power is used to convey
the data; the other two-thirds is consumed by the
carrier. This form of modulation is essentially
outmoded, although it is still used in the standard broadcast band from 535 to 1605 kHz. See
amplifying delay line A delay line that causes amplification of signals in a circuit intended for
pulse compression.
amplistat A self-saturating magnetic amplifier.
amplitron A backward-wave amplifier used in microwave circuits.
amplitude The extent to which an alternating or
pulsating current or voltage swings, positively
and negatively, from zero or from a mean value.
amplitude-controlled rectifier A thyratron- or
thyristor-based rectifier circuit.
amplitude density distribution A mathematical
function giving the probability that, at a given instant in time, a fluctuating voltage has a certain
amplitude distortion In an amplifier or network,
the condition in which the output-signal amplitude exhibits a nonlinear relationship to the input-signal amplitude.
amplitude error 1. The error in measuring the amplitude of a signal, normally expressed as a percentage of signal amplitude or as a percentage of
full scale. 2. The frequency at which the output
amplitude of a signal is in error by 1% with amplitude at 10% of full scale.
amplitude factor For an ac wave, the ratio of the
peak value to the rms value. The amplitude factor
of a sine wave is equal to the square root of 2 =
amplitude fading In the propagation of electromagnetic waves, a condition in which the amplitudes of all components of the signal (i.e., carrier
and sidebands) increase and decrease uniformly.
amplitude/frequency response Performance of
an amplifier throughout a specified range, as exhibited by a plot of output-signal amplitude versus frequency for a constant-amplitude input
amplitude gate A transducer that transmits only
those portions of an input wave that lie within
two close-spaced amplitude boundaries; also
called slicer.
amplitude limiter A circuit, usually with automatic gain control (AGC), that keeps an amplifier
output signal from exceeding a certain level, despite large variations in input-signal amplitude. A
dc-biased diode performs passive limiting action
via clipping.
amplitude-modulated generator A signal generator whose output is amplitude modulated. Usually, this instrument is an RF generator that is
modulated at an audio frequency.
transmitter A
radiofrequency transmitter whose carrier is varied in
amplitude, according to the rate of change of
some data-containing signal (such as voice, music, facsimile, television pictures, control signals,
or instrument readings).
amplitude modulation Abbreviation, AM. A
method of conveying intelligence in wireless com-
amplitude-modulation noise Spurious amplitude
modulation of a carrier wave by extraneous signals and random impulses, rather than by the intended data-containing signal.
amplitude noise In radar, amplitude fluctuations
of an echo returned by a target. This noise limits
the precision of the system.
amplitude of noise The level of random noise in a
system. The amplitude of noise is measured in
the same way that signal amplitude is measured.
amplitude range The maximum-to-minimum amplitude variation of a signal. It can be expressed
as a direct numerical ratio or in decibels.
amplitude response The maximum output obtainable at various frequencies over the range of an
instrument operating under rated conditions.
amplitude selection The selection of a signal, according to its correspondence to a predetermined
amplitude or amplitude range.
amplitude separator • analog integrator
amplitude separator In a television receiver, a circuit that separates the control pulses from the
composite video signal.
amplitude suppression ratio The ratio of an undesired output of a frequency-modulated (FM) receiver to the desired output, when the test signal
is amplitude modulated and frequency modulated simultaneously.
amplitude-versus-frequency distortion Distortion
resulting from varying gain or attenuation of an
amplifier or network, with respect to signal frequency.
AMTOR A form of amateur-radio data communications, in which the accuracy of a group of characters in a message is checked periodically by the
receiving station. If an error appears likely, then
the receiving station sends an instruction to the
transmitting station to retransmit that particular
group of characters. Characters are sent in
bunches with pauses for possible inquiries from
the receiving station.
AM tuner A compact radio receiver unit that handles amplitude-modulated signals and delivers
low-amplitude audio output to a high-fidelity amplifier. Compare AM/FM TUNER and FM TUNER.
amu Abbreviation of atomic mass unit.
amusement robot An electromechanical robot, often computer-controlled, that is intended for use
as a toy.
AN- A prefix designator used by American military
services to indicate commonality.
anacoustic Pertaining to the lack of sound or absence of reverberation or transmission of sonic
analog 1. A quantity that corresponds, point for
point or value for value, to an otherwise unrelated
quantity. Thus, voltage is the analog of water
pressure, and current is the analog of water flow.
2. Varying over a continuous range and, therefore, capable of attaining an infinite number of
values or levels. Compare DIGITAL.
analog adder An analog circuit or device that receives two or more inputs and delivers an output
equal to their sum.
analog adder/subtracter An analog circuit or device that receives two or more inputs and delivers
an output equal to their sum or difference (in any
combination), as desired.
analog channel In an ANALOG COMPUTER, an information channel in which the extreme limits of
data magnitude are fixed, and the data can have
any value between the limits.
analog communications Any form of communications in which a carrier, generally an electromagnetic wave or high-frequency current, is varied in
a continuous and controlled way by a datacontaining signal. See ANALOG, 2.
analog computer A computer in which input and
output quantities are represented as points on
continuous (or small-increment) scales. To represent these quantities, the computer uses voltages
or resistances that are proportional to the numbers to be worked on. When the quantities are
nonelectrical (such as pressure or velocity), they
are made analogous by proportional voltages or
analog data 1. Data represented in a quantitatively analogous way. Examples are the deflection
of a movable-coil meter, the positioning of a slider
on a slide rule, and the setting of a variable resistor to represent the value of a nonelectrical quantity. Also see ANALOG. 2. Data displayed along a
smooth scale of continuous values (as by a
movable-coil meter), rather than in discrete steps
(as by a digital meter).
analog differentiator An analog circuit or device
whose output waveform is the derivative of the
input-signal waveform, with respect to time.
analog divider An analog circuit or device that receives two inputs and delivers an output equal to
their quotient.
analog electronics Electronic techniques and
equipment that is based on uniformly changing
signals, such as sine waves, and often having
continuous-scale indicators, such as D’Arsonval
analog information Approximate numerical information, as opposed to digital information, which
is assumed to be exact.
analog integrator An analog circuit or device
whose output waveform is the integral of the input signal waveform, with respect to time.
analog inverting adder • AND circuit
analog inverting adder An analog adder that delivers a sum with the opposite sign to that of the
input quantities.
analog meter An indicating instrument that uses
a movable-coil arrangement or the equivalent,
causing a rotating pointer to indicate a particular
value on a graduated printed scale. Compare
analog multiplexer 1. A multiplexer used with
analog signals (see MULTIPLEXER). 2. An analog
time-sharing circuit.
analog multiplier An analog circuit or device that
receives two or more inputs and delivers an output equal to their product.
analog network A circuit that permits mathematical relationships to be shown directly by electric
or electronic means.
analogous pole In a PYROELECTRIC MATERIAL,
the end or face having the positive electric charge.
analog output An output quantity that varies
smoothly over a continuous range of values,
rather than in discrete steps.
analog record Also called analog recording. A
record or recording method in which some property of the recorded material, such as displacement or magnetization, varies over a continuous
range that is relative to time and/or physical position.
analog recorder Any recorder, such as a recording
oscillograph, potentiometric recorder, electroencephalograph, electrocardiograph, or lie detector,
that produces an analog record. The counterpart
is a digital recorder, which produces a readout in
discrete numbers (printed or visually displayed).
analog representation Representation of information within a smooth, continuous range, rather
than as separate (discrete) steps or points.
analog signal A signal that attains an infinite
number of different amplitude levels, as opposed
to one that can attain only a finite number of levels as a function of time.
analog subtracter An analog circuit or device that
receives two inputs and delivers an output equal
to their difference.
analog summer See ANALOG ADDER.
analog switch A switching device that will only
pass signals that are faithful analogs of transducer parameters.
analog-to-digital conversion 1. A process in
which an analog signal (such as a voice waveform) is changed into a digital or binary signal
that conveys the same information. This process
is commonly used in digital computers to encode
sounds and images. It is also used in communications systems to improve efficiency, minimize
the necessary bandwidth, and optimize the signal-to-noise ratio. 2. A process in which continuous mechanical motion is encoded into a digital
or binary electronic signal.
analog-to-digital converter Any circuit or device
analysis 1. The rigorous determination of the constants and modes of operation for electronic
equipment. Compare SYNTHESIS. 2. A branch of
mathematics dealing with point sets, relations,
and functions.
analytical engine A primitive mechanical calculating machine, invented in 1833 by Charles Babbage.
analyzer 1. Any instrument that permits analysis
through close measurements and tests (e.g., distortion analyzer, WAVE ANALYZER, or gas analyzer). 2. A computer program used for debugging
purposes; it analyzes other programs and summarizes references to storage locations. 3. An
analysis interface to an oscilloscope.
anastigmatic yoke Also called full-focus yoke. In a
television (TV) receiver, a deflection yoke with a
cosine winding for better focus at the edges of the
anchorage In plastic recording tape, the adhesion
of the magnetic oxide coating to the surface of the
ancillary equipment Equipment that does not directly enter into the operation of a central system.
Examples are input/output components of a computer and test instruments attached to a system.
AND circuit In digital systems and other switching
circuits, a logic gate whose output is high (logic 1)
only when all input signals are high. Otherwise
the output is low (logic 0). Compare OR CIRCUIT.
Anderson bridge • angle of beam
Anderson bridge An ac bridge circuit with six
impedances, permitting the value of an unknown
inductance to be determined in terms of a standard capacitance.
AND gate 1. AND circuit. 2. In a TV receiver, an
AND circuit that holds the keyed-AGC signal off
until a positive horizontal flyback pulse and a
horizontal sync pulse appear simultaneously at
the input.
android A sophisticated robot built in humanoid
form. Usually, it propels itself by rolling on
wheels or on a track drive. A rotatable head contains position sensors, a machine vision system,
and/or a machine hearing system. Mechanical
arms are equipped with end effectors to perform
various tasks. The most advanced androids have
self-contained computer control systems.
anechoic Pertaining to the absence of echoes. Examples: ANECHOIC CHAMBER, anechoic enclosure, or anechoic room.
anechoic chamber An enclosure that does not reflect sound waves that approach its walls. Such a
chamber is used to test certain audio devices.
anemograph An electromechanical device that
produces a recording of wind speed versus time.
Generally, it consists of an ANEMOMETER connected to a PEN-AND-INK RECORDER via a suitable electronic interface.
anemometer An instrument that measures or
indicates wind speed, or speed and direction (velocity).
angel 1. An extraneous image, usually of short duration, on a cathode-ray-tube (CRT) display. The
term applies particularly to anomalies in a radar
image caused by low-atmospheric reflection,
birds, or other mobile objects. 2. Air-deployed
metallic debris, also known as chaff, designed to
create radar echoes as a decoy or diversion tactic.
angle jamming A radar jamming technique in
which the return echo is jammed with a signal
containing improper azimuth or elevation angle
angle modulation Variation of the angle of a sinewave carrier in response to the modulating
source, as in FREQUENCY MODULATION and
angle noise In radar reception, the interference resulting from variations in the angle at which an
echo arrives from the target.
angle of arrival The angle which the line of propagation of an incoming radio wave makes with the
surface of the earth. Compare ANGLE OF DEPARTURE.
angle of azimuth The horizontal angle between
the viewer and object or target, usually measured
clockwise from north.
angle of beam The angle enclosing most of the
transmitted energy in the radiation from a directional antenna. It is usually measured between
the half-power points in the main lobe of the directional pattern. This angle can be measured in
the horizontal (azimuth) plane or in the vertical
(elevation) plane.
angle of conduction • anhysteresis
angle of conduction 1. Also called angle of flow.
The number of degrees of an excitation-signal cycle during which output (drain, collector or plate)
current flows in an amplifier circuit. 2. The number of degrees of any sine wave at which conduction of a device (e.g., a diode) begins.
angle of convergence 1. In any graphical representation, the angle formed by any two lines or
plots that come together at a point. 2. The angle
formed by the light paths of two photocells focused on the same object.
angle of declination The angle between the horizon and a descending line. Compare ANGLE OF
angle of deflection In a cathode-ray tube, the angle between the electron beam at rest and a new
position resulting from deflection.
angle of departure The angle, relative to the
horizon, made by the line of propagation of a
transmitted radio wave. Compare ANGLE OF
angle of depression See ANGLE OF DECLINATION.
angle of divergence In a cathode-ray tube, the angle formed by the spreading of an undeflected
electron beam as it extends from the gun to the
angle of elevation The angle that an ascending
line subtends, with respect to the horizon. Compare ANGLE OF DECLINATION.
angle of flow See ANGLE OF CONDUCTION.
angle of incidence The angle, measured relative to
the perpendicular (orthogonal) to a surface or
boundary, subtended by an approaching ray.
angle of lag The phase difference (in degrees or radians) whereby one component follows another in
time, both components being of the same frequency. Compare ANGLE OF LEAD. Also see
angle of lead The phase difference (in degrees or
radians) whereby one component precedes another in time, both components being of the same
frequency. Compare ANGLE OF LAG. Also see
angle of radiation 1. The angle, measured with respect to the horizon, at which the principal lobe of
an electromagnetic wave leaves a transmitting
antenna. 2. The angle, measured relative to the
horizon, of a receiving or transmitting antenna’s
optimum sensitivity.
angle of reflection The angle, measured relative to
the perpendicular (orthogonal) to a surface, subtended by a ray leaving the surface after having
been reflected from it. Compare ANGLE OF INCIDENCE.
angle of refraction The angle, measured relative
to the perpendicular (orthogonal) to a boundary
between two different media, subtended by a ray
leaving the boundary after having been refracted
thereat. Compare ANGLE OF INCIDENCE.
angle tracking noise Noise in a servo system that
results in a tracking error.
angstrom (Anders J. Angstrom, 1814 –1874). A
unit of length used to describe certain extremely
short waves and microscopic dimensions; 1
angstrom equals 10–4 microns (10–10 meters).
angular deviation loss The ratio of microphone or
loudspeaker response on the principal axis of response to the response at a designated angle from
that axis. Expressed in decibels.
angular difference See PHASE ANGLE.
angular displacement In an ac circuit, the separation, in degrees, between two waves. See PHASE
angular frequency The frequency of an ac signal,
expressed in radians per second (rad/sec) and approximately equal to 6.28f, where f is the frequency in Hertz.
angular length Length, as along the horizontal
axis of an ac wave or along the standing-wave
pattern on an antenna, expressed as the product
of radians and wavelength.
angular-mode keys On a calculator or computer,
the DEG, RAD, and GRAD keys for expressing or
converting angles in DEGREES, RADIANS, and
GRADS, respectively.
angular phase difference For two sinusoidal
waves, the phase difference, expressed in degrees
or radians.
angular rate In navigation, the rate of bearing
change, expressed in degrees or radians.
angular resolution The ability of a radar to distinguish between two targets by angular measurement.
angus pen recorder An instrument that makes a
permanent record of the time whenever a channel
is used.
anharmonic oscillator An oscillating device in
which the force toward the balance point is not
linear, with respect to displacement.
anhysteresis The magnetization of a material by a
unidirectional field containing an alternating field
component of gradually decreasing amplitude.
anhysteretic state • anomalous propagation
anhysteretic state The condition of a substance
after it has been subjected to a strong magnetic
field, the intensity of which alternates in direction
and diminishes gradually to zero.
animism A belief or philosophy, held especially in
Eastern civilizations, such as Japan, that all
things contain an essence of life. This theory renders irrelevant the question of whether or not machines, such as computers and robots can be
anion A negative ion. Also see ION.
anisotropic Pertaining to the tendency of some
materials to display different magnetic and other
physical properties along different axes.
anneal To heat a metal to a predetermined temperature and let it cool slowly. The operation prevents brittleness and often stabilizes electrical
annealed laminations Core laminations for transformers or choke coils that have been annealed.
annealed shield A magnetic shield for cathode-ray
tubes, that has been processed by annealing.
annealed wire Soft-drawn wire that has been subjected to annealing.
annotations 1. Marking on copies of original engineering-installation documents to show changes
made during the installation. 2. Any set of comments or notes accompanying a program, an
equipment or system, or a process.
annular 1. Pertaining to the region between two
concentric circles that lie in the same plane; ringshaped. 2. Pertaining to two or more concentric
circles that lie in a common plane.
annular conductor A number of wires stranded in
three concentric layers of alternating twists
around a hemp core.
annular transistor A mesa transistor in which the
base and collector take the form of concentric
rings around a central emitter.
annulling network A subcircuit that shunts a filter to cancel reactive impedance at the extreme
ends of the pass band of the filter.
annunciation relay A relay that indicates whether
or not a circuit is carrying current.
annunciator A device that produces loud sound
and/or conspicuous light to attract attention
(e.g., the electronic siren in an automotive security system).
anode 1. The positive electrode of a vacuum tube
or solid-state device (i.e., the electrode toward
which electrons move during current flow). 2. In
an electrochemical cell, the electrode that loses
electrons by oxidation. This is usually the negative electrode.
anode balancing coil Mutually coupled windings
used to maintain equal currents in parallel anodes operating from a common transformer terminal.
anode current Current flowing in the anode circuit
of a device.
anode efficiency Also called plate efficiency. In a
power amplifier using an electron tube, the ratio
Po/Pi, where Po is the output power in watts and Pi
is the dc anode power input in volt-amperes.
anode power input Symbol, PA(input). The product of
anode current and anode voltage.
anode power supply The ac or positive dc power
supply unit that delivers current and voltage to
the anode of a device.
anode saturation The point beyond which a further increase in anode voltage does not produce
an increase in anode current.
anode strap In a multicavity magnetron, a metal
strap connecting the anodes.
anode terminal 1. In a diode, the terminal to
which a positive dc voltage must be applied for
forward bias. Compare CATHODE TERMINAL. 2.
In a diode, the terminal at which a negative dc
voltage appears when the device is used as an ac
rectifier. Compare CATHODE TERMINAL. 3. The
terminal that is connected internally to the anodic element of any device.
anode voltage Symbol, EA or VA. The difference in potential between the anode and cathode of a device.
anodic Pertaining to the anode of a device, or to
anode-like effects.
anodizing An electrolytic process in which a protective oxide film is deposited on the surface of a
metallic body acting temporarily as the anode of
the electrolytic cell.
anomalous dispersion Dispersion of electromagnetic radiation that is characterized by a decrease
in refractive index with increase in frequency.
anomalous propagation 1. The low-attenuation
propagation of UHF or microwave signals through
anomalous propagation • antenna current
atmospheric layers. 2. Unusual, bizarre, or unexplainable electromagnetic-wave propagation (e.g.,
apparent F-layer ionospheric effects in the FM
broadcast band). 3. Rapid fluctuation of a sonar
echo because of variations in propagation.
anoxemia toximeter An electronic instrument for
measuring or alerting against the onset of anoxemia (deficiency of oxygen in the blood)—especially in airplane pilots.
AN radio range A navigational facility entailing four
zones of equal signal strength. When the aircraft
deviates from course, an aural Morse-code signal,
A (DIT DAH) or N (DAH DIT) is heard; but when the
aircraft is on course, a continuous tone is heard.
ANSI Acronym for American National Standards Institute.
AN signal The signal provided by an AN radio range
to apprise aircraft pilots of course deviation.
answerback The automatic response of a terminal
station to a remote-control signal.
answer cord In a telephone system, the cord used
for answering subscribers’ calls and incoming
trunk calls.
answering machine A device that automatically
answers a telephone and records an audio message from the caller.
answer lamp A telephone switchboard lamp that
lights when an answer cord is plugged into a line
jack; it switches off when the telephone answers
and lights when the call is completed.
ant Abbreviation of ANTENNA.
antenna In a communications system, a specialized transducer that converts incoming electromagnetic fields into alternating electric currents
having the same frequencies (receiving antenna),
or converts an alternating current at a specific
frequency into an outgoing electromagnetic field
at the same frequency (transmitting antenna). An
antenna can be a simple wire or rod, or a complicated structure. Thousands of geometries and
specifications are possible. The optimum antenna
type for a given situation depends on the communications frequency, the distance to be covered,
and various other factors.
antenna ammeter An RF ammeter, usually of the
thermocouple type, employed to measure current
flowing to a transmitting antenna.
antenna amplifier 1. A radio-frequency amplifier,
often installed at the antenna, used to boost signals before they reach a receiver (also called an
RF preamplifier). 2. Occasionally, the first RF amplifier stage of a receiver, also known as the front
antenna array See ARRAY.
antenna bandwidth The frequency range throughout which an antenna will operate at a specified
efficiency without needing alteration or adjustment.
antenna beamwidth A measure of the extent to
which a directional antenna focuses a transmitted electromagnetic field, or focuses its response
to incoming electromagnetic fields. Expressed as
the angle in degrees between opposite half-power
points in the main lobe of the directional pattern.
Usually determined in the horizontal plane, but
occasionally in the vertical plane.
antenna coil The primary coil of the input RF
transformer of a receiver, or the secondary coil of
the output RF transformer of a transmitter.
antenna coincidence The condition in which two
directional antennas are pointed directly toward
each other.
antenna-conducted interference Extraneous signals generated in a transmitter or receiver and
presented to the antenna, from which they are radiated.
antenna core A ferrite rod or slab around which a
coil of wire is wound to act as a self-contained antenna, usually in a miniature receiver.
antenna coupler A device consisting of an inductor, RF transformer, or a combination of inductor(s) and capacitor(s), used to match the
impedance of an antenna to that of a transmitter
or receiver. Also known as a transmatch or antenna tuner.
antenna coupling Inductive and/or capacitive
coupling used to optimize the transfer of energy
from an antenna to a receiver, or from a transmitter to an antenna.
antenna current 1. Radio-frequency current flowing from a transmitter into an antenna. 2. Radiofrequency current flowing from a receiving
antenna into a receiver.
antenna detector • antenna pattern
antenna detector A circuit that warns aircraft
personnel that they are being observed by radar.
It picks up the radar pulses and actuates a warning light or other device.
antenna diplexer A coupling device that permits
several transmitters to share one antenna without troublesome interaction. Compare ANTENNA
antenna directivity The directional characteristics of a transmitting or receiving antenna, usually expressed qualitatively (e.g., omnidirectional,
bidirectional, or unidirectional). A more precise
expression is ANTENNA BEAMWIDTH.
antenna director In a directional antenna, a PARASITIC ELEMENT situated in front of the radiator
and separated from it by an appropriate fraction
of a wavelength. Its function is to intensify radiation in the direction of transmission. Compare
antenna duplexer A circuit or device permitting
one antenna to be shared by two transmitters
without undesirable interaction.
antenna effect The tendency of wires or metallic
bodies to act as antennas (i.e., to radiate or receive radio waves).
antenna efficiency The ratio of radio-frequency
energy supplied to a wireless transmitting antenna, to the energy radiated into space. Electrically, the radiation resistance of the antenna (RR)
appears in series with loss resistance (RL). The efficiency Eff of the antenna can be determined by
the following formula:
Eff = RR/(RR + RL)
As a percentage,
Eff % = 100 (RR/(RR + RL)
The efficiency is always less than 1 (100 percent)
because, in practice, the loss resistance can
never be reduced to zero.
antenna factor A factor (in decibels) added to an
RF voltmeter reading to find the true open-circuit
voltage induced in an antenna.
antenna field The electromagnetic field immediately surrounding an antenna.
antennafier Low-profile antenna/amplifier device,
sometimes used with portable communications
systems. Also called an active antenna.
antenna front-to-back ratio For a directional antenna, the ratio of field strength in front of the antenna (i.e., directly forward in the line of
maximum directivity) to field strength in back of
the antenna (i.e., 180 degrees from the front), as
measured at a fixed distance from the radiator. It
is usually specified in decibels.
antenna gain For a given antenna, the ratio of signal strength (received or transmitted) to that obtained with a comparison antenna, such as a
simple dipole. Generally specified in decibels.
antenna ground system The earth, counterpoise,
guy wires, radials, and/or various conducting ob-
jects in the vicinity of an antenna which, taken
together, form the radio-frequency (RF) ground
system against which the antenna operates.
Some antennas require an extensive ground system to function efficiently; others need no ground
antenna/ground system An arrangement embodying both an antenna and a low-resistance
connection to the earth, as opposed to an antenna system that involves no connection to
antenna height 1. The height of an antenna above
the surface of the earth immediately beneath the
driven element(s). 2. The height of an antenna
above the effective radio-frequency (RF) ground
immediately beneath the driven element(s). 3.
The height of an antenna above average terrain,
determined against the mean altitude of a number of points on the earth’s surface that lie within
a certain radius of the antenna structure. Also
called height above average terrain (HAAT).
antenna impedance The complex-number impedance that an antenna presents to a transmission line. It can vary over a tremendous range,
and depends on the antenna type, antenna size,
antenna height, operating frequency, and various
other factors.
antenna-induced potential Also called antennainduced microvolts. The voltage across the opencircuited terminals of an antenna.
antenna lens Also called lens antenna. A radiator
designed to focus microwave energy in much the
same manner that an optical lens focuses light
rays. Lens antennas are made from dielectric materials and/or metals.
antenna loading 1. The insertion of inductance in
antenna elements to lower the resonant frequency of the system without necessarily making
the system physically larger or the elements
longer. 2. The insertion of capacitance in antenna
elements to raise the resonant frequency of the
system without necessarily making the system
physically smaller or the elements shorter.
antenna lobe A well-defined region in the radiation
pattern of an antenna in which radiation is most
intense, or in which reception is strongest. Also
antenna matching The technique of establishing a
satisfactory relationship between the antenna
impedance and the transmission-line or transmitter-output impedance, for maximum transfer
of power into the antenna. Also, the matching
of antenna impedance to receiver-input impedance, for delivery of maximum energy to the
antennamitter An antenna/oscillator combination that serves as a low-power transmitter.
antenna pattern A polar plot of antenna performance that shows field strength versus angle of
azimuth, with the antenna at the center. It is
usually specified in the horizontal plane.
antenna polarization • anthropomorphism
antenna polarization The orientation of electric
lines of flux, with respect to the surface of the
earth, for which an antenna is most efficient. A
vertical antenna radiates and receives vertically
polarized waves. A horizontal antenna radiates
and receives horizontally polarized waves broadside to itself, and vertically polarized waves at
high elevation angles off its ends. In other directions, the polarization is slanted at various angles.
antenna power Symbol, Pant. The RF power developed in an antenna by a transmitter; Pant equals
I 2R, where I is the antenna current and R is the
antenna resistance at point I is measured.
antenna power gain The ratio of the maximum effective radiated power (ERP) from a wireless
transmitting antenna to the ERP from a reference
antenna, expressed in decibels (dB). If the ERP
from an antenna under test is PT watts and the
ERP from the reference antenna is PR watts, then
the gain GdB is:
GdB = 10 log10 (PT/PR)
Power gain is always measured in the direction in
which the test antenna performs the best. The
reference antenna, usually a dipole, is chosen
with a gain assumed to be unity, or 0 dB. Gain
relative to a dipole is expressed in dBd (decibels
relative to a dipole). Alternatively, the reference
antenna can be an isotropic radiator, in which
case the gain is expressed in dBi (decibels relative
to an isotropic radiator). Gain figures in dBd and
dBi differ by a constant amount as follows:
GdBi = 2.15 + GdBd
antenna preamplifier A highly sensitive amplifier
used to enhance the gain of a receiver. It is usually used at the very high frequencies and above.
antenna radiation The propagation of radio waves
by a transmitting antenna.
antenna radiator The element of an antenna that
receives RF energy from the transmitter and radiates waves into space. Also known as the driven
antenna range 1. The frequency band, communication distance characteristically covered, or
other continuum of values that specify the operating limits of an antenna. 2. The region immediately surrounding an antenna in which tests and
measurements usually are made. Sometimes
antenna reflector In a directional antenna, a PARASITIC ELEMENT situated behind the radiator
and separated from the latter by an appropriate
fraction of a wavelength. Its function is to intensify radiation in the direction of transmission.
antenna relay In a radio station, a low-loss, heavyduty relay that enables the antenna to be
switched between transmitter and receiver.
antenna resistance The resistive component of
antenna resonant frequency The frequency, or
narrow band of frequencies, at which an antenna’s impedance appears resistive.
antenna stage 1. The first RF amplifier stage of a
receiver. 2. Occasionally, the final RF amplifier of
a transmitter.
antenna switch In a radio station, a low-loss,
heavy-duty switch that enables the antenna to be
connected to transmitter, receiver, or safety
antenna system Collectively, an antenna and all of
the auxiliary electrical and mechanical devices
needed for its efficient operation, including couplers, tuners, transmission lines, supports, insulators, and rotator.
antenna terminals 1. The points at which a transmission line is attached to an antenna. 2. The signal input terminals of a receiver. 3. The signal
output terminals of a transmitter.
antennaverter An antenna and converter combined into a single circuit, intended for connection to the antenna terminals of a receiver to
allow operation on frequencies outside the band
for which the receiver has been designed.
antenna wire 1. The radiator element of a wiretype antenna. 2. A strong solid or stranded wire
(e.g., hard-drawn copper, copper-clad steel, or
phosphor-bronze) used for antennas.
anthropomorphism The perception, by people, of
machines as having human qualities. This can
anthropomorphism • antiparticle
lead to emotional attachment to hardware, such
as computers and robots. The more sophisticated
the apparatus, in general, the more powerful this
perception can become.
antialiasing filter A low-pass or bandpass filter
that limits the bandwidth of an input signal to
prevent aliasing and its effects. See ALIASING, 1.
anticapacitance switch A switch whose members
are thin blades and stiff wires widely separated to
minimize capacitance between them.
anticathode The target electrode of an X-ray tube.
Anticipatory Sciences A group of futurists, people
who attempt to predict the course of technology.
Some futurists believe that progress will continue
until, for example, homes become fully automated
and artificial intelligence reaches a level comparable to human intelligence. Other futurists believe
that such things are highly improbable.
anticlutter circuit A supplementary circuit in a
radar receiver that minimizes the effect of extraneous reflections that would obscure the image of
the target.
anticlutter gain control In a radar receiver, a circuit that automatically raises the gain of the receiver slowly to maximum after each transmitter
pulse to reduce the effect of clutter-producing
anticoincidence Noncoincidental occurrence of
two or more signals. Compare COINCIDENCE.
anticoincidence circuit In computers and control
systems, a circuit that delivers an output signal
only when two or more input signals are not received simultaneously. Compare COINCIDENCE
anticoincidence operation An exclusive-OR operation.
anticollision radar A vehicular radar system that
is used to minimize the probability of a collision
with another vehicle, whether or not that other
vehicle has a similar system.
antiferroelectric 1. Pertaining to the property
wherein the polarization curve of certain crystalline materials shows two regions of symmetry.
2. A material that exhibits the aforementioned
antiferromagnetic Pertaining to the behavior of
materials in which, at low temperatures, the
magnetic moments of adjacent atoms point in opposite directions.
antihunt The condition in which hunting is counteracted, usually by removing overcorrection in
automatic control or compensation systems.
antihunt circuit 1. A circuit that minimizes or
eliminates hunting. Also see ANTIHUNT. 2. In a
television (TV) receiver, a circuit that stabilizes an
automatic frequency control (afc) system.
antijamming Pertaining to communications systems that are resistant to, or that counteract, the
effects of jamming.
antilogarithm Abbreviated, antilog or log–1. The
number corresponding to a given logarithm. For
example, log 10,000 = log 104 = 4, and thus antilog 4 = 104 = 10,000.
antilogous pole In a PYROELECTRIC MATERIAL,
the end that becomes negatively charged as the
temperature rises.
antimagnetic Pertaining to materials having extremely low RETENTIVITY.
antimatter Pertaining to particles that are the
counterparts of conventional particles (i.e.,
positrons instead of electrons, antineutrons instead of neutrons, and antiprotons instead of
protons). When a particle meets its antiparticle,
the two annihilate, releasing energy. Also see ANTIPARTICLE.
antimicrophonic See NONMICROPHONIC.
antimony Symbol, Sb. A metalloidal element.
Atomic number, 51. Atomic weight, 121.76. Often
used as n-type dopant in semiconductor manufacture.
antineutrino The antiparticle of the NEUTRINO,
emitted as a result of radioactive decay.
antineutron An uncharged particle with a mass
equal to that of the neutron, but with a magnetic
moment in the direction opposite that of the neutron.
antinode A point of maximum amplitude in a
standing wave.
antinoise carrier-operated circuit A circuit that
cuts off the audio output of a receiver while the
station transmitter is in use. This can be accomplished in the automatic-gain-control (AGC) circuit of the receiver, or in the speaker or audio
line. The circuit is actuated by energy from the
transmitted signal.
antinoise microphone Any microphone that discriminates against acoustic noise (e.g., a lip microphone or throat microphone).
antinucleon A particle with the mass of a nucleon,
but with the opposite electrical charge and direction of magnetic moment. Compare NUCLEON.
antioxidant A material, such as a lacquer coat or
an inactive oxide layer, that prevents or slows oxidation of a material exposed to air.
antiparticle A subatomic particle opposite in character to conventional particles, such as electrons,
neutrons, protons. Antiparticles constitute
antiphase • A plus
aperture 1. The larger, normally open end of a
horn antenna or horn loudspeaker. 2. An opening
in an opaque disk or mask that passes a predetermined amount of light or other radiant energy.
3. The portion of a directional antenna through
which most of the radiated energy passes.
aperture angle For an antenna or telescope or microscope, the half angle formed by the radius of
the detecting instrument, as viewed from the
antiphase The property of being in phase opposition (180 degrees out of phase).
antipincushioning magnets In some television
(TV) receivers, a pair of corrective magnets in the
deflection assembly on the picture tube that eliminate pincushion distortion (disfigurement of the
raster so that it resembles a pincushion—a rectangle with its sides bowed in).
antiproton A subatomic particle with a mass equal
to that of the proton, but with opposite electrical
antiquark An ANTIPARTICLE of a QUARK.
antirad substance A material that protects against
damage caused by atomic radiation.
antiresonance 1. Parallel resonance. 2. The condition of being detuned from a resonant frequency.
antiresonant circuit See PARALLEL-RESONANT
antiresonant frequency 1. The resonant frequency of a parallel-resonant circuit. 2. In a
piezoelectric crystal, the frequency at which
impedance is maximum (as in a parallel-resonant
antisidetone Pertaining to the elimination in telephone circuits of interference between the microphone and earphone of the same telephone.
antistickoff voltage The low voltage applied to the
coarse synchro control transformer rotor winding
in a dual-speed servo system to eliminate ambiguous behavior in the system.
antitransmit/receive switch Abbreviated ATR. In
a radar installation, an automatic device to prevent interaction between transmitter and receiver.
antivirus program A computer program or utility
designed to detect and eliminate viruses and Trojan horses in a computer system.
antivoice-operated transmission Radio communications that use a voice-activated circuit as a
transmitter interlock during reception on the
companion receiver.
apc 1. Abbreviation of automatic picture control. 2.
aperiodic Characterized by a lack of predictable
repetitive behavior. For example, the sferics or
“static” electromagnetic interference caused by
aperiodic current The unidirectional current that
follows an electromagnetic disturbance in an LCR
circuit, in which R is equal to or higher than the
critical circuit resistance.
aperiodic damping Damping of such a high degree
that the damped system, after disturbance,
comes to rest without oscillation or hunting.
aperiodic discharge A discharge in which current
flowing in an LCR circuit is unidirectional, rather
than oscillatory. For this condition, 1/LC is less
than or equal to R2/4L2.
aperiodic function A nonrepetitive function (e.g.,
a hyperbolic trigonometric function).
aperture antenna An antenna whose beamwidth
depends on the size of a horn, reflector, or lens.
aperture compensation In a television (TV) camera, the minimizing of APERTURE DISTORTION
by widening the video-amplifier passband.
aperture distortion In a television (TV) camera
tube, a form of distortion that occurs when the
scanning beam covers several mosaic elements
simultaneously. This condition, caused by excessive beam thickness, results in poor image resolution.
aperture mask In a three-gun color picture tube, a
thin, perforated sheet mounted behind the viewing screen to ensure that a particular color phosphor will be excited only by the beam for that
color. Also called shadow mask.
aperture synthesis In telescopes, a method of obtaining high resolution using several small antennas separated by great distances. The small
antennas are moved around to simulate the resolving power of a much larger antenna that
would, in practice, be impossible or impractical to
aphelion 1. The point at which a solar-orbiting
satellite attains its highest altitude. It occurs
once for every complete orbit. At this point, the
satellite travels slower than at any other point in
the orbit. 2. The altitude, measured from the
sun’s surface or the sun’s center, of a solarorbiting satellite at its most distant point.
APL Abbreviation for A Programming Language. A
high-level computer language designed for ease of
use, and characterized by the requirement for a
special character set.
apl 1. Abbreviation of average picture level. 2. Abbreviation of automatic phase lock.
A plus Also, A+. The positive terminal of an A battery. Also, pertaining to the part of a circuit connected to that terminal.
apogee • arc cosecant
apogee 1. The point at which an earth-orbiting
satellite attains its highest altitude. It occurs
once for every complete orbit. At this point, the
satellite travels slower than at any other point in
the orbit. 2. The altitude, measured from the
earth’s surface or the earth’s center, of an earthorbiting satellite at its most distant point.
A power supply A term sometimes used to denote
the unit that supplies energy to a vacuum-tube
filament. Compare B POWER SUPPLY.
apparent bearing In radio-direction finding, the
uncorrected direction from which a signal appears to arrive.
apparent power In an ac circuit, the power value
obtained by multiplying the current by voltage (P
equals IE), with no consideration of the effects of
phase angle. Compare TRUE POWER.
apparent power loss The loss in an ammeter or
voltmeter, caused by the imperfection of the instrument. At full scale, the ammeter has a certain
voltage across its terminals; the apparent power
loss is the current multiplied by this voltage. A
voltmeter carries a small current; the apparent
power loss is the product of the current and the
indicated voltage.
appearance potential The potential through
which an electron must move to produce a certain ion from the atom with which it is associated.
applause meter An instrument consisting essentially of a microphone, audio amplifier, and indicating meter (reading directly in sound level). It is
so called because of its familiar use in measuring
audience response, as indicated by loudness of
Applegate diagram For a velocity-modulated tube,
a plot of the positions of electron bunches in the
drift space versus time.
Appleton layer Collectively, the F1 and F2 layers
of the ionosphere, at a height between 150 and
400 kilometers above the surface of the earth.
apple tube A color picture tube, used in television,
with the red, blue, and green phosphor in vertical
appliance Electrical equipment in general. This
might include any home-operated device.
application A task or job for which an electronic
device or system is used. It especially pertains to
personal-computer software that has practical
application factor A factor involved in determining the failure rate of a circuit or system affected
by unusual operating conditions.
application schematic diagram A diagram of pictorial symbols and lines that illustrate the interrelationship of functional circuit blocks in a
specific program mode.
applicators 1. In dielectric heating, the electrodes
between which the dielectric body is placed and
the electrostatic field developed. 2. In medical
electronics, the electrodes applied to a patient
undergoing diathermy or ultrasonic therapy.
applied voltage The voltage presented to a circuit
point or system input, as opposed to the voltage
drop resulting from current flow through an element.
applique circuit A circuit for adapting equipment
to a specialized job.
approach-control radar A radar installation serving a ground-controlled approach (GCA) system.
approximate data 1. Data obtained through physical measurements. Such data can never be exact; all measurements are subject to error. 2.
Loosely estimated data or imprecise calculations.
LEVEL. A statistically defined quality level, defined in terms of percent defective, accepted on
an average of 95 percent of the time.
Aquadag A tradename for a material that consists
of a slurry of fine particles of graphite. Aquadag
forms a conductive coating on the inside and outside walls of some cathode-ray tubes.
aqua pura Pure water; in most instances, distilled
water. Formula, H2O. Pure water is a nonconductor with a dielectric constant of about 81.
Ar Symbol for ARGON.
arbitrary function fitter A circuit or device, such
as a potentiometer, curve changer, or analog
computer element, providing an output current
or voltage that is some preselected function of the
input current or voltage.
arc 1. A luminous sustained discharge between
two electrodes. Because it is sustained, rather
than intermittent, an arc is distinguished from a
spark discharge, the latter being a series of discharges (sparks)—even when it appears continuous. 2. In graphical presentations, a section of
curved line, as of a circle.
arc angle The angle in degrees traced out by a circular arc if the center point of the circle is considered to be the vertex of an angle formed by
two rays intersecting the arc at designated
arc cosecant Abbreviated arc csc or csc–1. 1. The
inverse of the cosecant function. 2. The angle, in
arc cosecant • area code
radians or degrees, corresponding to a given
arc cosine Abbreviated arc cos or cos–1. 1. The inverse of the cosine function. 2. The angle, in radians or degrees, corresponding to a given cosine.
arc cotangent Abbreviated arc cot or cot–1. 1. The
inverse of the cotangent function. 2. The angle, in
radians or degrees, corresponding to a given
arc failure 1. Damage to, and/or failure of, insulation or a dielectric as a result of ARCOVER. 2.
Failure of make-and-break contacts through
damage caused by arcover.
arc function An inverse trigonometric function. See
arc furnace A high-temperature electric furnace in
which heat is produced by one or more electrical
architecture The functional design elements of a
computer—especially the components of the central processing unit (CPU) and the manner in
which these elements interact.
archived file A computer file stored on some
backup medium, such as magnetic tape, diskette, or CD-ROM (compact disk, read-only memory), rather than being held on the hard disk.
Such a file will be apart from the operating system’s catalog of current files, but can be reconstituted as needed.
archives A complete, periodically updated set of
arcing See ARCOVER.
arcing contacts Make-and-break contacts between which an arc occurs when they are separated.
arcing ring A metal ring placed around an insulator in a high-voltage electrical system. This keeps
an arc from charring or breaking the insulator.
arcing time The elapsed time between the breaking of contacts and the end of the arc between the
arc lamp An electric lamp in which a brilliant arc
jumps between the tips of two rods (originally carbon).
arc length The length along a given arc, usually a
part of the circumference of a circle. If the circle
has circumference C and the arc measures x degrees, then the arc length is Cx/360 units.
arc minute See MINUTE.
arc oscillation Oscillations that can occur when
opening relay contacts arc.
arcover The occurrence of an electrical ARC between electrodes, contacts, or capacitive plates.
arcover voltage The voltage at which disruptive
discharge occurs, typically accompanied by an
arc resistance The ability of a material, usually a
dielectric, to resist damage from arcing. This
property is commonly expressed as the length of
time between the start of the arc and the establishment of a conductive path through the material.
arc secant Abbreviated arc sec or sec–1. 1. The inverse of the secant function. 2. The angle, in radians or degrees, that corresponds to a given
arc second See SECOND.
arc sensor A device for detecting visible arcs and
excessive reflected power in microwave systems.
arc sine Abbreviated arc sin or sin–1. 1. The inverse
of the sine function. 2. The angle, in radians or
degrees, that corresponds to a given sine.
arc suppression Extinguishing an arc discharge.
Disruptive arcs in electronic circuits are suppressed by means of auxiliary diodes or resistorcapacitor networks.
arc-suppressor diode A semiconductor diode used
to prevent arcing between make-and-break contacts.
arc tangent Abbreviated arc tan or tan–1. 1. The
inverse of the tangent function. 2. The angle, in
radians or degrees, corresponding to a given tangent.
arcthrough The puncturing of a material by an
area code In the United States, a three-digit
number that indicates the location, according to
specified assigned districts, of a telephone sub-
area code • arithmetic symmetry
scriber. When making a long-distance call, the
area code of the desired station must be given in
addition to the seven-digit telephone number.
area protection Coverage of a defined region, in
terms of area or volume, by an alarm system.
area redistribution A scheme to determine the effective duration of an irregularly shaped pulse. A
rectangle is constructed whose height is equal to
the peak height of the pulse, as displayed on an
oscilloscope. The rectangle width is adjusted until the area of the rectangle is the same as the
area under the curve representing the pulse. The
width of the rectangle then represents the effective duration of the pulse.
area search The scanning of a large group of computer records for those of a major category or
area sensor A transducer, used with an alarm system, that protects a defined region or volume,
such as an office or bedroom.
Argand diagram Named after Jean Robert Argand,
(1768-1822) of Geneva, for his work on the
graphical representation of complex numbers. A
graphical illustration of a complex number in the
form A + jB, where the real-number (A) axis is
perpendicular to the imaginary-number ( jB) axis.
The value j is the square root of -1, the unit imaginary number. The axes are perpendicular, usually with the A axis horizontal. The length of the
line from the point (0,0) to the point (A,jB) is the
amplitude of the vector X = A + jB. The direction
is specified as the angle, in degrees or radians, of
the vector measured counterclockwise from the A
argon Symbol, Ar. An inert gaseous element.
Atomic number, 18. Atomic weight, 39.94. Argon,
present in small amounts in the earth’s atmosphere, is used in various specialized devices,
such as lasers.
argon laser A laser whose tube is filled with argon
gas. It generates coherent light at specific wavelengths that are characteristic of elemental argon.
argument 1. The direction angle of a polar vector.
2. An independent variable whose value determines the value of a function.
arithmetic address An address obtained by performing an arithmetic operation on another address.
arithmetic and logic unit Abbreviation, ALU. The
part of a digital computer containing the circuits
that perform calculations and logic operations;
distinguished from mass storage, input/output,
and peripheral units.
arithmetic circuit Also called arithmetic element.
In a digital computer, a circuit that is involved in
the execution of calculations. Included are
adders, storage registers, accumulators, subtracters, and multipliers.
arithmetic mean The average of a group of quantities, obtained by dividing their sum by the number of quantities.
arithmetic operation In digital computer practice, a numerical process performed: addition,
subtraction, multiplication, division, comparison.
arithmetic progression A mathematical series in
which each term following the first is obtained by
adding a constant quantity to the preceding one.
For example, S = 1, 2, 3, 4, . . . n. Compare GEOMETRIC PROGRESSION.
arithmetic shift In a digital computer, the multiplication or division of a quantity by a power of
the base used in the notation.
arithmetic sum The sum of two or more quantities
disregarding their signs. Compare ALGEBRAIC
arithmetic symmetry A filter response that is exactly symmetrical about the center frequency
when the frequency scale is linear.
arm • arsenic
arm 1. Any of the distinct branches of a circuit or
network. Also called leg. 2. A movable element in a
device, usually containing a contact for switching.
armature 1. The rotating member of a motor. 2.
The rotating member of some types of electro-mechanical generator. 3. The movable member of a
relay, bell, buzzer, or gong. 4. The movable member of an actuator. 5. The soft-iron keeper placed
across the poles of a permanent magnet to conserve power.
armature coil A coil of insulated wire wound on a
ferromagnetic core to provide the electromagnetic
properties of an armature. In a motor or generator, the armature coil is distinguished from the
armature core The ferromagnetic core upon which
the armature coil of a motor or generator is
armature gap 1. In a motor or generator, the space
between an armature core and the pole of a field
magnet. 2. In a relay, the space between the armature and the relay-coil core.
armature hesitation A momentary delay in the
movement of a relay.
armature-hesitation contact chatter Undesired
(usually rapid, repetitive) making and breaking of
relay contacts. Generally caused by armature
chatter Undesired
(usually rapid, repetitive) making and breaking of
relay contacts, caused by contact bounce when
the armature strikes the relay core (closure) or
backstop (opening).
armature relay A relay that uses an electromagnet
to pull a lever toward or away from a set of fixed
armature travel The distance traveled by an armature during relay operation.
armor A protective metal cable covering.
Armstrong FM system (Edwin H. Armstrong,
1890 –1954). A phase-shift method of frequency
modulation. See PHASE MODULATION.
armature voltage control A means of controlling
motor speed by changing the applied armature
winding voltage.
armchair copy An amateur radio term for reception of exceptionally clear signals.
arming the oscilloscope sweep Enabling an oscilloscope to trigger on the next pulse by closing a
Armstrong oscillator (Edwin H. Armstrong,
1890–1954). An oscillator circuit that uses inductive feedback between the output and input.
Either the output coil or the input coil can be
tuned to set the oscillator frequency. The amount
of positive feedback is controlled by varying the
coupling between the coils.
Armstrong superheterodyne circuit See SUPERHETERODYNE CIRCUIT.
Armstrong superregenerative circuit See SUPERREGENERATIVE CIRCUIT.
ARPA Acronym for Advanced Research Projects
Agency, a subsidiary of the U.S. Department of
array 1. A directive antenna that consists of an assembly of properly dimensioned and spaced elements, such as radiators, directors, and
reflectors. 2. A coordinated group or matrix of
components, such as diodes, resistors, memory
cells, etc., often enclosed in one capsule. 3. Subscripted variables representing data arranged so
that a program can examine the array and extract
data relevant to a particular subscript.
array device A group of similar or identical components that are connected together in a certain
fashion, to perform a specific task.
arrester 1. A device used to protect an installation
from lightning. It consists of a varistor or an air
gap connected between an antenna or power line
and an earth ground. The device passes little or
no current under ordinary conditions, but passes
heavy current to ground during a lightning
stroke. Also called LIGHTNING ARRESTER. 2. A
self-restoring protective device used to reduce
voltage surges on power lines.
ARRL Abbreviation for American Radio Relay
arrowhead A wideband, log-periodic antenna with
linear polarization.
ARS Abbreviation of Amateur Radio Service.
arsenic Symbol, As. A metalloidal element. Atomic
number, 33. Atomic weight, 74.91. Arsenic is familiar as an n-type dopant in semiconductor processing.
ARSR • assemble
ARSR Abbreviation of air route surveillance radar.
articulation A measure of the effectiveness of voice
communications, expressed as the percentage of
speech units understood by the listener when the
effect of context is negligible.
artificial antenna See DUMMY ANTENNA.
artificial ear A microphone-type sensor, equivalent to the human ear, used to measure sound
artificial echo 1. In radar practice, the reflections
of a transmitted pulse returned by an artificial
target. 2. A signal from a pulsed radio-frequency
(RF) generator, delayed to simulate an echo.
artificial ground The effective ground provided by
the radials or disk of a ground-plane antenna, as
opposed to actual ground (the earth itself ). Compare TRUE GROUND.
artificial horizon In aircraft instrumentation, a
device that displays lines showing the position of
the aircraft in flight, with reference to the horizon.
artificial intelligence Abbreviation, AI. 1. A specialized field of computer science overlapping
with electronics, biology, physiology, and other
sciences, concerning attempts to develop advanced computer systems that can emulate the
processes of the human mind. 2. The ability of a
computer to learn from its mistakes, refine its
own processes, and perhaps ultimately reason in
a humanlike manner.
artificial ionization An artificial reflecting layer
that is created in the atmosphere to provide a
skip condition.
artificial language A language that is not commonly used, but has been devised for efficiency in
a particular situation—especially in a computer
artificial life 1. The ultimate endpoint of ARTIFICIAL INTELLIGENCE, wherein machines acquire
qualities, such as wisdom and the capability to
feel emotions. The state of the art is currently
nowhere near this point. 2. A hypothetical machine or set of machines with lifelike qualities, including human-level intelligence, wisdom, and
artificial stimulus An electronic method of robot
guidance and navigation using radar, sonar, vision systems, edge detection, and/or beacons.
artificial transmission line A network of capacitors and inductors with characteristics similar to
those of the more bulky transmission line it replaces in tests and measurements. It also serves
as a time-delay or phase-shift device and as a
pulse-forming network.
artificial voice A device used to test and calibrate
noise-canceling microphones, consisting essentially of a small loudspeaker that has a baffle
whose acoustical properties simulate those of the
human head.
artos stripper A machine that cuts and strips wire
for the fabrication of multiconductor cables.
artwork 1. In the manufacture of printed circuits,
the scaled drawings from which the mask or etch
pattern is obtained photographically. 2. Collectively, the illustrations depicting an electronic circuit, device, or system.
As Symbol for ARSENIC.
asbestos A nonflammable fibrous material consisting of calcium and magnesium silicates that is
used for high-temperature insulation.
A-scan A radar-screen presentation in which the
horizontal time axis displays distance or range,
and the vertical axis displays the amplitude of
signal pulse and echo pulses.
ascending node For a satellite orbiting the earth or
another planet, any point at which the groundtrack crosses the equator as it moves from the
southern hemisphere into the northern hemisphere. This node generally changes for each
succeeding orbit, because the earth or planet rotates underneath the orbit of the satellite. Compare DESCENDING NODE.
ascending pass For a specific point on the earth’s
surface, the time during which an artificial communications satellite is accessible when its latitude is moving northward. The duration of
accessibility depends on the altitude of the satellite, and on how close its groundtrack comes to
the earth-based point. Compare DESCENDING
ASCII Acronym (pronounced “ask-ee”) for American Standard Code for Information Interchange.
ASI Abbreviation for American Standards Institute.
A-scope A radar system that displays an A-SCAN.
Askarel A synthetic, nonflammable liquid dielectric.
aspect ratio The width-to-height ratio of a video
image, generally three units high by four units
asperities On the surface of an electrode, tiny
points at which the electric field is intensified and
from which discharge is highly probable.
ASR 1. Abbreviation of AIRBORNE (or AIRPORT)
surveillance radar. 2. Abbreviation of AUTOMATIC SEND/ RECEIVE.
ASRA Acronym for automatic stereophonic recording amplifier.
assemble 1. To gather subprograms into a complete digital computer program. 2. To translate a
assemble • astrionics
Symbols for ASCII teleprinter code
Last three signals
back space
carriage return
device control no. 1
device control no. 2
device control no. 3
device control no. 4
data link escape
end of medium
end of transmission
end of transmission
ETX: end of text
101 110 111
form feed
file separator
group separator
horizontal tab
line feed
do not acknowledge
record separator
shift in
shift out
start of heading
start of text
synchronous idle
unit separator
vertical tab
symbolic program language into a machine (binary) language program by substituting operation codes and addresses.
assembly 1. A finished unit that can be either a
practical working model or a dummy, a prototype, or a final model; an integrated aggregation
of subunits. 2. A low-level computer source-code
language that uses crude mnemonics that are
easier to remember than the machine-language
assembly language A source code that uses
mnemonic instructions. (See ASSEMBLY, 2.)
assembly program The program that operates on
a symbolic-language program to produce a machine language program in the process of assembly. Also called assembler.
assembly robot A form of industrial robot that puts
hardware together. Such a robot is generally a
component of an automated integrated manufacturing system (AIMS). The robot can do repetitive
work at high speed and precision for long periods
of time.
assign To reserve part of a computing system for a
specific purpose, normally for the duration of a
program run.
assigned frequency The radio carrier frequency or
band of frequencies designated for a transmitting
station by a licensing authority. Also see RADIO
associative memory Computer memory in which
locations are identified by content, rather than by
specific address.
assumed decimal point A decimal point that does
not occupy an actual computer storage space,
but is used by the computer to align values for
calculation; the decimal point is assumed to be at
the right unless otherwise specified.
astable Having two temporary states; BISTABLE.
astable circuit A circuit that has two unstable
states, and whose operation is characterized by
alternation between those states at a frequency
determined by the circuit constants.
astable multivibrator A free-running multivibrator. The common circuit uses two bipolar or fieldeffect transistors, their inputs and outputs being
cross coupled. Conduction switches alternately
between the two.
astatic 1. Without fixed position or direction. 2. In
a state of neutral equilibrium.
astatic galvanometer A galvanometer with a movable element consisting of two identical magnetized needles mounted nonparallel on the same
suspension. Each needle is surrounded by a coil.
The coils are wound in opposite directions, and
are connected in series to the current source. A
large permanent magnet provides the field
against which the needle assembly rotates. The
instrument functions independently of the geomagnetic field.
astatine Symbol, At. A radioactive elemental halogen produced from radioactive decay. Atomic
number, 85. Atomic weight, 210. Formerly called
A station One of the two stations in the transmitting system of LORAN (long-range navigation).
astigmatism A focusing fault in a cathode-ray
tube (CRT), in which electrons in different axial
planes focus at different points.
ASTM Abbreviation for American Society for Testing
and Materials.
astrionics The design, production, and application
of electronic devices and systems for use in space
vehicles and space navigation.
astronomical unit • atmospheric absorption noise
astronomical unit Abbreviation, AU. A unit of distance equal to 1.496 × 108 kilometers (9.296 × 107
miles). Approximately equal to the mean distance
between the earth and the sun.
A supply See A POWER SUPPLY.
asymmetrical cell A photocell exhibiting ASYMMETRICAL CONDUCTIVITY.
asymmetrical communications 1. Two-way communications in which the volume of transmitted
data is much greater in one direction than in the
other. 2. Two-way communications in which the
speed of transmitted data is much greater in one
direction than in the other. Compare SYMMETRICAL COMMUNICATIONS.
asymmetrical conductivity A condition in which
a device conducts well in one direction, but poorly
in the other direction. A rectifier diode is a common example of a component that exhibits this
asymmetrical distortion In a binary system,
lengthening or shortening of one of the states, by
comparison to the theoretical or ideal duration.
asymmetrical FET A FIELD-EFFECT TRANSISTOR in which the source and drain cannot be interchanged without degrading performance.
asymmetrical multivibrator An unbalanced multivibrator (i.e., one in which the circuit halves are
not identical). If the time constants of the halves
are different, the output pulses will be short and
widely separated.
asymmetrical sideband See VESTIGIAL SIDEBAND.
asymmetrical sideband transmission See VESTIGIAL SIDEBAND TRANSMISSION.
asymmetrical wave A wave whose upper (positive
half-cycle) and lower (negative half-cycle) portions have different amplitudes or shapes. Also
called asymmetric wave.
asymmetry control An adjustment in a device intended for measuring the pH (acidity/alkalinity).
This corrects the inaccuracies that results from
the differences between the electrodes.
asymptote In analytical geometry, a fixed straight
line or ray L with a special relationship to a
curve or part of a curve K that recedes to infinity. As the distance from the origin (0,0) increases without limit, the separation between K
and L approaches zero, but K and L never actually meet.
asymptotic breakdown voltage A voltage that will
cause dielectric breakdown if applied continuously for a sufficiently long time.
asymptotic expression An expression having a
very small error in terms of percentage.
asynchronous 1. Not synchronous, i.e., nonrecurrent (as in out-of-phase waves). 2. A mode of
computer operation in which the completion of
one operation starts another.
asynchronous device A device not regulated by
the system in which it is used, as far as its operating frequency or rate is concerned.
asynchronous input In digital circuitry, any flipflop input at which a pulse can affect the output
independently of the clock.
asychronous motor An ac motor whose speed is
not proportional to the supply frequency.
asynchronous transmission Data transmission
in which each character or symbol begins with a
start signal and ends with a stop signal. This
eliminates the need for the data to be sent at a
uniform speed.
asynchronous vibrator In a vibrator-type portable
power supply, a vibrator that only makes and
breaks the primary circuit of the step-up transformer. This is in contrast to the synchronous vibrator, which also makes and breaks the
secondary circuit in synchronism with the primary. Also called NONSYNCHRONOUS VIBRATOR.
AT A quartz crystal cut wherein the angle between
the x-axis and the crystal face is 35 degrees.
At Symbol for astatine.
AT-cut crystal A piezoelectric crystal cut at a 35degree angle, with respect to the optical axis of
the quartz. The frequency of such a crystal does
not appreciably change with variations in temperature.
atmosphere 1. The gas surrounding a planet, particularly the air sheathing the earth. 2. Abbreviation, atm. A unit of pressure equal to 1.013 × 106
dynes per square centimeter (about 14.7 pounds
per square inch).
atmospheric absorption 1. The conversion of
electromagnetic energy into heat, with resulting
loss, as the energy passes through the earth’s atmosphere. The extent of this effect depends on
the wavelength. 2. See ABSORPTION LOSS, 2.
atmospheric absorption noise Noise, principally
above 1 GHz, resulting from atmospheric absorption (see ABSORPTION LOSS, 2).
atmospheric bending • atomic radiation
atmospheric bending The refraction or reflection
of electromagnetic waves by the troposphere or
atmospheric duct A tropospheric stratum, often
associated with temperature inversions, lake effects, or weather fronts, through which electromagnetic energy at ultra-high and microwave
frequencies is efficiently propagated for long distances.
atmospheric electricity Static electricity present
in the atmosphere, which evidences itself in disturbance of radio communications and in displays of lightning.
atmospheric noise Receiver noise resulting from
or static.
atmospheric pressure Abbreviation, atm press. 1.
The pressure exerted by the earth’s atmosphere,
as indicated by a barometer at sea level; normally
between 29 and 31 inches of mercury. 2. A pressure of 1.013 × 106 dynes per square centimeter.
atmospheric radio wave See SKYWAVE.
atmospheric radio window The band of frequencies (approximately 10 MHz to 10 GHz), including
radio waves that can penetrate the earth’s troposphere and ionosphere.
atmospheric reflection The return of a radio wave
to earth, resulting from reflection by an ionized
portion of the atmosphere.
atmospheric refraction 1. Downward bending of
radio waves as a result of variations in the dielectric constant of the troposphere. 2. Downward
bending of radio waves in the ionosphere, resulting in long-range propagation at high frequencies.
atmospheric scatter 1. The scattering of very-high
frequency ( VHF) and ultra-high frequency (UHF)
radio waves by the lower atmosphere. 2. Communication via scattering of VHF and UHF radio
waves in the lower atmosphere.
atmospherics See ATMOSPHERIC NOISE.
atom 1. The smallest material particle that displays the unique characteristics and properties of
an element. Atoms consist of a dense, positively
charged central nucleus, around which less-massive, negatively charged electrons “swarm” at definite levels called shells. Also see BOHR ATOM
and RUTHERFORD ATOM. 2. In a computercompiling operation, an operator or operand.
atomechanics The physics of electron movement.
atomic battery A battery in which atomic energy is
converted into electrical energy.
atomic charge The electrification (i.e., the electron
charge) exhibited by an ion.
atomic clock Also called atomic time standard. A
highly accurate electronic clock, driven by the
characteristic oscillations of certain atoms.
atomic energy Energy released by the FUSION or
FISSION of atomic nuclei. Also see ATOMIC
atomic fission See FISSION.
atomic frequency The natural vibration frequency
of an atom.
atomic fusion See FUSION.
atomic pile See REACTOR, 2.
atomic mass unit Abbreviated amu. A unit that
expresses the relative mass of an elemental isotope. One amu is equal to 1⁄12 of the atomic mass
of carbon 12 (C12). A neutron has a mass of
roughly one amu.
atomic migration The transfer or “wandering” of a
valence electron between or among atoms in a
single molecule.
atomic number The number of protons in the nucleus of an atom. Also, the number of electrons if
the atom is electrically neutral. For example, the
atomic number for copper is 29, indicating 29
protons in the nucleus. An electrically neutral
atom of copper has 29 electrons. The atomic
number uniquely identifies an element.
atomic radiation The emission of radiant energy
by radioactive substances.
atomic reactor • attracted-disk electrometer
atomic reactor See REACTOR, 2.
atomic theory The scientific theory that all matter is
composed ultimately of atoms, which are the smallest particles retaining the identity of an element.
Atoms combine to form molecules, the smallest
particles that retain the identity of a compound.
Atoms themselves contain minute subatomic particles, some of which carry electric charges. See
atomic time 1. A means of time determination
that makes use of the resonant vibrations of certain substances, such as cesium. 2. Synchronized astronomical time, as determined by an
atomic unit of energy In a hydrogen atom, the potential energy of the electron in the lowest-energy
shell, as averaged over a certain length of time.
The shell represents the mean energy of the electron.
atomic weight 1. The mass of a particular atom in
ATOMIC MASS UNITS (amu). 2. A number characterizing the average mass of individual atoms
for a specific isotope of an element. Thus, carbon
12 (C12) has an atomic weight of 12, oxygen 16
(O16) has an atomic weight of approximately 16,
and uranium 238 (U238) has an atomic weight of
about 238.
atomistics The science of the atom and atomic energy. Also called atomics.
attack 1. The rise of a pulse from zero to maximum
amplitude. 2. The time required for a pulse to rise
from zero to maximum amplitude. 3. The initialization of a circuit voltage or current for a certain
purpose, such as an automatic gain control. 4.
The rise of a musical note from zero to full volume.
attack time The time required for an applied signal that suddenly increases in amplitude to reach
63.2 percent of its final, stable value.
attemperator An automatic temperature-controlling device; a thermostat.
attention display A computer-generated chart or
graph, displayed as an alert signal concerning a
particular situation.
attenuate To reduce in amplitude.
attenuation A reduction of signal amplitude.
attenuation characteristic Also called attenuation constant. 1. In an amplifier, network, or component, the decrease in signal amplitude as a
function of frequency, usually expressed in decibels per octave. 2. In a transmission line, the decrease in signal amplitude per unit length.
Usually expressed in decibels per 100 feet, decibels per mile, or decibels per kilometer.
constant See
attenuation distortion A type of distortion characterized by variation of attenuation with frequency within a given frequency range.
attenuation equalizer An equalizer that stabilizes
the transfer impedance between two ports at all
frequencies within a specified frequency band.
distortion Distortion
characterized by the attenuation of the frequency
components in a complex waveform. Frequencysensitive RC networks (such as a Wien bridge) exhibit this type of distortion when they attenuate a
fundamental and each harmonic unequally.
attenuation network A combination of components (R, C, or L singly or in any necessary
combination) that provide constant signal
attenuation with negligible phase shift throughout a frequency band.
attenuation ratio The ratio indicating a relative
current, voltage, power or energy decrease. For
example, for voltage, Einput/Eoutput = 6/2 = 3:1 = 3.
attenuator A device for reducing signal amplitude
in precise, predetermined steps, or smoothly over
a continuous range. A network of resistors, capacitors, or both. The simplest attenuator consists of one or more noninductive resistors.
attitude The position of an aircraft or space vehicle
relative to a (usually terrestrial) reference point,
often determined with electronic instruments.
atto- Abbreviated, a. A prefix meaning 10 –18 or
multiplication by 10–18.
attofarad Abbreviation, aF. An extremely small
unit of low capacitance; 1 aF equals 10 –18 F.
attracted-disk electrometer A device to measure
potential difference consisting of two parallel
metal disks—one of which is connected to a tension spring. The force between the disks indicates
the magnitude of the electric field.
attraction • audio-frequency filter
Audibility (dB)
10 – 20
30 – 40
40 – 60
60 – 70
70 – 80
80 – 90
90 – 100
110 – 120
130 – 140
Threshold of hearing
Electric fan at 10 feet
Running water at 10 feet
Speech at 5 feet
Vacuum cleaner at 10 feet
Passing train at 50 feet
Jet at 1000 feet altitude
Rock band on stage
Air hammer at 5 feet
frequency section). 3. A radio channel of fixed frequency that is reserved for voice communications.
audio clipping Brute-force limiting of the amplitude of an audio signal, usually accomplished using semiconductor diodes to prevent the positive
and negative peak amplitudes from exceeding a
certain level.
attraction The drawing together or pulling toward,
as in the attraction between electric charges or
magnetic poles. Dissimilar charges and poles attract each other (electric plus to minus, magnetic
north to south). Compare REPULSION.
ATV Abbreviation of amateur television, used in the
Amateur Radio Service.
Au Symbol for GOLD.
audibility The quality of being detectable by the
human ear. In a healthy listener, the threshold of
audibility is extremely low; at the threshold, the
pressure of a sound wave varies from normal by
approximately 10-4 pascal. The frequency range
of human audibility extends roughly from 20 Hz
to 20 kHz.
audibility table
audibility curve A graph (such as the FletcherMunson curve) that depicts the range of human
hearing in terms of frequency versus the sound
pressure at the threshold of AUDIBILITY.
audible Detectable by the human ear.
audible alarm device An ANNUNCIATOR that
produces an easily identifiable sound in response to an ALARM CONDITION in a security
audible frequency See AUDIO FREQUENCY.
audible tone A vibration of air molecules that can
be detected by the human ear, and with periodic
properties, such as a sine-wave vibration.
audio 1. Pertaining to the spectrum of frequencies
corresponding to the human hearing range
(about 20 Hz to 20 kHz), or to equipment or performance associated with that spectrum. 2. Any
disturbance, such as a current or compression
wave, falling within the range of about 20 Hz to
audio band The range (band) of audio frequencies.
audio channel 1. The portion of a complex signal
or waveform used to convey audio information exclusively. 2. The audio-frequency section of a
transmitter or receiver (as opposed to the radio-
audio component The audio-frequency portion of
any wave or signal.
audio converter A circuit in which a received radio-frequency (RF) signal is heterodyned with a
local RF oscillator signal to produce an audiofrequency (AF) beat-note output. The beat note is
then amplified by an AF amplifier. It is used especially by amateur radio operators in the reception of continuous-wave (CW) radiotelegraphy,
radioteletype, and packet radio at high frequencies.
audio frequency A frequency lying within the audible spectrum. Abbreviated AF. See AUDIOFREQUENCY SPECTRUM.
audio-frequency amplifier An amplifier that operates in part or all of the frequency range 20 Hz to
20 kHz. High-fidelity amplifiers function over a
somewhat wider range (e.g., 10 Hz to 50 kHz).
audio-frequency choke An inductor (usually having a ferromagnetic core) that blocks audio-frequency current, but passes direct current.
audio-frequency feedback 1. Electrical FEEDBACK (positive and/or negative) that affects audiofrequency circuits. 2. ACOUSTIC FEEDBACK.
audio-frequency filter A filter of any type that operates on any part of the frequency range 20 Hz to
20 kHz.
audio-frequency meter • audio mixer
audio-frequency meter An instrument to measure
frequencies in the audio-frequency spectrum (approximately 20 Hz to 20 kHz). Three types are
commonly used:
• Analog Gives direct indications of frequency on
the scale of a D’Arsonval meter; the usual range
is 20 Hz to 100 kHz.
• Digital Gives direct indications of frequency by
means of readout lamps; the usual range is 1 Hz
to 15 MHz. This instrument is useful also as a
radio-frequency meter.
• Bridge Consists of a frequency-sensitive bridge,
such as a Wien bridge, with a null-indicating
meter. The operator balances the bridge and
reads the unknown frequency from the dial of
the balance control.
audio-frequency noise Any electrical noise signal
causing interference within the audio-frequency
audio-frequency oscillator See AUDIO OSCILLATOR.
audio-frequency peak limiter Any circuit or device, such as a biased diode, that performs the
function of audio limiting.
audio-frequency-shift keying Abbreviation, AFSK.
Frequency-shift keying that is done at audio
frequencies (below approximately 20 kHz) rather
than at radio frequencies. There are two audio
sine-wave signals, one for logic 1 (high or mark)
pulses and the other for the logic 0 (low or space)
pulses. This scheme is commonly used with
telephone modems where the signal bandwidth is
severely limited by circuit characteristics. At
typical data speeds in twisted-pair telephone
lines (usually 28.8 or 57.6 kbps), signals of this
type sound like a hiss or roar.
audio-frequency-shift modulator A modulator for
audio-frequency-shift keying of a signal.
audio-frequency spectrum The band of frequencies extending from roughly 20 Hz to 20 kHz.
High-fidelity component specifications extend
this range somewhat in both directions (e.g., from
10 Hz to 50 kHz).
audio-frequency transformer Abbreviation, AF
transformer. A device used for the purpose of
matching impedances at frequencies within the
range of human hearing (up to approximately 20
kHz). This ensures the most efficient possible
transfer of power between stages of audio amplification, between an amplifier and a speaker or
headset, or between a microphone and an audio
preamplifier. These transformers are available
with various power ratings and impedancematching ratios. Some devices are tailored to
have a certain attenuation-versus-frequency response. At audio frequencies, transformers are
physically similar to the alternating-current
transformers used in power supplies. They are
wound on laminated or powdered-iron cores.
audio-frequency transistor A transistor that is
usually used only at audio frequencies.
audiogram A graph used to rate hearing, used by
audiologists and audiometrists.
audio image In a direct-conversion receiver, a response to a signal on one side of (above or below)
the local-oscillator (LO) frequency, when the operator is listening to a signal on the other side of
the LO frequency. These responses are reduced
or eliminated in single-signal receivers.
audio-level meter An ac meter for monitoring signal amplitude in an audio-frequency system. It
can indicate in volts, decibels, volume units (VU),
or arbitrary units, and is often permanently connected in the circuit.
audio limiter A limiter or clipper operated in the
audio-frequency (AF) channel of a receiver or
transmitter to hold the output-signal amplitude
constant, or to minimize the effect of noise peaks.
audiologist A person skilled in testing hearing (i.e.,
in using audiometers and other electronic instruments) and evaluating their indications for the
fitting of hearing aids.
audiometer An instrument used for hearing tests,
which consists of a specialized audio-frequency
(AF) amplifier with calibrated attenuators, output
meter, and signal source.
audiometrist A person skilled in the use of audiometers and other electronic instruments that
measure sound and human hearing, and who
deals with attendant health and behavior problems. Compare ACOUSTICIAN and AUDIOLOGIST.
audio mixer An amplifier circuit for blending two
or more audio-frequency (AF) signals, such as
those delivered by microphones or receivers.
audio oscillator • auroral propagation
audio oscillator 1. An oscillator that delivers an
output signal in the frequency range 20 Hz to 20
kHz. 2. An audio-frequency (AF) signal generator.
Some instruments of this type operate above and
below the limits of the common audio-frequency
spectrum (e.g., 1 Hz to 1 MHz).
audio output The output of an audio-frequency
oscillator or amplifier. It can be measured in
terms of peak or rms volts, amperes, or watts.
audiophile A sound-reproduction hobbyist.
audio power Alternating-current power at frequencies roughly between 20 Hz and 20 kHz. When
used in connection with transmitters and other
modulated radio-frequency (RF) equipment, the
term refers to modulator power output.
audio response unit A device that links digitized
responses, held in computer storage, to a telephone set or line to answer incoming calls and inquiries.
audio signal generator See AUDIO OSCILLATOR, 2.
audio spectrum The range of sine-wave frequencies detectable by the human ear when they occur as acoustic vibrations. This range is about 20
Hz to 20 kHz.
audio squelch A squelch circuit that operates only
on the audio channel of a receiver.
audio system 1. The portion of any electronic assembly that is used to process sound. 2. Special
computer equipment capable of storing and processing digitized audio-frequency (AF) data.
audiotape Magnetic tape for the recording and reproduction of data in the audio-frequency (AF)
audio taper In potentiometers, a semilogarithmic
variation of resistance versus rotation. Used in
volume and tone controls for audio circuits. At
midposition (the halfway point), the counterclockwise portion of the device has about 1⁄10 the
resistance of the clockwise portion. A listener will
hear sound at half-volume because of the logarithmic nature of the human audibility curve.
audio-visual Pertaining to a combination of sound
and sight (e.g., television and sound motion pictures).
auditory backward inhibition A subjective phenomenon, in which a sound is erased from the
memory of a listener by a second sound arriving
about 60 milliseconds later.
auditory inhibition The tendency of sound waves
to be partially or totally canceled by the
ears/mind of a listener, depending on the waves’
intensity, relative phase, and/or direction of impact.
auditory mirage See ACOUSTIC MIRAGE.
audit trail A history of the processes relating to a
record, transaction, or file in a computer system.
Created during the routine processing of data,
the trail is stored as a file. The audit trail allows
auditing of the system or the subsequent recreation of files.
augend In a calculation, the number to which another is to be added. Compare ADDEND.
augend register In a digital computer, the register
that stores the augend. Compare ADDEND REGISTER.
aural Pertaining to sound actually heard, as opposed to sound that exists only as audiofrequency currents or waves.
aurora A phenomenon sometimes called the northern lights or southern lights, as seen in the night
sky. In the Northern Hemisphere, it is known as
Aurora Borealis; in the Southern Hemisphere, it
is called Aurora Australis. It generally occurs a
few hours after a solar flare, when charged particles, emitted from the sun, arrive at the earth,
and are accelerated in the vicinity of the the geomagnetic poles.
auroral absorption Radio wave absorption by an
auroral flutter Rapid fading of a signal at high or
very high frequencies, so-called because it often
imparts a fluttering quality to the signal that is
caused by phase distortion and Doppler shift
when the waves are reflected from the aurora.
auroral interference 1. Interference to highfrequency radio propagation and also occasionally to medium-frequency and low-frequency
propagation, caused by the activity of the aurora.
2. Auroral flutter on a signal.
auroral opening A condition in which radio communication becomes possible via AURORAL
PROPAGATION. It can occur when communication between two points is normally impossible at
a certain frequency. Auroral openings allow longdistance communication well into the very-highfrequency (VHF) spectrum.
auroral propagation Reflection of radio signals
from aurora that occur during geomagnetic
storms. Theoretically, auroral propagation is possible when the aurora are active, between any two
points on the earth’s surface from which the same
part of the aurora lie on a line of sight. This type
of propagation seldom occurs when one end of the
auroral propagation • automatic chrominance control
circuit is at a latitude less than 35 degrees north
or south of the equator. Auroral propagation can
take place at frequencies well above 30 MHz. It is
characterized by deep, rapid fading and random
phase modulation of reflected signals.
auroral reflection The return of electromagnetic
waves that have been beamed toward an aurora.
Most often observed between 15 MHz and 150
authorized access switch A device that disables a
security system in a defined region or volume so
that authorized personnel can enter without triggering an alarm condition.
authorized channel The carrier frequency or band
assigned to a transmitting station by a licensing
authority. Also see RADIO SPECTRUM.
autoalarm A device that is actuated from a received signal to alert a radio or computer network
operator to the existence of a message.
autobaud 1. In digital communications, a function
that allows the equipment to adjust itself to the
speed of the terminal. 2. Any digital communications equipment capable of automatically adjusting to the speed of the terminal.
autocondensation The application of radiofrequency (RF) energy to the human body for
medical purposes. The living organs serve as an
impedance or load, across which the RF is applied.
autoconduction The
radiofrequency (RF) currents into the body, by placing
the living organ inside a coil and supplying the
coil with RF. Used for medical purposes.
autocorrelation function A measure of the similarity between delayed and undelayed versions of
a signal, expressed as a delay function.
autodyne reception Radio reception of cw signals
by means of an oscillating detector. This is in
contrast to heterodyne reception, in which a local
oscillator (LO) generates an audio beat note with
the cw signal in a separate detector.
autoionization A two-phase process of atomic ionization. The atom is excited beyond its ionization
potential, and then it is allowed to deionize, causing the emission of an electron. The result is a
positively charged atom (positive ion).
automated communications The transfer of data
without the use of operating personnel; generally
done with computers connected to communications equipment.
automated guided vehicle Abbreviation, AGV. A
robot cart that runs without a driver. It uses an
electric engine and is guided by the magnetic field
produced by a current-carrying wire embedded in
the floor or pavement. Alternatively, the robot can
run on a track.
automated home A residence in which many, or
most, of the routine chores are done by computers and/or robots. Examples of such tasks are
dishwashing, doing the laundry, mowing the
lawn, blowing snow, and vacuuming the floors.
automated integrated manufacturing system
Acronym, AIMS. An assembly line or factory that
uses robots, often controlled by one or more computers, to perform specific tasks that result in the
production of various hardware items.
automatic Self-regulating, independent of human
intervention. Some periodic adjustment might be
automatic base bias A method of obtaining base
bias in a bipolar transistor, where a resistor
develops a voltage drop because of the current
flowing through it. The resistor is usually placed
in the emitter circuit, raising the emitter above
ground potential.
automatic bass compensation Also called bass
boost. In audio high-fidelity systems, a resistorcapacitor (RC) network that increases the relative
amplitude of the bass at low volume levels. This
compensates for the ear’s inefficiency at low frequencies. The function can be automatically actuated by the setting of the volume control, or it
can be switched manually on and off.
automatic bias In an amplifier, dc base/gate/
grid bias obtained from the voltage drop produced
by collector/drain/plate current flowing through
a resistor common to the input and output. This
resistor is usually shunted by a capacitor and
placed in the emitter/source/cathode circuit.
automatic brightness control A circuit that uses
the same principles used in AUTOMATIC GAIN
CONTROL (AGC) to hold steady the average
brightness of a television (TV) picture.
automatic carriage Typewriters, automatic key
punches, and other devices that can control automatically the spacing and feeding of paper,
cards, and forms.
automatic check 1. In a digital computer, the automatic inspection of operation and performance
by a self-contained subsystem. 2. The circuit or
device for performing this inspection.
automatic chrominance control In a color television (TV) receiver, a subcircuit that controls the
automatic chrominance control • automatic intercept
gain of the chrominance bandpass amplifier by
automatically adjusting its bias.
automatic circuit breaker Any device that opens
a circuit automatically when the flow of current
becomes excessive. The breaker generally resets
automatically after a specified length of time, or
after power has been temporarily removed from
the circuit.
automatic coding The use of a computer to determine the steps for solving a problem, before the
actual program for the problem is written. This
can help software engineers develop long and/or
complex computer programs.
automatic contrast control A circuit that automatically adjusts the gain of the video IF and RF
stages of a television (TV) receiver to preserve
good picture contrast.
automatic controller In servo systems, any of several circuits or devices that samples a variable
signal, compares it with a standard (reference)
signal, and delivers a control or correction signal
to an actuator.
automatic crossover 1. Current limiting in a
power supply. 2. A device that switches a circuit
from one operating mode to another automatically when conditions change in a predetermined
automatic current limiter A circuit or device for
holding the output current of a power supply to a
safe value during overload.
automatic current regulator A circuit or device
that holds the output current of a generator or
power supply to a predetermined value, in spite of
wide variations in load resistance.
automatic cutout A device that shuts down a circuit or system when the safe limits of operation
are exceeded. A circuit breaker is an example of
such a device, as is a thermostat in a power amplifier.
automatic data processing Abbreviation, ADP.
The use of computers and accessories for calculations and tabulations using data gathered automatically by the system.
automatic degausser A system for automatically
demagnetizing the picture tube in a color television (TV) receiver.
automatic dialing unit Abbreviated, ADU. A device that automatically generates dialing digits.
Many telephone sets have these devices, some of
which can be programmed for several different
telephone numbers, including country codes and
area codes.
automatic dictionary A computer system component that substitutes codes for words and
phrases in information retrieval systems. In language-translating systems, it provides wordfor-word substitutions.
automatic direction finder Abbreviated ADF. A
specialized receiver/antenna combination for automatically showing the direction from which a
signal arrives.
automatic error correction A technique of correcting transmission errors using error-detecting
and error-correcting codes and, usually, automatic retransmission.
automatic exchange A transmission exchange in
which interterminal communications are accomplished without operators.
automatic focusing A method of focusing a picture tube automatically, in which a resistor connects the focusing anode to the cathode; thus, no
external focusing voltage is necessary.
automatic frequency control Abbreviation, AFC.
A system that keeps a circuit automatically tuned
to a desired signal frequency. A detector (such as
a discriminator) operated from the tuned circuit
delivers a dc output voltage only when the circuit
is operating above or below the signal frequency;
otherwise, it has zero dc output. The dc output,
when present, alters the capacitance of a varactor
in the tuned circuit to retune the stage to the desired frequency.
automatic gain control Abbreviated AGC. A system that holds the output of a receiver or amplifier substantially constant despite input-signal
amplitude fluctuations. A rectifier samples the ac
signal output and delivers a dc signal proportional to that output. The dc signal is filtered, and
the smoothed-out voltage is applied in correct polarity as bias to one or more preceding stages to
reduce their gain. The stronger the signal entering the system, the greater the reduction in gain.
As a result, weak signals are amplified much
more than strong ones. Various forms of this
scheme are used in many types of amplifiers and
communications systems.
automatic gate bias A method of obtaining gate
bias in a FET, where a resistor develops a voltage drop because of the current flowing through
it. The resistor is usually placed in the source
circuit, raising the source above ground potential.
automatic height control In a television (TV) receiver, a system that automatically maintains the
height of the picture, despite signal-amplitude
fluctuations, power-line voltage changes, and
gain variations.
automatic intercept A telephone answering machine. It allows messages to be recorded when the
subscriber is not able to answer the telephone.
automatic interrupt • automatic secure voice communications
automatic interrupt A program interruption
caused by hardware or software acting in response to some event independent of the program.
automatic level compensation See AUTOMATIC
automatic level control Abbreviation, ALC. 1. A
circuit that adjusts the input gain of a magnetictape recording device to compensate for changes
in the loudness of the sound reaching the microphone. 2. A form of AUTOMATIC GAIN CONTROL
used in single-sideband (SSB) radio transmitters
to maintain linearity while increasing the level of
the average power relative to the peak power.
automatic line feed In the digital transmission of
printed matter, the automatic insertion of a line
feed (LF) character immediately following every
carriage return (CR) character.
automatic modulation control Abbreviation,
AMC. In a frequency-modulated (FM) radio transmitter, a form of AUTOMATIC GAIN CONTROL
that regulates the gain of the audio amplifiers to
compensate for fluctuating audio input amplitude. This prevents overdeviation while optimizing signal intelligibility.
automatic noise limiter Abbreviation, ANL. Any
of several circuits for clipping noise peaks exceeding a predetermined maximum receivedsignal amplitude.
automatic phase control In a color television (TV)
receiver, a circuit that synchronizes the burst signal with the 3.58-MHz color oscillator.
automatic pilot An electronic device, often computer-controlled, that automatically keeps a ship,
airplane, or space vehicle on course.
automatic polarity In an electronic metering device, a means of automatically switching the input polarity of the instrument when the input
signal polarity is shifted. Also called bipolar operation.
automatic programming See AUTOMATIC CODING.
automatic protective device A circuit or device
(such as a fuse, circuit breaker, limiter, or regulator) that protects another circuit or device by
automatically removing, reducing, or increasing
the current or voltage during overload or underload.
automatic radio compass See AUTOMATIC
automatic ranging In a metering device, the automatic adjustment or optimization of the full-scale
range to compensate for large changes in the input parameter.
automatic regulation 1. Voltage regulation. In a
power supply, the automatic holding of the output
voltage to a constant value, despite variations in
the input voltage or load resistance. 2. Current regulation. In a power supply, the automatic holding
of the output current to a constant value, despite
variations in the input voltage or load resistance.
automatic relay The relaying of messages automatically from one station to another via intermediate points, without the need for human
automatic repeater station A station that receives signals and simultaneously retransmits
them, usually on a different frequency.
automatic reset 1. The self-actuated restoration
of a circuit or device to a given state (e.g., the
state of rest). 2. A circuit or device that restores
another circuit or device to a given state.
automatic scanning 1. The automatic (usually
repetitive) tuning or adjustment of a circuit or
system throughout a given frequency range. In a
radio receiver, the system can be programmed to
pause or stop at occupied channels, passing over
vacant ones; or it can be programmed to pause or
stop at vacant channels, passing over occupied
ones. 2. The repetitive sweep of a cathode-raytube (CRT) electron beam.
receiver Also
PANORAMIC RECEIVER. A radio receiver that is
automatically tuned (usually repetitively) over a
frequency band. Such a receiver either homes in
on a signal when one is found, or displays on a
cathode-ray-tube (CRT) screen the distribution of
signals in the band.
automatic secure voice communications A wideband and narrowband voice-digitizing application
automatic secure voice communications • auxiliary contacts
to a security network that provides encoded voice
automatic send/receive set A teletypewriter or
terminal that is capable of receiving and transmitting.
automatic sensitivity control 1. A self-actuating
circuit using principles similar to those used in
AUTOMATIC GAIN CONTROL. It varies the sensitivity of the radio-frequency (RF) and intermediate-frequency (IF) sections of a receiver in inverse
proportion to the strength of a received signal. 2.
In a bridge null detector, a circuit similar to the
one described in 1, which operates ahead of the
detector, varying the sensitivity of the latter automatically.
automatic sequencing The ability of a digital computer to perform successive operations without
additional instructions from the operator.
automatic short-circuiter A device that automatically short-circuits the commutator bias in some
single-phase commutator motors.
automatic short-circuit protection A circuit that
allows the output of a power supply to be shortcircuited without damage to the components
in the supply. It usually consists of a currentlimiting device.
automatic shutoff A switching arrangement that
automatically shuts off a device or circuit under
certain specified conditions.
automatic switch center A telephone-switching
network that routes calls to their destinations
without the need for a human operator.
automatic target control For a vidicon television
camera tube, a circuit that automatically adjusts
the target voltage in proportion to brightness of
the scene.
automatic telegraph reception Telegraph reception providing a direct printout of the received information, without intervention by an operator.
transmission Telegraph
transmission originating from tapes, disks, or other
records, rather than from a hand-operated key.
automatic telegraphy Communications that utilize automatic telegraph transmission and reception.
automatic time switch A time-dependent circuit
or device that opens or closes another circuit at
the end of a predetermined time interval.
automatic tracking A method of keeping a radar
beam automatically fixed on a target.
automatic trip A circuit breaker that automatically opens a circuit.
automatic tuning A process whereby a circuit
tunes itself to a predetermined frequency upon
receiving a command signal.
automatic voltage regulator A circuit that keeps
the output of a power supply constant, despite
the load resistance or input voltage to the supply.
automatic volume control Abbreviated AVC. The
use of AUTOMATIC GAIN CONTROL in an audio
amplifier system.
automatic zero In an electronic meter, a means of
automatically setting the indicator to zero in the
absence of an input signal.
automation 1. The control of machines or processes by self-correcting electronic systems. See
ROBOT. 2. The use of robots and/or computers,
rather than human beings, to perform repetitive
tasks. 3. The use of robots and/or computers to
assist human beings in industrial, office, governmental, and educational work.
automaton A simple robot that performs a task or
set of tasks without artificial intelligence (AI).
These machines have existed for decades. Compare ANDROID.
automonitor In digital computer operations, to require the machine to supply a record of its information-handling operations. Also, the program
for such instructions.
automotive battery A set of four or eight
rechargeable lead-acid cells connected in series
and housed in a common enclosure. The electrolyte is a free-flowing liquid acid. Provides approximately 6 volts (four cells) or 12 volts (eight
cells) under no-load conditions when fully
charged. The high mass results in large energystorage capacity. These batteries must be handled with care and always kept in an upright
position to prevent spillage of the acid. See
autonomous robot A self-contained robot with an
independent computerized control system. It
moves under its own power, usually by rolling on
wheels or a track drive. Compare INSECT ROBOT.
autopatch A remotely controllable device that interconnects a radio-communications system into
a telephone network.
autopilot A self-correcting control and guidance
device for the automatic management of an aircraft or missile.
autoranging See AUTOMATIC RANGING.
autosyn A device or system that operates on the
principle of the synchronous ac motor, in which
the position of the rotor in one motor (the transmitter) is assumed by the rotor in a distant motor
(the receiver) to which the first is connected.
auto tracking A method of controlling the output
voltages of many different power supplies simultaneously.
autotransducter A type of magnetic amplifier
whose power windings serve also as control windings.
autotransformer A single-winding transformer in
which the primary coil is a fraction of the entire
winding for voltage step-up, or the secondary coil
is a fraction of the entire winding for voltage stepdown.
auxiliary circuit A circuit that is supplementary to
the main system.
auxiliary contacts In switches and relays, contacts that are supplementary to the main contacts and are usually actuated with them.
auxiliary equipment • avalanche breakdown
auxiliary equipment 1. Also known as peripherals. An apparatus not directly governed by the
central processing unit of a digital computer,
such as a printer or personal robot. 2. Peripheral
equipment in any system. 3. Backup equipment.
auxiliary memory In a digital computer, a unit
that is supplementary to the main memory,
which it augments.
auxiliary receiver Also called standby receiver. In
a radio communications system, a receiver that is
available for use if the main receiver fails.
auxiliary relay 1. A standby relay. 2. A relay
whose operation supports that of another relay.
3. A relay that is actuated by the operation of another relay.
auxiliary switch 1. A standby switch. 2. A switch
wired in series or parallel with another switch. 3.
A switch that is operated by another switch.
auxiliary transmitter Also called standby transmitter. In a radio communications system, a
transmitter that is available for use if the main
transmitter fails.
a/v Abbreviation of AUDIO-VISUAL.
aV Abbreviation of attovolt.
availability The proportion of time during which
an apparatus is operating correctly. It is usually
given as a percentage.
available conversion gain The ratio of the input
power to the output power of a transducer or converter. It is generally given in decibels.
available gain The ratio Po/Pi, where Pi is the available power at the input of a circuit and Po is the
available power at the output.
available line The percentage of the length of a facsimile scanning line that is usable for picture signals.
available power The mean square of the opencircuit terminal voltage of a linear source divided
by four, times the resistive component of the
source impedance. The available power is the
maximum power delivered to a load impedance,
equal to the conjugate of the internal impedance
of the power source.
available power gain In a power transistor, the ratio of available transistor output power to the
power available from the generator. It depends on
the generator resistance, but not on the transistor load resistance.
available signal-to-noise ratio The ratio Ps/Pn,
where Ps is the available signal power at a given
point in a system and Pn is the available randomnoise power at that point.
available time 1. The time during which a computer is available and ready for immediate use. 2.
The amount of time a computer is available to an
avalanche The phenomenon in semiconductors
operated at high reverse bias voltage, whereby
carriers acquire sufficient energy to produce new
electron-hole pairs as they collide with atoms.
The action causes the reverse current to increase
avalanche breakdown In a semiconductor P-N
junction, a condition that occurs when the reverse bias voltage exceeds a certain value. If the
electric field in the vicinity of the junction becomes strong enough, charge carriers are dislodged from the atoms and the carriers (electrons
and holes) flow freely across the P-N junction in
the opposite direction from normal. The mini-
avalanche breakdown • AX.25
mum reverse-bias voltage required to cause this
phenomenon varies among different kinds of
diodes. Some diodes are manufactured to have
precise avalanche voltages. See ZENER DIODE.
avalanche conduction In a semiconductor junction, the enhanced reverse-bias conduction
caused by a condition of AVALANCHE.
avalanche current The high current that flows
through a semiconductor junction when
avalanche diode See ZENER DIODE.
avalanche impedance The reduced impedance of
a diode during avalanche.
avalanche noise Electrical noise generated in a
junction diode operated at the point at which
avalanche just begins.
avalanche transistor A transistor that operates at
a high value of reverse-bias voltage, causing the
pn junction between the emitter and base to conduct because of avalanche breakdown.
avalanche voltage In a semiconductor P-N junction, the minimum applied reverse-bias voltage
AVC Abbreviation of automatic volume control.
avdp Abbreviation for Avoirdupois, a weightmeasurement scheme that is used in Englishspeaking countries and is based on the pound.
average absolute pulse amplitude The average
(disregarding algebraic sign) of the absolute amplitudes of a pulse, taken over the duration of the
average brightness The average brilliance of a
television (TV) picture, cathode-ray-tube (CRT)
computer display, or oscilloscope image.
average calculating operation The operating time
considered typical for a computer calculation
(i.e., one that is longer than an addition and
shorter than a multiplication); it is frequently
taken as the average of nine additions and one
average current Abbreviation, Iavg. The average
value of alternating current flowing in a circuit.
Taking polarity into account, this value is zero for
a pure sine wave. For other waveforms, it can
vary. When polarity is not considered, the sinewave value of Iavg is equal to 0.637 times Ipk, the
peak value of current; Iavg = 0.637 Ipk.
average life See MEAN LIFE.
average noise figure The ratio of the total noise
output from a circuit to the thermal noise output
at 290 degrees Kelvin. It is usually expressed in
decibels, with the noise taken at all frequencies.
average power The average value of power in an ac
circuit. In a resistive circuit, it is the square of the
effective (rms) current times the resistance; Pavg =
(Irms)2R (for sine waves).
average pulse amplitude Also called effective
pulse amplitude. The value obtained by integrating the pulse amplitude, with respect to time,
from the start of the pulse to its end, then dividing this integral by the pulse duration.
average rectified current Abbreviation, Iavg. The
average value of rectifier output current before filtering. For a full-wave rectifier with a sine wave
input and a resistive load, Iavg is equal to the maximum current Im multiplied by 0.637.
average rectified voltage Abbreviation, Eavg. The
average value of rectifier output voltage before filtering. For a full-wave rectifier with a sine-wave
input and a resistive load, Eavg is maximum voltage Em multiplied by 0.637.
average value 1. The arithmetic mean of two or more
quantities. 2. The geometric mean of two or
more quantities. 3. The harmonic mean of two
or more quantities. 4. In ac operation, the average current, voltage, or power.
average voltage Abbreviation, Eavg. The average
value of ac voltage in a circuit. Taking polarity into
account, this value is zero for a pure sine wave.
For other waveforms, it can vary. When polarity is
not considered, the sine-wave value of Eavg is equal
to 0.637 times Epk, the peak value of voltage.
avg Abbreviation of average.
aviation channels Frequency channels assigned
Aviation services The radio-communication services used by aeronautical-mobile and radio navigation personnel.
avigation Acronym for aviation navigation. Aircraft
navigation by means of electronic equipment.
avionics Acronym for aviation electronics. The design, production, and application of electronic devices and systems for use in aviation, navigation,
and astronautics.
Avogadro’s constant (Amedeo Avogadro, 1776–
1856.) Symbol, NA. The number of molecules in a
kilogram-molecular weight of any substance; NA
equals 6.025 × 1026 (kg-mole)–1.
A voltage The filament voltage in a vacuum-tube
aW Abbreviation of attowatt.
AX.25 A signal format used in some digital communications systems, notably amateur packet radio.
axial leads • azusa
axial leads The centrally located leads emanating
from the ends of cylindrical components, such as
resistors and diodes.
axial ratio The ratio of the minor to major axes of a
waveguide’s polarization ellipse.
axis 1. A coordinate in a graphical presentation or
display (e.g., horizontal and vertical axes in a
rectangular coordinate system). 2. The real or
imaginary straight line around which a body rotates, or the line that passes through the center
of a symmetrical arrangement (line of symmetry).
axis of abscissas The horizontal axis (x-axis) of a
rectangular-coordinate graph or screen. Compare
axis of imaginaries The vertical axis of the complex plane in which rectangular vectors lie. Compare AXIS OF REALS.
axis of ordinates The vertical (y-axis) of a rectangular-coordinate graph or screen. Compare AXIS
axis of reals The horizontal axis of the complex
plane in which rectangular vectors lie. Compare
Ayrton-Mather galvanometer shunt A stepadjustable universal shunt resistor for varying
the sensitivity of a galvanometer. It has the virtue
of keeping the galvanometer critically damped.
The shunt is also useful in multirange
milliammeters, microammeters, and ammeters.
The sensitive meter movement is never without a
shunting resistor during range switching.
Ayrton-Perry winding A noninductive winding
comprising two inductors conducting current in
opposite directions; the opposing flow cancels the
magnetic field.
azel display A plan-position display that incorporates two different radar traces on a single
cathode-ray tube (CRT), one giving bearing, the
other elevation.
azimuth Also called compass direction. Angular
measurement in the horizontal plane, clockwise
from north. It is important in radio and television
communications, navigation, direction finding,
land surveying, and radar.
azimuth alignment In a tape recorder, the alignment of record and playback head gaps so that
their centerlines are parallel.
azimuth blanking In a radar system, blacking-out
of the image as the antenna sweeps across a
specified range of azimuth angles. Effectively
eliminates nuisance echoes from stationary, permanent objects (such as tall buildings or communications towers).
azimuth resolution In a radar system, the minimum azimuth separation of two targets whose
range (distance from the station) are equal that is
required for the system to show two echoes, rather
than one. It is generally measured in degrees.
azusa An electronic tracking system, in which a
single station provides slant range and two direction cosines for a distant airborne object. This accurately defines the coordinates of the distant
object in three-dimensional space.
1. Symbol for SUSCEPTANCE. 2. Symbol for
FLUX DENSITY. 3. Abbreviation of BATTERY. 4.
Symbol for BORON. 5. Symbol for base of transistor (see BASE, 1). 6. Abbreviation of BASS. 7.
Abbreviation of BEL. 8. Anode voltage or main operating voltage in any circuit (when used with
sign). Also see B VOLTAGE.
b 1. Symbol for SUSCEPTANCE. 2. Symbol for
base of transistor (see BASE, 1). 3. Abbreviation
of BASS. 4. Symbol for BARN.
B5-cut crystal A piezoelectric plate cut from a
quartz crystal in such a way that the face of the
plate is at an angle, with respect to the z-axis of
the crystal. This type of crystal has good frequency stability under conditions of changing
BA Abbreviation of BATTERY. Also see B and BAT.
Ba Symbol for BARIUM.
babbit A relatively soft, tin-base alloy of various
compositions. One composition contains 7.4%
antimony, 3.7% copper, and 88.9% tin.
babble Interference caused by crosstalk from a
number of channels.
babble signal A jamming signal containing babble
components. See BABBLE and JAMMING.
baby monitor A short-range radio transmitter and
receiver that can be used to listen at a distance to
the sounds in an infant’s room. The transmitter
contains a sensitive microphone, a whip antenna,
and a power supply. The unit can be placed on a
table or desk, or even on the floor near the baby’s
crib. The receiver is similar to a handheld
“walkie-talkie.” It is battery-powered and can be
carried around. It has an inductively loaded, short
“rubber duckie” antenna similar to the antennas
on cordless telephone sets. The receiver can pick
up signals from the transmitter at distances of up
to about 200 feet. The radio-frequency signals
pass easily through walls, ceilings, and floors.
back bias 1. A feedback signal (negative or positive). 2. Reverse bias (also see BIAS). 3. A reverse
bias voltage, obtained from a voltage divider connected between a voltage source and ground.
Copyright © 2001 by The McGraw-Hill Companies, Inc.
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R1, R2
back bias, 3
backbone • back resistance
backbone A form of transmission line with capacitive connections between the generator and the
back conduction Conduction of current in the reverse direction, as across a semiconductor junction that is reverse-biased.
back contact A contact that closes a circuit when a
relay, switch, or jack is in its normal rest position.
back current Symbol, Ib. The normally small current flowing through a reverse-biased pn semiconductor junction. Also called reverse current and
inverse current. Compare FORWARD CURRENT.
back diode A semiconductor diode that is normally
back-biased (reverse-biased).
back echo An echo resulting from the rear lobe of
an antenna radiation pattern.
back emf See BACK VOLTAGE.
Back-Goudsmit effect See ZEEMAN EFFECT.
background 1. The context or supporting area of a
picture (e.g., the background of a television picture). 2. Background noise.
background control In a color television receiver,
a potentiometer used to set the dc level of the
color signal at one input of the three-gun picture
background count Residual response of a radioactivity counter in an environment as free as
practicable of radioactivity. This background is
caused largely by cosmic rays and inherent radioactivity of surrounding buildings and other
background job A low-priority, relatively longrunning computer program that can be interrupted so that a higher-priority program can be
background noise Electrical noise inherent to a
particular circuit, system, or device that remains
when no other signal is present.
background processing In a computer, the running of programs having low priority.
background radiation Nuclear radiation from materials in the environment. Also see BACKGROUND COUNT.
background response The response of a radiation
detector to background radiation.
backing store In a computer, a device that stores
large amounts of information. In most small computers, this is done via MAGNETIC DISK and/or
MAGNETIC TAPE. A backing store can also be an
optical storage medium, such as CD-ROM (compact disk, read-only memory).
backlash 1. Slack or lag in action of moving parts.
Example: delay between initial application of a
force (such as that required to turn a knob) and
movement of a part or device (e.g., a potentiometer or variable capacitor). 2. On a mechanical
analog tuning dial, an arc within which slack or
lag is discernible.
backloaded horn A loudspeaker enclosure in
which the front of the speaker cone feeds sound
directly into the listening area, and the rear of the
cone feeds sound into the same area through a
folded horn.
backloading In a cascaded series of amplifiers, the
tendency of loading effects to be passed to earlier
stages. A change in the output impedance of a final amplifier circuit, for example, could also result in a change in the output impedance of the
driver circuit, and perhaps even in a change in
the output impedance of the predriver.
back lobe In the pattern of a directional antenna,
the lobe directly opposite the major lobe, representing the radiation or response in or from a direction 180 degrees from that in which the gain is
backplate A flat electrode in a television (TV) camera tube that receives the stored-charge image via
capacitive coupling.
back porch In a television (TV) horizontal sync
pulse, the time interval between the end of the
rise of the blanking pedestal and the beginning of
the rise of the sync pulse. That portion of the flat
top of the blanking pedestal behind the sync
pulse. Compare FRONT PORCH.
back-porch effect In transistor operation, the continuation of collector-current flow for a short time
after the input signal has fallen to zero.
back-porch tilt The departure of the top edge of a
back porch from true horizontal.
back pressure sensor A device that detects and
measures the torque that a motor is applying,
and produces a signal whose amplitude is proportional to the torque. This signal can be used
for various purposes. In a robotic device, for example, the sensor output can be fed back to the
motor control to limit the applied force.
back resistance Symbol, Rb. The resistance of a reverse-biased pn semiconductor junction. Also
back scatter • bail
back scatter Scattering of a wave back toward a
radio transmitter from points beyond the skip
zone. This phenomenon is caused by ionospheric
reflection. Compare FORWARD SCATTER.
backstop A contact or barrier (such as a screw or
post) that serves to limit the BACKSWING of the
armature of a relay.
backswing 1. The tendency of a pulse to overshoot,
or reverse direction after completion. Backswing
is measured in terms of the overshoot amplitude
as a percentage of the maximum amplitude of the
pulse. 2. The extent to which a relay armature
moves back from a contact when the relay contacts are open.
back-to-back connection The connection of
diodes or rectifiers in reverse parallel (i.e., the anode of one to the cathode of the other) across a
signal line to pass both half cycles of ac in certain
control circuits.
back-to-back sawtooth A symmetrical sawtooth
wave in which the rise slope is equal to the fall
slope. Also called triangular wave and pyramidal
backup 1. An element, such as a circuit component, that is used to replace a main component,
in case of main-component failure. 2. Any process or scheme that serves to maintain operation of a system in case of main-component
failure. 3. A battery that maintains volatile
memory data stored in one or more integrated
circuits. 4. A computer file, or set of files, stored
in a nonvolatile medium, such as diskettes or
magnetic tape, to prevent catastrophic data loss
in the event of hard-disk failure. 5. A battery or
alternative power source that keeps an alarm
system operational in the event of a utility power
backup battery 1. In a computer or microcomputer-controlled electronic device, a source of
voltage to preserve volatile memory data if the
power is removed. 2. A battery used for powering
a system in the event that the main power source
should fail.
backup facility In an electrical or communications
system, a facility that is intended for use when
the primary, or main, facility is not operational.
back voltage 1. Voltage induced in an inductor by
the flow of current through the inductor, so called
because its polarity is opposite to that of the applied voltage. Also called counter emf. 2. A voltage
used to obtain bucking action (e.g., the voltage
used to zero the meter in an electronic voltmeter
circuit). 3. Reverse voltage applied to a semiconductor junction.
backwall In a pot core, the plate or disk that connects the sleeve and center post to close the magnetic circuit.
backward diode A semiconductor diode manufactured in such a way that its high-current flow occurs when the junction is reverse biased. Such a
diode is also a negative-resistance device.
backward-wave oscillator Abbreviation, BWO. A
microwave oscillator tube similar to the travelingwave tube. Like the traveling-wave tube, the BWO
contains a helical transmission line. In the electron beam, electron bunching results from interaction between the beam and the electromagnetic
field, and reflection occurs at the collector. The
wave moves backward from collector to cathode,
and oscillation is sustained because the backward wave is in phase with the input. Output is
taken from the cathode end of the helix.
Helical line
backward-wave oscillator
back wave The oscillator signal present in an amplifier-keyed, continuous-wave (CW), Morse-code
transmitter. Normally, this signal is at the same
frequency as the transmitter output, but is not
sufficiently strong to be radiated over the air.
back-wave radiation The condition wherein a back
wave is strong enough to be heard on a continuous-wave (CW) keyed signal at the receiving station. This results from ineffective amplifier keying.
baffle A board on which a loudspeaker is mounted
to separate acoustic radiation from the back of
the cone from radiation emanating from the front.
The baffle improves bass response by increasing
the wavelength (lowering the frequency) at which
phase cancellation occurs.
baffle plate 1. See BAFFLE. 2. A metal plate
mounted in a waveguide to reduce the crosssectional area.
bail A wire loop or chain that holds one member of
a two-member assembly to prevent loss (e.g., the
short chain holding the dust cap of a jack).
Bakelite • balanced low-pass filter
Bakelite The trade name for a specialized plastic
dielectric material. Its chemical composition is
phenol-formaldehyde resin.
baker An obsolete phonetic alphabet code word for
letter B. BRAVO is commonly used instead.
baking-out In the process of evacuating a system,
the procedure of heating the system to a high
temperature to drive out gases occluded in the
glass and metal parts.
balance 1. See BRIDGE. 2. To null a bridge or similar circuit. 3. To equalize loads, voltages, or signals between two circuits or components. 4. In a
high-fidelity stereo sound system, a control or set
of controls that adjusts the relative loudness of
the left and right channels. 5. Alignment of a balanced modulator for minimum carrier output amplitude. 6. A condition in which two branches of a
circuit have identical impedances, relative to
balance coil 1. A type of autotransformer that enables a three-wire ac circuit to be supplied from a
two-wire line. A series of taps around the center of
the winding enables the circuit to be compensated
for unequal loads. 2. See BALANCING COIL.
balance control A variable component, such as a
potentiometer or variable capacitor, that is used
to balance bridges, null circuits, or loudspeakers.
balanced Having identical impedances, with respect to ground.
balanced amplifier Any amplifier with two
branches that have identical impedances, with
respect to ground. Usually, the two branches are
in phase opposition (180 degrees out of phase).
balanced antenna An antenna system where two
halves are exact replicas of each other, geometrically and electrically. Such an antenna normally
must either be fed with a balanced transmission
line or with a coaxial cable and balun.
balanced antenna system A balanced antenna, fed
with a balanced transmission line, that has currents of equal magnitude in each side. An example
feed line
balanced antenna system
is a half-wave dipole at uniform height above electrical ground, fed at the center with parallel-wire
line. It is important that the transmission line
runs away from the antenna at a right angle for at
least 1⁄4 wavelength, preferably 1⁄2 wavelength or
more, to prevent line imbalance caused by currents induced from the radiated field.
balanced bridge Any four-leg bridge circuit in
which all legs are identical in all electrical respects.
balanced circuit 1. A circuit that has its electrical
midpoint grounded, as opposed to the singleended circuit, which has one side grounded. 2. A
bridge circuit in the condition of null.
balanced converter See BALUN.
balanced currents Currents with the same value.
In the two conductors of a balanced transmission line, these currents are equal in amplitude
and opposite in phase at every point along the
balanced delta A set of coils or generators in a
three-phase system, connected so that the currents in any two coils differ in phase by 120 degrees.
balanced detector A symmetrical demodulator,
such as a full-wave diode detector or a discriminator.
balanced electronic voltmeter An electronic voltmeter circuit in which two matched transistors
are connected in a four-arm bridge arrangement.
The drift in one half of the circuit opposes that in
the other half; the resulting drift of the zero point
is virtually eliminated.
balanced filter A filter consisting of two identical
sections, one in each branch of a balanced system, such as a parallel-wire transmission line.
balanced input An input circuit whose electrical
midpoint is grounded. Compare SINGLE-ENDED
balanced input transformer An input transformer
in which the center tap of the primary winding is
balanced line A pair of parallel wires that possesses a uniform characteristic impedance. The
two conductors are of the same material and have
identical diameters. The distance between them
is constant. In a balanced two-wire line, the currents in the two conductors are of equal amplitude and opposite phase.
balanced lines In high-fidelity audio systems, a
cable that consists of two parallel conductors
surrounded by a single braid. The parallel wires
carry the audio-frequency (AF) signals, and the
braid is grounded for shielding.
balanced loop antenna A loop antenna with a
grounded electrical midpoint, determined by the
junction of two identical series-connected capacitors shunting the loop.
balanced low-pass filter A low-pass filter used in
a balanced system or balanced transmission
balanced method • balun
balanced method A system of instrumentation in
which a zero-center scale is used. The reading
can be either side of the zero reading.
balanced modulator A symmetrical modulator circuit using bipolar transistors, field-effect transistors, an integrated circuit, or diodes as principal
components, that delivers an output signal containing the sidebands, but not the carrier. It is
commonly used to generate a double-sideband
(DSB) signal that can be filtered to obtain a
single-sideband (SSB) signal.
balanced multivibrator A switching oscillator circuit in which the two halves are identical in configuration, and as nearly identical as practicable
in performance.
balanced network Any network intended to be
used with a balanced system or balanced transmission line. It is characterized by a pair of terminals, each of which shows the same impedance
with respect to ground.
balanced oscillator A PUSH-PULL OSCILLATOR.
balanced output Output balanced against ground
(e.g., where the electrical midpoint of the output
circuit is grounded).
balanced output transformer 1. A push-pull output transformer with a center-tapped primary
winding. 2. An output transformer with a
grounded center tap on its secondary winding.
balanced output transformer, 2.
balanced probe A probe, such as one for an electronic voltmeter or oscilloscope, that has a balanced input and (usually) a single-ended output.
balanced-tee trap A wavetrap constructed in a T
configuration, with a resonant section in each
conductor of a balanced transmission line.
balanced telephone line A telephone transmission line that has two sides, similar to a balanced
radio-frequency transmission line. Either side
has the same impedance, with respect to ground.
balanced termination A load device (or the practice of using such a device) in which the sections
provide identical termination for each of the sections or conductors of a balanced system, such
as a balanced line.
balanced-to-unbalanced transformer See BALUN.
balanced transmission line See BALANCED LINE.
balanced varactor tuning A two-varactor, backto-back circuit for adjusting the value of a capacitor using an applied dc voltage. This
arrangement has an advantage over a singlevaractor (unbalanced) circuit, because hightuned-circuit Q is maintained and harmonic
generation is reduced.
balanced voltages In any symmetrical system,
such as a balanced line or push-pull circuit, two
or more input or output voltages that are adjusted to have the same amplitude and (usually)
opposite phase.
balanced-wire circuit A circuit or conductor system with identical halves that are symmetrical,
with respect to ground and to other conductors.
balancing circuit See BUCKING CIRCUIT.
balancing coil In a receiver, a center-tapped antenna coil that is balanced to ground to eliminate
ballast 1. A component that is used to stabilize the
current flow through, or operation of, a circuit,
stage, or device. 2. An iron-core choke connected
in series with one of the electrodes in a fluorescent or other gas-discharge lamp.
ballast resistor 1. A nonlinear inductive power resistor whose voltage-current (EI) characteristic is
such that current through the resistor is independent of voltage over a useful range. This feature enables the ballast resistor to act as an
automatic voltage regulator when it is simply
connected in series with a power supply and load.
2. A small (usually high-resistance) resistor operated in series with a glow lamp, such as a neon
lamp, to prevent overload.
ballast transformer A misnomer often used in
place of BALLAST, 2.
ballistic galvanometer An undamped galvanometer that is used particularly to observe electric charges by noting the single throw resulting
from the momentary flow of current through the
galvanometer coil.
ballistics The electronics-supported science concerned with the motion of projectiles and similar
bodies in air or space.
balloon antenna A vertical antenna consisting of a
wire or wires held aloft by a captive balloon. Occasionally, used by radio amateurs and shortwave
listeners at low and medium frequencies. A potentially dangerous antenna because of large staticelectric buildup, a tendency to attract lightning,
the possibility of its breaking loose, and the risk of
accidental contact with high-voltage power lines.
balop Contraction of BALOPTICON.
balopticon An opaque-picture projecting system in
which the picture is viewed by a television (TV)
camera, such as a vidicon, and displayed by a
picture tube. Also called balop.
balun A specialized impedance-matching radiofrequency (RF) transformer. It is a wideband device,
balun • bandstop
usually providing a 1:1 or 1:4 impedance ratio
and available in several different forms. It is so
called because it has an unbalanced input suitable for coaxial transmission lines, and a balanced output suitable for dipole, Yagi, and quad
banana jack The female half of a two-part quickconnector combination. Splicing of a circuit is
completed by inserting a BANANA PLUG into this
banana plug The male half of a two-part quickconnector combination, with sides usually composed of flat springs that ensure contact with the
female BANANA JACK into which it is inserted.
banana jack and plug
band 1. A continuous range of radio or television
communications frequencies or wavelengths,
usually designated by the lowest and highest frequencies, or the approximate wavelength (e.g.,
the 20-meter amateur radio band). 2. A set of discrete radio or television frequency channels
within a specified range (e.g., the standard AM
broadcast band). 3. A range of wavelengths for infrared, visible, ultraviolet, X-ray, or gamma-ray
energy. 4. A range of energy levels. 5. A colored
stripe on a resistor or capacitor that forms part of
the code that indicates component value and tolerance.
band center 1. In a given radio or television communications band, the arithmetic mean of the
lowest and highest frequencies. 2. In a given
band, the geometric mean of the longest and
shortest wavelengths.
band-elimination filter See BAND-REJECTION
band gap In any atom, the difference in electron energy between the conduction and valence bands.
bandpass 1. The frequency limits between which a
transmits ac energy with negligible loss. 2. The
ability to allow passage of signals at a given frequency or band of frequencies while blocking
other signals. Compare BANDSTOP.
bandpass amplifier An amplifier that is tuned to
pass only those frequencies between preset limits.
bandpass coupling A coupling circuit with a flattopped frequency response so that a band of frequencies, rather than a single frequency, is
coupled into a succeeding circuit. Also see BANDPASS, 1.
bandpass filter Any resonant circuit, or combination of resonant circuits, designed to discriminate
against all frequencies except a specific frequency
f0, or a band of frequencies between two limiting
frequencies f0 and f1. In a parallel inductancecapacitance (LC) circuit, the device exhibits high
impedance at the desired frequency or frequencies and a low impedance at unwanted frequencies. In a series configuration, the filter has a low
impedance at the desired frequency or frequencies and a high impedance at unwanted frequencies. Compare BAND-REJECTION FILTER,
bandpass flatness The degree to which a bandpass
device’s attenuation-versus-frequency curve is a
straight line with zero slope within the passband.
band pressure level The net acoustic pressure of a
sound source within a specified frequency range
band-rejection filter Also called a band-stop filter.
Any resonant circuit, or combination of resonant
circuits designed to discriminate against a specific frequency f0, or a band of frequencies between two limiting frequencies f0 and f1. In a
parallel inductance-capacitance (LC) circuit, the
device exhibits high impedance at the desired frequencies, and a low impedance at the unwanted
frequency or range of frequencies. In a series configuration, the filter has a low impedance at the
desired frequencies and a high impedance at the
unwanted frequency or range of frequencies.
band selector Any switch or relay that facilitates
switching the frequency of a radio transmitter, receiver, or transceiver among various bands.
bandset capacitor In some older communications
receivers, a variable capacitor is used to preset
the tuning range in each band to correspond to
graduations on the tuning dial. This capacitor is
a trimmer or padder operated in conjunction with
the main tuning capacitor.
bandspreading In some older communications receivers, the process of widening the tuning range
within a given frequency band to cover the entire
dial. Otherwise, the band would occupy only a
portion of the dial, and tuning would be difficult.
It is usually accomplished with a BANDSPREAD
TUNING CONTROL whose range is preset via the
main tuning control and/or a BANDSET CAPACITOR.
bandspread tuning control An analog adjustment
in some older communications receivers that allows continuous tuning over a desired band of
frequencies. This control is separate from the
main tuning control.
bandstop 1. The frequency limits between which a
BAND-REJECTION FILTER blocks, or greatly
attenuates, ac energy. 2. The ability to suppress
or block signals of a given frequency or band
of frequencies, while allowing signals of other
frequencies to pass with little or no attenuation.
bandstop filter • bar meter
bandstop filter See BAND-REJECTION FILTER.
band suppression 1. The property of blocking, or
greatly attenuating, signals within a specific frequency band. 2. The frequency limits between
which a device or circuit rejects or blocks ac energy, while passing energy at other frequencies
with negligible loss.
band-suppression filter
bandswitch A low-reactance selector switch (usually
rotary) that facilitates changing the tuning range of
a radio receiver, transmitter or transceiver from
one band of frequencies to another.
bandswitching In a receiver, transmitter, or test
instrument, the process of switching selfcontained tuned circuits to change from one frequency spectrum to another within the range of
the device’s intended operation.
bandwidth 1. For a communications or data signal, a measure of the amount of spectrum space
the signal occupies. Usually, it is given as the difference between the frequencies at which the signal amplitude is nominally 3 dB down with
respect to the amplitude at the center frequency.
These frequencies represent the half-power
points of the amplitude-versus-frequency function. In general, the bandwidth increases as the
data rate (in bits per second, baud, or words per
minute) increases. 2. Also called NECESSARY
BANDWIDTH. The minimum amount of spectrum
space normally required for effective transmission and reception of a communications or data
signal. 3. See BANDPASS, 1.
bank A collection of usually similar components
used in conjunction with each other, usually in a
parallel configuration. Some examples are resistor bank, lamp bank, and transformer bank.
banked transformers Parallel-operated transformers.
bankwound coil A coil wound in such a way that
most of its turns are not side by side, thus reducing the inherent distributed capacitance.
bar 1. Abbreviation, b. The cgs unit of pressure, in
which 1 b = 105 pascals per square centimeter. 2.
A horizontal or vertical line produced on a television (TV) screen by a bar generator and used to
check linearity. 3. A thick plate of piezoelectric
crystal. 4. A solid metal conductor, usually uninsulated, of any cross section. 5. A silicon ingot
from which semiconductor devices can be fabricated.
bar code A printed pattern that contains data that
can be recovered by laser scanning. It is commonly used for the pricing and identification of
store merchandise. It can also be used by an assembly or maintenance robot as an aid to identifying tools.
bar-code reader A laser scanning device that recovers the data from a tag that contains a BAR
CODE. The laser beam moves across the tag. The
beam is reflected from the white regions between
the lines, but is absorbed by the dark lines themselves. This produces modulation of the reflected
beam by the data contained in the tag.
bare conductor A conductor with no insulating covering, a common example being bare copper wire.
bar generator A special type of radio-frequency
signal generator that produces horizontal or vertical bars on the screen of a television receiver. It
is used in adjustment of horizontal and vertical
bar graph A graphical presentation of data, in
which numerical values are represented by horizontal bars of width that correspond to the values. This type of graph is nonstandard in the
sense that the ordinate is horizontal, whereas it is
usually vertical. Compare COLUMNAR GRAPH.
bar-graph meter See BAR METER.
barium Symbol, Ba. An elemental metal of the alkaline-earth group. Atomic number, 56. Atomic
weight, 137.36. It is present in some compounds
used as dielectrics (e.g., barium titanate).
barium-strontium oxides The combined oxides of
barium and strontium used as coatings of
vacuum-tube cathodes to increase electron emission at relatively low temperatures.
barium strontium titanate A compound of barium, strontium, oxygen, and titanium that is
used as a ceramic dielectric material. It exhibits
ferroelectric properties and is characterized by a
high dielectric constant.
barium titanate Formula, BaTi02. A ceramic used
as the dielectric in ceramic capacitors. It exhibits
high dielectric constant and some degree of ferroelectricity.
Barkhausen effect The occurrence of minute
jumps in the magnetization of a ferromagnetic
substance as the magnetic force is increased or
decreased over a continuous range.
Barkhausen interference Interference that results
from oscillation because of the BARK-HAUSEN
bar magnet A relatively long permanent magnet in
the shape of a bar with a rectangular or square
cross section.
bar meter A digital meter that displays a quantity, such as signal strength, incrementally, using a set of LEDs or LCDs arranged in a straight
line. Its main advantage is that it has no moving
parts, yet (unlike direct-readout digital meters)
gives the viewer some impression of the way a
rapidly fluctuating quantity changes. Its chief
bar meter • baseband frequency response
disadvantage is that it does not provide a precise
barn Symbol, b. A non-SI unit of nuclear cross section equal to 100 square femtometers or 10– 24
square centimeters. This unit is approved as
compatible with SI (International System of
Barnett effect The development of a small amount
of magnetization in a long iron cylinder that is rotated rapidly about its longitudinal axis.
barograph A recording barometer, using either a
drum recorder (pen recorder) or a computer to
store the data as a function of atmospheric pressure versus time.
barometer An instrument for measuring atmospheric pressure.
barometer effect A relation that appears to exist
between the intensity of cosmic rays and the atmospheric pressure. It is an inverse relation; that
is, increasing pressure seems to correlate with reduced intensity of cosmic rays. It is said to be approximately to 1 or 2% per centimeter of mercury.
barometric pressure The atmospheric pressure,
usually given in inches of mercury. The average
barometric pressure at the surface of the earth is
just under 30 inches of mercury.
bar pattern A series of spaced lines or bars (horizontal, vertical, or both) produced on a television
picture screen by means of a BAR GENERATOR.
It is useful in adjusting horizontal and vertical
linearity of the picture.
barrage array An antenna array in which a string
of collinear elements are vertically stacked. The
end quarter wavelength of each string is bent in
to meet the end quarter wavelength of the opposite radiator to improve balance.
barrage jamming The jamming of many frequencies, or an entire band, at the same time.
barrell distortion Television picture distortion
consisting of horizontal and vertical bulging.
barrier 1. The carrier-free space-charge region in a
semiconductor pn junction. 2. An insulating partition placed between two conductors or terminals to lengthen the dielectric path.
barrier balance The state of near equilibrium in a
semiconductor pn junction (after initial junction
forming), entailing a balance of majority and minority charge carrier currents.
barrier capacitance 1. The capacitance in a bipolar
transistor between the emitter and collector. It
varies with changes in applied voltage, and also
with the junction temperature. 2. The capacitance
across any pn junction that is reverse-biased.
barrier height The difference in voltage between
opposite sides of a barrier in a semiconductor
barrier layer See BARRIER, 1.
barrier-layer cell A photovoltaic cell, such as the
copper oxide or selenium type, in which photons
striking the barrier layer produce the potential
barrier potential The apparent internal dc potential across the barrier (see BARRIER, 1) in a pn
barrier strip A terminal strip having a barrier (see
BARRIER, 2) between each pair of terminals.
barrier strip
barrier voltage The voltage required for the initiation of current flow through a pn junction.
Bartlett force See EXCHANGE FORCE.
baryon A subatomic particle made up of three
base 1. In a bipolar transistor, the intermediate region between the emitter and collector, which
usually serves as the input or controlling element
of transistor operation. 2. A substance that dissociates in water solution and forms hydroxyl
(OH) ions. For example, sodium hydroxide. 3. The
constant figure upon which logarithms are computed (10 for common logs, 2.71828 for natural
logs). 4. The radix of a number system (e.g., base
10 for the decimal system, base 8 for the octal
system, base 16 for the hexadecimal system, and
base 2 for the binary system). 5. A fixed nonportable radio communications installation.
base address The number in a computer address
that serves as the reference for subsequent address numbers.
baseband The frequency band of the modulating
signal in a communications, broadcast, or data
transmitter. For voice communications, this is
generally the range of voice frequencies necessary
for intelligible transmission. For high-fidelity music broadcasting, it is approximately the range of
human hearing. For fast-scan television, it
ranges up to several megahertz. It can be restricted or expanded, depending on the nature of
the transmitted signal. See BASEBAND FREQUENCY RESPONSE.
baseband frequency response 1. The amplitudeversus-frequency characteristic of the audiofrequency (AF) or composite video section of a
transmitter that defines the BASEBAND, or range
of modulating frequencies. 2. The range of frequencies over which a radio transmitter can be
modulated to convey information. For single sideband (SSB), it is approximately 300 Hz to 3 kHz;
for high-fidelity, frequency-modulated (FM) music
baseband frequency response • BASIC
transmission, it is about 10 Hz to 20 kHz or 30
kHz; for fast-scan television, it consists of frequencies up to several megahertz. This range is
determined by bandpass and/or lowpass filters
in the AF or composite video section of the transmitter.
base bias The steady dc voltage applied to the base
electrode of a transistor to determine the operating point along the transistor characteristic
base-bulk resistance The resistance of the semiconductor material in the base layer of a bipolar
base-charging capacitance In the commonemitter connection of a bipolar transistor, the internal capacitance of the base-emitter junction.
base current Symbol, IB. Current flowing through
the base electrode of a bipolar transistor. Also see
base electrode See BASE, 1. Also called base element.
base element 1. Base electrode. 2. One of the basic metals, such as iron or tin, that are not generally considered precious (as opposed to
base-e logarithm See NAPIERIAN LOGARITHM.
base film The plastic substrate of a magnetic
recording tape.
base frequency 1. The frequency of the principal,
or strongest, component in a complex signal or
waveform; also called basic frequency. 2. The frequency of operation of a base-station transmitter
when the receiver is tuned to a second channel.
base-input circuit A common-collector circuit,
common-emitter circuit, or emitter follower.
base insulator A stout dielectric insulator, used to
support a heavy conducting element and keep the
conductor isolated from other possible conductors or conductive paths.
base line In visual alignment procedures involving
an oscilloscope and radio-frequency (RF) sweep
generator, a zero-voltage reference line developed
by the generator as a horizontal trace on the oscilloscope screen.
baseline stabilizer A clamping circuit that holds
the reference voltage of a waveform to a predetermined value. Also called DC RESTORER.
base-loaded antenna A usually vertical antenna or
radiating element, the electrical length of which is
adjusted by means of a loading coil or tuned circuit in series with, and positioned at the bottom
of, the antenna or radiator.
base material In printed circuits, the dielectric
material used as a substrate for the metal pattern. Also called base medium.
base notation The numbering or radix system
used in any application (as octal, decimal, binary,
or hexadecimal).
base number See BASE, 4.
base pin One of the straight prong-like terminals
on an electrical or electronic component; it is
base line
used to provide support for the device and to allow a physical connection between the socket terminal, into which it fits, and one of the internal
electrodes of the device.
base plate The chassis plate upon which components are mounted before wiring.
base potential See BASE VOLTAGE.
base region See BASE, 1.
base resistance Symbol, RB. Resistance associated
with the base electrode of a bipolar transistor.
base resistor The external resistor connected to
the base of a bipolar transistor. In the commonemitter circuit, the base resistor is analogous to
the gate resistor of a field-effect transistor (FET)
base spreading resistance Symbol, rBB. In a bipolar transistor, the bulk-material resistance of
the base region between the collector junction
and emitter junction.
base station The head station or fixed home station in a communication network.
base-10 logarithm Abbreviation, log10. A logarithm
based on the decimal number 10. If log10 (x) = y,
then 10y = x. Base-10 logarithms are commonly
used in engineering. Compare NAPIERIAN LOGARITHM.
base voltage Symbol, VB. The voltage at the base
electrode of a bipolar transistor. Also see AC
primitive, but versatile and easy-to-learn computer language developed at Dartmouth College.
basic frequency • battery
basic frequency 1. The FUNDAMENTAL FREQUENCY of a signal, as opposed to one of its harmonics. 2. See BASE FREQUENCY, 1.
basic protection Devices and procedures essential
to minimize the risk of damage to electronic
equipment, and/or injury or death to its operators, as a result of lightning. Hardware provisions
include a substantial earth ground, heavy-gauge
grounding wire, lightning arrestors for antennas,
and transient suppressors for power connections.
The safest procedure is to disconnect and ground
all antennas, and unplug all equipment from utility outlets, during electrical storms and/or when
the apparatus is not in use. Radio communications equipment with outdoor antennas, in
particular, should not be operated during
basket The structure that supports the cone in an
acoustic loudspeaker.
basket-weave coil A type of single-layer inductor
in which adjacent turns do not parallel each
other around the circumference, but zigzag oppositely as a strand does in the woven pattern of a
basket. This reduces distributed capacitance.
bass Low audio frequencies (AF) corresponding to
low-frequency musical notes or sounds.
bass boost 1. The special emphasis given to low
audio frequencies (the bass notes) by selective
circuits in audio systems. 2. The technique of increasing the loudness of the bass, relative to the
higher audio frequencies, to render a more faithful reproduction of sound at low volume levels.
bass compensation See BASS BOOST, 2.
bass control 1. A manually variable potentiometer
for adjusting bass boost of an amplifier or sound
system. 2. The arrangement of components that
are required to achieve amplitude variation of
bass in an audio signal.
bass port In a loudspeaker, a hole in the cabinet
that enhances the low-frequency (bass) sound
output. Used in high-fidelity audio systems.
bass-reflex enclosure A loudspeaker cabinet with
a critically dimensioned duct or port that allows
back waves to be radiated in phase with front
waves, thus averting unwanted acoustic phase
bass-reflex loudspeaker A loudspeaker mounted
in a bass reflex enclosure. Also see ACOUSTICAL
bass-resonant frequency The low frequency at
which a loudspeaker or its enclosure displays
resonant vibration.
bass roll-off 1. The attenuation of the low-frequency (bass) component in a high-fidelity audio
signal. 2. A control that allows adjustable attenuation of the low-frequency component in a highfidelity audio signal.
bass suppression In speech transmission, the removal of all frequencies below about 300 Hz, on
the assumption that those frequencies contribute
little to intelligibility. This suppression permits
the speech level to be increased without overmodulating a transmitter. It also allows smaller audio
transformers to be used because transformer
core size must increase as the frequency it passes
bassy In audio and high-fidelity applications, a
sound in which the low-frequency components,
below about 500 Hz, are overly predominant.
BAT Abbreviation of BATTERY.
batch fabrication process The manufacture of devices in a single batch from materials of uniform
grade. Particularly, the manufacture of a large
number of semiconductor devices from one batch
of semiconductor material by means of carefully
controlled, identical processes.
batch processing In digital-computer operations,
the processing of quantities of similar information during a single run.
bat-handle switch A toggle switch, the lever of
which is relatively long and thick, and is shaped
like a baseball bat.
bat-handle switch
bathtub capacitor A (usually oil-filled) capacitor
housed in a metal can that looks like a miniature
bathyconductorgraph An instrument that is used
to measure the electrical conductivity of seawater.
bathythermograph An instrument that plots a
graph of temperature versus depth in a body of
water, such as a lake or an ocean.
batten Supporting bars or braces that hold a loudspeaker in place within its cabinet, and/or that
hold the cabinet panels in place.
battery Abbreviations, B, BA. BAT. A device consisting of two or more interconnected electrochemical or photovoltaic cells that generate dc
electricity. The cells can be connected in series to
supply a desired voltage, in parallel to supply a
desired current-delivering capability, or in seriesparallel to obtain a desired voltage and currentdelivering capability. Also see CELL, EDISON
battery • beacon
length, the interpretation of which depends on
the history of the previous transmission or an additional case bit.
baud rate 1. A colloquial expression for data speed
in BAUD. 2. Colloquial, and technically inaccurate, expression for data speed in BITS PER SECOND.
Baume (Antione Baume, 1728–1804). Abbreviation,
Be. Pertaining to the Baume scales for hydrometers. The two such scales are for liquids heavier
than water and for liquids lighter than water.
bay One of several sections of a directional antenna array.
bayonet base The insertable portion of a plug-in
component (e.g., a lamp) that has a projecting pin
that fits into a slot or keyway in the shell of the
socket into which the component is inserted.
bayonet socket A socket with a suitably slotted
shell for receiving the bayonet base of a plug-in
bazooka A linear BALUN, in which a quarter wavelength of metal sleeving surrounds a coaxial
feeder, and is shorted to the outer conductor of
the feeder to form a shorted quarter-wave section.
bb Abbreviation of BLACKBODY.
BBC Abbreviation of British Broadcasting Corporation.
BBM Abbreviation of BREAK BEFORE MAKE.
b-box The index register of a computer.
BC Abbreviation of BROADCAST.
B channel One of the channels of a two-channel
stereophonic system. Compare A CHANNEL.
BCL Amateur radio abbreviation of BROADCAST
BCN Abbreviation of BEACON.
BCST Abbreviation of BROADCAST.
B display A radar display in which the target is
represented by a bright spot on a rectangularcoordinate screen. Compare A DISPLAY and J
Be Symbol for BERYLLIUM.
Be Abbreviation of BAUME.
beacon 1. A beam of radio waves, or a radio signal,
that is used for navigation and/or direction finding. 2. A transmitter that radiates a beam of radio
waves, or a radio signal, as an aid in navigation
and/or direction finding. 3. A signal transmitted
continuously on a specific frequency, to help radio operators ascertain propagation conditions.
4. A station or transmitter that generates and radiates a signal to help radio operators determine
propagation conditions. 5. In robotics, a device or
system that aids in navigation. For example, tricorner reflectors can be positioned in strategic
locations, and a mobile robot equipped with a
battery acid 1. A chemical acid, such as sulfuric
acid, used as the electrolyte of a battery. 2. Colloquially, any cell or battery electrolyte, whether
acid, base, or salt.
battery capacity The current-supplying capability
of a battery, usually expressed in ampere-hours
battery cell See CELL, 1.
battery charger 1. A specialized dc power supply,
usually embodying a stepdown transformer, rectifier, and filter. It is used to charge a storage battery from an ac power line. 2. A motor-generator
combination used to charge a storage battery
from an ac power line. 3. A combination of solar
cells, generators, or other voltaic transducers,
that are used to charge a storage battery with dc
obtained from a nonelectrical energy source.
battery clip 1. A heavy-duty metallic clamp that is
used for quick, temporary connection to a large
cell terminal, such as that of a lead-acid storage
battery. 2. A small connector of the snap-fastener
type, used for quick connection to a small power
source, such as a transistor-radio battery.
battery eliminator A specialized dc power supply,
usually embodying a transformer, rectifier, and
filter, that permits battery-powered equipment to
be operated from an ac power line.
battery holder 1. A case or container of any kind
for holding a cell or battery. 2. A shelf for holding
a cell or battery. 3. A small, metal bracket-type
device for holding a cell or battery between two
battery life 1. The ampere-hour or watt-hour capacity of a battery. 2. The number of times that a
rechargeable electrochemical battery can be cycled before it becomes unusable. 3. The nominal
length of time (e.g., hours, days, or weeks) that an
electrochemical battery will function effectively in
a given application before it must be discarded or
battery memory See MEMORY DRAIN.
battery receiver A usually portable radio or television receiver operated from self-contained batteries.
battery substitute See BATTERY ELIMINATOR.
bat wing On a television (TV) or frequency-modulation (FM) broadcast receiving antenna, a metallic
element with a shape that resembles that of a
bat’s wing.
baud A unit of communications processing speed
in telegraphy and digital data communications
systems. Often confused with bits per second
(bps). Baud refers to the number of times per second that a signal changes state. The speed in bps
is generally higher than the speed in baud, sometimes by a factor of several times. Compare BITS
Baudot code A machine communications code
that uses five parallel binary digits of equal
beacon • beam parametric amplifier
scanning infrared laser. The robot controller determines the distance to any given reflector by
measuring the time required for the laser beam to
return. In this way, two mirrors can allow the
robot to locate its position in two dimensions;
three mirrors can facilitate position determination in three-dimensional space.
beacon direction finder A direction finder using a
signal received from a beacon station.
beacon receiver A receiver that is specially
adapted for the reception of beacon signals (see
BEACON, 1 and 3).
beacon station 1. A station broadcasting beacon
signals (see BEACON, 1 and 3) for direction finding, navigation, and/or determination of radiowave propagation conditions. 2. Sometimes, a
radar transmitting station.
transmitter A transmitter specially
adapted for the transmission of beacon signals
(see BEACON, 1 and 3).
bead 1. A small ferromagnetic ring that is used as
a passive decoupling choke by slipping it over the
input power leads of a circuit or stage, or around
a coaxial transmission line. 2. A magnetic memory element in a ferrite-core matrix.
beaded coax A low-loss, coaxial transmission line,
in which the inner conductor is separated from
the outer conductor by means of spaced dielectric
beaded support A plastic or dielectric bead that is
used to support the inner conductor of an airinsulated transmission line of coaxial construction.
bead thermistor A thermistor consisting essentially
of a small bead of temperature-sensitive resistance
material into which two leads are inserted.
beam 1. The more-or-less narrow pattern of radiation from a directional antenna. 2. A directional
antenna—especially a YAGI ANTENNA. 3. The
stream or cloud of electrons emitted by the cathode in an electron tube—especially a BEAM
beam alignment 1. The lining-up of a directional
transmitting antenna with a directional receiving
antenna for maximum signal transfer. 2. In a
beam alignment
television (TV) camera tube, the lining-up of the
electron beam so that it is perpendicular to the
target. 3. In a cathode-ray tube, the positioning of
the electron rays so that they converge properly
on the screen, regardless of the deflection path.
beam angle In the radiation from an antenna, the
direction of most intense radiation, the side limits
of which are determined by the points at which
the field strength drops to half the value in the
principal direction.
beam antenna 1. A multielement directional antenna, consisting of a half-wave driven dipole and
one or more parasitic elements. See YAGI ANTENNA. 2. Any directional antenna used for
transmitting and receiving radio-frequency (RF)
beam bender 1. In a television (TV) picture tube,
the ion-trap magnet. 2. Deflection-plate correction device or circuit.
beam bending Deflection of an electron beam by
electric or magnetic fields.
beam blanking See BLANK, 2.
beam convergence The meeting, at a shadowmask opening, of the three electron beams in a
three-color television picture tube. See BEAM
beam coupling A method of producing an alternating current between two electrodes by passing a
density-modulated beam of electrons between the
electrodes. This, in effect, demodulates the electron beam, recovering the information.
beam crossover Either of the half-power points
in the beam of a directional antenna, usually in
the horizontal plane. The reference point is considered to be the direction of maximum radiation.
beam current The current represented by the flow
of electrons in the beam of a cathode-ray tube.
beam cutoff In an oscilloscope or television picture
tube, the complete interruption of the electron
beam, usually as a result of highly negative control-grid bias.
beam deflector A deflection plate in an oscilloscope tube.
beam efficiency In a cathode-ray tube, the ratio of
the number of electrons generated by the gun to
the number reaching the screen. The efficiency is
high in electromagnetic-deflection tubes and
lower in electrostatic-deflection tubes.
beam lead In an integrated circuit, a relatively
thick and strong lead that is deposited in contact
with portions of the thin-film circuit. It provides
stouter connections than continuations of the
thin film would provide.
beam-lead isolation In an integrated circuit, reduction of distributed capacitance and other interaction through use of beam leads.
beam modulation See INTENSITY MODULATION.
beam parametric amplifier A PARAMETRIC AMPLIFIER in which the variable-reactance component is supplied by a modulated electron beam.
beam-positioning magnet • beat marker
beam-positioning magnet In a three-gun color
television picture tube, a permanent magnet that
is used to position one of the electron beams correctly, with respect to the other two.
beam power tube A tetrode or pentode vacuum
tube, in which special deflector plates concentrate
the electrons into beams in their passage from
cathode to plate. The beam action greatly increases
plate current at a given plate voltage. It is used in
some radio-frequency (RF) power amplifiers.
beam-rider control system A missile-guidance
system in which a control station sends a radio
beam to a missile. The beam is moved in such a
way that as the missile stays within the beam, it
hits the target.
beam-rider guidance 1. An aircraft landing guidance system, in which the aircraft follows a radio
beam in its glide path. 2. The circuitry in a guided
missile using a beam-rider control system.
beam splitter A device used to divide a light beam
(as by a transparent mirror) into two components, one transmitted and the other reflected;
beam splitting In radar, a method of calculating
the mean azimuth of a target from the azimuth at
which the target is first revealed by one scan, and
the azimuth at which the target information
beam-splitting mirror In an oscilloscope-camera
system, a tilted, transparent mirror that allows
rays to pass horizontally from the oscilloscope
screen to the camera and to be reflected vertically
to the viewer’s eye.
beamwidth of antenna The angular width of the
main lobe of the pattern of radiation from a directional antenna. Generally, it is measured beHalf-power
tween the half-power points in the horizontal
plane. Occasionally, it is measured in the vertical plane.
bearing The direction of an object or point expressed in degrees within a 360° horizontal clockwise boundary, with the center of the circle
serving as the observation point.
bearing resolution In radar operations, the minimum horizontal separation of two targets, in degrees, that permits the individual targets to be
displayed as two echoes, rather than one.
beat Any one of the series of pulsations constituting a beat note, which results from heterodyning
one signal against another.
beat frequency Either of two frequencies fC1 and
fC2 resulting from the mixing of two signals of different frequencies fA and fB. Frequency fC1 is the
sum of the two input frequencies; fC1 = fA + fB.
Frequency fC2 is the difference; fC2 = fA – fB when
fA is the higher of the two input frequencies.
beat-frequency oscillator Abbreviation, BFO. An
oscillator used to set up audible beat frequencies with an incoming received signal and installed in the intermediate-frequency (IF) stages
of a superheterodyne communications receiver.
For single-sideband (SSB) reception, the BFO is
set at the frequency of the received suppressed
carrier. In continuous-wave (CW) Morse code reception, the BFO is set at a frequency that differs from that of the incoming signal by about
400 to 1000 Hz. The resulting tone has an audio
frequency equal to the difference between the
BFO frequency and the received signal carrier
frequency. For reception of frequency-shiftkeyed (FSK) signals, the BFO is set to such a frequency that the resulting audio beat notes are
appropriate for the mark and space inputs of a
terminal unit or modem.
IF stage
beat-frequency oscillator
beamwidth of antenna
beating 1. Also called heterodyning. The combination of signals of different frequencies resulting in
sum and difference frequencies. 2. The fluttering
noise heard when two audio tones, very close in
frequency and very similar in amplitude, are
emitted at the same time.
beat marker In the visual (oscilloscopic) alignment
of a tuned circuit, a marker pip that results from
the beat note between the sweep-generator signal
and the signal from a marker oscillator.
beat note • Be0
beat note The sum or difference frequency that results from the heterodyning of two signals or, under some conditions, of more than two signals.
beat-note reception 1. Reception in which a radio-frequency carrier is made audible by heterodyning it with a beat-frequency oscillator (BFO) to
produce an audible beat note. 2. Superheterodyne reception (see SUPERHETERODYNE CIRCUIT).
beat tone A beat note in which the frequency is
within the range of hearing.
beaver tail A flat or elongated radar beam, wide in
the azimuth plane. Primarily used to determine
the altitude of a target. The beam is moved up
and down to find the target elevation.
Becquerel effect A phenomenon in which a voltage is produced when radiant energy, such as infrared, visible light, ultraviolet, or X-rays, falls on
one electrode in an electrolytic cell.
bedspring A directional antenna consisting of a
broadside array with a flat reflector and one or
more helical driven elements.
beep A test or control signal, usually of single tone
and short duration.
beeper 1. A pocket- or hand-carried transceiver—
especially one for maintaining two-way contact
with personnel who are away from their base. 2.
An acoustic transducer that produces a beep in
response to an input signal.
beetle A urea formaldehyde plastic used as a dielectric material and as a container material.
bel Abbreviation, B. The basic logarithmic unit
(named for Alexander Graham Bell) for expressing gain or loss ratios. One bel is equivalent to a
power gain of 10. Also see DECIBEL.
bell An electric alarm device consisting of a metallic gong that emits a ringing sound when it is
struck by an electrically vibrated clapper.
Bellini-Tosi direction finder A direction finder in
which the sensing element consists of two triangular vertical antennas crossed at right angles,
the antennas being open at the top and accordingly not acting as conventional coil antennas.
bell-shaped curve A statistical curve (so called
from its characteristic shape) that exhibits a normal distribution of data. Typically, the curve describes the distribution of errors of measurement
around the real value.
bell transformer A (usually inexpensive) stepdown
transformer that operates an electric bell or similar alarm or signaling device from the ac power
bell wire Insulated 18-gauge (AWG) solid copper
wire, so called because of its principal early use
in the wiring of electric-bell circuits.
belt generator Also known as a Van de Graaff generator. A very-high-voltage electrostatic generator, a principal part of which is a fast-traveling
endless belt of dielectric material. At the lower
end, charges of one sign are sprayed on the belt
at 10 to 100 kV dc and are carried to the inside of
a hollow metal sphere at the upper end, where
they are removed and spread to the surface of the
sphere, which they raise to a potential up to several million volts.
benchmark A test standard to measure product
benchmark routine A routine designed to evaluate
computer software and/or hardware, producing a
good indication of how well the software or hardware will perform in real-life situations. In particular, tests instructions per second and
throughput, thereby producing an indication of
the overall computer power in applications, such
as word processing, database, spreadsheet,
graphics, animation, and mathematical calculations.
bench test An extensive checkout of a piece of
equipment in the test laboratory—either to find
an intermittent problem, or to check for reliability.
bend An angular shift in the lengthwise direction of
a waveguide.
bending effect 1. The downward refraction of a
radio wave by the ionosphere. 2. The lowatmosphere turning of a radio wave downward by
temperature discontinuity and atmospheric inversions.
Benito A continuous-wave method of measuring
the distance of an aircraft from the ground, involving the transmission of an audio-modulated
signal from ground and the retransmission back
to ground by the aircraft. The phase shift between
the two signals is proportional to the distance to
the aircraft.
bent antenna An antenna that has its driven element bent, usually near the ends and at right angles, to conserve space.
bent gun A television picture tube neck arrangement having an electron gun that is slanted to direct the undesired ion beam toward a positive
electrode, but which allows the electron beam to
pass to the screen. This prevents the ion beam
from “burning” a permanent spot on the phosopor of the screen.
Be0 Formula for beryllium oxide. Also see BERYLLIA.
Ion trap
First anode
Second anode
bent gun
berkelium • biased off
berkelium Symbol, Bk. A radioactive elemental
metal produced artificially. Atomic number, 97.
Atomic weight, 247.
beryllia Formula, Be0. Beryllium oxide, used in
various forms as an insulator and structural element (as in resistor cores).
beryllium Symbol, Be. An elemental metal. Atomic
number, 4. Atomic weight, 9.01218. Beryllium is
present in various dielectrics and alloys used in
electronic components.
functions Sophisticated mathematical
functions for dealing with periodic electronic phenomena in which the waveform often displays
decrement. Also called cylindrical functions.
beta Symbol, β. The current gain of a commonemitter bipolar transistor stage. It is the ratio of
the induced change of collector current to the applied change of base current: β = dIC/dIB.
beta circuit The output-input feedback circuit in
an amplifier.
beta cutoff frequency The frequency at which the
current amplification of a bipolar transistor falls
to 70.7% of its low-frequency value.
beta particles Minute radioactive subatomic bits
identical to the electron or positron, and emitted
by some radioactive materials. Also see BETA
beta rays Rays emitted by the nuclei of radioactive
substances, consisting of a stream of beta particles (i.e., electrons or positrons) that move at velocities up to 299.8 million meters per second.
beta-to-alpha conversion For a bipolar transistor,
the conversion of current amplification expressed
as beta (β) to current amplification expressed as
alpha (α): α = β/(β + 1).
betatron A particle accelerator in which injected
electrons are given extreme velocity by being propelled in circular paths in a doughnut-shaped
glass container. The term comes from the fact
that high-speed electrons constitute BETA PARTICLES.
beta videocassette recorder The earliest scheme
for videocassette recording, developed by Sony
corporation in the 1970s. Compare VHS videocassette recorder.
beta zinc silicate phosphor Formula, (Zn0 +
Si02):Mn. A phosphorescent substance used to
coat the screen of a cathode-ray tube. The fluorescence is green-yellow.
BeV Abbreviation of billion electronvolts. Also see
ELECTRONVOLTS. This abbreviation has been
supplanted by the SI (International System of
Units) abbreviation GeV, for GIGAELECTRONVOLTS.
bevatron An accelerator (see ACCELERATOR, 1)
similar to the synchrotron, which accelerates
particles to levels greater than 10 GeV.
Beverage antenna (Harold H. Beverage.) A nonresonant, directional long-wire antenna, erected a
few feet above ground and run in a straight line
for one to several wavelengths. It is generally
used for reception at low and medium frequencies, the best response is to vertically polarized
signals arriving from one or both directions in
line with the wire. It can be left unterminated for
bidirectional response, or it can be terminated at
its far end by a noninductive resistor of about 600
ohms for a unidirectional response.
beyond-the-horizon propagation See FORWARD
bezel A faceplate for an electronic instrument,
usually having a fitted rim and cutouts for knobs,
switches, jacks, etc.
Also abbreviated BWG.
B-H curve A plot showing the B and H properties of
a magnetic material. Magnetizing force H is plotted along the horizontal axis, and flux density B
is plotted along the vertical axis.
B-H meter Any instrument for displaying or evaluating the hysteresis loop of a magnetic material.
bhp Abbreviation of brake horsepower.
Bi Symbol for BISMUTH.
bias 1. Any parameter of which the value is set to a
predetermined level to establish a threshold or
operating point. Although it is common to think
of bias currents and bias voltages, other parameters (e.g., capacitance, resistance, illumination,
magnetic intensity, etc.) can serve as biases. 2. In
a high-fidelity audio system, a circuit in a tape
recorder/player that optimizes performance for a
particular type of recording tape.
bias current A steady, constant current that presets the operating threshold or operating point
of a circuit or device, such as a transistor,
diode, or magnetic amplifier. Compare BIAS
bias current drift The ratio of a change in input
bias current to a change in ambient temperature,
generally expressed in nanoamperes per degree
bias distortion Distortion caused by operation of a
tube or transistor with incorrect bias so that the
response of the device is nonlinear.
biased diode A diode having a dc voltage applied in
either forward or reverse polarity. Current flows
readily through the forward-biased diode; the reverse-biased diode appears as an open circuit.
The biased diode is the basis of clippers, limiters,
slicers, and similar circuits.
biased off In a circuit or device, the state of cutoff
caused by application of a control-electrode bias.
Examples include collector-current cutoff (when
the dc base bias of a bipolar transistor reaches a
critical value), and drain-current cutoff (when the
dc gate bias reaches a critical value in a fieldeffect transistor).
biased search • bifilar electrometer
biased diodes
biased search A scheme that a mobile robot can
use to find its way to a destination or target, by
deliberately searching off to the side and then
homing in as the approach progresses. It is so
called because the general nature of the initial error (bias) is known, although its exact extent need
not be known.
bias oscillator In a magnetic recorder, an oscillator operated at a frequency in the 40-kHz to 100kHz range to erase prerecorded material and bias
the system magnetically for linear recording.
bias resistor A usually fixed resistor, such as the
source resistor in a field-effect-transistor (FET) circuit or the emitter resistor in a bipolar-transistor
circuit, across which a desired bias voltage is developed by current flowing through the resistor.
bias set A control, such as a potentiometer or variable autotransformer, that facilitates manual adjustment of the dc bias of a circuit.
bias stabilization 1. The maintenance of a constant bias voltage, despite variations in load
impedance or line voltage. It is usually accomplished by means of automatic voltage regulation.
2. The stabilization of transistor dc bias voltage
by means of resistance networks or through the
use of barretters, diodes, or thermistors.
bias supply 1. Batteries that provide bias voltage
or current for bipolar or field-effect transistors. 2.
A line-operated unit for supplying dc bias and
consisting of a transformer, rectifier, and highgrade filter.
bias voltage A steady voltage that presets the operating threshold or operating point of a circuit or
device, such as a transistor. Compare BIAS CURRENT.
bias windings The dc control windings of a saturable reactor or magnetic amplifier.
biconical antenna A form of broadband antenna,
consisting of two conical sections joined at the
apexes. The cones are at least 1⁄4 wavelength in diagonal height. The vertex angles of the cones can
vary, although the apex angle is usually the same
in each cone. The vertex angle affects the feedpoint impedance. Such an antenna radiates, and
responds optimally to, signals with polarization
parallel to the axis of the cones.
biconical horn antenna A double-horn microwave antenna that radiates along relatively sharp
front and back beams.
biconical antenna
bidecal base The 20-pin base of a cathode-ray
tube. Also see DIHEPTAL, DUODECAL, and
bidirectional Radiating or receiving (usually
equally) from opposite directions (e.g., front-andback radiation from an antenna or loudspeaker,
or front-and-back pickup with an antenna or microphone).
bidirectional antenna An antenna with a directional pattern that consists of maximum lobes
180 degrees apart.
bidirectional bus In computers, a data path over
which both input and output signals are routed.
bidirectional bus driver In a microcomputer, a
signal-driving device that permits direct connection of a buffer-to-buffer arrangement on one end
(the interface to I/O, memories, etc.) and data inputs and outputs on the other. This device permits bidirectional signals to pass and provides
drive capability in both directions.
bidirectional counter A counter that can count
consecutively up from a given number or down
from that number. Also called UP-DOWN
bidirectional current A current that flows in both
directions. Utility alternating current (ac) is a
common example.
bidirectional loudspeaker A loudspeaker that delivers sound waves to the front and rear.
bidirectional microphone A microphone that
picks up sound waves equally well from the front
and rear.
bidirectional transistor A symmetrical transistor
(i.e., one in which the two main current-carrying
electrodes can be interchanged without influencing device performance). Some field-effect transistors (FETs) are of this type; the drain and the
source can be interchanged.
bifilar electrometer An electrometer in which the
sensitive element consists of two long platinizedquartz fibers. When an electric potential is ap-
bifilar electrometer • bimorphous cell
plied, the fibers separate by a distance proportional to the voltage.
bifilar resistor A wirewound resistor with two oppositely wound filaments. The nature of the winding tends to cancel the inductance, making the
device useful at a much higher frequency than an
ordinary wirewound resistor.
bifilar transformer A transformer in which unity
coupling is approached by interwinding the primary and secondary coils (i.e., the primary and
secondary turns are wound side by side and in
the same direction).
bifilar winding 1. A method of winding a coil (such
as a resistor coil) in the shape of a coiled hairpin
so that the magnetic field is self-canceling and
the inductance is minimized. 2. A method of
winding transformers to minimize leakage reactance.
bifilar winding
bifurcated contact A forked contact whose parts
act as two contacts in parallel for increased reliability.
bilateral amplifier An amplifier that transmits or
receives in either direction equally well (i.e., the
input and output can be exchanged at will).
bilateral antenna A bidirectional antenna, such as
a loop antenna or a half-wave dipole.
bilateral element A circuit element or component
(as a capacitor, resistor, or inductor) that transmits energy equally well in either direction. Compare UNILATERAL ELEMENTS.
bilateral network A network, usually passive and
either balanced or unbalanced, that has BILATERAL SYMMETRY. Thus, the input and output
terminals can be exchanged without affecting the
performance of the network in any way.
bilateral symmetry 1. Exhibiting symmetry, with
respect to a vertical line or plane. 2. For a network, having the property that if the input and
output are reversed, the circuit behavior remains
precisely the same. See BILATERAL NETWORK.
3. For an amplitude-versus-frequency response
curve, having the property that the right-hand
and left-hand halves are mirror images of each
billboard antenna A phased group of dipole antennas that lie in one plane. A reflector might be
used behind the entire array.
bilobe pattern An antenna radiation pattern consisting of two major lobes in a given plane, usually the horizontal plane. Often the lobes exist in
opposite directions relative to each other, as in a
bilateral network
half-wave dipole. But they can be at varying angles, as in a long-wire antenna.
bimetal A union of two dissimilar metals—especially those having a different temperature coefficient of expansion. The two are usually welded
together over their entire surface.
bimetallic element A strip or disk of bimetal.
When the element is heated, it bends in the direction of the metal that has the lower temperature coefficient of expansion; when cooled, it
unbends. Usually, an electrical contact is made
at one extreme or the other so that the element
can serve as a thermostat.
bimetallic switch A temperature-sensitive switch
based on a bimetallic element.
bimetallic thermometer A thermometer based on
a bimetallic element that is mechanically coupled
(as through a lever and gear system) to a pointer
that moves over a temperature scale.
bimetallic thermostat A thermostat in which a
bimetallic element closes or opens a pair of
switch contacts.
bimorphous cell A piezoelectric transducer that
consists of two crystal plates, such as Rochelle
salt, bound intimately face to face. In a crystal
microphone, vibration of the transducer results
in a voltage output; in a crystal headphone, an ac
signal voltage impressed on the transducer
causes vibratory mechanical motion.
BiMOS • binaural
circuit to be preset to deliver an output pulse only
after a predetermined number of input pulses.
binary relay See BISTABLE RELAY.
binary scaler In its simplest form, a single twostage device, such as a flip-flop, which functions
as a divide-by-two counter, because one output
pulse results from every two input pulses.
Higher-order scaling is obtained by cascading
binary search A system of search entailing the
successive division of a set of items into two parts
and the rejection of one of the two until all items
of the sought-for kind are isolated.
BiMOS A combination of bipolar and MOSFET
transistors in an integrated circuit. Thus, a typical BiMOS device can have MOSFET input for
high impedance and bipolar output for low
binant electrometer An electrometer in which a
thin platinum vane (“the needle”) is suspended
within two halves of a metal pillbox-shaped container. The halves or binants are biased with a dc
voltage of 1 to 12 V, and the unknown voltage is
applied to the vane. It is also called DUANT
binary 1. Pertaining to the base-2 number system.
Thus, binary arithmetic uses two digits: 0 and 1.
2. Pertaining to two-element chemical compounds.
binary arithmetic Mathematical operations performed using only the digits 0 and 1.
binary cell In a computer memory, an element
that can display either of two stable states.
binary chain A cascade of binary elements, such
as flip-flops, each unit of which affects the stable
state of the succeeding unit in sequence.
binary channel Any channel whose use is limited
to two symbols.
binary code A system of numbers representing
quantities by combinations of 1 and 0; a binarynumber system.
binary-coded decimal notation In digital computer operations, a system of notation in which
each digit of a decimal number is represented by
its binary equivalent. Thus, the decimal number
327 in BCD notation becomes 0011 0010 0111.
(By contrast, in pure binary notation, 327 is
binary-coded octal notation A method of numbering in which each base-8 digit is represented
by a binary number from 000 to 111.
binary-controlled gate circuit A gate circuit controlled by a binary stage. An example is a gating
transistor that receives its on/off pulses from a
binary counter A counter circuit consisting of a
cascade of bistable stages. Each stage is a scaleof-two counter because its output is on for every
second input pulse. At any instant, the total binary count in a multistage counter thus is shown
by the on and off states of the various stages in
binary decoder A device or stage that accepts binary signals on its input lines, and provides a
usually exclusive output (representing a decimal
digit, for example).
binary digit See BIT.
binary number system The base-two system of
notation. This system uses only two symbols, 0
and 1, and accordingly is easily applied to twoposition switches, relays, and flip-flops.
binary preset switch In a binary counter or binary
control circuit, a selector switch that allows the
binary search
binary signal Any signal that can attain either of
two states. Such a signal is always a digital signal.
binary-to-decimal conversion 1. The automatic
conversion of a number represented by a series of
binary pulses into the corresponding decimal
number, which then is displayed by a readout device. 2. The arithmetic operation of converting a
binary number into a decimal number; this can
be done by noting the powers of 2 represented by
the various binary digits in a number, and then
adding the decimal values of these powers.
binary word A binary numeral that has a particular meaning, agreed upon by convention. For example, the letters A through Z can be represented
by binary numbers 00001 through 11010; a word
can be represented by several blocks of five digits.
binaural Literally, two-eared. In sound recording
and reproduction, the transcription of a broad
sound source using two microphones spaced at
approximately the distance between the ears on a
human head, and played back using headphones
binaural • biofeedback monitor
to re-create the stereo effect. The technique
evolved into multichannel stereophonic reproduction.
binaural machine hearing Also called stereo machine hearing. The ability of a machine, such as a
robot, to sense the direction and distance to a
source of sound, using two acoustic transducers
and a computer to process their output signals.
The machine determines the location of the
sound source by comparing the relative amplitude and phase of the signals from the two transducers. It functions according to the same
principle as human hearing, in which a person
can determine the general direction and distance
to a sound source by subconsciously comparing
the relative amplitude and phase of the sounds
arriving at the left and right ears.
binaural sound The equivalent of a listener hearing a concert through a pair of earholes; it takes
earphones to reproduce the signal. If speakers
are substituted for the earphones, the listener
hears monophonically, as if standing back several feet from the earholes.
binder A material (such as lacquer) that acts as a
holder and cohesive medium for the particles of
another material. It is used in carbon resistors,
ceramic dielectric bodies, powder cores, and resistive and metallic paints.
binding energy A property of the nucleus of an
atom. The binding energy of a nucleus is equal to
the difference between the nuclear weight and the
sum of the weights of the lighter particles making
up the nucleus. The nucleus is stable when the
binding energy is high.
binding force Any one of the electrostatic forces
that bind crystals together.
binding post A screw-type terminal of various
styles, often having a hole into which a wire or tip
can be inserted and gripped. It is used for temporary indoor connections only.
binding post
binistor A semiconductor switching device that exhibits two stable states and also negative resistance.
binocular machine vision Also called stereoscopic
machine vision. The ability of a machine vision
system to provide depth and perspective data.
Uses two optical sensors spaced a fixed distance
apart. The left sensor sees a slightly different image than the right sensor. These two images are
combined and processed by a computer, allowing
the machine (such as a mobile robot) to determine the distances to various objects in its environment. Functions on the same principle as
stereoscopic human vision.
bin picking In robotics, the selection of a particular object from a container (bin) in which there
are many objects. Can be done using object
recognition, bar coding, or passive transponders.
It requires a sensor, operating in conjunction
with a computer that processes the sensed data
and controls the movements of the robot.
binomial An algebraic expression containing two
terms joined by a plus or minus sign. Examples:
a2 + b2, 3x 3 – 6x.
binomial theorem The theorem, proven by Isaac
Newton, permits a binomial to be raised to any
desired power without performing the multiplications. In electronics, power series are convenient
for expressing such expressions.
biochemical cell A fuel-cell energy source in
which electricity is generated chemically through
the oxidation of biological substances. Also called
biochemical fuel cell.
biochip 1. A natural, living organism with a physical structure that in some way resembles that of
an electronic integrated circuit (IC). 2. A theoretical possibility, according to some scientists, but
not yet a practical reality: An IC manufactured by
a laboratory process that mimics the way in
which nature builds living organisms. A form of
artificial life, harnessed for electronic and/or
computing applications.
bioelectricity 1. Electric currents in living tissues,
generated by the organism and not applied by external means. 2. The science or study of such
bioelectrogenesis The study and application of
electricity generated by living animals, including
humans, in the powering and control of electronic
bioelectronics Electronics in relation to the life
sciences—especially the electronic instrumentation of biological experiments.
bioengineering 1. The engineering of equipment,
such as electron microscopes, electroencephalographs, centrifuges, irradiators, etc., for study
and experimentation in the life sciences. 2. The
engineering of equipment, such as pacemakers,
hearing aids, X-ray apparatus, shock-therapy
units, etc., for aid or support-of-life processes.
biofeedback A technique in which changes in skin
temperature and resistance are detected and displayed by an electronic device.
biofeedback monitor A system that provides an
indication of skin temperature and resistance to
a user. Because skin temperature and resistance
are affected by emotions, such as fear, nervous-
biofeedback monitor • Birmingham wire gauge
ness, anger, etc., these monitors might be of
value to people who wish to gain improved control
of their emotions, and thus perhaps minimize the
physiological effects of stress.
biological robot Believed by some researchers to
be possible, but not yet a practical reality: A living
organism created by biological cloning, whose
brain has been programmed exactly as a computer is programmed.
biological shield An absorbent shield that blocks
or attenuates ionizing radiation to protect personnel working near radioactive materials.
bioluminescence 1. The emission of light by a living organism. 2. The light itself so produced by
living organisms.
biomechanism An electromechanical device that
simulates the workings of some part of a living
being’s body. Examples are electromechanical
hands, arms, and legs. Such a device is often difficult to distinguish from its biological counterpart when obscured by clothing.
biomechatronics A contraction of the words biology, mechanics and electronics. Research, development and manufacturing that encompasses
aspects of all three fields. This is especially important in robotics.
biometrics Mathematics, and in particular, statistics and probability, applied to biology.
biometric security system An advanced intrusion-prevention system that measures biological
characteristics of the people who are authorized
to enter a property. Such a machine can employ
vision systems, object recognition, and/or pattern recognition to check a person’s face. The machine might use speech recognition to identify
people by the waveforms of their voices. It might
record a hand print, a fingerprint, or an iris print,
or a combination of all these things. A powerful
computer analyzes the data obtained by the sensors and determines whether the person is authorized to enter the premises.
bionics The study, design, and application of microelectronic systems that simulate the functions
of living organisms.
biotelemetry The use of telemetry to collect data
from living organisms or to direct their movement.
biotelescanner An instrument that monitors body
functions via radio, from a great distance.
Biot/Savart law A principle of electromagnetism
that expresses the intensity of magnetic field H in
the vicinity of a long, straight wire carrying a
steady current I. The basic formula is H = 2I/r,
where H is in oersteds, I is in amperes, and r is
the distance in centimeters from the wire.
bip Abbreviation of binary image processor.
biphase half-wave rectifier An alternative term
for FULL-WAVE RECTIFIER; also, each leg of a
two-diode full-wave rectifier.
BIPM Abbreviation of International Bureau of
Weights and Measures.
bipolar The condition of possessing two pole sets. In
a conventional (non-FET) transistor, one pole set
exists between the base and collector, and another
pole set exists between the base and emitter.
bipolar driving unit A magnetic headphone or
loudspeaker in which both poles (north and
south) of a magnet actuate a diaphragm or lever.
bipolar operation See AUTOMATIC POLARITY.
bipolar transistor A two-junction transistor whose
construction takes the form of a pnp or an npn
“sandwich.” Such devices are current-operated,
compared with field-effect transistors, which are
voltage-operated. The bipolar transistor (of which
the familiar npn and pnp types are examples)
uses both electron and hole conduction.
biquinary code A variety of binary-coded-decimal
notation in which seven bits are used to represent each decimal digit. A number is written in
two groups of bits: a two-bit group followed by a
five-bit group. The positional values are 5 and 0
for the two-bit group, and 4, 3, 2, 1, and 0 for the
five-bit group.
biquinary decade A decade counter that consists
of a binary stage, followed by a quinary stage.
bird 1. Slang for orbiting SATELLITE. 2. Slang for
guided missile.
birdie 1. A spurious beat note in a superheterodyne receiver. So called because of the characteristic chirping sound it makes as the operator
tunes by the frequency on which it occurs. 2. A
parasitic oscillation in a radio transmitter, also
called a spurious emission or spur.
Birmingham wire gauge Abbreviation, BWG. Also
called Stubs gauge. A method of designating the
various sizes of solid wire. BWG diameters are
somewhat larger than corresponding AMERICAN
WIRE GAUGE diameters for a given wire-size
Birmingham Wire Gauge (BWG) Diameters
bismuth • black box
terrelated smaller capacity processors (e.g., a 16bit unit derived from eight 2-bit “slices”).
bits per second Abbreviation, bps. An expression
of digital data speed. Commonly used in computer communications. This unit is often confused with, and improperly called, the baud.
There is generally a difference between the speed
of a signal in baud, and the speed of the same signal in bps. Compare BAUD.
bitter pattern A pattern produced in a suspension
of ferromagnetic powder in the presence of an imperfection in a magnet. The pattern appears as an
irregularity that is easy to see.
Bjerknes’ equation An expression for the total
(primary plus secondary) decrement of a tuned
circuit, based on measurements of the tank current at the resonant frequency and at a frequency
near resonance.
BK 1. Radiotelegraph signal for BREAK. 2. Abbreviation of BREAK-IN.
Bk Symbol for BERKELIUM.
black-and-white Also called monochrome and
gray-scale. Any system of image reproduction,
transmission, or reception in which the image is
composed of opaque elements (black) and white
or bright areas, as in noncolor television reception.
black area An area in which there is only an encrypted signal.
blackboard system A method via which computers can recognize, and to some extent determine
the meaning of, spoken words and visual images.
Incorporates machine vision and/or machine
hearing in conjunction with artificial intelligence
(AI). Incoming voices and/or images are digitized
and entered into a large-capacity random-access
memory (RAM). The data is evaluated by sophisticated software to determine the most logical or
probable interpretations of the sounds and images.
blackbody An ideal surface or object, that completely absorbs energy of any wavelength that
strikes it. Such an object is a theoretically perfect
radiator of energy at all wavelengths.
blackbody radiation Electromagnetic radiation
from a heated ideal BLACKBODY. This radiation
is conceived as covering the entire ELECTROMAGNETIC FREQUENCY SPECTRUM. It can be
expressed graphically as a characteristic curve
with a peak at a wavelength that depends on the
absolute temperature of the object. As the absolute temperature increases, the peak occurs at
progressively shorter wavelengths (higher frequencies). This enables radio astronomers to get
a reasonably good idea of the temperatures of distant celestial objects, such as planets.
black box 1. Any “box” or “block” that can be included in an analysis or synthesis based upon
the BLACK-BOX CONCEPT. 2. Any functional
unit (such as a module) whose operating characteristics are known, and that can be inserted into
bismuth Symbol, Bi. A metallic element. Atomic
number, 83. Atomic weight, 209.
bismuth flux meter A flux meter in which the sensor contains a length of bismuth wire, which acts
as a magnetoresistor.
bismuth thermocouple A thermocouple that uses
the junction between bismuth and antimony
wires. Used in thermocouple-type meters.
bistable Having two stable states.
bistable device Any device, such as a flip-flop, the
operation of which exhibits two stable states and
which can be switched at will from one state to
the other.
bistable multivibrator A multivibrator, the operation of which exhibits two stable states. More
commonly known as a FLIP-FLOP. These circuits
are abundant in digital electronic equipment.
bistable multivibrator
bistable relay A relay that has two stable states:
open and closed. Successive actuating pulses
open and close the relay, two consecutive pulses
being required to return the relay to a given state.
Also called binary relay, relay flip-flop, and electromechanical flip-flop.
bistatic radar A radar set in which the transmitting and receiving antennas are separate.
bistate Having two states. Example: the performance of a FLIP-FLOP.
bit An acronym formed from the words binary digit.
The smallest or elementary unit of data in digital
electronics. Represented either by logic 0 (low) or
logic 1 (high). These states can be represented by
any dichotomy, such as off/on, false/true, minus/plus, dark/bright, red/green, etc.
BIT Abbreviation of built-in test.
bit density The number of digital bits per unit area
or volume, as the number of bits per square centimeter of magnetic tape.
BITE Abbreviation of built-in test equipment.
bit rate The speed in BITS PER SECOND (bps) at
which digital data bits are transmitted or handled.
bit-slice processor A microprocessor whose word
or byte capacity is achieved through the use of in-
black box • bleeder resistor
a system in development or maintenance operations. 3. Any subcircuit or stage that can be specified in total as required in a system, in terms of
its known or prescribed performance, but whose
internal structure need not be known.
black-box concept A technique for development of
equivalent circuits and of considering their operation. The “box” has a pair of input terminals and
a pair of output terminals; one input terminal is
often common to one output terminal. The contents of the box need not be known, but from the
input and output current and voltage relationships, its nature can be determined. Moreover,
from the available input signal and desired output signal, the internal circuit of the box can be
specified. Integrated circuits (ICs) are often
treated as black boxes by engineers designing
complex electronic equipment.
black compression Attenuation of the level of dark
areas in a television picture.
blacker than black The video-signal amplitude region above the level that just darkens the screen.
Signal information (such as control pulses) in
this region are therefore not seen.
black light
1. Ultraviolet radiation—especially
when used to cause visible fluorescence in certain materials. 2. A lamp that produces a principal portion of its radiation in the ultraviolet
region, causing visible fluorescence of certain
substances. Such lamps are used in some scientific experiments, and also for creating special effects at presentations or parties. It is hazardous
to look directly at the output of such a lamp with
unprotected eyes.
blackout 1. A complete interruption of ac utility
power to numerous customers at the same time.
2. A complete cessation of ionospheric radio-wave
propagation, such as might be caused by a solar
flare. 3. Complete blanking of the screen of an oscilloscope or picture tube.
black reference In a television signal, the blanking
level of pulses, beyond which the sync pulse is in
the blacker-than-black region.
black reference level In a television signal, the
voltage threshold of the BLACK REFERENCE
(i.e., its level above zero volts).
black transmission A system of picture or facsimile transmission in which the maximum copy
darkness corresponds to the greatest amplitude
(in an amplitude-modulated transmitter) or the
lowest instantaneous frequency (in a frequencymodulated
blank 1. A piezoelectric plate cut from a quartz
crystal, but not yet finished to operate at a desired frequency. 2. To obscure or interrupt a signal or electron beam (usually momentarily), as in
z-axis blanking in an oscilloscope. 3. A silicon
wafer cut from a large slab, containing dopants
only. 4. A magnetic diskette or tape on which
nothing is recorded. 5. An optical diskette on
which nothing is recorded. 6. A location (such as
a symbol or space) that is used to verify proper
data character grouping and values.
blanketing A form of radio interference accompanied by severe degradation of reception, virtually
unaffected by tuning, over a wide range of frequencies. An example is ac line noise caused by
an arcing power transformer or electrical appliance in the vicinity of a receiving antenna. It
tends to occur most often at low, medium, and
high frequencies.
blanking Obscuring or momentary elimination of a
signal (see BLANK, 2).
blanking interval The short period during which
the electron beam of a cathode-ray tube is cut off
so that the beam can return to its start position
without creating a trace on the screen.
blanking level The discrete, predetermined level
(usually a threshold voltage) at which BLANKING
blanking pedestal In the horizontal pulse of a television signal, the lower portion between zero volts
and the blanking level.
blanking pulse A pulse that produces momentary
blanking (see BLANK, 2).
blanking time The time interval during which the
electron beam of a cathode-ray tube is interrupted by a blanking signal.
blank tape 1. Magnetic tape that has never been
subjected to the recording process and that is
substantially free from noise. 2. Magnetic tape
from which all preexisting information has been
blasting 1. Severe overloading of a sound system,
usually caused by setting the volume control at
or near maximum and then applying a significant
input signal to the amplifier. Accompanied by distortion, in its worst form, it can cause damage to
speakers and/or headsets. 2. In a communications receiver, the result of a strong signal coming
in unexpectedly when the automatic gain control
(AGC) has been switched off, and the audiofrequency (AF) and radio-frequency (RF) gain controls are set high for reception of weak signals.
bleeder A resistor or group of resistors, used permanently to drain current from charged capacitors. It establishes the predetermined initial load
level for a power supply or signal source, and it
serves as a safety device in high-voltage power
bleeder current The current normally flowing
through a bleeder.
bleeder divider A network of resistors, seriesstrung across the output of a power supply or its
regulator. As a load resistor, the bleeder improves
regulation and protects against no-load voltage
surges. The resistor junctions allow various voltages to be drawn from the supply.
bleeder power Power dissipated as heat in a
bleeder resistor See BLEEDER.
bleeder temperature • blocking interference
Bloch functions Solutions of the Schrodinger
wave equation for a single electron surrounded
by an electric field. The field varies periodically
with distance from the source.
Bloch wall The transition layer between adjacent
ferromagnetic domains (see DOMAIN).
block 1. A group of data words or digits. 2. A group
of memory storage spaces. 3. A circuit that operates as an identifiable unit. 4. The symbol for a
circuit, stage, unit, or device in a BLOCK DIAGRAM.
block diagram A simplified diagram of an electronic system, in which circuits, stages, units, or
devices are shown as two-dimensional boxes with
the internal wiring and detail circuitry omitted.
This makes it possible to clearly show the interconnection among circuits, stages, units or devices. It also provides a concise rendition of the
overall functional concept of the system.
bleeder divider
bleeder temperature The operating temperature
in a bleeder. It is generally high because of power
dissipation in the form of heat.
bleeding whites A flowing of the white areas of a
television picture into the black areas; an overload condition.
blemish See BURN.
blind flight The flying of aircraft entirely by means
of instruments and electronic communications.
blind landing Landing of an aircraft entirely by
means of instruments and electronic commnications.
blind zone 1. In radar operations, an area that gives
no echoes. 2. Skip zone (see ZONE OF SILENCE).
blip 1. The pulse-like figure on a radar scan, indicating the transmission or reflection (see A-SCAN
and J-SCAN). Also called PIP. 2. In visual alignment of a tuned circuit using a sweep generator
and marker generator, the pulse or dot produced
on the response curve by the marker signal. 3. A
short, momentary signal pulse, such as a single
Morse dot.
BLIP Abbreviation for background-limited infrared
blip-scan ratio The number of radar scans necessary to show a visible blip, or echo, on a radar
block diagram
(of a radio transmitter)
blocked impedance The input impedance of a
transducer, whose output load is a theoretically
infinite impedance.
blockette In a computer, the subdivision of a character block that is handled as a unit during data
blocking action Obstruction of circuit action, usually abrupt, through internal action or by the
application of an external signal. Thus, the
operation of an amplifier can be blocked (output
reduced to zero) by an input signal or by excessive feedback, either of which overloads the
blocking capacitor A capacitor inserted into a circuit to prevent the passage of direct current while
easily passing alternating current.
blocking choke Any inductor, such as a choke
coil, that is used to prevent the flow of an alternating current while allowing direct current to
pass with little resistance.
blocking interference Radio interference from signals strong enough to reduce the receiver output
through blocking action.
blocking oscillator • BNC
blocking oscillator An oscillator that turns itself
off after one or more cycles. It does this as a result of an accumulation of negative charge on its
input electrode (base of a bipolar transistor or
gate of a field-effect transistor). The action is
repetitive. In the self-pulsing type of blocking oscillator, a series of pulses consisting of trains of
sine waves with intervening spaces is generated.
In the single-swing type of blocking oscillator, the
output consists of a series of single cycles with
long intervals between them.
blocking oscillator synchronization 1. In the
BLOCKING OSCILLATOR used in the vertical deflection circuit of a television receiver, the oscillator is synchronized with vertical sync pulses
arriving in the video signal. 2. Synchronization of
the repetition rate of any blocking oscillator with
a suitable external control signal.
blocking system In a telephone system, a method
of dealing with the condition of having more subscribers than connection paths. Allocation is
made on a demand basis. If all channels are in
use, it is impossible to make new calls. This prevents excessive degradation of the quality of existing connections.
block length The number of characters, bits, or
words that compose a defined unit word or character group.
block transfer The conveyance of a word or character grouping in a computer register to another
register or a peripheral device.
blooming On a cathode-ray-tube (CRT) screen, an
enlargement of the electron-beam spot, caused by
poor focusing. This results in poor image
blooper 1. A radio receiver that is in oscillation,
and is transmitting a signal that causes interfer-
ence. 2. A parasitic oscillation in a radio transmitter. 3. In broadcasting, a statement in which a
radio or television announcer makes an embarrassing error or breach of etiquette.
blow The opening of a fuse or circuit breaker as a
result of excessive current.
blower A fan used to remove heat from electronic
circuits. These are often used in tube-type radiofrequency (RF) power amplifiers, where much
heat is generated, and in computers to cool the
microprocessor and surrounding components.
blowout 1. An alternate term for BURNOUT. 2. The
forceful opening of a circuit breaker. 3. The extinguishing of an arc.
blowout coil An electromagnet that provides a field
to extinguish an arc.
blowout magnet A permanent magnet that provides a field to extinguish an arc.
blst Abbreviation of ballast.
blue-beam magnet In a color television picturetube assembly using three electron guns, a small
permanent magnet to adjust the static convergence of the beam for blue phosphor dots.
blue box An accessory device (sometimes unlawfully used) that generates tones that switch a telephone circuit in the placing of calls.
blue glow 1. In a neon lamp, a bluish light that
results from high-voltage arcing. 2. The normal
color of the gas discharge in an argon glow
lamp. 3. The bluish glow between anode and
cathode of a gassy vacuum tube. 4. The normal
color of the discharge that fills a mercury-vapor
blue gun The electron in a three-gun color picture
tube, the beam from which strikes the blue phosphor dots.
blueprint 1. A type of contact-print reproduction
in which a sheet of sensitized paper is exposed to
an image on a translucent or transparent film,
under strong light, and is then developed and
fixed. Although this process is still used to reproduce electronic illustrations and typescripts, it
has been superseded largely by other (dry) processes. 2. Loosely, any plan or design for the development of a system.
blue restorer In a three-gun color television circuit, the dc restorer in the blue channel.
blue ribbon program A computer program that
has been hand-prepared and debugged completely before its first computer run.
blue video voltage The signal voltage presented to
the grid of the blue gun of a three-gun color picture tube.
blurring 1. BLOOMING. 2. A defocusing of a television picture or oscilloscope trace. 3. An obscuring of a signal by echoes or trailing (e.g., the slow
decrement of a Morse code signal element).
B-minus Also called B-negative. The negative terminal of a B-power supply.
BNC Abbreviation of bayonet Neill-Concelman. A
type of coaxial connector that can be quickly con-
BNC • Boltzmann’s principle
nected and disconnected. It is commonly used
with test equipment.
B-negative Alternative expression for B-MINUS.
BNL Abbreviation
BO Abbreviation of beat oscillator. Also abbreviated
board 1. A panel containing patch jacks. 2. A
printed circuit.
boat A type of crucible in which a semiconductor
material is melted and sometimes processed. The
material of which the boat is made (e.g., graphite)
does not react with or contaminate the semiconductor material.
bobbin 1. A usually nonmetallic spool on which a
coil is wound. 2. The form onto which the voice
coil of a loudspeaker is wound.
Bode plot A pair of curves plotted to the same frequency axis, one showing the gain of a network or
amplifier and the other showing its phase shift.
Phase and amplitude of active and passive networks can be exhibited. Also called Bode curve
and Bode diagram.
body-antenna effect The tendency of the human
body to act as a receiving antenna when a finger
is touched to the antenna input terminal of a receiver or when a hand (or the whole body) is
brought close enough to the circuit to provide capacitive coupling.
body capacitance Capacitance between the body
of the operator (as one plate of an equivalent capacitor) and a piece of electronic equipment (as
the other plate). This phantom capacitance is often the cause of detuning and of the injection of
interfering signals and noise because the body
acts as a pickup antenna.
body electrode 1. An electrode attached to the
human body (or to the body of a laboratory animal) to conduct body-generated currents to an
instrument, as in cardiography, electroencephalography, and myography. 2. An electrode attached to the human body (or to the body of a
laboratory animal) to conduct currents into the
body, as in shock therapy and skin-resistance
body leakage Leakage of current through the bulk
or body of a dielectric material, as opposed to
body temperature In a thermistor, a rating that
represents the temperature measured on the
surface of the device. It is any combination of
ambient temperature, power dissipation, and
operation of the internal heater element (if the
thermistor has one).
bof Abbreviation of barium oxide ferrite.
boffle A loudspeaker enclosure consisting of
stretched screens that are sound absorbing and
bogie Also called bogey. 1. The exact value of a
specified characteristic. Thus, if resistance is
given as 1 kΩ ±0.5%, the bogie value is 1 kΩ. 2.
The average value (i.e., the ARITHMETIC MEAN).
3. A false or unidentified echo on a radar screen.
Bohr atom The concept of the nature of the atom,
proposed by Niels Bohr in 1913 partly to explain
why the electrons in the Rutherford atom do not
fly off into space or fall into the nucleus. The Bohr
theory places the electrons in permissible orbits
where they cannot radiate energy (see BOHR RADIUS). They can radiate or absorb energy, however, if they go to a lower orbit or to a higher orbit,
respectively. Compare RUTHERFORD ATOM.
bohrium Symbol, Bh. Also called unnilseptium
(Uns). Atomic number, 107. The most common
isotope has atomic weight 262. Classified as a
transition metal. It is human-made and is not
known to occur in nature.
Bohr radius Symbol, a0. A physical constant
whose value is approximately 5.291772 × 10–11
boiling point Abbreviation, bp. The temperature at
which a liquid vaporizes. The boiling point of water in air at a pressure of one atmosphere is
100°C or 212°F.
bolometer Any device that is essentially a small,
nonrectifying, temperature-sensitive resistor that
can be used for heat sensing, radio-frequency
power measurement, curve changing, demodulation, circuit protection, etc. Included in this category are the BARRETTER, the THERMISTOR, and
the wire-type FUSE.
bolometer bridge A dc bridge in which a bolometer
is one of the four arms. The bridge is balanced
first with the bolometer cold. The bolometer then
is excited with a radio-frequency (RF) current,
whereupon the resultant heating changes the
bolometer resistance. The bridge is rebalanced for
the new resistance. The RF power driving the
bolometer is determined according to a predetermined function of bridge settings versus RF input
Boltzmann constant Symbol, k. A figure that enters into the calculation of thermionic emission
and of thermal noise factor. It represents the temperature equivalent of work function, in electron
volts per Kelvin (eV/K) or joules per Kelvin (J/K).
The values are approximately:
k = 8.617 × 10–5 eV/K = 1.38 × 10–23 J/K
Boltzmann’s principle A description of the statistical distribution of large numbers of tiny particles under the influence of a force, such as an
electric or magnetic field. When the system is in
Boltzmann’s principle • booster
statistical equilibrium, the number of particles in
any portion of the field is given by:
NE = N0e–E/kT
where E is the potential energy of a particle in the
observed area, N0 is the number of particles per
unit volume in a part of the field where E is zero,
k is the BOLTZMANN CONSTANT, T is the absolute temperature of the system of particles, and e
is approximately equal to 2.718.
bombardment The usually forceful striking of a
target with rays or a stream of particles.
bond 1. An area in which two or more items are securely and intimately joined. 2. The attractive
force that holds an atomic or subatomic particle
or particle group together.
bonded-barrier transistor A bipolar transistor in
which the connection at the base region is alloyed.
bonded negative-resistance diode A diode that
displays a negative-resistance characteristic over
part of its current curve. This results from
avalanche breakdown.
bond energy In a molecule, the energy necessary
to break an atomic bond.
bonding 1. The formation of bonds between adjacent atoms in a crystalline material, such as a
semiconductor. See specifically COVALENT
fastening together of conducting surfaces, as by
soldering or brazing, to produce a high-conductance, leak-free continuum.
bond strength The minimum stress required to
separate a material from another to which it is
bone-conduction transducer A device used in
place of the earphone in a hearing aid to convey
sound energy to the bone structure of the head.
Bongard problem A method of evaluating how well
a machine vision system can differentiate among
patterns. Similarities and differences are noted
between objects in two sets of boxes. It was developed for object-recognition systems, mainly for
use in intelligent robots.
book capacitor A variable capacitor in which the
metal plates are bonded along one edge and separated from each other by means of mica sheets.
The capacitance is varied by opening and closing
the assembly book fashion. It is used as a padder
or trimmer.
Boolean algebra A system of symbolic logic. Statements are represented as symbols, usually variables such as x, y, and z. The logical AND operation is represented by multiplication; the logical
inclusive OR operation is represented by addition; the logical NOT operation is represented by
a minus sign or a line over the element symbol.
The system has rules, definitions and axioms via
which theorems can be derived. Used by engineers in the design of digital electronic circuits.
Boolean truth table
Boolean function In mathematical logic, a function that makes use of BOOLEAN ALGEBRA.
Boolean theoreams
x + 0 = x (additive identity)
x1 = x (multiplicative idenity)
x0 = 0
xx = x
(x’)’ = x (double negation)
x + x’ = 1
x’x = 0
x + y = y + x (commutativity of addition)
xy = yx (commutativity of multiplication)
x + xy = x
xy’ + y = x + y
x + y + z = (x + y) + z = x + (y + z)
(associativity of addition)
15. xyz = (xy)z = x(yz) (associativity of multiplication)
16. x(y + z) = xy + xz (distributivity)
17. (x + w) (y + z) = xy + xz + wy + wz (distributivity)
boom 1. A horizontal support for a microphone,
enabling the microphone to be suspended over a
sound source, but out of the sight of a camera.
2. A horizontal support for a small antenna that is
undergoing tests or sampling the field of another
antenna. 3. The supporting element in a Yagi,
quad, or log-periodic antenna. It establishes the
center of gravity and directional axis of the radiation pattern. The driven element(s) and parasitic element(s) are attached, usually at right
boost capacitor In the damper circuit of a television receiver, the capacitor that is used to boost
the B-plus voltage. Also called booster capacitor.
boost charge A high-current, short-interval charge
used to revitalize a storage battery quickly. Also
called booster charge.
booster 1. Any device used to increase the amplitude of a signal (e.g., as an amplifier or preamplifier) or of an energy source (e.g., to boost the
output of a power supply). 2. A radio-frequency
preamplifier used ahead of a television receiver.
booster battery • bow-tie test
booster battery 1. A battery used to forward bias a
diode detector into a favorable region of its conduction curve, or to bias a bolometer into the
square-law region of its response. 2. A battery
supplying power to a booster.
booster gain The amplification (usually in terms of
voltage gain) provided by a booster (see especially
boot 1. The powering-up routine in a digital computer, in which the machine executes a series of
programs to get itself ready for use. 2. The
resetting of a computer, by pressing certain keyboard keys (e.g., CTRL-ALT-DEL), pressing a reset button, or by powering-down, waiting about
two minutes, and then powering-up again. 3. To
install a computer diskette and instruct the computer to execute one or more programs on the
diskette. 4. A usually flexible protective nipple or
jacket pulled over a cable or connector, so called
from its resemblance to a foot boot.
boot loader A form of computer program that operates on the BOOTSTRAP ROUTINE.
bootstrap A technique for making a device or process achieve a condition through its own actions;
see BOOTSTRAP CIRCUIT, for example.
bootstrap circuit A specialized form of follower
circuit that presents very high input impedance.
Its chief feature is the return of the control-element resistor to a tap on the source or emitter resistor. The technique takes its name from the
figurative notion that such a circuit “lifts its input
impedance by its own bootstraps.”
Signal input
Signal output
bootstrap circuit
(with junction-type field-effect transistor)
bootstrap routine 1. Also called bootstrap program. In a digital computer, and especially in a
personal computer, the routine that the machine
follows when first powered-up. See BOOT, 1.
2. In a digital computer, a routine in which the first
few instructions put in storage are later used to
complete the routine, as supplemented by some
operator instruction. 3. A portion of a computer
program that is used to establish an alternate
version of the program.
borax-aluminum cell An electrolytic cell that consists essentially of an aluminum electrode and a
lead electrode in a saturated solution of sodium
tetraborate (borax). After electroforming, such a
cell can be used either as a rectifier or as an electrolytic capacitor.
boric acid Formula, H3BO3. A compound used variously in electronics—especially as the electrolyte
in electrolytic capacitors.
bornite Formula, Cu5FeS4. A natural mineral that
is a sulfide of copper and iron. Its crystalline
structure made it important in early semiconductor diodes (crystal detectors).
boron Symbol, B. A metalloidal element. Atomic
number, 5. Atomic weight, 10.82. It is used as a
dopant in semiconductor processing.
bot 1. Abbreviation for beginning of tape. 2. Abbreviation of bottom.
bottoming Excessive movement of the cone of a
loudspeaker or the diaphragm of a headphone so
that the magnet or supporting structure is struck
by the moving-coil piston assembly. It produces a
clapping sound, particularly on bass (lowfrequency) audio peaks.
bounce 1. The springback or vibration of the armature of a relay on closure. 2. An abnormal,
abrupt change in the brightness of the image in a
television receiver or cathode-ray-tube (CRT)
computer monitor.
boundary 1. In a polycrystalline substance, the
area of contact between adjacent crystals. 2. The
area of meeting of two regions (such as n and p)
in a semiconductor.
boundary defect A condition in which a piezoelectric crystal has two regions, intersecting in a
plane, with different polarizations.
boundary effect In audio systems, a pheno-menon
in which the proximity of an acoustic transducer
to a flat surface enhances the pickup and/or
transmission of sound. Occurs because of reflection of acoustic waves from the surface.
bound charge The portion of the electric charge on
a conductor that does not escape to ground when
the conductor is grounded. This occurs because
of induction from neighboring charge carriers.
bound electron An electron held tightly in its orbit
within an atom so that it is not ordinarily free to
drift between atoms and contribute to electric
current flow.
bow-tie antenna A center-fed antenna in which
the two horizontal halves of the radiator are triangular plates that resemble a bow tie. A flat reflector consisting of closely spaced horizontal
wires is mounted behind the triangles.
bow-tie test An oscilloscope-display checkout of a
single-sideband (SSB) signal, in which the appearance of the display indicates the signal quality. The transmitter output signal is fed to the
bow-tie test • brass pounder
vertical deflection plates of the oscilloscope. The
exciter audio output is fed to the horizontal sweep
input of the scope.
boxcars Long pulses with short separating spaces
between them.
box-shaped loop The characteristic square-loop
hysteresis curve (B-H loop) that result when a
sine wave of current is used to magnetize a sample of magnetic material. In this plot, which covers all four quadrants, the horizontal axis (H)
displays magnetizing force, and the vertical axis
(B) displays magnetization. Also see HYSTERESIS.
Boys radiomicrometer A detector for radiant energy. The device consists of a thermocouple and a
galvanometer. When energy falls on the thermocouple, a voltage is produced, and this is measured by the galvanometer.
bp 1. Abbreviation of BOILING POINT. 2. Abbreviation of BANDPASS.
bpi Abbreviation of bits per inch.
B-plus Also called b-positive. 1. Symbol, B+. The
positive dc voltage required for certain electrodes
of vacuum tubes, transistors, etc. 2. The positive
terminal of a B power supply.
B positive See B-PLUS.
B power supply A name used sometimes for the
unit that supplies high-voltage dc energy to a
vacuum tube plate or screen circuit.
bps Abbreviation of BITS PER SECOND.
Br Symbol for BROMINE.
bracketing A troubleshooting routine characterized by isolating progressively smaller areas in a
circuit or chain of stages until the defective subcircuit or stage is located.
Bradley detector A locked-oscillator circuit that
was once used as an FM detector.
braid 1. A woven network of fine metal wires used
for grounding purposes. It is usually made of fine
copper conductors. The increased surface-areato-volume ratio improves the conductivity, at radio frequencies, over a single conductor that has
the same cross-sectional area. Braid can be
tinned (saturated with solder) to retard corrosion.
2. It is also called a shield. The outer conductor in
prefabricated coaxial cable.
braided wire A length of braid. Used for grounding
or shielding purposes.
brain waves Alternating or pulsating voltages that
are caused by electrical activity in the brain of an
animal or human being. The voltages can be
picked up by electrodes attached to the scalp,
and amplified to be viewed on a cathode-ray-tube
(CRT) screen, heard by headphones or speakers,
or traced by an electroencephalograph.
branch 1. Any one of the separate paths of a
circuit. With respect to the layout of its components, a branch can be series, parallel, seriesparallel, parallel-series, or any combination of
these. It is also called a LEG. 2. See BRANCH
branch circuit In electrical wiring, a group of outlets served through a single cutout from a source
of power-line ac voltage. The source can be a distribution center, subdistribution center, main, or
submain. Interior lighting circuits are usually
branch circuits because many lights are connected to one circuit controlled by a single fuse or
circuit breaker.
Subdistribution center
branch circuit
(enclosed in broken lines)
branch current Current flowing through a branch
of a circuit, whose magnitude, with respect to the
total current of the circuit depends on the nature
of the branch.
branched In molecular polymers, the condition of
side chains being attached to the main chain.
branched windings Forked windings of a polyphase transformer.
branching In robotics and artificial intelligence
(AI), a set of routines or programs containing
points at which a computer must select from
among two or more alternatives. Such routines
are used in critical processes, such as the manufacture of precision equipment.
branch point See JUNCTION POINT.
branch voltage The voltage, or voltage drop,
across a branch of a circuit.
brass 1. An alloy of copper and zinc that is widely
used in electronics. Compared to annealed copper, this metal has four times the resistivity (or 1⁄4
the conductivity), half the temperature coefficient, more than twice the tensile strength, and a
lower melting point (900°C). 2. A colloquialism for
an old-fashioned, straight telegraph key.
brass pounder 1. Colloquialism for telegraph operator or radiotelegraph operator. 2. A radio ama-
brass pounder • brevity code
teur who handles large amounts of message traffic, particularly via Morse code. 3. A radio amateur proficient in Morse code operation.
Braun electroscope An electroscope consisting essentially of a fixed metal vane to which a movable
needle is fastened at a pivot. The repulsion between the two, when an electric charge is applied,
causes the needle to move over a calibrated scale.
bravo Phonetic representation of the letter B.
brazing The joining of two metal (usually iron or
steel) parts together with a suitable melted copper-alloy metal. Compare SOLDERING.
breadboard 1. A perforated board, a chassis, or
any basic framework on which electronic components can be mounted and quickly wired for the
preliminary test of a circuit. It is so called because the first such foundation units of this sort
actually were wooden breadboards. 2. Any preproduction electronic prototype circuit. 3. To set
up a circuit on a breadboard.
breadboard model 1. The preliminary model of an
electronic device, often built on a breadboard (see
BREADBOARD, 1). 2. Loosely, any prototype.
break 1. An open circuit. 2. To open a circuit. 3. In
communications, a word indicating a desire to
transmit on a wavelength already occupied by radio traffic. 4. See BREAK-IN, 1.
break-before-make contacts Contacts, especially
in a rotary selector switch, that open one circuit
before closing the next one.
breakdown 1. Failure of a circuit or device, caused
mainly by excessive voltage, current, or power. A
sudden high current, however, does not always
indicate failure. 2. AVALANCHE BREAKDOWN.
3. The separation of an electronics problem or
project into its constituent parts for an easier
breakdown diode See ZENER DIODE.
breakdown region The region, in a pn junction, in
which avalanche breakdown occurs.
breakdown strength See DIELECTRIC STRENGTH.
breakdown voltage 1. The voltage at which current suddenly passes in destructive amounts
through a dielectric. 2. The voltage at which a gas
suddenly ionizes, as in a gas tube. 3. The voltage
at which the reverse current of a semiconductor
junction suddenly rises to a high value (nondestructive if the current is limited). See
break-in 1. A technique of radio communication in
which one station interrupts a transmission from
another station, rather than waiting until the end
of the latter’s transmission. 2. Also called full
break-in. In a radio communications transceiver
or transmitter/receiver combination, extremely
rapid transmit/receive switching, approaching
full duplex communications. Every pause in
transmission, even of only a few milliseconds,
creates a “receive window” allowing reception
between spoken words or Morse code elements.
breaking current The momentary current that
flows when the contacts of a switch or relay are
break-in keying A system of radiotelegraph keying
in which the receiver is in operation whenever the
key is open. See BREAK-IN, 2.
break-in operation In radiotelegraph or singlesideband (SSB) communications, the practice of
interrupting at any time to “talk back” to the
other transmitting station. This operation is
made possible by high-speed transmit/receive
switching. See BREAK-IN, 2.
break-in relay An electromechanical or solid-state
relay that enables break-in operation. Largely
supplanted by solid-state switching devices.
breakover point In a silicon-controlled rectifier,
the source-voltage value at which the load current is suddenly triggered to its steep climb. Also
breakover voltage In a silicon-controlled rectifier
with open gate circuit, the anode voltage at which
anode current is initiated.
breakpoint A point in a computer program when,
for the purpose of obtaining information for the
program’s analysis, the sequence of operations is
interrupted by an operator or a monitor program.
breakpoint frequencies The upper- and lowerfrequency points at which the gain-versusfrequency response of an amplifier or network
departs from flatness.
breakpoint instruction An instruction that stops
a computer.
breakthrough 1. A new discovery, insight, or solution to a problem that results in an advancement
in the state of the art. 2. See PUNCHTHROUGH.
break time The time taken for a relay to drop out
completely or a switch to open. Compare MAKE
breathing Slow, rhythmic pulsations of a quantity,
such as current, voltage, brightness, beat note,
breezeway In a sync pulse in NTSC color television, the part of the back porch between the trailing edge of the pulse and the color burst.
B-register An index register in a computer for storing words that are used to change an instruction
before it is executed by the program.
Bremsstrahlung radiation The radiation emitted
by a charged particle whose speed is altered when
it passes through the electric field in the vicinity
of an atomic nucleus.
brevity code A code not intended to conceal information, but to shorten the number of characters
in a message or data file. The Q SIGNALS are an
example of a brevity code used in communications. In computer data transfer and communications, brevity codes allow compression, speeding
up the transfer rate and reducing the storage
space for a given amount of data.
Brewster angle • bridge-type meter
Brewster angle From BREWSTER’S LAW, the polarizing angle at which the reflected and refracted
rays of incident light are perpendicular to each
Brewster’s law (Sir David Brewster, 1781–1868).
For any dielectric reflector, the relationship in
which the refractive index is equal to the tangent
of the polarizing angle.
bridge 1. A network, usually consisting of four
branches, connected so that an input signal can
be applied between two opposite points and the
output taken between the other two opposite
points. When the component values are in a certain ratio, the voltage between the output points
is zero, and the bridge is said to be balanced or
set to null. 2. A circuit such as that described in
(1) used for electrical measurements. 3. An audio
or servo amplification system in which the load is
driven from two outputs having opposite polarity,
neither of which are at ground potential. 4. A
communications path between or among two or
more networks. This allows the subscribers in
any network to obtain data from, or send data to,
any other network, in effect creating a network of
bridge balance control A potentiometer, variable
capacitor, or variable inductor that is used to adjust a bridge circuit to balance.
bridge-connected amplifier 1. A dc amplifier
stage in which the transistors and resistors are
connected in a four-arm bridge circuit, with respect to dc. When the bridge is initially balanced,
all dc is eliminated in the output load. The input
signal unbalances the bridge, which results in an
amplified output signal in the load. 2. An amplifier pair having opposing outputs across which a
load can be bridged to obtain twice the power output of either amplifier alone.
bridged differentiator See HALL NETWORK.
bridge detector The output-indicating device
(e.g., meter, oscilloscope, or headphones) that
indicates whether a bridge is balanced or unbalanced. Also called null detector or null indicator.
bridged integrator A null network that consists of
a two-stage resistance-capacitance (RC) integrator circuit bridged by a capacitor. This network
produces a shallow null at a single frequency determined by the R and C values in the integrator.
bridged-tee attenuator An attenuator consisting
of a tee section, between the input and output of
which is bridged a single-series arm.
bridged-tee circuit Any circuit (of resistors, capacitors, inductors, or a combination of these)
that consists of a tee section, bridged by a singleseries section, from input to output.
bridged-tee null network A bridged-tee circuit of
resistance (R) and capacitance (C), proportioned
so that at some setting of the R and C values, the
output of the circuit is zero.
C1 = C2 = C3
R1 = R2 = R3
fnull = 1.732
bridged integrator
bridged-tee oscillator A low-distortion oscillator
circuit whose frequency is determined by a
bridged-tee null network inserted into the negative-feedback path of the circuit.
bridge feedback A combination of current feedback and voltage feedback around an amplifier
circuit. It is so called because, in the feedback circuit, the resistors and the output resistance of
the amplifier form a four-arm bridge.
bridge generator The power source (e.g., a battery
or oscillator) that supplies the signal to a BRIDGE
used for electrical measurements.
bridge indicator See BRIDGE DETECTOR.
bridge oscillator See BRIDGE GENERATOR.
bridge rectifier A full-wave rectifier circuit in
which four rectifying diodes are connected in a
bridge configuration. Each half-cycle of ac input
is rectified by a pair of diodes in opposite quarters
of the bridge and in series with each other. The
bridge does not require a transformer with a
center-tapped secondary, as does the FULLWAVE, CENTER-TAP RECTIFIER circuit.
bridge source See BRIDGE GENERATOR.
bridge-type meter A frequency-sensitive bridge
(such as the Wien bridge) that can be used to
measure audio frequency. Because the bridge
can be balanced at only one frequency at a time,
bridge-type meter • British Standard wire gauge
light, per unit area, emitted or reflected perpendicular to a light-emitting surface.
brightness control 1. In a computer monitor, television receiver, or oscilloscope, a potentiometer
that varies the negative bias voltage on the control grid of the cathode-ray tube (CRT). The
brightness of the image is inversely proportional
to this negative bias voltage. 2. The control of the
brightness of an illuminated area.
brilliance See BRIGHTNESS.
brilliance control 1. The BRIGHTNESS CONTROL
in a television receiver or computer monitor. 2.
The brightness control in a cathode-ray oscilloscope. 3. A control for adjusting the level of the
tweeter output in a speaker system.
British Standard wire gauge Abbreviation, NBS
SWG. A classification of wire sizes sometimes
used in England, Australia, and New Zealand.
The higher the number, the thinner the wire. The
designator does not take into account any coatings on the wire, such as enamel, rubber, or plastic insulation. In the United States, the American
wire gauge is more often used. See AMERICAN
its adjustable arm can be calibrated to read the
frequency directly.
bridge-type impedance meter An impedancemeasuring circuit in which unknown impedance
Z is connected in series with a calibrated variable
resistor R. An ac voltage is applied to the series
circuit. The separate voltage drops across the resistor and impedance are measured successively
as the value of R is varied. When the two voltage
drops are identical, Z equals R, and the
impedance can be read from a calibrated dial on
the variable-resistor control.
bridge-type oscillator A resistance-capacitance
(RC) tuned oscillator in which a Wien bridge is
used as the frequency-determining circuit in the
feedback loop.
bridge-type power meter 1. See BOLOMETER
BRIDGE. 2. A four-arm bridge specially designed
to operate at radio frequencies. At null, the
impedance of the unknown is read directly from
the balancing dial or calculated from bridge constants. This instrument is used to measure the
impedance of circuit components, antennas, and
transmission lines.
bridge-type SWR meter A four-arm bridge that is
specially designed to operate at radio frequencies.
At null, the standing-wave ratio (SWR) is calculated from the bridge resistance values or read
from a direct-reading scale on the null-indicating
bridging amplifier An amplifier whose input impedance is so high that it can be considered infinite for practical purposes. Thus, the amplifier
can be connected across a load or line without
significantly affecting the operation of the system.
bridging coupler A voltage-dependent resistor that
permits an occasionally used device (such as a bell)
to be connected permanently across a regularly
used device (such as a telephone) without continuously short-circuiting the latter. Thus, the bridging
coupler ordinarily has very high resistance; but
when the line voltage is momentarily raised, the resistance lowers and the occasionally used device is
actuated (e.g., the bell rings).
bridging gain The gain of a bridging amplifier expressed as the ratio (in decibels) of the power developed in the amplifier load to the power in the
load to which the input terminals of the amplifier
are connected.
bridging loss The loss that results from the shunting of a speaker, microphone, earphone, or other
transducer by a resistor, capacitor, or inductor.
Generally, the loss is expressed as a power ratio
in decibels.
Briggsian logarithm (Henry Briggs, 1556-1631). A
base-10 logarithm, generally known as a
brightness SI unit, candela per square meter
(cd/m2); cgs unit, lambert (L). The quantity of
British Standard Wire Gauge (NBS SWG) Diameters
British thermal unit • broad response
British thermal unit Abbreviation, Btu. The
amount of heat required to raise the temperature of
a pound of water by one degree Fahrenheit, in an
ambient environment of slightly greater than 39°F.
broadband Also called wideband. Possessing a
characteristic wide bandwidth or range of operating frequencies. This term can be applied at audio
frequencies (AF) or radio frequencies (RF), and is
frequently used to describe the performance of
oscillators, amplifiers, antennas, and various
types of networks. The term can also be applied to
describe the nature of electromagnetic emissions
or noise. Examples are given in the following several definitions. Compare NARROWBAND.
broadband amplifier An amplifier that has very
wide frequency response, such as 10 Hz to 10
MHz. Examples are an instrument amplifier and
a video amplifier.
broadband antenna An antenna that operates satisfactorily over a comparatively wide band of fre-
+12 V
broadband amplifier
quencies without requiring retuning at individual
frequencies. Examples are the log-periodic and
discone antennas.
broadband electrical noise Electrical noise that is
present over a wide frequency spectrum (e.g., 3
kHz to 30 MHz).
broadband I-F An intermediate-frequency (IF) amplifier or amplifier chain. The wide frequency response is important when an increased bandpass
is preferred to high selectivity, as in high-fidelity
radio tuners.
broadband interference Interference, other than
noise, that is present over a wide band of frequencies. An example is over-the-horizon shortwave radar, recognizable by its characteristic
“woodpecker” sound in communications receivers
at high frequencies.
broadband Klystron A Klystron oscillator with a
broadbanded tuned circuit.
broadband tuning Receiver tuning characterized
by a selectivity curve having a pronounced flat
top or broad nose that passes a wide band of frequencies. Also called broadband response.
broadcast 1. A radio-frequency transmission of an
intelligence-bearing signal that is directed to numerous unspecified receiving stations. 2. The
transmission or dissemination of signals to a
large, unspecified number of receiving stations.
broadcast band Any band of frequencies allocated
for broadcasting (see BROADCAST SERVICE, 1),
but particularly the U.S. standard amplitudemodulation (AM) and frequency-modulation (FM)
radio broadcast bands at 535 to 1605 kHz (AM)
and 88 to 108 MHz (FM).
broadcasting The dissemination of signals for reception by the general public, not for communications purposes.
broadcast interference Abbreviation, BCI. Interference to normal reception by broadcast receivers, usually arising from signals emitted by
other stations.
broadcast receiver A receiver intended primarily
to pick up standard broadcast stations. Also see
broadcast service 1. Any radio transmitting service (including television) that exists for the purpose of sending out electromagnetic signals for
general reception, rather than addressing them to
specific receiving stations. 2. The service provided
by a station operating in the broadcast band.
broadcast station Any station in the broadcast
service, but especially one assigned to operate in
the standard U.S. broadcast bands. Also called
broadcasting station.
broadcast transmitter A radio transmitter designed specifically for, and operated in, the
broadcast service.
broad response Slow deflection of an indicator,
such as a meter, over a relatively wide range of
values of the input quantity.
broadside • bubble memory
broadside In a perpendicular direction; for example, broadside radiation from an antenna.
broadside antenna See BROADSIDE ARRAY.
broadside array Also called broadside antenna. A
phased group of antennas arranged so maximum
radiation occurs in directions perpendicular to
the plane containing the driven elements. This requires that all of the antennas be fed in phase.
The elements can be half-wave dipoles or fullwave, center-fed conductors. Full-wave elements
have a slight gain over half-wave elements. At
high frequencies, this type of array is usually
constructed from two driven antennas. At veryhigh and ultra-high frequencies there can be several driven antennas. The antennas can each
consist of a single element, or they can be Yagis,
loops, or other systems with individual directive
properties. In general, the larger the number of
elements in the entire array, the greater the gain
and directivity.
broadside array
broad tuning Tuning that is characterized by
pronounced signal width, often resulting in
adjacent-channel interference. A common cause
of such impaired selectivity is low Q in the tuned
Broca galvanometer A device consisting of an
astatic magnetic arrangement, with a coil enclosing central consequent poles. The device is characterized by fast response and high sensitivity.
bromine Symbol, Br. A nonmetallic element of the
halogen family. Atomic number, 35. Atomic
weight, 79.90.
bronze An alloy of copper and tin that has various
uses in electronics. Also see PHOSPHOR BRONZE.
Brown and Sharpe gauge See AMERICAN WIRE
Brownian movement (Robert Brown, 1773 –1858).
Random movement of microscopic particles—
especially in solutions. It occurs because of colli-
sions of molecules with the particles. Einstein
showed, in his early work, a connection between
this movement and the Boltzmann constant.
brownout A deliberate lowering of line voltage by a
power company to reduce load demands. Minor
events of this type often pass unnoticed by the
average consumer. More pronounced events produce observable effects, such as shrinkage of
television and cathode-ray-tube (CRT) computerdisplay images.
Bruce antenna A vertical collinear array that consists of several resonant sections connected by
short, rigid, parallel-conductor stubs. The currents in the radiating sections are in phase. Maximum radiation and response occur broadside to
the antenna (omnidirectional in the horizontal
plane). Polarization is vertical. The antenna
produces gain at low radiation and response
angles, and is commonly used in repeater installations and fixed communications stations at
very-high frequencies (VHF) and ultra-high frequencies (UHF).
brush A usually metal or carbon strip, blade, or
block, that slides in contact with another part, as
in a motor commutator.
brush discharge Also called Saint Elmo’s fire. A
cloud of repelled ions around the tip of a pointed
conductor charged to a high voltage. It often produces a visible glow in the air.
brush holder The housing for a brush in a motor,
generator, rheostat, slip-ring junction in a rotating data-transmission system, etc.
brute force 1. The transmission of a signal of excessive or unnecessary power. 2. An inefficient
approach to a problem, which might solve the
problem, but requires far more energy, effort, or
computer memory/storage space than the minimum needed to accomplish the same result.
brute-force filter A pi-type lowpass dc power
supply filter, so called because of the extremely
large inductances and capacitances that are
generally used.
brute supply An unregulated power supply.
B-scope A cathode-ray tube (CRT), used in radar,
that presents a B DISPLAY.
B service A teletype communication system operated by the Federal Aviation Administration
B-supply The dc power supply that provides anode
operating voltages, such as plate and screen voltages in a vacuum-tube radio-frequency (RF)
power amplifier.
BT-cut crystal A piezoelectric plate cut from a
quartz crystal at an angle of rotation (relative to
the x-axis) of -49°. It has a zero temperature coefficient of frequency at approximately 25°C. Also
Btu Abbreviation of BRITISH THERMAL UNIT.
BuAer Abbreviation of Bureau of Aeronautics.
bubble memory In digital-computer practice, a
special type of static magnetic memory. The mag-
bubble memory • bulk effect
netic material is divided into regions that are
magnetized in different directions. So called because the flux lines of the tiny magnetized regions
are shaped somewhat like, and move around after the fashion of, bubbles on the surface of a
glass of soda.
bubble shift register A shift register that uses a
magnetic bubble (see BUBBLE MEMORY) that
can be moved sequentially from electrode to electrode on a wafer.
bubbling See MOTORBOATING.
bucket A computer memory or a designated location in such a memory.
bucking The process of counteracting one quantity, such as a current or voltage, via series or
parallel application of a similar quantity that has
opposite polarity (180 degrees out of phase).
bucking circuit 1. A circuit used to obtain bucking action. The simplest form is a battery and potentiometer that supply a variable voltage of
polarity opposite to that of the voltage to be
bucked. A more sophisticated form is an ac transformer, the secondary of which is connected in
series and out of phase with the ac utility line. 2.
The zero-set circuit in an electronic voltmeter.
bucking coil A coil placed and positioned so that
its magnetic field partially or completely cancels
the field of another coil. Troublesome hum fields
sometimes are neutralized with such a coil.
bucking voltage See BACK VOLTAGE, 2.
buckling The warping of storage-battery plates, usually resulting from excessive charge or discharge.
buckshot In an amplitude-modulated (AM) or single-sideband (SSB) radio transmission, broadband signal splatter caused by excessive modulation, or detuned multiplier circuits.
buffer 1. An amplifier used principally to match
two dissimilar impedance points and isolate one
stage from a succeeding one in a cascaded system, and thus to prevent undesirable interaction
between the two. 2. In a digital computer, a storage site used temporarily during data transfers to
compensate for differences in data flow rates. 3.
In digital-computer operations, a follower stage
that is used to drive a number of gates without
overloading the preceding stage.
buffer, 2.
buffer amplifier See BUFFER, 1.
buffer capacitor A high-voltage fixed capacitor
that is placed across a transformer secondary to
suppress voltage spikes and sharp waveforms—
especially when the input is a square wave.
buffer circuit 1. In a data system that uses a keyboard, an electronic circuit that allows the operator to type ahead of the data output. 2. See
BUFFER, 1, 2 and 3.
buffered output An output (power, signal, etc.)
that is delivered from the generating device
through an isolating stage, such as a buffer amplifier. This arrangement protects the device from
variations in the external load. Compare UNBUFFERED OUTPUT.
buffer storage 1. A buffer that is used to interface
between data systems with different rates of
transmission. 2. See BUFFER, 2.
bug 1. Slang for WIRETAP, 1. 2. Slang for circuit
fault, 1. 3. A semiautomatic key that some radiotelegraph operators use to send Morse code.
bug key See BUG, 3.
building-block technique The process of assembling electronic equipment by quickly connecting
together already completed stages (in the form of
boxes or blocks) and supplying power and signals
to the setup. Also called modular technique and
modular construction.
building-out circuit A short section of transmission line shunting another line; it is used for
impedance matching. Also called building-out
buildup 1. The process whereby the voltage of a rotating generator starts at a point that is determined by the residual magnetism of the machine,
and gradually increases to a voltage representing
the point at which the resistance line crosses the
magnetization curve. 2. The (usually gradual) accumulation of a quantity (e.g., the buildup of
charge in a capacitor).
bulb A globe-like container having any of a number
of characteristic shapes from spherical to tubular
and usually evacuated, for enclosing the elements of an electron device, such as a vacuum
tube, gas tube, photocell, or lamp.
bulge 1. A nonlinear attenuation-versus-frequency
curve in a transmission line. 2. A localized nonlinearity in a function.
bulk The body or mass of a semiconductor specimen, as opposed to junctions within the specimen. Current flows through a junction, but it can
also flow, more or less, through the mass of semiconductor wafer into which the junction has been
bulk effect An effect, such as current, resistance,
or resistivity, observed in the overall body of a
sample of material, as opposed to a region within
the material or on its surface. Thus, a silicon
diode can display junction resistance (i.e., resistance offered by a junction processed in a wafer of
silicon), as well as bulk resistance (i.e., the effec-
bulk effect • burst generator
tive resistance of all paths around the junction,
through the mass of the wafer). Compare SURFACE EFFECT.
bulk-erased tape Recording tape whose signal
content has been removed via a bulk eraser.
bulk-erase noise 1. The residual magnetic impulses that remain on a magnetic tape after it has
been bulk-erased. 2. Noise generated by bulkerased tape when the latter passes through deenergized record or erase heads in a tape machine.
bulk eraser A type of power-line-frequency degausser that erases an entire reel of magnetic
tape without requiring that the tape be unreeled
and passed continuously under an erase head.
This saves considerable time, but often leaves
some BULK-ERASE NOISE on the tape. Also
bulletin board In personal computing or amateur
packet communications, a system that allows
subscribers to leave messages for each other for
access via a modem or terminal node controller.
bulletin station A station intended for the transmission of bulletins of interest to certain parties,
such as military personnel or amateur radio operators. An example is W1AW in Newington, Connecticut, an amateur radio station that transmits
bulletins and code practice.
buncher In a Klystron, a cavity resonator that contains two grids mounted parallel to the electron
stream. The electrostatic field of the grids alternately accelerates and retards the electrons, velocity-modulating the stream into bunches.
buncher grids In a Klystron, the closely spaced
grids that velocity-modulate the electron beam
into successive bunches.
buncher resonator In a velocity-modulated tube,
such as a Klystron, the input cavity resonator.
buncher voltage The radio-frequency (RF) grid-togrid voltage in the buncher resonator of a
bunching The production of electron bunches in a
velocity-modulated tube, such as a Klystron. Also
bunch stranding A technique for combining several thin wires into a single thick wire. Often used
in guy wires and electrical conductors to improve
tensile strength and flexibility. At radio frequencies, bunch stranding also improves electrical
conductivity by increasing the ratio of surface
area to cross-sectional area. This minimizes
losses caused by skin effect.
Bunet’s formula A formula for calculating the inductance of a multilayer air-core coil that has a
diameter less than three times the length:
L = a2N 2/(9a + 10l + 8.4c + 3.2cl/a)
where N is the number of turns, a is the average
coil radius, c is the winding thickness, and l is the
length of the coil.
Bunsen cell A cell consisting of a zinc rod in a sulfuric acid solution contained in a porous pot,
Bunet s formula
which is in a nitric acid solution. The zinc rod
serves as the negative pole; the positive pole is a
piece of hard carbon. The cell produces about 1.9
volts and delivers relatively high current.
burn 1. A blemish on the screen of a cathode-ray
tube (CRT), caused by destruction of the phosphor there. This results from prolonged focusing
of an intense electron beam in one spot. 2. A
blemish on the screen of a television picture tube,
usually resulting from ions that reach the screen
when the ion trap is not working correctly.
burn-in A long, thorough, carefully controlled preliminary test of a component, device, or system,
to stabilize its electrical characteristics after
manufacture and to ensure that it will function
according to rated specifications. An important
test for equipment whose reliability must be
guaranteed, such as an emergency communications transceiver.
burnout 1. Failure of a conductor or component
caused by overheating from excess current or
voltage. 2. The open-circuiting of a fuse. 3. Electrical failure of any type.
burst 1. The abrupt ionization of the gas in an ionization chamber by cosmic rays. 2. An abrupt increase in the amplitude of a signal. Also, the type
of signal that results from burst action. 3. See
burst amplifier In a color-television receiver, the
amplifier that separates the burst pulse from the
video signals and amplifies the former. See
burst gate timing In a color-television receiver,
the timing of the gating pulse with the input signal of the burst amplifier.
burst generator A signal generator delivering a
burst output (see BURST, 2) for testing various
types of equipment. Its output is intermediate
between sine waves and square waves, and is
convenient for rapidly appraising the perfor-
burst generator • button microphone
mance of such devices as amplifiers, filters, electronic switches, transducers, and loudspeakers.
burst transmission A short transmission at high
speed. This method of transmission saves time,
but increases the necessary bandwidth of a signal by the same factor as the ratio of the high
speed to the original speed.
bus 1. A main conductor in a circuit. A bus can be
high in the sense that its potential is above or
below ground, or it can be low or at ground reference. 2. In computer operations, a common
group of paths over which input and output signals are routed.
bus driver A buffering device designed to increase
the driving capability of a microprocessor, which
itself might be capable of driving no more than a
single load.
business machine Any piece of electronic or electromechanical equipment used mainly, or entirely,
for business purposes. Examples are photocopiers,
facsimile (fax) machines, printers, and computers.
busing The parallel interconnection of circuits.
busy test A check conducted to find out whether or
not a certain telephone subscriber line is in use.
busy tone Also called busy signal. An intermittent
tone that indicates that the subscriber line being
called is in use.
Butler oscillator An oscillator that consists of a
two-stage amplifier with a quartz crystal in the
positive-feedback path from output to input.
butterfly capacitor A plate-type variable capacitor
that has two stator sections and a single rotor
section common to the two stators. External connections are made to the stators only. Thus, no
wiping contact is required to the rotor, and the
troubles associated with such a contact are
avoided. The butterfly capacitor is actually two
variable capacitors in series. The unit is so called
from the shape of its rotor.
circuit. The ring supplies the inductance, and the
butterfly supplies the capacitance. It is also
called butterfly tank and butterfly resonator.
Butterworth filter A high-pass, low-pass, bandpass or band-rejection filter, characterized by a
flat passband (absence of passband ripple) and
high attenuation at frequencies far removed from
the passband.
Butterworth function A mathematical function
that is used in the design of a BUTTERWORTH
button 1. Usually, a small switch that is actuated
by finger pressure. It is also called pushbutton
and pushbutton switch. Sometimes, the term is
applied only to the insulated knob or pin which is
pushed to operate the switch. 2. A tiny lump of
impurity material, placed on the surface of a
semiconductor wafer for alloying with the wafer
to form a junction. See ALLOY JUNCTION. 3. The
carbon element(s) in a BUTTON MICROPHONE.
button capacitor A button-shaped ceramic or silvered-mica fixed capacitor. Because of its disk
shape and mode of terminal connection, it offers
very low internal inductance.
button microphone A microphone in which a button-shaped carbon element is attached to a diaphragm, which is set into vibration by sound
waves. This motion causes the button resistance
to vary, modulating a direct current that passes
Single button
Stator 1
Stator 2
butterfly capacitor
butterfly circuit A combination of a butterfly capacitor and a ring, of which the stator plates of
the capacitor are an integral part. The resulting
structure is a compact variable-frequency tuned
Double button
button microphone
button microphone • byte
through the button. A single-button microphone
has only one button, whereas a double-button
microphone has two—one mounted on each side
of the center of the diaphragm.
buzz 1. A low-pitched rough sound with highfrequency components, usually the result of electrical interference from nonsinusoidal voltages
generated by neighboring equipment or devices.
2. The waveform associated with such a sound.
3. Fastening two conducting surfaces by a KELLIE BOND.
buzzer A nonringing device used principally to
generate sound other than that achievable with
sine waves. In an electromechanical vibratingreed buzzer, the reed acts as an armature, which
is mounted close to the core of an electromagnet.
At quiescence, the reed rests against a stationary contact. When voltage is applied to the electromagnet, the reed is attracted to the core,
moving away from the contact; but this breaks
the circuit, the magnetism ceases, and the reed
springs back to the contact. The action is repeated continuously at a frequency that depends
on the reed dimensions and its distance from the
BX Symbol and abbreviation for armored and insulated flexible electrical cable.
bypass A route (either intended or accidental)
through which current easily flows around a
component or circuit instead of through it.
bypass capacitor A capacitor that is used to conduct an alternating current around a component
or group of components. Often the ac is removed
from an ac/dc signal, the dc being free to pass
through the bypassed component.
B voltage The dc voltage required by certain electrodes of vacuum tubes and transistors. It especially pertains to voltages required by the plate
and screen of a vacuum tube, as opposed to the
filament voltage and control-grid voltage.
bw 1. Abbreviation of bandwidth. 2. Abbreviation
of black-and-white.
BWA Abbreviation of backward-wave amplifier.
B-Y signal In a color television receiver, the colordifference signal which, when combined with a
luminance (Y) signal, forms a blue primary signal
for the three-gun picture tube.
In digital-computer and data-communications operations, a unit of data consisting of eight
contiguous bits. In packet communications, the
term octet is often used.
1. Abbreviation of CAPACITANCE. 2. Symbol for
COLLECTOR of a transistor. 3. Symbol for CARBON. 4. Abbreviation of CELSIUS. 5. Symbol for
COULOMB. 6. Abbreviation of CALORIE.
c 1. Abbreviation of CENTI. 2. Abbreviation of
CENTS. 3. Symbol for CAPACITANCE. 4. Symbol
for SPEED OF LIGHT in a vacuum.
Ca Symbol for CALCIUM.
cabinet An enclosure for a piece of apparatus. It
might or might not incorporate electromagnetic
cable 1. A usually flexible (but sometimes rigid)
medium, via which electrical power or signals are
transferred. Although the term is occasionally applied to a single conductor, especially when it is a
braid or weave of a number of wires, cable usually
means a bundle of separate, insulated wires or
strands of fiberoptic material. 2. CABLEGRAM.
cable address A code word that specifies the recipient of a CABLEGRAM.
cable assembly A special-purpose cable with connectors.
cable attenuation Reduction of signal intensity
along a cable, usually expressed in decibels per
foot, hundred feet, mile, etc.
cable capacitance Capacitance between conductors in a cable or between conductors and the
outer sheath of a cable. 2. Sometimes, capacitance between a cable and earth.
cable clamp A support device for cable runs in
equipment and systems.
cable communications Telegraphy or telegraphy
via a (usually undersea) cable.
cable connector A connector, such as a coaxial fitting, that joins cable circuits or connects a cable
to a device.
cabled wiring Insulated leads connecting circuit
points; they are tied together with lacing cord or
with spaced fasteners.
cablegram A (usually printed) message transmitted or received via undersea cable. Compare
cable run The path taken by a cable.
cable splice 1. An electrical attachment between
two sections of cable that has identical or similar construction, with or without the use of connectors. 2. To electrically attach two sections of
cable that have identical or similar construction,
with or without the use of connectors.
cable tie A short piece of wire or plastic that holds
wires or cables in a bundle.
cache memory A short-term, high-speed, highcapacity computer memory. Similar to a scratchpad or read-write memory.
CAD Acronym for computer-aided design.
CAD/CAM Acronym for computer-aided design and
cadmium Symbol, Cd. A metallic element. Atomic
number, 48. Atomic weight, 112.41. Many electronic structures are cadmium plated for protection.
cadmium borate phosphor Formula, (CdO +
B2O3): Mn. A substance used as a phosphor coating on the screen of cathode-ray tubes. The characteristic fluorescence is green-orange.
cadmium cell Also called Weston standard cell.
An electrochemical standard cell used as a reference voltage source. Produces 1.0186 volt at
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cadmium plating • calibrated sweep
cadmium plating The process of coating a conductor or component with cadmium to increase its
resistance to corrosion.
cadmium selenide photocell A photoconductive cell in which cadmium selenide is the lightsensitive material.
cadmium silicate phosphor Formula, (CdO +
SiO2). A substance used as a phosphor coating on
the screen of cathode-ray tubes; the characteristic fluorescence is orange-yellow.
cadmium standard cell See STANDARD CELL.
cadmium sulfide photocell A photoconductive cell in which cadmium sulfide is the lightsensitive material.
cadmium tungstate phosphor Formula, CdO +
WO3. A substance used as a phosphor coating on
the screen of cathode-ray tubes; the characteristic fluorescence is light blue.
cage A completely shielded enclosure, such as a
screen room, which is covered with a grounded
fine-mesh conductive screen on all sides.
cage antenna An antenna, usually center-fed and
balanced, that consists of multiple parallel conductors arranged in a cylindrical cage configuration. The cage results in a much broader
bandwidth than is the case with an antenna
made up of a single conductor. Cage antennas
are typically used at frequencies between about
10 and 200 MHz.
cage antenna
CAI Abbreviation for computer-assisted instruction.
CAL An acronym for conversional algebraic language, a general-purpose problem-oriented computer programming language used in time-sharing
calcium Symbol, Ca. A metallic element of the
alkaline-earth group. Atomic number, 20. Atomic
weight, 40.08.
calcium phosphate phosphor Formula, Ca3(PO4)2.
A substance used as a phosphor coating on the
screen of long-persistence cathode-ray tubes; the
characteristic fluorescence is white, as is the
calcium silicate phosphor Formula, (CaO +
SiO2): Mn. A substance used as a phosphor coat-
ing on the screen of cathode-ray tubes; the characteristic fluorescence ranges from green to
calcium tungstate phosphor Formula, CaWO4. A
substance used as a phosphor coating on the
screen of short-persistence cathode-ray tubes;
the characteristic fluorescence is blue, as is the
calculate To perform the steps of an intricate
mathematical operation. Compare COMPUTE.
calculating punch A data-processing peripheral
that reads punched cards, makes calculations,
and punches new data into those cards or new
calculator A machine that performs mathematical
operations, especially arithmetic. Typically, the
device is a small box with buttons and a miniature numeric display. Used only in mathematical
applications. In contrast, a COMPUTER can be
used for a much wider variety of jobs, such as
word processing, graphics, and data-base. Many
personal computers have calculator programs;
the “buttons” are actuated by pointing and clicking with a mouse.
calculus 1. The symbology and rules comprising a
system of logic, such as BOOLEAN ALGEBRA. 2.
A branch of mathematical analysis concerned
with rates of change and accumulation. See DIFFERENTIAL CALCULUS and INTEGRAL CALCULUS.
calendar age The age of a piece of equipment, measured since the date of manufacture. Specified in
years, months, and days. The actual manufacture date might alternatively be given.
calendar time The time available in a working period [i.e., a 40-hour work week represents a calendar time of 120 hours (five days times 24 hours
per day)].
calibrate To compare and bring into agreement
with a standard.
calibrated measurement 1. A measurement made
with an instrument that has been calibrated with
a standard reference source. 2. A measurement
that is corrected for instrument error.
calibrated meter An analog or digital meter that
has been adjusted to agree as closely as possible
with a reference source.
calibrated scale 1. A scale whose graduations
have been carefully checked for accuracy (i.e.,
they correspond to the true values of the quantity
that they represent). The scale is graduated to
read directly in units of the quantity, such as milliamperes, kilohertz, volts, etc. 2. A scale with
fixed, plain numeric graduations (e.g., 0 to 100)
that do not directly indicate the magnitude of a
quantity, but that can be converted to various
quantities via graphs, nomographs, tables, or
calibrated sweep In an oscilloscope, a sweep circuit calibrated to indicate sweep frequency or
time at all control settings.
calibrated triggered sweep • CAN
Frequency (MHz)
calibrated triggered sweep In an oscilloscope, a
triggered sweep circuit calibrated in terms of
sweep time or frequency.
calibration 1. Determining the accuracy with
which an instrument indicates a quantity. 2. Determining the degree to which the response of a
circuit or device corresponds to desired performance. 3. Marking a scale to show actual values
of a quantity in the form of a direct readout. For
example, the scale of an analog meter might be
calibrated in milliamperes (mA) from 0 to 50 in increments of 1 mA.
calibration accuracy 1. A quantitative expression
of the agreement between the value of a quantity,
as indicated by an instrument, and the true
value. Usually expressed as the maximum percentage of the true value by which the indicated
value can be expected to deviate in either direction (e.g., ±0.5 percent). 2. The precision of a direct-reading meter in terms of its full-scale
deflection (e.g., ±2.0 percent of full scale).
calibration curve A graph showing the relation between the actual values of a quantity and the setting or indication of an instrument or component.
Usually plotted in rectangular coordinates.
20 40 60 80 100
Log scale reading
calibration curve
calibration marker A pip or blip, superimposed on
a pattern displayed on a cathode-ray-tube (CRT)
screen, to identify a point closely as to frequency,
voltage, distance, or some similar term.
calibrator A device used to perform a calibration
(e.g., a signal generator).
calibrator crystal A highly accurate and stable
quartz crystal, used in an oscillator as a frequency standard. An example is the 100-kHz
crystal oscillator and harmonic generator used in
some communications receivers.
californium Symbol, Cf. A radioactive element produced artificially. Atomic number, 98. Atomic
weight, 251.
call 1. In communications, a transmission by a
station for the purpose of either alerting a particular receiving station for which there is a mes-
sage, or alerting all receiving stations to prepare
them for a general broadcast message. 2. In a
computer program, a branch to a closed subroutine; also, to branch to such a subroutine.
call direction code Abbreviation, CDC. In telegraph networks, a special code that, when transmitted to a terminal, causes the teleprinter to be
automatically switched on.
calling sequence 1. Computer program instructions needed to establish the conditions for a call
(see CALL, 2). 2. Subroutine instructions providing a link to the main program.
call instruction A computer program instruction
that makes a program controller branch to a subroutine; it also locates and identifies the parameters needed for the subroutine’s execution. Also
known as subroutine call.
call letters Letters and/or numbers assigned to,
and used to identify, licensed radio stations.
calorie Abbreviation, cal or C. The amount of heat
energy, at a pressure of 1 atmosphere, that will
raise the temperature of 1 gram of water by 1 degree Celsius.
calorimeter An instrument for measuring heat energy. By adaptation, a calorimeter can be used to
measure radio-frequency (RF) power—especially
at microwave frequencies (see CALORIMETRIC
calorimeter system See CALORIMETRIC POWER
calorimetric power meter A specialized form of
wattmeter, in which the power to be measured is
dissipated in an oil or water bath that has a
known and fixed mass. The wattage is determined indirectly, by measuring the extent to
which the temperature of the liquid increases in a
certain amount of time.
CAM 1. Abbreviation of computer-aided manufacturing. 2. Abbreviation of content-addressed
cambric Finely woven cotton or linen used for insulation. One type of spaghetti (conductor insulation), for example, is varnished cambric tubing.
camera cable A multiwire cable that conducts the
video signal from a television camera to control
camera chain In television, the camera and the
equipment immediately associated with it, excluding the transmitter and its peripherals.
camera signal The output signal delivered by a
television camera.
camera tube Any video pickup tube, such as an
iconoscope or orthicon, that converts light reflected by a scene into a corresponding television
Campbell bridge A circuit that is used for comparing mutual inductance with capacitance.
camp-on In a telephone system, a method of engaging a line that is busy until it becomes available for use.
can • capacitive coupling
maintain its voltage and smooth out the ripples in
the voltage applied to it.
capacitance-inductance bridge A combination ac
bridge that can be used for either capacitance or
inductance measurement. Both capacitance and
inductance can be measured in terms of a standard capacitance; however, some of these bridges
use standard inductors in the inductancemeasuring mode.
capacitance meter A direct-reading meter for
measuring capacitance. In most available types, a
stable ac voltage is applied to the meter circuit, to
which an unknown capacitor is connected in series; meter deflection is roughly proportional to
the reactance of the capacitor. Also called MICROFARAD METER.
capacitance ratio In a variable capacitor, the ratio
of maximum to minimum capacitance.
capacitance relay A relay circuit that operates
from a small change in its own capacitance. It
consists of an RF oscillator whose tank capacitance is very low. When a finger is brought near
the circuit’s short pickup antenna, the attendant
increase in capacitance detunes the oscillator,
activating the relay. Also called PROXIMITY RELAY and PROXIMITY SWITCH.
capacitance-resistance bridge A combination ac
bridge that can be used for either capacitance or
resistance measurement. The unknown resistance is measured against a standard resistor;
the unknown capacitance against a standard capacitor.
capacitance sensor See CAPACITANCE TRANSDUCER.
capacitive amplifier See DIELECTRIC AMPLIFIER.
capacitive attenuator An ac attenuator whose elements are capacitors in any desired combination
of fixed and/or variable units. The desired attenuation is afforded by the capacitance ratio.
capacitive coupling A means of coupling between
circuits that uses a series capacitor for directcurrent blocking. The signal passes through the
capacitor, but the blocking effect allows different
bias voltages to be applied to the two stages.
can 1. A metal enclosure or container roughly resembling a tin can (though not necessarily cylindrical), used for shielding or potting components.
2. Colloquial expression for HEADPHONE.
Canada balsam A transparent cement derived
from the turpentine distilled from balsam fir
resin. It is useful in optical technology and in certain areas of electro-optics.
Canadian Standards Association The Canadian
equivalent of the National Bureau of Standards in
the United States. An agency that publishes
agreed-on standards for industries.
cancel character 1. IGNORE CHARACTER. 2. A
control character indicating that the associated
data is erroneous.
cancellation The elimination of one quantity by
another, as when a voltage is reduced to zero by
another voltage of equal magnitude and opposite
candela Symbol, cd. The SI unit of luminous intensity; 1 cd represents 1⁄60 of the radiating power of
one square centimeter of a perfect radiator at the
temperature of freezing platinum.
candle Abbreviation, c. Also called international
candle. A unit of light intensity that is the value of
emission by the flame of a sperm-whale-oil candle
burning at the rate of 7.776 grams per hour.
candle power Abbreviation, cp. Luminous intensity in international candles: the luminous intensity resulting from the burning of a
sperm-whale-oil candle at 7.776 grams per hour.
candoluminescence White light produced without
extreme heat.
cannibalization The deliberate use of parts from
operational equipment to temporarily repair or
maintain other equipment. It is a last-resort,
emergency measure.
cap 1. Abbreviation of CAPACITANCE. 2. Abbreviation of CAPACITOR.
capacimeter See CAPACITANCE METER.
capacitance Symbol, C. Unit, farad. The property
exhibited by two conductors separated by a dielectric, whereby an electric charge becomes
stored between the conductors. Capacitance is
thought of as analogous to mechanical elasticity.
Also see FARAD.
capacitance bridge A four-arm ac bridge for gauging capacitance against a standard capacitor. In
its simplest form, it has a standard capacitor in
one arm and resistors in the other three.
capacitance coupling The transfer of ac energy
between two circuits or devices by a capacitor or
capacitance effect. Also see COUPLING.
capacitance diode See VARACTOR.
capacitance divider An alternating-current voltage divider that uses capacitors, rather than resistors. It is used in certain oscillators, such as
the Colpitts type.
capacitance filter A filter consisting of only a
high-capacitance capacitor. Because the capacitor cannot discharge instantaneously, it tends to
capacitive coupling
capacitive diaphragm • capacitive window
capacitive diaphragm A metal plate deliberately
placed in a waveguide to introduce capacitive reactance and, thereby, cancel an inductive reactance.
capacitive-discharge ignition An electronic ignition system for automotive engines. Provides
nearly constant high voltage, regardless of engine
speed. A dc-to-dc step-up converter charges a
large capacitor (typically to 300 volts) when the
distributor breaker points are closed; when they
are open, the capacitor discharges through the
ignition coil, thereby generating an ignition pulse
of several thousand volts.
capacitive division Reduction of an ac voltage by
a capacitive voltage divider.
capacitive feedback Feeding energy back from the
output to the input of an amplifier or oscillator
through a capacitor.
capacitive-input filter A smoothing filter for ac
power supplies, in which the element closest to
the rectifier is a capacitor, regardless of the components or circuits placed subsequently.
capacitive load A load consisting of a capacitor or
a predominantly capacitive circuit.
capacitive loading In an antenna, the addition of
capacitance in series with the element(s). This
raises the resonant frequency for a radiator having a given physical length. It can also serve to increase the physical length required for a radiator
having a specified resonant frequency. Compare
capacitive post A protrusion inside a waveguide
for the purpose of introducing capacitive reactance to cancel an inductive reactance.
capacitive potentiometer See CAPACITIVE VOLTAGE DIVIDER.
capacitive pressure sensor A pressure sensor
that uses a radio-frequency oscillator and a pair
of metal plates separated by dielectric foam. The
circuit is designed so a change in the capacitance
between the plates causes the oscillator frequency to change. This change is sensed. A signal
is sent to an analog-to-digital converter (ADC)
and then to a microcomputer that calculates the
extent of the pressure.
capacitive proximity sensor A transducer used in
mobile robots that detects the presence of certain
kinds of objects. It consists of an oscillator whose
frequency is determined by an inductancecapacitance (LC) circuit to which a metal plate
is connected. When a conducting or partially conducting object comes near the plate, the mutual
capacitance changes the oscillator frequency.
This change is detected and sent to the robot
capacitive reactance Symbol, XC. Unit, ohm. The
reactance exhibited by an ideal capacitor, considered as a negative pure-imaginary quantity;
XC = –j/(6.28f C), where f is the frequency in
hertz, C is the capacitance in farads, and j is the
unit imaginary number (the square root of –1).
Alternatively, f can be specified in megahertz
and C in microfarads. In a pure capacitive reactance, current leads voltage by 90 degrees. Also
capacitive speaker See ELECTROSTATIC SPEAKER.
capacitive transducer A transducer consisting essentially of a refined variable capacitor whose
value is varied by a quantity under test, such as
pressure, temperature, liquid level, etc.
capacitive tuning Variable-capacitor tuning of a
capacitive voltage divider A capacitive attenuator
usually consisting of two series-connected capacitors whose values are such that an applied ac
voltage is divided across them in the desired ratio.
capacitive welding An electronic welding system
in which energy stored in a capacitor is discharged through the joint to be welded. This develops the heat necessary for the operation.
capacitive window A pair of capacitive diaphragms used in a waveguide to introduce capacitive reactance.
capacitor • carbon-button amplifier
capacitor A passive electronic-circuit component
consisting of, in basic form, two metal electrodes
or plates separated by a dielectric (insulator).
capacitor amplifier See DIELECTRIC AMPLIFIER.
capacitor antenna See CONDENSER ANTENNA.
capacitor bank A network of capacitors connected
in combination, yielding a desired characteristic.
capacitor braking The connection of a capacitor to
the winding of a motor after the removal of power,
to speed up the process of braking.
capacitor color code See COLOR CODE.
capacitor decade See DECADE CAPACITOR.
capacitor filter In a direct-current power supply, a
filter consisting simply of a capacitor connected
in parallel with the rectifier output.
dc input
dc output
capacitor filter
capacitor-input filter A filter whose input component is a capacitor. The capacitor-input powersupply filter is distinguished by its relatively high
dc output voltage, but somewhat poorer voltage
regulation, compared with the CHOKE-INPUT
capacitor leakage Direct current flowing through
the dielectric of a capacitor. In a good nonelectrolytic capacitor, this current is normally less
than 1 microampere. In an electrolytic capacitor,
it can be up to several milliamperes, depending
on the capacitance and the applied voltage.
loudspeaker See ELECTROSTATIC
capacitor microphone See CONDENSER MICROPHONE.
capacitor motor An ac motor that uses a capacitor in series with an auxiliary field winding for
starting purposes. Initially out-of-phase current
in the auxiliary field (starting winding) causes a
rotating field that turns the rotor. When the rotor
reaches a safe speed, a centrifugal switch disconnects the capacitor and auxiliary field, and
the motor continues running as an induction
capacitor series resistance The ohmic loss in
a capacitor. It results partly from conductor
losses, and partly from losses in the dielectric
capacitor substitution box An enclosed assortment of selected-value capacitors arranged to be
switched one at a time to a pair of terminals. In
troubleshooting and circuit development, any of
several useful fixed capacitance values can be
thus obtained.
capacitor voltage 1. The voltage at the terminals
of a capacitor. 2. The maximum voltage rating of
a capacitor.
capacitor voltmeter See ELECTROSTATIC VOLTMETER.
capacity 1. A measure of a cell’s or battery’s ability
to supply current during a given period. 2. CAPACITANCE. 3. The number of bits or bytes a
computer storage device can hold. 4. The limits of
numbers that a register can process.
capacity lag In an automatic control system, a delay caused by the storing of energy by the components. For example, in a heating system, capacity
lag results from the time taken to heat the air or
fluid after the thermostat turns on the heat.
capillary electrometer A sensitive voltage indicator, consisting of a column of mercury in a
transparent capillary tube, in which is suspended a small drop of acid. When a voltage is
applied to both ends of the mercury column, the
acid drop moves toward the low-potential end of
the column over a distance proportional to the
capstan The driven spindle or shaft of a magnetic
tape recorder or transport.
capture area The effective ability of a radio antenna
to pick up electromagnetic signals. The larger the
capture area, the greater the antenna gain.
capture effect 1. In frequency-modulation (FM)
radio receivers, the effect of domination by the
stronger of two signals, or by the strongest of several signals, on the same frequency. 2. In an
automatic-frequency-control system, the tendency
of the receiver to move toward the strongest of
several signals near a given frequency. 3. In general, the tendency of one effect to totally predominate over other effects of lesser amplitude.
capture ratio A measure of frequency-modulation
(FM) tuner selectivity: The amplitude difference,
in decibels, between unwanted signals and the
one being tuned in.
carbon Symbol, C. A nonmetallic element. Atomic
number, 6. Atomic weight, 12.011. Carbon, besides being an invaluable material in electronics,
is an important constituent of organic compounds.
carbon arc The arc between two electrified pencils
of carbon or, as in an arc converter, between a
carbon pencil and a metal electrode.
carbon brush A contact made of carbon or some
mixture of carbon and another material, used in
motors, generators, variable auto-transformers,
rheostats, and potentiometers.
carbon-button amplifier An audio-frequency
amplifier having as the active component an
earphone whose diaphragm is attached to a carbon microphone button. The input signal applied to the earphone makes its diaphragm
vibrate. The vibrating button modulates a local
carbon-button amplifier • cardistimulator
direct current. Amplification results from the
large ratio of modulated local current to inputsignal current.
carbon-composition resistor A non-inductive resistor made from a mixture of finely powdered
carbon with a non-conductive substance, usually
phenolic. The resulting clay-like material is
pressed into a cylindrical shape, and wire leads
are inserted in the ends. The resistance depends
on the ratio of carbon to the non-conducting material, and on the physical distance between the
wire leads. This type of resistor is useful from direct current to ultra-high radio frequencies. Compare FILM RESISTOR, WIREWOUND RESISTOR.
carbon/disk rheostat A rheostat consisting of a
stack of carbon disks or washers, arranged so
that a controllable pressure can be exerted on the
stack. As a knob is turned, a screw increases or
decreases the pressure, varying the total resistance of the stack.
carbon-film resistor A stable resistor whose resistance element is a film of carbon, vacuumdeposited on a substrate, such as a ceramic.
carbonization The application of a coat of carbon
onto an electrode, either by electroplating or by
any other means.
carbon microphone A microphone that includes
one or two carbon buttons. See BUTTON MICROPHONE.
carbon-paper recorder A recorder in which a
signal-actuated stylus writes, by impression only,
through a sheet of carbon paper onto a plain
sheet underneath. This eliminates the need for an
ink-carrying stylus.
carbon-pile regulator A voltage regulator in
which a stack of carbon disks or washers is in
series with the shunt field. The pile resistance
and field current depend on pressure applied to
the pile by a wafer spring acting through a movable iron armature. Voltage drops increase the
pressure and voltage rises decrease the pressure, thus regulating the generator with which
it is associated.
To dc load
carbon-pile regulator
carbon-pile rheostat See CARBON-DISK RHEOSTAT.
carbon recording 1. A record made with a
CARBON-PAPER RECORDER. 2. The use of a carbon-paper recorder in data acquisition, facsimile,
communications, and similar applications.
carbon resistor A resistor made from carbon,
graphite, or some composition that contains carbon.
carbon/silicon-carbide thermocouple A thermocouple that is a junction between carbon and silicon carbide.
carbon transfer recording A method of facsimile
reception in which the image is reproduced by
carbon particles sprayed on the paper, a process
controlled by the received signal.
carbon-zinc cell See ZINC-CARBON CELL.
Carborundum Formula, SiC. Trade name for a
synthetic silicon carbide used as a semiconductor, refractory, or abrasive. Also see SILICON
Carborundum crystal Trade name for a characteristically superhard crystal of silicon carbide.
Carborundum varistor A voltage-dependent resistor made from Carborundum.
carcinotron A special kind of oscillator tube used
at ultra-high and microwave frequencies.
card 1. A usually thin, rectangular board containing a PRINTED CIRCUIT, often equipped with an
edge connector that makes it easy to install, remove, or replace. Common in electronic and computer equipment having modular construction. 2.
The usually flat, thin insulating strip on which a
resistor element is wound.
cardiac monitor An electronic device that displays
or records electrical impulses from the heart for
medical observation or diagnosis.
cardiac pacemaker An electrical cardiac stimulator that causes the heart to beat at certain intervals. Used when the patient has heart disease
that prevents the heart from regulating itself.
cardiac stimulator An electronic device (sometimes implanted in the subject) that supplies
electric pulses to stimulate heart action. Also
card image In memory storage, the data contained
on a single card.
cardioid diagram A polar response curve in the
shape of a cardioid pattern.
cardioid microphone A microphone with a (roughly)
heart-shaped sound-field pickup pattern.
cardioid pattern A radiation/response pattern
with one sharp null in the direction opposite the
single main lobe. The lobe is extremely broad. In
two dimensions, the curve is shaped somewhat
like a “Valentine” heart.
cardiotachometer A device that indicates the
pulse rate.
cardistimulator See CARDIAC STIMULATOR.
Carey-Foster bridge • carrier line
Carey-Foster bridge A special version of the slidewire bridge that is useful for measuring an unknown resistance, whose value is close to that of
a standard resistance.
Carey-Foster bridge
Carey-Foster mutual inductance bridge An ac
bridge that permits the measurement of mutual
inductance in terms of a standard capacitor.
R2 = 0
M = R1R4C
( )
R3 = R4 L1 −1
Carey-Foster mutual inductance bridge
carnauba wax A wax obtained from the Brazilian
wax palm. Used as an electrical insulator, and as
the dielectric in some electrets.
Carnot theorem In thermodynamics, the proposition that in a reversible cycle, all available energy
is converted into mechanical work. Also called
Carnot’s principle.
carrier 1. See CARRIER WAVE. 2. See CHARGE
carrier amplifier See DIELECTRIC AMPLIFIER.
carrier beating 1. The mixing of two radiofrequency carriers that are separated by a small
amount of frequency, resulting in an audible tone
in a receiver. 2. A heterodyne in a facsimile or
television signal, resulting in a pattern of cross
hatches in the received image.
carrier choke A radio-frequency (RF) choke, inserted in a line to block a carrier component.
carrier chrominance signal For conveying color
television information, sidebands of a modulated
chrominance subcarrier.
carrier color signal For conveying color information in color television transmission, the sidebands of a modulated chrominance subcarrier
(plus the unsuppressed chrominance subcarrier)
added to the monochrome signal.
carrier concentration In a semiconductor material,
the number of charge carriers per unit volume.
carrier control 1. The modification, adjustment,
or switching of a carrier wave. 2. Adjustment of a
circuit or device by means of a carrier wave.
carrier current The current component of a carrier
wave, or the amplitude of that current. Compare
communication See
carrier-current control 1. Control of the current
component in a carrier wave. 2. Remote control
by means of wired wireless.
carrier-current receiver See WIRED-RADIO RECEIVER.
carrier-current relay A radio-frequency (RF) relay
circuit, operated over a wire line by means of a
carrier-current transmitter See WIRED-RADIO
carrier deviation See CARRIER SWING.
carrier dispersion In a semiconductor, the spreading out of electrons and holes that leave the emitter simultaneously, but arrive at the collector at
various times after following different paths.
carrier frequency The center frequency of a CARRIER WAVE.
carrier-frequency pulse A pulse that contains
radio-frequency oscillation.
carrier-frequency range The band of carrier frequencies over which a transmitter or signal generator can operate.
carrier injection The apparent emission (injection)
of electrons or holes into a semiconductor when a
voltage is applied to the junction.
carrier leak 1. A point at which carrier-wave energy escapes a circuit or enclosure. 2. The residual carrier voltage present in the output of a
carrier-suppressing circuit.
carrier level The amplitude of an unmodulated
carrier wave.
carrier lifetime In a semiconductor, the interval
before an injected current carrier (see CARRIER
INJECTION) recombines with an opposite carrier
and ceases to be mobile.
carrier line In carrier-current systems (see WIRED
WIRELESS), the line or cable conducting the
carrier-wave energy.
carrier mobility • carry system
carrier mobility Symbol, µ. In a semiconductor
material, the average drift velocity of electrons
and holes per unit electrostatic field.
carrier noise Modulation of a carrier when there is
no input from the modulator itself; unwanted
carrier noise level The noise signal amplitude that
results from unintentional fluctuations of an unmodulated carrier.
carrier-on-light transmission A form of transmission in which many different signals are sent simultaneously by modulating a beam of light at
multiple frequencies.
carrier-on-microwave transmission A form of
transmission in which many different signals are
sent simultaneously by modulating a microwave
signal at multiple lower frequencies.
carrier-on-wire transmission A form of transmission in which many different signals are sent at
the same time over a wire, by using radiofrequency carriers. Also called CARRIER-CURRENT
carrier oscillator In a single-sideband receiver,
the radio-frequency (RF) oscillator that supplies
the missing CARRIER WAVE.
carrier power The actual power represented by a
radio-frequency (RF) carrier applied to an antenna, measured by either the direct or indirect
method. The direct method involves determination of power according to the formula P = I 2R,
where I is antenna current and R is antenna resistance at the point of current measurement.
The indirect method involves determination of
power according to the formula P = EIF, where E
and I are antenna voltage and current, and F is a
factor less than 1.0, whose value depends on the
type of modulation used.
carrier power-output rating The power delivered
by an unmodulated transmitter or generator to
the normal load or its equivalent.
carrier shift In an amplitude-modulated transmitter or generator, the undesired change of average
carrier voltage during modulation.
carrier-shift indicator An instrument for detecting carrier shift. It usually contains only a
pickup coil, semiconductor diode, and dc milliammeter in series. Meter deflection is steady
until carrier shift is detected; then, the needle
carrier signaling In wire telephony, the use of
carrier-wave signals to operate such functions as
dialing, ringing, busy signal, etc.
carrier storage In a semiconductor device, the tendency of mobile carriers to stay near a junction
for a short time after the junction voltage has
been removed or reversed in polarity.
carrier suppression The elimination of the carrier
in an amplitude-modulated signal so that only
the sideband energy remains.
carrier swing In frequency-modulated or phasemodulated transmission, the total deviation (low-
est to highest instantaneous frequency) of the
carrier wave.
carrier system The transmission of many signals
over one circuit, accomplished by modulating
various different carriers at different frequencies.
Different signals can use different modulation
carrier telegraphy 1. Continuous-wave telegraphy
by WIRED WIRELESS. 2. Wired-wireless telegraphy in which a radio-frequency carrier is modulated by an audio-frequency keying wave.
carrier telephony Telephone communication by
carrier terminal 1. At each end of a carrier-current
line or cable, the equipment for generating, modifying, or utilizing the carrier energy. 2. In a balanced modulator, the point of carrier insertion.
carrier-to-noise ratio The ratio of carrier amplitude to noise-voltage amplitude.
carrier transmission Transport of information by
a carrier, as by an amplitude-modulated radio
wave that carries the low-frequency information
as the AF modulation envelope and delivers it to
the demodulator at the receiving station.
carrier-type dc amplifier A high-frequency ac amplifier, ahead of which is operated a generator
and transducer. A dc voltage applied to the transducer modulates the carrier supplied by the generator; the amplifier boosts the modulated wave,
and the resultant output is rectified at a level
higher than that of the dc input signal.
carrier voltage The voltage component of a carrier
wave; also, the amplitude of this component. Compare CARRIER CURRENT and CARRIER POWER.
carrier wave A sine wave that is modulated to
convey information in wireless and cable communications systems. The lowest frequency normally used for wireless signal transmission is 9
kHz, corresponding to a wavelength of approximately 33 km. The highest frequency is less well
defined; some systems make use of visible light
waves, whose wavelengths are as short as approximately 4 × 10–7 m. For modulation to work
effectively, the carrier must have a frequency at
least 10 times the highest frequency of the modulating signal.
carry 1. In adding a column of figures, the digit
added to the column at the left when the sum exceeds one less than the radix value. 2. In digital
computers and counters, a pulse that corresponds to the arithmetic operation in which a figure is carried to the next column in addition.
carrying capacity The ability of a conductor, such
as copper wire, to carry current safely (expressed
in maximum amperes).
carry-complete signal In an arithmetic computation by a computer, an adder-produced signal indicating that the pertinent carries have been
carry system A communications system in which
several carries occupy one circuit.
carry time • cascaded amplifier
Current (amperes)
−5 −4 −3
−2 −1
Wire size (AWG)
carrying capacity
(of some AWG sizes of copper wire)
carry time The time taken for a digital computer or
counter to perform a carry operation (See CARRY,
Cartesian coordinate geometry Also called rectangular coordinate geometry. In robotic systems, a
movement scheme in two or three dimensions.
The position of the robot arm is determined by linear coordinates, relative to an origin point. These
coordinates are specified along linear axes—each
of which is perpendicular to the others at the origin. See CARTESIAN COORDINATES, CARTESIAN PLANE, and CARTESIAN THREE-SPACE.
Cartesian coordinates Also called rectangular coordinates. A mathematical system that uniquely
defines the position of a point on a plane, in space,
or in general, in an n-dimensional hyperspace
when n is a whole number greater than 3. There
are n axes for n dimensions, each axis intersects
all the others at a single point, called the origin.
The axes are mutually perpendicular at this origin.
The axes are scaled in units with the origin having
coordinate values that are all equal to zero (usually). Positive values go along the axes in one direction; negative numbers go in the opposite
direction for each axis. Usually, the axes are graduated in equal-sized units. The system gets its
name from the mathematician Rene Descartes.
Cartesian plane A linear, two-dimensional coordinate plane commonly used for graphing equations in one variable.
Cartesian three-space A linear, three-dimensional
graph-coordinate system used for rendering
equations in one or two variables.
Cartesian three-space
Cartesian three-space graph A three-dimensional
graph that shows an equation in one or two variables. Three-space graphs are often displayed
more clearly by means of computer graphics, in
which the entire display can be rotated to show
the characteristics of the surface resulting from a
given equation or function.
Cartesian n-space The coordinate space defined
by a Cartesian system of n coordinates, where n
is a whole number of 2 or greater.
cartridge 1. The replaceable transducer assembly
of a microphone. 2. A magnetic-tape magazine.
Also see TAPE CARTRIDGE. 3. A removable computer mass-storage medium, containing a tape,
magnetic diskette, or optical diskette. 4. An insulating tube housing a fuse, semiconductor component, resistor, capacitor, or other part.
cartridge fuse A fuse consisting of a fusible wire
enclosed in a cartridge, having a ferrule at each
end for plug-in connection.
cascadable Capable of, or designed for, being connected in cascade with other similar or identical
cascade 1. Components or stages connected and
operated in sequence, as in a three-stage amplifier. The components or stages are often but not
necessarily identical. 2. To form a cascade.
cascade control 1. In an automatic control system, a controller whose setting is varied by the
output of another controller. 2. An automatic
control system in which the control units are connected in stages, so that one unit must operate
before the next one can function.
cascaded amplifier A multistage amplifier in which
the stages are forward-coupled in succession.
cascaded carry • cathode
cascaded carry In digital computer practice, a system of performing the carry operation (see
CARRY) in which the n + 1 place receives a carry
pulse only when the nth place has received carry
information to generate the pulse.
cascade thermoelectric device A thermoelectric
component or circuit that consists of several cascaded sensors (see CASCADE, 1).
cascade voltage doubler A voltage-doubler circuit
(see VOLTAGE DOUBLER) consisting of two
diode-capacitor combinations in cascade. Unlike
the conventional voltage-doubler circuit with two
capacitors in the output, the cascade voltage doubler has one in the input and one in the output.
cascode A high-gain, low-noise, high-inputimpedance amplifier circuit, consisting of a
grounded-emitter or grounded-source input stage
coupled directly to a grounded-base or groundedgate output stage.
(field-effect transistor
case temperature The temperature at a designated point on the outside surface of a component’s case or housing.
Cassegrain antenna A dish antenna that uses
Main dish
focus reflector
Cassegrain antenna
Cassegrain feed A dish-antenna feed system in
which the feed point is located at the center of the
dish itself. For transmission, the radio-frequency
energy emerges from a waveguide and is directed to
a small convex reflector at the focal point of the
dish. The small reflector directs the signal back to
the dish, spreading the energy out to cover the entire surface of the dish. The dish reflects the energy
again and collimates it in the desired direction of
propagation. For reception, the process is reversed;
the dish focuses the energy on the small reflector,
which propagates it back to the feed point.
cassette 1. A holder (magazine) of reels of magnetic tape that is itself a mechanical subassembly, which can be easily inserted into and
removed from a tape deck. 2. A lightweight holder
of photographic film or X-ray plates (before, during, and after exposure).
castor oil A viscous insulating oil extracted from
castor beans. Highly refined castor oil is used as
an impregnant in some oil-filled capacitors. Dielectric constant, 4.3 to 4.7. Dielectric strength,
380 V/mil.
catalysis The process whereby an agent, called a
catalyst, enhances a chemical reaction without
entering into the reaction. Catalysts are used in
electronics, for example, to promote the setting of
resins in potting and encapsulating operations.
catalytic agent A substance that accomplishes
cataphoresis As caused by the influence of an
electrostatic field, the migration toward the cathode of particles suspended in a liquid.
catastrophic failure 1. Sudden, unexpected failure of a component or circuit. 2. Failure that can
result in the breakdown of an entire system. Also
called catastrophic breakdown.
catcher In a Klystron, the second reentrant cavity.
catcher diode A diode that is connected to regulate
the voltage at the output of a power supply. The
cathode is connected to a source of reference voltage. If the anode, connected to the source to be
regulated, becomes more positive than the cathode, the diode conducts and prevents the regulated voltage from rising more than 0.3 volt above
the reference voltage (for germanium diodes) or 0.6
volt above the reference voltage (for silicon diodes).
catcher grids In a Klystron, the grids through
which the bunched electrons pass on their way
from the buncher to the collector. Catcher grids
absorb energy from the bunched electrons and
present it to the collector circuit.
category In a computer system, a group of magnetic disk volumes containing information related
by a common application.
category storage A computer-file storage section
that contains a number of categories and used by
an operating system.
catenation See CONCATENATION.
cathode 1. The negative electrode of a device (i.e.,
the electrode from which electrons move when a
cathode • cavity laser
current passes through the device). 2. In an electrochemical cell, the electrode that gains electrons. This is generally the positive electrode. 3.
In a vacuum tube, the electron-emitting electrode
(filament or indirectly heated cathode sleeve).
cathode current Symbol IK. The current flowing in
the cathode circuit of a tube. Cathode current is
the total of grid, plate, screen, and suppressor currents, and can have an ac and a dc component.
cathode dark current The electron emission from
the photocathode of a camera tube when there is
no illumination.
cathode element In a vacuum tube, an indirectly
heated emitter of electrons. Also see CATHODE, 2.
cathode emission 1. The giving up of electrons by
the cathode element of a device, such as a vacuum tube. Electrons can be emitted by either hot
or cold cathodes, depending on the tube. 2. Collectively, electrons released by a cathode.
cathode heating time The time required for the
temperature of a tube cathode to increase from
cold to its maximum specified operating temperature after the cathode current has been initiated.
Also called cathode warmup time.
cathode luminous sensitivity For a photomultiplier tube, the cathode’s sensitivity to light. This
sensitivity figure is the ratio of photocathode current to incident light flux.
cathode-ray oscillograph An instrument that provides a permanent record, by photographic or
other means, of the image on the screen of a
cathode-ray tube.
cathode-ray oscilloscope See OSCILLOSCOPE.
cathode rays Invisible rays emanating from the
cathode element of an evacuated tube operated
with a high voltage between the anode and cathode. Cathode rays (electrons) cause certain substances, PHOSPHORS, to glow upon striking them.
cathode-ray scanning tube Any tube in which an
electron beam is deflected horizontally and vertically to scan an area. These include oscilloscope
tubes, some computer monitors, radar displays,
and television camera tubes.
cathode-ray tube 1. An evacuated tube containing
an anode and cathode that generates cathode
deflecting deflecting
Glass stem
cathode-ray tube
Viewing screen
rays when operated at high voltage. 2. An oscilloscope tube. 3. A picture tube.
cathode terminal 1. In a diode (semiconductor or
tube), the terminal to which a negative dc voltage
must be applied for forward-biasing the diode.
Compare ANODE TERMINAL. 2. In a diode, the
terminal at which a positive dc voltage appears
when the diode acts as an ac rectifier. Compare
ANODE TERMINAL. 3. The terminal connected
internally to the cathode element of device. 4. In
a vacuum tube, an indirectly heated electron
cathode voltage Symbol, EK. The voltage between
ground (or B-minus) and the cathode of a tube; it
can have both ac and dc components.
cathodic protection A method of preventing corrosive galvanic action in underground metal
pipes or the submerged hulls of ships. The part to
be protected is used as the cathode of a circuit
through which a direct current is passed in the
direction opposite to that which caused the corrosion, thus counteracting it.
cathodofluorescence Fluorescence resulting from
a material’s exposure to cathode rays.
cathodoluminescence In a vacuum chamber in
which a metal target is bombarded with highvelocity electrons (cathode rays), the emission of
radiation of a wavelength characteristic of the
cation A positive ion. Also see ION.
CAT scanner The X-ray apparatus for COMPUTERIZED AXIAL TOMOGRAPHY.
TELEVISION (usually cable television).
caustic soda electrolyte Symbol, NaOH. Sodium
hydroxide solution, as used in some secondary
cells and experimental devices.
cavitation The local formation of cavities in a fluid
used in ultrasonic cleaning because of the reduction in pressure at those points.
cavitation noise In an ultrasonic cleaner, the
noise resulting from the collapse of bubbles produced by cavitation.
cavity A metallic chamber (can) in which energy is
allowed to reflect, sometimes resulting in resonance.
cavity filter A microwave (usually band rejection)
filter consisting of a resonant cavity and associated coupling devices.
cavity frequency meter See CAVITY WAVEMETER.
cavity impedance The impedance across a cavity
at a particular frequency. At resonance, the cavity impedance is purely resistive.
cavity laser A laser that employs a resonant cavity
filled with gas, such as helium/neon or argon,
and a pair of reflectors. Resonance occurs between the reflectors, one of which is totally reflective and the other of which is approximately 95
percent reflective. Output is from the partially reflective end of the device.
cavity magnetron • cell constant
cavity magnetron A magnetron whose anode is a
series of resonant cavities.
cavity oscillator An oscillator with a cavity-tuned
cavity radiation Energy radiated from a tiny hole
in an otherwise sealed chamber. The radiation
occurs at all electromagnetic wavelengths; the
greater the temperature within the chamber, the
greater the frequency at which the radiation has
its maximum amplitude.
cavity resonance The phenomenon whereby a
hollow cavity resonates; specifically, resonance in
small metal cavities at microwave frequencies.
cavity resonator See RESONANT CAVITY.
cavity wavemeter An absorption wavemeter whose
adjustable element is a tunable resonant cavity
into which radio-frequency (RF) energy is injected
through a waveguide or coaxial cable. Such an instrument is useful at microwave frequencies.
CB Abbreviation of CITIZENS BAND.
Cb Symbol for COLUMBIUM.
CB Symbol for BASE CAPACITANCE of a transistor.
C band The band of radio frequencies between 3.9
and 6.2 GHz.
CC Symbol for collector capacitance of a transistor.
cc 1. Alternative abbreviation of cubic centimeter.
The International Organization for Standardization recommends cm3. 2. Abbreviation of
CCIR Abbreviation of Comite Consultatif International des Radiocommunications (International Radio Consultative Committee).
CCIT Abbreviation of Comite Consultatif International Telegrafique (International Telegraph Consultative Committee).
CCITT Abbreviation of Comite Consultatif International Telegrafique et Telephonique (International
Telegraph and Telephone Consultative Committee).
CCS 1. Abbreviation of CONTINUOUS COMMERCIAL SERVICE. 2. Abbreviation of commonchannel signaling.
CCTV monitor A video monitor that receives a signal from a CCTV transmitter.
CCTV signal The picture signal in a CCTV system.
It can be either a modulated radio-frequency signal or a composite video signal.
ccw Abbreviation of COUNTERCLOCKWISE.
CD Abbreviation of COMPACT DISK.
Cd Symbol for CADMIUM.
cd Abbreviation of CANDELA.
CD-4 A method of obtaining quadraphonic reproduction on a phonograph disk using modulated
carriers with frequencies above the human hearing range.
C display A radar display showing the target as a
dot whose coordinates represent the bearing (horizontal) and angle of elevation (vertical). Compare
cd/m2 Candelas per square meter, the SI unit of
Ce Symbol for CERIUM.
Ce Symbol for EMITTER CAPACITANCE of a transistor.
ceiling 1. The maximum possible power output
from a transmitter. 2. The maximum possible
current or voltage that a circuit can deliver. 3. In
aviation, the level of the cloud base.
ceilometer An instrument for measuring ceiling
(cloud height).
cel In animated graphics, an individual image or
cell 1. A single (basic) unit for producing dc electricity by electrochemical or photovoltaic action,
as in a battery or a solar panel. Also see PRIMARY
addressable, one-word-capacity storage element
in a computer memory. 3. The geographic region
covered by a specified repeater in a cellular communications network. See CELLULAR COMMUNICATIONS. 4. An electrostatic charge dipole in
the atmosphere, usually occurring in or near
thunderstorms. 5. A thunderstorm.
cell constant The surface area of the electrodes in
a cell divided by the distance between them. The
basic linear units must be the same: for example,
square centimeters for surface area and centimeters for distance.
cell counter • center-tapped filament
center frequency 1. The frequency, in a communications receiver, that is midway between the
lower and upper 3-dB-down amplitude points.
2. The average frequency of a modulated carrier.
3. The carrier frequency of a modulated signal,
whether or not the carrier is suppressed.
cell counter A bioelectronic instrument used to
count blood cells and other minute particles.
cell reversal A condition that can occur in some
rechargeable electrochemical cells and batteries,
such as nickel-cadmium batteries. It most often
results from neglecting to recharge the cell or battery when it has become fully discharged.
cell-type enclosure A room designed to prevent
the entrance or escape of radio-frequency (RF)
electromagnetic fields, characterized by doublewalled copper-mesh shielding.
cellular coil A coil having a crisscross (usually
multilayer) winding. Examples: lattice-wound
coil, honeycomb coil, basket-weave coil.
cellular communications A radio, telephone, or
television communications network that makes
use of numerous fixed repeaters. Subscribers use
mobile or portable transceivers that are always
within range of at least one repeater. The most
common form is known as cellular telephone or
cellular mobile radio telephone.
celluloid A thermoplastic dielectric material that is
a blend of cellulose nitrate and camphor. Dielectric constant, 4 to 7. Dielectric strength, 250 to
780 V/mil.
cellulose acetate A plastic dielectric material used
as a substrate for magnetic tapes, photographic
film, and similar applications. Dielectric constant, 6 to 8. Dielectric strength, 300 V to 1
kV/mil. Also see ACETATE.
cellulose acetate base See ACETATE BASE.
cellulose acetate butyrate A thermoplastic dielectric material that is an acetic and butyric acid ester of cellulose.
cellulose acetate tape See ACETATE TAPE.
cellulose nitrate The nitric acid ester of cellulose,
a plastic insulating material.
cellulose propionate A thermoplastic molding material that is a propionic acid ester of cellulose.
Celsius scale A temperature scale in which 0 degrees is the freezing point of water, and 100 degrees the boiling point of water. Also called
cent An audio-frequency interval of 0.01 (1⁄100) of
a half step. A half step is the frequency difference between two immediately adjacent keys on
a piano.
center channel In high-fidelity stereo, a phantom
sound source that appears to exist midway between the left and right speakers or earpieces.
The effect is caused by identical, or nearly identical, signals in the left and right channels.
center-fed antenna An antenna in which the feeders are connected to the center of the radiator.
center feed 1. Attaching a feeder or transmission
line to the center of the radiator of an antenna. 2.
Connection of signal-input terminals to the center of a coil. 3. Descriptive of paper tape whose
feed holes are aligned with character hole centers. Compare ADVANCE FEED TAPE.
center frequency, 3.
centering control In an oscilloscope circuit, a potentiometer used to position the image on the
screen (particularly in the center). Separate controls are provided for horizontal and vertical centering.
center loading In an inductively loaded antenna,
placement of the loading coil(s) at or near a point
or points midway between the feed point and the
end(s) of the radiating element.
center of beam 1. In a directional antenna system,
the direction, denoted by a straight ray, where
the signal strength or response is the greatest. 2.
In a beam of visible light, the geometric center of
the spot produced when the beam strikes a surface perpendicular to the beam. 3. In a beam of
visible light, the axis within the beam where the
intensity is greatest.
center of channel The frequency that is midway
between the lowest and highest frequency components of a communications channel.
center of radiation The point from which the energy radiated by an object appears to arrive.
center tap A connection made to the centermost
turn of a coil or to the center-value point of a resistor, filament, or capacitor pair.
center-tapped coil See CENTER-TAPPED WINDING.
center-tapped filament A tube or lamp filament
that has a tap at its center.
center-tapped inductor • ceramic-to-metal seal
center-tapped inductor An inductor that has a
tap at half the total number of turns (the physical
center of the winding).
center-tapped potentiometer A potentiometer
that has a tap at half the total resistance of the
resistance element.
center-tapped resistor A fixed resistor that has a
tap at half the total resistance.
center-tapped transformer A transformer that
has one or more center-tapped windings.
center-tapped winding A winding that has a tap
at half the total number of turns (the physical
center of the winding).
center-tapped winding
center tracking frequency In three-frequency
alignment (tracking) of a circuit, the frequency
between the upper and lower frequency limits
(alignment or tracking points of the circuit).
center-zero meter A meter that has its zero point
at the center of the scale (e.g., a dc galvanometer).
centi- Abbreviation, c. Prefix meaning hundredth(s) (10–2).
centigrade scale See CELSIUS SCALE.
centimeter Abbreviation, cm. A unit of length
equal to 10-2 meter, or 0.3937 inch.
centimeter-gram-second system Abbreviation,
cgs. A system of units, now seldom used, in
which the centimeter is the fundamental unit of
length, the gram is the fundamental unit of
mass, and the mean solar second is the fundamental unit of time. Electrical units in the cgs
system fall into two categories: electrostatic and
electromagnetic. The names of cgs electrostatic
units have the prefix stat- (e.g., STATAMPERE,
STATVOLT, etc.). Cgs electromagnetic units
have the prefix ab- (e.g., ABAMPERE, ABVOLT,
centimetric waves See MICROWAVES.
centipoise A cgs measure of the dynamic viscosity
of liquids. Equal to 10–2 poise.
central office In telephone systems, a switching
network at which numerous circuits or subscriber lines converge.
central processing unit Abbreviation, CPU. In a digital computer, the section containing the arithmetic
and logic unit (ALU), control circuits, and internal
memory circuits. Also called central processor.
Central Radio Propagation Laboratory A government laboratory that studies radio propagation and collects, correlates, and analyzes data
for predicting propagation conditions. The organization also studies methods of measuring
centrifugation potential An electric potential that
occurs in a colloidal solution when the solution is
centrifugal switch A switch actuated by rotational
motion (e.g., the automatic disconnection switch
in a capacitor motor).
centripetal force The force that draws the mass of
a rotating body toward the axis of rotation.
ceramal See CERMET.
ceramet seal See CERAMIC-TO-METAL SEAL.
ceramic-based microcircuit A tiny circuit printed
or deposited on a ceramic substrate.
ceramic capacitor A component made with sheets
of metal stacked alternately with wafers of ceramic. This material, like mica, has low loss, and
therefore allows for high efficiency. For low values of capacitance, only one layer of ceramic is
needed, and two metal plates can be glued to a
disk of porcelain, one on each side. Alternatively,
a tube or cylinder of ceramic can be employed,
and metal ink applied to the inside and outside of
the tube. These capacitors have values ranging
from a few picofarads to about 0.5 µF. Their voltage ratings are comparable to those of paper capacitors. Compare ELECTROLYTIC CAPACITOR,
ceramic dielectric 1. A ceramic used as a dielectric in capacitors. Examples: barium titanate,
barium strontium titanate, and titanium dioxide.
Ceramic dielectrics provide high dielectric constant. 2. A ceramic used as an insulator. Examples: isolantite, porcelain, and steatite.
ceramic filter A resonant filter similar to a crystal
filter, but using a piezoelectric ceramic material.
ceramic magnet A permanent magnet made of a
magnetic ceramic material, such as mixtures of
barium oxide and iron oxide.
ceramic microphone A microphone that uses a
waves into electrical impulses.
ceramic piezoelement A component that uses a
piezoelectric ceramic material. Examples: ceramic
filter, ceramic microphone, ceramic phono pickup,
ceramic transducer, and electrostrictive transducer. Also called PIEZOELECTRIC CERAMIC.
ceramic resistor A carborundum resistor whose
value is voltage-dependent. It usually displays a
negative temperature coefficient of resistance
(but a positive coefficient is available) and a negative voltage coefficient of resistance.
ceramics 1. Clay-based materials used as dielectrics and insulators in electronics. Examples:
barium titanate, titanium dioxide, porcelain,
isolantite, and steatite. 2. The science and art of
using and developing ceramics.
ceramic-to-metal seal A bond in which ceramic
and metal bodies are joined, for example, the
bonding of a metal lead to a ceramic disk,
through which it passes to provide a leak-proof
seal. Also called ceramet seal.
ceramic transducer • change record
ceramic transducer A transducer that uses a CERAMIC PIEZOELEMENT to translate such parameters as pressure and vibration into electrical
ceramic tube A high-temperature vacuum tube
that uses a ceramic material, instead of glass, as
the envelope; the tube offers low losses at high
Cerenkov radiation Light emanating from a transparent material that is traversed by charged particles, whose speed is higher than the speed of
light through the material.
Cerenkov radiation
Cerenkov rebatron device An apparatus for generating radio-frequency energy by passing an
electron beam through a piece of dielectric having
a small aperture.
ceresin wax A yellow or white wax obtained by refining ozocerite. Used as an insulant and sealant
against moisture. Dielectric constant, 2.5 to 2.6.
cerium Symbol, Ce. A metallic element of the rareearth group. Atomic number, 58. Atomic weight,
cerium metals A group of metals belonging to
the rare-earth group: cerium, lanthanum,
neodymium, praseodymium, promethium, and
cermet An alloy of a ceramic, such as titanium
carbide, and nickel, a metal. A thin film of cermet
is used as a resistive element in some microcircuits. Cermet is an acronym for ceramic metal.
certified tape A magnetic recording tape that has
been thoroughly checked and found to have no
cesium Symbol, Cs. A metallic element of the alkali-metal group. Atomic number, 55. Atomic
weight, 132.91. The oscillations of this element’s
atoms have been used as atomic time standards.
The element is used in some phototubes as the
light-sensitive material, and in some arc lamps.
cesium-vapor lamp A low-voltage arc lamp used
as an infrared source.
Cf Symbol for CALIFORNIUM.
cgs Abbreviation of CENTIMETER-GRAM-SECOND.
chad The punched-out particle(s) constituting refuse from paper-tape punching.
chadded tape Punched paper tape in which the
chad is left partially attached to the tape’s
punched holes.
chadless tape Punched paper tape without CHAD.
chafe 1. An area that has been abraded by rubbing
or scraping. 2. To produce a chafe.
chaff Strips of metal foil used to create radar interference or ambiguity in locating a target by multiple reflections of the beam. Also called MIRROR.
chain broadcasting Simultaneous transmissions
from a number of broadcast transmitters connected together in a network by wire line, coaxial
cable, or microwave link.
chain calculation As performed by a calculator, a
calculation that can be entered as it would normally be written (i.e., without the need for regrouping operands).
chain printer In the readout channel of a digital
computer, a high-speed printer carrying printer’s
type on a revolving chain.
chain radar system A number of radar stations
along a missile-flight path that are connected in a
communications or control network.
chain reaction A reaction (as in nuclear fission)
that is self-sustaining or self-repeating. Unless
controlled from outside, such a reaction runs to
chain switch A switch that is actuated by pulling a
light metal chain. Successive pulls turn the
switch alternatively on and off.
chain switch
change dump In computer operation (especially in
debugging), the display of the names of locations
that have changed following a specific event.
change file See TRANSACTION FILE.
change of control In a sequence of computer
records being processed, a logical break that initiates a predetermined action, after which processing continues.
changer In a high-fidelity disk player, a device that
allows several disks to be played, one after the
other, without the need for manually exchanging
the disks.
change record A computer record that changes information in a related master record. Also called
transaction record.
change tape • character density
change tape See TRANSACTION TAPE.
channel 1. A frequency (or band of frequencies) assigned to a radio or television station. 2. See KEYWAY. 3. A subcircuit in a large system [e.g., the
radio-frequency (RF) channel of a receiver, the
vertical-amplifier channel of an oscilloscope, or the
modulator channel of a radio transmitter]. 4. The
end-to-end electrical path through the semiconductor body in a field-effect transistor. 5. One of
the independent audio circuits in a stereo sound
system (e.g., the left channel or the right channel).
channel analyzer A (usually multiband) continuously tunable instrument, similar to a tuned radio receiver, used in troubleshooting radio
communications circuits by substituting a perfect channel for one that is out of order.
channel balance The state in which the apparent
amplitude of two or more channels is identical.
channel bank In a transmission system, the terminal equipment used for the purpose of multiplexing the individual channels.
channel capacity The fullest extent to which a
channel can accommodate the information (frequencies, bits, words, etc.) to be passed through it.
channel designator A name, number, or abbreviation given to a channel in a communications system.
channel effect The possible current flow through a
high impedance between the collector and emitter
in a bipolar transistor.
channel frequency The CENTER FREQUENCY of
a communications channel.
channeling Multiplex transmission in which separate carriers within a sufficiently wide frequency
band are used for simultaneous transmission.
channelizing The subdivision of a relatively wide
frequency band into a number of separate subbands.
channel reliability 1. The proportion of time, usually expressed as a percentage, that a communications channel is useful for its intended purpose.
2. The relative ease with which communications
can be carried out over a particular channel.
channel reversal In stereo reproduction, interchanging the left and right channels.
channel-reversing switch In a stereo system, a
switch that allows channel reversal without the
need for reorienting speaker cables or connectors.
channel sampling rate The rate at which individual channels are sampled. For example, in the
electronic switching of an oscilloscope, the number of times per second each input-signal channel is switched to the instrument.
channel selector A switch or relay used to put any
of a series of channels into functional status in a
channel separation 1. The spacing between communications channels, expressed in kilohertz. 2.
In stereo reproduction, the degree to which the
information on one channel is separate from the
other; usually expressed in decibels.
channel separation, 1.
channel slot On a carrier modulated by numerous
signals, the position or frequency of a specific
modulating signal.
channel shift The interchange of communications
channels (e.g., the shift from a calling frequency
to a working frequency).
channel strip A fixed-channel amplifier for a television receiver.
channel time slot In a frame of transmitted information, such as a television picture, a time interval designated to a channel for the transmission
of a character signal or other information.
channel-to-channel connection A device, such as
a channel adapter, used to transfer data rapidly
between any two channels of two digital computers, at the data speed of the slower channel.
channel-utilization index An indication of the extent to which channel capacity is used. For a
given channel, the index is the ratio of information rate to channel capacity, each expressed in
units per second.
channel wave An acoustic wave that travels
within a region or layer of a substance because of
a physical difference between that layer and the
surrounding material. An example of a channel
wave is the propagation of sound over a still lake.
channel width In a frequency channel, the difference f2 – f1, where f1 is the lower-frequency limit
and f2 is the upper-frequency limit of the channel.
chapter A self-contained computer program section.
character 1. One of the symbols in a code. 2. In
computer operations, a digit, letter, or symbol
used alone or in some combination to express information, data, or instructions.
character code In a communications or computer
system, the combination of elements (e.g., bits)
representing characters.
character crowding A reduction of the time interval between successive characters—especially
those read from tape.
character density The number of characters that
can be stored in a given length or surface area of
character density • charge carrier
a medium. On a magnetic tape, it might be specified in characters per millimeter; on a magnetic
disk, it might be specified in characters per
square millimeter.
character emitter A coded-pulse generator in a
digital computer.
character generator A device that converts coded
information into readable alphanumeric characters.
characteristic 1. A quantity that characterizes
(typifies) the operation of a device or circuit. Examples are emitter current, output power, and
frequency deviation. 2. In floating point notation,
the exponent.
characteristic curve A curve showing the relationship between an independent variable and a dependent variable, with respect to the parameter(s)
for a device or circuit. Example: the collector voltage-collector current characteristic curve of a
characteristic distortion 1. In a digital signal,
pulse distortion caused by the effects of the previous pulse or pulses. 2. Distortion in the characteristic curve of a component or device.
characteristic frequency The frequency peculiar
to a given channel, service, or response.
characteristic impedance Symbol, Z0. 1. Theoretically, the impedance that would be simulated
by a given two-conductor or coaxial line of uniform construction, if that line were of infinite
length. This value is determined by the materials
used for the two conductors, the dielectric used
to insulate the two conductors, the diameters of
the conductors, and the spacing between them.
2. In practice, for a transmission line or waveguide terminated with a load that produces no
standing waves on the line, the ratio of radio-frequency (RF) voltage to RF current. This ratio is
the same at all points along the length of a perfectly matched line, and depends on the physical
construction of the line. Coaxial lines typically
have Z0 between 50 and 100 ohms. Twinlead is
available with 75-ohm and 300-ohm Z0 values.
Open-wire line has Z0 between 300 and 600
ohms, depending on the spacing between the
conductors, and also on the type of dielectric (insulating material) employed to keep the spacing
constant between the conductors. 3. Experimentally, the value of impedance that, if it terminates
a transmission line or waveguide, results in no
reflected power from the load end of line. This is
always a pure resistance; that is, it contains no
characteristic overflow In floating-point arithmetic, the condition that occurs when a characteristic exceeds the upper limit specified by a
program or computer.
characteristic spread The range of values over
which a characteristic extends. For example, if an
amplifier’s output ranges from 15 W to 25 W, its
characteristic spread is 10 W.
characteristic underflow In floating-point arithmetic, the condition that occurs when a characteristic exceeds the lower limit specified by a
program or computer.
character modifier In address modification, a
constant (compare VARIABLE) that refers to a
specific character’s location in memory.
character-oriented A computer in which character locations, rather than words, can be addressed.
character printer A computer output device that
prints matter in the manner of a conventional
character reader Also called an optical scanner. In
a digital computer, an input device that can read
printing and script directly.
character recognition The reading of a written or
printed character by a computer, including its
identification and encoding.
character sensing The detection of characters by
a computer input device. This can be done galvanically, electrostatically, magnetically, or optically.
character set The set of characters in a complete
language, or in a communications system.
character signal The set of elements or bits representing a character in a digital transmission system. The signal can also represent the quantizing
value of a sample.
characters per minute An expression of the speed
of transmission of a digital signal. The number of
characters (on average) transmitted in a period of
one minute. In Morse code (CW) transmission,
this is generally taken as the number of times the
word paris plus the subsequent space, multiplied
by six (five letters and one space following), can
be sent in one minute.
characters per second An expression of the speed
of transmission of a digital signal. The number of
characters (on average) transmitted in a period of
one second.
character string A one-dimensional character array [i.e., a list of characters that, when printed or
displayed, would appear in a row or column, but
not both (as in a matrix)].
character subset A classification of characters
within a set.
Charactron A cathode-ray readout tube that displays letters, numbers, and symbols on its
screen. More commonly called a monitor.
charcoal tube In a system for producing a high
vacuum, a trap containing activated charcoal,
which is heated to dull red, then cooled by liquid
air to absorb gases.
charge 1. A quantity of electricity associated with a
space, particle, or body. 2. To electrify a space,
particle, or body (i.e., to give an electric charge).
3. To store electricity, as in a storage battery or
capacitor. Compare DISCHARGE.
charge carrier 1. An ELECTRON whose movement
constitutes a flow of electric current. 2. An elec-
charge carrier • checking program
tron deficiency (HOLE) whose movement constitutes a flow of electric current. 3. Any particle,
such as a charged atom (ION), PROTON, ALPHA
PARTICLE, or BETA PARTICLE, whose movement
constitutes a flow of electric current.
charge-coupled device Abbreviation, CCD. A
form of analog-to-digital converter that generates
a digital signal output representing an analog
image input. The transfer of stored charges provides the method of operation. Used in machine
vision systems and in numerous scientific applications.
charge density The degree of charge or currentcarrier concentration in a region.
charged particle 1. See CHARGE CARRIER. 2. See
charged voltage 1. The voltage across a fully
charged capacitor. 2. The terminal voltage of a
fully charged storage cell.
charge holding See CHARGE RETENTION.
charge of electron The negative electric charge
carried by a single electron. Approximately equal
to 1.602 × 10–19 coulombs.
charger 1. See BATTERY CHARGER. 2. Any device
or circuit that charges a capacitor.
charge retention 1. The holding of an electric
charge by a cell or battery when no current is being drawn from it. 2. A measure of the ability of a
cell or battery to maintain an electric charge
when no current is drawn from it. Often specified
in terms of shelf life. 3. The holding of a charge by
a capacitor.
charge-storage tube A cathode-ray tube that holds
a display of information on its screen until the operator removes it by pressing an erase button.
charge-to-mass The ratio of the electric charge to
the mass of a subatomic particle.
charge-to-mass ratio of electron The ratio of the
charge (e) of the electron to the mass (me) of the
electron, in coulombs per kilogram (C/kg). For an
electron at rest, e/me is approximately equal to
1.602 × 10–19 C divided by 9.11 × 10–31 kg = 1.76
× 1011 C/kg.
charge transfer 1. The switching of an electric
charge from one capacitor to another. 2. The capture of an electron by a positive ion from a neutral
atom of the same kind, resulting in the ion becoming a neutral atom, and the previously neutral atom becoming a positive ion.
charge transfer device A semiconductor in which
an electric charge is moved from location to location. Applications include delay lines, video signal
processing, and signal storage.
charging 1. The process of storing electrical energy
in a capacitor. 2. The process of storing electrochemical energy in a storage cell or battery.
charging current 1. The current flowing into a capacitor. 2. The current flowing into a previously
discharged storage cell.
charging rate 1. The rate at which charging current flows into a storage cell or battery, expressed
in amperes or milliamperes. For most cells and
batteries, the rate is greatest initially, when the
cell or battery is depleted or nearly depleted; the
rate decreases as the cell or battery becomes
charged. 2. The instantaneous rate at which
charging current flows into a capacitor or capacitance-resistance circuit, expressed in amperes,
milliamperes, or microamperes.
charged voltage 1. The voltage across a fully
charged capacitor. 2. The terminal voltage of a
fully charged storage cell.
Charlie Phonetic alphabet code word for the letter C.
chassis A (usually metal) foundation on which
components are mounted and wired.
chassis ground A ground connection made to the
metal chassis on which the components of a circuit are mounted. When several ground connections are made to a single point on the chassis, a
chatter 1. A rapidly repetitive signal, caused by interruption or variation of a current (usually interference). 2. Extraneous vibration, as of the
armature in a relay.
chatter time The interval between the instant that
contacts close (for example, in a relay) and the instant at which chatter ends.
cheater cord An extension cord used to conduct
power to a piece of equipment (especially a television receiver) by temporarily bypassing the safety
switch or interlock. Use of such a cord presents a
potentially fatal shock hazard to personnel using,
or working on, the equipment.
Chebyshev filter Also spelled Tschebyscheff or
Tschebysheff. A form of inductance-capacitance
(LC) lowpass, highpass, bandpass, or bandrejection filter, characterized by an attenuationversus-frequency curve with ripple in the
check 1. A test generally made to verify condition,
performance, state, or calculations; specifically, in
computer operations, it applies to operands or results. 2. The usually abrupt halting of an action.
check bit A binary CHECK DIGIT.
check character In a group of characters, one
whose value depends on the other characters,
which it checks when the group is stored or
check digit Also called check number. In computer
operations, a number added to a group of digits,
forming a code that identifies entities in the system (including personnel) and can be used for
verification. The check digit is the remainder
when the number code (for example, 459) is divided by a fixed number (for example, 5); in this
case, the check digit (the remainder of 459/5) is
4, and the amended code number is 4594.
check indicator An indication, made via a video
display, that something has been shown to be invalid according to a check.
checking program Also called checking routine.
For debugging purposes, a diagnostic computer
checking program • chirp
program capable of detecting errors in another
checkout A test routine that ascertains whether or
not a circuit or system is functioning according to
checkout routine A routine used by programmers
to debug programs.
checkpoint A point in a digital-computer program
at which sufficient information has been stored to
allow restarting the computation from that point.
checkpoint dump The process of recording details
of a computer program run. This process might
be necessary in the event of a system failure that
requires reconstruction of a program or programs.
checkpointing The writing of a computer program
in such a manner that, during a program run, information is frequently dumped as insurance
against possible loss in the event of a system failure.
check problem A presolved problem used to check
the operation of a digital computer or program.
check register In some digital computers, a register in which transferred information is stored so
that it can be checked against the same information as it is received a second time.
check routine A special program designed to ascertain if a program or computer is operating correctly. Also see CHECK PROBLEM.
checksum Used as part of a summation check, a
sum derived from the digits of a number. For example, the checksum of 23,335 is 16. Also called
check symbol For a specific data item, a digit or
digits obtained by performing an arithmetic
check on the item, which it then accompanies
through processing stages for the purpose of
checking it.
check total See CONTROL TOTAL.
check word A check symbol in the form of a word
added to, and containing data from, a block of
chelate Pertaining to cyclic molecular structure in
which several atoms in a ring hold a central
metallic ion in a COORDINATION COMPLEX.
chemical deposition The coating of a surface with
a substance resulting from chemical reduction of
a solution. In mirror making, for example,
formaldehyde reduces a solution of silver nitrate,
and deposits metallic silver on the surface of polished glass. Also see CHEMICALLY DEPOSITED
chemical detector See ELECTROLYTIC DETECTOR.
chemical effect An alteration in the chemical
makeup of a substance or solution, resulting
from the passage of an electric current through it.
Examples include electrolysis, electroplating, and
the reduction of ores.
chemical energy Energy that is stored in the
chemical bonds of a material or solution. An ex-
ample is the stored energy in terms of watt hours
in an electrolytic cell.
chemical load An arrangement of a chemical material or device for the passage of electricity
through it. Examples: electroplater, electrolytic
cell for the production of hydrogen gas, and storage battery.
chemically deposited printed circuit A printed
circuit in which the pattern of metal lines and areas are chemically deposited on a substrate.
chemically pure Abbreviation, CP. Free from impurities.
chemical rectifier See ELECTROLYTIC CELL.
chemical reduction The process of making a
chemical compound (usually in solution) into a
metal, by removing the nonmetallic component
from the compound. For example, when copper
oxide is heated in the presence of hydrogen (a reducting agent), the oxygen (the nonmetallic component) is driven out, and copper (along with
some water) remains.
chemical resistor See ELECTROLYTIC RESISTOR.
switch See
CHIL Abbreviation for current-hogging injection
logic. A form of bipolar digital logic technology.
chip 1. An INTEGRATED CIRCUIT. 2. A small slab,
wafer, or die of dielectric or semiconductor material, on which a subminiature component or circuit is formed or deposited.
chip capacitor A subminiature capacitor formed
on a chip.
chip resistor A subminiature resistor formed on a
chip tray A chad receptacle located at a card or paper tape punching site.
Chireix-Mesny antenna A high-frequency (HF)
beam antenna, in which each dipole section constitutes one side of a diamond. Cophased horizontal and vertical components of current flow in
each of the diagonals, and radiation is broadside
to the plane of the driven element.
Chireix-Mesny antenna
chirp A rapid change in the frequency of a continuous-wave Morse-code signal. The chirp usually
occurs at the beginning of each dot or dash, and
chirp • chopper power supply
can go up or down in frequency. Chirp occurs because of a change in the output impedance of an
oscillator as it is keyed. Modern code transmitters
do not exhibit significant chirp.
chirp modulation A form of modulation in which
the frequency of a signal is deliberately changed
in a systematic way. Used in some radar systems.
chirp radar A radar system that uses CHIRP MODULATION.
Chladni’s plates Conducting plates that are used
to evaluate the nature of a vibration in a solid material. The plates are clamped to the material, and
sand is sprinkled on the surface. This produces
patterns that indicate the nature of the vibrations.
chlorinated diphenyl A synthetic organic substance used as an impregnant in some oil-filled
chlorinated naphthalene See HALOWAX.
chlorine Symbol, Cl. A gaseous element of the
halogen family. Atomic number, 17. Atomic
weight, 35.453.
choke 1. To restrict or curtail passage of a particular current or frequency by means of a discrete
component, such as a choke coil. 2. See CHOKE
choke air gap A fractional-inch opening in the iron
core of a filter choke, usually filled with wood or
plastic. The gap prevents saturation of the core
when the choke coil carries maximum rated direct current.
choke coil 1. A large-value inductor that provides
a high impedance to alternating current (ac),
while offering virtually no opposition to direct
current (dc). 2. In radio-frequency (RF) applications, an inductor that provides a high
impedance to RF signals while showing low
impedance for audio-frequency (AF) signals and
direct currents (dc).
modulation An
amplitudemodulation (AM) scheme, in which the modulator
is coupled to the radio-frequency (RF) amplifier
through a shared iron-core choke coil.
choke flange At the end of a waveguide, a flange in
which a groove forms a CHOKE JOINT.
choke-input filter A filter whose input component
is an inductor (choke). The choke-input powersupply filter is distinguished by its superior
choke joint A joint connecting two waveguide sections and permitting efficient energy transfer
without requiring electrical contact with the inside wall of the waveguide.
chopped dc See INTERRUPTED DC.
chopped mode In a single-gun cathode-ray-tube
(CRT) oscilloscope, a technique for sequentially
displaying several signals that are not referenced
to the oscilloscope sweep.
chopped signal An ac or dc signal that is periodically interrupted, as by means of a CHOPPER.
dc input
dc output
choke-input filter
chopper A device or circuit that interrupts a direct
current (dc) at some predetermined rate. Ideally,
such a device is characterized by distinct on and
off operation.
chopper amplifier A circuit that amplifies the output of a CHOPPER. Used in conjunction with a
CHOPPER CONVERTER in dc amplification.
chopper converter A device that interrupts a direct current (dc), and changes it to a pulsating,
rectangular-wave current or voltage that can be
handled by a stable ac amplifier and rectified to
supply amplified dc.
chopper power supply Also called power inverter.
A circuit that delivers high-voltage ac from a dc
source. The input is typically 12 volts dc, and the
output is usually 117 volts rms ac. These devices
facilitate the use of small appliances such as
computers, television sets, and communications
radios in portable and mobile environments. The
output of a low-cost power inverter is generally
not a good sine wave. More sophisticated inverters produce good sine waves and have a frequency close to 60 Hz.
chopper stabilization • chrominance modulator
chopper stabilization 1. Stabilization of directcurrent (dc) amplification by using a CHOPPER
CONVERTER ahead of a stable ac amplifier, and
rectifying the amplifier output. 2. In a regulated
power supply, use of a CHOPPER AMPLIFIER at
the control-circuit input to improve regulation.
chopper-stabilized amplifier See CHOPPER AMPLIFIER and CHOPPER STABILIZATION, 1.
chopper transistor A transistor that provides
rapid and repeated on/off switching of direct current (dc), in the manner of an electromechanical
interrupter. See CHOPPER.
chopping frequency The frequency at which a
chopper interrupts a signal.
chord 1. A harmonious mixture of musical tones of
various frequencies. 2. A straight line that joins
two points on a curve (such as an arc of a circle).
3. The width of an airfoil.
chord organ An electronic organ that will sound a
musical chord when a key is pressed (see
CHORD, 1).
choreographer program A computer program
similar to one originally written by Charles Lecht
of Lecht Sciences, Inc. The computer operator
gives commands that cause a human form, portrayed on the display screen, to make various
movements. Used in animated computer graphics.
chorus Signals at very low radio frequencies
(VLF), natural in origin, that sweep upward in
frequency. Believed to result from lightninggenerated electromagnetic fields that circulate in
the magnetosphere (earth’s magnetic field). The
term is derived from the sound the signals make
in high-gain audio-frequency (AF) amplifiers connected directly to VLF receiving antennas.
Christiansen antenna A radio-telescope antenna
for obtaining high resolution. Two straight arrays
are placed at an angle, intersecting approximately at their centers. The resulting interference
pattern has extremely narrow lobes.
Christmas tree A tree-like pattern on the screen of
a television receiver, caused by loss of horizontal
chroma The quality of a color: hue and saturation.
chroma circuit In color television, one of several
circuits whose ultimate purpose is to produce a
color component on the screen.
chroma-clear raster In color television reception,
the clear raster resulting from a white video signal, or from operation of the chroma circuits of
the receiver (as if they were receiving a white
transmission). Also called white raster.
chroma control In a color television receiver, a
rheostat or potentiometer that permits adjustment of color saturation through variation of the
chrominance-signal amplitude before demodulation.
chromatic fidelity See COLOR FIDELITY.
chromaticity 1. The state of being chromatic (see
CHROMA). 2. A quantitative assessment of a
color in terms of dominant or complementary
wavelength and purity.
chromaticity coordinate For a color sample, the
ratio of any one of the three tristimulus values
(primary colors) to the sum of the three.
chromaticity diagram A rectangular-coordinate
graph in which one of the three CHROMATICITY
COORDINATES of a three-color system is plotted
against another coordinate.
chromaticity flicker Flicker caused entirely by
chromaticity fluctuation (see CHROMATICITY, 2).
chromel A nickel-chromium alloy with some iron
content, used in thermocouples.
chromel-alumel junction A thermocouple that
uses wires of the alloys chromel and alumel.
chromel-constantan thermocouple A thermocouple consisting of a junction between wires or
strips of chromel and constantan. Typical output
is 6.3 mV at 100°C.
chrome plating The process of coating a metal
with chromium. Generally protects against corrosion.
chrome recording tape Also called chrome tape or
chromium tape. Tape that is manufactured from
the compound chromium dioxide. Noted for its
ability to faithfully record and reproduce music.
chrominance In color television, the difference between a reproduced color and a standard reference color of the same luminous intensity.
chrominance amplifier In a color television circuit, the amplifier separating the chrominance
signal from the total video signal.
chrominance cancellation On a black-and-white
picture tube screen, cancellation of the fluctuations in brightness caused by a chrominance signal.
chrominance-carrier reference In color television, a continuous signal at the frequency of the
chrominance subcarrier; it is in fixed phase
with the color burst and provides modulation
or demodulation phase reference for carrierchrominance signals.
chrominance channel In color television, a circuit
devoted exclusively to the color function, as opposed to audio and general control channels.
chrominance component In the NTSC color television systems, either of the components (I-signal
or Q-signal) of the complete chrominance signal.
chrominance demodulator In a color television
receiver, a demodulator that extracts videofrequency chrominance components from the
chrominance signal, and a sine wave from the
chrominance subcarrier oscillator.
chrominance gain control A rheostat or potentiometer in the red, green, and blue matrix channels of a color television receiver, used to adjust
the primary-signal amplitudes.
chrominance modulator In a color television
transmitter, a device that generates the chrominance signal from the I and Q components and
the chrominance subcarrier.
chrominance primary • circuit diagram
chrominance primary One of the transmission
primaries (red, green, and blue) upon which the
chrominance of a color depends.
chrominance signal The signal component in
color television that represents the hues and saturation levels of the colors in the picture.
chrominance subcarrier In color television, the
3579.545-kHz signal that serves as a carrier for
the I- and Q-signals.
chrominance-subcarrier oscillator In a color television receiver, a crystal-controlled oscillator that
generates the subcarrier signal (see CHROMINANCE SUBCARRIER).
chrominance video signals Output signals from
the red, green, and blue channels of a color television camera or receiver matrix.
chromium Symbol, Cr. A metallic element. Atomic
number, 24. Atomic weight, 51.996. Commonly
used as a plating for metals to improve resistance
to corrosion.
chronistor An elapsed-time indicator in which
current, flowing during a given time interval,
electroplates an electrode. The duration of the
interval is determined from the amount of deposit.
chronograph 1. An instrument that provides an
accurate time base along the horizontal axis of its
permanent record. 2. Stopwatch.
chronometer A precision clock. Electronic chronometers often use a highly accurate and stable
crystal oscillator, followed by a string of multivibrators to reduce the crystal frequency to an audio frequency (such as 1 kHz) that drives the
clock motor.
chronoscope An instrument for precisely measuring small time intervals.
CHU Call letters of the Canadian time-signal station whose primary frequency is 7.335 MHz.
CIE Abbreviation for International Commission on
cinching In a reel of magnetic tape, the slipping of
tape as force is applied.
cinematograph See KINEMATOGRAPH.
cipher A code used for the purpose of preventing
interception of a message by third parties.
circ 1. Abbreviation of circuit. 2. Abbreviation of
circle graph Also called a pie graph. A representational device consisting of a disk subdivided
into various triangular areas (radiating from the
center of the circle), which are proportional to
represented quantities.
circle of confusion A circular image of a point
source of light, resulting from an aberration in an
optical system.
circle of declination The graduated circular scale
of a declinometer.
circlotron amplifier A high-powered microwave
amplifier of the one-port, cross-field, nonlinear
type using a magnetron.
circuit 1. A closed path through which current
flows from a generator, through various components, and back to the generator. (An electronic
circuit is often a combination of interconnected
subcircuits.) 2. The wiring diagram of an electronic device or system.
circuit analysis The careful determination of the
nature and behavior of a circuit and its various
parts. It can be theoretical, practical, or both.
circuit analyzer See CIRCUIT TESTER.
circuit board A panel, plate, or card on which electronic components are mounted and interconnected to provide a functional unit.
circuit breaker A resettable fuse-like device that is
designed to protect a circuit against overloading.
In a typical circuit breaker, the winding of an
electromagnet is connected in series with the load
circuit and with the switch contact points. Excessive current through the magnet winding causes
the switch to be opened.
Load circuit
in series with coil
Power supply
circuit breaker
capacitance The
(lumped, distributed, and stray) present in a circuit.
circuit capacity 1. The ability of a circuit to handle a quantity (such as current, voltage, frequency, power, etc.) safely and efficiently. 2. The
maximum value of some parameter at which a
circuit can function safely and efficiently (e.g., a
circuit capacity of 50 A). 3. The number of channels that can be accommodated simultaneously
by a circuit.
circuit component 1. Any of the electronic devices
or parts (capacitors, resistors, transistors, etc.)
that are connected through wiring to form a circuit. 2. An electrical quantity required for, or
arising from, circuit operation. Examples: input
voltage, feedback current, stray capacitance, and
circuit noise.
circuit diagram A drawing in which symbols and
lines represent the components and wiring of
an electronic circuit. Also called CIRCUIT
circuit diagram • circular magnetic wave
connection is maintained even during periods of
silence (no data transmitted by either subscriber). Compare PACKET SWITCHING.
circuit synthesis The development of a circuit under the guidance of theoretical or practical knowledge of basic electronics principles and
component parameters. Compare CIRCUIT
circuit tester An instrument for checking the performance of electronic circuits. Often consists of
a specialized continuity tester, but occasionally it
includes a dynamic performance tester.
circuit tracking The alignment and/or pretuning
of circuits for identical or optimum response. It
applies especially to cascaded circuits, whose
variable elements, such as tuned inductancecapacitance (LC) networks, must follow each
other in step when ganged together.
circular angle The angle described by a radius vector as it rotates counterclockwise around a circle.
circular antenna A half-wave horizontally polarized antenna, whose driven element is a rigid
conductor bent into a circle with a break opposite
the feed point. Also called halo antenna. Used primarily at very-high frequencies (VHF).
circular electric wave An electromagnetic wave
with circular electric lines of flux. An example is
the field in the immediate vicinity of a CIRCULAR
circuit dropout A momentary interruption of circuit operation, often caused by a break in the circuit.
circuit efficiency A quantitative measure of the
effectiveness of circuit operation, customarily expressed as the ratio of the useful output power to
the total input power.
circuit element See CIRCUIT COMPONENT, 1.
circuit engineer An electronics engineer who specializes in circuit analysis, circuit synthesis, or
circuit fault 1. Malfunction of a circuit. 2. An error
in circuit wiring.
circuit hole A perforation within the conductive
area of a printed-circuit board, for the insertion
and connection of a pigtail, terminal, etc., or for
connecting the conductors on one side of the
board with those on the other.
circuit loading Intentionally or unintentionally
drawing power from a circuit.
circuit noise 1. Electrical noise generated by a circuit in the absence of an applied signal. 2. In wire
telephony, electrical noise as opposed to acoustic
circuit noise level The ratio of circuit-noise amplitude to reference-noise amplitude, expressed in
decibels above the reference amplitude.
circuit-noise meter A meter that measures the intensity of the noise generated within a circuit.
circuit parameter See CIRCUIT COMPONENT, 2.
circuit protection Automatic safeguarding of a
circuit from damage from overload, excessive
drive, heat, vibration, etc. Protection is afforded
by various devices and subcircuits, ranging from
the common fuse to sophisticated limiters and
circuit reliability A quantitative indication of the
ability of a circuit to provide dependable operation as specified. See MEAN TIME BEFORE FAILURE and MEAN TIME BETWEEN FAILURES.
circuitry 1. Collectively, electronic and electrical
circuits. 2. A detailed plan of a circuit and its
subcircuits. 3. Collectively, the components of a
circuit schematic See CIRCUIT DIAGRAM.
circuit simplification 1. In circuit analysis, the
reduction of a complex circuit to its simplest representation to minimize labor and to promote
clarity. Thus, through application of Kirchhoff’s
laws, a complicated circuit could theoretically be
reduced to a single generator in series with a single impedance. 2. In circuit synthesis, the arrangement of a circuit so as to provide desired
performance with the fewest components and
least-complex wiring.
circuit switching In telephony, a method of connection in which a single circuit is maintained between two subscribers for the entire duration of
the call. The signal path does not change. The
Electric lines
of flux
carrying ac
circular electric wave
circular functions Trigonometric functions of the
angle described by a vector rotating counterclockwise around a circle. Also see COSINE,
circular magnet See RING MAGNET.
circular magnetic wave An electromagnetic wave
in which the magnetic lines of flux are circular.
An example is the field in the immediate vicinity
of a straight-conductor antenna.
circular mil • class-A amplifier
Magnetic lines
of flux
carrying ac
circular magnetic wave
circular mil A unit of cross-sectional area equivalent to 0.785 millionths of a square inch, or the
area of a circle having a diameter of 0.001 inch.
Generally, the circular mil is used to specify the
cross-sectional area of a conductor, such as wire.
circular mil foot A unit of volume in which the
length is 1 foot and the cross-sectional area is 1
circular mil.
circular polarization A form of electromagneticwave polarization in which the orientation of the
electric flux rotates continuously and uniformly
as the wave propagates through space. Circular
polarization can occur in either a clockwise or
counterclockwise sense.
circular radian The angle enclosed by two radii of
a unit circle and subtended by a unit arc. Equal
to about 57.296 angular degrees.
circular scan A radar scan in which the electronbeam spot describes a circle centered around the
transmitting antenna.
circular sweep In an oscilloscope, a sweep obtained when the horizontal and vertical sinusoidal deflecting voltages have the same
amplitude and frequency, but are out of phase by
90 degrees (1 ⁄4 cycle).
circular trace An oscilloscope pattern consisting
of a circle obtained with a circular sweep of the
electron beam.
circular waveguide A waveguide with a circular
cross section.
circulating register In a digital computer, a register in which digits are taken from locations at one
end and returned to those at the other end.
circulating tank current The alternating current
that oscillates between the capacitor and inductor within a tank circuit.
circulator A multi-terminal coupler in which microwave energy is transmitted in a particular direction from one terminal to the next.
circumvention In a security or alarm system, the
evasion of detection. Can be done by physically
avoiding regions of coverage, or by defeating the
system electronically.
cis A prefix meaning “on this side of.” For example,
the cislunar field is the field on this side of the
Citizen Band Abbreviation, CB. A band of radio
frequencies allocated for two-way communication
between private citizens (apart from amateur and
commercial services).
Citizens Radio Service Two-way radio communication in a CITIZEN BAND. In the United States,
the FCC licenses users of this service without requiring them to take an examination.
C/kg Abbreviation of coulombs per kilogram, the
unit for electron charge-to-mass ratio.
C/kmol Abbreviation of coulombs per kilomole, the
unit for the Faraday constant.
ckt Abbreviation of CIRCUIT.
Cl Symbol for CHLORINE.
cl Abbreviation of CENTILITER.
cladding The bonding of one metal to another to
minimize or prevent corrosion. A common example is copper-clad steel wire, ideal for use in
radio-frequency antenna systems. The copper
provides excellent conduction, and the steel provides high tensile strength with a minimum of
wire stretching.
clamper A device that restricts a wave to a predetermined dc level. Also called DC RESTORER.
clamping 1. Fixing the operation of a device at a
definite dc level. Also see CLAMPER. 2. In television, establishing a fixed level for the picture signal at the start of each scanning line.
clamping circuit See CLAMPER.
clamping diode A diode used to fix the voltage
level of a signal at a particular reference point.
clapper In a bell, the ball or hammer that strikes
the bell; in an electric bell, it is affixed to the vibrating armature.
Clapp-Gouriet oscillator A Colpitts oscillator in
which a capacitor is connected in series with the
inductor. The circuit offers high frequency stability in the presence of input and output capacitance variations.
Clapp oscillator A series-tuned hybrid Colpitts oscillator, having a tuning capacitor in series with
the inductor, rather than in parallel with the inductor. The circuit allows the use of a smaller
tuning capacitor, resulting in improved stability.
class-A amplifier An amplifier whose bias is set at
approximately the midpoint of the characteristic
curve. Output electrode current flows during the
class-A amplifier • click method
Clapp oscillator
complete ac driving-voltage cycle. The input signal never drives the device into the nonlinear portion of the characteristic curve.
class-AB amplifier Either a CLASS-AB1 AMPLIFIER or a CLASS-AB2 AMPLIFIER.
class-AB1 amplifier An amplifier whose bias is adjusted to a level between that of a class-A amplifier and that of a class-AB2 amplifier. Output
electrode current flows during the entire ac driving-voltage cycle. The input signal drives the
device into the nonlinear portion of the
characteristic curve during part of the cycle.
class-AB2 amplifier An amplifier whose bias is adjusted to a level between that of a class-AB1 amplifier and that of a class-B amplifier. Output
electrode current flows during more than 50 percent, but less than 100 percent, of the input signal cycle.
class-AB modulator A modulator whose output
stage is a class-AB1 or class-AB2 amplifier.
class-A modulator A circuit for obtaining amplitude-modulated signals; essentially a class-A amplifier with two inputs, one for the carrier and the
other for the modulating signal.
class-A operation The operation of a transistor,
field-effect transistor, or vacuum tube, in which
the collector, drain, or plate current flows during
the entire signal cycle.
class-B amplifier An amplifier whose bias is adjusted to operate at the cutoff point in the characteristic curve. Output current flows during
approximately 50 percent of the input signal cycle.
Efficiency is higher than that of a class-A amplifier.
class-B modulator A push-pull modulator whose
output stage is a class-B amplifier.
class-B operation The operation of a transistor,
field-effect transistor, or vacuum tube, in which
the collector, drain, or plate current flows for approximately half the signal cycle.
class-C amplifier An amplifier whose input-electrode bias is adjusted for operation at a point
considerably beyond cutoff. Output current flows
during less than half of the input signal cycle.
Such an amplifier requires comparatively high
driving power, but is capable of excellent efficiency. Commonly used in continuous-wave
(CW), amplitude-modulated (AM), and frequencymodulated (FM) radio transmitters.
class-C operation The operation of a transistor,
field-effect transistor, or vacuum tube, in which
the collector, drain, or plate current flows for significantly less than half the signal cycle.
class-D telephone A telephone restricted to use by
emergency services, such as fire departments
and guard alarm installations.
classical electron radius Abbreviated re. The
quantity expressed as e 2/(mec 2), where e is the
electron’s charge in electrostatic units, me is its
rest mass, and c is the speed of light. The value
re is equal to approximately 2.82 × 10–13 cm or
2.82 × 10–15 m.
clean room A room for the assembly or testing of
critical electronic equipment. The term is derived
from the extraordinary steps taken to remove
dust and other contaminating agents. The personnel wear carefully cleaned garments (or disposable clothing), gloves, caps, and masks; in
some situations, they are required to walk between ceiling and floor ducts of a vacuum system
upon entering the room.
cleanup process In the process of electron tube
evacuation, a technique used to remove residual
and occluded gases from the vacuum apparatus
and from the device being evacuated.
clear 1. In computer operations, to restore a
switching element (e.g., a flip-flop) or a memory
element to its standard (e.g., zero) state. 2. In
computer practice, an asynchronous input.
clearance The distance between two live terminals,
or between one live terminal and ground.
clear band In optical character recognition, the
part of a document that must remain unprinted.
clear channel 1. A channel in the standard amplitude-modulation (AM) broadcast band that is designated to only one station within the area covered
by the signal from that station. 2. In television
broadcasting, a channel for which there are no restrictions on the nature of the programming.
clear memory A function in a calculator or small
computer that erases the contents of the memory.
clear raster The raster on the screen of a television
picture tube in the absence of a signal, noise, or
faulty beam deflection.
cleavage In a crystalline substance, the quality of
splitting along definite planes. Also, a fragment
resulting from such a cleft.
click filter See KEY-CLICK FILTER.
click method An emergency technique for rendering an electric current audibly detectable, by
click method • closed-circuit security system
making and breaking the circuit carrying the current to a headset or earphone. A single click results from each make and each break. Also see
click suppressor See KEY-CLICK FILTER.
climate chamber A test chamber that provides accurately controlled temperature, humidity, and/or
barometric pressure, for evaluating the performance of electronic components and circuits. Also
climatometer An instrument incorporating a hygrometer and bimetallic thermometer, whose dial
pointers intersect to indicate comfort zones (best
temperature-to-humidity ratio).
clinometer An electromechanical device that measures the steepness of a slope. When the device is
level (horizontal), the output voltage is zero. If the
device is tipped in one direction, a negative voltage is produced; if it is tipped in the other direction, a positive voltage is produced. The output
voltage is proportional to the angle at which the
device is tipped. Used in mobile robots.
clip A pinch-type connector whose jaws are normally held closed by a spring.
clipped-noise modulation Modulation of a jamming signal through clipping action to increase
the sideband energy and resulting interference.
clipper A circuit whose output voltage is fixed at a
value for all input voltages higher than a predetermined value. Clippers can flat-top the positive,
negative, or both positive and negative peaks of
an input voltage.
clipper amplifier An amplifier operated so that the
positive, negative, or both positive and negative
peaks are clipped in the output signal. The clipping action results from feeding a regular symmetric waveform into an amplifier so that on
negative excursion extremes, the stage is cut off;
on positive excursion extremes, the amplifier is
driven into saturation.
clipper limiter A device that delivers an output signal whose amplitude range corresponds to inputsignal voltages between two predetermined limits.
It can be used as a noise limiter with an element or
elements that clip all pulses whose amplitudes are
greater than the signal being processed.
clipping 1. Leveling off (flat-topping) a signal peak
at a predetermined level. Also see CLIPPER. 2. In
audio practice, the loss of syllables or words because of cutoff periods in the operation of the circuit (usually caused by overdriving a stage).
clock In a digital computer or controller, the device
or circuit that supplies timing pulses to pace the
operation of the system.
clocked flip-flops A master-slave arrangement of
direct-coupled flip-flops. Information entered into
the master unit when the input-trigger pulse amplitude is high is transferred to the slave unit
when the amplitude is low.
clock frequency In a digital computer or control,
the reciprocal of the period of a single cycle, expressed in terms of the number of cycles occurring in one second of time (hertz, kilohertz, or
clock generator A test-signal generator that supplies a chain of pulses identical to those supplied
by the clock of a digital computer.
clock module A complete plug-in or wire-in digital
unit whose readout indicates time of day or
elapsed time. Connected to a suitable power supply, it serves as either a clock or timer.
clock pulse A time-base pulse supplied by the
clock of a digital computer, expressed as a period
whose reciprocal is frequency.
clock rate See CLOCK FREQUENCY.
clock track On a magnetic tape or disk for data
storage, a track containing read or write control
(clock) pulses.
clockwise Abbreviation, cw. Rotation in a righthand direction around a circle, starting at the
clockwise-polarized wave An elliptically polarized
electromagnetic wave whose electric-intensity
vector rotates clockwise, as observed from the
point of propagation. Compare COUNTERCLOCKWISE-POLARIZED WAVE.
clone A machine manufactured by a relatively unknown company that performs all the same functions, in basically the same way, as another
machine manufactured by a well-known, major
corporation. The term is used especially in reference to computers and computer peripherals. If a
device is compatible with a certain computer,
then clones of that device are generally compatible with that computer. Also, the device is likely
to be compatible with all clones of the computer.
close coupling Also called tight coupling. In a
transformer, the placement of the primary and
secondary coils as close together as possible for
maximum energy transfer. Compare LOOSE
closed capacitance The value of a variable capacitor whose rotor plates are completely meshed with
the stator plates. Compare OPEN CAPACITANCE.
closed circuit A continuous unbroken circuit (i.e.,
one in which current can flow without interruption). Compare OPEN CIRCUIT.
closed-circuit cell A primary cell, such as the
early gravity cell, designed for heavy and polarization-free service.
closed-circuit communication Communication
between units only within a defined, hard-wired
system, not extending to other units or systems.
closed-circuit security system An electronic security or alarm system, consisting of subsystems
closed-circuit security system • CMR
interconnected so that a disturbance anywhere in
the circuit will result in an alarm signal pinpointing the location of the disturbance.
closed-circuit signaling Signaling accomplished
by raising or lowering the level of a signaling current flowing continuously in a circuit.
closed-circuit television Abbreviation, CCTV. A
usually in-plant television system, in which a
transmitter feeds one or more receivers through a
closed core A magnetic core generally constructed
in an “O” or “D” configuration to confine the magnetic path to the core material. Compare OPEN
closed-core choke A choke coil wound on a
closed-core choke
closed-core transformer A transformer wound on
Laminated core
closed-core transformer
closed loop 1. The feedback path in a self-regulating control system. An oscillator, for example, is a
closed-loop amplifier. 2. A loop within a program
that would continue indefinitely, except for an external exit command.
closed-loop bandwidth The frequency at which
the gain of a closed-loop circuit (see CLOSED
LOOP, 1) drops 3 decibels from the direct-current
or midband value.
closed-loop control system A control system in
which self regulation is obtained by means of a
feedback path (see CLOSED LOOP). An example
is a voltage regulator, in which a rise in output
voltage is fed back to the input. This changes the
input voltage and reduces the output voltage to
its correct value. Compare OPEN-LOOP CONTROL SYSTEM.
closed-loop input impedance The input impedance of an amplifier that has feedback.
closed-loop output impedance The output impedance of an amplifier that has feedback.
closed-loop voltage gain The voltage gain of an
amplifier that has feedback.
closed magnetic circuit A magnetic circuit in
which the flux is uninterrupted, as in a ferromagnetic core, which has no air gap. Also see
closed subroutine In a digital computer program,
a subroutine that can be accessed and left by
branch instructions, such as GOSUB and RETURN in the high-level language BASIC.
close-spaced array A beam antenna in which the
elements (radiator, director, and reflector) are
spaced less than a quarter-wavelength apart.
close-talk microphone A microphone that must
be placed close to the mouth. Such a microphone
is less susceptible to background noises than an
ordinary microphone, and is useful in environments where the ambient noise level is high.
closing rating A specification for closure conditions in a relay, including duty cycle and contact
life (total guaranteed closures before contact
closure 1. The act of closing or being closed (e.g.,
switch closure or relay closure). 2. Circuit completion (i.e., the elimination of all discontinuities).
cloud The mass of electrons constituting the space
charge in a vacuum tube.
cloverleaf antenna An omnidirectional transmitting antenna in which numerous horizontal,
four-element radiators (stacked vertically, a quarter-wavelength apart) are arranged in the shape
of a four-leaf clover.
C/L ratio See LC RATIO.
clutter Extraneous echoes that interfere with the
image on a radar display.
clutter gating In radar operations, a switching
process that causes the normal video to be displayed in regions free of clutter, and the video indicating target movement to be displayed only in
cluttered areas.
Cm Symbol for CURIUM.
cm Abbreviation of CENTIMETER.
c.m. Abbreviation of CIRCULAR MIL.
cm2 Abbreviation of square centimeter.
cm3 Abbreviation of cubic centimeter.
Cmax Abbreviation of maximum capacitance.
Cmin Abbreviation of minimum capacitance.
CMRR • coaxial capacitor
C network A circuit with three impedances connected in series, the free leads being connected to
a pair of terminals and the two internal junctions,
to another pair of terminals.
Co Symbol for COBALT.
coalesce In computer operations, to create one file
from several.
coarse adjustment Adjustment of a quantity in
large increments. Compare FINE ADJUSTMENT.
coarse-chrominance primary See Q SIGNAL.
coastal bending A change in the horizontal direction of a line-of-sight radio wave when it crosses a
coast station In the Maritime Mobile Radio Service, a land station that communicates with shipboard stations.
coating 1. The application of a substance to another substance by means of electroplating, electrophoresis, or similar process, for the purpose of
protecting the material, isolating it from the environment, or improving the conductivity of an
electrical connection to some other object. 2. The
magnetic material on a recording tape. 3. In a
computer system, the magnetic material on a
magnetic diskette or hard disk.
coating thickness On magnetic tape or magnetic
disks, the depth of the magnetic coating applied
to the base.
coax Abbreviation of COAXIAL CABLE or COAXIAL
coaxial antenna A half-wave vertical antenna that
is center-fed by coaxial cable. The cable runs upward through a 1⁄4-wave section of tubing that
composes the lower half of the antenna. The
outer conductor of the cable is connected to this
tubing through a shorting disk at the top. The inner conductor of the cable is connected to a 1 ⁄4-
wave vertical radiator that is insulated from, and
that extends upward from the top of, the lower
coaxial cable An unbalanced cable consisting of
two concentric conductors: an inner wire and an
outer, braided sleeve. The inner and outer conductors are separated by a dielectric, usually
solid or foamed polyethylene. The outer conductor is generally grounded while the inner conductor carries the signals. This cable is used in
community-antenna television (CATV) networks,
and as a transmission line connecting antennas
to radio transmitters, receivers, and transceivers
at low, medium, high, and very-high frequencies.
It is also used in some high-fidelity sound systems—especially to connect microphones, compact-disc players, tape players, tuners, and
speakers to audio amplifiers.
coaxial cable
(From left to right: insulating jacket,
woven outer conductor, low-loss insulating
sleeve, inner conductor.)
Characteristics of
prefabricated coaxial transmission lines.
impedance, Velocity
hard line
hard line
dia. (in.)
per foot
coaxial capacitor 1. A somewhat uncommon, but
highly effective, capacitor that uses two telescoping sections of tubing. It works because there is a
certain effective surface area between the inner
and the outer tubing sections. A sleeve of plastic
dielectric is placed between the sections of tubing. This allows the capacitance to be adjusted by
sliding the inner section in or out of the outer section. Coaxial capacitors are especially useful in
antenna systems for tuning and/or impedance
matching. Their values are generally from a few
coaxial capacitor • code
picofarads up to about 100 pF. 2. A short length
of coaxial cable that is used as a capacitor rather
than a transmission line because of the inherent
capacitance between its center conductor and
coaxial cavity A cavity consisting of a cylindrical
metal chamber housing a central rod. The cavity
can be tuned to resonance by means of a piston.
coaxial connector A device used to splice coaxial
line or to connect a coaxial line to a transmitter,
receiver, or other piece of apparatus.
coaxial connector
coaxial diode A semiconductor diode housed in a
cylindrical metal shell acting as one contact, and
provided with a recessed, concentrically mounted
end pin, which serves as the other contact.
coaxial driver See COAXIAL SPEAKER.
coaxial filter 1. A filter that uses a coaxial cable as
a tuned circuit. 2. A filter designed to be used in
a coaxial transmission line.
coaxial jack A female receptacle or connector,
whose concentric terminals have the same spacing as a male coaxial-cable connector designed to
fit it.
coaxial line A signal transmission line consisting
coaxial-line frequency meter A microwave absorption wavemeter (see WAVEMETER) with input and output receptacles for insertion into a
coaxial line.
coaxial-line oscillator See CONCENTRIC-LINE
coaxial loudspeaker See COAXIAL SPEAKER.
coaxial plug A male connector whose concentric
terminals have the same spacing as a female
coaxial cable connector designed to fit it.
coaxial receptacle A coaxial connector, such as a
coaxial jack or plug. Receptacles are installed in
equipment, whereas plugs are usually attached
to the end of coaxial cables.
coaxial relay A relay designed to connect and disconnect, or to interchange, coaxial cables in a
transmission line without disturbing the characteristic impedance of the line.
coaxial speaker Also called coaxial driver and coaxial loudspeaker. A large low-frequency speaker
and a small high-frequency speaker mounted
concentrically, the smaller within the larger.
When used with a crossover network, this arrangement provides fairly good wide-range audiofrequency response, and saves physical space,
compared with the use of separate speakers.
coaxial stub 1. A length of coaxial cable acting as
a branch to another coaxial cable. Commonly
used for impedance matching. 2. A length of
coaxial cable, usually cut to 1 ⁄4 or 1 ⁄ 2 wavelength, and connected across a coaxial transmission line to act as a WAVETRAP. Commonly used
to reject strong interfering signals.
coaxial switch A switch designed to connect and
disconnect, or to interchange, coaxial cables in a
transmission line without disturbing the characteristic impedance of the line.
coaxial tank A tank circuit consisting of a rod
within a cylinder. The tank is usually tuned by a
small variable capacitor connected between the
rod and cylinder at one end of the combination.
Generally used at ultra-high frequencies (UHF).
coaxial-tank oscillator A stable, self-excited oscillator that uses a COAXIAL TANK. Also see
coaxial transistor A transistor in which a semiconductor wafer is mounted centrally in a metal
cylinder (the base connection) and is contacted
on opposite faces by the emitter and collector
whiskers, which are axially mounted.
coaxial transmission line A transmission line
that is a COAXIAL CABLE.
coaxial wavemeter A type of absorption wavemeter in which the tunable element is a section of
coaxial line (i.e., a metal cylinder surrounding a
metal rod). An internal short-circuiting disk is
moved along the cylinder to connect its inner wall
to selected points along the rod’s length, thereby
varying the resonant frequency. The instrument
is useful at microwave frequencies.
cobalt Symbol, Co. A metallic element. Atomic
number, 27. Atomic weight, 58.94.
cochannel interference Interference between similar signals transmitted on the same channel.
Cockcroft-Walton accelerator A proton accelerator in which nuclei of hydrogen atoms are given
high velocity through a straight tube by a high dc
codan Any of several muting (SQUELCH) systems.
In particular, a squelch circuit that suppresses
noise in a sensitive receiver equipped with automatic gain control (AGC). The receiver is quiet
until a carrier of predetermined strength is received. The name is an acronym for carrieroperated device antinoise.
codan lamp A lamp that alerts a radio operator
that a signal of satisfactory strength is being received. Also see CODAN.
code 1. A set of symbols for communications (e.g.,
the Morse code of radiotelegraphy and wire telegraphy in which dots and dashes correspond to
code • coherence
coding sheet A form on which program instructions are written prior to input.
codiphase radar A radar system that uses beam
forming, signal processing, and a phased-array
codistor A voltage-regulating semiconductor device.
coefficient 1. A factor in an indicated product.
Thus, in 4y, 4 is the coefficient of y. 2. A parameter that indicates a specific characteristic of
some component or device (e.g., COEFFICIENT
coefficient of coupling Symbol k. The ratio of MUTUAL INDUCTANCE between two inductors to
the maximum possible (theoretical) value of mutual inductance. This ratio is always greater than
or equal to 0 (no coupling between inductors),
and less than or equal to 1 (perfect coupling between inductors).
coefficient of current detection See CURRENTDETECTION COEFFICIENT.
coefficient of reflection A measure of the amount
of electromagnetic field reflected in a transmission line from the load feed point. The coefficient
of reflection is equal to the square root of the reflected power divided by the forward power.
coercive force The demagnetizing force required
to remove residual magnetism from a material.
coercivity See COERCIVE FORCE.
cogging Nonuniform rotation of a motor armature.
The velocity increases as an armature coil enters
the magnetic field and decreases as it leaves the
coherence In electromagnetic radiation, a condition in which all the wavefronts are in phase. This
results in high energy concentration, and makes
possible the long-distance transmission of infrared, visible light, and ultraviolet, because the
rays are almost perfectly parallel. It also makes
possible the extreme radiation intensity characteristic of some LASER devices.
Same frequency
same phase
letters, numbers, and marks of punctuation). 2.
In a computer program, symbolically represented
instructions. 3. ENCODE.
codec In encoding and decoding equipment, a
coder/decoder, usually in a single package and
operating at 8 kHz for an input signal with a
passband of 3100 Hz (300 to 3400 Hz).
code character 1. The representation of character
in a particular code form. 2. A sequence of dots
and dashes in the Morse code.
code conversion The translation of a coded signal
from one form of code to another.
coded decimal digit A number expressed in binary form (computer code), that is, in terms of zeros and ones only.
code-directing characters Characters added to a
message to indicate how and where it is going.
coded program See PROGRAM.
coded signal 1. A wire- or radiotelegraph signal in
which secrecy is achieved by using letters in cipher groups, instead of straight language. 2.
coded stop See PROGRAMMED HALT.
code elements The smallest identifiable parts that
compose a digital code. For example, in computer
code, the elements are ones and zeroes (high and
low logic states); in Morse code, they are dots and
code holes In a punched card or tape, holes representing data.
code line A written computer program instruction.
code machine Any one of several devices for
recording or reproducing code signals.
code position The part of a data medium (e.g.,
card row) reserved for data.
code-practice oscillator A simple keyed audio oscillator intended for practicing Morse code.
coder 1. In computer operations, a person who
prepares instructions from flow charts and procedures devised by a programmer. 2. A device that
delivers coded signals.
code receiver A radiotelegraph receiver.
code ringing A method of ringing a telephone subscriber in a predetermined manner to convey a
certain message.
code segment The instruction part of computer
storage associated with a process. Compare
code set The collection of codes representing all of
the characters in a language.
code speed See KEYING SPEED.
code transmitter 1. A radiotelegraph transmitter.
2. A tape-operated keyer for wire telegraphy or radiotelegraphy.
coding 1. Performing the service of a CODER. 2.
Writing instructions for a digital computer; a part
of programming.
coding check A pencil-and-paper verification of a
routine’s validity.
coherent bundle • cold resistance
coherent bundle A bundle of optical fibers, such
that the individual fibers are in the same relative
positions at either end of the bundle.
coherent carrier A carrier that agrees in frequency
and phase with a reference signal.
coherent electroluminescent device See LASER
coherent light Visible light in which the phase relationship between successive waves is such that
the beam consists of parallel rays that provide a
high concentration of energy. Also see LASER.
coherent-light radar See COLIDAR.
coherent oscillator In a radar system, an oscillator that provides a COHERENT REFERENCE.
coherent-pulse operation Pulse operation characterized by a fixed phase relationship between
coherent radiation Radiation characterized by
coherent reference A stable reference frequency
with which other signals are phase locked for coherence.
coherent transponder A transponder in which the
frequency and phase of the input and output signals have a fixed relationship.
coil A long conductor or group of conductors wound
into a tight helical package, often in several layers
on a cylindrical form. This takes advantage of the
resulting concentration of magnetic flux, maximizing the inductance that can be obtained in a component of limited physical size. Further increases
in inductance can be realized by the use of ferromagnetic core materials. See also INDUCTOR.
coil antenna See LOOP ANTENNA.
coil checker An alternating-current (ac) meter or
simple bridge for checking inductors. Such instruments usually only indicate inductance values, but some list readings of resistance or
approximate inductor Q factor.
coil dissipation The power wasted in a coil as
heat. Generally, this dissipation or loss is proportional to the resistance of the coil, and to the
square of the current passing through the coil.
coil form The insulating support around which an
air-core coil is wound.
coil loading The insertion of one or more inductors
into a transmission line or antenna element, for
the purpose of impedance matching, alteration of
the resonant frequency, or both.
coil magnification factor The Q factor of an inductor. Generally given by the ratio XL/RL, where
XL is the inductive reactance of the coil in ohms,
and RL is the resistance of the coil in ohms.
coil neutralization See INDUCTIVE NEUTRALIZATION.
coil resistance The resistance of a coil (inductor),
as distinct from its reactance. It is almost entirely
the result of ohmic loss in the wire from which
the coil is manufactured.
coilshield A metal can designed to provide efficient
electrostatic and electromagnetic shielding of a
coil, preventing unwanted inductive coupling to
other components.
coincidence The simultaneous occurrence of two
or more signals. Compare ANTICOINCIDENCE.
coincidence amplifier An amplifier that delivers
an output signal only when two or more input signals occur simultaneously.
coincidence circuit See AND CIRCUIT.
coincidence counter A circuit or device, such as a
gate, that delivers an output pulse only when two
or more input pulses occur simultaneously; the
output pulses go to a device that counts them.
coincidence detector See AND CIRCUIT.
coincidence gate See AND GATE.
coincident-current selection Selection of a magnetic core (in a core memory or similar device) by
applying two or more currents simultaneously.
coin shooting Searching for coins and similar
small, buried metallic objects using a METAL LOCATOR.
coke A porous material obtained from the destructive distillation of coal. It is valued for the
production of carbon components for electronics, such as dry-cell electrodes and motor
cold 1. Pertaining to an electrical circuit, component, or terminal that is at ground potential. 2. A
term denoting a bad solder joint. 3. Pertaining to
an unheated electrode or element. See COLD
cold alignment The alignment of a tracking system (especially of its tuned circuits) when the system is not in operation, as when transistor power
is off. Also called QUIET ALIGNMENT.
cold cathode 1. In an electron tube, a cathode that
emits electrons without being heated. 2. A cathode electrode operated at a temperature below
ambient temperature.
cold chamber An enclosure in which electronic
equipment can be tested at selected, precise low
temperatures. Compare OVEN.
cold flow The (usually gradual) change in the dimensions of a material, such as plastic in a
molded part.
cold junction In a thermocouple system, an auxiliary thermocouple connected in series with the
hot thermocouple, and immersed in ice or operated at ambient temperature.
cold light Light produced without significant heat,
as from the ionization of a gas by a high voltage
(as in neon bulbs and fluorescent lamps), or by
electroluminescence, bioluminescence, cathodoluminescence, or a similar phenomenon.
cold pressure welding Welding sometimes used in
the fabrication of electronic equipment, in which
the metal parts to be joined are pressed together
tightly to the point of deformation, whereupon
they become welded.
cold resistance The resistance of an unheated
electronic component. Compare HOT RESISTANCE.
cold rolling • collector voltage
collector efficiency In a bipolar transistor circuit,
the ratio of ac power output to dc collector-power
collector family For a bipolar transistor, a group
of collector current versus collector voltage
curves. Each is plotted for a particular value of
base current (common-emitter circuit) or emitter
current (common-base circuit).
Collector current
cold rolling A method of manufacturing an inductor core so that the magnetic grains are all arranged lengthwise.
cold solder joint A solder joint in which insufficient heat has been applied, resulting in a bad
cold spot 1. An area of a circuit or component
whose temperature is ordinarily lower than that
of the surrounding area. 2. A node of current or
voltage. Compare HOT SPOT.
cold weld A welded joint produced by means of
colidar An optical radar system using unmodulated, coherent (laser-produced) light. The term is
an acronym for coherent light detection and
collate In data processing, to produce an ordered
set from two or more similarly ordered sets (as
punched cards).
collator In a punched-card system, a device that
collates (see COLLATE) punched cards.
collector 1. In a bipolar transistor, the electrode
toward which emitted current carriers travel. 2.
In a Klystron, the final electrode toward which
electrons migrate after passing through the
buncher and catcher. 3. In an iconoscope, a
cylindrical electrode around the circumference of
the tube, which gathers and conducts away the
electrons released by the mosaic. 4. The final (target) electrode in a backward-wave or travelingwave tube. 5. A computer program segment that
collates compiled segments so that they can be
loaded into the computer.
collector capacitance 1. Symbol, CC. The capacitance of the collector junction in a bipolar transistor. 2. The capacitance of the collector
electrode in a Klystron, iconoscope, backwardwave tube, or traveling-wave tube.
collector current 1. Symbol, IC. The current flowing in the collector circuit of a bipolar transistor.
COLLECTOR CURRENT. 2. Current flowing in
the collector circuit of a Klystron, iconoscope,
backward-wave tube, or traveling-wave tube.
collector-current cutoff See COLLECTOR CUTOFF.
collector cutoff In a bipolar transistor, the condition in which the collector current is cut off (i.e.,
reduced to the residual value). Also see CUTOFF
collector cutoff current See CUTOFF CURRENT.
collector-diffusion isolation A method of making integrated circuits that contain bipolar
transistors. Provides electrical separation of
the transistors in a semiconductor integrated
collector dissipation Symbol, PC. In a bipolar
transistor, the power dissipation of the collector
electrode. The collector dc power dissipation is
the product of collector current and collector voltage: PC = VC IC.
Collector voltage
(EB or
collector family
collector junction In a bipolar transistor, the
junction between collector and base layers.
collector mesh In a cathode-ray storage tube, a
flat, fine wire screen that attracts and conducts
away the secondary electrons knocked out of the
storage mesh by the electron beam.
collector multiplication In a bipolar transistor,
an increase in the number of electrons at the collector electrode, caused by a momentary alteration of the charge density of the collector
junction by injected carriers reaching the junction.
collector resistance In a bipolar transistor, the internal resistance of the collector junction. See AC
collector ring 1. A rotating, brush-contacted ring
electrode connected to one end of a coil in an ac
generator. 2. A similar ring which, with a brush,
serves as a connection to a rotating element, as in
a signal-gathering system. 3. The collector electrode in an iconoscope.
collector transition capacitance The capacitance
between the collector and base of a bipolar transistor under normal operating conditions. This
capacitance has a limiting effect on the operating
frequency of a bipolar device.
collector voltage Symbol, VC. In a bipolar transistor, the voltage on the collector electrode. See AC
collector voltage • color fringing
zontal blanking pedestal in the composite color
colorcast A color television broadcast.
color code 1. A system that uses colored stripes or
dots to mark the nominal values and other characteristics on capacitors, resistors, and other
components. 2. A code that represents the various frequencies being used by radio-control modelers in competition, and used on flags attached
to transmitters, for example, as a safeguard
against jamming.
color coder See COLOR ENCODER.
color contamination In a color television system,
faulty color reproduction resulting from incomplete separation of the red, green, and blue channels.
color-coordinate transformation In a color television system, the computation (performed electrically in the system) of the tristimulus (primary)
values with reference to one set of primaries, from
the same colors derived from another set of primaries.
color depth An expression for the extent to which
an image can accurately render color. Generally
expressed in bits or in number of colors. Some
systems can reproduce millions of different colors.
color-difference signal Designated B-Y, G-Y, and
R-Y. The signal resulting from reducing the amplitude of a color signal by an amount equal to
the luminance-signal amplitude. Also see B-Y
color dot 1. A phosphor spot on the screen of a
color television picture tube. 2. One of the spots
stamped on a capacitor, indicating the capacitance, voltage, and tolerance (see COLOR CODE,
1). 3. A spot stamped on a resistor, indicating the
number of zeros to be added to the value indicated by the color bands.
color edging In a color television picture, an aberration consisting of false color at the boundaries
between areas of different color.
color encoder In a color television transmitter, the
circuit or channel in which the camera signals
and the chrominance subcarrier are combined
into the color-picture signal.
color equation A mathematical means of determining the resultant color obtained by adding
primary colors in various proportions.
color fidelity The faithfulness with which a color
television system, lens, or film reproduces the
colors of a scene.
color filter A transparent plate or film that transmits light of a desired color, and eliminates or attenuates all other colors.
color flicker In a color television system, image instability that occurs when the luminance and
chromaticity both fluctuate.
color fringing In a color television picture, false
color around objects, sometimes causing them to
appear separated into different colors.
collimated rays Electromagnetic waves made parallel or nearly parallel. This can be done by
means of a reflector, a lens, or a laser.
collimation 1. The process of rendering electromagnetic rays parallel. 2. Adjustment of the line
of sight of an instrument, such as a level or transit.
collimation equipment Optical-alignment equipment.
collimator A device for producing parallel rays of
light or other radiation. In electronics, the most
common example is a dish antenna.
collinear antenna A broadside directional antenna
consisting of two or more half-wave radiators;
the current is kept in phase in each section by
quarter-wave stubs between each radiating section. The radiators are stacked end to end horizontally or vertically. Also called FRANKLIN ANTENNA.
Collins coupler A single-section, pi-filter circuit,
used to match a radio transmitter to a wide range
of antenna impedances. Also called pi coupler and
Collins network.
collodion A viscous solution of pyroxylin and a
solvent (such as acetone, alcohol, or ether) sometimes used as a binding agent for coils and other
cologarithm Abbreviation, colog. The logarithm of
the reciprocal of a number; colog x = log (1/x) =
log x –1 = –log x.
color A perceived characteristic, and a direct function, of visible-light wavelength. Seen by the human eye as a spectrum of hues, ranging from red
at the longest visible wavelengths, through orange, yellow, green, blue, indigo, and finally violet
at the shortest visible wavelengths. See HUE.
coloration In audio applications, a blending of
sounds as a result of mixing among components
at different frequencies. Sometimes this is done
deliberately; in other instances, it is undesirable.
color balance In a color television receiver, adjustment of the beam intensities of the individual
guns of a three-gun picture tube. Compensates
for the difference in light emissivity of the red,
green, and blue phosphors on the tube screen.
color bar-dot generator A radio-frequency (RF)
signal generator that produces a bar or dot pattern on the screen of a color television picture
tube. Used for testing and alignment.
color-bar pattern A color television test pattern of
vertical bars—each of a different color.
color breakup A transient separation of a color
television picture into its red, green, and blue
components, as a result of a sudden disturbance
of viewing conditions (blinking of eyes, moving of
head, intermittent blocking of screen, etc.).
color burst As a phase reference for the 3.579545MHz oscillator in a color television receiver, approximately nine cycles of the chrominance
subcarrier added to the back porch of the hori-
color generator • color spectrum
color generator A special radio-frequency (RF) signal generator to adjust or troubleshoot a color
television receiver. The color signals it delivers
are identical to those produced by a broadcast
color graphics Computer graphics displayed in
color on a cathode-ray tube (CRT) or liquidcrystal display (LCD).
colorimeter A device used to quantitatively measure the color intensity of a sample relative to a
colorimetric A characteristic of visible light, representing the wavelength concentration. Refers to
the perceived color of a light beam.
colorimetry The science and art of color measurement.
color killer In a color television receiver, a circuit
that, in the absence of a color signal, delivers a
negative bias to cut off the bandpass amplifier.
color match In photometry, the condition in which
color agreement exists between the halves of an
area. Also see COLOR MATCHING.
color matching The art of selecting colors that are
identical in hue, saturation, and brilliance. This
can be done with the unaided eye or with the help
of an instrument.
color media Substances that transmit essentially
one color of visible light while blocking other colors.
color meter A photoelectric instrument for measuring color values, and comparing and matching
color mixture An additive combination of two or
more colors. Thus, red + yellow = orange, blue +
red = violet, red + blue + green = white, etc.
color oscillator The oscillator in a color television
receiver that coordinates the color response. This
oscillator is operated at 3.579545 MHz, to within
plus or minus 10 Hz.
color palette In a color video image, the total number of possible colors that can be displayed.
color phase In color television, the phase difference between an I or Q chrominance primary signal and the chrominance carrier reference.
color-phase diagram In color television, a quadrant diagram showing (for each of the three primary and complementary colors) the difference in
phase between the color-burst signal and the
chrominance signal, as well as the peak amplitude of the chrominance signal. Also shown are
the peak amplitude and polarity of both in-phase
and quadrature components required for the
chrominance signals. For color TV receiver adjustment, the color-phase diagram is displayed,
in effect, by a VECTORSCOPE when a suitable
signal from a color generator is applied to the receiver.
color picture signal 1. In color television and/or
computer graphics, an electrical signal containing components corresponding to the hue, saturation, and brilliance of a fixed or changing visual
image. 2. In color television, the combination of
chrominance and luminance signals minus
blanking and sync signals.
color picture tube A specialized type of cathoderay tube (CRT), used in color television receivers
and computer displays. Three different images
are produced: one in red, one in blue, and one in
green. The three monochrome images are combined to form a complete color image.
color primaries 1. Also called additive primaries or
primary colors. In color television, the hues red
(R), green (G), and blue (B). When these colors are
mixed in various ratios, any visual color can result. 2. Also called subtractive primaries or primary pigments. In color printing, the hues
magenta (M), cyan (C), and yellow (Y). These
roughly correspond to red (R), blue (B) and yellow
(Y). Sometimes black (K) is also included. When
these pigments are mixed in various ratios, any
visual pigment can result.
color purity The ratio of wanted to unwanted components in a color. In a pure color, there are no
components other than those required to produce
the color. Color, in this context, includes white,
black, and all shades of gray.
color-purity magnet A permanent magnet on the
neck of a color television picture tube, used to
help ensure color purity by maintaining proper
displacement of the electron beam.
color registration In color television reception, the
precise superimposition of red, green, and blue so
that the composite is free from COLOR EDGING.
color rendering index A mathematical expression
defining the effect of the color of a light source on
an object. For example, in red light, a blue object
appears nearly black.
color sampling rate The number of times per second that each primary color is sampled in a color
television receiver.
color saturation A measure of the purity of a hue.
The extent to which a hue is without a white component; 100% saturation indicates a complete
absence of white.
color sensing In machine vision systems, the ability to distinguish between light of different wavelengths. Usually done with red, green and blue
color filters and three separate cameras.
color sensitivity 1. The degree of which a photosensitive device, such as a photocell or camera
tube, responds to various colors of light. 2. The
degree to which photographic film responds to
various colors of light.
color signal See COLOR PICTURE SIGNAL.
color spectrum The band of electromagnetic energy containing visible light; it extends from red
(at the longest wavelengths) to violet (at the shortest). Commonly measured in nanometers (nm),
where 1 nm = 10–9 m. Also expressed in
Angstroms, where 1 Angstrom = 10–10 m = 0.1
nm. In order of decreasing wavelength, the colors
are red at 750 to 700 nm (7500 to 7000
color spectrum • coma lobes
Wavelength, µm
Gamma rays
radio waves
as violet, blue, green, yellow, orange, and red, in
order of increasing intensity.
Colpitts oscillator A radio-frequency (RF) oscillator that uses a single, untapped inductor. A combination of two fixed capacitors in series is
connected in parallel with the inductor. The feedback is controlled by the ratio of capacitances. A
permeability-tuned coil or a roller inductor can be
used to obtain variable-frequency operation. Stability is enhanced when the output of the oscillator is taken from the emitter or source portion of
the circuit. To prevent the output signal from being short-circuited to ground, an RF choke is connected in series with the emitter or source.
color spectrum
Angstroms), orange, yellow, green, blue, indigo,
and violet at 410 to 390 nm (4100 to 3900
color subcarrier A modulated monochrome signal
whose sidebands convey color information.
color-sync signal See COLOR BURST.
color system Also called RGB color model. A means
of representing a color in terms of mathematical
coordinates. This can be done in three dimensions because there are three COLOR PRIMARIES. Each color primary is represented by an
axis. Any COMPOSITE COLOR can be represented by a unique vector. The relative amount of
each color primary is given by the length of the
composite-color vector components along each
color television Television in which the picture
approximates natural color. It operates on the basis of mixing three primary colors (red, blue, and
green) of phosphors on the picture tube screen.
color television receiver A television receiver designed to reproduce color pictures.
color television signal The signal transmitted by
a color television transmitter, containing all of the
information needed to reproduce a complete, fullcolor, moving image.
color transmission The television transmission of
a picture in color.
color triad On the screen of a color picture tube,
one of the color cells, each of which contains one
of the three phosphor dots: red, green, and blue.
color triangle A triangle that can be inscribed on a
chromaticity diagram to reveal the chromaticity
range resulting from adding the three color primaries.
color TV signal The complete signal (video, color,
and sync components) required for transmitting a
picture in color.
color weather radar A computer-enhanced radar
rendition of weather patterns, usually showing
various intensities of precipitation as different
colors. Commonly, areas of precipitation show up
Colpitts oscillator
columbium Symbol, Cb. The former name of the
metallic element niobium. Atomic number, 41.
Atomic weight, 92.9064.
column See CARD COLUMN.
columnar graph A graphical presentation of data,
in which the ordinates are represented by vertical
columns whose height depends on the value.
Commonly used in presentation graphics, but less
common in analytical graphics.
column binary Binary number representation on
punched cards, wherein consecutive digits correspond to consecutive column punching positions.
column speaker An acoustic speaker with a long
cabinet, so that a large column of air is used for
resonating or reinforcing purposes. This type of
speaker radiates over a wide azimuth angle, while
providing a narrow beam in the elevation plane.
column split On a punched card machine, the device for reading, as two separate characters or
codes, two parts of a single column.
COM 1. Abbreviation for communications port.
2. Abbreviation for computer output on microfilm.
coma An aberration that causes the beam spot on
the screen of a cathode-ray tube to resemble a
coma lobes An aberration in the radiation or response pattern of a dish antenna that occurs
when the radiating element is not exactly at the
focal point of the reflector. When the directional
coma lobes • commercial data processing
pattern is altered by moving the driven element,
rather than turning the entire antenna, these
lobes appear.
comb amplifier An arrangement of several sharply
tuned bandpass amplifiers whose inputs are connected in parallel and whose outputs are separate; the amplifiers separate various frequencies
from a multifrequency input signal. The name is
derived from the comb-like appearance of the response pattern of various output peaks displayed
along a frequency-base axis.
comb filter A selective device that passes several
narrow bands of frequencies within a larger band,
while rejecting frequencies in between the narrow
bands. So called because its frequency-response
curve resembles the teeth of a comb when observed on a spectrum analyzer. Also see COMB
comb filter response
comb generator 1. A signal generator that provides outputs at evenly spaced frequencies. So
called because, on a spectrum analyzer, its output looks like the teeth of a comb. 2. A transmitter with many spurious signals at its output.
combination 1. A functional, usually stationary,
installation consisting of two or more pieces of
equipment. Examples: transmitter/receiver combination, motor/generator combination, and
tuner/amplifier combination. 2. In mathematics,
a selection of several factors from a group, without regard to order. Thus, from the group ABC,
the three possible combinations are AB, AC, and
combinational circuit Two or more basic logic circuits, combined in such a way that the output
state depends entirely on the input states.
combination bridge A bridge that affords two or
more classes of measurement, usually selectable by means of a function switch. Examples:
capacitance-inductance bridge, and capacitanceresistance bridge.
combination cable A cable that has conductors
grouped in pairs, threes, quads, or similar arrangements.
combination feedback See CURRENT-VOLTAGE
combination microphone Two or more microphones combined into one unit.
combination speaker Two or more loudspeakers
combined into one (e.g., a COAXIAL SPEAKER).
combination tone An acoustic tone resulting from
the combination of two other acoustic tones. If
the original tones have frequencies f1 and f2
(where f1 is higher than f2), then the first-order
combination frequencies are f1 + f2 and f1 – f2.
Higher-order combination tones can result from
mixing among the original tones and the firstorder combination tones.
combinatorial logic A form of digital logic, in
which the output states depend on the input
states, but on no other factor.
combined head See READ-WRITE HEAD.
combined reactance The net reactance (X) in a
circuit, obtained by vectorially adding the inductive reactance (XL ) and the capacitive reactance
combiner A circuit or device for mixing various signals to form a new signal. Also see MIXER.
combiner circuit In a color television camera, the
circuit that combines the chroma and luminance
with the sync.
comeback A spurious response in a bandpass or
band-rejection filter, at a frequency well above or
below the passband or stopband.
command 1. In computer operations, the group of
selected pulses or other signals that cause the
computer to execute a step in its program. 2. Instruction.
command chain Part of a computer operation carried out independently as a series of input/
output instructions.
command control In automation, electronic control, and computer operations, the performance
of functions in response to a transmitted signal.
command destruct signal A signal for instigating
the destruction of a missile in flight.
command guidance system A system in which a
guided missile and its target are both tracked by
command language A computer language made
up of command operators.
command link In a command guidance system,
the section that transmits missile-steering commands.
command network A radio communications network in which the chain of command is rigorously defined and followed.
command reference The current or voltage to
which a feedback signal is referenced in a control
system or servomechanism.
comment A statement written into a computer
program for a documentation, rather than implementation (e.g., to describe the purpose of a step
or subroutine).
comment field A record or file in which instructions or explanations are given.
commercial data processing A commercial
(rather than industrial, scientific, or personal) application of data processing.
commercial-level security • common-mode input capacitance
commercial-level security See LEVEL-2 SECURITY.
commercial killer A usually remote-controlled,
electronic relay for disabling a radio or television
receiver during advertisements.
commercial language A computer programming
language for commercial applications (payroll, for
common 1. Grounded. 2. Pertaining to a connection shared by several different points in a circuit
or system. 3. See COMMON GROUND.
common area A computer storage area usable by
several programs or segments within a program.
common-base circuit A bipolar transistor circuit
in which the transistor base is the common (or
grounded) electrode. Also called grounded-base
common battery 1. A battery shared by two or
more different circuits or pieces of equipment. 2.
In wire telephony, a central office battery that
supplies the entire system.
common-battery office In wire telephony, a central office that provides a common battery.
common business-oriented language See COBOL.
common-capacitor coupling The process of coupling one tuned circuit to another by means of a
capacitor that is common to both circuits.
common-drain circuit A field-effect transistor circuit in which the drain terminal is the common
(or grounded) electrode. Also called groundeddrain circuit and SOURCE FOLLOWER.
common-emitter circuit A bipolar transistor circuit in which the emitter is the common (or
grounded) electrode. Also called grounded-emitter
common-gate circuit A field-effect transistor circuit in which the gate is the common (or grounded)
electrode. Also called grounded-gate circuit.
common-grid circuit A tube circuit in which the
control grid is the common (or grounded) electrode. Also called grounded-grid circuit.
common ground A single ground-point connection
shared by several portions of a circuit.
common impedance A single impedance shared
by parts of a circuit. Because currents from the
various parts flow through this impedance simultaneously, coupling (desired or undesired) can
occur between them.
common-inductor coupling The process of coupling one tuned circuit to another by means of an
inductor that is common to both circuits.
L2 Output
L3 Output
common-capacitor coupling
common-inductor coupling
common-carrier fixed station A fixed radio station that provides public service.
common-cathode circuit A tube circuit in which
the cathode is the common (or grounded) electrode. Also called grounded-cathode circuit.
common-channel interference Radio interference
resulting from two stations transmitting on the
same channel. It is characterized principally by
beat-note (heterodyne whistle) generation, and
suppression or capture of the weaker signal by
the stronger one.
common-collector circuit A bipolar-transistor
circuit in which the collector is the common (or
grounded) electrode. Also called grounded-collector circuit and EMITTER FOLLOWER.
common communications carrier A communications company authorized by the licensing agency
to furnish public communications.
common language A language recognized by all
the equipment in a data processing system.
common logarithm Abbreviation, log10. Also
called base-10 logarithm. A logarithm in which
the base number is 10. Also see LOGARITHM.
common mode Pertaining to signals or signal
components that are identical in amplitude and
common-mode characteristics In an operational
amplifier, characteristics denoting amplifier performance when a common signal is applied to inverting and noninverting inputs.
common-mode gain The voltage gain of a differential amplifier with a common-mode input.
common-mode impedance input The impedance
between ground and one of the inputs of a differential amplifier. Compare COMMON-MODE INPUT IMPEDANCE.
common-mode input capacitance In a differential amplifier, the internal capacitance of the
common-mode input circuit.
common-mode input circuit • commutating capacitor
common-mode input circuit In a differential amplifier, the input circuit between ground and the
inputs connected together.
common-mode input impedance In a differential
amplifier, the open-loop impedance between
ground and the inputs connected together. Compare COMMON-MODE IMPEDANCE INPUT.
common-mode input signal A signal applied to
the common-mode input circuit of a differential
amplifier (i.e., to both inputs connected together).
common-mode input voltage In a differential amplifier, the maximum voltage that can be applied
safely between ground and the inputs connected
common-mode interference A form of interference that occurs across the terminals of a
grounded system.
common-mode rejection The extent to which a
differential amplifier will reject a signal presented simultaneously to both inputs in phase,
or of two signals identical in amplitude, frequency, and phase applied separately to the two
common-mode rejection ratio In a differential
amplifier, the extent to which the amplifier cancels undesired signals. It is the ratio of the differential gain to the common-mode gain. Also see
common-mode signal The algebraic average of
two signals applied simultaneously to the two
ends of a balanced circuit, such as a differential
amplifier. Compare COMMON-MODE INPUT SIGNAL.
common-mode voltage The part of the input that
is common to both inputs of a differential amplifier circuit. It is quantitatively defined as the
arithmetic mean of the voltages at the inputs.
common-mode voltage gain See COMMONMODE GAIN.
common-mode voltage range The range limited
by the maximum nonsaturating input voltage
that can be applied to both inputs of an operational amplifier.
common pool An assigned memory store, utilized
by two or more circuits or systems.
common-resistor coupling The process of coupling one circuit to another by means of a resistor
that is common to both circuits.
L2 Output
common-resistor coupling
common-source circuit A field-effect transistor
circuit in which the source terminal is the
common (or grounded) electrode. Also called
grounded-source circuit.
common-user channels Communication channels
open to all licensees in a particular service.
communication band A band of frequencies
whose use is authorized expressly for communications, rather than for other services (such as
broadcasting, education, remote control, etc.).
communication channel 1. In radio or wire service, a (usually auxiliary) channel for direct exchange of information between units of the
service (e.g., a “talking circuit” between a broadcast studio and the transmitter house). 2. A data
transmission channel between two points (e.g., a
remote terminal and a central computer system).
communication link 1. Collectively, the equipment providing a communication channel between two transmitters. 2. Data terminal
communication protocol The specifications of a
digital signal, including the speed in bits per second (bps) or bauds, the code type, the bit duration, the mark-to-space ratio, etc.
communications The science and art of using and
developing electronic equipment and processes
for the transmission and reception of information.
communications common carrier An organization licensed to provide public communication
communications network An organization of
transmitting and receiving stations for the reliable exchange of intelligence. Also called net.
communications receiver A general-coverage or
multiband radio receiver, designed primarily for
listening to amateur, weather, or other nonbroadcast stations. Compare BROADCAST RECEIVER.
communications satellites Satellites in earth orbit that provide propagation paths (e.g., by reflection or retransmission) for radio waves between
terrestrial transmitters and receivers. Also see
television Abbreviation,
CATV. A system in which an advantageously located receiving station receives television signals,
amplifies them if necessary, and distributes them
in the community served by the system. Commonly called cable TV.
commutating capacitor 1. In a flip-flop circuit, a
capacitor connected in parallel with the crosscoupling resistor to accelerate the transition from
one stable state to the other. Also called speedup
capacitor. 2. A capacitor connected in parallel between silicon-controlled rectifier (SCR) stages to
momentarily reverse the current going through
the SCR, thereby causing the SCR to go into the
cutoff condition.
commutation • compass
commutation 1. In a direct-current (dc) generator,
periodic reversal of the current in the armature
coils as the coils alternately pass the north and
south poles of the magnetic field. When the ends
of each coil are connected to opposite bars of the
commutator, the electrical polarity at the commutator brushes remains constant. 2. In a thyratron or silicon-controlled rectifier (SCR) circuit,
momentarily reversing the polarity to cut the device off.
commutator 1. In a direct-current (dc) motor,
generator, or rotating selector, an arrangement
of parallel metal bars or strips on a rotating
drum. As the drum turns, the bars contact one
or more brushes that are in sliding contact with
the commutator. 2. An electronic circuit that
switches a single input sequentially to a series of
output terminals, or switches a number of inputs sequentially to a single pair of output terminals.
commutator ripple The pulsating voltage superimposed on the direct-current (dc) voltage delivered by an unfiltered dc generator.
compact disc Abbreviation, CD. A digital, highdensity optical disc, used in high-fidelity stereo
sound systems. Also used to store computer data.
The information is encoded as tiny pits on the
surface of the disc, and is recovered by a laser, a
sensor and a digital-to-analog (D/A) converter.
These disks have largely superseded magnetic
tapes, and have rendered long-playing vinyl disks
and turntables obsolete. See also COMPACTDISK READ-ONLY MEMORY.
compact-disk read-only memory Abbreviation,
CD-ROM. A digital COMPACT DISC used for the
long-term storage of computer data and/or software programs. Usually the same size as a highfidelity stereo disk, it can hold over 600
megabytes of data. Although data can be read
from the disk, it cannot be overwritten.
compander Term for compressor/expander. In the
transmission and reception of audio-frequency
(AF) intelligence, a system that uses an amplitude
compressor at the transmitter and an amplitude
expander at the receiver. The compressor reduces
the dynamic range before transmission, and the
expander restores it after reception. Provides improved signal-to-noise ratio under marginal communications conditions. Also increases the ratio
of average power to peak power. See COMPANDING.
companding A process in which a signal is compressed at the transmitting end of a circuit and
expanded at the receiving end, yielding a signal
like the original at the receiver output. Signals
are more efficiently transmitted when they are
compressed because the average power increases, relative to the peak power. This improves
the average signal-to-noise ratio for weak signals.
companding law The mathematical function used
for companding. It is an output-amplitude versus
input-amplitude function for the compression at
the transmitter, and the inverse of this function
for the expansion at the receiver.
companion keyboard An auxiliary keyboard connected to a regular keyboard and operated remotely.
companionship machine A computer or robot
with sufficient machine intelligence to provide entertainment and mental stimulation for humans.
comparator 1. An integrated circuit (IC) with two
inputs, called A and B. The device compares the
voltages that appear at these inputs. If the input
voltage at A is significantly greater than the input
voltage at B, the output is about +5 V. If the input voltage at A is not greater than the input
voltage at B, the output voltage is about +2 V.
These ICs are used to actuate, or trigger, other
devices such as relays and electronic switching
circuits. 2. In general, any circuit that compares
some characteristic of two input signals and produces an output that depends on the relationship between the inputs. 3. An instrument for
checking the condition of a component by comparing it directly with an identical component of
known quality has a scale reading in percentage
deviation, or simply “GO/NO-GO.” Examples: capacitor comparator, resistor comparator, coil
compare In computer operations, a relational test
performed on two quantities to determine their
relative magnitude, including an indication of the
test result and, sometimes, the taking of action.
Example: the process and acton resulting from
execution of the statement “IF A > B THEN GO TO
LINE 250.”
comparison 1. An expression of the relationship between two voltages, currents, phase angles, component values, or other quantities in an electrical
or electronic circuit or system. 2. An examination
of different data bits or items, which results in a
conclusion about some aspect of their relationship.
comparison bridge A bridge designed especially
for the quick comparison of components (e.g., the
comparison of resistors with a standard resistor,
inductors with a standard inductor, and capacitors with a standard capacitor).
comparison measurement A measurement in
which a quantity or component is compared with
a known, similar quantity or component value,
rather than having the measurement displayed
directly by a meter. Examples: bridge measurements, potentiometric measurements, and frequency matching.
compass 1. Any of several instruments for determining direction on the earth’s surface [e.g., magnetic (mariner’s) compass and gyrocompass]. 2. A
radio direction finder. 3. An instrument for drawing circles.
compatibility • compensation theorem
compatibility 1. A desirable condition in which
devices or systems can function efficiently together, without any modification of equipment. 2.
In computer operations, a desirable condition in
which different computers can run the same software, without any modification of hardware or
compatible color television A color-television
system whose transmissions can be received in
black and white by any ordinary monochromatic
compatible integrated circuit A hybrid integrated
circuit (IC) that has an active element inside the
integrated structure and a passive element deposited on its insulated outer surface.
compensated amplifier A wideband amplifier
whose frequency range is extended by special
components and circuit modifications. Also see
compensated diode detector A diode detector in
which a positive dc voltage from the automaticgain-control (AGC) rectifier is applied to the diode
anode. The voltage is always proportional to the
signal carrier. The arrangement allows the diode
to handle a heavily modulated AM signal without
producing excessive distortion.
compensated-impurity resistor A resistor consisting of a diffused semiconductor material to
which are added controlled amounts of n- or ptype dopants (impurities).
compensated-loop direction finder A direction
finder whose loop antenna is complemented by
another antenna for polarization-error compensation.
compensated semiconductor A doped semiconductor material in which the acceptor impurity
cancels the effects of the donor impurity.
compensated volume control A combination volume-tone control that provides bass boost at low
volume levels to compensate for the ear’s deficiency at low frequencies.
compensating capacitor 1. A capacitor that has a
temperature coefficient of capacitance numerically
equal to, but having the opposite sign from, that of
another capacitor in a tank or other circuit. When
the capacitors are connected in parallel, a temperature-induced value change in the main capacitor
is balanced by an equal and opposite change in
the compensating capacitor; the net capacitance of
the circuit does not change. This greatly reduces
frequency drift. 2. In a video amplifier, a large capacitance connected between ground and a tap on
the collector or drain resistor to boost lowfrequency response. Compare COMPENSATION
COIL. 3. A usually low-capacitance capacitor of
known temperature coefficient, operated in combination with a main capacitor to reduce capacitance/temperature drift of the latter to zero or to
some desired positive or negative value.
compensating diode A junction diode used to
temperature-stabilize a transistor circuit. It is
usually forward-biased in the base-bias network
of the transistor.
compensating filter 1. A selective filter used for
the purpose of eliminating some irregularity in
the frequency distribution of received energy. 2. A
filter used to change the wavelength distribution
of electromagnetic energy.
compensating resistor 1. A low-value resistor
of known temperature coefficient, connected in
series with a main resistor to reduce the
resistance/temperature drift to zero, or to some
desired positive or negative value. 2. See TRIMMER RESISTOR.
compensating capacitor, 1.
compensating resistor, 1.
compensation Adjusting a quantity, manually or
automatically, to obtain precise values, or to
counteract undesired variations. Example: temperature compensation of electronic components.
For illustration, see COMPENSATING CAPACITOR, 1.
compensation coil In a video amplifier, an inductor connected in series with the collector or drain
resistor, or in the coupling path between stages,
or both, to boost high-frequency response.
compensation filter See COMPENSATING CAPACITOR, 2.
compensation signal A signal recorded on a tape
track containing computer data, to ensure that
the tape plays back at exactly the correct speed at
all times.
compensation theorem An impedance (Z ) in a
network can be replaced by a generator having
compensation theorem • complementary wave
zero internal impedance, and whose generated
voltage equals the instantaneous potential difference produced across Z by the current flowing through it. Compare MAXIMUM POWER
compensator A device or circuit that facilitates the
adjustment of a quantity, manually or automatically, to obtain precise values, or to counteract
undesired variations.
compilation time The period during which a program is compiled, as distinct from RUN TIME.
compile 1. To unify computer subroutines into an
all-encompassing program. 2. To gather information or data together into a single file or file
compiler In computer operations, a program that
changes a HIGH-LEVEL LANGUAGE, such as
BASIC, C, C++, COBOL, or FORTRAN, into MACHINE LANGUAGE. A compiler must be written
especially for the high-level language being used.
compiler language Any computer language that
serves as an interface between the operator and
the computer.
compiler program A program that converts compiler language into machine language.
compiling routine In digital computer operation, a
routine permitting the computer itself to construct a program to solve a problem.
complement 1. The difference between a number
and the radix (modulus or base) of the number
system. For example, the complement of 7 is
equal to 3 (because 10 – 7 = 3) in the decimal
(radix-10) number system. 2. Also called ones
complement. In computer operations, a representation of the negative value of a binary number. All the available digits are set to 1, and then
the number in question is subtracted. For example, the complement of 101 is equal to 010
(because 111 – 101 – 010); the complement of
1001 is equal to 0110 (because 1111 – 1001 =
complementary A Boolean operation whose result
is the same as that of another operation, but with
the opposite sign; thus, OR and NOR operations
are complementary.
complementary colors 1. In the additive color
system, two colors that produce light gray or
white when combined. 2. In the subtractive
color system, two pigments that produce dark
gray or black when combined. 3. Colors or pigments that are opposite each other on the color
complementary constant-current logic A form of
bipolar logic with high operating speed and high
component density.
Also sometimes called complementary metal-oxide
silicon. Acronym, CMOS (pronounced “seamoss”).
A digital integrated-circuit (IC) technology, in
which logic gates are formed by n-channel/
p-channel pairs of metal-oxide-semiconductor
field-effect transistors (MOSFETs) fabricated on a
substrate. Noted for high speed and low current
complementary operator The logical negation
(NOT) operation.
complementary pushpull circuit See COMPLEMENTARY-SYMMETRY CIRCUIT.
complementary rectifier In the output circuit of a
magnetic amplifier, nonsaturating half-wave rectifier elements.
complementary silicon-controlled rectifier A
silicon-controlled rectifier that has polarity
opposite from the usual silicon-controlled rectifier.
complementary-symmetry circuit A bipolartransistor circuit that uses an npn and pnp transistor. The transistors conduct during opposite
half-cycles of the input signal, the result being
that push-pull output is provided with a singleended input; no phase-splitting input circuit is
required. The complementary-symmetry circuit
offers very low output impedance, permitting a
loudspeaker voice coil (or other low-impedance
load) to be operated directly without a coupling
complementary-symmetry circuit
complementary tracking A control system in
which several secondary (slave) devices are controlled by a primary (master) device.
complementary transistors A transistor pair of
opposite polarity operated in a complementarysymmetry circuit or its equivalent.
complementary wave An electromagnetic wave in
a transmission line that occurs as a result of reflection. Any impedance discontinuity will result
in complementary waves.
complementer • component
complementer A logic circuit that provides an output pulse when there is no input pulse, and vice
versa. Also called INVERTER and NOT CIRCUIT.
complement number In a base-n number system,
for a given positive integer p less than n, the positive integer m such that m + p = n. For example, in
the decimal (base-10) system, the complement of 4
is 6, the complement of 7 is 3, and the complement
of 9 is 1. In the hexadecimal (base-16) number
system, the complement of 4 is 12, the complement of 7 is 9, and the complement of 9 is 7.
complement-number handling A computer system in which the operations are carried out via
the complements of the input numbers.
complement-setting technique A process of determining the number of pulses required to complete the switching of a counter circuit when it is
started at some state higher than full zero. The
number of pulses required for completion is equal
to the number that represents the starting state’s
complete carry In digital computer operation, a
system permitting all carries to generate carries.
complete circuit See CONTINUOUS CIRCUIT.
complete modulation Modulation to the maximum extent possible while maintaining acceptable circuit or system operation.
complete operation In computer operations, the
condition in which the machine rigorously follows
program instructions.
complete routine A vendor-supplied computer
program that is usable without modification.
complex function 1. A mathematical function of a
complex-number variable. 2. An integrated circuit (IC) containing two or more subcircuits that
perform an operation more complicated that of
any one of the circuits alone.
complex notation Notation taking into consideration both the real-number and imaginary-number components of a quantity. Thus, impedance
(Z ) is a complex quantity that includes a resistive
(real) component (R) and a reactive (imaginary)
component ( j X ). See COMPLEX NUMBER and
complex number A number expressed in complex
notation (e.g., a + jb, where a and b are real numbers and j is the COMPLEX OPERATOR). Can
also be expressed as a point or a vector in an ARGAND DIAGRAM.
complex operator The unit imaginary number,
represented as j by engineers and as i by mathematicians. This number is defined mathematically as the positive square root of –1.
complex parallel permeability An expression of
the permeability of an inductor core under actual
operating conditions, assuming zero loss in the
conductors of the coil winding. A parallel combination of reactance and resistance.
complex periodic wave A periodic wave composed
of a sine-wave fundamental and certain harmonics in specific proportions.
complex permeability An expression of inductorcore permeability, obtained from the mathematical ratio of the magnitudes of the vectors
representing the induction and electromagnetic
field strength within the core.
complex plane A Cartesian coordinate system
with real numbers on the horizontal axis and
imaginary numbers on the vertical axis. Used for
vectorial representation of complex numbers. See
complex quantity A quantity containing both real
and imaginary components. Example: Impedance (Z ) is a complex combination of resistance R (a real component) and reactance jX (an
imaginary component): Z = R + jX.
complex radar target A radar target that is large
enough in theory to be detected by radar, but, because of its geometry, cannot be detected. This effect is the result of phase combinations of signal
components reflected from various surfaces on
the target.
complex series permeability An expression of
complex permeability of an inductor core under
actual operating conditions, assuming zero loss
in the conductors of the coil winding. A series
combination of reactance and resistance.
complex steady-state vibration Periodic vibration
with more than one sine-wave component.
complex tone An audio tone made up of more
than one sine-wave component.
complex variable A variable having real and imaginary parts.
complex waveform The shape of a COMPLEX
PERIODIC WAVE. It is the resultant of the individual sine-wave components (i.e., of the fundamental and the harmonics).
complex-wave generator A signal generator
whose output signal is any of several selectable
waveforms and frequencies (or repetition rates).
compliance 1. The ease with which a material can
be flexed or bent, an important characteristic of
transducers (such as loudspeakers). Expressed
in cm/dyne, compliance is the reciprocal of stiffness, and is the acoustical or mechanical equivalent of capacitance. 2. A measure of the output
impedance of a switched-current signal source.
Generally given as maximum current for a certain
change in the voltage.
compliance range The voltage range required to
maintain a constant current throughout a loadresistance range.
compliance voltage The range over which the output voltage of a constant-current power supply
must swing in order to maintain a steady current
in a varying load.
compliance-voltage range The output voltage
range of a constant-current power supply.
component 1. A device or part used in a circuit to
obtain some desired electrical action [e.g., a resistor (passive component) or an integrated circuit
component • compress
composition resistor A resistor made from a mixture of materials, usually finely powdered carbon
and a binder.
compound A substance in which the atoms of two
or more elements have united chemically to form
a molecule. For example, an atom of cadmium
(Cd) and one of sulfur (S) combine to form a
molecule of cadmium sulfide (CdS).
compound connection A direct connection of two
transistors, the amplified output of the first being
further amplified by the second. The connection
provides extremely high current gain. Also called
compound generator A generator that has both
series and shunt fields. Also called compoundwound generator.
compound horn A horn reflector used for transmission of microwave energy. The faces of the
horn approach four geometric plane surfaces as
the distance from the center increases.
compound modulation A system of successive
modulation, the modulated wave from one step
becoming the modulating wave in the next. Also
called multiple modulation.
(active component)]. Also see ACTIVE COMPONENT and PASSIVE COMPONENT. 2. An attribute inherent in a device, circuit, or
performance (e.g., the REACTIVE COMPONENT
of an inductor). 3. A specified quantity or term
(e.g., the WATTLESS COMPONENT of ac power).
4. A piece of equipment in a high-fidelity sound
component density The number of components
(see COMPONENT, 1) in an electronic assembly of
a given physical volume.
component failure rate 1. The percentage of
components, out of a specified group, that can
be expected to fail within a specified length of
time. 2. The frequency with which a given component, in a certain application, can be expected
to fail.
component layout The mechanical arrangement
of components (see COMPONENT, 1) in an electronic assembly.
component stress The electrical or mechanical
strain to which a component is subjected. In general, the greater the stress, the higher the component failure rate.
composite cable A cable containing other cables of
different types.
composite circuit A circuit handling telegraphy
and telephony simultaneously without causing
mutual interference.
composite color A color that is not one of the
COLOR PRIMARIES, but instead, consists of a
combination of the three color primaries.
composite color signal The complete color television signal, including all picture, color, and control components.
composite conductor A set of wires connected in
parallel. The wires are often, but not necessarily,
of identical size and constitution.
composite current A current having both alternating-current (ac) and direct-current (dc) components; an alternating current superimposed on
a direct current. Also called fluctuating current.
composite curve A curve or pair of curves showing
two modes of operation, as of biased and unbiased conditions.
composite filter A filter consisting of more than
one section. The sections might be, but often are
not, identical.
composite video signal The television picture signal containing picture information and sync
composite-video-signal distortion Distortion of
the composite video signal as evidenced by overshooting, ringing, and sync-pulse shortening.
composite voltage A voltage having both alternating-current (ac) and direct-current (dc) components; an ac voltage superimposed on a dc
voltage. Also called fluctuating voltage.
composite wave filter Two or more wave filters
(not necessarily of the same type) operated in cascade.
compound modulation
compound motor An electric motor having both
series and shunt fields. Also called compoundwound motor.
compound transistor Two or more transistors directly coupled in the same envelope for increased
amplification. Also see COMPOUND CONNECTION.
compound-wound generator See COMPOUND
compound-wound motor See COMPOUND MOTOR.
compress 1. In communications, to reduce or minimize the bandwidth of a signal. 2. In communications, the processing of a signal to increase
low-level components and thereby raise the average power level relative to the peak power level. 3.
In computer operations, to reduce or minimize
the number of bits in a digital signal or file, while
compress • computer graphics
still retaining all the essential information. Compare EXPAND.
compressed-air capacitor A high voltage airdielectric capacitor enclosed in a case in which
the air pressure is held at several atmospheres.
The device exploits the dielectric strength of compressed air, which is higher than that of air at
normal pressure.
compressed-air speaker A speaker that uses an
airtight chamber to enhance the acoustic reproduction at certain frequencies.
compression 1. In communications, the reduction
or minimization of signal bandwidth. 2. In communications, the processing of a signal to increase low-level components and thereby raise
the average power level relative to the peak power
level. Usually, a logarithmic function. 3. In computer operations, the reduction or minimization
of the number of bits in a digital signal or file,
while still retaining all the essential information.
compression ratio In a system using COMPRESSION, the ratio A1/A2, where A1 is the gain (or
transmission) at a reference-signal level and A2 is
the gain (or transmission) at a specified higher
signal level.
compression wave A wave disturbance that travels via longitudinal motion of particles in a
medium. Sound waves through air are the most
common example.
compressor A circuit or device that limits the amplitude of its output signal to a predetermined
value, despite wide variations in input signal amplitude.
compressor driver unit A loudspeaker that works
into an air space connected by a throat to a horn,
rather than by driving a diaphragm.
Compton diffusion An effect that occurs when a
photon and electron collide. Some of the energy
from the photon is transferred to the electron. On
a large scale, such collisions result in diffusion of
electromagnetic waves.
Compton effect The increase in wavelength (decrease in frequency) of X-rays scattered by the
electrons of lighter atoms bombarded with the
Compton shift See COMPTON EFFECT.
compute To perform a mathematical operation by
means of a relatively simple process. Thus, a digital computer solves intricate problems using
simple arithmetic steps. Compare CALCULATE.
computer A device or machine for performing
mathematical operations on data, and producing
the results as information or control signals.
There are numerous types, the most common being the digital computer.
computer-aided design Abbreviation, CAD. The
use of computers in conceiving, developing, and
perfecting new products.
manufacturing Abbreviation,
CAM. The use of automated manufacturing systems, such as assembly lines, that are partially or
totally controlled by computers.
computer antibody Also called vaccine. A small
subprogram designed to eliminate viruses from
computer systems.
computer-assisted instruction Abbreviation, CAI.
The use of computers as teaching and training
computer code See MACHINE LANGUAGE.
computer consciousness The degree to which a
machine can be considered aware of its own existence. Until recently, this idea was considered
ridiculous. But as microprocessor power continues to grow, some researchers now consider it
worth thinking about.
computer-controlled catalytic converter A microprocessor-controlled system for automatically
supervising gaseous emissions exhausted by a
motor vehicle. An oxygen sensor monitors the exhaust stream, and the associated electronic system adjusts the air-to-fuel ratio of the carburetor
to reduce smog-producing pollutants in the exhaust.
computer diode A semiconductor diode having
low capacitance and fast RECOVERY TIME, thus
suiting it to rapid switching in computer circuits
and to very-high-frequency applications.
computer engineer A person skilled in the theory
and application of computers, related equipment,
and associated mathematics.
computer file See FILE.
computer game See VIDEO GAME.
computer graphics 1. The use of computers to
assist in drawing and drafting, and in the processing of video images such as photographs.
2. Broadly, any computer-generated or computerprocessed image.
computer instruction • condenser microphone
computer instruction See INSTRUCTION.
computer interfacing apparatus The equipment
used to connect a computer to other systems,
and to peripherals.
computerized axial tomography Abbreviation,
CAT. A multiple X-ray system that enables the
observer to obtain cross-sectional images of the
internal organs of the body.
computer map A blueprint, used in conjunction
with machine vision, sonar, radar or beacons,
that a mobile robot can use as a navigational aid.
One or more such blueprints are stored in the
robot controller’s main memory.
computer music 1. Music that is composed by a
computer program See PROGRAM.
computer programmer A person skilled in devising and/or writing the routines that a digital
computer uses to solve problems or process data.
computer storage tube A cathode-ray tube in
which the electron beam scans and stores information in thousands of memory cells on a target.
A cell “remembers” by acquiring and holding an
electrostatic charge when it is struck by the beam
from the writing gun. Information taken is read
out of a cell by a second beam from the reading
computer system A central processor and its associated online and offline peripherals, such as a
monitor, modem, printer, optical scanner, magnetic disk drives, CD-ROM drive, and tape
computer technician A professional skilled in
building, repairing, and maintaining computers,
and who, occasionally, designs them. Usually
works under the supervision of a computer engineer.
computer terminal 1. A teleprinter or video display unit and keyboard, used by human operator(s) of a computer. 2. An interface between a
computer and its human operator(s).
computer/TV interface A device or circuit for delivering the output of a digital computer to a standard television receiver so that the latter can
computer virus A deliberately created and disseminated subprogram or piece of programming code,
that electronically spreads through computer
systems and hinders operation. Usually diverts
the computer(s) from intended functions; sometimes causes a catastrophic malfunction. Often
exists undetected, being transferred from one
computer to another by means of diskettes or
computer word See WORD.
computing amplifier See OPERATIONAL AMPLIFIER.
computing machine See COMPUTER.
concatenation 1. A method of speed control for a
3-phase motor in which two induction motors are
operated with their shafts coupled together. The
stator of the first motor is connected to the 3phase supply, and the slip rings of this motor are
connected to the field of the second motor. The
slip rings of the second motor are connected to
the three ganged sections of a Y-rheostat used for
adjusting the speed. 2. Arrangement of a set into
a series.
concentrated-arc lamp A brilliant low-voltage
lamp, containing nonvaporizing electrodes in an
inert-gas atmosphere. An arc across the electrodes creates the light source.
concentrated winding A coil winding that has a
large number of turns in a small space.
concentration cell An electrolytic cell in which
two electrodes are immersed in solutions of the
same compound but having different combinations. The voltage is usually very small, 0.1 volt or
concentration gradient Between points in a semiconductor, the difference in electron or hole concentration.
concentric cable See COAXIAL CABLE.
concentric capacitor A fixed or variable capacitor
whose plates are concentric cylinders. Also called
concentric-plate capacitor.
concentric jack See COAXIAL JACK.
concentric line See COAXIAL LINE.
concentric-line oscillator A stable, self-excited
oscillator whose frequency-determining tank consists principally of a section of concentric (coaxial) line. Used primarily at ultra-high frequencies
concentric plug See COAXIAL PLUG.
concentric receptacle See COAXIAL RECEPTACLE.
concentric tank See COAXIAL TANK.
concentric-wound coil A combination of two or
more coils wound on top of, and insulated from,
each other.
conceptual modeling A technique for solving
problems by devising a mathematical model
based on the results of an experiment; experiments performed on the model are used to verify
its validity.
concurrent conversion In computer operations,
running conversion and conventional programs
together. Also see CONVERSION PROGRAM.
concurrent processing See MULTIPROGRAMMING.
condenser 1. An obsolete term for CAPACITOR. 2.
A mirror or lens for concentrating light (on an object, for example). 3. Something that condenses a
gas or vapor. 4. See CONDENSER MICROPHONE.
condenser antenna A two-wire horizontal antenna
system in which the radiator is a wire situated
above a counterpoise.
condenser microphone Also called capacitor microphone. A microphone in which a tightly
stretched metal diaphragm forms one plate of an
condenser microphone • conductor
1/2 -Wave
Feed line
condenser antenna
air capacitor, and a closely situated metal plug
forms the other plate. A dc bias voltage is applied
to the arrangement. Impinging sound waves
cause the diaphragm to vibrate, varying the capacitance and causing the output current to fluctuate accordingly.
condensing routine In computer operations, a
program that compresses data. See COMPRESSION, 3.
condensite A plastic insulating material whose
base is phenol formaldehyde resin.
conditional Pertaining to a quantity or phenomenon that depends on some external factor,
and is therefore subject to change.
conditional branch A point in a computer program where a relational test is performed, and
the statement line in which the test is made is left
so that an out-of-sequence instruction can be implemented. Such a branch might be made, for example, following a statement, such as “IF Z = Y
conditional branch instruction The instruction
in a computer program that causes a CONDITIONAL BRANCH.
conditional implication operation A Boolean operation in which the result of operand values X
and Y are such that the output is high only if input X is high and input Y is low. Also called inclusion or if-then operation.
conditional jump See CONDITIONAL BRANCH.
conditional stop instruction In a computer program, an instruction that can cause a halt in the
run, as dictated by some specified condition.
conditional transfer See CONDITIONAL BRANCH.
condition code A set of constraints for a computer
program; sets limits on what can be done with the
computer under certain circumstances.
conditioning 1. The process of making equipment
compatible for use with other equipment. Generally involves some design or installation changes.
2. Interfacing.
Condor A continuous-wave navigational system
that produces a cathode-ray-tube display for automatically determining the bearing and distance
from a ground station.
conductance Symbol, G. Unit, siemens. The ability
of a circuit, conductor, or device to conduct electricity. Conductance in siemens is the reciprocal
of resistance: G = 1/R, where R is the resistance
in ohms.
conducted heat Heat transferred by conduction
through a material substance, as opposed to convection and radiation. A heatsink conducts dissipated energy away from a transistor, whereupon
convection and radiation allow heat to escape
from the sink.
conduction 1. The propagation of energy through
a medium, depending on the medium for its
travel. 2. The transfer of electrons through a wire.
3. The transfer of holes through a P-type semiconductor material. 4. Heat transfer through a
material object (see CONDUCTED HEAT).
conduction angle See ANGLE OF CONDUCTION.
conduction band In the arrangement of energy
levels within an atom, the band in which a free
electron can exist; it is above the valence band in
which electrons are bound to the atom. In a
metallic atom, conduction and valence bands
overlap; but in semiconductors and insulators,
they are separated by an energy gap.
conduction current 1. The electromagnetic-field
flow that occurs in the direction of propagation. A
measure of the ease with which the field is propagated. 2. Current in a wire or other conductor.
conduction-current modulation In a microwave
tube, cyclic variations in the conduction current;
also, the method of producing such modulation.
conduction electron See FREE ELECTRON.
conduction error In a temperature-acutated
transducer, error caused by conduction of heat
between the sensor and the mounting.
conduction field An energy field that exists in the
vicinity of an electric current.
conductive coating A conducting layer applied to
the glass envelope of a cathode-ray tube, such as
an oscilloscope tube or picture tube.
conductive coupling See DIRECT COUPLING.
conductive material See CONDUCTOR.
conductive pattern The pattern of conductive
lines and areas in a printed circuit.
conductivity Unit, S/m (siemens per meter). An
expression of conductance per unit length of a
material; the reciprocal of resistivity.
conductivity meter A device for measuring electrical conductivity. Generally, such a device is
calibrated in siemens.
conductivity modulation In a semiconductor, the
variation in conductivity that results from a variation of charge-carrier density.
conductivity-modulation transistor A transistor
in which the bulk resistivity of the semiconductor
material is modulated by minority carriers.
conductor 1. A material that allows charge carriers (usually electrons) to move with ease among
atoms. Examples are metals, electrolytes, and
ionized gases. Substances vary widely in their
suitability as conductors; the conductivity of
commercial copper, for example, is almost twice
that of aluminum. Compare INSULATOR. 2. An
individual conducting wire in a cable, insulated
or uninsulated.
conduit • conic sections
conduit A hollow tube, made of plastic or metal,
through which wires, cables, and other transmission media are fed.
cone The conical diaphragm of a (usually dynamic)
cone antenna An antenna in which the radiator is
a sheet-metal cone or a conical arrangement of
rods or wires.
Conelrad An early amplitude-modulation (AM)
broadcast protocol, intended for use in the event
of a nuclear war. Now replaced by the EMERGENCY BROADCAST SYSTEM.
cone marker A UHF marker beacon whose conical
energy lobe radiates vertically from a radio-range
beacon station. Aircraft in flight use such markers to accurately locate the beacon station.
cone of protection The zone surrounding a lightning rod, in which the chances of a lightning
strike are greatly reduced. The cone has an apex
angle of 45°, relative to the rod. Objects entirely
within this cone are unlikely to be struck (although it is still possible).
45° 45°
cone of protection
cone of silence A small zero-signal zone directly
over a low-frequency radio-range beacon. The
zone is the product of the combined directive
properties of the beacon transmitting antenna
and the antenna on an aircraft.
cone speaker A loudspeaker having a soundproducing cone (diaphragm) made of specially
treated paper or other material, as opposed to a
loudspeaker having a flat diaphragm.
confetti On a color TV screen, color spots caused
by chrominance-amplifier noise.
confidence The probability that a predicted result
will occur.
confidence factor Confidence, expressed either as
a fraction (between 0 and 1) or as a percentage.
confidence interval The range over which a parameter can vary so that a given confidence factor
is maintained.
confidence level See CONFIDENCE FACTOR.
confidence limitations The maximum and minimum points of a confidence interval. Outside the
confidence-limitation points, the confidence factor drops below the required minimum.
configuration 1. The characteristic arrangement
of components in an electronic assembly, or of
the equipment symbols in the corresponding circuit diagram. 2. Computer system.
configuration state In a computer system, an expression of the availability status of a device for a
given application. A configured-in device is available; a configured-out device is available, but is
restricted to certain users; a configured-off device
is unavailable.
configuration table Within a computer’s operating
system, a table that provides the configuration
state for various system units.
configured-in See CONFIGURATION STATE.
configured-off See CONFIGURATION STATE.
configured-out See CONFIGURATION STATE.
conformance The degree to which a quantity or
variable corresponds to a standard or to expectations.
conformance error The extent (usually expressed
as a percentage) to which conformance is lacking.
conical antenna See CONE ANTENNA.
conical horn A horn (antenna, loudspeaker, or
sound pickup) having the general shape of a
cone: the cross-sectional area varies directly as
the square of the horn’s axial length.
conical monopole antenna An unbalanced broadband antenna that derives its name from its
shape. It is usually constructed from wire and
must be operated against a good radio-frequency
(RF) ground.
Feed point
conical monopole antenna
conical scanning In radar transmission, a method
of scanning in which the beam describes a cone,
at the apex of which is the antenna.
conic sections The geometric plane figures that
result from the intersection of a cone with a
conic sections • constant-current source
program, data items that remain unchanged for
each run.
constant-amplitude recording In sound recording, the technique of holding the maximum amplitude of the signal steady as the frequency
constantan An alloy of copper and nickel used in
some thermocouples and standard resistors.
constantan-platinum thermocouple A thermocouple that uses the junction between constantan and platinum wires, which is contained in
thermocouple-type meters.
constant area As allocated by a computer program, an area of memory that holds constants.
constant bandwidth In a broadband tuned circuit, bandwidth that does not change with frequency.
constant current A current that undergoes no
change in value as it flows through a changing resistance. Compare CONSTANT VOLTAGE.
constant-current characteristic A condition in
which the current through a circuit remains constant—even if the voltage across the circuit increases or decreases.
constant-current curve A graph in which the dependent variable is an electric current that levels
off at, or approaches, a specific maximum. An example is the collector-current versus collectorvoltage curve for a bipolar transistor.
Collector current
plane. These figures are the circle, the ellipse, the
parabola, and the hyperbola.
conjugate For a given complex number A + jB, the
quantity A – jB. When complex conjugates are
multiplied together, the result is A2 + B2.
conjugate branches In a network, two branches of
such a nature that a signal in one has no effect on
the other.
conjugate bridge A bridge in which the detector
and generator occupy positions opposite to those
in a conventional bridge of the same general type.
conjugate impedance For a given complex impedance, R + jX, where R is the resistive component and jX is the reactive component, the
impedance: R – jX. The resistance is identical; the
reactance is of equal magnitude, but opposite
sign (capacitive as opposed to inductive, or vice
conjunction The logical AND operation.
connect To provide an electrical path between two
connection The point at which two conductors are
physically joined.
connective An operation symbol written between
connector 1. A device that provides electrical connection. 2. A fixture (either male or female) attached to a cable or chassis for quickly making
and breaking one or more circuits. 3. A symbol
that connects points on a flowchart.
conoscope A device that uses focused polarized
light to examine crystals (as in checking the optical axis of a quartz crystal).
consequent poles The poles of an equivalent single magnet that is formed when two magnets are
aligned with their two identical poles together.
Thus, when the two north poles are placed together, the consequent poles are a south pole at
each end and a north pole at the center.
conservation of energy 1. The preservation of
the potential for work by a given quantity of energy—even when it undergoes a change in form
within a system. 2. The law of conservation of
energy, which states that energy can be neither
created nor destroyed, but only changed in
console 1. The main station or position for the
control of electronic and/or computer equipment.
2. The equipment at a fixed location. 3. An equipment-containing cabinet that stands on the floor.
4. Equipment permitting communication with a
computer. Also called dumb terminal.
consonance 1. Harmony between audio tones. 2.
Acoustical or electrical resonance between bodies
or circuits that are not physically connected.
constant 1. A quantity whose value remains
fixed, such as the speed of light in a vacuum.
Compare VARIABLE. 2. The value of a component specified for use in a particular electronic
circuit. 3. An electronic component, particularly
a capacitance or inductance. 4. In a computer
Constantcurrent region
Collector voltage
+10 V
constant-current curve
constant-current drive Driving power obtained
from a constant-current source.
modulation See
constant-current power supply See CONSTANTCURRENT SOURCE.
constant-current sink See CURRENT SINK.
constant-current source A power supply whose
current remains steady during variations in
load resistance. Also called constant-current
supply and current-regulated supply. Compare
constant-current supply • contactor noise
supply See
constant-current transformer A transformer supplied from a constant-voltage source that automatically delivers a constant current to a varying
secondary load.
constant-k filter Also called a Zobel filter. A filter
section in which Z1Z2 equals k2 at all frequencies,
where Z1 is the impedance of the series element
and Z2 is the impedance of the shunt element.
constant-power dissipation line A line connecting points on a family of current-voltage characteristic curves, the points corresponding to the
maximum power that can safely be dissipated by
the device to which the curves apply.
constant-resistance network A circuit of resistors
that, when terminated in a resistance load, presents a constant resistance to a driving source
under various conditions of operation.
constant-speed motor 1. Also called a shunt motor. A motor whose speed varies little, or not at all,
with variations in the armature current. 2. A motor that runs at an unvarying speed through the
action of associated automatic electronic control
constant voltage A voltage that does not change
as the load resistance varies. Compare CONSTANT CURRENT.
constant-voltage, constant-current supply A
combination current-regulated and voltageregulated power supply; delivers constant current to low load resistances and constant voltage
to high load resistances.
constant-voltage drive Driving power obtained
constant-voltage source A power supply whose
output voltage remains steady during variations
in load current. Also called constant-voltage supply and voltage-regulated supply.
constant-voltage transformer A special transformer used to reduce variations in power-line
voltage. A capacitor in the device causes a winding
to resonate at the line frequency (e.g., 60 Hz). This
tends to maintain a more constant current than
would be the case in an ordinary transformer.
construct A source (user’s) computer program
statement that, when implemented, produces a
predetermined effect.
consumer reliability risk 1. The chance a consumer takes when buying a component or piece
of equipment that has not been subjected to
quality-assurance/quality-control (QA/QC) testing. 2. An expression of the failure rate for a consumer item.
contact 1. A conducting body (such as a button,
disk, or blade) that serves to close an electric circuit when pressed against another conductor.
Example: switch contact and spring contact. 2.
The state of being touched together, as when two
conductors are brought into contact to close a
contact arc The arc that initially occurs when
current-carrying contacts are separated.
contact area 1. The face of an electrical contact.
2. The common area shared by two conductors in
mutual contact.
contact bounce The springing apart or vibration of
contacts upon making or breaking.
contact chatter The abnormal vibration of mating
contacts, caused by contact bounce or by an extraneous alternating current.
contact-closure input The input circuit of a device, such as a control-system amplifier, that is
actuated by the closing of switching contacts.
contact combination The set of contacts on a
switch or electronic relay.
contact detector A rectifier or demodulator, composed of two dissimilar materials in contact with
each other. Semiconductor diodes are of this general type. Some contact-detector action can be
obtained with two dissimilar fine wires (such as
copper and iron) by touching their tips lightly together.
contact EMF Short for contact electromotive force;
also called contact potential. A low direct-current
(dc) voltage that is sometimes generated by the
contact of two dissimilar materials.
contact follow The tendency of relay contacts to
follow the actuating signals.
contact force 1. The force with which relay contacts close with a given amount of coil current. 2.
The force with which a pair of relay contacts are
held together when current flows through the
coil. 3. In a mercury-wetted relay, the force exerted by the mercury on the contacts as the relay
contact gap The distance between contacts when
they are open.
contact load 1. The power dissipated by a load
that is connected to a power supply through a
closed set of contacts. 2. The current passing
through a set of closed contacts.
contact microphone A microphone placed in direct contact with a vibrating surface for pickup.
Actuated by the vibration of a solid, rather than
by the movement of air molecules.
contact miss 1. The improper alignment of contacts in a switch or relay. 2. The condition of relay contacts not lining up properly.
contact modulator An electromechanical CHOPPER.
contact-open input The input circuit of a device,
such as a control-system amplifier, that is actuated by the opening of switching contacts. Compare CONTACT-CLOSURE INPUT.
contactor A switch used for frequent opening or
closing of a circuit. An example is a relay contactor used for keying a transmitter.
contactor noise 1. Electrical noise that is the
product of make-and-break contact action or
fluctuations in conduction when the contacts are
contactor noise • Continuous Commercial Service
Fixed coil
Object carrying
sound disturbance
contact microphone
closed. 2. Sounds coming directly from contacts
that are opening and closing.
contact potential The small direct-current (dc)
voltage that results from the bombardment of an
electrode by electrons, when the electrode has no
external voltage applied to it.
contact pressure The pressure that holds contacts together.
contact protector A component (such as a diode,
capacitor, resistor, or combination of these) that
serves to suppress contact arcing.
contact rating The maximum current, voltage,
and/or power specified for a given set of contacts.
contact rectifier A rectifier consisting of two dissimilar materials in direct contact. Examples:
copper and copper oxide, magnesium and copper
sulfide, selenium and aluminum, and germanium and indium.
contact resistance The resistance of the closed
contacts of switches, relays, and other similar devices. Normally, this is a very small resistance.
contact separation See CONTACT GAP.
contact strip See TERMINAL STRIP.
contact switch An electromechanical switch that
uses contacts to make and break a circuit, as
compared with an electronic switch that uses
semiconductor devices.
contact travel The distance over which a relay or
switch contact must move to close a circuit.
contact wetting The use of mercury (a conducting
liquid) to improve the action of a relay contact or
contact wipe A sliding motion between closed contacts. Helps to establish a good connection and to
keep the contact surfaces clean.
container file See CONTROLLING FILE.
contaminated material 1. A semiconductor material containing some undesired substance. 2. A
material unintentionally made radioactive.
contamination 1. The presence of an impurity in a
substance. 2. The addition of a radioactive material to a substance. 3. In a coaxial cable, the tendency for the jacket material to bleed through the
outer braid into the dielectric, resulting in increased loss.
content-addressed storage In a computer, memory- or data-storage locations identified by content (see CONTENTS), instead of by address. Also
called associative storage.
contention The result of interference among more
than one transmitting station on the same communications channel.
contents 1. The data in a computer randomaccess memory (RAM). 2. The data in a specific
storage location, such as on a hard disk, diskette,
or CD-ROM.
context 1. The environment in which a word is
used in a natural language (such as English,
Spanish, or Russian). Important in speech
recognition and speech synthesis. 2. The environment in which a string of characters, composing a data unit or word, is used in a
computer program.
Continental code A version of the Morse code
used internationally in radiotelegraphy. Also
called International Morse code and general service code. Compare AMERICAN MORSE CODE.
continuity A condition of being uninterrupted—
especially pertaining to current flowing in an
electrical or electronic circuit.
continuity test A test of the completeness of an
electrical path. Ideally, the only concern is
whether the circuit is open or closed, but sometimes circuit resistance is also of interest.
continuity tester A device (such as an ohmmeter,
battery and buzzer, and battery and lamp) with
which a continuity test can be made.
continuity writer The person who prepares copy
for a radio or television broadcaster.
continuous carrier A medium (such as a radiofrequency wave) that will convey information (as
when the carrier is modulated) with no disruption
of the medium itself.
continuous circuit An uninterrupted circuit.
Continuous Commercial Service Abbreviation,
CCS. A category in which safe operating parameters are listed for electronic components and
communications equipment operated over long,
uninterrupted periods. Compare INTERMITTENT
continuous duty • contrast
– •– •
– ••
••– •
– •–
•– ••
•–– •
–– •–
•– •
– ••–
– •––
–– ••
Break (pause)
– ••••
–– •••
––– ••
•– •– •–
–– ••––
••–– ••
– ••– •
– ••••–
– •••–
– •– •– •
––– •••
Continental code
Test probe
continuity tester
continuous duty The requirement of a device to
sustain a 100-percent duty cycle for a prolonged
period of time.
continuous-duty rating A maximum current, voltage, or power rating for equipment operated for
extended periods at a 100-percent duty cycle.
continuous load A load that requires a continuous
feed for a prolonged period of time.
continuous memory See NONVOLATILE MEMORY.
continuous-path motion In robotics, machine
movement that occurs in a smooth fashion,
rather than in discrete steps. Allows precise positioning of a mechanical arm or gripper.
continuous power The maximum sine-wave power
that an amplifier can deliver for 30 seconds.
continuous recorder An instrument that provides
an uninterrupted recording.
continuous recording A record made on a continuous sheet or tape, instead of on separate sheets
or tapes. An example is a continuous-playing
tape used for repeated public announcements.
continuous spectrum 1. The range of all electromagnetic frequencies between a specified lower
limit f1 and a specified upper limit f2. 2. A range
of electromagnetic frequencies that exhibits similar behavior between its lower and upper limits.
continuous stationery Also called fanfold paper.
The pack of paper a line printer uses. It consists
of sheets connected by perforated or tear-off
edges, folded in accordion fashion. It usually has
tear-off perforated strips along either side to facilitate feed through the printer mechanism.
continuous variable A variable that can attain any
value within a specific range of values. An example is a frequency within the 75- to 80-meter amateur radio band, from 3.5 to 4.0 MHz.
continuous wave Abbreviation, CW. 1. A periodic
wave, such as a radio-frequency (RF) carrier, that
is not interrupted at any point between its normal
start and termination, and that is unmodulated.
2. An RF carrier that is interrupted digitally with
a keying device according to some code (such as
Morse), for the purpose of conveying information.
continuous-wave laser See CW LASER.
continuous-wave radar See CW RADAR.
contour A control on an audio reproduction system that increases the base and treble amplitudes at low levels to compensate for the ear’s
natural losses in these ranges. Alternatively, this
control can attenuate signals in the 3-kHz region,
where the human ear is most sensitive.
contours of equal loudness See AUDIBILITY
CONTRAN A computer language that requires no
compiler, or translating, interface between the
operator and the machine. The programming is
done in a language similar to machine language.
contrast 1. In a video image, the degree to which
adjacent areas of a picture are differentiated. Insufficient contrast makes for a “flat” picture; ex-
contrast • controlling file
Output level
cessive contrast, a “hard” picture. 2. In optical
character recognition, the degree to which a character is distinguishable from its background.
contrast control A potentiometer for adjusting the
gain of the video in a television receiver or cathode-ray-tube (CRT) computer display and, accordingly, the image contrast.
contrast range In an image or pattern, the brightness range from the lightest to the darkest parts.
contrast ratio In a video image, the ratio of maximum to minimum luminance.
control 1. An adjustable component, such as a
rheostat, potentiometer, variable capacitor, or
variable inductor, that allows some quantity to be
varied at will. 2. A test or experiment conducted
simultaneously with another similar test conducted under conditions lacking the factor under
consideration. Thus, if 100 resistors coated with
a special varnish are tested at 120°F, 100 identical unvarnished resistors could be tested (as a
control) under the same conditions; in this way,
the effect of the varnish would be ascertainable.
3. As a computer function, understanding and
implementing instructions or carrying out tasks,
according to specific conditions.
control ampere-turns The ampere-turns of the
control winding in a magnetic amplifier.
control block A storage block for control information in a computer.
control bus In a digital computer, the electrical
conductors linking the central-processing-unit
(CPU) control register to the memory circuits.
control card A card that provides control information for a computer.
control character A character (bit group) used to
start the control of a peripheral.
control characteristic A representation (such as a
collector-current versus collector-voltage curve)
depicting the extent to which the value of one
quantity affects or controls the value of another.
control circuit 1. A circuit in which one signal or
process is made to control another signal or pro-
cess. 2. In a digital computer, a circuit that handles and interprets instructions and commands,
particularly in the arithmetic and logic unit
control computer A computer that receives signals concerning the parameters in some process,
and responds with signals that control those parameters.
control counter See CONTROL REGISTER.
control data 1. In a computer record having a key,
information used to put the records in some sequence. 2. Information affecting a routine’s selection or modification.
control electrode An electrode to which an input
signal can be applied to control an output signal.
Common examples are the base of a bipolar transistor, the gate of a field-effect transistor, and the
inputs of a logic gate.
control field 1. In direct-current generators of the
amplifying type, an auxiliary field winding used
for feedback and regulation, in contrast to the
self-excited field winding (which is the conventional field winding of the generator). 2. A computer record field containing control data.
control flux In an amplidyne, magnetic flux generated by current flowing through the control winding.
control grid See GRID, 1.
control-grid bias The negative dc voltage applied
between ground and the control grid of a vacuum
tube to establish the operating point.
control language Within the operating system of a
computer, the command set that the operator or
programmer uses to control the running of a program or the operation of peripherals. Also called
job control language or system control language.
control language interpreter See CONTROL LANGUAGE and INTERPRETER.
controlled avalanche diode Also called avalanche
diode or Zener diode. A diode that has a welldefined avalanche voltage. Used primarily for
voltage regulation in power supplies.
controlled-carrier modulation See QUIESCENT
controlled-carrier transmission See QUIESCENT
controlled rectifier A rectifier whose dc output
can be varied by adjusting the voltage or phase of
a signal applied to the control element. See
controller 1. The control signal of an electronic
control (or servo), system. 2. A device, such as a
specialized variable resistor, used to adjust current or voltage. 3. A computer that oversees and
controls the operation of a robot or fleet of robots.
controller function The control of the movements
of a servo system.
controlling file A computer storage area encompassing several complete magnetic disk cylinders; its size can be changed to accommodate a
number of files.
control loop • convergence magnet
Air currents
Air currents
convection current 1. The motion of current carriers or a charge across the surface of a conductor or dielectric. 2. Air currents rising above a
heat source or heated body.
convective discharge The continuous highvoltage current discharge across a spark gap.
convectron A device that indicates the angle, with
respect to the vertical, based on convection cooling of a straight wire. The temperature difference
is greatest when the angle is 0 degrees (the wire is
vertical); the temperature difference decreases as
the angle increases, reaching a minimum at 90
degrees (when the wire is horizontal).
convenience outlet 1. In North America, a wall
outlet providing a nominal 117 volts alternating
current (ac) at 60 Hz for common household appliances. 2. An outlet in a laboratory that provides power for a certain application.
conventional current The notion that current
flows from the positive pole to the negative pole in
an electric circuit. This representation is used
most often by physicists. Electron flow is opposite
to conventional current flow; positively charged
particles, such as holes, move in the same direction as the conventional current.
convergence 1. The eventual meeting of values or
bodies at some point (sometimes at infinity, as in
certain mathematical series). 2. The intersection
point of the beams from separate electron guns in
a cathode-ray tube (CRT).
convergence coil One of a pair of coils used in a
color television receiver to produce dynamic beam
convergence (see CONVERGENCE, 2).
convergence control In a color television receiver,
a potentiometer in the high-voltage circuit for convergence adjustment (see CONVERGENCE, 2).
convergence electrode An electrode that provides
an electrostatic field for converging electron
convergence frequency The frequency of the last
member of a spectrum series.
convergence magnet An assembly that provides a
magnetic field to converge electron beams. Compare CONVERGENCE ELECTRODE.
control loop See CONTROL TAPE.
control mark See TAPE MARK.
control panel 1. An accessible surface on which are
mounted switches, buttons, potentiometers, meters, digital indicators, monitoring devices, and
other apparatus essential to regulating and supervising an electronic system. 2. The console that a
computer operator or programmer uses to communicate with the central processing unit (CPU).
control plate The metallic plate or disk that serves
as the antenna of a CAPACITANCE RELAY or
control program A program that arranges computer-operation programs in a certain order. Puts
information in the computer memory for later
control rectifier A semiconductor diode device,
used for the purpose of switching large currents.
A small control signal can provide switching of
high-power devices.
control register In a computer, the register that
stores the address of the next instruction in the
program being run.
control sequence The order in which instructions
are executed in a digital computer.
control stack In a computer system, a unit of
hardware having storage locations and used to
perform arithmetic, assist in allocating memory
to programs, and to control internal processes.
control statement In a programming language, an
instruction that causes some action to be taken,
as specified by a condition; it is also applicable to
source program statements that affect the compiler’s operation without modifying the machine
control tape Punched paper or plastic tape in the
form of a closed loop and used to control printing
devices. Also called control loop.
control total For a file or record group, a total derived during an operation; it is used to verify that
all the records have been processed similarly.
control transfer The situation in which the control
unit of a digital computer leaves the main sequence of instructions and takes its next instruction from an out-of-sequence address.
control transfer instruction See BRANCH INSTRUCTION.
control-voltage winding In a servomotor, the
winding that receives a varying voltage of a phase
different from that applied to the fixed-voltage
control winding In a magnetic amplifier, the winding that conducts the control-signal current.
control word A word (a bit group) stored in a computer memory and used for a control function.
convection The flow of a gas or liquid that results in
the transfer of heat from one location to another.
convection cooling The removal of excess heat
from a component, such as a power vacuum tube
or transistor, via upward movement of surrounding air that has been heated by the component.
convergence phase control • coordinates
convergence phase control In a three-gun color
picture tube, a variable resistor or variable inductor used to adjust the phase of the dynamic convergence voltage.
convergence plane 1. In a color picture tube, the
plane in which the red, green, and blue beams all
focus. 2. In a cathode-ray tube, the plane in
which the electron beam reaches its sharpest focus.
convergent series A mathematical series that approaches a specific, finite numerical value as the
number of terms increases. Thus, the series 0.3 +
0.03 + 0.003 + . . . approaches a limiting value of
converging lens A lens having a real focus for parallel rays; generally a convex lens.
conversational compiler In computer operations,
a compiler that, using the CONVERSATIONAL
MODE of operation, shows the programmer
whether or not each statement entered into the
computer is valid, and whether or not to proceed
with the next instruction.
conversational mode High-level computer operation or programming, in which the computer
gives responses to the operator’s input.
conversion 1. The deliberate mixing of radiofrequency (RF) signals to produce signals at the
sum and/or difference frequencies. 2. The process of changing direct current (dc) to alternating
current (ac). 3. The process of changing low-voltage dc to high-voltage dc. 4. The changing of a
computer file to another format and, possibly,
transferring it to a different storage medium (e.g.,
from tape to internal memory). 5. The processing
of a program or file written for one computer or
application into a form suitable for another computer or application.
conversion efficiency In a converter (see CONVERTER, 1), the ratio of output-signal amplitude to input-signal amplitude. For example, in
a superheterodyne converter, a large intermediate-frequency (IF) output for a low radiofrequency (RF) input indicates high conversion
conversion equipment In a computer system, an
offline device for transferring data from one
medium to another [e.g., a disk-to-tape converter
(tape drive)]. Also called CONVERTER.
conversion exciter An exciter for transmitters, in
which an output signal of a desired frequency is
obtained by beating the output of a variablefrequency self-excited oscillator with the output
of a fixed-frequency oscillator (such as a crystal
conversion gain Amplification as a byproduct of
conversion loss Conversion gain of less than 1.
conversion program In computer operations, a
program for data conversion (see CONVERSION,
4 and 5).
conversion rate Also called sampling rate. The
number of samples per second taken by an
conversion time In digital computer operation,
the time required for the machine to read out all
the digits in a coded word.
conversion transconductance See CONVERSION
convert 1. To perform frequency conversion (see
CONVERSION, 1). 2. To perform voltage conversion (see CONVERSION, 2 and 3). 3. In computer
operations, to change information from one number base to another. 4. To perform data conversion (see CONVERSION, 4 and 5).
converter 1. A heterodyne mixer in which two input signals of different frequency are mixed to
yield a third (output) signal of yet a different frequency. 2. A machine for converting direct current (dc) to alternating current (ac) (e.g., a
chopper converter). 3. A transistor circuit for converting a low-voltage dc to higher-voltage dc. 4.
Conversion equipment. 5. A circuit or device that
changes analog data to digital data or vice versa.
converter amplifier See CHOPPER AMPLIFIER.
converter stage A circuit used principally to mix
two signals (such as a received signal and localoscillator signal in a superheterodyne receiver),
and deliver the resultant signal.
convexo-concave Pertaining to a lens having a
convex face of greater curvature than its concave
coolant A liquid (often water or oil) used to remove
heat from an electronic component.
Coolidge X-ray tube An X-ray tube containing a
heated filament (with focusing shield) and a
slanting tungsten target embedded in a heavy
copper anode.
cooling Maintenance of the operating temperature
of an electronic component or system at a safe
level. Common devices for cooling are heatsinks,
circulating or forced air, and circulating liquid.
coordinate bond A covalent bond that consists of
a pair of electrons supplied by only one of the
atoms joined by the bond.
Coordinated Universal Time Abbreviation, UTC.
Astronomical time at the Greenwich meridian
(zero degrees longitude). The UTC day begins at
0000 hours and ends at 2400 hours. Based on
the mean, or average, synodic (sun-based) rotational period of the earth. The earth is slightly behind UTC near June 1, and is slightly ahead near
October 1.
coordinate digitizer A device or circuit that encodes a coordinate graph into digital signals for
storage or transmission.
coordinate of chromaticity See CHROMATICITY
coordinates A set of axes with points that can be
uniquely defined or located on a line, in a plane,
or in space. See CARTESIAN COORDINATES and
coordinate system • cordless modem
coordinate system A mathematical means of
uniquely defining or locating a point on a line, in
a plane, or in space. The most common coordinates are CARTESIAN COORDINATES (also
called rectangular coordinates), consisting of
numbered lines intersecting at right angles.
coordinate system
coordination complex An ion or compound having a central (usually metallic) ion combined by
coordinate bonds with a definite number of surrounding groups, ions, or molecules.
coplanar array A set of antennas that lie in the
same plane, and are fed by a common transmission line.
copper Symbol, Cu. A metallic element. Atomic
number, 29. Atomic weight, 63.546. An excellent
conductor of electricity and heat, commonly used
in the manufacture of wires and cables.
copper-clad wire Iron or steel wire plated with
copper-constantan thermocouple A thermocouple consisting of a junction between wires or
strips of copper and constantan. Typical output
is 4.24 mV at 100°C.
copper loss Power (I 2R) loss in copper wires, cables, and/or coils.
copper-oxide diode A small diode in which the
semiconductor material is copper oxide. Such
diodes, widely used before the ready availability
of selenium and silicon, are still occasionally
found in meter-rectifier service.
copper-oxide modulator An amplitude modulator
whose action is derived from the nonlinear conduction characteristic of copper-oxide diodes.
copper-oxide photocell A photoelectric cell in
which the light-sensitive material is copper oxide.
copper-oxide rectifier A rectifier in which the
semiconductor material is copper oxide. Rectifiers of this type are suitable for low-voltage ser-
vice; they were widely used before the advent of
germanium, silicon, and selenium rectifiers.
copper pyrites See CHALCOPYRITE.
copper-sulfide rectifier A rectifier in which the
unilateral junction is between copper-sulfide and
magnesium elements. Like the copper-oxide rectifier, the copper-sulfide unit was once widely
used in low-voltage applications.
copy 1. Also called hard copy. Printed or written
text. 2. In communications, a qualitative expression of the extent to which received data is intelligible (e.g., a radio operator’s signal report, “You
are solid (perfect) copy.”). 3. To duplicate data in
a storage system, the original being in another
system, or in a different location in the same
system. 4. An exact duplicate of data in any
copying telegraph A descriptive term for a facsimile system.
Corbino disk A variable resistor consisting of a
semiconductor disk capable of exhibiting the
CORBINO EFFECT. The disk is inserted into an
adjustable magnetic field, which serves as the
control medium.
Corbino effect A phenomenon similar to the HALL
EFFECT, in which a current flows around a disk
carrying a radial current when the disk is inserted into a magnetic field whose lines of flux are
perpendicular to the disk. Compare HALL EFFECT.
Corbino effect
cord 1. A length of flexible, insulated cable, usually
having two or three conductors. 2. Tough, insulating string (e.g., dial cord or lacing cord).
cordless 1. Descriptive of a plug without a flexible
cord. 2. Pertaining to radio-frequency (RF) or infrared short-range links for communications and
control (e.g., a cordless telephone set).
cordless keyboard A computer keyboard that employs an infrared (IR), very-high frequency (VHF),
or ultra-high-frequency (UHF) transmitter and receiver. Commonly used with so-called Web TV
systems and in presentations using a display projection system. Operates according to the same
electronic scheme as a CORDLESS MOUSE.
cordless modem See WIRELESS MODEM, 3.
cordless mouse • corner reflector
cordless mouse A hand-controlled computer
mouse that employs an infrared (IR), a very-high
frequency (VHF), or an ultra-high-frequency
(UHF) transmitter and receiver. The transmitter
is inside the device, and the receiver is contained
either inside the computer main unit, or in a
small box attached to the computer main unit by
a cord. The box can be placed somewhere out of
the way; for example, at the back of the desk.
Then the mouse can be moved around freely. This
link is effective at distances of up to 20 or 30 feet.
cordwood A type of construction in which electronic components are sandwiched perpendicularly between layers of components. So called
because it looks somewhat like stacked cordwood.
cordwood module A module containing discrete
components mounted perpendicularly between
two parallel printed circuits.
core 1. The body or form on which a coil or transformer is wound. Can be made of ferromagnetic
or dielectric material. The properties depend on
the application. 2. CORE MEMORY.
core dump Dumping core memory content to an
output peripheral. Also see DUMP.
coreless induction heater An induction heater in
which the body to be heated receives energy directly from the field of the energizing coil (there is
no intervening core). Compare CORE-TYPE INDUCTION HEATER.
core loss Loss of energy in a magnetic core, caused
by eddy currents and hysteresis in the core material.
core memory An older memory technology, consisting of a series of small ringshaped magnetic
cores, into or out of which data can be written or
read by changing the magnetization of the cores.
core plane A usually flat assembly of special magnetic cores, through which pass associated
current-conducting wires to provide a CORE
core saturation The condition in which a core of
magnetic material accommodates the maximum
number of magnetic lines characteristic of that
material. Increasing the magnetizing force produces no additional magnetization.
core shift register A shift register that uses special magnetic cores as bistable components. See
core storage A high-speed magnetic core storage
unit. Also see CORE MEMORY and CORE PLANE.
core transformer A transformer whose coils are
wound around a ferromagnetic core.
core wrapping The placing of an insulating layer
over an inductor or transformer core. This minimizes the chances of short-circuiting between the
windings and the core material.
core-type induction heater An induction heater
in which the body to be heated is magnetically
linked, by a core, to the energizing coil. Compare
corner 1. An abrupt turn in the axis of a waveguide. 2. The line, and the region in the vicinity
thereof, at which two intersecting plane surfaces
meet (e.g., the reflector screen of a CORNERREFLECTION ANTENNA). The plane surfaces are
usually perpendicular to each other. 3. The point,
and the region in the vicinity thereof, at which
three intersecting plane surfaces meet. Generally,
the plane surfaces are mutually perpendicular. 4.
The passband frequency limit(s) of a bandpass,
band-rejection, high-pass, or low-pass filter. 5. A
sharp bend in the attenuation-versus-frequency
curve of a bandpass, band-rejection, high-pass,
or low-pass filter, depicting the limit(s) of the
corner diffraction 1. The bending of sound waves
around a corner. 2. The bending of radiofrequency (RF) energy around an object, when the
wavelength is great, compared with the size of the
corner effect A rounding off of the frequency response of a filter at the corner(s) [i.e., at the
limit(s) of the passband].
corner frequency See CORNER, 4.
corner reflection The reflection of a beam of light
(or of microwave energy or other short-wavelength energy) from a corner reflector, so the
beam leaves the reflector in exactly the opposite
direction from which it approaches. See CORNER
corner-reflection antenna A directional antenna
consisting of a dipole radiator situated at the
apex formed by two nonparallel, flat reflecting
sheets or a single folded sheet. See CORNER REFLECTOR, 1.
corner reflector 1. An antenna with a half-wave
driven element and a reflector made of wire mesh,
screen, or sheet metal that resembles an open
folder. The flare angle of the reflecting element is
about 90 degrees. The antenna is used at ultra-
corner reflector • corrosion-resistant
corner reflector, 2
high and microwave frequencies for television reception and satellite communications. Sometimes several half-wave dipoles are fed in phase
and arranged along a common line with a single,
elongated reflector. 2. Also called tricorner reflector. A set of three flat metal surfaces or screens,
attached together in a manner identical to the
way two walls meet the floor or ceiling in a room.
Such a device, if it is at least several wavelengths
across, returns electromagnetic energy in exactly
the same direction from which it arrives. Devices
of this type are used as radar dummy targets and
in optical and infrared (IR) wireless ranging
corona A luminous discharge in the space surrounding a high-voltage conductor; caused by
ionization of the air. The discharge constitutes a
loss of energy.
corona effect The production of a luminous discharge, especially at the end of a pointed terminal, when the voltage gradient reaches a critical
corona failure A form of high-voltage failure, resulting from the erosion of an object (such as an
electrical insulator) by corona.
corona loss Loss caused by energy dissipation
through a corona. It occurs as a result of the
emission of electrons from the surface of electrical conductors at high potentials, and depends
on the curvature of the conductor surface, with
most emission occurring from sharp points and
the least from surfaces with a large radius of curvature. It is often accompanied by a blue glow
and a crackling or hissing sound.
corona resistance The length of time that an insulating material can withstand a specified level of
field-intensified ionization before completely
breaking down.
corona shield A shield surrounding a high-voltage
point to prevent corona by redistributing the electric flux.
corona starting voltage The minimum voltage between two electrodes, or on a single electrode in
free space, at which corona occurs.
corona voltmeter A voltmeter used to measure the
peak value of a voltage in terms of corona discharge. It consists of a metal tube in which a central wire is mounted, the parts being connected to
the voltage source. The air density in the tube is
varied until corona occurs.
corpuscle A tiny particle. It was the name given to
the ELECTRON by some early experimenters and
correction 1. The addition of a factor that provides
greater accuracy in a measurement. 2. A change
in the calibration of an instrument to increase the
correction factor A percentage, or numerical factor, added to or subtracted from a reading to provide a greater degree of accuracy. Often used with
instruments known to be inaccurate by a certain
corrective feedback Feedback that is used to correct (bring to a prescribed level) a quantity constituting the input to a system.
corrective maintenance The repair of a circuit or
system after it has malfunctioned or broken
corrective network A network that improves the
performance of the circuit into which it is inserted.
corrective stub A combination tuning-matching
stub used in some antenna systems. It matches
the resistive component of the antenna impedance to the characteristic impedance of a feed
line, and also eliminates any reactance that
might be present at the antenna feed point.
correed relay A sealed reed relay used as a highspeed switching device in communications equipment.
correlation A statistical expression or measure of
the degree to which two sets of data are related.
Can be given qualitatively (high-positive, lowpositive, zero, low-negative, or high-negative) or
quantitatively (as a number between –1 and 1).
Does not necessarily imply causation.
correlation detector A detector that compares a
signal of interest with a standard signal at every
point, delivering an output that is proportional to
the correspondence between the two signals.
correlation distance The smallest distance between
two antennas that results in fading of signals under conditions of tropospheric propagation. It is
used at very-high frequencies (VHF) and above, to
determine the maximum range over which communications can be carried out reliably.
correlation tracking A method of target tracking
in which phase relationships are used to determine positions.
correspondence The ability of a binocular machine vision system to tell when both of its optical
sensors are processing an image from the same
object; also, the ability of the system to keep both
sensors tracking the same object.
corrosion-resistant Pertaining to materials that
are treated to be immune to corrosion by the elements. Such substances are preferable for use in
marine or tropical environments, where corrosion
is especially severe.
corruption • counterpoise
corruption The altering of data or a code as a result of a program error or machine fault.
cosecant Abbreviation, csc. A trigonometric function; csc q = c/a, where c is the hypotenuse of a
right triangle and a is the side opposite q. The
cosecant is the reciprocal of sine: csc q = 1/sin q.
cosecant-squared antenna A radar antenna that
cosecant-squared beam A radar beam whose intensity varies directly with the square of the cosecant of the angle of elevation.
cosech Abbreviation of HYPERBOLIC COSECANT.
Also abbreviated as csch.
cosh Abbreviation of HYPERBOLIC COSINE.
cosine Abbreviation, cos. A trigonometric function;
cos q = b/c, where b is the side adjacent to q and
c is the hypotenuse of the right triangle.
cosine law The brightness in any direction from a
perfectly diffusing surface is proportional to the
cosine of the angle between the direction vector
and a vector perpendicular to the surface.
cosine wave A periodic wave that follows the cosine of the phase angle. It has a shape identical
with a SINE WAVE, but differs by 90 degrees of
cosine yoke A magnetic-deflection yoke that has
nonuniform windings for improved focus at the
edges of a television picture. Also called anastigmatic yoke and full-focus yoke.
cosmic noise Radio noise produced by signals
from extraterrestrial space.
cosmic rays Extremely penetrating rays consisting
of streams of atomic nuclei entering the earth’s
atmosphere from outer space.
COS/MOS IC An integrated circuit (IC), such as an
operational amplifier, utilizing metal-oxide-semiconductor (MOS) field-effect transistors in a complementary-symmetry (COS) arrangement.
cost analysis In a commercial or industrial organization, ascertaining the expense associated with
a service, process, or job.
cot Abbreviation of COTANGENT.
cotangent Abbreviation, cot. A trigonometric function; cot q = b/a, where a is the side adjacent to q
and b is the side opposite q (in a right triangle).
Cotangent is the reciprocal of tangent: cot q =
1/tan q.
coth Abbreviation of HYPERBOLIC COTANGENT.
Cottrell process Dust precipitated by high voltage.
Dust in the air is made to flow through a
grounded metal chamber that contains a wire
maintained at high voltage. The dust particles become charged and adhere to the chamber walls,
from which they are later collected.
coul-cell A coulometer of the electrolytic-cell type.
coulomb (Charles Augustin Coulomb, 1736–
1806). Abbreviation, C. The unit of electrical
charge quantity, equal to the charge contained in
6.24 × 1018 electrons. A current of one ampere
(1 A) represents 1 coulomb per second (C/s).
Coulomb’s law The force between two electrically
charged objects is directly proportional to the
product of the charge quantities in coulombs,
and inversely proportional to the square of the
distance between the charge centers. This force is
an attraction for opposite charges, and a repulsion for similar charges.
coulometer An instrument that measures electrical charge quantity in coulombs. A typical version
keeps a cumulative count of coulombs (ampereseconds) by integrating current, with respect to
time. Also called coulombmeter.
Coulter counter See CELL COUNTER.
count 1. The number of pulses tallied by a counting system in a given period of time. 2. A single
response by a radioactivity counter. 3. A record of
the number of times an instruction or subroutine
in a computer program is executed (by increasing
the value of a variable by one, as stated in a FORNEXT loop, for example).
countdown A decreasing count of time units remaining before an event or operation occurs
showing time elapsed and time remaining.
counter 1. A circuit, such as a cascade of flipflops, that tracks the number of pulses applied to
it and usually displays the total number of
pulses. 2. A mechanism, such as an electromechanical indicator, that tracks the number of impulses applied to it and displays the total. 3. An
electronic switching circuit, such as a flip-flop or
stepping circuit, that responds to sequential input pulses applied to it, giving one output pulse
after receiving a certain number of input pulses.
counter- Prefix meaning “opposite to” or “contrary
to.” Examples: counter EMF, counterclockwise.
counterclockwise Abbreviation, ccw. Pertaining to
rotational motion in a sense opposite that of a
typical analog clock. Movement is to the left at the
top of the rotational circle, and to the right at the
bottom of the circle. Compare CLOCKWISE.
counterclockwise-polarized wave An elliptically
polarized electromagnetic wave whose electricintensity vector rotates counterclockwise as observed from the point of propagation. Compare
counter efficiency The sensitivity of a radiation
counter or scintillation counter to incident X-rays
or gamma rays.
counterelectromotive cell A cell used to counteract a direct-current voltage.
counter-meter A radioactivity instrument, such as
a Geiger counter, that indicates the number of radioactive particles per unit time.
counterpoise A means of obtaining a radiofrequency (RF) ground by using a grid of wires or
tubing in a plane parallel to the earth’s surface or
counterpoise • CPU
to average terrain. The radius of the grid is usually at least 0.25 wavelength, but might be
smaller if the feed-point impedance of the antenna is very high.
counterpoise ground system A counterpoise with
a radius such that resonance is obtained with a
quarter-wavelength antenna operated at a height
of more than 0.25 wavelength above actual
ground. Usually such a system consists of three
or four radials measuring 0.25 wavelength each,
and extending outward from the base of the antenna nearly parallel to the average terrain.
ground system
counter tube A tube, such as the Geiger-Meuller
tube, in which a penetrating radioactive particle
ionizes a gas and produces an output pulse.
counter voltage See BACK VOLTAGE and KICKBACK.
counting-type frequency meter A direct-reading
analog or digital frequency meter that indicates
the number of pulses (or cycles) per second applied to it.
count-remaining technique See COMPLEMENTSETTING TECHNIQUE.
couple Two dissimilar metals in contact with each
other or immersed in an electrolyte.
coupled circuits Circuits between which energy is
transferred electrostatically, electromagnetically,
by some combination of the two, or by direct connection.
coupled impedance The impedance that a circuit
“sees” when it is coupled to another circuit. Thus,
when the secondary of a transformer is terminated with an impedance, the primary “sees” a
combination of that impedance and its own.
coupler A device for transferring energy between
two circuits and using capacitive coupling, direct
coupling, inductive coupling, or some combination of these.
coupling 1. Also called electrostatic coupling or capacitive coupling. The linking of two circuits or de-
vices by electric flux. 2. Also called magnetic coupling or inductive coupling. The linking of two circuits or devices by magnetic flux. 3. Also called
direct coupling. The linking of two circuits or devices by direct connection. 4. Also called resistive
coupling. The linking of two circuits or devices
through a resistance. 5. Also called optical coupling. The linking of two circuits or devices
through an optoisolator.
coupling aperture A hole in a waveguide that is
used to transmit energy to the waveguide, or receiving energy from outside the waveguide.
coupling capacitor A capacitor used to conduct ac
energy from one circuit to another. Also see CAPACITIVE COUPLING.
coupling coefficient See COEFFICIENT OF COUPLING.
coupling diode A semiconductor diode connected
between the stages of a direct-coupled amplifier.
When the diode is connected in the correct polarity, it acts as a high resistance between stages
when there is no signal, and does not pass the
high dc operating voltage from one stage to the
next. When a signal is present, the diode resistance decreases, and the signal gets through.
coupling efficiency A measure of the effectiveness
of a coupling system (i.e., the degree to which it
delivers an undistorted signal of correct amplitude and phase).
coupling loop 1. A single turn of a coupling transformer. 2. A small loop inserted into a waveguide
to introduce microwave energy.
coupling probe A usually short, straight wire or
pin protruding into a waveguide to electrostatically introduce microwave energy into the waveguide. It acts like a miniature whip antenna.
coupling transformer A transformer used primarily to transfer alternating-current (ac) energy
electromagnetically into or out of a circuit.
covalent binding forces In a crystal, the binding
forces resulting from the sharing of valence electrons by neighboring atoms.
covalent bonding The binding together of the
atoms of a material as a result of shared electrons
or holes.
coverage 1. The area within which a broadcast or
communication station can be reliably heard. 2.
The shielding effectiveness of a coaxial cable.
coversed sine Abbreviation, covers. The trigonometric functional equivalent of the versed sine of
the complement of an angle [i.e., the difference
between the sine of an angle and unity (1)]. Thus,
covers q = 1 – sin q.
CP Abbreviation of chemically pure.
cp 1. Abbreviation of CANDLE POWER. 2. Abbreviation of central processor.
cps 1. Abbreviation of CYCLES PER SECOND. Cycles per second, to denote ac frequency, has been
supplanted by HERTZ. 2. Abbreviation of characters per second.
CQ • critical field
CQ A general call signal used in radio communication, especially by amateur stations, to invite a
response from any station that hears it.
Cr Symbol for CHROMIUM.
cracked-carbon resistor A high-stability resistor
in which the resistance material is particulate
cracker A hacker with malicious intent (also see
HACKER). Such a person attempts to gain access
to computer systems or databases in order to
steal something or inflict damage. Examples include theft, erasure, or mutilation of data; fraudulent debiting of bank accounts; alteration of
credit information; and identity theft.
cradle guard See GUARD WIRE.
cradlephone A telephone set in which the microphone and earphone are mounted on opposite
ends of a handle. This handle, called the receiver,
rests on the crossmember of a stand connected to
a base containing the dial and ringing circuits.
Also called French phone, French telephone, and
crash 1. A condition in which a computer or network server becomes inoperative because of a
software or memory-management problem. 2. In
a computer hard disk or diskette drive, contact of
the read/write head with the surface of a disk or
platter. Usually, it is the result of excessive physical vibration or shock.
crate A foundation unit into which modules are
plugged to establish a circuit.
crawl 1. See CREEPING COMPONENT. 2. The
credits (names of staff and their contribution to
content) superimposed and moving on a television picture at the end of a program.
crazing The formation of tiny cracks in materials,
particularly in such dielectrics as plastic and ceramic.
creep See COLD FLOW.
creepage Current leakage across the surface of a
creeping component A quantity, such as current,
voltage, or frequency, that slowly changes in
value with time.
crest factor See AMPLITUDE FACTOR.
crest value The maximum amplitude of a composite current or voltage.
crest voltmeter A peak-reading (or sometimes
peak-responsive) voltmeter.
crippled mode The mode of operation for a computer or other hardware in which some of the
components are inoperable. Compare GRACEFUL DEGRADATION.
neutralization See
crisscross rectifier circuit A conventional bridge
rectifier circuit configured in such a way that two
of the diodes are connected in crisscross fashion
between the input and output terminals.
critical angle 1. In radio communications, an angle of departure that a transmitted electromag-
netic field subtends, with respect to the horizon
at the transmitting (TX) point, below which the
ionosphere will reliably return the signal to the
earth, and above which the ionosphere will not
reliably return the signal. This angle (shown by
the double arc marked X in the drawing) depends
on the frequency of the transmitted electromagnetic wave, and also on ionospheric conditions. 2.
For an electromagnetic wave or ray approaching
a boundary at which the index of refraction
abruptly decreases, the minimum angle of incidence (relative to a line perpendicular to a plane
tangent to the boundary) at which the energy is
totally reflected.
Ionized layer
Earth’s surface
critical angle, 1
critical characteristic A parameter that has a disproportionate effect on other variables. A small
change in this characteristic can result in a large
change in the operating conditions of a circuit or
critical component A component or part that is
especially important in the operation of a circuit
or system.
critical coupling The value of coupling at which
maximum power transfer occurs. Increasing the
extent of coupling beyond the critical value decreases power transfer.
critical damping The value of damping that yields
the fastest transient response without overshoot.
critical dimension The cross-sectional size of a
waveguide that determines its minimum usable
critical failure A component or circuit failure that
results in shutdown of a system, or a malfunction
that results in improper operation.
critical field The smallest magnetic-field intensity
in a magnetron that keeps an electron, emitted
from the cathode, from reaching the anode.
critical frequency • cross modulation
critical frequency For a particular layer of the
ionosphere, the high frequency at which a vertically propagated wave is no longer reflected back
to the earth.
critical inductance In a choke-input powersupply filter, the minimum inductance that will
maintain a steady value of average load current.
critical potential The potential difference required
for an electron to excite or ionize an atom with
which it collides.
critical voltage The voltage at which a gas ionizes.
critical wavelength The wavelength that corresponds to CRITICAL FREQUENCY.
CRO Abbreviation of cathode-ray oscilloscope.
Crookes dark space In a glow-discharge tube, the
narrow dark space next to the cathode. Also see
Crookes tube A glow-discharge tube containing an
anode, cathode, and a small amount of gas under
low pressure.
cross antenna An antenna in which two (usually
equal-length) horizontal radiators cross each
other at right angles and are connected together
to a feeder at their point of intersection. It takes
its name from its horizontal-cross shape.
cross assembler A program used with one computer to translate instructions for another computer.
crossband operation 1. Communications in which
two frequency bands are used. Station X, for example, might transmit on frequency fA in band A
and receive on frequency fB in band B; station Y
would then transmit on fB and receive on fA. 2. In
satellite communications, the use of two frequency bands to facilitate full-duplex operation
and to allow the satellite transponder to effectively function. The transponder receives signals
from the earth within a specific frequency band,
and converts this entire band of signals to a set of
signals that occupies an equal amount of spectrum space on another frequency band. The converted signals are then retransmitted back to
crossbar switch A three-dimensional array of
switch contacts in which a magnetic selector
chooses individual contacts, according to their
coordinates in the matrix.
cross bearings A method of radionavigation, in
which directional readings are taken from a receiving station (such as a ship or aircraft) for two
fixed transmitting stations whose locations are
known. Lines are drawn on a map from the transmitting stations, in directions 180 degrees opposite the bearings obtained from the receiving
station. The intersection point of these lines is the
location of the receiving station.
cross beat A spurious frequency arising from
cross-check To compare the result of a calculation
or computer routine with the result obtained by a
different method.
cross color In the chrominance channel of a color
television receiver, crosstalk interference caused
by monochrome signals.
cross-connected neutralization Neutralization of
a push-pull amplifier by feedback through two
capacitors—each connected from the output circuit of one transistor to the input circuit of the
cross-coupled multivibrator A multivibrator circuit in which feedback is provided by a coupling
capacitor between the output of the second stage
and the input of the first stage; the stages are
forward-coupled by a capacitor of the same value.
cross coupling 1. The state of being cross-coupled
(see, for example, CROSS-COUPLED MULTIVIBRATOR). 2. Undesired coupling between two circuits.
cross current A current that flows in the opposite
direction from some other current.
crossed-pointer indicator 1. Also called crossedneedle meter. A combination of two analog metering instruments in one case. Each needle has its
own independently calibrated scale. A third scale
corresponds to the intersection point of the needles. Commonly used in directional wattmeters
that simultaneously show forward power, reflected power, and standing-wave ratio (SWR). 2.
A two-pointer meter used in aircraft to show the
position of the aircraft, relative to the glide path.
crossed-wire thermoelement Two wires or strips
of dissimilar metals joined or twisted at a point
that constitutes a thermoelectric junction. In
usual operation, a high-frequency current is
passed through one wire, and a proportional
direct-current (dc) voltage, generated by thermoelectric action, appears at the other wire.
cross flux The magnetic flux component that is
perpendicular to the flux produced by field magnets.
cross-hair pattern A television test pattern consisting of a single vertical line and a single horizontal line, which form a simple cross. The
pattern resembles the cross hairs of an optical instrument.
generator A
radiofrequency (RF) signal generator that produces a
crosshatch pattern on a picture-tube screen.
crosshatch pattern A grid of horizontal and vertical lines produced on a picture-tube screen by a
cross-hatch generator. It is used in checking horizontal and vertical linearity.
cross modulation 1. A type of radio-frequency interference (RFI) between two strong stations that
are close in frequency. The desired carrier is modulated by the interfering signal. 2. The production of signals by rectifier junctions in pipes and
wiring near a radio receiver. These objects pick
up waves and deliver energy at a different frequency, which finds its way into the receiver. Also
called external cross modulation. 3. The interaction between signals of different frequency when
cross modulation • cryotron
they magnetize a core of nonlinear magnetic material. Also see CROSSTALK.
cross-modulation factor An expression of the
amount of cross modulation (or crosstalk) present in a particular instance. It is equal to M1/M2,
where M1 is the modulation percentage that a
modulated wave produces in a superimposed unmodulated wave, and M2 is the modulation percentage of the modulated wave.
circuit See
crossover 1. In a circuit diagram, a point at which
lines representing wires intersect, but are not
connected. 2. In a characteristic curve, point at
which the plot crosses an axis or operating point.
crossover distortion Distortion of a characteristic
at a crossover point (see CROSSOVER, 2); for example, a bend in the curve where the plot of a
waveform passes through zero.
crossover frequency The frequency at which a
crossover network delivers equal power to the two
circuits it supplies.
crossover network Following final amplification in
a sound-reproduction system, an outboard filter
circuit that facilitates delivery of the low and high
audio frequency (AF) components to the correct
crossover point See CROSSOVER, 2.
crossover S-curve The S-shaped image obtained
on an oscilloscope screen during sweep-generator
alignment of a frequency-modulation (FM) detector. In correct alignment, the exact center of the
S-curve (the crossover point) coincides with the
zero point on the screen.
cross product Also called vector product. For vectors A and B having lengths A and B, respectively,
and subtending an angle θ relative to each other,
the cross product A × B points in a direction perpendicular to the plane containing both A and B.
The length of A × B is equal to AB sin θ.
cross product
cross-sectional area 1. The surface area of a face
of a conductor after cutting through it at a right
angle. Specified in square inches, square millimeters, or circular mils. 2. The total of the crosssectional areas of all the wires in a stranded
cross-sectional testing In quality assurance and
quality control (QA/QC), a method of checking a
large lot of units or components. Instead of testing every device, a fraction of the devices is
tested. The sampling is taken uniformly from the
group (e.g., every fifth unit).
crosstalk Undesired transfer of signals between or
among telephone lines, data lines, or system
components. In computer operations, this effect
places a practical limit on the lengths of parallel
data cables.
crosstalk coupling Undesired coupling between
circuits, caused by crosstalk.
crosstalk factor See CROSS-MODULATION FACTOR.
crosstalk level The amplitude of crosstalk, usually
expressed in decibels above a reference level.
crosstalk loss Loss of energy caused by crosstalk.
crowbar An action producing a high overload on a
circuit protection device.
crowfoot 1. A pattern formed by the cracking or
crazing of solid plastics of solidified encapsulating compounds, so called from its resemblance to
a bird’s footprint. 2. In a gravity battery cell, the
zinc electrode, so called from its resemblance to a
bird’s foot.
CRT Abbreviation of CATHODE-RAY TUBE.
crud 1. Broadband electrical noise, originating inside and/or outside a system. 2. Undesired signals that interfere with a desired signal.
cryogenic device A device that exhibits unique
electrical characteristics (such as superconductivity) at extremely low temperatures.
cryogenic motor A motor designed for operation
at extremely low temperatures.
cryoelectronics The study of the behavior of electronic devices, circuits, and systems at extremely
low temperatures.
cryogenics The branch of physics dealing with the
behavior of matter at temperatures approaching
absolute zero. Also concerned with methods of
obtaining such temperatures in controlled environments.
cryosar A semiconductor switch utilizing lowtemperature avalanche breakdown.
cryoscope An instrument used to determine freezing point.
cryostat A chamber for maintaining a very low
temperature for cryogenic operations. Also see
cryotron A switching device consisting essentially
of a straight tantalum wire, around which a
single-layer control coil is wound. The magnetic
field generated by control current flowing through
the coil causes the tantalum wire to become
cryotron • crystal loudspeaker
Z axis
(center of crystal)
X cut
Y Y cut
AT cut
crystal cuts
quency, temperature, and thickness. Also see
crystal detector A rudimentary form of semiconductor diode consisting of a mounted lump of
mineral (the crystal) in contact with a springy
wire (“cat’s whisker”). The point of the wire is
moved to various points of contact on the crystal
surface until the most-sensitive rectifying spot is
crystal diffraction The tendency of electromagnetic waves to be scattered when passing through
a crystal material.
crystal diode Archaic term for SEMICONDUCTOR
crystal earphone An earphone in which the transducer is a piezoelectric crystal. Electrical impulses applied to the crystal vary its shape and
cause a vibration that is transmitted to a diaphragm; this in turn produces corresponding
sound waves.
crystal filter See CRYSTAL RESONATOR.
crystal headphone See CRYSTAL EARPHONE.
crystal holder A fixture specially designed to hold
a piezoelectric crystal; it ensures minimum distortion of crystal dimensions and minimum residual capacitance, inductance, and resistance.
crystal imperfection A flaw in the lattice structure of a crystal.
crystal lattice The orderly, redundant pattern of
atoms and molecules within a crystalline material; it is a characteristic of a given material.
crystal-lattice filter A crystal resonator in which
piezoelectric crystals are used to give a desired
shape to the filter response curve.
crystalline material A material exhibiting the
characteristic properties of a crystal (see CRYSTAL, 1).
crystallogram An X-ray photograph or other
record of crystal structure.
crystallography The science dealing with crystals
and their properties (see CRYSTAL, 1).
crystal loudspeaker A loudspeaker whose transducer is a piezoelectric crystal. Electrical impulses applied to the crystal vary its shape and
superconductive at a temperature of approximately 4.4 degrees K.
cryotronics Low-temperature electronics, concerned with such phenomena as superconductivity. The term is an acronym from cryogenics and
electronics. Also see CRYOGENICS.
cryptanalysis The breaking of ciphers.
crypto- A prefix added to words, that implies encoding for the purpose of changing or hiding the
meaning of a message or signal.
cryptography The creating and writing of ciphers.
cryptology The art and science of creating, writing, unscrambling, and breaking ciphers.
crystal 1. A material distinguished by the arrangement of its atoms into a redundant pattern called
a lattice that presents, in fragments of various
sizes, a characteristic polyhedral shape. Common
shapes include cubes, parallelepipeds, and
hexagonal prisms. 2. A fragment of material as
defined in (1). 3. A plate or bar cut from a piece of
piezoelectric material.
crystal amplifier 1. A semiconductor diode circuit
using carrier storage. Transistor action and, accordingly, pulse amplification is obtained by alternately making one electrode of the diode an
emitter or collector. 2. Archaic term for TRANSISTOR.
crystal audio receiver An audio radar receiver,
consisting of a crystal detector and audio-amplifier stages.
crystal axes The imaginary lines traversing a piezoelectric crystal, along which (or perpendicular
to which) plates are cut for oscillators, resonators, or transducers.
crystal calibrator A crystal oscillator used to
generate harmonic checkpoints for frequency
calibration. Common fundamental calibrator
frequencies are 100 kHz and 1 MHz.
crystal capacitor See VARACTOR.
crystal control The control of the operating frequency of a circuit by means of a piezoelectric
crystal-controlled receiver A superheterodyne
radio receiver whose local oscillator is crystal
crystal-controlled transmitter A radio transmitter whose master oscillator is crystal controlled.
crystal counter A device for counting the frequency of subatomic particles, based on their
ability to change the conductivity of a crystal. The
particles can be photons, electrons, protons, neutrons, or the nuclei of atoms.
crystal current Current flowing through a crystal;
specifically, the radio-frequency (RF) current
flowing through a quartz plate in a crystalcontrolled oscillator.
crystal cuts The classification of piezoelectric
plates according to the angle at which they were
cut from a quartz crystal. Common cut designations are AT, BT, CT, DT, X, Y, and Z. Various
cuts afford such complementary factors as fre-
crystal loudspeaker • crystal tester
cause vibrations that are transmitted to a diaphragm or cone, which produces corresponding
sound waves.
crystal meter A rectifier-type ac meter using a
semiconductor diode in series with a dc milliammeter or microammeter.
crystal microphone A microphone whose transducer is a natural or synthetic piezoelectric
crystal. Sound waves striking the crystal (directly or via a diaphragm) vary its shape, making it produce an audio-frequency (AF) output
crystal pulling 1. The extraction of a single crystal
from a molten mass of crystalline material. Single
crystals are used for high-quality semiconductor
devices. Also see CZOCHRALSKI METHOD, SINGLE CRYSTAL, and SINGLE-CRYSTAL MATERIAL. 2. The use of an inductor or capacitor in a
crystal-controlled radio-frequency (RF) oscillator
circuit to allow adjustment of the frequency over
a small range.
crystal receiver See CRYSTAL SET.
crystal rectifier 1. A semiconductor diode used
for the purpose of rectifying alternating current
(dc), usually in a power supply.
crystal resistor A temperature-sensitive resistor
made from silicon, and exhibiting a positive temperature coefficient of resistance.
crystal resonator A highly selective resonant circuit in which the center frequency is the resonant
frequency of a piezoelectric quartz-crystal plate.
crystal sensor See CRYSTAL TRANSDUCER.
crystal set A simple radio receiver that uses a
tuned circuit, semiconductor-diode detector, and
crystal microphones
crystal mixer A mixer (converter) circuit utilizing
the nonlinearity of a semiconductor diode to mix
crystal operation 1. The characteristics of a piezoelectric crystal in a particular circuit. 2. Crystal
frequency control.
crystal oscillator An oscillator whose operating
frequency is determined by the dimensions of an
oscillating piezoelectric quartz-crystal plate.
crystal oven A constant-temperature chamber for
stabilizing the frequency of a quartz crystal by
maintaining its operating temperature at a fixed
crystal photocell A photoelectric cell in which the
light-sensitive material is a crystalline substance,
such as germanium, selenium, silicon, etc.
crystal pickup A phonograph pickup whose transducer is a natural or synthetic piezoelectric crystal. The crystal is attached (either directly or
through a mechanical linkage) to a stylus, whose
movement in the disk groove varies the shape of
the crystal. The resultant vibration generates a
corresponding audio-frequency (AF) output voltage across the crystal.
crystal probe A radio-frequency (RF) probe, whose
rectifying element is a semiconductor diode.
crystal set
crystal slab See QUARTZ BAR.
crystal socket 1. A low-capacitance, low-loss
socket for a piezoelectric crystal. 2. A socket for a
semiconductor diode.
crystal tester 1. An oscillator used to check quartz
crystals. Most such units check only the crystal’s
ability to oscillate; more elaborate ones also check
crystal current, frequency, temperature coefficient, activity, filter action, etc. 2. An instrument
for checking the electrical characteristics of semiconductor diodes. 3. An instrument for checking
the performance of piezoelectric ceramics.
crystal tetrode • current antinode
crystal tetrode A transistor having four elements:
emitter, collector, and two bases.
crystal transducer A transducer using a piezoelectric crystal as the sensitive element. Examples: crystal earphone, crystal loudspeaker,
crystal microphone, and crystal pickup.
crystal triode See TRANSISTOR.
Cs Symbol for CESIUM.
CS 1. Symbol for standard capacitance. 2. Symbol
for source capacitance.
csc Abbreviation of COSECANT.
C scan See C DISPLAY.
csch Abbreviation of HYPERBOLIC COSECANT.
C scope A cathode-ray tube used in radar to provide a C DISPLAY.
CT-cut crystal A piezoelectric plate cut from a
quartz crystal at an angle of rotation around the
X-axis of +38°. Such a plate has a zero temperature coefficient of frequency at 25°C. Also see
CTL Abbreviation
Cu Symbol for COPPER.
cube 1. A regular polyhedron with six identical
square faces and eight vertices. At each vertex,
three edges converge at mutual right angles. 2.
The third power of a number; thus the cube of n
is written n3.
cube tap An electrical adapter, in which a set of
male prongs and three sets of female contacts are
on the sides of a molded cube. Allows three appliances to be used with a single electrical socket.
To wall
cube tap
cubical antenna An antenna in which the elements form the outline of a geometric cube or
rectangular prism. The most common example is
cubical quad antenna See QUAD ANTENNA.
cubic equation A polynomial equation of the third
degree. Its general form is ax 3 + bx2 + cx + d = 0.
cue A condition or signal that alerts an operator,
circuit or system to act in a specific manner.
cue circuit A device for transmitting cues used in
program control.
cueing receiver 1. A (usually miniature) radio receiver used to pick up cues. Example: a receiver
carried by a technician, actor, or lecturer. 2. A receiver or other pickup circuit that receives a cuing pulse, which it uses to set another circuit.
cu ft Abbreviation of cubic foot or cubic feet.
cu in Abbreviation of cubic inch or cubic inches.
cumulative error In a sum or other final value, the
total error that has accumulated from the individual errors in the terms. Also called systematic
cup core A coil core that also forms a magnetic
shield around the coil.
rectifier See
cur Abbreviation of CURRENT.
curie Abbreviation Ci. A unit of radioactivity; 1
curie is the amount of radiation from (or in equilibrium with) 1 gram of radium. Also equivalent to
3.7 × 1010 atomic breakdowns per second.
Curie point 1. The temperature above which a ferromagnetic material loses its magnetism or becomes paramagnetic. 2. The temperature at
which the ferroelectric properties of a substance
curie temperature As a magnetized substance is
heated, the lowest temperature at which magnetization is lost. It is generally measured in degrees
Celsius or degrees Kelvin. For iron, this temperature is 760 degrees Celsius; for nickel, it is 356
degrees Celsius.
Curie’s law For a paramagnetic substance, the ratio of the magnetization to the magnetizing force
is inversely proportional to the absolute temperature.
Curie-Weiss law Above the Curie point, the susceptibility of a paramagnetic material varies inversely as the excess of temperature above the
Curie point increases. This law is invalid for applications at or below the Curie point.
curium Symbol, Cm. A radioactive metallic element produced artificially. Atomic number, 96.
Atomic weight, 247.
current Symbol, I or i. The movement of charge
carriers, such as electrons, holes, or ions. Also
current amplification 1. An electronic process
in which the instantaneous, average, or peak
magnitude of a current is increased. 2. The extent to which a current increases in a circuit;
the ratio (always greater than one) of output
current to input current, Iout/Iin. Also called current gain.
current amplifier An amplifier operated primarily
to increase a signal current. Compare POWER
current antinode See CURRENT LOOP.
current attenuation • current relay
current attenuation 1. The reduction of current
amplitude along a line. 2. The extent to which a
current decreases in a line or circuit; the ratio (always less than one) of output current to input
current, I out/I in.
current balance An instrument for determining
the size of the ampere. This is done by measuring
the force between two current-carrying conductors.
current-balance switch A switch or relay, operated by the existence of a difference between two
current-carrying capacity The maximum current
(usually expressed in amperes) that a conductor
or device can safely conduct.
current coil The series coil in a nonelectronic
wattmeter. Compare POTENTIAL COIL.
current-controlled amplifier Abbreviation, CCA.
An amplifier in which gain is controlled by means
of a current applied to a control-input terminal.
current density The current (usually expressed in
amperes per square centimeter) passing through
a cross-sectional area of a conductor.
current drain 1. The current supplied to a load by
a generator or generator-equivalent. 2. The current required by a device for its operation; also,
the current taken by the device during standby
current echo Reflected current in a transmission
line that is not terminated in an impedance exactly matching its characteristic impedance.
current-fed antenna An antenna in which the
transmission line is attached to the radiator at a
current loop (voltage node). Compare VOLTAGEFED ANTENNA.
current feed 1. The delivery of power to a device or
circuit at a point where current dominates. Compare VOLTAGE FEED. 2. In an antenna, feeding
it at a current maximum.
Current feed
current feedback 1. A feedback signal consisting
of current fed from the output to the input circuit
of an amplifier. 2. A system or circuit for obtaining current feedback.
current-feedback pair A two-stage, direct-coupled
transistor amplifier having direct-current shuntseries feedback.
current flow Charge carriers passing through a
solid, liquid, gas, or vacuum. Also see CURRENT
current hogging 1. An undesirable condition that
sometimes takes place when two or more transistors are operated in parallel. One device tends to
do all the work, taking all the current. The result
can be destruction of that device. 2. The tendency
of one component in a group of identical parallelconnected components to dissipate most of the
current-hogging injection logic Acronym, CHIL.
A form of bipolar digital logic, similar to currenthogging logic but having the greater density characteristic of injection logic.
current instruction register A register in which
are held instructions ready for execution by a
program controller.
current lag A circuit condition in which current
variations are delayed by up to 180 degrees of
phase relative to voltage variations. Compare
current lead A circuit condition in which current
variations occur earlier than voltage variations by
up to 180 degrees of phase. Compare CURRENT
current limiting The controlling of current so that
it does not exceed a desired value.
current-limiting resistor A series resistor inserted into a circuit to limit the current to a prescribed value.
current loop A point on a transmission line or antenna radiator at which the current reaches a local maximum. Compare CURRENT NODE.
current meter A usually direct-reading instrument, such as an ammeter, milliammeter, or microammeter, used to measure current strength.
current-meter operation The operation of a voltmeter as a current meter by connecting it to respond to the voltage drop across a resistor that
carries the current of interest.
current-mode logic In computer operations, transistor logic in which the transistors operate in the
unsaturated mode.
current node A point on a transmission line or antenna radiator at which the current reaches a local minimum. Compare CURRENT LOOP.
current noise Electrical noise produced by current
flowing through a resistor.
current probe A transformer usually having a
snap-around, one-turn coil that picks up energy
from a conductor and couples it into an alternating-current ammeter.
current rating 1. A specified value of operating
supply See
current regulation The stabilization of current at
a predetermined level or value.
current regulator See BARRETTER.
current relay A relay actuated by specific values of
pickup and dropout current.
current saturation • cutoff frequency
current saturation In the operation of a device
(such as a transistor, saturable reactor, or magnetic amplifier), the leveling off of current at a
value beyond which no further increase occurs—
even though an input parameter is further increased.
current sense amplifier An amplifier used to increase the sensitivity of, or to decrease the loading of, a current-sensing component.
current sensing Sampling a current (e.g., when
the voltage drop across a series resistor is used as
a proportional indication of the current flowing
through the resistor).
current-sensing resistor A low-value resistor inserted into a circuit primarily for current sensing.
current sensitivity In a current meter or galvanometer, current (in amperes or fractions
thereof) per scale division.
current-sheet inductance Symbol, LS. The lowfrequency inductance of a single-layer coil, calculated with the formula L S = (0.10028 a2 N 2)/s,
where L S is in microhenrys, a is the coil radius in
inches, N is the total number of turns, and s is
the coil length in inches.
current shunt 1. A resistor connected in parallel
with a voltmeter to convert it into an ammeter. 2.
A resistor connected in parallel with the input of
a voltage amplifier to make the response of the
amplifier proportional to input-signal current.
current sink A circuit or device through which a
constant current can be maintained.
current-sinking logic A form of bipolar digital
logic. Current flows from one stage to the input of
the stage immediately before.
current-squared meter An ammeter or milliammeter whose deflection is proportional to the
square of the current.
current-stability factor In a common-base connected bipolar transistor, the ratio dIE/dIC, where
IE is the emitter current and IC is the collector
current strength The magnitude of electric current (see CURRENT) (i.e., the number of carriers
flowing past a given point per unit time, expressed in coulombs per second or in amperes).
current transformer 1. A transformer used to increase or decrease current flow. A primary-tosecondary step-up turns ratio reduces the
current; a primary-to-secondary step-down turns
ratio increases the current. 2. A particular transformer (as in 1) used to change the range of an alternating-current milliammeter or ammeter.
current vector In a vector diagram, a line with an
arrowhead (vector) showing the magnitude and
phase of a current. Compare VOLTAGE VECTOR.
current-voltage feedback In an amplifier or oscillator, the process of applying some of the output
current and voltage to the input. This feedback
might be in phase (positive) or out of phase (negative), with respect to the input.
cursor 1. A marker that indicates the position
where a character can be entered in a video alphanumeric display. Commonly used in computers and word processors. 2. The sweeping line on
a radar display. 3. The movable marker on a slide
curve trace 1. A device that supplies a special
variable test voltage to a component or circuit under test, at the same time supplying a sweep voltage to an oscilloscope. The component’s output
voltage is also presented to the oscilloscope. As a
result, the response curve of the component appears on the oscilloscope screen. 2. A device that
produces a permanent record (photographic or
graphic) of an electrical phenomenon. Also called
curvilinear trace A trace made on paper with
curved vertical lines. The lines are curved to
match the arc through which the recording pen
cut-in angle In a semiconductor rectifier circuit, a
phase angle slightly greater than zero degrees, at
which current conduction begins. Compare CUTOUT ANGLE.
Cutler antenna A parabolic-dish antenna, in
which the driven element consists of a waveguide that has two apertures on opposite sides of
a resonant cavity.
Cutler feed An aircraft antenna feed system in
which radio-frequency (RF) energy is fed to the reflector by a resonant cavity at the end of a waveguide.
Cutler tone control A dual resistance-capacitance
(RC) filter circuit of the general bridged-tee variety. Variation of the series leg provides adjustable
treble boost; variation of the shunt leg provides
adjustable bass boost.
cutoff 1. The process of reducing some operating
parameter, such as collector current, to zero by
adjusting the bias at the input electrode. 2. The
point on the characteristic curve of an amplifying
device, at which the output current drops to zero
under no-signal conditions. 3. The lowest
frequency at which a waveguide will efficiently
function. 4. The frequency or frequencies corresponding to the point or points in a filter
response, at which the attenuation is three
decibels greater than the lowest attenuation within
the passband. See also CUTOFF FREQUENCY.
cutoff attenuator A variable, nondissipating attenuator consisting of a variable length of waveguide used at a frequency below cutoff.
cutoff bias In a transistor or vacuum-tube circuit,
the value of control-electrode bias that produces
output current cutoff.
cutoff current Symbol, Ico. In a transistor, the
small collector current that flows when the emitter current is zero (common-base circuit) or when
the base current is zero (common-emitter circuit).
cutoff frequency 1. Symbol, fco. The high frequency at which the current-amplification factor
cutoff frequency • cyclic variations
of a transistor drops to 70.7% of its 1-kHz value.
2. In a filter, amplifier, or transmission line, the
frequency point(s) at which transmission loss or
filter rejection begins. It is generally specified as
the half-power point(s), or the point(s) at which
the attenuation is three decibels, relative to
the lowest attenuation. Examples: the highfrequency cutoff of an amplifier and the upper
and lower cutoff points of a bandpass filter.
cutoff limiting Output-peak clipping that results
from overdrive in an amplifying device. Compare
cutoff potential See CUTOFF BIAS.
cutoff voltage See CUTOFF BIAS.
cutoff wavelength 1. The wavelength corresponding to cutoff frequency. 2. For a waveguide, the
ratio of the velocity of electromagnetic waves in
free space (3 × 108 meters per second) to the cutoff frequency of the waveguide in Hz. The result is
thus expressed in meters.
cutout 1. A device, such as a circuit breaker, that
automatically disconnects a circuit, usually to
prevent overload, but occasionally to prevent underload. 2. Emergency switch. 3. Fuse.
cut-out angle In a semiconductor rectifier circuit,
a phase angle slightly less than 180 degrees at
which current conduction ceases. Compare CUTIN ANGLE.
cutout base A fuse block.
cut rate 1. The speed at which a cutter moves
across the surface of a blank vinyl disk during the
recording process. 2. The number of cut lines per
inch in a vinyl disk recording.
CW 1. Abbreviation of CONTINUOUS WAVE. 2. Abbreviation of CLOCKWISE.
CW filter In a communications receiver, a highly
selective filter in the intermediate-frequency (IF)
or audio-frequency (AF) stage. The bandwidth is
typically 200 Hz to 500 Hz; some audio filters
can be set for bandwidths as low as about 50
CW laser A laser that emits energy in an uninterrupted stream, rather than in pulses.
CW oscillator 1. In a radio receiver, a variablefrequency oscillator that heterodynes a radiotelegraph signal in the intermediate-frequency (IF)
amplifier chain, to make audible the continuouswave dits and dahs. 2. Sometimes, an external
variable-frequency radio-frequency (RF) oscillator, whose output beats against the actual carrier
of a continuous-wave radiotelegraph signal, making it audible as dits and dahs. 3. An unmodulated, unkeyed oscillator.
CW radar A radar system in which radio-frequency
(RF) energy is transmitted continuously.
signal A sinusoidal radiofrequency (RF) signal, used to control the conduction time of a synchronous demodulator in
color television.
cyan Blue-green, one of the three primary pigments.
cyber- A prefix that indicates relevance to, or involvement with, computers, computer systems,
and electronic control systems.
cybernetics The study of control system theory in
terms of the relationship between animal and
machine behavior.
Cyber Sapiens An expression for a computer or
robot with artificial intelligence (AI) on the forefront of current technology.
cyberspace 1. Alternative expression for INFORMATION SUPERHIGHWAY. 2. Alternative expression for VIRTUAL REALITY.
cyborg Acronym of the words cybernetic and organism. 1. A human being with at least one artificial body part, such as a prosthesis (artificial
limb). 2. A human being who is largely composed
of robotic body parts.
cycle 1. Abbreviation, c. One complete, 360-degree
revolution of the current or voltage vector in an
alternating-current (ac) wave. An ac frequency of
1 cycle per second is 1 Hz (see HERTZ). 2. A complete sequence of operations.
cycle counter A device that totals the number of
cycles of a phenomenon repeated during a given
cycle index The number of times that a particular
cycle has been, or must be, iterated in a computer program.
cycle index counter A variable that indicates how
often a cycle of computer program instructions
has been executed. In a program, for example,
this can be accomplished by increasing, through
instruction, the value of a location’s content every
time a loop operation is performed.
cycle life The total number of charge-discharge cycles a rechargeable cell or battery can tolerate before becoming useless.
cycle reset To change the value of a cycle count
(making it zero or some other value).
cycle shift See CYCLIC SHIFT.
cycles per second Abbreviation, cps. Archaic term
for HERTZ.
cycle time Pertaining to an operation, the duration of a complete cycle.
cycle timer A timer that switches a circuit or device on and off, according to a predetermined cycle. Also called programmed timer.
cyclic code See GRAY CODE.
cyclic memory In computer operations, a memory
whose locations can only be accessed points in a
cycle, as of a magnetic diskette.
cyclic shift The moving of data out of one end of a
storage register and reentering it character-bycharacter or bit-by-bit at the other end in a closed
loop (e.g., 87654 cyclically shifted one place to
the right becomes 48765).
cyclic variations Periodic changes in the features
of the ionosphere, occurring on a daily, seasonal,
or sunspot-related basis. These changes are fairly
cycling • Czochralski method
cycling The tendency of a parameter to oscillate
back and forth between two different values.
cyclogram A method of showing the relationship
between two signals on an oscilloscope. The two
signals must have a fixed phase relationship.
cyclotron A type of particle accelerator. An applied
electromagnetic field, acting together with an intense applied magnetic field, cause charged subatomic particles to travel with increasing velocity
in a spiral path between two semicircular metal
boxes called dees. When the particles go fast
enough in the correct path, they are expelled and
strike a target in their path.
cylindrical contour The most common curvature
of the face of a magnetic tape recording head; it is
a section of a cylinder having a constant radius of
0.5 inch to 1 inch.
cylindrical coordinate geometry A scheme for
robot-arm movement. There are three coordinates, called reach, angle, and elevation. It allows
precise positioning of a robot end effector within a
region consisting of two concentric cylinders and
all the volume in between.
cylindrical coordinates A method of locating a
point in three-space in which height, distance,
and angle are used to uniquely define points.
h axis
Path of
P = (h, r,θ)
Dee 2
Dee 1
cyclotron frequency The angular frequency of a
charged particle in a cyclotron. The cyclotron frequency depends on the number of times per second the magnetic field of the device is reversed.
cyclotron radiation An electromagnetic field produced by the circular movement of charged particles in a fluctuating magnetic field.
cylinder In computer operations, the combination
of equal-radius tracks on the platters of a hard
cylinder magnet A permanent magnet in the
shape of a cylinder.
cylindrical capacitor See CONCENTRIC CAPACITOR.
cylindrical coordinates
cylindrical magnet See CYLINDER MAGNET.
cylindrical wave An electromagnetic wave whose
field surfaces are nearly perfect cylinders.
cylindrical waveguide A waveguide resembling a
round pipe.
cylindrical winding A method of coil winding in
which the wire is formed into a helix. There might
be only one layer, or there might be several layers. The length of the coil is greater than the diameter. Also called a linear winding.
Czochralski method A technique for obtaining a
relatively large single crystal from a substance,
such as the semiconductors germanium and silicon. The method consists essentially of dipping a
seed crystal into a molten mass of the same substance, then slowly withdrawing it while rotating it.
D 1. Symbol for DEUTERIUM. 2. Symbol for ELECTRIC DISPLACEMENT. 3. Symbol for ELECTRIC
FACTOR. 5. Symbol for drain (see DRAIN, 3). 6.
Abbreviation of DISSIPATION. 7. Symbol for determinant. 8. Symbol for DIFFUSION CONSTANT.
d 1. Abbreviation of DECI. 2. Symbol for DIFFERENTIAL. 3. Symbol for distance. 4. Symbol for
DENSITY. 5. Symbol for drain (see DRAIN, 3). 6.
Abbreviation of DISSIPATION. 7. Abbreviation of
day. 8. Abbreviation of DEGREE. 9. Abbreviation
of diameter. 10. Abbreviation of DRIVE.
D/A Abbreviation of DIGITAL-TO-ANALOG. See
dA 1. Symbol for DIFFERENTIAL OF AREA. 2.
Symbol for differential of amplification. 3. Seldomused abbreviation of deciampere.
da Abbreviation of DEKA.
DACI Abbreviation of direct adjacent-channel interference.
daisy chain A method of transferring a signal in a
computer from one stage to the next.
daisy wheel A form of printing device consisting
of a disk having several dozen radial spokes,
each of which has a character molded on its
face. The disk rotates to the proper position in
the printing process, and a hammer strikes the
spoke to press the molding against the ribbon
and paper.
DAM Abbreviation of data-addressed memory.
Damon effect The change that the susceptibility of
ferrite undergoes under the influence of high RF
damped galvanometer A galvanometer with a provision for overswing limiting or oscillation prevention.
damped loudspeaker A loudspeaker in which undesirable excursions are prevented by damping in
the associated amplifier or speaker circuit.
damped meter 1. A meter with a provision for
overswing limiting or oscillation prevention. 2. A
meter that is protected during transport by a
shorting bus between the two meter terminals.
damped natural frequency 1. The frequency at
which a damped system having one degree of
freedom will oscillate after momentary application of a transient force. 2. In the presence of
damping, the rate at which a sensing element oscillates freely.
damped oscillations Oscillations in which the amplitude of each peak is lower than that of the preceding one; the oscillation eventually dies out (the
amplitude becomes zero). Compare CONTINUOUS WAVE.
damped speaker See DAMPED LOUDSPEAKER.
damped wave A wave whose successive peaks decrease in amplitude (i.e., it decays), eventually
reaching an amplitude of zero. Compare CONTINUOUS WAVE and UNDAMPED WAVE.
damped-wave decay See DECREMENT, 1.
dampen To cause the amplitude of a signal to
damper diode See DAMPING DIODE.
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damper winding • data-acquisition system
damped wave
damper winding A special short-circuited motor
winding that opposes pulsation or rotation of the
magnetic field.
damping 1. See DAMPING ACTION. 2. In a loudspeaker, sound-absorbent material used to minimize resonant effects within the enclosure.
damping action 1. Quenching action. 2. The prevention of overswing, dither, or flutter in a meter
or loudspeaker (see DAMPED GALVANOMETER,
The prevention of oscillation or ringing in a circuit. 4. Inhibition of the vibration of an acoustic
transducer to prevent ringing and other unwanted effects.
damping coefficient A figure expressing the ratio
of the damping in a system to critical damping.
damping diode A diode used to prevent oscillation
in an electric circuit (e.g., the diode that prevents
ringing in the power supply of a television receiver). Also called damper.
damping factor 1. Symbol, a. For a coil of inductance L and RF resistance R in a damped-wave
circuit, the value R/2L, where L is in henrys and
R in ohms. 2. Abbreviation, Fo. For a torque motor, the ratio of the stall torque to the no-load rotational speed.
damping magnet A permanent magnet so situated, with respect to a moving conductor, disk, or
plate, that the resulting field opposes the movement.
damping ratio See DAMPING COEFFICIENT.
damping resistance 1. The value of shunt resistance required to prevent ringing in a coil. 2. The
value of resistance required for critical damping
of a galvanometer.
damping resistor 1. A shunt across a coil to prevent ringing. 2. A resistor used to provide critical
damping of a galvanometer.
Daniell cell A nonpolarizing primary wet cell with
zinc (negative) and copper (positive) electrodes.
The zinc plate is in a porous cup containing a
weak zinc-sulfate solution with a little sulfuric
acid; the cup is in a jar filled with a saturated copper-sulfate solution in which the copper electrode
is immersed. Typical voltage for the cell is 1.1 V.
daraf The unit of ELASTANCE. Elastance in darafs
is the reciprocal of capacitance in farads.
dark conduction The flow of dark current in a
photoconductive or glow-discharge device.
dark current The usually tiny current flowing
through a darkened photoconductive cell, phototransistor, or glow-discharge device.
dark discharge The occurrence of a discharge in a
gas, without the production of visible light.
dark-spot signal A spurious signal generated by
some camera tubes, arising from secondaryemission effects.
dark-trace tube An oscilloscope tube on whose
white screen a long-persistence magenta image is
traced by the electron beam. Illuminating the
screen with bright light intensifies the image.
Darlington amplifier A high-gain amplifier that
uses a COMPOUND CONNECTION of two bipolar
Darlington pair See COMPOUND CONNECTION.
D’Arsonval current A large, low-voltage, highfrequency current at one time thought to be
D’Arsonval meter A electromechanical analog meter, in which a coil turns on jeweled pivots between the poles of a strong magnet and against
the force of spiral springs. A pointer is attached to
the coil. The pointer moves over a calibrated scale.
D’Arsonval movement The mechanism of a
D’Arsonval meter.
DART Abbreviation of data analysis recording tape.
dart leader A flow of electrons along a path traveled by a lightning stroke, preceding a second
stroke. The dart leader, if any, occurs a few milliseconds after the first stroke. Several strokes
could occur, each preceded by a dart leader,
within less than 1 second.
dash The longer of the two characters (DOT and
DASH) of the telegraph code. The duration of the
dash is three times longer than that of a dot.
dashpot A delayed-action device in which the
movement of a piston is slowed by air or a liquid
in a closed cylinder.
dashpot relay A time-delay relay assembly in
which the delay is obtained with a DASHPOT.
DAT 1. Abbreviation of DIGITAL AUDIO TAPE. 2.
Abbreviation of diffused-alloy transistor.
data 1. A collection of digital bits (binary digits)
with informational content (e.g., a computer file,
a digital image, or a digital sound recording). 2.
General expression for information, especially in
encoded or written form.
data acquisition The reception and gathering of
data-acquisition system A computer or dumb terminal used to gather data from one or more external points.
data analysis display unit • data processor
data analysis display unit A video display peripheral for online data analysis.
data area A computer memory area that holds data
only (i.e., one that does not contain program instructions).
data bank A data file stored in a direct-access storage device, which can be drawn from by many
system users through remote terminals.
database 1. A computer file containing often-used
information (e.g., names and addresses, or electronic part numbers). 2. A popular form of computer software that allows users to create,
maintain, and modify information.
data block A set of data bits, comprising an identifiable item.
data bus A conductor or medium over which digital
data is transmitted from one place to another
within a computer.
data carrier storage A medium of data storage
outside of a computer (e.g., a magnetic disk).
data code A set of abbreviations or codes for data
characters or words.
data collection The pickup of signals representing
test data and their transmission to a computer,
data processor, or recorder. Also see DATA SYSTEM, 1.
datacom Acronym for DATA COMMUNICATION.
data communication The transmission and reception of data signals between or among points
in a system.
data communication terminal A computer peripheral providing an input and output link to a
central computer system, and that can be used
offline for other functions.
data compression 1. The process of reducing the
size of a data file by eliminating redundancies. 2.
The process of minimizing the length of a data
transmission by eliminating redundancies. 3.
The process of reducing the bandwidth of a data
transmission. 4. The process of reducing the dynamic amplitude range of a data transmission.
data control The automatic control of incoming
and outgoing data in a data processing system.
data conversion The process of changing data
from one form to another, e.g., from analog to digital (A/D), digital to analog (D/A), parallel to serial, or serial to parallel.
data converter 1. A circuit or device for performing DATA CONVERSION. 2. An analog-to-digital
(A/D) converter. 3. A digital-to-analog (D/A) converter. 4. A parallel-to-serial converter. 5. A
serial-to-parallel converter.
data description The description of a unit of data,
as included in a computer source program.
data display A device, such as a cathode-ray tube
(CRT) or liquid-crystal display (LCD), that presents data for visual examination. Compare
data element 1. A component of a data signal (e.g.,
a number, letter, symbol, or the equivalent electrical pulses). 2. A device or circuit for acquiring
or processing data. 3. A unit of data (e.g., a field
in a file).
data-flow diagram A block diagram showing the
movement of data through a data-processing system.
data format The form of data in a record or file
(e.g., character format or numerical format).
data gathering See DATA COLLECTION.
data-handling capacity 1. The amount of data
that can be stored in a memory circuit. 2. The
amount of data that can be transmitted over a
certain medium. 3. The rate at which data can be
transferred under certain conditions.
data-handling system A system that gathers,
routes, transmits, or receives data, but does not
necessarily process it.
data item A logical element (character, byte, or bit)
describing a characteristic of a record used by a
system for which there is a specific application.
data level Descriptive, through a programming
language, of the relative weight of logical elements (data items) in a computer record. Also
called data hierarchy.
data link The portion of a computer system that
gathers data and, if necessary, converts it to a
form acceptable by a computer.
data matrix Variables and their possible values
stored as a series of columns and rows of values
in a computer memory.
data name An operand specified in a computer
source program.
data pickup 1. A transducer that collects data signals from a source; it converts nonelectrical data
into corresponding electrical signals and delivers
its output to a data processing system. 2. Data
data playback The reproduction of data signals
stored by some method of data recording.
data plotter See X-Y PLOTTER.
data printout 1. A device that prints a record of
data or the results of a computation. 2. A permanent printed record, usually of a calculation or
computation—especially the printed output of a
computer peripheral device.
data processing Work performed on acquired
data, as in solving problems, making comparisons, classifying material, organizing files. Usually done by a computer.
data-processing equipment A digital computer
and the peripheral equipment needed to collate,
store, analyze, and reduce data.
data-processing machine A computer or system
used to collate, store, analyze, and reduce data,
as opposed to a computer or system used primarily to solve problems or perform routine tasks.
Also called data processor.
data-processing system An electronic system for
automatic data processing. It can be based on
analog and/or digital techniques.
data receiver • daylight lamp
data-processing system
data storage The preservation of data, particularly
computer files, for long periods of time in nonvolatile form (no source of power is required to
ensure that the data remains intact).
data storage media Hardware that preserves data,
particularly computer files, for long periods of
time in nonvolatile form (no source of power is required to ensure that the data remains intact).
Common media include magnetic disks, magnetic tape, and optical disks.
data synchronizer A device used to synchronize
data transmission within a computing or processing system.
data system 1. An arrangement for collecting,
recording, and routing data in the form of electrical signals. 2. An arrangement for processing
data (i.e., for correlating, computing, routing,
storing, etc.).
data terminal A remote input/output device connected to a central computer.
data throughput In a computer system, the
amount of data per unit time (bytes, kilobytes,
megabytes, gigabytes, or terabytes per second or
minute) that can be transferred from one place to
data transducer In tests and measurements, a
transducer that converts a monitored phenomenon into electrical quantities that can be
used for computer analysis or calculations.
data transmission Sending data signals from a
pickup point or processing stage to another point
within a data-processing system; also, sending
such signals to points outside the system.
data-transmission system A data transmitter and
its associated equipment.
data transmission utilization measure The ratio
of the useful data output of a data-transmission
system to the total data input.
data transmitter A circuit or device for sending
data from point to point within or outside of a
data-processing system.
data unit Characters in a group that are related in
a way that makes them a meaningful whole (e.g.,
a text word, or an object such as a circle in vector
data value A measure of the amount of information contained in a certain number of data bits.
The greater the ratio of the actual information to
the number of bits, the higher the data value.
data words In digital computer operations, words
(bit groups) representing data, rather than program instructions.
David Phonetic alphabet code word for letter D.
daylight effect The modification of transmission
paths during the day because of ionization of the
upper atmosphere by solar radiation.
daylight lamp An incandescent lamp whose filament is housed in a blue glass bulb, which absorbs some red radiation and transmits most of
data receiver At a particular point in a dataprocessing system, a circuit or device for
receiving data from a data transmitter.
data reception Receiving data signals from some
point within or outside a data-processing system.
data-reception system A data receiver and its associated equipment.
data record A computer-processed record containing a data unit.
data recorder A machine for storing data acquired
in the form of electrical signals (see DATA
data recording 1. The preservation of data signals
by some process, such as magnetic-disk encoding, optical-disk encoding, or tape recording, for
future use or as a backup. 2. A record of data signals, as on magnetic tape.
data reduction The summarization of a mass of
electronically gathered data.
data-reduction system A system used to minimize
the amount of data necessary to convey given information.
data representation Values and data as described
by numerals, symbols, and letters (e.g., computer
program instructions).
data segment As related to a particular computer
process, a subunit of allocated storage containing
data only.
data selector/multiplexer A digital circuit that
has several or many input signals, and feeds one
of them onto a common line.
data set A device that connects a data processor to
a telegraph or telephone line.
data signal 1. A signal (such as one of binary bit
combinations) that can represent data as numbers, letters, or symbols. 2. A signal current or
voltage proportional to some sampled quantity,
and that can be used to actuate indicating instruments during tests or measurements.
data statement A computer source program statement identifying a data item and specifying its
daylight lamp • dc converter
the green, blue, and violet. So called because the
spectral output resembles that of typical daylight.
daylight range The distance over which signals
from a given transmitter are consistently received
during the day.
DB 1. Abbreviation of DIFFUSED BASE of a transistor. 2. Abbreviation of DOUBLE BREAK (relay).
dB 1. Abbreviation of DECIBEL or decibels. 2.
Symbol for differential of susceptance.
dBa Abbreviation of ADJUSTED DECIBELS.
dBc Abbreviation of decibels referred to the carrier.
DBD Abbreviation of double-base diode.
dBd The power gain of an antenna in the direction
of maximum radiation, compared to the radiation
in the favored direction of a half-wave dipole in
free space receiving the same amount of power.
Expressed in decibels.
dBi The power gain of an antenna in the direction
of maximum radiation, compared to the radiation
from a theoretical isotropic antenna in free space
receiving the same amount of power. Expressed
in decibels.
dBj The level of an RF signal, in decibels, relative to
1 millivolt.
dBk Abbreviation of DECIBELS REFERRED TO 1
DBM Abbreviation of database management.
dBm Abbreviation of DECIBELS REFERRED TO 1
dBm0 Signal level in dBm, referred to a zero-transmission level.
dBm0p Noise in dBm0, measured with set phosphometric weighting.
dB meter A usually high-impedance ac voltmeter
with a scale reading directly in decibels.
dBmp The level in dBm, measured with phosphometric weighting. Generally equal to dBm –2.5,
for a noise level that is flat within the communications audio range.
dBmr Decibels measured with respect to zero
transmission level.
dBrn Abbreviation for decibels above reference
noise. A level of 0 dBrn is defined as noise power
of 10–9 W (1 nanowatt).
dBrnc Noise power in dBrn for a circuit with message weighting c.
dBrnc0 Noise in dBrnc measured with respect to
zero transmission level.
dBV Abbreviation of DECIBELS REFERRED TO 1
dBW Abbreviation of DECIBELS REFERRED TO 1
dC Symbol for differential of capacitance.
dc 1. Abbreviation of DIRECT CURRENT. 2. Abbreviation of direct-coupled.
dc-ac converter A circuit that converts a dc input
voltage into an ac output voltage, with or without
step-up or step-down. Also called INVERTER.
dc alpha The current amplification factor (ALPHA)
of a common-base transistor stage for a dc input
(emitter) signal. Compare DC BETA.
dc amplifier 1. A direct-coupled amplifier. 2. An
amplifier for boosting direct-current signals.
dc balance 1. Adjustment of a circuit or device for
dc stability or dc null. 2. Adjustment of a circuit
for dc stability during gain changes. 3. A potentiometer or other variable component used to stabilize or null a dc circuit.
dc bar See DC BUS.
dc base current Symbol, IB(dc). The static direct
current in the base element of a bipolar transistor.
dc base resistance Symbol, RB(dc). The static dc resistance of a bipolar transistor’s base element;
RB(dc) = VB/IB.
dc base voltage Symbol, VB(dc). The static dc voltage at the base element of a bipolar transistor.
dc beta The current amplification factor (BETA) of
a common-emitter-connected transistor for a dc
input (base) signal. Compare DC ALPHA.
dc block A coaxial section that has a capacitance
in series with the inner or outer conductor, or
both, to block dc while passing RF. Compare DC
dc bus A supply conductor carrying direct current
dcc Abbreviation of double cotton covered (wire).
dc cathode current Symbol, IK(dc). The static direct
current in the cathode element of an electron
dc cathode resistance Symbol, RK(dc). The static dc
resistance of the cathode path of an electron
dc cathode voltage Symbol, VK(dc). The static dc
voltage at the cathode of an electron tube.
dc circuit breaker A circuit breaker operated by
direct-current overload or underload, depending
on its design and application.
dc collector current Symbol, IC(dc). The static direct current in the collector element of a bipolar
dc collector resistance Symbol, RC(dc). The static
dc resistance of a bipolar transistor’s collector element; RC(dc) = VC/IC.
dc collector voltage Symbol, VC(dc). The static dc
voltage at the collector element of a bipolar transistor.
dc component In a complex wave (i.e., one containing both ac and dc), the current component
having an unchanging polarity. The dc component constitutes the mean (average) value around
which the ac component alternates, pulsates, or
dc converter A dynamoelectric machine for converting low-voltage dc into higher-voltage dc. It is
essentially a low-voltage dc motor coupled me-
dc converter • dc plate resistance
dc component
dc component
chanically to a higher-voltage dc generator. Compare DC INVERTER.
dc coupling See DIRECT COUPLING.
dc drain current Symbol, ID(dc). The static direct
current in the drain element of a field-effect transistor.
dc drain resistance Symbol, RD(dc). The static dc
resistance of an FET’s drain element; RD(dc) =
dc drain voltage Symbol, VD(dc). The static dc voltage at the drain element of a field-effect transistor.
dc dump In digital computer operation, removing
dc power from a computer, which would eradicate
material stored in a volatile memory.
dc emitter current Symbol, IE(dc). The static direct
current in the emitter element of a bipolar transistor.
dc emitter resistance Symbol, RE(dc). The static dc
resistance of a bipolar transistor’s emitter element; RE(dc) = VE/IE.
dc emitter voltage Symbol, VE(dc). The static dc
voltage at the emitter element of a bipolar transistor.
dc equipment Apparatus designed expressly for
operation from a dc power supply. Compare AC
dc erase head In a magnetic recorder, a head supplied with a dc current for the purpose of removing data.
dc error voltage In a television receiver, the dc
output of the phase detector, which is used to
control the frequency of the horizontal oscillator.
dc gate current Symbol, IG(dc). The very small static
direct current in the gate element of a field-effect
dc gate resistance Symbol, RG(dc). The very high,
static dc resistance of an FET’s gate element;
RG(dc) = VG/IG.
dc gate voltage Symbol, VG(dc). The static dc voltage at the gate element of a field-effect transistor.
dc generator 1. A rotating machine (dynamo) for
producing direct current. Also see DYNAMOELECTRIC MACHINERY. 2. Generically, a device
that produces direct current: batteries, photocells, thermocouples, etc.
dc generator amplifier A special type of generator
that provides power amplification. The input sig-
nal energizes the field winding of a constantspeed machine; because the output voltage is
proportional to field flux and armature speed, a
high output voltage is obtained. Also see AMPLIDYNE.
dc grid bias Steady dc control-grid voltage used to
set the operating point of an electron tube.
dc grid current Symbol, IG(dc). The static direct current in the control-grid element of an electron tube.
dc grid resistance Symbol, RG(dc). The static dc resistance in the control-grid element of an electron
tube; RG(dc) = VG/IG.
dc grid voltage Symbol, VG(dc). The static dc voltage
at the control grid of an electron tube.
dc inserter In a television transmitter, a stage that
adds the dc pedestal (blanking) level to the video
dc inverter An electrical, electronic, or mechanical
device that converts dc to ac. Also called INVERTER.
dcl Abbreviation of dynamic load characteristic.
dc leakage The unintended flow of direct current.
dc leakage current 1. The direct current that normally passes through a correctly polarized electrolytic capacitor operated at its rated dc working
voltage. 2. The zero-signal reverse current in a
semiconductor pn junction.
D/CMOS Combination of DMOS and CMOS on a
monolithic chip.
dc motor A motor that operates from direct current only.
dc noise Noise heard during the playback of magnetic tape that was recorded while direct current
was in the record head.
dc noise margin In a digital or switching circuit,
the difference Vo – Vi , where Vo is the outputvoltage level of a driver gate and Vi is the input
threshold voltage of a driven gate.
dc operating point For a bipolar transistor, fieldeffect transistor, or vacuum tube, the static, zerosignal dc voltage and current levels.
dc overcurrent relay A relay or relay circuit actuated by dc coil current rising above a specified
dc overvoltage relay A relay or relay circuit actuated as a result of the dc coil voltage rising above
a specified level. Compare DC UNDERVOLTAGE
dc patch bay A patch bay in which the dc circuits
of a system are terminated.
dc picture transmission In television, transmission of the dc component of the video signal; this
component corresponds to the average illumination of the scene.
dc plate current Symbol, IP(dc). The static direct
current in the plate element of an electron tube.
dc plate resistance Symbol, RP(dc). The static dc resistance of the internal plate-cathode path of an
electron tube; RP(dc) = VP/IP.
dc plate voltage • dead band
dc plate voltage Symbol, VP(dc). The static dc voltage at the plate electrode of an electron tube.
dc positioning Alignment of the spot on the screen
of an oscilloscope tube, by means of adjustable dc
voltages applied to the horizontal and vertical deflecting plates.
dc power Symbol, Pdc. Unit, watt. The power in a
dc circuit; Pdc = EI, where E is in volts and I is in
amperes. Compare AC POWER. Also see POWER.
dc power supply A power unit that supplies direct
current only. Examples: battery, transformer/
rectifier/filter circuit, dc generator, and photovoltaic
cell. Compare AC POWER SUPPLY.
dc relay A relay having a simple coil and core system for closure by direct current, which can be
rectified ac.
dc resistance Resistance offered to direct current,
as opposed to in-phase ac resistance.
dc resistivity The resistivity of a sample of material measured using a pure dc voltage under
specified conditions (physical dimensions, temperature, etc.).
dc restoration The reinsertion of the dc component into a signal from which the component has
been extracted through a capacitor or transformer.
dc restorer A circuit that reinserts the average dc
component of a signal after the component has
been lost because the signal passed through a capacitor or transformer.
dc shift A shift in the DC OPERATING POINT.
dc short A coaxial fitting providing a dc path between the center and outer conductors, while
permitting radio-frequency (RF) current to flow
easily through the coaxial section. Compare DC
dc signaling A signaling procedure that uses direct
current as the medium (e.g., simple wire telegraphy or telephony).
dc source 1. DC GENERATOR. 2. A live circuit
point from which one or more direct currents can
be taken.
dc source current Symbol, IS(dc). The static direct
current in the source element of a field-effect
dc source resistance Symbol, RS(dc). The static dc
resistance of an FET’s source element.
dc source voltage Symbol, VS(dc). The static dc
voltage at the source element of a field-effect
dc-to-dc inverter See DC INVERTER.
dc transducer 1. A transducer that depends on direct current for its operation (i.e., it has a dc
power supply whose output is modulated by the
sensed phenomenon). 2. A transducer that converts a direct current into some other form of energy, such as heat, pressure, or sound.
dc transformer A dc-to-dc converter providing
voltage step-up. The applied dc is usually first
converted to ac, which is then stepped up by a
transformer. The higher-voltage ac is then rectified to produce a high dc output voltage.
dc transformer
dc transmission 1. Sending dc power from a generating point to a point of use. 2. In television
transmission, the retention of the dc component
in the video signal.
dc tuning voltage The capacitance-varying dc
voltage applied to a varactor in an inductancecapacitance (LC) tuned circuit.
dcu Abbreviation of decimal counting unit.
dc undercurrent relay A relay or relay circuit that
is actuated as a result of the dc coil current dropping below a specified level. Compare DC OVERCURRENT RELAY.
dc undervoltage relay A relay or relay circuit that
is actuated as a result of the dc voltage dropping
below a specified level. Compare DC OVERVOLTAGE RELAY.
dcv Abbreviation of DC VOLTS or DC VOLTAGE.
dc voltage Abbreviation, dcv. A voltage that does
not change in polarity, an example being the voltage delivered by a battery or dc generator. Also
dc working voltage Abbreviation, dcwv. The rated
dc voltage at which a component can be operated
continuously with safety and reliability.
dc working volts Abbreviation, dcwv. The actual
value, expressed in volts, of a DC WORKING
dcwv Abbreviation of DC WORKING VOLTAGE.
dD Symbol for differential of electric displacement.
DDA Abbreviation of digital differential analyzer.
D display See D SCOPE.
DE Abbreviation of decision element.
dE Symbol for differential of voltage.
deac In frequency-modulation (FM) receivers, a device used for deemphasis. The name is short for
deactuating pressure For an electrical contact,
the pressure at which contact is made or broken
as the pressure reaches the level of activation.
dead 1. Unelectrified. 2. Lacking electromagnetic
signals or fields. 3. Electrically or mechanically
dead band 1. A radio-frequency band on which no
signals are heard. 2. A range of values for which
an applied control quantity (e.g., current or voltage) has no effect on the response of a circuit.
deadbeat • decade capacitor
deadbeat The state wherein a moving body (such
as the pointer of a meter or the voice coil of a
loudspeaker) comes to rest without overswing or
deadbeat galvanometer See DEADBEAT INSTRUMENT.
deadbeat instrument A meter or recorder that is
highly damped to ensure that overswing or oscillation does not occur.
deadbeat meter See DEADBEAT INSTRUMENT.
dead break An unreliable contact of a relay,
caused by insufficient pressure.
dead circuit A circuit that is electrically disabled.
dead end The unused end of a tapped coil (i.e., the
turns between the end of the coil and the last
turn used).
dead-end tower A supporting tower for an antenna
or transmission line that can withstand stresses
caused by loading or pulling.
dead file A computer file that is not in use, but is
being kept in a record.
dead front panel A metal panel that, for safety and
desensitization, is completely insulated from voltage-bearing components mounted on it; it is often
dead interval See DEAD TIME.
dead line A deenergized line or conductor.
dead period See DEAD TIME.
dead room An anechoic room in which acoustic
tests and studies are made.
dead short A short circuit with extremely low (virtually no) resistance from dc into the radiofrequency spectrum.
dead space See DEAD BAND.
dead spot 1. An area in which radio waves from a
particular station are not received. 2. On a
vacuum-tube cathode (directly or indirectly
heated), a spot from which no electrons are
dead stretch The tendency of insulating materials
to permanently retain their approximate dimensions after having been stretched.
dead time 1. DOWN TIME. 2. An interval during
which there is no response to an actuating signal.
3. In a computer system, an interval between related events that is allocated to prevent interference between the events.
dead volume In a pressure transducer, the zerostimulus volume of the pressure port cavity.
dead zone See ZONE OF SILENCE.
debatable time Computer time that cannot be
placed in any other category.
debounced switch A switch in sensitive computer
or control systems that has circuitry for eliminating the electrical effects of bounce (see BOUNCE,
de Broglie waves Electromagnetic waves that are
believed to be associated with moving particles
(such as electrons, protons, and neutrons).
debug 1. To eliminate errors in, and maximize the
efficiency of, a computer program or group of pro-
grams. 2. To optimize the design and construction of electronic equipment.
debugging A process by which engineers eliminate
the flaws in a circuit, machine, or computer program.
debugging aid routine A computer program used
to test other programs.
debugging period The time interval following completion of a software design, a hardware interconnection, or the manufacture of a piece of
electronic equipment, during which errors and
imperfections are sought and corrected.
debunching In a velocity-modulated tube, such as
a Klystron, a beamspreading space-charge effect
that destroys electron bunching.
Debye length The maximum distance between an
electron and a positive ion over which the electron is influenced by the field of the ion.
Debye shielding distance See DEBYE LENGTH.
deca- A prefix that indicates multiplication by 10.
decade 1. A frequency band whose upper limit is 10
times the lower limit. Example: 20 Hz to 200 Hz. 2.
A set of 10 switched or selectable components in
which the total value is 10 times that of individual
values. Example: a decade capacitor. Also called
DECADE BOX. 3. A group, sometimes a unit of access, of 10 computer storage locations.
decade amplifier An amplifier or preamplifier
whose gain can be adjusted in increments of 10
(×1, ×10, ×100, etc.).
decade box A group of components that provides
values in 10 equal steps selected by a switch or
jacks. For compactness, the components and the
associated hardware are enclosed in a box or can.
See, for example, DECADE CAPACITOR.
decade capacitor A composite capacitor whose
value is variable in 10 equal steps. For example,
the values might be set at 100 picofarads (pF),
200 pF, 300 pF, etc., up to 1000 pF. Compare
decade box
decade counter • decimal code
decade counter A counter (see COUNTER, 1, 2) in
which the numeric display is divided into
sections, each having a value 10 times that of the
next and displaying a digit from zero to nine.
decade inductor An inductor whose value is variable in 10 equal steps. Compare DECADE CAPACITOR and DECADE RESISTOR.
decade resistor A resistor whose value is variable
in 10 equal increments. Compare DECADE CAPACITOR and DECADE INDUCTOR.
decade scaler A scale-of-10 electronic counter
(i.e., a circuit delivering one output pulse for each
group of 10 input pulses).
decametric waves Waves in the 10- to 100-meter
band (30 to 3 MHz).
decay 1. The decrease in the value of a quantity,
e.g., current decay in a resistance-capacitance
circuit. 2. The gradual, natural loss of radioactivity by a substance.
decay characteristics 1. The decay of a parameter; usually an exponential function. 2. The persistence time in a storage oscilloscope.
decay curve A curve, usually logarithmic, representing the function of quantity versus time for a
signal decrement, the decrement of radioactivity,
or other natural process.
decay rate A quantitative expression for the rapidity with which a quantity decreases. Generally
listed in decibels per second (dB/s) or decibels
per millisecond (dB/ms).
decay time The time required for pulse amplitude
to fall from 90% to 10% of the peak value. Also
called FALL TIME.
Decca A 70- to 130-kHz CW radio navigation system (British).
decelerated electron A high-speed electron that is
abruptly decelerated upon striking a target, causing X-rays to be emitted.
decelerating electrode A charged electrode that
slows the electrons in an electron beam.
deceleration Acceleration that results in a decrease in speed.
deceleration time 1. The time taken by magnetic
tape to stop moving after the last recording or
playback has finished. 2. The time taken by a
mechanical data storage medium, such as
a hard disk, to come to rest after completion
of a read or write operation, or on poweringdown.
decentralized data processing Data processing in
which the computing equipment is distributed
among managerial subgroups.
deception A method of producing misleading
echoes in enemy radar.
deception device A radar device, or radar-associated device, for deception.
deci- Abbreviation, d. A prefix meaning one-tenth
(10–1). Examples: DECIBEL, DECIMETER.
decibel Abbreviation, dB. A practical unit of relative gain. In terms of power, the relative gain in
decibels is equal to:
Gain (dB) = 10 log10(Pout/Pin ),
where Pout is the output power and Pin is the input
power. For voltage, if the input and output
impedances are the same, the gain in decibels is
given by:
Gain (dB) = 20 log10(Vout/Vin ),
where Vout is the output voltage and Vin is the input voltage. For current, if the input and output
impedances are the same, the gain in decibels is
given by:
Gain (dB) = 20 log10(Iout/Iin),
where Iout is the output current and Iin is the input
current. Losses are indicated by negative dB gain
decibels above reference acoustic power Abbreviation, dBrap. The ratio of a given acoustic
power level to a lower reference acoustic power
level, specified in decibels.
decibels above reference noise Abbreviation,
dBrn. The ratio of the noise level at a selected
point in a circuit to a lower reference noise level,
in decibels.
decibels referred to 1 millivolt Abbreviation,
dBmV. The relative voltage level of a signal when
compared with a 1-mV signal measured at the
same terminals.
decibels referred to 1 milliwatt Abbreviation,
dBm. The ratio, in decibels, of an applied power
level to the power level of 1 mW.
decibels referred to 1 volt Abbreviation, dBV. The
ratio, in decibels, of a given voltage to 1 V, expressed in decibels.
decibels referred to 1 watt Abbreviation, dBW.
The ratio of a given power level to the power level
of 1 W, expressed in decibels.
decigram A unit of mass equal to 0.1 gram.
deciliter A unit of volume equal to 0.1 liter, or 10–4
cubic meter.
decilog A unit equal to 0.1 times the common logarithm of a ratio.
decimal 1. Pertaining to the base-10 number system (see DECIMAL NUMBER SYSTEM). 2. A
base-10 numerical fraction, represented by figures to the right of the radix point (decimal point),
and arranged serially according to negative
powers of 10. Examples: 0.12 = 1.2 × 10–1,
0.00135 = 1.35 × 10–3.
decimal attenuator An attenuator circuit whose
resistances are chosen for attenuation in decimal steps. Thus, one section provides attenuation in steps of 0.1 times the applied voltage,
another in steps of 0.01 times the applied voltage, another in steps of 0.001 times the applied
voltage, etc.
decimal code A method of defining numbers, in
which each place has a value of ten times that immediately to the right.
decimal-coded digit • decommutation
decimal-coded digit 1. A numeral from 0 to 9. 2.
3. A binary representation of a decimal value
from 0 to 9.
decimal digit A numeral from 0 to 9.
decimal equivalent The decimal number equal to
a given fraction (e.g., the decimal equivalent of
64 is 0.3281).
decimal fraction See DECIMAL, 2.
decimal notation See DECIMAL NUMBER SYSTEM.
decimal number system The familiar base-10 or
radix-10 number system, in which the digits 0
through 9 represent values according to their position, relative to the decimal point (also called
the radix point). Positions to the left of the point
represent successive positive powers of 10, and
those to the right represent successive negative
powers of 10.
decimal point The radix point in a decimal number. It serves to separate the integral part from
the fractional part of the number.
decimeter waves See MICROWAVES.
decimetric waves Electromagnetic waves having
lengths ranging from 0.1 meter to 1 meter (3000
MHz to 300 MHz). Also known as ultrahigh frequency (UHF).
decineper A natural-logarithmic unit equal to 0.1
decipher See DECODING, 3.
decision 1. A choice based on the evaluation and
comparison of data, and the identification of a
specified objective. 2. In digital computer operations, the automatic selection of the next step in
a sequence, on the basis of data being compared
by a relational test.
decision box A block on a computer flowchart indicating the point at which a decision (see DECISION, 2) must be made as to which of several
branches the program will take.
decision elements See LOGIC CIRCUITS.
instruction A
instruction to compare the values of operands
and take an appropriate action, as per the BASIC
instruction “IF A = B THEN GO TO (line number).”
decision procedure In decision theory, a series of
calculations made to optimize the speed or efficiency of a process, or to minimize risk, failure,
cost, etc.
decision theory A statistical discipline concerned
with identifying and evaluating choices and alternatives, and determining the best sequence of
steps to take in reaching an objective.
decision tree In decision theory, a diagram showing alternative choices, so called from its resemblance to a tree with branches.
decision value A value that defines the boundary
between two intervals in the encoding process.
deck 1. See TAPE DECK. 2. A pack of punched
cards in a computer file.
declarative macroinstruction As part of an assembly language, instructions to the compiler to
do something or record a condition without affecting the object program.
declarative statement A computer source program instruction specifying the size, format, and
kind of data elements and variables in a program
for a compiler.
declination 1. The angle representing the deviation of magnetic north from true north; it is the
angle subtended by a freely turning magnetic
needle and the meridian. Compare INCLINATION.
2. Celestial latitude.
θ = Declination
Compass needle
declination, 1
declinometer An instrument for measuring declination.
decode 1. To unscramble a coded message. 2. In
digital computer operations, to deliver a specific
output from character-coded inputs. 3. In a multiplex system, the separation of the subcarrier
from the main carrier.
decoder A circuit or device for performing DECODING.
decoder/demultiplexer A circuit that places an
input signal on a selected output line.
decoder/driver An integrated circuit containing a
decoder and driver.
decoding 1. In computer and data-processing operations, DIGITAL-TO-ANALOG CONVERSION.
2. The conversion to English of a message received in a code. 3. Translating a message from a
secret code (i.e., deciphering a message). 4. The
automatic conversion of a signal into the appropriate switching action (as the enabling of a
transmitter or receiver by a tone in a selective
calling system).
decoding circuit A circuit intended for the purpose of translating a code into ordinary language.
decollator An offline computer device for separating the parts of output continuous stationery
decommutation The extraction of a signal component from the composite signal, resulting from
decommutator • definite-purpose component
decommutator A circuit or device for performing
decommutation, including demodulators, demultiplexers, and signal separators.
decoupler A device that isolates two circuits so
that a minimal amount of coupling exists between them.
decoupling The elimination or effective minimization of coupling effects, as in decoupling amplifier
stages to prevent interaction through a common
power-supply lead.
decoupling capacitor 1. A capacitor that provides
a low-impedance path to ground to prevent
undesired stray coupling among the circuits in a
system. 2. The capacitive member of a resistancecapacitance (RC) decoupling filter.
decoupling filter A resistance-capacitance (RC) filter, usually inserted into a common dc line in a
multistage amplifier to prevent interstage feedback coupling through the common impedance of
the line.
decoupling network One or more decoupling filters.
decoupling resistor The resistive member of a resistance-capacitance (RC) decoupling filter.
decoy In radar, an object that provides misleading
reflections. Also see CHAFF.
decreasing function A function whose curve has a
negative slope at all points in the domain.
decrement 1. Also called logarithmic decrement.
The rate at which a damped wave dies down. The
decrement value is the natural (base-e) logarithm
of the ratio of two successive peaks of the same
polarity. 2. A quantity used to lessen the value of
a variable. 3. To lower the value (of a register, for
example) by a single increment.
decremeter An instrument for measuring the decrement of a radio wave.
decremeter capacitor A variable capacitor for use
in a decremeter. The rotor plates are shaped so
that equal angular rotations correspond to the
same decrement at all settings. Thus, the percentage of capacitance change for a given angle of rotation is constant throughout the capacitance range.
decryption The conversion of an encrypted signal
from a cipher into plain text, graphics, or other
commonly recognizable form. Also see CIPHER.
decryption key An algorithm, or a set of algorithms,
that converts an encrypted signal from a cipher
into plain text, graphics, or other commonly recognizable form. Each cipher has its own unique
algorithm or set of algorithms for this purpose.
The signal cannot be decrypted unless all the
components of the key are present.
dedicated Assigned exclusively to a certain purpose [e.g., a dedicated facsimile (fax) line].
deductive logic A form of symbolic logic used to
demonstrate that a certain conclusion will always
follow, given a certain set of circumstances. The
logic of digital circuits is deductive. Compare INDUCTIVE LOGIC.
dee In a cyclotron, one of the D-shaped chambers
in and between which particles accelerate in a
spiral path to high velocity.
dee line In a cyclotron, a support for the dee, with
which it forms a resonant circuit.
deemphasis In frequency modulation, the introduction of a low-pass characteristic (response
falls as modulating frequency increases) to complement the rising response of preemphasis. Also
called postemphasis or postequalization. Compare PREEMPHASIS.
deemphasis amplifier An amplifier used to remove the high-frequency preemphasis applied to
signals prior to broadcasting, multiplexing, tape
recording, or telemetering. Also see DEEMPHASIS and PREEMPHASIS.
deemphasis circuit A low-pass filter that provides
deemphasis in an FM receiver.
deemphasis network See DEEMPHASIS CIRCUIT.
deenergize To take a circuit or device out of operation (i.e., to remove its power or signal excitation).
deep cycle Pertaining to a rechargeable cell or battery that can operate until it is almost completely
discharged. It generally has a high ampere-hour
deep-diffused junction A pn junction made by diffusing the impurity material deep in the semiconductor wafer. Compare SHALLOW-DIFFUSED
deep discharge The nearly complete discharge of a
cell or battery; usually done prior to recharging.
deep-space net A radar system intended for constant monitoring of spacecraft.
defeating 1. The disabling or circumvention of an
alarm or security system, leaving the protected
property vulnerable to intrusion. 2. The dangerous, and potentially lethal, disabling of a safety
device in an electrical or electronic system.
defect 1. Absence of an electron (hence, presence
of a hole) in the lattice of a semiconductor crystal.
2. An abnormality of design, construction, or performance of an electronic circuit or device. 3. In a
computer system, a hardware or software fault
that could be the eventual cause of a failure. 4. A
flaw in a crystalline substance.
defect conduction In a semiconductor material,
conduction via holes.
deferred addressing Indirect addressing in which
a preset counter makes several references to find
a desired address.
deferred entry An entry into a computer subroutine, delayed because of a delay in the exit from a
control program.
deferred exit An exit from a computer subroutine,
delayed because of a particular command.
defibrillation Use of a CARDIAC STIMULATOR to
halt fibrillation of the heart, as caused by electric
defibrillator See CARDIAC STIMULATOR.
definite-purpose component A component designed for a specific use, rather than for a wide
definite-purpose component • degenerate parametric amplifier
range of possible applications (e.g., a video detector diode, as opposed to a general-purpose diode).
definition 1. Clarity of a video image (i.e., one having good contrast and faithful tones). 2. Good intelligibility of reproduced sounds.
deflecting coil One of a set of external coils carrying sawtooth currents, which provide electromagnetic deflection of the cathode-ray beam in
picture tubes, camera tubes, radar display tubes,
sonar display tubes, and some oscilloscopes. Also
called deflection coil.
deflecting electrode An electrode, such as a deflecting plate, used to alter the direction an electron beam. Also called deflection electrode.
deflecting plate In a cathode-ray tube, a plate that
attracts or repels the electron beam, causing the
spot to move horizontally or vertically on the
screen. Also called deflection plate.
Path of
deflecting plate
deflecting torque The torque required to move the
pointer of a meter, or the pen or mirror of a
deflection 1. In a cathode-ray tube, movement of
the electron beam by electric or magnetic fields.
2. Movement of the pointer of a meter or the pen
or mirror of a recorder by an applied current or
deflection factor Symbol, G. The reciprocal of DEFLECTION SENSITIVITY.
deflection plane In a cathode-ray tube, the plane
perpendicular to the axis of the tube. This plane
contains the electromagnetic and/or electrostatic
lines of flux that result in deflection of the electron beam.
deflection coil See DEFLECTING COIL.
deflection electrode See DEFLECTING ELECTRODE.
deflection plate See DEFLECTING PLATE.
deflection polarity In a cathode-ray tube, the polarity of the voltage applied to a particular deflecting plate to move the electron beam in a
particular direction.
deflection sensitivity Symbol, S. A quantitative
measure of the extent to which the input voltage
will displace the electron beam on the screen of
an electrostatic cathode-ray tube. Expressed in
volts per centimeter (V/cm) or volts per inch
deflection voltage The potential difference between the deflection plates of an electrostatic
cathode-ray tube. It is used to control the direction of the electron beam striking the phosphor
deflection yoke An assembly of deflection coils in
picture and camera tubes, and in some magnetically deflected oscilloscope tubes. The usual combination is two series-connected horizontal
deflection coils and two series-connected vertical
deflection coils.
deflector 1. A beam-forming plate in a beampower tube. 2. A deflection plate in a cathode-ray
tube. 3. A deflection coil or yoke in a picture tube,
camera tube, or magnetic-deflection oscilloscope
tube. 4. A mechanical attachment for improving
the angle of radiation of a loudspeaker by spreading the higher-frequency waves.
defocusing Blurring of the image on the screen of
a cathode-ray tube, caused by spreading of the
electron beam.
deformation potential The voltage generated
when a crystal lattice is subjected to pressure. An
example is the voltage produced by a crystal microphone when acoustic waves strike the crystal.
defruiting The elimination of non-synchronized
echoes in a radar system.
deg Abbreviation of DEGREE.
degassing During the evacuation of a vacuum tube
or similar device, the removal of gas, including
that which has bonded to the glass and metal
degauss See DEMAGNETIZE.
degausser 1. A circuit that performs DEGAUSSING. 2. A device for bulk erasing magnetic tape;
also called a bulk tape eraser.
degaussing 1. The demagnetization of an object; in
particular, the removal of all residual magnetism.
2. The erasure of data from a magnetic or
magneto-optical data-storage medium.
degaussing circuit In a color television receiver, a
circuit including a thermistor, voltage-dependent
resistor, and coil for automatically demagnetizing
the picture tube when the receiver is switched on.
degaussing coil A coil carrying an alternating current; the resulting magnetic field demagnetizes
objects that have become accidentally magnetized.
degeneracy In microwave practice, the appearance
of a single resonant frequency for two or more
modes in a resonator.
degenerate modes In microwave operations, a set
of modes with the same resonant frequency or
propagation constant.
degenerate parametric amplifier An inverting
parametric amplifier, in which the two signals are
of the same frequency, which is half the pump
degenerate semiconductor • deka-
degenerate semiconductor A semiconductor that
behaves like a metal over a wide range of temperatures.
degeneration In an amplifier, the technique of
feeding a portion of the output back to the input
out of phase with the input signal, to improve fidelity at the expense of gain. Also called negative
feedback or inverse feedback. Compare REGENERATION.
degenerative resistor An unbypassed emitter resistor in a common-emitter bipolar-transistor
circuit, or an unbypassed source resistor in a
common-source field-effect transistor circuit.
Signal current flowing through the resistor
produces negative feedback current (degeneration), which reduces the gain of the stage, but
increases the linearity of the transfer characteristic.
degenerative resistor
degradation 1. Gradual deterioration in the condition or performance of a circuit or device. 2. In a
computer system, compromised performance
caused by component failure.
degradation failure Failure occurring at the terminal point of degradation.
degraded operation See DEGRADATION.
degree 1. A unit of circular angular measurement
equal to 1/360 of the circumference of a circle. Also
called GEOMETRIC DEGREE. 2. A unit of
degree absolute Symbol, K. The unit of temperature on the absolute scale. Also see ABSOLUTE
degree Celsius Symbol, °C. The unit of temperature on the CELSIUS SCALE.
degree centigrade Symbol, °C. The unit of temperature on the centigrade scale (now called CELSIUS SCALE).
degree Fahrenheit Symbol, °F. The unit of temperature on the FAHRENHEIT SCALE.
degree of current rectification For a rectifier, the
ratio of the average direct output current to the
root-mean-square (rms) alternating input current.
degree of voltage rectification For a rectifier, the
ratio of the average direct-current (dc) output
voltage to the root-mean-square (rms) alternating-current (ac) input voltage.
degree Reaumur Symbol, °R. The unit of temperature on the REAUMUR SCALE.
degrees of freedom 1. The ways in which a point
can move or a system can change. In threedimensional space, a rigid body has six degrees of
freedom: motion in three linear directions, and
rotation around three linear axes extending
through its center. 2. The ways in which a robot
arm can move, including linear motion and rotational motion.
degrees of rotation A measure of the extent to
which a robot joint, or a set of robot joints, can be
turned. Some reference axis is always used; angles are specified in degrees, relative to that axis.
degrees-to-radians conversion The conversion of
angles in degrees to angles in radians. To change
degrees to radians, multiply degrees by 0.01745.
deion circuit breaker A circuit breaker in which
the arc occurring when the contacts open is
quickly extinguished by an external magnetic device.
deionization The conversion of an ionized substance, such as a gas, to a neutral (non-ionized)
state. The process changes the ions into uncharged atoms.
deionization potential The voltage at which an
ionized substance becomes deionized; for example, the voltage at which a glow discharge is extinguished when the gas ions become neutral
atoms at that voltage. Also called extinction potential.
deionization time The time required for an ionized
gas to become neutral after the removal of the
ionizing voltage.
deionization voltage See DEIONIZATION POTENTIAL.
deionize To restore to an electrically neutral condition (i.e., to convert ions to neutral atoms, as in
the deionization of the gas when the discharge in
a glow tube is extinguished).
deka- A prefix meaning ten(s) (e.g., DEKAMETER).
dekahexadecimal number system • delay time
delayed repeater A repeater that receives and
stores information, and retransmits the information later, in response to a switching or interrogation signal.
delayed repeater satellite An active communications satellite that acts as a delayed repeater (i.e.,
it receives and records information at one time
and retransmits it at a later time).
delayed sweep 1. In an oscilloscope or radar, a
sweep that starts at a selected instant after the
signal under observation has started. 2. The
(usually calibrated) circuit for producing a sweep,
as defined in (1).
delayed updating Updating a computer record or
record set so that the record fields are left unchanged until all other changes attendant to the
pertinent event are processed.
delay equalizer A network that corrects DELAY
delay-frequency distortion Distortion caused by
variation of envelope delay within a frequency
delay line A device (not always a line) that introduces a time lag in a signal. The lag is the time required for the signal to pass through the device,
minus the time necessary for the signal to traverse the same distance through a wire, cable,
optical fiber, or free space.
delay-line memory In a digital computer, a memory that uses a delay line, associated input- and
output-coupling devices, and an external regenerative-feedback path. Information is kept stored
by causing it to recirculate in the line by regeneration.
delay-line register In a digital computer, a register
that operates in the manner of a DELAY-LINE
MEMORY and has a register length (capacity) of
an integral number of words.
delay-line storage See DELAY-LINE MEMORY and
delay multivibrator See MONOSTABLE MULTIVIBRATOR.
delay-power product Unit, watt-second. The figure of merit for an integrated circuit (IC) gate. Increasing gate power reduces propagation delay.
delay relay A relay that opens or closes at the end
of a predetermined time interval.
delay switch A switch having delayed make, delayed break, or both.
delay time 1. The interval between the instant a
voltage or current is applied and the instant a
circuit or device operates. 2. In an output pulse,
the interval between the instant an ideal pulse
is applied to the input of a system and the instant the output pulse reaches 10% of its maximum amplitude. 3. The time elapsed between
the presentation of a pulse to the input of a delay line and the appearance of the pulse at the
dekahexadecimal number system See HEXADECIMAL NUMBER SYSTEM.
delamination The splitting apart, in layers, of an
insulating material, such as mica or bonded plastic film.
delay 1. The interval between the instant at which
a signal or force is applied or removed and the instant at which a circuit or device subsequently
responds in a specified manner. 2. The time required for a signal to traverse a given medium,
such as air, mercury, or quartz.
delay action Response occurring some time after a
stimulus has been applied or removed (e.g., the
retarded opening of a delayed-dropout relay).
delay circuit 1. A circuit, such as a resistance-capacitance (RC) or resistance-inductance (RL)
combination, that introduces a time delay. 2. See
delay coincidence circuit A coincidence circuit
(see AND CIRCUIT) triggered by two pulses, one of
which lags behind the other.
delay counter In a digital computer, a device that
halts a program run long enough for an operation
to be completed.
delay distortion 1. Distortion resulting from variations in the phase delay of a circuit or device at
different points in its frequency range. 2. In a facsimile (fax) signal, variations in the delay of different frequency components of the signal.
delayed automatic gain control An automatic
gain control circuit that operates only when
the signal amplitude exceeds a predetermined
threshold level, thus providing maximum amplification of weaker signals.
delayed automatic volume control See DELAYED AUTOMATIC GAIN CONTROL.
delayed break In relay or switch operation, contacts separating some time after the switch has
been thrown or the relay deenergized. Compare
delayed close See DELAYED MAKE.
delayed closure See DELAYED MAKE.
delayed contacts Contacts that open or close at a
predetermined instant after their activating signal is applied or removed.
delayed drop-in See DELAYED MAKE.
delayed dropout See DELAYED BREAK.
delayed loop In security applications, a circuit or
system that registers an alarm some time after
intrusion is first detected. The delay can usually
be selected or preadjusted.
delayed make In relay or switch operation, contacts closing some time after the switch has been
thrown or the relay has been energized. Compare
delayed open See DELAYED BREAK.
delayed PPI Plan-position indicating radar having
a delayed time base.
delayed pull-in See DELAYED MAKE.
delay timer • demodulator
delay timer 1. A timer that starts or stops an operation after a prescribed length of time. 2. A delay relay or switch.
delay unit In a radar system, a circuit for delaying
delete 1. To erase or blank out a signal. 2. The
elimination from a computer file of a record or
record group. 3. To remove a computer program
from memory or storage.
deletion record In the master file of a digital computer, a new record that causes existing ones to
be deleted.
delimiter In digital computer operations, a character limiting a sequence of characters of which it is
not itself a member.
Dellinger effect The sudden disappearance of a
radio signal as a result of an abrupt increase in
atmospheric ionization caused by a solar eruption.
deliquescent material A material that absorbs
enough moisture from the air to get wet. For example; calcium chloride, a deliquescent material,
is often used to keep electronic equipment dry.
delta circuit A three-phase electrical circuit with
no common ground.
delta connection A triangular connection of coils
or load devices in a three-phase system, so called
from its resemblance to the Greek letter delta.
delta-matched antenna See WYE-MATCHED IMPEDANCE ANTENNA.
delta-matched impedance antenna See WYEMATCHED IMPEDANCE ANTENNA.
delta matching transformer In a WYE-MATCHED
IMPEDANCE ANTENNA, the fanned-out (roughly
delta-shaped) portion of the two-wire feeder at its
point of connection to the radiator. It matches the
impedance of the feeder to that of the radiator.
feed line
delta-matching transformer
delta modulation The conversion of an analog signal into a digital pulse train that can be decoded
to yield the original analog signal.
delta network See DELTA CONNECTION.
delta pulse-code modulation In wire or radio
communications, the conversion of an audio signal into a digital pulse train.
delta quantity An increment (i.e., the difference
between two values of a variable).
delta rays The emission of secondary electrons as
a result of radioactivity.
delta-sigma modulation A method of analog-todigital conversion. The output is a pulse density
function of the input. The input can be obtained
by low-pass filtering of the output.
delta tune Also called receiver incremental tuning
(RIT). In high-frequency (HF) communications
transceivers, a control that allows the receiver
frequency to be adjusted up to several kilohertz
higher or lower than the transmitter frequency.
delta waves Brain waves having a frequency less
Deluc’s pile See DRY PILE.
dem Abbreviation of DEMODULATOR.
demagnetization curve The portion of a magnetic
hysteresis curve, showing reduction of demagnetization.
demagnetization effect The phenomenon in
which uncompensated magnetic poles at the surface cause a reduction of the magnetic field inside
a sample of a material.
demagnetize To remove magnetism from an object, either temporarily or permanently.
demagnetizer See DEGAUSSER.
demagnetizing current The half-cycle of an alternating current (or polarity of a direct current)
flowing through a coil wound on a permanent
magnet (as in a headphone, permanent-magnet
loudspeaker, or polarized relay), that reduces the
magnetic field.
demagnetizing force 1. A magnetic force whose
direction reduces the residual induction of a
magnetized material. 2. An effect that reduces the
magnetism of a permanent magnet, such as high
temperature or a physical blow.
demand factor In the use of electric power, the ratio of the consumer’s maximum demand to the
actual power consumed.
demand processing Descriptive of a system that
processes data as it is available, without storing
demarcation strip An interface between a terminal unit and a carrier line.
Dember effect The appearance of a voltage between regions in a semiconductor when one of
the regions is illuminated.
demodulation The process of retrieving the information (modulation) from a modulated carrier. In
receivers and certain test instruments, this process is called DETECTION.
demodulator 1. A circuit that recovers the information from a modulated analog or digital signal.
In radio communications, such a device is
usually called a DETECTOR. 2. In computer
communications, a device that performs
online signals.
demand read (write) • depth of discharge
demand read (write) Inputting or outputting data
blocks to or from a central processor, as needed
for processing.
demodulator probe A diode probe that removes
the modulation envelope from an applied amplitude-modulated signal, and presents the envelope to a voltmeter or oscilloscope.
demonstrator A device used to show and teach the
way in which a component, circuit, or system operates.
DeMorgan’s theorem A rule of sequential or digital logic. It states that the negation of (A AND B),
for any two statements A AND B, is equivalent to
NOT A OR NOT B. Also, the negation of (A OR B)
is equivalent, logically, to NOT A AND NOT B.
demultiplexer A circuit or device that separates
the components of a multiplexed signal transmitted over a channel.
demultiplexing circuit See DEMULTIPLEXER.
denary band A band in which the highest frequency is 10 times the lowest frequency.
dendrite 1. The branching (tree-like) structure
formed by some materials, such as semiconductors, as they crystallize. 2. The branching portion
of a nerve cell; hence, the corresponding circuit
element in the electronic model of such a cell.
dendritic growth 1. Dendrite (see DENDRITE, 1).
2. The process of growing long, flat semiconductor crystals.
dendron See DENDRITE, 2.
dens Abbreviation of DENSITY.
dense binary code A binary representation system, in which any possible combination of characters is assigned some correspondent.
densitometer An instrument for measuring the
density of a body.
density 1. Mass per unit volume of a material. 2.
Concentration of charge carriers or of lines of
flux. 3. The number of items per unit volume,
area, distance, or time.
density modulation Modulation of the density,
with respect to time, of electrons in an electron
Electron beam
(Most) (Least)
density modulation
density of electrons The concentration of electrons (i.e., the number per unit volume, area, distance, or time).
density packing A figure indicating the quantity of
bits per inch or per centimeter, stored on a magnetic tape.
dependent equations Equations that are alike
and have an infinite number of solutions. Compare INDEPENDENT EQUATIONS and INCONSISTENT EQUATIONS.
dependent linearity Linearity (especially in its deviation from an ideal slope) as a dependent variable.
dependent variable A changing quantity whose
value at any instant is governed by the value at
that instant of another changing quantity (the independent variable). Compare INDEPENDENT
depletion-enhancement-mode MOSFET A metaloxide-semiconductor field-effect transistor (MOSFET) designed for zero gate-bias voltage. An ac
gate signal voltage drives the MOSFET alternately
into the depletion mode (negative signal halfcycle) and enhancement mode (positive signal
half-cycle). Compare DEPLETION-TYPE MOSFET
depletion field-effect transistor A field-effect
transistor whose operation is based on the control of depletion layer width.
depletion layer See BARRIER, 1.
depletion-layer capacitance See JUNCTION CAPACITANCE.
depletion-layer rectification Rectification provided by a semiconductor junction.
depletion-layer transistor A transistor whose action depends on modulation of current carriers in
a space-charge region (depletion layer).
depletion mode Operation characteristic of the
depletion region See BARRIER, 1.
depletion-type MOSFET A metal-oxide-semiconductor field-effect transistor (MOSFET) in which
the channel directly under the gate electrode is
narrowed by a negative gate voltage (in an nchannel device) or by a positive gate voltage (in a
p-channel device).
depolarization 1. In a primary cell, the removal of
the agents that have caused polarization. 2. The
addition of a polarization-inhibiting substance to
the electrolyte of a primary cell.
depolarizer A substance that retards polarization
in an electrochemical cell. An example is the
manganese dioxide used in dry cells.
depolarizing agent See DEPOLARIZER.
deposition The application of a layer of one substance (usually a metal) to the surface of another
(the substrate), as in evaporation, sputtering,
electroplating, silk-screening, etc.
depth indicator 1. A sounding instrument for determining the depth of a body of water. 2. On an
ACOUSTIC DEPTH FINDER, the meter that indicates the depth of water.
depth of cut On a phonograph disk, the depth of
the recorded groove.
depth of discharge Abbreviation, DOD. In a rechargeable cell or battery, a measure of the extent
depth of discharge • designation
to which discharging has occurred. It is generally
specified as a percentage. For example, if the
DOD of a 10-ampere-hour (10-AH) battery is 80
percent, then 8 AH have been used up, and 2 AH
remain before recharging will be necessary.
depth of heating In dielectric heating, the depth of
heat penetration in the sample when both electrodes are applied to one of its faces.
depth of modulation The degree to which a carrier
wave is modulated.
depth of penetration The extent to which a skineffect current penetrates the surface of a conductor.
depth sounder See ACOUSTIC DEPTH FINDER.
de-Q 1. To reduce the Q of a component or tuned
circuit. 2. To inhibit laser action during an
interval when an ion population excess is
pumped up.
derating To reduce an operating parameter (e.g.,
current, voltage, power) as another factor (such
as temperature) increases, to ensure efficient, reliable, and safe operation.
derating curve A graph that shows the extent to
which a quantity (such as allowable power dissipation) must be reduced as another quantity
(such as temperature) increases.
derating factor The amount by which a current,
power, or voltage must be decreased to ensure
safe and efficient operation of a circuit or device
in a given environment (temperature, altitude,
humidity, etc.). Also see DERATING and DERATING CURVE.
derivative 1. A mathematical expression indicating the rate at which a function changes, with
respect to the independent variable. See
DERIVATIVE FUNCTION. 2. The slope of a line
tangent to a curve at a given point. 3. The output
signal of a DIFFERENTIATOR, relative to the
input signal.
derivative action In a control system, an action
producing a corrective signal proportional to the
dx = (Positive)
dx = (Negative)
rate of change (derivative) of the controlled
derivative control A method of automatic control,
actuated according to the number of errors per
derivative function For a mathematical function
f (x), the function f '(x) = df (x)/dx, over the domain
of f. For any specific point x0 in the domain of f,
the value of f '(x0) is equal to the slope of a line
tangent to f at the point (x0, f (x0)).
derived center channel The sum or difference of
the left and right channels in a stereophonic system.
Dershem electrometer A variation of the quadrant
electrometer. In the Dershem instrument, the
needle (to which a small mirror is attached) rotates within slots cut in the quadrant plates and,
therefore, can never accidentally touch the
descending node For a satellite orbiting the earth
or another planet, any point at which the groundtrack crosses the equator as it moves from the
northern hemisphere into the southern hemisphere. This node generally changes for each succeeding orbit, because the earth or planet rotates
underneath the orbit of the satellite. Compare
descending pass For a specific point on the earth’s
surface, the time during which an artificial communications satellite is accessible when its latitude is moving southward. The duration of
accessibility depends on the altitude of the satellite and on how close its groundtrack comes to
the earth-based point. Compare ASCENDING
description A data element that is part of a record
and is used to identify it.
desensitization 1. The process of making a circuit
or device less responsive to small values of a
quantity. 2. Also called desensing. In a communications receiver, an unwanted, often intermittent
reduction in front-end gain, caused by an extremely strong local signal.
desensitize 1. To reduce the sensitivity of a receiver. 2. To reduce the gain of an amplifier. 3. To
reduce the small-quantity response of an instrument.
desiccant A compound, such as cobalt chloride,
used for the purpose of keeping enclosed items
design 1. A unique, planned arrangement of electronic components in a circuit, in accordance
with good engineering practice, to achieve a desired end result. 2. A unique layout of components or controls, in accordance with good
engineering practice, esthetics, and (often) ergonomics. 3. Invention. 4. Plan. 5. To produce a
design, as defined in 1, 2, 3, or 4.
designation Within a computer record, coded information identifying the record so that it can be
handled accordingly.
design-center rating • detector blocking
design-center rating A specified parameter that, if
not exceeded, should provide acceptable average
performance for the greatest number of the components so rated.
design compatibility The degree to which a transmitter and receiver are designed for the rejection
of unwanted electromagnetic noise.
design engineer An engineer who is skilled in the
creation of new designs and in the comparative
analysis of designs.
design-maximum rating See MAXIMUM RATING.
design-proof test A performance test made on a
newly completed circuit or device to determine
the suitability of the design.
Desk-Fax A facsimile transceiver that can be
placed on a desktop, used for wire or radio transmission and reception of still images.
desk microphone A microphone equipped with a
stand that sits on a table or desktop. It allows the
operator to use both hands for equipment adjustment, taking notes, etc.
desktop computer A personal computer designed
for nonportable use, usually equipped with a
built-in hard disk, one or more diskette drives, a
CD-ROM drive, and a fax/modem. It generally
uses an external cathode-ray-tube display,
printer, and keyboard. The power supply is intended for use with 117-volt utility circuits.
desolder To unsolder joints, usually with a special
tool that protects delicate parts and removes
melted solder by suction.
destaticization A chemical process used to minimize the retention of electrostatic charges by certain substances.
phone line
drive #1
desktop computer
(main unit only)
drive #2
destination 1. The point in a system to which a
signal of any sort is directed. 2. In communications, a receiving station.
destination file A computer file that receives data
output during a specific program run.
destination register In a digital computer, a register into which data is entered.
Destriau effect Light emission resulting from the
action of an alternating electric field on phosphors embedded in a dielectric.
destructive addition A computer logic operation
in which the sum of two operands appears in
the memory location occupied by one of the
destructive breakdown A breakdown in which the
effects are irreversible (e.g., permanent damage to
a dielectric by excessive applied voltage).
destructive interference Interference resulting
from the addition of two waves that have the
same frequency, but opposite phase.
destructive read In a computer or calculator, the
condition in which reading the answer erases the
data (as from a location) used in the calculation.
destructive test A test that unavoidably destroys
the test sample. Compare NONDESTRUCTIVE
DETAB A COBOL-based computer programming
language permitting the programmer to present
problems as decision tables.
detail constant Pertaining to a video signal, the
ratio VH/VL, where VH is the amplitude of highfrequency components, and VL is the amplitude of
the low-frequency reference component.
detected error In a computer system, an error
that is identified, but remains uncorrected until
final output is available.
detection 1. See DEMODULATION. 2. The sensing
of a change in the operating parameters of a circuit or system.
detection range In security applications, the radius within which transducers or sensors can be
expected to reliably operate. This radius varies,
depending on the environment, the sensitivity of
the receiving circuits and transducers, and the
strength of the transmitted signal (if any).
detectophone A device for eavesdropping on a
conversation. The device can use a tape recorder
or a tiny radio transmitter.
detector 1. In radio communications, a device or
circuit that extracts the information from a modulated carrier. Also sometimes called a demodulator. 2. A device that senses a signal or condition
and indicates its presence.
detector balanced bias In a radar system, bias obtained from a controlling circuit and used to reduce or eliminate clutter.
detector bias Steady dc voltage applied to a detector to set its operating point.
detector blocking In a regenerative receiver, a
phenomenon in which a strong signal tends to
pull the detector oscillator into phase with itself,
thereby causing the detector to oscillate at the
signal frequency.
detector circuit A demodulator circuit (i.e., one
used to recover the intelligence from a modulated
detector probe See DEMODULATOR PROBE.
detector pull-in See DETECTOR BLOCKING.
detector stage In a receiver or instrument, the
separate stage that contains the detector circuit.
Some systems, such as a superheterodyne receiver, have more than one detector. Also see
detent A mechanical stop used on a rotary switch
to hold the switch pole securely in each selected
detune 1. To adjust a circuit to some frequency
other than its resonant frequency. 2. To set the
frequency of a receiver or transmitter to some
point other than the frequency normally used. 3.
To stagger-tune a receiver intermediate-frequency system.
detuning Tuning to a point above or below the frequency to which a device or system is normally
(or initially) adjusted (usually the resonant frequency of the device).
detuning stub A device used for the purpose of
coupling a feed line to an antenna, while choking
off currents induced on the feed line as a result of
the near-field radiation of the antenna.
deupdating Producing an earlier form of a computer file by substituting older records for current ones.
deuterium Symbol, D, d, H2, or 2H. Also called
heavy hydrogen. The hydrogen isotope having a
nucleus consisting of one proton and one neutron.
deuterium oxide Symbol, D2O. Also called heavy
water. This compound has wide use in nuclear
deuteron The nucleus of a deuterium atom.
deuton See DEUTERON.
deutron See DEUTERON.
deviation 1. In a frequency-modulated (FM) radio
signal, the instantaneous amount of carrier frequency shift away from the unmodulated frequency. It is usually expressed in kilohertz;
directly proportional to the amplitude of the modulating signal, up to a certain maximum that depends on the bandwidth allowed. 2. The
maximum instantaneous carrier frequency shift
in a FM signal. 3. The extent or amount by which
a quantity drifts from its proper value.
deviation distortion In a frequency-modulation
(FM) receiver, distortion resulting chiefly from
discriminator nonlinearity and restricted bandwidth.
deviation ratio In a frequency-modulated (FM)
signal, the ratio between the highest modulating
frequency and the maximum carrier deviation.
deviation sensitivity For a frequency-modulation
(FM) receiver, the smallest deviation that will pro-
Instantaneous deviation (kHz)
detector blocking • diagnosis
− 5 kHz
duce a specified audio output power. Expressed
in kilohertz, or as a percentage of rated deviation
of the receiver, measured with the receiver set for
maximum gain.
device 1. A simple or complex discrete electronic
component. 2. A subsystem used as a unit, and
regarded as a single component.
device complexity The number of components in
an integrated circuit.
device independence A characteristic of a computer, that allows operation independent of the
types of input/output devices used.
dew point For a gas containing water vapor
(typically air), the highest temperature at which
the vapor condenses as the gas is cooled. The dew
point depends on the amount of vapor in the gas.
dew-point recorder An instrument for determining and recording the temperature at which water
vapor in the air condenses to a liquid.
DF Abbreviation of DIRECTION FINDER.
DF antenna An antenna that is mechanically rotatable or has an electrically rotatable response
pattern for use with a direction finder.
DF antenna system Two or more DF antennas arranged for maximum directivity and maneuverability, together with associated feeders and
D flip-flop A delayed flip-flop. The state of the input determines the state of the output during the
following pulse, rather than during the current
dg Abbreviation of decigram.
dia Abbreviation of diameter.
diac A two-terminal, bilateral, three-layer semiconductor device that exhibits negative resistance.
When the applied voltage exceeds a critical value,
the device conducts.
diagnosis 1. Determination of the cause and location of a hardware malfunction. 2. In computer
operations, determination of the cause of a system operation error.
diagnostic routine • diamond lattice
diagnostic routine 1. An efficient sequence of diagnostic tests for rapid, foolproof trouble-shooting of electronic hardware. 2. A computer
software package intended for debugging
programs, or for finding the cause of a hardware
or operating-system malfunction. Also called
diagnostic, diagnostic program, or diagnostic
diagnostic test 1. A test made primarily to
ascertain the cause of dysfunction in electronic
equipment. Compare PERFORMANCE TEST. 2.
To apply a diagnostic routine to hardware faults,
or to implement one to prevent such a fault.
diagnotor In digital computer operations, a troubleshooting routine combining both diagnosis
and editing.
diagram A (usually line) drawing depicting a circuit, assembly, or organization. See, for example,
dial 1. A graduated scale, arranged horizontally,
vertically, in a circle, or over an arc. Used to show
the distance through which a variable component
(such as a potentiometer, variable capacitor, or
switch) has been adjusted. A pointer can move
over the scale, or the scale can be moved past a
stationary pointer. 2. The graduated face of a meter. 3. In a telephone system, to press the keys or
actuate the tones that establish contact with another subscriber.
dial cable A flexible cable or belt conveying motion
on the shaft of an adjustable component (such as
a potentiometer or variable capacitor) to a dial.
dial-calibrated attenuator A variable attenuator
with a dial reading directly in decibels.
dial-calibrated capacitor A variable capacitor
with a dial reading directly in picofarads.
dial-calibrated inductor A variable inductor with
a dial reading directly in microhenrys.
dial-calibrated potentiometer A potentiometer
with a dial reading directly in output volts,
percentage of input voltage, number of turns
(when resistance is a linear function), or other
dial-calibrated resistor A variable resistor with a
dial reading directly in ohms, kilohms, or
dial-calibrated rheostat See DIAL-CALIBRATED
dial cord A form of dial cable. Cord usually designates a fabric string, whereas a cable is a flexible,
braided wire.
dial knob The knob used to turn a dial under a
pointer, or to turn a pointer over a dial scale.
dial lamp See DIAL LIGHT.
dial light A small lamp sometimes used to illuminate a dial. Can also serve as a pilot light.
dial lock A small mechanism used to lock a dial at
a particular setting to prevent further turning.
dialing key In a telephone system, a dial that uses
keys, rather than a rotary dial.
dial jack In a telephone system, a set of jacks that
facilitates interconnections between dial cords
and external lines.
dial light A lamp or light-emitting diode placed in
the dial mechanism of a radio receiver, transmitter, or transceiver. Allows the dial to be read in
dim light or in darkness.
dialog equalizer In sound transmission and recording, a high-pass filter that reduces lowfrequency response during dialog and extreme
dial pulse An interruption of the direct current in a
telephone system when the dial contacts of the
calling telephone open. The number of such interruptions corresponds to the digit dialed.
dial scale The graduated portion of a dial.
dial system 1. See DIAL TELEPHONE SYSTEM.
2. The arrangement of dials and knobs that facilitates adjustment of electronic equipment.
dial telephone A telephone set in which a numbered rotatable disk is used to produce the switch
interruptions that cause generation of the transmitted multidigit telephone numbers.
dial telephone system The complete automatic
circuit, including central-office facilities, for dial
telephone operation.
dial tone In a telephone system, a constant hum or
whine heard before dialing, indicating that the
system is operational.
dial-up In a telephone system, the calling of one
subscriber by another, using a dial system.
diam Abbreviation of diameter.
diamagnetic Pertaining to a material having magnetic permeability less than unity.
diamagnetism The state of having magnetic permeability less than unity. A material with this property reduces the flux density of a magnetic field,
relative to the flux density in air or in free space.
diamond antenna Also called rhombic antenna.
A nonresonant wideband directional antenna
whose horizontal wire elements are arranged in
the shape of a diamond (rhombus). The arrangement is fed at one corner, the opposite corner being terminated with a noninductive resistor.
diamond lattice The orderly internal arrangement
of atoms in a redundant pattern in crystalline
materials, such as germanium or silicon.
≈ 600 Ω
All sides x are equal
diamond antenna
diamond stylus • dielectric constant
diamond stylus A phonograph “needle” having as
its point a small, ground diamond.
diapason 1. Either of the two principal stops (open
and closed) of an electronic organ that cover the
entire range of the instrument. When one is used,
a note played is automatically sounded in several
octaves. 2. Tuning fork.
diaphony See DISSONANCE.
diaphragm A usually thin metal or dielectric disk
used as the vibrating member in headphones,
loudspeakers, and microphones, and as the pressure-sensitive element in some sensors and
diaphragm gauge A sensitive gas pressure gauge
using a thin metal diaphragm stretched flat. Increments of pressure move the diaphragm,
relative to a nearby electrode, varying the
capacitance between the two.
diathermic Pertaining to a substance that efficiently transfers heat or infrared energy.
diathermotherapy The use of diathermy in the
treatment of various physiological disorders.
diathermy 1. In medicine and physical therapy,
the production of heat in subcutaneous (below
the skin) tissues by means of high-frequency radio waves. 2. A radio-frequency (RF) power oscillator and associated equipment used to produce
heat in subcutaneous tissues.
diathermy interference Radio-frequency interference (RFI) resulting from the operation of
unshielded and/or unfiltered diathermy equipment.
diathermy machine See DIATHERMY, 2.
diatomic Having two atoms (e.g., a DIATOMIC
diatomic molecule A molecule (such as that of
oxygen) composed of two atoms. Compare MONATOMIC MOLECULE.
dibble A mathematical function in which a number
(usually an integer) is doubled, and then one is
added to the result. Thus, dibble n = 2n + 1.
dibit A combination of two binary digits (bits). The
four possible dibits are 00, 01, 10, and 11.
dice Plural of DIE, 1, 3.
dichotomizing search Also called binary search.
In digital computer operations, locating an item
in a table of items that are arranged by key values
in serial order. The required key is compared with
a key halfway through the table; according to this
relational test, half of the table is accepted and
again divided for comparison, etc. until the keys
match and the item is found.
dichotomy Characterized by the usually repetitive
branching into two sets, groups, or factions.
dichroism Also called dichromatism. 1. The property of a crystal showing different colors,
depending on which axis corresponds to the line
of sight. 2. The property of a solid taking on different colors as the thickness of the transmitting
layer changes. 3. The property of a liquid changing color, according to solution concentration.
dichromate cell An electrolytic cell consisting of
electrodes of carbon and zinc. The zinc electrode
is immersed in a diluted solution of sulfuric acid,
and the carbon electrode in a solution of potassium dichromate.
dicing The cutting of a semiconductor melt, crystal
wafer, or other material into dice (see DIE).
dictionary A table of specifications for the size and
format of computer file operands, and data
names for field and file types.
die 1. A small wafer of useful electrical material,
such as a semiconductor or a precision resistor
chip. 2. A casting designed to mold molten metal
into a specific configuration until the metal hardens. 3. Any small object of roughly cubical proportions. 4. To lose power or energy completely,
usually unintentionally. 5. In a computer program, to produce unpredicted and useless results
following an initial run.
die bonding The bonding of dice or chips to a substrate.
die casting Making a casting by forcing molten
metal (such as an aluminum alloy, lead, tin, or
zinc) under high pressure into a die or mold.
dielectric A material that is a nonconductor of
electricity; especially, a substance that facilitates
the storage of energy in the form of an electric
field. Such materials are commonly used in capacitors and transmission lines.
dielectric absorption The ability of certain dielectric materials to retain some of their electric
charge—even after being momentarily shortcircuited. Capacitors with this property must be
shorted out continuously for a certain length of
time before the dielectric has completely discharged.
dielectric amplifier A voltage amplifier circuit in
which the active component is a capacitor having
a nonlinear dielectric. A signal voltage applied to
the capacitor varies the capacitance, thus varying the current. The modulated current flows
through a load resistor, developing an outputsignal voltage higher than the input-signal voltage.
dielectric antenna An antenna in which some or
all of the radiating element is made of a dielectric
material, such as polystyrene. Primarily used at
microwave frequencies.
dielectric breakdown Sudden, destructive conduction through a dielectric when the applied
voltage exceeds a critical value.
dielectric breakdown voltage The voltage at
which DIELECTRIC BREAKDOWN occurs in an
insulating material. Varies, depending on the
particular dielectric substance.
dielectric capacity See DIELECTRIC CONSTANT.
dielectric constant Symbol, k. For a dielectric material, the ratio of the capacitance of a two-plate
capacitor using the dielectric material, to the capacitance of the equivalent capacitor with dry air
as a dielectric. Also called inductivity and specific
inductive capacity.
dielectric current • dielectric wire
dielectric current 1. Current flowing over the surface of a dielectric material in response to a varying electric field. 2. Current flowing through a
dielectric as a result of its finite insulation resistance.
dielectric dissipation For a dielectric material in
which an electric field exists, the ratio of the lost
(dissipated) electrical energy to the recoverable
electrical energy.
dielectric dissipation factor The cotangent of the
dielectric phase angle, also equal to the reciprocal
of the Q factor.
dielectric fatigue In some dielectric materials
subjected to a constant voltage, the deterioration
of dielectric properties with time.
dielectric guide A waveguide made from a solid dielectric, such as polystyrene.
dielectric heater A high-frequency power generator used for DIELECTRIC HEATING.
dielectric heating The heating and forming of a
dielectric material, such as a plastic, by temporarily making the material the dielectric of a
two-plate capacitor. This capacitor is connected
to the output of a high-power radio-frequency
(RF) generator. Losses in the dielectric cause its
heating. Compare INDUCTION HEATING.
dielectric hysteresis See DIELECTRIC ABSORPTION.
dielectric isolation In a monolithic integrated circuit (IC), the isolation of circuit elements from
each other by a dielectric film, as opposed to isolation by reverse-biased pn junctions.
dielectric lens A molded piece of dielectric material used to focus microwaves. Its operation is
analogous to that of an optical lens.
dielectric lens
dielectric loss For a dielectric material subjected
to a changing electric field, the rate of transformation of electric energy into heat.
dielectric loss angle Ninety degrees minus the DIELECTRIC PHASE ANGLE.
dielectric loss factor For a dielectric material, the
product of the dielectric constant and the tangent
of the dielectric loss angle.
dielectric loss index See DIELECTRIC LOSS FACTOR.
dielectric matching plate A dielectric plate used
in some waveguides for impedance matching.
dielectric mirror A reflector containing a number
of layers of dielectric material. Its action depends
on electromagnetic energy being partially reflected from the interfaces between materials
having unequal indexes of refraction.
dielectric phase angle For a dielectric material,
the angular phase difference between a sinusoidal voltage applied to the material and the
component of the resultant current having the
same period as that of the voltage.
dielectric phase difference See DIELECTRIC
dielectric polarization The effect characterized by
the slight displacement of the positive charge in
each atom of a dielectric material, with respect to
the negative charge, under the influence of an
electric field.
dielectric power factor The cosine of the dielectric
phase angle, or the sine of the dielectric loss angle.
dielectric puncture voltage See DIELECTRIC
dielectric rating The breakdown voltage, and
sometimes the power factor, of the dielectric material used in a device, such as a relay, motor, or
dielectric ratings Electrical characteristics of a dielectric material: breakdown voltage, power factor, dielectric constant, etc.
dielectric resistance See INSULATION RESISTANCE.
dielectric rigidity See DIELECTRIC STRENGTH.
dielectric-rod antenna A unidirectional antenna
that uses a dielectric substance to obtain power
dielectric soak See DIELECTRIC ABSORPTION.
dielectric strain The distorted internal state of a
dielectric, caused by the influence of an electric
field. Also called DIELECTRIC STRESS.
dielectric strength The highest voltage a dielectric
can withstand before DIELECTRIC BREAKDOWN
occurs. Usually expressed in volts or kilovolts per
mil of material thickness.
dielectric stress The distortion of electron orbits
in the atoms of a dielectric material subjected to
an electric field.
dielectric susceptibility For a polarized dielectric,
the ratio of polarization to electric intensity.
dielectric tests Laboratory experiments performed to determine the dielectric characteristics of a
substance—especially the dielectric constant and
the dielectric breakdown voltage.
dielectric waveguide See DIELECTRIC GUIDE.
dielectric wedge A wedge-shaped dielectric slug
placed inside a waveguide for impedance matching.
dielectric wire A small dielectric waveguide that
acts as a wire to carry signals between points in a
Dietzhold network • differential input
Dietzhold network A four-terminal, shunt m-derived circuit used in some wideband amplifiers.
Dietzhold peaking In some wideband amplifiers,
frequency compensation obtained with a shunt
m-derived network (see DIETZHOLD NETWORK).
difference amplifier See DIFFERENTIAL AMPLIFIER.
difference channel In a stereophonic amplifier, an
audio channel that handles the difference between signals in the right channel and those in
the left channel.
difference detector A detector whose output is the
difference between two simultaneous input signals.
difference frequency A signal frequency produced
by mixing or heterodyning of signals at two other
frequencies. If the lower input signal frequency is
f1 and the higher input signal frequency is f2,
then the difference frequency fd is equal to f2 – f1.
difference of potential The absolute value of the
algebraic difference of voltages at two points of
different electrical potential. Thus, the difference
of potential between a +5-V point and a –5-V
point is +5 – (–5) V = 10 V. Also see POTENTIAL
difference quantity See INCREMENT.
difference signal 1. The resultant signal obtained
by subtracting, at every instant for at least one
full cycle, the amplitudes of two signals. 2. The
difference of the left- and right-channel outputs
in a stereo system.
differential 1. A device, consisting of a gear system, that adds or subtracts angular motions and
delivers the result. 2. A gear system in which the
motion of a shaft is transferred to two other
shafts aligned with each other and perpendicular
to the first shaft. 3. One of two coils arranged to
produce opposite polarities at a point in a circuit.
4. Pertaining to a difference between two signals
or quantities.
differential amplifier A circuit, usually an operational amplifier, that amplifies the voltage difference between two input signals. The
instantaneous output voltage is equal to some
constant multiple of the difference between the
instantaneous input voltages.
differential analyzer An analog computer that
solves differential equations using integrators.
differential angle For a mercury switch, the angle
between operation and release positions.
differential capacitor A dual variable capacitor
with two identical stator sections, and a single rotor section that turns into one stator section and
out of the other. The capacitance of one section
decreases while that of the other increases.
differential coil See DIFFERENTIAL, 3.
differential comparator A linear integrated circuit
(IC) that delivers an output proportional to the
difference between two input signals.
differential compound dc generator A compound-wound dc generator in which the magne-
End view
Stator A
Stator B
differential capacitor
tomotive force of the series field opposes that of
the shunt (main) field.
differential compound dc motor A compoundwound dc motor in which the magnetomotive
force of the series field coil opposes that of the
shunt (main) field coil.
differential cooling Reducing temperature at different points on a surface at different rates.
differential delay The difference dmax – dmin across
a frequency band, where dmax is the maximum
frequency delay and dmin is the minimum frequency delay.
differential discriminator A device that passes
pulses, whose amplitudes are between two predetermined values above or below zero.
differential distortion In an automatic-gaincontrol circuit, distortion from effects that cause
shunting of the diode load resistor.
differential flutter Fluctuations in the speed of a
magnetic tape that are nonuniform in different
parts of the tape.
differential gain In a differential amplifier, the average gain of the two sections of the amplifier.
differential gain control A circuit or device for
setting the gain of a radio receiver in terms of an
anticipated change in signal strength, to reduce
the receiver output signal differential.
differential galvanometer A galvanometer in
which currents in two similar coils neutralize
each other; thus, there is zero deflection when the
currents are equal.
differential gap The smallest range of values that
a controlled variable must take to change a threeposition controller’s output from on to off, or vice
differential heating Increase of temperature at
different points on a surface at different rates.
impedance See
differential induction coil An induction coil having two differentially wound primary coils.
differential input In a differential amplifier, the
circuit between input terminals 1 and 2, as opposed to the circuit between input 1 or input 2
and ground.
differential-input amplifier • differential-wound field
(f1) superimposed on a low-frequency, sine-wave
signal (f2), the difference in phase shift of f1
throughout the system for two specified levels of
differential phase-shift keying Keying of a carrier
by varying the carrier phase.
differential pressure The difference in pressure
between two points.
differential-pressure transducer A transducer
that delivers an output proportional to the difference between two sensed actuating pressures.
differential protective relay A differential relay
that operates to protect equipment or personnel
when the difference between the two actuating
quantities reaches a prescribed level.
differential receiver A synchro differential that receives the electrical output of two synchro transmitters. The receiver can subtract one input
voltage from the other.
differential relay A relay actuated by the difference between two currents or voltages.
differential selsyn A selsyn in which the position
assumed by the rotor is proportional to the sum
of rotor and stator field values.
differential stage See DIFFERENTIAL AMPLIFIER.
differential transducer A dual-input, single-output sensor, such as a pressure transducer, that
is actuated by two sensed quantities and delivers
an output proportional to their difference.
differential transformer A variable inductance
transformer having a (usually cylindrical) core
that is moved in and out to provide adjustable
coupling between the interwound primary and
secondary windings. This permits adjustment of
the amplitude and phase of the transformer output voltage, with respect to the input voltage.
differential transmitter A synchro differential
connected to a synchro transmitter. In a synchro
receiver supplied by this combination, the change
in rotor position is the algebraic difference between the transmitter-rotor position and the differential-rotor position.
differential unbalance For a differential amplifier,
the average difference in gain between the two
amplifier sections. Compare DIFFERENTIAL
differential voltage 1. The voltage difference between the input signals to a differential device. 2.
The breakdown voltage minus the operating voltage for a lamp.
differential voltage gain 1. The ratio, in decibels,
between the differential output and differential input voltages of an amplifier. 2. The instantaneous
ratio, in decibels, between the rate of change of
the output signal voltage and the rate of change of
the input signal voltage in an amplifier.
differential-wound field In a motor or generator, a
field winding having series and shunt coils whose
fields are opposing.
differential-input amplifier A differential amplifier whose output is proportional to the difference
between two input signals—each applied between
an input terminal and common ground.
differential-input capacitance In a differential
amplifier, the capacitance between the input terminals.
differential-input impedance In a differential amplifier, the impedance between the input terminals.
differential-input measurement For a differential
amplifier, a floating measurement made between
the input terminals.
differential-input rating In an operational amplifier, the greatest difference signal that can be
placed between the inputs while allowing proper
differential-input resistance In a differential amplifier, the resistance between the input terminals.
differential-input voltage In a differential amplifier, the signal voltage presented to the floating
input terminals.
differential-input voltage range In a differential
amplifier, the range of signal voltages that can be
applied between the differential input terminals
without overdriving the amplifier.
differential input-voltage rating The maximum
differential-input voltage that can be applied
safely to a differential amplifier.
differential instrument A galvanometer or other
meter in which deflection results from the differential effect of currents flowing in opposite directions through two identical coils. Also see
differential keying A system of break-in keying, in
which the oscillator stage of a transmitter containing a keyed amplifier is disabled when the key
is open to prevent interference with the receiver
at the keying station, and is enabled when the
key is closed.
differential-mode gain In an operational amplifier, the ratio, in decibels, between the output
voltage and the differential input voltage.
differential-mode input In an operational amplifier in differential mode, the difference between
the two input signal voltages.
differential-mode signal In a balanced threeterminal circuit, such as the input of a differential amplifier, a signal applied between the
floating (ungrounded) input terminals.
differential multiplexer An analog multiplexer
that selects both the high and low portion of the
input signal.
differential nonlinearity Incremental error from
an ideal analog output difference when the input
is changed by a certain value. Generally expressed as a fraction of full-scale output.
differential permeability The derivative of normal
induction, with respect to magnetizing force.
differential phase In a television system tested
with a low-level, high-frequency sine-wave signal
differentiate • diffused sound
differentiate 1. To produce an output signal, the
instantaneous amplitude of which is proportional
to the instantaneous rate of change of the input
amplitude. 2. To determine the derivative of a
mathematical function.
differentiating circuit See DIFFERENTIATING
differentiating network A four-terminal resistance-capacitance (RC) network whose output
voltage is the derivative of the input voltage, with
respect to time. Compare INTEGRATING NETWORK.
differentiation 1. The processing of an input signal to create an output signal whose voltage
waveform represents the derivative, with respect
to time, of the input voltage waveform. 2. The process of computing a mathematical derivative.
differentiator 1. See DIFFERENTIATING NETWORK. 2. An operational amplifier whose output
waveform is the mathematical derivative of the
input waveform.
Eo = −RC (dEi/dt)
differentiator, 2
diffracted wave A wave or ray of energy undergoing DIFFRACTION.
diffraction 1. Interference of one part of an energy
beam with another part when the beam is deflected along two or more paths having different
lengths. When this happens with visible light,
dark and light bands or colored bands appear.
This effect is responsible for the rainbow-like appearance of light reflected from the surface of a
compact disc. 2. The bending of electromagnetic
waves around an object. This effect explains why
radio signals can propagate around large obstructions, such as buildings and hills. The effect
becomes more pronounced as the wavelength increases (the frequency decreases). 3. The bending
of acoustic waves around an object. This effect
explains why sound propagates around large obstructions, such as buildings. The effect becomes
more pronounced as the wavelength increases
(the frequency decreases).
diffraction grating A transparent plate containing
thousands of parallel lines or grooves spaced extremely close together. Light passing through the
slits between the lines produces a rainbow spectrum as a result of DIFFRACTION.
diffraction spectrum 1. The spectrum produced
in visible light by a diffraction grating. 2. The dis-
tribution of energy at various frequencies, produced by diffraction of electromagnetic waves. 3.
The distribution of energy at various frequencies,
produced by diffraction of acoustic waves.
diffractometer An instrument for measuring the
diffraction of radiation, such as light or X-rays.
diffuse 1. To produce or cause DIFFUSION. 2. Energy that is diffused.
diffused-alloy transistor See DRIFT-FIELD TRANSISTOR.
diffused-base transistor A bipolar transistor in
which the base region has been diffused into the
semiconductor wafer. Also see DIFFUSED JUNCTION.
diffused device A semiconductor device in which
the junction is produced by diffusion (see DIFFUSION, 1). Examples: DIFFUSED-BASE TRANSISTOR, DIFFUSED DIODE, DIFFUSED-JUNCTION
diffused diode A semiconductor diode having a
diffused junction.
diffused-emitter-and-base transistor A transistor
in which n and p materials both have been diffused into the semiconductor wafer to provide
emitter and base junctions. Also see DIFFUSION,
diffused junction In a semiconductor device, a pn
junction formed by diffusing a gas into a semiconductor at a high temperature that is below the
melting point of the semiconductor. Typically, a
gas containing an n-type impurity is diffused into
p-type semiconductor material. Compare ALLOY
diffused-junction rectifier A semiconductor rectifier using a diffused junction.
diffused-layer resistor In an integrated circuit, a
resistor produced by diffusing a suitable material
into the substrate.
diffused-mesa transistor A transistor whose base
is a n-type layer diffused into a p-type wafer (the
remaining p-type material serving as the collector); its emitter is a small p-type area diffused
into or alloyed with the n-layer. Unwanted diffused portions are etched away, leaving the transistor in a mesa shape.
diffused planar transistor A diffused transistor in
which emitter, base, and collector electrodes are
exposed at the face of the wafer, which has an oxide layer to forestall leakage between surface electrodes.
diffused resistor See DIFFUSED-LAYER RESISTOR.
diffused sound 1. Sound distributed so that its
energy flux is the same at all points. 2. Sound
whose source is difficult to locate or seems to
shift, as that heard from out-of-phase stereo
diffused transistor • digital comparator
diffused transistor A transistor in which one or
both electrodes are created by diffusion. See DIFFUSED JUNCTION.
diffusion 1. In the fabrication of semiconductor
devices, the slow, controlled introduction of a material into the semiconductor, for example, the
high-temperature diffusion of a n-type impurity
(from a gas containing it) into a p-type wafer to
form a diode. 2. The random velocity and movement of current carriers in a semiconductor, resulting from a high-density gradient. 3. The
characteristic spreading of light reflected from a
rough surface or transmitted through a translucent material. 4. The spreading-out of sound
waves, for example when reflected from acoustic
baffles. 5. The migration of atoms from one substance to another, as in the spreading of one gas
throughout another.
diffusion, 3
diffusion bonding A method of joining different
substances by diffusing atoms of one into the
other. This technique is employed in the manufacture of certain semiconductor diodes, transistors, and other devices.
diffusion capacitance The current-dependent capacitance of a forward-biased semiconductor
diffusion current Current resulting from the diffusion of carriers within a substance (see DIFFUSION, 2).
diffusion length In a semiconductor junction, the
distance a current carrier travels to the junction
during carrier life.
diffusion process 1. The technique of processing
semiconductor devices by diffusion (see DIFFU-
SION, 1). 2. Producing a high vacuum by means
of diffusion (see DIFFUSION PUMP).
diffusion pump A pump for fast, efficient creation
of a high vacuum in electron tubes and similar
devices. In one form, the pump, in conjunction
with a force pump, uses mercury vapor as the
pumped medium. Gas molecules evacuated from
the device diffuse into a chamber, where condensing mercury vapor traps and carries them
diffusion theory The notion that, in a homogeneous medium, current density is directly
proportional to the gradient of particle flux
diffusion transistor A transistor whose operation
is based principally on the diffusion of current
carriers (see DIFFUSION, 2).
diffusor In acoustics, a device or structure deliberately installed to spread sound waves throughout
a region.
dig-in angle A stylus angle of 90 degrees, relative
to the surface of a phonograph disc. Compare
DIGIRALT Acronym for digital radar altimetry. A
system that utilizes digital techniques to enhance
the accuracy of an altimeter using radar.
digit A single symbol in a numbering system (e.g.,
0 through 9 in the decimal system, or 0 or 1 in
the binary system), whose value depends on its
position in a group and on the radix of the particular system used.
digital 1. Pertaining to components, circuits, or
systems that use signals having an integral number of discrete levels or values, rather than signals, whose levels or values vary over a
continuous range. 2. Pertaining to a numeric
readout or display. 3. See BINARY, 1.
digital annunciator An annunciator that gives an
alphanumeric digital display of information, as
well as sounding an alarm.
digital audio tape Abbreviation, DAT. A magnetic
tape intended for recording digitally encoded audio data. Used in some high-fidelity applications,
and also for computer data storage.
digital barometer An electronic barometer providing a digital readout.
digital capacitance meter Abbreviation DCM. A
meter with a digital readout for measuring capacitance values.
digital circuit A circuit affording a dual-state
switching operation (i.e., on or off, high or low,
etc.). Also called binary circuit.
digital communications Radio or wire communications using a dual-state mechanism (on/off,
positive/negative, or modulated/unmodulated)
to represent information.
digital comparator A comparator that presents
two digital values, one for each of the quantities
being compared.
digital computer • digital representation
digital computer A high-speed, electronic machine for performing mathematical operations,
file management, machine control, or other “intelligent” functions, and whose basic internal
operations (data storage, comparing, and computation) are based on semiconductor devices assuming one of two states (on or off, high or low).
digital data Information represented and processed in the form of combinations of digits (0
and 1, in the binary system).
digital-data cable A cable designed to conduct
high-speed digital pulses with minimal distortion
and loss.
digital data-handling system A system that accepts, sorts, modifies, classifies, or records digital
data, displaying the final result or passing the
data to a computer.
digital delay circuit A device that stores digitized
audio data, and releases it after a specified delay.
digital device 1. A digital integrated circuit (IC). 2.
Any circuit or system that operates by digital
digital differential analyzer Abbreviation, DDA. A
digital computer that can perform integration using specialized circuitry.
digital display A presentation of information (such
as the answer to a problem) in the form of actual
digits, as opposed to one in the form of, for example, a meter deflection. See, for example, DIGITAL-TYPE METER.
digital divider In a computer, a device that can divide (i.e., provide a quotient and remainder using
dividend and divisor signals).
digital electrometer An electrometer that has a
digital current or voltage indicator.
digital electronics The branch of electronics concerned with components, circuits, and systems
that use signals having an integral number of discrete levels or values, as opposed to signals
whose levels or values vary over a continuous
digital frequency meter A direct-reading frequency meter using high-speed electronic switching circuits and a digital readout. Such
instruments read frequency from less than 1 Hz
to many gigahertz.
digital HIC A hybrid integrated circuit (HIC) designed for digital applications. Also see DIGITAL
digital incremental plotter A device that can
draw, according to signals received from a computer, graphs depicting solutions to problems.
digital information See DIGITAL DATA.
digital information display See DIGITAL DISPLAY.
digital integrated circuit An integrated circuit
(IC) intended for binary operations, such as
switching, gating, etc. Compare LINEAR INTEGRATED CIRCUIT.
digital integrator A device that can perform integration, in which increments in input variables,
and an output variable, are represented by digital
digital logic A form of Boolean algebra, consisting
of negation, conjunction, and disjunction, in
which the binary digit 1 has the value “true” and
0 the value “false” (in positive logic) or vice versa
(in negative logic). Digital logic is the basis by
which all digital devices function.
digital-logic module 1. A circuit that performs
digital operations. 2. A logic gate.
digital meter A meter that produces a readout in
discrete blocks or directly as numerals. The first,
more primitive and less precise type, is known as a
BAR METER. The second, more sophisticated type
can resolve to several significant digits and often
includes a fixed or floating radix point. This
scheme eliminates the need for personnel to interpolate the reading on a scale. There is little chance
for error on the part of the technician or engineer,
because the readout is straightforward. Another
advantage is the fact that there are no moving
parts to wear out or be damaged by physical shock.
multimeter Abbreviation,
voltohm-milliammeter producing a digital readout of measured values.
digital multiplex 1. The combination of several or
many digital signals into a single digital signal. 2.
Also called digital demultiplex. The reverse process from that defined in 1, in which the original
signals are obtained from the combination signal.
3. Communication using the techniques defined
in 1 and 2.
digital multiplex equipment Equipment that accomplishes digital multiplexing or the reverse
process, digital demultiplexing.
digital multiplier In a digital computer, a device
that produces a product signal from multiplier
and multiplicand signals.
digital output An output signal of digital pulses
representing a number equal or proportional to
the value of a corresponding input signal.
digital panel meter A numeric-readout meter whose
relatively small size allows mounting on a panel.
digital phase shifter A phase shifter actuated by a
digital control signal.
digital photometer An electronic photometer providing a digital readout of illumination values.
digital power meter An electronic wattmeter providing a digital readout of measured power.
digital readout An indicating device that displays
a sequence of numerals that represent a measured value.
digital recording A system for tape-recording
high-fidelity sound. The audio is converted from
analog to binary digital form, and the binary digits (bits) are recorded on magnetic tape.
digital representation The use of digital signals to
represent information as characters or numbers.
digital rotary transducer • digit delay element
digital rotary transducer A device that delivers a
digital output signal proportional to the rotation
of a shaft.
Digital Satellite System Abbreviation, DSS. Trade
name for a satellite television (TV) system developed by RCA. The analog signal is changed into
digital pulses at the transmitting station via
analog-to-digital (A/D) conversion. The digital
signal is amplified and uplinked to a geostationary satellite. The satellite has a transponder that
receives the signal, converts it to a different frequency, and downlinks it back to the earth. The
downlink is picked up by a portable dish that can
be placed on a balcony or patio, on a rooftop, or
in a window. A tuner selects the channel that the
subscriber wants to watch. The digital signal is
amplified. If necessary, digital signal processing
(DSP) can be used to improve the quality of reception under marginal conditions. The digital
signal is changed back into analog form, suitable
for viewing on a conventional TV set, via digitalto-analog (D/A) conversion.
digital signal A signal having an integral number
of discrete levels or values, as opposed to a signal
whose levels or values vary over a continuous
digital signal
digital signal processing Abbreviation, DSP. A
method of signal enhancement that operates by
eliminating confusion between digital states. This
improves dynamic range and frequency response,
reduces the number of errors, and virtually eliminates noise. It is used extensively in digital communication and recording, often in conjunction
with analog-to-digital (A/D) and digital-to-analog
(D/A) conversion to enhance the quality of analog
signals and recordings.
digital sound Sound recording and reproduction
accomplished with digital, rather than analog,
signals. Advantages include wideband frequency
response, superior dynamic range, and relative
immunity to noise.
digital speech communications A system of voice
communications, in which the analog voice signal
is encoded into digital pulses at the transmitter,
and decoded at the receiver.
digital subtractor In a computer, a device that produces an output signal whose value is equal to the
difference of the values of two input signals.
digital switching Routing operations carried out
on digital signals to establish communications
links between specified system users.
digital television 1. A television system in which
the picture information is encoded into digital
form at the transmitter, and decoded at the receiver. 2. A form of television picture transmission that functions according to picture motion,
rather than absolute brightness.
digital temperature indicator See DIGITAL
digital thermometer An electronic thermometer
that provides a digital readout of temperature.
digital-to-analog conversion The conversion of a
digital quantity into an analog representation,
such as shown by a performance curve. Compare
digital-to-analog converter A circuit or device
digital transmission 1. A method of signal
transmission in which the modulation occurs
in defined increments, rather than over a continuous range. 2. A message that is sent in digital form.
digital-type meter An indicating instrument in
which a row of numeral indicators displays a
value. Compare ANALOG-TYPE METER.
digital voltmeter Abbreviation, DVM. An electronic voltmeter having a direct numerical readout, rather than an analog display.
digital wattmeter See DIGITAL POWER METER.
digital compression In digital computer operation, the process of representing data with an
economy of characters to reduce file size.
digit current In digital computer operations, the
current associated with writing or reading a digit
into or out of a memory cell.
digit delay element A logic element (gate) whose
output signal lags the input signal by one digit
digit filter • diode-capacitor memory cell
digit filter A device for detecting designations. See
digitize 1. To express the results of an analog
measurement in digital units. 2. To convert an
analog signal into corresponding digital pulses.
digit period In a digital circuit or system, the time
interval between the start of one digital pulse and
the start of the next pulse.
digit place See DIGIT POSITION.
digit plane In a matrix-type computer memory, the
plane within a three-dimensional array of memory storage elements representing a DIGIT POSITION.
digit position The ordinal position of a digit in a
numeral, the first position being occupied by the
least-significant digit (e.g., 7 is in the third position in the numeral 756).
digit pulse A pulse that energizes magnetic core
memory elements representing a digit position in
several words.
digitron A display in which all of the characters lie
in a single, flat plane.
digit time The duration of a digit signal in a series
of signals.
digit time slot In digital communications, the interval of time assigned to one bit or one digit.
digit-transfer bus In a digital computer, a main
line (of conductors) that transfers information
among various registers; it does not handle control signals.
diheptal CRT base The 14-pin base of a cathoderay tube. Also see BIDECAL, DUODECAL, and
DIIC Abbreviation for dielectric-isolated integrated
circuit. Several separate integrated-circuit wafers
are contained in a single package, and kept electrically insulated by layers of dielectric.
dilatometer An instrument used to measure expansion.
dimension 1. Any measurable quantity, such as
distance, time, temperature, humidity, etc. 2. An
axis in the three-dimensional Cartesian coordinate system. 3. An independent variable in a
function of one or more variables.
dimensional analysis A mathematical procedure
whereby an equation involving quantities with
different units is verified as being dimensionally
correct. The original variables are replaced with
fundamental quantities, such as resistance (R),
current (I ), length or displacement (d ), and time
(t), applicable to electrical systems. The equation
is dimensionally correct if it can be shown that
the left and right sides of the equation are identical.
dimensional ratio In magnetism, the ratio of the
longest diameter of an elongated ellipsoid of revolution to the shortest.
dimensional stability Nonvariance or little variance in the shape and size of a medium (such as
film) during the processing of that material.
dimensionless quantity A quantity that is merely
a real number. Example: logarithm, exponent,
numerical ratio, etc. In contrast are physical
quantities: 3 volts, 5000 hertz, 10 amperes, etc.
diminished radix complement See COMPLEMENT.
dimmer An electronic device used for controlling
the brightness of incandescent lamps. Using amplified control, the device enables high-wattage
lamp loads to be smoothly adjusted via a small
rheostat or potentiometer. A photoelectric-type
dimmer automatically controls lamps in accordance with the amount of daylight.
dimmer curve The function of a light-dimmer voltage output as a function of setting on a linear
DIN Abbreviation for Deutsche Industrie Normenausschuss. A German association that sets
standards for the manufacture and performance
of electrical and electronic equipment, as well as
other devices.
D indicator In radar operations, an indicator combining type B and C indicators (see B DISPLAY
Dingley induction-type landing system An aircraft landing system that provides lateral and
vertical guidance; instead of radio, it uses the
magnetic field surrounding two horizontal cables
laid on or under either side of the runway.
diode A two-element device containing an anode
and a cathode, and providing unidirectional conduction. The many types are used in such devices
as rectifiers, detectors, peak clippers, mixers,
modulators, amplifiers, oscillators, and test instruments.
diode action 1. The characteristic behavior of a
diode (i.e., rectification and unidirectional conduction). 2. Two-electrode rectification or unidirectional conductivity in any device other than a
diode (e.g., asymmetrical conductivity between
the collector and base of a transistor).
diode amplifier 1. A parametric amplifier employing a varactor. 2. An amplifier utilizing holestorage effects in a semiconductor diode. 3. A
negative-resistance amplifier using a tunnel diode.
diode array A combination of several diodes in a
single housing.
diode assembly See DIODE ARRAY.
diode bias A steady direct-current (dc) voltage applied to a diode to establish its operating point.
diode capacitance The capacitance existing at the
p-n junction of a semiconductor diode when the
junction is reverse-biased. The capacitance generally varies, depending on the reverse-bias voltage.
diode capacitor 1. A capacitor normally operated
with a diode. 2. A voltage-variable capacitor utilizing the junction capacitance of a semiconductor diode (e.g., a varactor).
diode-capacitor memory cell A high-value capacitor in series with a high-back-resistance semi-
diode-capacitor memory cell • diode peak detector
conductor diode. A data pulse forward-biases the
diode and charges the capacitor, which remains
charged, thus holding the data bit, because of the
long time constant of the high capacitance and
the high back resistance of the diode.
diode characteristic The current-versus-voltage
curve for a diode.
diode checker An instrument for testing semiconductor diodes. There are two forms: A static
checker, which measures forward and reverse
current; and a dynamic checker (see DYNAMIC
DIODE TESTER), which displays the entire diode
response curve on an oscilloscope screen.
diode chopper A chopper using an alternately biased diode as the switching element.
diode clipper A clipper using one or more diodes.
A single biased diode will limit the positive or negative peak of an applied alternating-current (ac)
voltage, depending on diode polarity and bias.
Two biased diodes with opposing polarity will clip
both peaks. Also see LIMITER.
diode clipper
diode converter See DIODE MIXER.
diode current The forward or reverse current flowing through a diode.
diode current meter A direct-current (dc) milliammeter or microammeter with a semiconductor-diode rectifier that allows the measurement of
alternating current (ac).
diode curve changer A diode or network of diodes
used to make a linear current-voltage curve acquire some nonlinear shape.
diode demodulator See DEMODULATOR PROBE
diode detector A detector circuit in which a diode
demodulates a signal. The diode, a simple device,
provides linear response at high signal amplitudes, but affords no amplification.
diode feedback rectifier 1. In a rectified-carrier,
negative-feedback system for an amplitudemodulated (AM) transmitter, the diode that
rectifies the modulated carrier and provides the
audio envelope for use as negative-feedback
voltage. This voltage is applied to the speech
amplifier/modulator channel to reduce distortion,
noise, and hum, at the same time providing
automatic modulation control. 2. The diode that
rectifies a part of the signal at the output of an
audio amplifier and provides a proportional
direct-current (dc) voltage for use as bias in an
automatic-gain-control (AGC) circuit.
diode field-strength meter A simple meter for
measuring the intensity of a radio-frequency
(RF) electromagnetic field. It consists of a short
whip antenna, an inductance-capacitance (LC)
tuned circuit, a diode detector, and a directcurrent (dc) microammeter. The deflection of the
meter is roughly proportional to the RF signal
diode gate A passive switching circuit of biased
diodes. Also see AND CIRCUIT and OR CIRCUIT.
diode impedance The vector sum (resultant) of the
resistive and reactive components of a diode. In a
semiconductor diode, the inductive component of
reactance is almost entirely the inductance of
leads and electrodes, whereas the capacitive component of reactance is the shunting capacitance
between leads and electrodes, plus the voltagevariable capacitance of the pn junction. The
resistive component is almost entirely the voltage-variable resistance of the pn junction.
diode isolation A means of insulating an integrated-circuit chip from its substrate. The chip is
surrounded by a pn junction that is reversebiased. This prevents conduction between the
chip and the substrate.
diode lamp See LASER DIODE.
diode laser See LASER DIODE.
diode light source See LASER DIODE.
diode limiter See DIODE CLIPPER.
diode load 1. The current drawn from a diode acting as a rectifier or demodulator. 2. The output
(load) resistor into which a diode operates.
diode load resistance The required value for a
diode load resistor.
diode load resistor A resistor usually connected to
the output of a diode rectifier or diode detector.
diode logic Digital circuitry, such as AND and OR
circuits, using diodes as the principal components.
diode matrix In some digital devices, a grid of
wires, the intersections of some being interconnected through diodes, whose polarities determine circuit operation. A series of AND circuits is
provided by this arrangement, which acts as a
high-speed rotary switch when it is supplied with
input pulses.
diode mixer A frequency converter that operates
via the nonlinearity of semiconductor diodes.
diode noise limiter A noise limiter circuit having
one or more biased diodes.
diode oscillator An oscillator based on the negative resistance or breakdown characteristics of
certain diodes, such as high-reverse-biased germanium diodes, tunnel diodes, Gunn diodes, and
four-layer diodes. It is generally used at microwave frequencies.
diode pack A device containing more than one
diode. An example is the full-wave bridge-rectifier
integrated circuit.
diode peak detector A diode detector whose load
resistance is high at modulation frequencies; the
voltage across the resistance is proportional to
the peak amplitude of the modulated signal.
diode peak voltmeter • diplex reception
diode oscillator, 1
diode peak voltmeter A diode-type alternatingcurrent (ac) voltmeter, in which the deflection of
the direct-current (dc) milliammeter or microammeter is proportional to the peak value of the applied ac voltage.
diode probe A test probe containing a diode used
as either a rectifier or demodulator.
diode recovery time The interval during which relatively high current continues to flow after the
voltage across a semiconductor junction has been
abruptly switched from forward to reverse. Recovery time is attributable to DIODE STORAGE.
diode rectification Conversion of alternating current (ac) to pulsating direct current (dc) by diode
diode rectifier 1. A diode device that converts alternating current (ac) to pulsating direct current
(dc) in a power supply. 2. A small-signal diode device that converts ac to dc in the automatic-gaincontrol (AGC) circuit of a superheterodyne
receiver. Also called AGC rectifier.
diode resistor 1. A resistor usually operated with
a diode. 2. A voltage-variable resistor utilizing the
(usually forward) resistance of a semiconductor
diode storage The charge carriers (electrons and
holes) remaining within a pn junction for a short
time after forward bias has been either removed
or switched to reverse polarity.
diode storage time See DIODE RECOVERY TIME.
diode switch See DIODE GATE.
diode sync separator A diode used in a television
receiver circuit to separate and deliver the sync
pulses from the composite video signal.
diode temperature stabilization 1. Keeping the
temperature of a diode at a constant level. 2. Using the temperature-resistance characteristic of a
forward-biased semiconductor diode to stabilize a
circuit (such as a transistor amplifier stage) (i.e.,
to prevent variations caused by temperature
diode tester See DIODE CHECKER.
diode transistor 1. See UNIJUNCTION TRANSISTOR. 2. A semiconductor diode whose operation
simulates that of a transistor by means of pulsed
operation that alternately makes the single junction an emitter or collector. 3. A transistor connected to operate solely as a diode.
diode-transistor logic Abbreviation, DTL. Logic
circuitry in which a diode is the logic element and
a transistor acts as an inverting amplifier.
diode-type meter A rectifier-type alternatingcurrent (ac) meter consisting of a semiconductor
diode(s) and a direct-current (dc) milliammeter or
microammeter. The diode rectifies the ac input,
the resulting dc deflecting the meter.
diode varactor A conventional semiconductor
diode or rectifier used as a makeshift varactor
(voltage-variable capacitor).
diode variable resistor See DIODE VARISTOR.
diode varistor A conventional diode used as a
makeshift varistor (voltage-variable resistor).
diode voltage reference See ZENER VOLTAGE
diode voltage regulator See ZENER VOLTAGE
dip 1. A distinct decrease in the value of a varying
quantity, followed by an increase [e.g., the sudden drop, followed by a rise, in collector current
when a bipolar-transistor radio-frequency (RF)
power amplifier is tuned through resonance]. 2.
Also called magnetic inclination. The slanting of a
compass needle, resulting from the orientation of
the geomagnetic lines of flux, with respect to the
earth’s surface. It varies, depending on magnetic
dip adapter An external accessory that allows a radio-frequency (RF) signal generator to be used as
dip coating 1. Applying a protective coat of insulating material to a conductor or component by
dipping it into the liquid material, then draining
and drying it. Compare SPRAY COATING. 2. The
coat applied in this way.
dip encapsulation Embedding a component or circuit in a protective block of insulating material
(such as a plastic) while the material is in a liquid
state, and then allowing the material to harden in
ambient air or in an oven.
dip impregnation Saturating a component or material (such as absorbent film) with a substance
(such as oil or wax) by dipping or vacuum forcing.
diplexer A coupler that permits two or more transmitters to operate simultaneously into a single
diplex operation 1. Simultaneous transmission or
reception of two signals using a single antenna.
2. Simultaneous transmission or reception of two
signals on a single carrier.
diplex reception The reception of signals while
transmitting with the same antenna.
diplex transmission • direct-conversion receiver
diplex transmission The transmission of signals
while receiving with the same antenna.
dip meter A tunable radio-frequency (RF) instrument that, by means of a sharp dip of an indicating meter, indicates resonance with an external
circuit under test. Specific names are derived
from the active component used: grid-dip meter,
gate-dip meter, etc.
dip needle See INCLINOMETER.
dipolar Also, bipolar. Possessing two poles (usually electric or magnetic).
dipolarization See DEPOLARIZATION.
dipole 1. A pair of electrically opposite charge
poles separated by a specific distance. 2. A pair of
magnetically opposite poles separated by a specific distance. 3. See DIPOLE ANTENNA. 4. See
dipole antenna Also called dipole and doublet. A
half-wavelength radiator fed at the center with a
two-wire or coaxial transmission line. Each “leg”
of the antenna is one-quarter wavelength long.
Such an antenna can be oriented horizontally or
vertically, or at a slant. The radiating element is
usually straight. For a straight wire radiator,
properly insulated at the ends and placed well
away from obstructions, the length L ft (in feet) at
a design frequency f (in megahertz) is approximately
L ft = 467/f
The length Lm (in meters) is close to
L m = 143/f
Because of its simplicity, this antenna is popular
among shortwave listeners and radio amateurs,
especially at frequencies below 10 MHz. A fullsize antenna of this type has a feed-point
impedance of approximately 73 ohms, purely resistive. Compare FOLDED DIPOLE.
dipole antenna
dipole disk feed A method of coupling radio-frequency energy to a disk-shaped antenna. The energy is applied to a dipole located adjacent to the
dipole feed A method of coupling radio-frequency
energy to an antenna by means of a half-wave
dipole. The dipole is directly fed by the transmission line, and the dipole radiates energy to the
rest of the system.
dip oscillator The oscillator that provides the signal for a DIP METER.
dipotassium tartrate Abbreviation, DKT. An organic piezoelectric material.
dipped component A discrete electronic component that has been given a protective coating by
dipping into a suitable material (such as oil, varnish, or wax) and draining off the surplus.
dipper Collective term for resonance-type instruments, such as a DIP METER or DIP ADAPTER.
dipper interrupter A cyclic switching device in
which a contact pin is part of a revolving wheel
partially immersed in mercury.
dipping 1. The application of a protective coating
or impregnant to a component by immersing it in
a suitable material. Also see DIP COATING, DIP
In a resonant (tuned) amplifier circuit, the adjustment of the resonant circuit for minimum
current through the amplifying device.
dipping needle See INCLINOMETER.
dip soldering 1. Soldering leads or terminals by
dipping them into molten solder and then removing excess solder. 2. Tinning printed-circuit patterns by dipping the boards into molten solder or
placing them in contact with the surface of a solder bath. 3. Soldering leads in printed circuits by
the methods defined in (2).
DIP switch A switch (or group of miniature
switches) mounted in a dual-inline package (DIP)
for easy insertion into an integrated-circuit
socket or printed-circuit board.
direct-access storage device A computer memory
in which data access time is unaffected by the
data location. Also called random-access memory
direct-acting recorder See GRAPHIC RECORDER.
instrument See
direct address The actual address of a computer
storage location (i.e., the one designated by machine code 0. Also called absolute address or real
direct capacitance The capacitance between two
points in a circuit, as opposed to the capacitance
between either point and other objects (including
direct allocation In digital computer operations,
to specify the necessary memory locations and
peripherals for a particular program when it is
direct coding Computer programming in machine
direct control Control of one machine by another,
for example, the control of a computerized mobile
robot by a central computer system.
direct-conversion receiver A heterodyne receiver
in which the incoming radio-frequency (RF) signal
direct-conversion receiver • direct ground
RF amp.
AF amp.
Speaker or
direct-conversion receiver
is amplified, then mixed with the RF output of a
tunable local oscillator, producing an audiofrequency (AF) beat note. The AF is amplified;
audio filtering can be added. Although the directconversion receiver somewhat resembles the
superheterodyne type, it has no intermediatefrequency (IF) chain, and does not normally
provide single-signal reception. Also see ZEROBEAT RECEPTION.
direct-coupled amplifier An amplifier in which
the output circuit of one stage is wired directly to
the input circuit of the following stage (i.e., there
is no intervening capacitor or transformer). Such
an amplifier can handle alternating-current (ac)
or direct-current (dc) signals, and has wide frequency response.
direct-coupled transistor logic Abbreviation,
DCTL. In digital computer and switching circuits,
a logic system using only direct-coupled transistor stages.
direct coupling Direct connection of one circuit
point to another for signal transmission (i.e.,
without intermediate capacitors or transformers).
Because coupling devices aren’t used, direct coupling provides transmission of direct current (dc),
as well as alternating current (ac).
direct current 1. Abbreviation, dc. A current that
always flows in the same direction (i.e., the polarity never reverses). The current might be constant, as from a battery or a regulated power
supply; it might be pulsating, as from an unfiltered rectifier. 2. Pertaining to current that always flows in the same direction. 3. Descriptive
of a voltage, resistance, or other parameter under conditions in which there is a usually constant current that always flows in the same
direct-current amplifier An amplifier for boosting
direct-current (dc) signals, as opposed to dc voltage signals.
direct-current bar See DC BAR.
direct-current beta See DC BETA.
direct-current block See DC BLOCK.
direct-current bus See DC BUS.
direct-current circuit breaker See DC CIRCUIT
direct-current component See DC COMPONENT.
direct-current converter See DC CONVERTER.
direct-current coupling See DC COUPLING.
direct-current dump See DC DUMP.
direct-current equipment See DC EQUIPMENT.
direct-current erase head See DC ERASE HEAD.
direct-current generator See DC GENERATOR.
direct-current inverter See DC INVERTER.
direct-current leakage See DC LEAKAGE.
direct-current motor See DC MOTOR.
direct-current noise See DC NOISE.
direct-current power See DC POWER.
direct-current relay See DC RELAY.
direct-current resistance See DC RESISTANCE.
direct-current shift See DC SHIFT.
direct-current short See DC SHORT.
direct-current signaling See DC SIGNALING.
direct-current source See DC SOURCE.
direct-current transducer See DC TRANSDUCER.
direct-current transformer See DC TRANSFORMER.
direct-current transmission See DC TRANSMISSION.
direct digital control In a digital computer, multiplexing or time sharing among a number of controlled loops.
direct display unit A cathode-ray-tube (CRT) peripheral that displays data recalled from memory.
direct-distance dialing A form of telephone service that allows dialing of long-distance numbers
without involving a human operator.
direct drive 1. Pertaining to electromechanical accessories for electronic equipment. 2. The transmission of power directly from a source (such as
a motor) to a driven device without intermediate
gears, belts, or clutches.
direct-drive robot A robot that uses the minimum
possible number of gears and other drive systems.
direct-drive torque motor In a positioning or
speed-control system, a servoactuator connected
directly to the driven load.
direct-drive tuning A tuning or adjusting mechanism in which the shaft of the variable component (such as a potentiometer or variable
capacitor) is turned directly by a knob (i.e., without gearing, dial cable, or similar linkage).
directed number A number having direction as
well as magnitude; a vector quantity.
direct electromotive force A direct-current (dc)
voltage that does not fluctuate or pulsate.
direct ground 1. A ground connection made by the
shortest practicable route. Compare INDIRECT
GROUND. 2. An earth ground.
direct induced current • directional wattmeter
+j 4
4 + j4
+j 2
5 − j2
directed number
directional coupler A microwave device that couples an external system to waves traveling
through the coupler in one direction.
directional diode A high-back-resistance semiconductor diode inserted into a direct-current
(dc) signal circuit or control circuit. Permits unidirectional current flow.
directional filter In carrier-current transmission,
a filter that halves the frequency band, one half
being for transmission in one direction, and the
other half being for transmission in the opposite
directional gain Symbol, kS. The ratio of the power
that would be radiated by a loudspeaker if the
free-space axial sound pressure were constant
over a sphere, to the actual radiated power. Usually expressed in decibels.
directional homing A scheme for locating the
source of a radio signal. An effort is made to keep
the bearing of the target or guiding station constant. Therefore, the search path is as direct (as
nearly a straight line) as practicable.
directional horn See DIRECTIVE HORN.
directional hydrophone A hydrophone whose response pattern strongly favors one direction.
directional lobe In the spatial response pattern of
a device, such as an antenna or loudspeaker, a
portion showing emphasized response in a given
directional microphone A microphone that
strongly favors sound emanating from in front of
directional pattern See DIRECTIVITY PATTERN.
directional phase shifter A phase-shifting circuit
in which the characteristics are different in one
direction, as compared with the other direction.
directional power relay A relay that is actuated
when the monitored power reaches a prescribed
level in a given direction.
directional relay See POLARIZED RELAY.
directional response For any form of transducer,
a radiation or sensitivity pattern that is concentrated in certain directions.
directional separation filter See DIRECTIONAL
directional transducer A device that senses or
emits some effect to an extent that depends on
the direction from which the effect comes. Directional effects are often, but not always, accompanied by gain in the favored direction(s).
Examples: directional microphone, directional
speaker, and directional antenna.
directional variation of radio waves Changes in
the field strength of radio waves, depending on
the direction. There are various causes, including
antenna directivity, ground characteristics, ionospheric factors, weather conditions, and the presence of obstructing objects.
directional wattmeter A device that can measure
radio transmitter output power and can also give
an indication of how well an antenna is matched
direct induced current A transient current induced in the same direction as the induction current when it is interrupted.
directing antenna See DIRECTIONAL ANTENNA.
direct-input circuit A circuit, especially an amplifier, whose input is wired directly to the input
electrode of the active device (i.e., without a coupling capacitor or transformer).
direct-insert subroutine In digital computer operations, a subroutine directly inserted into a larger
instruction sequence. It must be rewritten at every point it is needed.
direct instruction A computer program instruction that indicates the location of an operand in
directional 1. Depending on direction or orientation. 2. Having a concentration in an identifiable
direction. 3. Pertaining to a transducer in which
radiation, or sensitivity, is concentrated in certain directions at the expense of radiation or sensitivity in other directions.
directional antenna An antenna that transmits
and receives signals more effectively in some directions than in others. Also called beam, beam
antenna, and directive antenna.
directional array 1. A directional antenna having
a set of elements assembled in such a way that
their combined action shapes the radiation into a
unidirectional pattern. 2. A group of antennas
spaced and phased to produce unidirectional radiation and reception patterns.
directional beam 1. An antenna whose radiation
or reception pattern strongly favors a specific direction. 2. The radiation or reception pattern of
such an antenna.
directional characteristic The precise directional
properties of an antenna or transducer.
directional CQ In amateur radio, a transmission
that invites replies only from stations in a certain direction or in a particular city, state, or
directional wattmeter • directivity index
to a transmission line. Such meters fall into two
categories. One type has a single scale, calibrated
in watts, and sometimes also in milliwatts or kilowatts (switch selectable). The meter reads either
forward power or reflected power, depending on
the position of a switch or rotatable internal element. Another type has two needles in a single
enclosure, with a different calibrated scale for
each needle. Both of these scales are graduated
in watts, and sometimes also in milliwatts or kilowatts. One needle/scale indicates forward power
and the other needle/scale indicates reflected
power. There is a third scale, calibrated for the
point where the two needles cross. This scale indicates the standing-wave ratio (SWR). See also
direction angle In radar operations, the angle between the center of the antenna baseline and a
line going to the target.
direction finder A receiver specially adapted to
show the direction from which a signal is received, thus revealing the direction of the receiver
with respect to the transmitting station, and vice
versa. In its simplest form, it is a receiver with a
loop antenna that is rotatable over a map or compass card. For increased accuracy, checks are
made with signals from two transmitting stations; the exact location of the receiver is pinpointed by triangulation.
direction finding The taking of bearings by means
of a direction finder.
direction of lay In a multiconductor cable, the lateral direction of winding of the topmost conductors as they recede from the observer; called
Position of
vessel sending
distress signal
direction finding
left-hand lay or right-hand lay. If the cable is
viewed from either end, left-hand lay is equivalent
to conductors that rotate clockwise as they recede from the viewer; right-hand lay is equivalent
to conductors that rotate counterclockwise as
they recede from the viewer.
direction of polarization The direction of the electrostatic field in a linearly polarized wave.
direction of propagation The direction in which
energy moves from a transmitter, or between
equivalent points in a sector of space under consideration.
direction rectifier In a control system, a rectifier
whose direct-current (dc) output voltage has a
magnitude and polarity dependent on the magnitude and phase of an alternating-current (ac) selsyn error voltage.
direction resolution 1. The smallest difference in
azimuth that a direction-finding device can detect. 2. The smallest angular separation between
two targets that allows a radar set to show two
separate echoes rather than a single echo.
directive In a computer source program, a statement directing the compiler in translating the
program into machine language without being
translated itself. Also called control statement.
directive antenna An antenna designed for best
propagation or reception in one (often steerable)
horizontal direction. Also called beam antenna
and directional antenna.
directive gain For a directional antenna, a rating
equal to 12.566(Pr/Pt), where Pr is the radiated
power per steradian in a given direction and Pt is
the total radiated power.
directive horn A microwave antenna having the
shape of a (usually rectangular) horn.
directivity 1. In an antenna, a directional response. 2. The degree to which the radiation or
sensitivity of a transducer is concentrated in certain directions. 3. The angle between the halfpower points of a directive antenna in the
azimuth plane. 4. In an antenna system, the ratio, in decibels, between the power in the favored
direction and the power in the exact opposite direction; also called front-to-back ratio. 5. The forward power gain of an antenna, with respect to a
dipole in free space. 6. The forward power gain of
an antenna, with respect to an isotropic radiator
in free space.
directivity diagram A graph of the radiation/
response pattern of a beam antenna or other
directional device, usually in a horizontal or
vertical plane. Also see DIRECTIVITY PATTERN.
directivity factor 1. A measure of the directivity of
an antenna or transducer. 2. In acoustics, the ratio, in decibels, between the gain in the maximum
direction and the gain in the minimum direction,
for a transducer, such as a speaker or microphone.
directivity index 1. For an acoustic-emitting
transducer, the ratio, in decibels, of E1 to E2,
directivity index • directrix
where E1 is the average intensity over an entire
sphere surrounding the transducer, and E2 is the
intensity on the acoustic axis. 2. For an acoustic
pickup transducer, the ratio, in decibels, of E1 to
E2, where E1 is the average response over an entire sphere surrounding the transducer, and E2 is
the response on the acoustic axis.
directivity of antenna For a beam antenna, the
ratio Emax/Eavg, where Emax is the maximum field
intensity at a selected distance from the antenna
and Eavg is the average field intensity at the same
directivity of directional coupler The ratio, in
decibels, of P1 to P2, where P1 is the power at the
forward wave-sampling terminals (measured with
a forward wave in the transmission line) and P2 is
the power at the terminals when the wave is reversed in direction.
directivity pattern The calculated or measured radiation or response pattern (transmission or reception) of an antenna, microphone, loudspeaker,
or similar device, with particular attention to the
directional features of the pattern.
directivity signal A spurious output signal resulting from finite directivity in a coupler.
direct light Light rays traveling directly from a
source to a receptor or target without reflection.
directly grounded Connected to earth or to the
lowest-potential point in a circuit, without any intervening resistance or reactance.
directly heated cathode A vacuum-tube filament.
It is so called because, when heated, it becomes
the cathode of the tube (i.e., the emitter of electrons).
directly heated thermistor A thermistor whose
temperature changes with the surrounding temperature, and also as a result of power dissipation in the device itself. Compare INDIRECTLY
directly heated thermocouple A meter thermocouple heated directly by signal currents passing
through it. Compare INDIRECTLY HEATED
direct measurement Immediate measurement of
a quantity, rather than determining the value of
the quantity through adjustments of a measuring
device (e.g., measuring capacitance with a capacitance meter, rather than with a bridge). Compare
direct memory access Abbreviation, DMA. The
transfer of data from a computer memory to some
other location, without the intervention of the
central processing unit (CPU).
direct numerical control In a computer or data
system, the capability for distributing information among numerically controlled machines
whenever desired.
director In a multielement directional antenna, an
element that is usually mounted in front of the
radiator element, and that is phased and spaced
to direct the radiation forward. The director func-
tions in conjunction with the reflector element,
which is usually mounted behind the radiator.
directory See DICTIONARY.
direct pickup The broadcasting, especially in television, of events at the same time as they occur
(e.g., without recording/reproduction).
direct piezoelectricity The production of a piezoelectric voltage by mechanically stressing a suitable crystal.
direct playback In audio or video recording, the
reproduction of a recording without additional
processing (e.g., the playing of an original
recorded tape, rather than a tape that has been
mass produced).
direct-point repeater A relay-operated telegraph
repeater. The received signals actuate the relay,
which switches the second line.
direct-radiator loudspeaker A loudspeaker whose
cone or diaphragm is directly coupled to the air.
direct ray An electromagnetic ray (wave) that
reaches a receiver without reflection or refraction,
and without encountering obstructions.
direct recording 1. A record produced by a
graphic recorder. 2. The technique of producing
such a record.
direct-recording instrument A device, such as a
graphic recorder, that directly produces a permanent record (such as an inked trace) of the variations of a quantity.
direct resistance coupling A form of coupling in
which the output of the first amplifying device is
connected through a resistor directly to the input
of the second device. The resistance value can
vary; sometimes the connection is a short circuit.
directrix A fixed line to which a curve is referred
(e.g., the axis of a parabola).
direct resistance coupling
direct scanning • discrete capacitor
direct scanning In television, the sequential viewing of parts of a scene by the camera—even
though the entire scene is continuously illuminated.
direct serial file organization A technique of organizing files stored in a direct access device, in
which a record can be chosen by number and
amended where it is without altering other members of the file.
direct sound wave A sound wave arriving directly
from its source—especially a wave within an enclosure that is not affected by reflection.
direct substitution 1. An exact component replacement. 2. Installing an exact component replacement.
direct synthesizer A device for producing random,
rapidly changing frequencies for security purposes. A reference oscillator provides a comparison frequency; the output frequency is a
rational-number multiple of this reference frequency.
direct voltage See DC VOLTAGE.
direct wave A wave that travels from a transmitter
to a receiver without being reflected by the ionosphere or the ground. Compare SKYWAVE.
direct Wiedemann effect Twisting force (torque)
in a wire carrying current in a longitudinal magnetic field. Occurs because of interaction between
the longitudinal field and the circular magnetic
field around the wire.
direct-wire circuit A communications or control
line of wires connecting a transmitter (or control
point) and a receiver (or controlled point) without
an intermediary, such as a switchboard.
recorder See
direct-writing telegraph 1. See PRINTING TELEGRAPH. 2. See TELAUTOGRAPH.
dis- A prefix meaning “deprived of.” For the formation of electronic terms, the prefix must be distinguished from un-, meaning “not.” For example, a
discharged body is one that was charged, but has
been emptied of its charge. An uncharged body is
one that ordinarily or presently is not charged.
disable 1. To deliberately render a circuit, device,
or system inoperative. 2. In digital computer
operations, to defeat a software or hardware
disc See DISK.
disc engraving 1. Recording sound by cutting a
groove in a record disc. 2. The groove resulting
from such a process.
discharge The emptying or draining of electricity
from a source, such as a battery or capacitor. The
term also denotes a sudden, heavy flow of current, as in DISRUPTIVE DISCHARGE. Compare
discharge current 1. Current flowing out of a capacitor. 2. Current flowing out of a cell—especially a storage cell. Compare CHARGING
discharge key See DISCHARGE SWITCH.
discharge lamp A gas-filled tube or globe in which
light is produced by ionization of the gas between
electrodes. Familiar examples are the neon bulb
and fluorescent tube.
discharge phenomena The effects associated with
electrical discharges in gases, such as luminous
discharge potential See IONIZATION POTENTIAL.
discharger 1. A short-circuiting tool for discharging capacitors. 2. A spark gap or other device for
automatically discharging an overcharged capacitor.
discharge rate 1. The current that can be supplied
by an electrochemical cell or battery reliably during its discharging cycle. Usually expressed in
milliamperes or amperes. 2. An expression of the
speed with which a battery is being discharged at
a specific point in time. It is usually specified in
amperes or milliamperes.
discharge switch A switch for connecting a
charged capacitor to a resistor or other load,
through which the capacitor discharges. In some
circuits, when the switch is in its resting position,
it connects the capacitor to the charging source.
discharge voltage See IONIZATION POTENTIAL.
discharging 1. The conversion of chemical energy
to electrical energy by an electrochemical cell or
battery. 2. The release of stored electrical energy
from a capacitor, or from a network containing
discharging tongs See DISCHARGER, 1.
discone antenna An antenna consisting of a horizontal metal or wire-mesh disk above a metal or
wire-mesh cone. The antenna has an omnidirectional radiation pattern in the horizontal plane,
and provides a good match to a coaxial transmission line over a frequency range of several octaves. Commonly used at very-high frequencies
(VHF) and ultra-high frequencies (UHF).
disconnect 1. To separate leads or connections,
thereby interrupting a circuit. 2. A type of connector whose halves can be pulled apart to open
a cable or other circuit quickly. 3. To open a
switch or relay.
disconnect signal A signal sent over a telephone
line, ending the connection.
disconnect switch A switch whose main function
is to open a circuit quickly (either manually or
automatically) in the event of an overload.
discontinuity 1. A break in a conductor. 2. A
point at which the impedance in a transmission
line abruptly changes.
discontinuous wave trains See DAMPED WAVES.
discrete 1. Complete and self-contained, as opposed to a part of something else. 2. Composed of
individual, separate members.
discrete capacitor Capacitance that is entirely
self-contained, rather than being electrically dis-
discrete capacitor • disk capacitor
discrete circuit A circuit comprised of discrete
components, such as resistors, capacitors,
diodes, and transistors, not fabricated into an integrated circuit.
discrete component A self-contained device that
offers one particular electrical property in lumped
form (i.e., concentrated at one place in a circuit,
rather than being distributed). A discrete component is built especially to have a specific electrical
property, and exists independently, not in combination with other components. Examples: disk
capacitor, toroidal inductor, and carbon-composition resistor. Compare DISTRIBUTED COMPONENT.
discrete device Any component or device that operates as a self-contained unit.
discrete element A discrete device that forms part
of a larger system.
discrete inductor An inductive component that is
entirely self-contained, rather than being electrically spread out. Also called lumped inductor.
discrete information source A source of data containing a finite number of individual elements,
rather than a continuously variable parameter.
discrete part See DISCRETE COMPONENT.
discrete resistor A resistive component that is entirely self-contained, rather than being electrically spread out. Also called lumped resistor.
discrete sampling Sampling of individual bits or
characters, one or more at a time.
discrete thin-film component A discrete component produced by the thin-film process (e.g., thinfilm capacitor, thin-film potentiometer, etc.).
discretionary wiring A method of interconnecting
the components and circuits on a semiconductor
wafer for optimum performance. This requires a
separate analysis and wiring pattern for every
discrimination 1. Sharp distinction between electrical quantities of different value. 2. The detection
of a frequency-modulated (FM) signal (i.e., the delivery of an audio signal corresponding to the frequency or phase variations in the FM carrier).
discriminator A second detector for frequencymodulated (FM) signals, in which two diodes are
operated from the center-tapped secondary of a
special intermediate-frequency (IF) transformer.
The circuit is balanced for zero output when the
instantaneous received signal frequency is at the
unmodulated carrier frequency; the circuit delivers output when the instantaneous received
signal frequency swings above or below the
unmodulated carrier frequency. Also see FOSTER-SEELEY DISCRIMINATOR and TRAVIS DISCRIMINATOR.
discriminator transformer The special input
transformer in a DISCRIMINATOR.
discriminator tuner A device that tunes a discriminator to a selected subcarrier.
discriminator tuning device See DISCRIMINATOR TUNER.
dish antenna A transmitting and/or receiving antenna consisting of a driven element and a large
reflector. The reflector has the shape of a shallow,
circular section of a paraboloid or sphere. The
feed point is at the focus of the reflector. This antenna, noted for its high directivity and gain, is
used mainly at ultra-high and microwave frequencies for communications and satellite television. Large antennas of this type are used in
some radio telescopes.
dish-type construction A type of panel-and-chassis construction in which the chassis is fastened
vertically to the back of the panel.
disintegration 1. The destructive breakdown of a
material. 2. The stripping of a vacuum-tube cathode of its emissive coating (see DISINTEGRATION
VOLTAGE). 3. The decay of a radioactive material.
disintegration voltage The anode voltage at which
the cathode of a gas tube begins to be stripped of
its electron-emitting material. For safety and reasonable tube life, the anode working voltage must
be between the ionization and disintegration values.
disintegrator An ultrasonic device for reducing
crystals or particles to fine suspensions.
disjunction The logical inclusive-OR operation.
disk 1. A flat, circular plate (e.g., rectifier disk). 2.
See DISKETTE. 3. See HARD DISK. 4. See COMPACT DISC. 5. See CD-ROM. 6. A phonograph
record or the equivalent unrecorded blank.
disk capacitor A fixed (usually two-plate) capacitor consisting of a disk of dielectric material on
whose faces are deposited metal-film plates.
disk capacitor
disk coil • display loss
disk coil See DISK WINDING.
disk dynamo A rudimentary direct-current (dc)
generator, in which a copper disk rotates between
the poles of a permanent magnet. The outer edge
of the disk becomes positively charged; the center
of the disk becomes negatively charged.
diskette A magnetic recording disk used for microcomputer data storage. Housed in a square, flat
case. In personal computing, there are two sizes:
5.25 inches square and 3.5 inches square. The
5.25-inch version is flexible and is sometimes
called a floppy disk.
disk files An information-storage system in which
data are recorded on rotating magnetic disks.
disk generator 1. See DISK DYNAMO. 2. A disktype electrostatic generator.
disk memory A common misnomer for DISK
Disk Operating System Abbreviation, DOS. Any of
several command-driven operating systems commonly used in IBM-compatible personal computers.
disk pack In disk files, a set of disks that can be
handled as a single unit.
disk recorder A device for recording (and usually
also playing back) sound or other signals on
record disks.
disk recording 1. Recording sound or other signals on disks. 2. A disk resulting from such a
recording. See DISK.
disk rectifier A semiconductor rectifier (such as
copper-oxide, selenium, magnesium-coppersulfide, or germanium type) in which the active
material is deposited on a metal disk.
disk resistor A resistor consisting of a resistive
material deposited on a metal disk; or a disk of
resistive material. In the latter, electrodes are
plated on the faces of the disk, one or more of
which are held between clips or screws for connections.
disk storage In digital computer systems, an online or offline data storage scheme, in which information is recorded on the magnetic coating of
a rotating disk or set of disks. See DISKETTE,
disk system A sound-motion-picture system using
audio disks synchronized with the film.
disk thermistor A thermistor having the general
shape of a disk.
disk-type storage See DISK STORAGE.
disk varistor A varistor having the general shape
of a disk.
disk winding An armature or coil winding that is
flat, rather than cylindrical. Also called disk coil,
pancake coil, and spiral coil.
dislocation A crystal region in which the arrangement of atoms does not have the perfect lattice
structure of the crystal.
dispersion 1. The property of a material that
causes energy at different wavelengths to pass
through it at different speeds. 2. The separation
of a wave into its various component frequencies
(as when white light is broken up into the color
spectrum by a prism). 3. The scattering of a microwave beam when it strikes an obstruction. 4.
The scattering of sound or ultrasound as it emanates from an acoustic transducer. 5. A suspension of finely divided particles within another
dispersive medium A medium that disperses a
wave passing through it.
displacement 1. A change in the position of a
point, particle, figure, or body. 2. The vector representing a change in the position of a point, particle, figure, or body. 3. Movement of a member
through a specified distance.
displacement current 1. An alternating current
proportional to the rate of change of an electric
field, and existing in addition to usual conduction
current. 2. The current flowing into a capacitor
immediately after application of a voltage. This
current continues to flow, although continually
diminishing in value, until the capacitor becomes
fully charged.
displacement of porches In a television signal,
the amplitude difference between the front porch
and back porch of a horizontal sync pulse.
displacement of vectors Vector rotation through
a specified number of angular degrees or radians.
displacement transducer A transducer in which
movement (displacement) of a rod, armature,
core, reed, or other object converts mechanical
energy into proportionate electrical energy.
display 1. Visually observable presentation of information, such as data entered into a computer,
an answer to a problem solved by a computer, the
value of a measured quantity, or a graph of a
function. 2. The screen in a computer system or
terminal that visually portrays text and graphical
data. In laptop, notebook, and portable computers, this is usually a liquid-crystal display (LCD);
in desktop computers and terminals, it is usually
a cathode-ray tube (CRT ). 3. To portray information in a visual manner (e.g., as text, numerals,
symbols, or graphic images).
display blanking See DISPLAY INHIBIT.
display console In a computer system, a peripheral that is used to access and display data being
processed or stored; often, it is a unit with a
cathode-ray tube (CRT), keyboard, and light pen.
display control An interface device between a central processor and several visual display units
display dimming See DISPLAY INHIBIT.
display inhibit In a digital meter, the blanking or
dimming of the display when the instrument is
not being used. It is used to conserve battery energy.
display loss The ratio P1/P2, where P1 is the minimum input-signal power that can be detected by
an ideal output device at the output of a receiver,
and P2 is the minimum input-signal power value
display loss • distance-double law
seen by an operator using an output device with
the same receiver. Also called visibility factor.
display mode 1. A particular method of presenting
a display. For example, a character display on a
video unit might consist of bright characters on a
dark background, or dark characters on a light
background. 2. An operating mode for a particular device, in which a display is used.
display module A self-contained unit with circuitry and readouts for indicating a numerical
display primaries Also called primary colors. In a
color television receiver, the colors red, green,
and blue. When mixed correctly, these three colors can produce any visible hue.
display-storage tube A special cathode-ray tube in
which patterns and other information can be
stored for later viewing. The tube has two electron
guns: a writing gun and a reading (viewing) gun.
display unit A device that presents information for
visual reading. Included are analog and digital
meters, cathode-ray tubes, data printers, graphic
recorders, etc. Also see DISPLAY CONSOLE.
display visibility The ease with which a display
can be read by an operator.
display window 1. In a panoramic display, the
width of the presented frequency band in hertz.
2. The panel opening through which the indication of a display unit appears.
displayed part That portion of a number displayed
in the readout of a calculator or computer. There
might be digits that are not displayed, but which
the machine might take into consideration
when making calculations. For example, in a
245.789378214895 would be displayed as
245.7893782. Depending on the calculator design, the machine might truncate (disregard) the
undisplayed digits (14895), or take the undisplayed digits into account when making calculations.
disposable component A circuit component or
machine part that is so inexpensive that it is
more cost-effective to discard it than to repair it
when it fails.
disruptive discharge Sudden, heavy current flow
through a dielectric material when it fails completely under electric stress.
dissector A transducer that samples an illuminated image point by point.
dissector tube A camera tube using a flat photocathode, upon which the image is focused by the
lens system. Electromagnetic deflection from
external coils provides scanning. Electrons pass
sequentially from the image cathode to a scanning tube at the opposite end of the camera tube.
Also called Farnsworth dissector tube and orthiconoscope.
dissipation 1. The consumption of power, often
without contributing to a useful end, and usually
accompanied by the generation of heat. 2. In an
dissector tube
amplifier, the difference between the collector,
drain, or plate input power and the usable output
dissipation constant For a thermistor, the ratio of
the change in power dissipation to a corresponding change in body temperature.
dissipation factor 1. For a dielectric material, the
tangent of the dielectric loss angle. Also called
loss tangent. 2. Symbol, D. For an impedance
(such as a capacitor), the ratio of resistance to reactance; D = R/X. It is the reciprocal of the figure
of merit (Q).
dissipation line A resistive section of transmission
line, used for dissipating power at a certain
impedance. Two parallel lengths of resistance
wire are terminated by a large, noninductive resistor that has a value equal to the characteristic
impedance of the line.
dissipator 1. A device used primarily to consume
power (i.e., a power sink). 2. A device for removing heat generated by a device’s operation (e.g., a
heatsink attached to a power transistor).
dissociation The condition that characterizes electrolytes (certain acids, bases, or salts in water solution) in which the molecules of the material
break up into positive and negative ions.
dissonance The unpleasant effect (especially in
music) produced by nonharmonious combinations of sounds.
dissymmetrical network A network having unequal input and output image impedances.
dissymmetrical transducer A transducer having
unequal input and output image impedances.
distance-double law A theoretical rule for determining the rate at which sound intensity decreases as distance increases. Under ideal
conditions, when the distance from a sound
source is doubled, the sound pressure is reduced to one-fourth of its original level, a reduction of 6 decibels. This is analogous to the
inverse-square law for visible light and other radiant energy.
distance mark • distributed component
distance mark On a radar screen, a mark indicating the distance from the radar set to the target.
distance measurement Also called ranging. A
method or system that allows a robot to navigate
in its environment. It also allows a central computer to track the locations of robots under its
control. Can use radar, sonar, visible light, or infrared.
distance-measuring equipment In radionavigation, a system that measures the distance of the
interrogator to a transponder beacon in terms of
the transmission time to and from the beacon.
distance protection The use of a protective device
within a specified electrical distance along a circuit.
distance relay In circuit protection, a relay that
operates to remove power when a fault occurs
within a predetermined distance along the circuit.
distance resolution 1. Qualitatively, the ability of
a ranging system to differentiate between two objects or beacons that are almost, but not quite,
the same distance away. See RANGING. 2.
Quantitatively, the minimum radial separation of
objects or beacons necessary for a ranging
system to tell them apart. 3. For two targets
having the same azimuth bearing, the minimum
difference in range for which a radar display
renders them as distinct blips.
distant control See REMOTE CONTROL.
distorted-drive multiplier A frequency multiplier
whose excitation signal is a peaked wave that has
been predistorted to decrease the angle of flow in
the device, thus increasing its efficiency.
distorted nonsinusoidal wave A nonsinusoidal
wave whose ideal shape (square, rectangular,
sawtooth, etc.) has been altered.
distorted sine wave A wave that is approximately
of sinusoidal shape (i.e., it is not an exact plot of a
sine wave because of the presence of harmonics).
distortion 1. Deformation of a signal waveform. 2.
The additional deformation of a signal exhibiting
a less-than-ideal waveshape when it passes
through a circuit. Some distortion originates
within the signal generator itself; other forms result from circuits and devices transmitting the
signal. 3. Any degradation in the quality of a
high-fidelity audio signal. 4. See TOTAL HARMONIC DISTORTION.
distortionless 1. Having no distortion. 2. Having a
propagation velocity that does not depend on frequency.
distortion meter An instrument for measuring
harmonic distortion. It consists of a highly selective band-rejection filter (notch filter) that removes the fundamental frequency of the signal
under test, and a sensitive voltmeter that can be
switched between the filter input and the filter
output. The distortion percentage is determined
from the ratio between filter-output and filterinput voltages.
distortion meter
distortion tolerance The maximum amount of
distortion that can be present in a signal without
making it useless. This varies over wide limits.
The maximum harmonic distortion that might be
acceptable in a high-fidelity sound system could
be less than 0.1% total, whereas in some applications of ac power, 10% would be acceptable.
distress frequency A radio frequency on which an
emergency signal is transmitted. Ships at sea and
aircraft over the sea use 500 kHz (by international agreement). In Citizen Band communications, channel 9 has been set aside for emergency
distress signal A signal indicating that trouble exists at the transmitting station and imploring aid
from the recipient. The international radiotelegraph distress signal is the three-letter combination SOS; the international radiotelephone
distress signal is the word mayday, the phonetic
equivalent of the French m’aidez (help me).
distributed Existing over a measurable interval,
area, or volume; not concentrated in a single
place or places.
distributed amplifier A wideband, untuned amplifier whose active devices are spaced (distributed) along parallel, artificial delay lines
consisting of coils that act in combination with
the input and output capacitances of the active
devices. Adding active devices to the lineup increases the gain. Commonly used as preamplifiers for television receivers.
distributed capacitance Symbol, Cd. Capacitance
that is dispersed throughout a component or system, rather than being lumped in one place. An
example is the distributed capacitance of a coil.
distributed component An electrical property that
is spread throughout a circuit or device, rather
than being concentrated at one point, as in a discrete component. For example, DISTRIBUTED
CAPACITANCE and DISTRUBUTED INDUCTANCE are spread along the length of a transmission line. Another example is the DISTRIBUTED
RESISTANCE of a wire coil. Distributed compo-
distributed component • diversity gain
nents are often unintended, but they can be useful. Compare DISCRETE COMPONENT and
distributed constant See DISTRIBUTED COMPONENT.
distributed-constant delay line A delay line
whose capacitance and inductance are distributed throughout the line. Compare LUMPEDCONSTANT DELAY LINE.
distributed inductance Symbol, L d. Inductance
that is dispersed throughout a system or component, rather than being lumped in one place,
such as in a coil (e.g., the inductance of an antenna or capacitor).
distributed network 1. A network in which electrical properties (such as resistance, inductance,
and capacitance) are distributed over a measurable interval, area, or volume. 2. A network
whose characteristics do not depend on frequency within a given range.
distributed-parameter network A network composed of distributed components, rather than
lumped components.
distributed pole In a motor or generator, a pole
distributed resistance Symbol, Rd. Resistance
that is dispersed throughout a component or circuit, rather than being lumped in one place, such
as in a resistor. An example is the high-frequency
resistance of an antenna system.
distributed-shell transformer A transformer having two complete closed cores that are perpendicular to each other.
distributed winding In a motor or generator, a
winding that is placed in several slots (rather
than in one slot) under a pole piece.
distributing amplifier An amplifier having a single
input and two or more outputs that are isolated
from each other; it distributes signals to various
distributing cable 1. In cable television, the cable
connecting the receiver to the transmission cable.
2. In power service, the cable running between a
feeder and a consumer’s house.
distribution 1. The selective delivery of a quantity
(e.g., power distribution). 2. In statistical analysis, the number of times particular values of a
variable appear. Also called frequency distribution.
distribution amplifier A low-output-impedance
power amplifier that distributes a radio, television, or audio signal to a number of receivers or
distribution cable See DISTRIBUTING CABLE.
distribution center 1. The central point from
which a signal is routed to various points of use.
2. In electric power operations, the point at which
generation, conversion, and control equipment is
operated to route power to points of use.
distribution factor For a polyphase alternator, the
factor by which the total voltage VT can be deter-
mined in terms of the coil voltage VC and the
number of coils n: VT = nVC. Distribution factor
kd = (sin(sd/2))/(s × sin(d/2)), where s is the
number of slots per phase per pole, and d is the
angle between adjacent slots.
distribution function In statistical analysis, the
function F(x) expressing the probability that F
takes on a value equal to or less than x.
switchboard 1. A switchboard
through which signals can be routed to or among
various points. 2. A switchboard for routing electric power to points of use.
distribution transformer A step-down transformer used to supply low-voltage alternatingcurrent (ac) utility power to one or more
consumers from a high-voltage line.
distributor 1. See COMMUTATOR. 2. A switching
device consisting of a rotating blade and a number of contacts arranged in a circle. Accomplishes
sequential switching of a voltage to a number of
points in a circuit. A common example is the distributor in the ignition system of an automotive
disturbance An undesired variation in, or interference with, an electrical or physical quantity.
disturbed-one output In digital computers, the
one output of a magnetic cell that has received
only a partial write pulse train because it was last
written into. Compare UNDISTURBED-ONE
disturbed-zero output In digital computers, the
zero output of a magnetic cell that has received
only a partial write pulse train since it was last
dither 1. Vibrate; quiver. 2. The condition of vibration or quivering (e.g., the dither of a meter
pointer). 3. To blend pixels in a digitized image to
obtain various shades and colors.
divergence 1. The tendency of a collimated beam
of energy to spread out. 2. The extent to which a
collimated beam of energy spreads out, generally
measured in seconds of arc, minutes of arc, angular degrees, or angular radians.
divergence loss Loss of transmitted sound energy,
resulting from spreading.
diverging lens A lens having a virtual focus for
parallel rays; generally a concave lens.
diversity 1. The property of consisting of two or
more independent components or media. 2. See
diversity factor 1. A measure of the degree to
which a system exhibits unity among its constituents. 2. The sum of the requirements of each
constituent of a system, divided by the total requirement of the system.
diversity gain 1. Signal gain achieved by using
two or more receiving antennas. 2. Signal gain
achieved by using two or more transmitting antennas.
diversity reception • DNL
diversity reception Also called dual-diversity reception. A method of minimizing the effects of fading in ionospheric communication at high
frequencies (HF). Accomplished using two receivers whose antennas are 5 to 10 wavelengths
apart. Each receiver, tuned to the same signal,
feeds a common audio amplifier. The timing of
the fading is different at the two antennas because of phasing effects. The composite signal,
therefore, fades less than either of the component
signals. Some diversity systems use three or more
antennas and receivers to reduce the effects of
fading even further; this is sometimes called
multiple-diversity reception.
5 to 10
Mixer and
Mixer and
diversity reception
diversity transmission Also called dual-diversity
transmission or multiple-diversity transmission. A
scheme similar to DIVERSITY RECEPTION, except applied at the transmitting end of a communication circuit. The signals from two or more
transmitters, at identical frequencies, are fed to
antennas spaced several wavelengths apart.
diverter-pole generator A well-regulated directcurrent (dc) generator, whose shunt winding is on
the main field pole, the series winding being on a
diverter pole whose flux opposes that of the main
divide-by-seven circuit A three-stage binary circuit having feedback from stage three to stage
one. Stage three is switched on by the fourth input pulse; at that time, the feedback pulse
switches on stage one, simulating one input
pulse and reducing the usual counting capacity
from eight to seven.
divide-by-two circuit A circuit that delivers one
output pulse for each two successive input pulses
(i.e., a flip-flop).
divide-by-seven circuit
divided-carrier modulation Modulation obtained
by adding two identical frequency carriers that
are 90 degrees out of phase.
divided circuit A parallel circuit.
divided equipment A system of modular electronic components interconnected with cables. A
simple example is a radio receiver having an external power supply and external loudspeaker.
divider 1. See VOLTAGE DIVIDER. 2. See FREQUENCY DIVIDER. 3. See PULSE-COUNT DIVIDER. 4. A computing circuit or device for
performing mathematical division.
divider probe A test probe that divides an applied
signal voltage by some factor (such as 2, 5, or 10)
to place it within the range of the instrument with
which the probe is used.
dividing network See CROSSOVER NETWORK.
division 1. Separating a quantity into a number of
equal parts, as indicated by the divisor. 2. Voltage division (see VOLTAGE DIVIDER). 3. Frequency division (see FREQUENCY DIVIDER). 4.
Pulse-count division (see PULSE-COUNT DIVIDER).
division of vectors 1. The quotient of two rectangular vectors determined by the principle of rationalization in algebra (i.e., by multiplying the
numerator and denominator of the indicated division by the conjugate of the denominator, simplifying, and performing the division). 2. To find the
quotient of two polar vectors: the quotient of their
moduli and the difference of their arguments.
dj Abbreviation of diffused junction.
DKT Abbreviation of dipotassium tartrate.
D layer A layer of the ionosphere that is below the
E layer; its altitude is approximately 60 kilometers.
dm Abbreviation of decimeter.
and direct memory addressing.
DMOS Abbreviation for double-diffused metal-oxide
semiconductor, a type of field-effect transistor
that exhibits extremely low capacitance and low
source-drain resistance when conducting.
DNS • donut pattern
domestic electronics Also called consumer electronics. The branch of electronics concerned with
appliances, automatic controls, protective devices, entertainment systems, communications
devices, and other equipment for the home.
domestic induction heater A household cooking
utensil heated by currents induced in it. A primary coil (connected to the power line) is imbedded in the utensil, which acts as a short-circuited
secondary coil.
dome tweeter A speaker designed for highfrequency (treble), high-fidelity audio, and often
functional at frequencies considerably above the
limit of the human hearing. Characterized by a
convex diaphragm. Usually part of an assembly
including a woofer and midrange speaker.
dominant In statistical analysis, the nature of any
quantity that imposes its effects even in the presence of other quantities.
dominant mode In a waveguide, the propagation
mode exhibiting the lowest cutoff frequency.
dominant wave In a waveguide, the wave having
the lowest cutoff frequency.
dominant wavelength For visible light of a given
hue, the wavelength at which the emitted energy
is the greatest.
donor An electron-rich impurity added to a semiconductor to make it into an n-type material. So
called because it donates its excess electrons.
donor atom An atom having an excess electron.
When a substance having such atoms is added to
an intrinsic semiconductor, the extra electron is
donated, making the semiconductor into an ntype material.
donor impurity A substance whose atoms have
excess electrons, and that donates electrons to
the atomic structure of the semiconductor crystal
to which it is added. Donor elements make semiconductors into n-type materials. Also see
do-nothing instruction A computer program instruction that causes no action to be taken. Can be
used to provide space for future program updating,
or to fill out a block of instructions, as needed by a
compiler. Also called dummy instruction.
don’t-care state In a logic function or gate, an input digit whose state (high or low) does not affect
the output.
donut capacitor A flat, ring-shaped capacitor.
donut coil See TOROIDAL COIL.
donut crystal A relatively large, zero-temperaturecoefficient piezoelectric quartz crystal cut in the
form of a torus with the y-axis passing through
the center of rotation.
donut magnet See RING MAGNET.
donut pattern The three-dimensional radiofrequency (RF) radiation/response pattern of a
free-space straight antenna element measuring
⁄2 wavelength, neglecting the effects of ground
and nearby objects.
DNS Abbreviation of Doppler navigation system.
doctor To use unconventional (sometimes substandard) methods in fixing a circuit or device or
in correcting a bad design.
document 1. In digital computer operations, especially in file maintenance, a form that provides information pertinent to a transaction. Also see
TRANSACTION. 2. To perform documentation (see
DOCUMENTATION, 2). 3. A computer text file.
documentation 1. Paperwork explaining the scope
of programs and how they can be optimized. 2. Annotating a computer program at critical points during its writing (e.g., so that the purpose of various
segments are understood). A measure of good programming, documentation becomes especially
valuable for program modification or debugging.
document reader An electronic device that reads
printed cards, usually for data entry into a computer.
dog 1. A malfunctioning circuit or device. 2. The
cause of a circuit or device malfunction.
doghouse An enclosure for antenna loading inductors and other resonating components, placed at
the base of a vertical broadcasting tower.
Doherty amplifier A highly efficient linear radiofrequency (RF) amplifier in which a carrier tube and
a peak tube operate jointly, both receiving amplitude-modulated RF excitation. During unmodulated intervals, the carrier tube supplies carrier
power to the load, while the peak tube, biased to
cutoff, idles. On positive modulation peaks, the
peak tube supplies output power that combines
with that of the carrier tube, the increase in power
corresponding to the condition of full modulation of
the carrier. On negative modulation peaks, the
peak tube does not supply power, and the output
of the carrier tube is reduced to zero.
Dolby An electronic method of improving the audio
reproduction quality of magnetic-tape systems.
The gain is increased for low-level sounds during
the recording process. During playback, the gain
of the low-level sounds is reduced back to its original level.
Dolby A A Dolby system with four frequency
ranges, operated independently. It is used mostly
by recording professionals.
Dolby B A modified form of Dolby A, with only one
band of noise-reducing circuitry. It is used primarily by hobbyists.
Dolezalek electrometer See QUADRANT ELECTROMETER.
dolly 1. A low, wheeled frame or platform for transporting electronic equipment. 2. A tool with
which one end of a rivet is held while the head is
hammered out of the other end.
domain 1. A region of unidirectional magnetization
in a magnetic material. 2. A region of unidirectional polarization in a ferroelectric material. 3. A
region in which a variable is confined.
doohickey • dot
doohickey A usually unnamed device—especially
one used to achieve some significant modification
of circuit performance.
doorknob capacitor A high-voltage fixed capacitor, so called from its round package, which
somewhat resembles a doorknob.
doorknob tube A special UHF vacuum tube, so
called from its characteristic shape. The unique
design provides short electron-transit time and
low interelectrode capacitance. Largely replaced
in recent years by semiconductor devices.
dopant An impurity added in controlled amounts
to a semiconductor to make it an n-type or p-type
material. Also see ACCEPTOR and DONOR.
dope To add impurities to a semiconductor material. Doping allows the manufacture of n-type or
p-type semiconductors with varying degrees of
conductivity. In general, the greater the extent of
doping, the higher the conductivity.
doped junction In a semiconductor device, a junction produced by adding a dopant to the semiconductor melt.
doping Adding a dopant to a semiconductor to alter the way it conducts current.
doping agent See DOPANT.
doping compensation Opposite doping (i.e., adding a donor impurity to p-type semiconductor
material or adding an acceptor impurity to n-type
semiconductor material).
doping gas A gas diffused into a semiconductor
material to dope it. For example, phosphorus
pentoxide gas can be used to create an n-type region in a p-type silicon chip.
doping level The relative concentration of impurity
added to a semiconductor material to obtain a
certain resistivity and polarity. The greater the
doping level, the lower the resistivity.
Doppler broadening In a spectrum, the spreading
out or blurring of a spectral line caused by
DOPPLER EFFECT, in turn resulting from motion
of molecules, atoms, or other particles in the
Doppler cabinet A loudspeaker enclosure with
which a vibrato effect is achieved by rotating or
reciprocating either the loudspeaker or a baffle
board; the length of the sound path is altered
Doppler effect A change in the frequency of a wave
that occurs when the source and observer are in
relative motion. The frequency of the wave increases (the wavelength shortens) as the source
and observer approach each other; the frequency
decreases (the wavelength becomes greater) as
the source and observer recede from each other.
This effect is often observed with sound waves, as
when the pitch of an automobile horn seems to
rise as the car approaches and to fall as the car
passes. The effect is also observable in electromagnetic radiation at all wavelengths. It affects
satellite communication and space communication.
Doppler enclosure See DOPPLER CABINET.
Doppler radar A radar that uses the change in carrier frequency of the signal returned by a moving
target (approaching or receding) to measure its
velocity. Used by law enforcement officers to determine the speed of moving vehicles. Also used
by meteorologists to evaluate air circulation patterns in thunderstorms, and to determine wind
speeds in hurricanes and tornadoes.
Doppler ranging See DORAN.
Doppler shift The extent to which the frequency or
wavelength of a signal changes because of
DOPPLER EFFECT. Can be measured in Hertz
(for frequency) or in meters (for wavelength). In
astronomy, the shift is also measured as displacement of absorption or emission lines in an
infrared, visible, or ultraviolet spectrum.
Doppler’s principle See DOPPLER EFFECT.
doran A continuous-wave trajectory-measuring
system utilizing Doppler shift (see DOPPLER EFFECT). The name is a contraction of doppler ranging.
dorsal column stimulator Abbreviation, DCS. A
machine that generates radio-frequency energy
that is applied to human tissues for the temporary relief of pain.
dosage meter See DOSIMETER.
dose The total quantity of radiation received upon
exposure to nuclear radiation or X-rays.
dosimeter An instrument for measuring the
amount of exposure to nuclear radiation or
dot 1. The shorter of the two characters (dot and
dash) of the telegraph code. The dot, a short
sound, mark, or perforation, is one-third the
dot • double buffering
length (duration) of a dash. Compare DASH. 2.
One of the small spots of red, green, or blue phosphor on the screen of a color-television picture
tube or cathode-ray-tube (CRT) computer display. 3. A small spot of material alloyed with a
semiconductor to form an alloy junction. 4. The
junction of two lines on a schematic diagram,
representing a wired connection; also called
solder dot.
dot AND Externally connected circuits or functions
whose combined outputs result in an AND function. Compare DOT OR.
dot-and-dash telegraphy Telegraphy (wire or radio) by means of dot and dash characters.
dot cycle One period of an alternation between two
signaling conditions, each of which is of unit duration (e.g., a unit mark followed by a unit space).
dot encapsulation A method of packaging cylindrical components by pressing them into the
holes of perforated disks; interconnections are
made, to complete a circuit, on each face of the
dot generator A special radio-frequency (RF) signal generator used to produce a pattern of red,
green, and blue dots on the screen of a color television receiver.
dot matrix A rectangular array of spaces, some of
which are filled in to form alphanumeric and
punctuation characters.
dot matrix
dot-matrix display A display that shows characters in dot-matrix form.
dot-matrix printer A computer output peripheral
that prints characters and images on paper as a
fine grid of dots. A print head, containing several
pins, presses the ribbon against the paper as it
moves laterally across each line. Can be used to
print text and/or graphics.
dot movement pattern The movement of the red,
green, and blue dots on the screen of a color television picture tube as the red, green, and blue
magnets and the lateral magnet are adjusted for
convergence of the dots at the center. The blue
dots move horizontally or vertically; the red and
green dots, diagonally.
dot OR Externally connected circuits or functions
whose combined outputs result in an OR function. Compare DOT AND.
dot pattern In color television testing with a dot
generator, dots of color (a red group, green group,
and blue group) produced on the screen. With
overall beam convergence, the three groups blend
to produce white.
dot-sequential system The color television system
in which the image is reproduced by means of primary-color dots (red, green, blue) sequentially activated on the screen of the picture tube.
double-amplitude-modulation multiplier A modulating system in which a carrier is amplitudemodulated first by one signal and then by a second signal. The resulting signal is fed to a
detector, the output of which contains the product of the two modulating signals.
double-anode diode A semiconductor diode having two anodes and a common cathode.
double armature An armature (such as that of a
dynamotor or a two-voltage generator) that has
two separate windings on a single core, and has
two separate commutators.
double-balanced mixer See BALANCED MIXER.
modulator See
double-base diode See UNIJUNCTION TRANSISTOR.
double-base junction transistor A junction transistor having the usual emitter, base, and collector electrodes, plus two base connections, one on
either side of the base region. The additional base
connection acts as a fourth electrode to which a
control voltage is applied. Also called tetrode transistor.
double-beam oscilloscope See DUAL-BEAM OSCILLOSCOPE.
double-bounce calibration In radar operations, a
calibration technique for determining zero-beat
error. Round-trip echoes are observed, the correct range being the difference between the two
double-bounce signal A signal that is received after having been reflected twice.
double-break contacts The member of a set of
contacts that is normally closed on two others.
double-break switch A switch that opens a previously closed circuit at two points simultaneously
on closing. Compare DOUBLE-MAKE SWITCH.
double bridge See KELVIN DOUBLE BRIDGE.
double buffering In the input/output operation of
a computer peripheral, the use of two memory areas for temporary storage.
double-button microphone • double-extended Zepp antenna
double-button microphone A carbon microphone
having two buttons mounted on each side of the
center of a stretched diaphragm, and connected
in push-pull. Also see BUTTON MICROPHONE.
double-channel duplex Two-way communication
over two independent channels. One station
transmits on one channel, and the other station
transmits on the other channel. The result is conversation-mode communications, in which one
operator can interrupt the other at any time; both
receivers are always operational.
double-channel simplex A system of communication in which two channels are used. One station
transmits on one channel, and the other station
transmits on the other channel. Interruption is
not possible because whenever either operator
transmits, the station receiver is muted.
double-checkerboard pattern In a magnetic core
memory, the maximum noise that appears when
half of the half-selected cores are in the one state
and the others are in the zero state. Also called
worst-case noise pattern.
double circuit tuning A circuit whose output and
input are tuned separately. Such tuning provides
increased selectivity when the input and output
are resonant at the same frequency, and decreased
selectivity when they are tuned to different frequencies. Also see DOUBLE-TUNED AMPLIFIER.
double clocking A phenomenon that occurs in
some digital circuits when the input pulse is
nonuniform, and appears as two pulses to the device. The device is thus actuated at twice the desired frequency.
double-coil direction finder A radio direction
finder (RDF) using an antenna that consists of
two identical, perpendicular coils. The directivity
of the antenna is the resultant of the directivity of
the individual coils.
double conversion 1. Two complete frequency
conversions in a superheterodyne system. For example, the incoming signal might be converted to
a 9-MHz first intermediate frequency (first IF); at
a later stage, this signal might be converted to a
455-kHz second IF. The high first IF widely sepa1st
rates the signal from the image; the low second IF
allows superior selectivity to be achieved at a reasonable cost. Also called dual conversion. 2. Pertaining to a superheterodyne receiver with two
intermediate frequencies.
double-conversion receiver Also called doubleconversion superheterodyne. A superheterodyne
receiver using DOUBLE CONVERSION to achieve
optimum selectivity and image rejection.
double-current generator 1. A dynamo-type generator supplying both alternating current (ac) and direct current (dc) from one armature winding. 2. A
rotary converter operating on dc and delivering ac.
double-diamond antenna A broadband antenna
consisting of two rhomboid plates, one attached
to each side of the feeder.
double-diffused epitaxial mesa transistor A transistor in which a thin mesa crystal is overlaid on
another mesa crystal. Also called epitaxial-growth
mesa transistor.
transistor See
double diode See DUODIODE.
double-diode limiter A limiter in which two diodes
are connected back to back in parallel, to limit
both peaks of an alternating-current (ac) signal.
double-doped transistor See GROWN-JUNCTION
double edit In audio tape recording, to make two
changes in a given span of the tape. For example,
a producer might dislike the wording of a certain
sentence, and re-record the sentence. Then,
changing his or her mind, the producer might
record the original sentence back over the rerecorded sentence. These changes increase the
risk of audible irregularities appearing in the final
double emitter follower See COMPOUND CONNECTION.
double-ended amplifier See PUSH-PULL AMPLIFIER and DOUBLE-ENDED CIRCUIT.
double-ended circuit A symmetrical circuit (i.e.,
one having identical halves, each operating on a
half-cycle of the input signal). Example: a pushpull amplifier.
double-extended Zepp antenna A horizontal,
collinear, center-fed antenna, in which each section measures 0.65 wavelength. This antenna
gives increased gain over that of the Zepp and
double Zepp (see DOUBLE ZEPP ANTENNA).
double conversion
double-extended Zepp antenna
double-hump resonance curve • double-sideband system
double-hump resonance curve A resonant response that is flattened by double tuning; it
exhibits two resonance peaks. Also see DOUBLETUNED AMPLIFIER.
double-hump wave See DOUBLE-PULSE WAVE.
double image Two overlapping television pictures,
one usually fainter than the other. Caused by the
signal arriving over two different paths (one possibly attributable to reflection of the wave) and,
hence, at different instants in time. The fainter
image is called a GHOST.
double insulation The use of two layers of insulation on a conductor, made of different materials.
double ionization Ionization resulting from an
electron colliding with an ion. In a gas, for example, a neutral atom might collide with an electron,
which can knock an electron out of the atom. The
atom then becomes a positive ion; it might in turn
be bombarded by an electron, releasing still another electron.
double-junction photosensitive semiconductor
double local oscillator A mixer system in which a
local oscillator generates two accurate radiofrequency (RF) signals separated by a few hundred hertz. The difference frequency is used as a
reference in some applications.
double-make contacts A set of normally open contacts of which one closes against two others
double-make switch A switch that closes a previously open circuit at two points simultaneously.
double moding In microwave operations, the
abrupt changing of frequency at irregular intervals.
double modulation Using a modulated carrier to
modulate another carrier of a different frequency.
double-play tape A thin magnetic recording tape
that has approximately twice the playing time of
the usual tape. Although the playing time is
longer, double-play tape is more subject to jamming and stretching than standard-thickness
recording tape.
double-pole Having two poles or switchable circuits (e.g., a double-pole switch).
double-pole, double-throw switch or relay Abbreviation, DPDT. A switch or relay having two
contacts that can be closed simultaneously in
one of two directions, to close or open two circuits.
double precision The use of two computer words
to represent a single number to gain precision.
double-pole, single-throw switch or relay Abbreviation, DPST. A switch or relay having two contacts that can be closed in only one direction, to
simultaneously close or open two circuits.
double precision hardware Within a computer,
arithmetic units permitting the use of double-
precision operands, sometimes also accommodating floating-point arithmetic.
double-precision number In digital computer operations, a number represented by two words for
greater precision.
double pulse reading Pertaining to a magnetic
core in a computer memory, recording bits as two
states held simultaneously by one core having
two areas that can be magnetized with alternate
polarities. For example, positive-negative could
represent zero, and negative-positive could represent one.
double-pulse wave An alternating-current (ac)
wave having two successive positive peaks followed by two successive negative peaks within
each cycle. The output voltage of a varistor bridge
has such a waveshape for an ac input.
double-pulsing station A loran station that transmits at two pulse rates upon receiving two pairs
of pulses.
double pumping A method of obtaining increased
peak output power from a laser by pumping it for
a comparatively long interval and then immediately pumping it for a short interval.
doubler 1. A circuit or device for multiplying a frequency by two (see FREQUENCY DOUBLER). 2.
A circuit or device for multiplying a voltage by two
double probe A test probe that multiplies an applied signal voltage by two, so it can be handled
more effectively by the instrument with which the
probe is used.
double punching In perforating a punched card,
putting two holes in one column; it is an error if it
occurs in a field of a card that is part of a record.
double rail A form of logic system in which two
lines are used, with three possible states. The
output can be high, low, or undecided.
double response 1. Two-point response, as that
associated with tuning a receiver to a signal and
then to its image. 2. See DOUBLE-HUMP RESONANCE CURVE.
double screen A cathode-ray tube having a twolayer screen on which there is an additional,
long-persistence coating of a different color.
double shield Two independent electromagnetic
shields for a circuit enclosure or cable. The
shielding structures are concentric, and can be
connected together at a single point (the common
double sideband Abbreviation, DSB. In a modulated signal, the presence of both sidebands.
double-sideband suppressed carrier Abbreviation,
DSSC. A transmission technique in which both
sideband products of modulation are transmitted
and the carrier is suppressed. Compare LOWER
double-sideband system A modulation or demodulation system utilizing both sidebands, with or
without the carrier.
double-sideband transmitter • double Zepp antenna
Outer shield
Inner shield
double shield
double-sideband transmitter A modulated transmitter using a double-sideband system.
double signal In reception, the property of having
a signal on either side of the carrier frequency, as
in a direct-conversion receiver. The two signals
represent the sum and difference of the local oscillator signal and the actual received signal.
Because the two signals convey identical
information, the phenomenon is wasteful of received spectrum, and degrading to receiver selectivity and sensitivity.
double-signal receiver A receiver, such as a direct-conversion type, in which the signals occur
in replicated form on either side of the local oscillator signal. Compare SINGLE SIGNAL.
double-spot tuning In a superheterodyne receiver,
tuning in the same signal at two different places
on the dial, a condition caused by image response.
double squirrel-cage induction motor A polyphase induction motor having a double squirrelcage rotor. The rotor slots contain two bars, an
upper bar having low reactance (being near the
air gap) and high resistance, and a lower bar having high reactance and low resistance. This motor
has low starting current, high starting torque,
and a full-load slip of less than 5%.
double-stream amplifier A traveling-wave tube in
which microwave amplification results from the
interaction of two electron beams of different average velocity.
double-stub tuner Two stubs (see STUB) connected in parallel with a transmission line and
usually spaced 0.375 wavelength (135 electrical
degrees) apart; it is used as an impedance
double superheterodyne reception See DOUBLECONVERSION SUPERHETERODYNE.
double-surface transistor See COAXIAL TRANSISTOR.
double-throw Operating in opposite directions as
selected (e.g., a double-throw relay or switch).
double-throw circuit breaker A circuit breaker that
closes in both its pull-in and dropout positions.
double-throw switch or relay A switch or relay
having two ganged poles.
double-trace recorder See DOUBLE-TRACK RECORDER, 2.
double tracing Displaying two signals simultaneously on the screen of an oscilloscope through
the use of an electronic switch.
double-track recorder 1. A tape recorder whose
head is positioned so that separate recordings
can be made as two tracks on the tape. 2. A
graphic recorder that produces two separate parallel tracings.
doublet trigger A two-pulse, constant-spaced trigger signal used for coding.
double-tuned amplifier An amplifier whose input
and output circuits are both tuned.
double-tuned circuit A circuit, such as an amplifier or filter, using separate input and output tuning. Also see DOUBLE CIRCUIT TUNING and
Input L1
Input tuning: L2 and C1
L4 Output
Output tuning: L3 and C2
double-tuned circuit
double-tuned detector A form of frequencymodulation (FM) discriminator with two resonant
circuits. One is tuned slightly higher than the
channel center frequency, and the other is tuned
an equal amount below the center.
double-vee antenna A broadband, modified dipole
antenna resembling two vees in line. Also see
double-winding generator A dynamo-type generator having separate armature windings for supplying two voltages, either of which can be direct
(dc voltage) or alternating (ac voltage).
double-wye rectifier A heavy-load circuit using six
rectifier diodes, each conducting for 120 degrees
of the cycle. An interphase winding is used. The
circuit is equivalent to two three-phase, half-wave
rectifiers connected in parallel.
double-Y rectifier See DOUBLE-WYE RECTIFIER.
double Zepp antenna A usually horizontal,
straight, center-fed, full-wavelength antenna.
double Zepp antenna • dress
Also called two half waves in phase. Its name was
derived because it is, in fact, two Zepp antennas
forming a collinear array.
doubling 1. Producing the second harmonic of a
signal. 2. In communication, unintentional simultaneous transmission by both operators, resulting in missed information. 3. In a speaker,
distortion resulting in large amounts of secondharmonic output.
doubly balanced modulator See BALANCED
doughnut capacitor See DONUT CAPACITOR.
doughnut coil See TOROIDAL COIL.
doughnut crystal See DONUT CRYSTAL.
doughnut magnet See RING MAGNET.
down convert In superheterodyne conversion, to
heterodyne a signal to an intermediate frequency
lower than the signal frequency. Compare UP
down lead See LEAD-IN.
downlink The signal sent down from an active
communications satellite to the earth, usually on
a different frequency than the signal sent up. See
downlink beamwidth The angle subtended between the half-power points of the downlink signal from an active communications satellite.
downlink frequency The frequency of the downlink signal from an active communications satellite. Usually, the downlink signals occupy a
certain band of frequencies, anywhere from several kilohertz to several megahertz wide.
downlink power 1. The output power of the downlink transmitter in an active communications
satellite. 2. The effective radiated power (ERP) of
the downlink signal from an active communications satellite.
down time A period of time during which electronic equipment is completely inoperative (for
any reason).
downturn A usually sudden dip in a performance
curve. Compare UPTURN.
downward modulation Modulation in which the
average carrier component decreases during
modulation. Example: amplitude modulation of a
transmitter in which the antenna current decreases during modulation. Compare UPWARD
DP Abbreviation of DATA PROCESSING.
DPDT Abbreviation of double-pole, double-throw
(switch or relay).
DPM 1. Abbreviation of digital power meter. 2. Abbreviation of DIGITAL PANEL METER. 3. Abbreviation of disintegrations per minute.
DPS Abbreviaton of disintegrations per second.
DPST Abbreviation of double-pole, single-throw
(switch or relay).
dr Abbreviation of dram.
drag 1. A retarding force, caused by friction, acting
on a moving body in contact with another moving
or stationary body or medium. 2. A retarding
force introduced by an applied magnetic or electric field.
drag angle In disk recording, an angle of less than
90° between the stylus and the disk. The acute
angle causes the stylus to drag instead of digging
drag cup A cup of nonmagnetic metal (usually copper or aluminum) that, when rotated in a magnetic field, acquires a voltage proportional to the
speed of rotation. The device is often used as a
drag-cup motor A servomotor whose shaft has a
copper or aluminum drag cup that rotates in the
field of a two-phase stator. Eddy currents set up
in the cup by the field winding produce torque;
braking action, direction control, and speed control are obtainable by means of associated electronics.
drag magnet In a motor-type meter, a braking
magnet (i.e., one used to reduce speed through
eddy-current effects). Also called retarding magnet.
drain 1. The current or power drawn from a signal
or power source. 2. A load that absorbs current
or power. 3. The electrode in a field-effect transistor (FET) from which the output is usually taken;
equivalent to the collector of a bipolar transistor.
drainage equipment Devices and systems for protecting circuits against transients generated by
circuit breakers and similar safety devices.
drain-coupled multivibrator An oscillator that
uses two field-effect transistors (FETs) in the circuit equivalent of a collector-coupled bipolartransistor multivibrator. The drain of one stage is
capacitance-coupled to the gate of the other
+ dc
drain-coupled multivibrator
D-region A low region of the ionosphere beneath
the E-region, whose ionization varies with the inclination of the sun. The greatest ionization is at
midday; the layer disappears at night.
dress The (usually experimental) arrangement of
leads for optimum circuit operation (minimum
dress • driver element
capacitance, best suppression of oscillation, minimum pickup, etc.).
dressed contact A contact having a permanently
attached locking spring member.
drift 1. Within a conductor or semiconductor, the
controlled, directed movement of charge carriers
resulting from an applied electric field. 2. A usually gradual and undesirable change in a quantity, such as current, as a result of a disturbing
factor, such as temperature or age.
drift current In a semiconductor, the current resulting from a flow of charge carriers in the presence of an electric field. The charge carriers are
electrons in n-type material and holes in p-type
drift field The inherent internal electric field of a
drift-field transistor An alloy-junction, bipolar,
radio-frequency (RF) transistor for which the impurity concentration is graded from high on the
emitter side of the base wafer to low on the collector side. This creates an internal drift field that
accelerates current carriers and raises the upper
frequency limit of the transistor.
drift-matched components Active or passive
components that have been closely matched in
terms of the drift of one or more parameters, with
respect to time, temperature, etc.
drift mobility For current carriers in a semiconductor, the average drift velocity per unit electric
drift space 1. In a vacuum tube, a space that is
nearly free of alternating-current (ac) fields from
the outside, and in which the repositioning of
electrons is governed by the space-charge forces
and the velocity distribution of the electrons. 2.
In a Klystron, the space between buncher and
catcher cavities in which there is no field.
drift speed The average velocity of charge carriers
moving through a medium.
drift transistor See DRIFT-FIELD TRANSISTOR.
drift velocity The net velocity of a charged particle
(electron, hole, or ion) in the direction of the field
applied to the conducting medium.
drift voltage The usually gradual change in voltage resulting from such causes as internal heating. Also called voltage drift.
drip loop In a transmission line for an antenna or
power service, a loop near the point of entry to the
building for the purpose of allowing condensation
or rain water to drip off.
drip-proof motor A motor with ventilating apertures arranged so that moisture and particles
cannot enter the machine.
drip-tight enclosure A housing designed to prevent entry of rain, snow, and dust; it also prevents accidental contact with the enclosed
apparatus or machinery.
drive 1. To excite (i.e., to supply with input-signal
current, power, or voltage) (see DRIVING CURRENT, DRIVING POWER, and DRIVING VOLT-
AGE). 2. Input-signal excitation (see DRIVING
VOLTAGE). 3. A device that moves a recording
medium (e.g., tape drive and diskette drive). 4.
The transmission of mechanical energy from one
place to another (e.g., motor drive).
drive array A set of two or more hard-disk drives in
a computer system. They function together to
minimize the possibility of data loss. Such a system can also increase the amount of fast-access
data storage.
drive belt A continuous belt used to transmit mechanical energy from a driving pulley to a driven
drive circuit 1. A circuit used to provide the excitation to a motor. 2. An amplifier that supplies
drive to a more powerful amplifier.
drive control In a television receiver, the potentiometer used to adjust the ratio of horizontal
pulse amplitude to the level of the linear portion
of the sawtooth scanning-current wave.
driven element In a multielement antenna, an element to which electromagnetic energy is fed directly, as opposed to a PARASITIC ELEMENT,
which is excited by a nearby radiator element.
driven-element directive antenna A multielement directional antenna whose elements are
driven from the feed line (i.e., no element is parasitic). Compare PARASITIC-ELEMENT DIRECTIVE ANTENNA.
driven multivibrator A multivibrator whose operation or frequency is controlled by an external
synchronizing or triggering voltage. Compare
driven single sweep A single oscilloscope sweep
that is initiated by the signal under observation.
drive pattern A pattern of interference in a facsimile system that is caused by improper synchronization of the recording spot.
driven sweep An oscilloscope sweep that is initiated by the signal under observation.
drive pin A pin used to prevent a record from slipping on the rotating turntable of a recorder or reproducer. It is similar to, and located near, the
center pin of the turntable.
drive pulse In digital computer operations, a pulse
that magnetizes a cell in a memory bank.
driver 1. A device that supplies a useful amount of
signal energy to another device to ensure its
proper operation (e.g., a current driver for a magnetic-core memory, an oscillator driving a loudspeaker). 2. A power amplifier stage that supplies
signal power to a higher-powered amplifier stage.
3. In a digital computer, a stage that increases
the output current or power of another stage
(e.g., a clock driver). 4. The cone and magnet of a
dynamic speaker.
driver element In a multielement directive antenna, the element excited directly by the feeder,
the other elements (directors and reflectors) being
driver impedance • dropsonde
driver impedance 1. The output impedance of a
driver stage. 2. The impedance “seen” from the
driven stage of an amplifier, through the driver
transformer, to the driver stage. It is the vector
sum of driver reactance and resistance.
driver inductance In an amplifier’s driver transformer, the inductance, as “seen” looking through
the transformer from the driven stage into the
driver stage.
driver resistance In an amplifier’s driver transformer, the resistance “seen” looking through the
transformer from the driven stage into the driver
driver stage An amplifier stage whose chief purpose is to supply excitation (input-signal current,
power, or voltage) to the next stage. Also see
driver transformer The transformer that couples a
driver stage to a driven stage. Example: the interstage transformer inserted between the collector
of a single-ended driver transistor and the two
bases of a push-pull power-output stage in an
audio amplifier.
driving current In a power amplifier, the input
signal current required to produce a given
amount of output power.
driving-point admittance The reciprocal of
driving-point impedance The input impedance of
a network.
driving power In a power amplifier, the input signal power required to produce a given amount of
output power.
drive wire The wire forming the coil around the
toroidal cell in a magnetic core memory; supplies
pulses that magnetize the cell.
driving-range potential In cathodic protection,
the difference of potential between the anode and
(protected) cathode.
driving signal 1. Drive (see DRIVE, 2). 2. In television, time-scanning signals (line-frequency pulses
and field-frequency pulses) at the pickup location.
driving spring In a stepping relay, the spring that
moves the wiper blades.
driving voltage In a power amplifier, the input signal voltage required to produce a given amount of
output power.
DRO Abbreviation of DIGITAL READOUT.
drone A pilotless radio-controlled aircraft without
a human pilot.
drone cone An undriven loudspeaker cone that is
mounted in a bass-reflex enclosure with other
speakers. Also called PASSIVE RADIATOR.
droop 1. A dip in the graph of a function. 2. In a
pulse train, the decrease in mean amplitude (in
percent of maximum amplitude) at a given instant after attainment of maximum amplitude.
drooping radials In a ground-plane antenna, radials that slope downward to provide a transmission-line impedance match. The slope angle
Approx. 135°
drooping radials
depends on the characteristic impedance of the
line; typically, the angle is between 45 degrees
and 70 degrees, relative to horizontal.
drop 1. In wire communications, the line connecting a telephone cable to a subscriber’s building.
drop bar A device that automatically grounds or
short-circuits a capacitor when the door of a protective enclosure is opened.
drop cable See DISTRIBUTING CABLE, 1.
drop channel In a communications system utilizing several channels, a channel that is not used.
drop-in The unintentional creation of bits when a
magnetic storage device is being read from or
written into. Compare DROP-OUT, 4.
drop indicator In a signaling system, such as an
annunciator, a hinged flap that drops into view
when the signaling device is actuated.
drop-out 1. The opening of a relay or circuit
breaker. 2. In digital computer operations, variation in signal level of the reproduced taperecorded data. Such variation can result in errors
in data reproduction. 3. In the production of
monolithic circuits, a special image placed at a
desired point on the photomask. 4. Digit loss
during a read or write operation involving a magnetic storage device.
dropout current See DROPOUT VALUE.
dropout power See DROPOUT VALUE.
dropout value The level of current, power, or voltage at which a device, such as a circuit breaker or
relay, is released.
dropout voltage See DROPOUT VALUE.
dropping resistor A series resistor providing a
voltage reduction equal to the voltage drop across
itself. For example, a 1000-ohm resistor in series
with a 45-V battery, and carrying a current of 10
mA, will provide a voltage reduction equal to 10 V
(IR = 0.01 × 1000 = 10 V), thus dropping the 45 V
to 35 V.
drop relay In a telephone system, a relay that is
activated by the ringing signal. The relay is used
to switch on a buzzer, light, or other device.
drop repeater A repeater intended for a termination of a communications circuit in a telephone
dropsonde A parachute-supported radiosonde
dropped from a high-flying aircraft.
drop-tracks • dry flashover voltage
drop-tracks The tracks of radioactive particles made
visible by moisture in an ionization chamber.
drop wire A wire that runs from a building to a
pole (for line extension) or to a cable terminal (for
cable extension).
drum 1. A rotating cylinder coated with a magnetic
material on which digital information can be
recorded in the form of tiny magnetized spots.
These spots are read as the drum rotates under
pickup heads, or erased when the stored information is no longer needed. 2. In some graphic
recorders, facsimile receivers, etc., a rotating
cylinder carrying the recording sheet.
drum capacitor See CONCENTRIC CAPACITOR.
drum controller The device that regulates the recording process on a drum memory.
drum mark On a track of a magnetic drum, a character that signifies the end of a character group.
drum memory In digital computers, a memory
based on a magnetic drum (see DRUM, 1). They
have been largely replaced in recent years by electronic random-access memory, in the form of integrated circuits (ICs) and/or PCMCIA standard
adapter cards.
drum parity The degree of accuracy in a drum
recording/reproducing system.
drum programmer A device for sequencing operations. Its heart is a rotating drum, around whose
surface contacts or points can be placed to actuate or terminate operations at selected times.
drum receiver A facsimile receiver using recording
paper or photographic film wound around a revolving drum.
drum recorder A graphic recorder in which the
record sheet is wound around a rotating drum.
Armature with
drum recorder
drum resistor A resistor consisting of a hollow
cylinder of resistive material. Such a resistor can
be cooled by circulating air or liquid through the
drum speed The speed, usually measured in revolutions per minute (rpm), of the rotating drum in
a graphic recorder, facsimile transmitter, or facsimile receiver.
drum storage The storage of data as magnetic
impulses on a cylindrical, or drum-shaped,
medium. Largely supplanted in recent years by
magnetic disks, optical disks, and magnetic
drum switch A sequential switch whose contacts
are pins or teeth placed at points around the outside of a revolving drum.
drum transmitter A facsimile transmitter in which
the sheet bearing the material to be transmitted
is wound around a revolving drum.
drum-type controller A motor-driven drum switch
arranged to time various operations through sequential switching.
drum varistor A varistor that is a hollow cylinder
of nonlinear resistance material. This varistor
can be cooled by circulating air or liquid through
drum winding In a motor or generator, an armature whose conductors are on the outer face of
the core, the two branches of a turn lying under
adjacent poles of opposite polarity.
drunkometer An instrument for testing the extent
of alcoholic intoxication. It electronically measures blood alcohol content through analysis of
the subject’s breath.
dry In an electric cell, a term used to describe an
electrolyte that is semiliquid or solid.
dry battery A battery of dry cells.
dry cell 1. A Leclanche primary cell in which the
positive electrode is carbon, the negative electrode is zinc, and the electrolyte is a gel of ammonium chloride and additives. Also see CELL and
PRIMARY CELL. 2. A cell whose electrolyte is a
gel or paste.
dry circuit A circuit in which the maximum voltage is 50 mV and the maximum current 200 mA.
dry-contact rectifier See DRY-DISK RECTIFIER.
dry contacts Contacts that neither make nor
break a circuit.
dry-disk rectifier A solid-state rectifier, such as a
copper-oxide, magnesium-copper-sulfide, or selenium type, that consists of a metal disk coated
with a semiconductor material. The name was
originally used to distinguish this rectifier from
the wet electrolytic rectifier.
dry electrolytic capacitor An electrolytic capacitor whose electrolyte is a paste or solid. Compare
dry flashover voltage The breakdown voltage between electrodes in dry air when all insulation is
clean and dry.
dry pile • dual-cone speaker
DSS Abbreviation of direct station selection (telephone).
DTA Abbreviation of differential thermoanalysis.
DT-cut crystal A piezoelectric plate cut from a quartz
crystal at an angle of rotation about the z-axis of
–53 degrees. It has a zero temperature coefficient of
frequency at approximately 30 degrees Celsius.
DTn Abbreviation of DOUBLE TINNED.
DTS 1. Abbreviation of DATA-TRANSMISSION SYSTEM. 2. Abbreviation of digital telemetry system.
DU Abbreviation of DUTY CYCLE.
dual 1. Pertaining to a combination of two components such as diodes, transistors, etc., in a single
housing. The components are often carefully
matched. Compare QUAD. 2. Pertaining to a device or circuit that behaves in a manner analogous to that of another operating with component
and parameter counterparts. Thus, a current amplifier can be the dual of a voltage amplifier;
a series-resonant circuit, the dual of a parallelresonant circuit; or a field-effect transistor, the
dual of a bipolar transistor.
dual-beam CRT A cathode-ray tube having two
separate electron guns, for use in a dual-beam
dual-beam oscilloscope Also called dual-trace oscilloscope. An oscilloscope having two electron
guns and deflection systems; it can display two
phenomena on the screen simultaneously for
dual capacitor 1. Two fixed capacitors combined
in a single housing, sometimes sharing a common capacitor plate. 2. A two-section, ganged
variable capacitor.
dual-channel amplifier An amplifier having two
separate, independent channels (e.g., a stereo
high-fidelity audio amplifier).
dual-cone speaker A speaker designed for a wide
range of audio frequencies. One cone responds to
the bass (low) and midrange audio frequencies,
and a smaller cone responds to the treble (high)
audio frequencies.
dry pile A voltaic pile containing numerous disks
silvered or tinned on one face and covered with
manganese dioxide on the other.
dry reed A metal contact, generally used as a relay
or switch, that moves toward or away from another fixed contact under the influence of a magnetic field.
dry-reed relay See DRY-REED SWITCH.
dry-reed switch A switch consisting of two thin,
metallic strips (reeds) hermetically sealed in a
glass tube. The tube is surrounded by a coil of
wire. When a current flows in the coil, a magnetic
field affects the reeds. In the normally open dryreed switch, the magnetic field causes the reeds
to come together and close the circuit. In the normally closed dry-reed switch, the magnetic field
causes the reeds to separate, opening the circuit.
dry run 1. The preliminary operation of equipment
for testing and appraisal. Such a procedure precedes putting the equipment into regular service.
2. A step-by-step, paper-and-pencil “run” of a
computer program before it is machine-implemented.
dry shelf life The life of a battery cell stored without its electrolyte.
dry-transfer process A method of transferring
printed-circuit patterns and panel labels from
sheets by rubbing them onto the substrate or
dry-type forced-air-cooled transformer A DRYTYPE TRANSFORMER that is cooled by convection of air circulated by a blower or fan. This
increases the amount of power that the transformer can safely handle.
dry-type self-cooled transformer A DRY-TYPE
TRANSFORMER that is cooled by natural air circulation (convection), without the use of a blower
or fan.
dry-type transformer A transformer that, rather
than being immersed in oil, is cooled entirely by
the circulation of air.
DSB Abbreviation of DOUBLE SIDEBAND.
dsc Abbreviation of double silk covered (wire).
D scope A radar whose display resembles that of a
C scope, the difference being that blip height
gives an approximation of the distance.
D service A Federal Aviation Agency service providing radio broadcasts of weather data, notices
to aircraft personnel, and other advisory messages.
D-shell connector A multi-pin connector (either
male or female) with a characteristic shape that
ensures proper pin placement. Commonly used
for computer ports, and for connections of peripherals to electronic equipment.
dsp Abbreviation of double silver plated.
dual diode • Duant electrometer
dual diode A discrete component consisting of two
diodes in one package.
dual-diversity receiver A receiver or receiver system for DIVERSITY RECEPTION.
dual-diversity reception See DIVERSITY RECEPTION.
dual-emitter transistor A low-level silicon pnp
chopper transistor of the planar passivated epitaxial type; it has two emitter electrodes.
dual-frequency calibrator A secondary frequency
standard providing two fundamental test frequencies (e.g., 100 kHz and 1 MHz).
dual-frequency induction heater An induction
heater whose work coils carry energy of two different frequencies. The coils heat the work either
simultaneously or successively.
dual gate 1. A digital integrated circuit (IC) consisting of two logic gate units. 2. Pertaining to a
field-effect transistor (FET) with two gates or gate
electrode connections.
dual-gate FET A field-effect transistor with two
gate (input) electrodes.
dual-gate MOSFET A metal-oxide-semiconductor
field-effect transistor (MOSFET) with two gate (input) electrodes.
dual-inline package Abbreviation, DIP. A flat,
molded integrated-circuit (IC) package having terminal pins along both long edges.
dual-inline package
duality 1. The condition of being dual (see DUAL).
This can be an aid in the design of certain circuits
requiring complementary parameters, e.g., current-operated circuit analogs of voltage-operated
circuits. 2. See DUALITY OF NATURE.
duality of nature 1. Any of various situations in
which a phenomenon exhibits two distinct and
different natures. A commonly cited example is
the dual model of light. In some instances, visible
light behaves like a barrage of particles, but in
other environments it appears to be a wave effect.
Another example is the dual model of electro-
static energy, behaving as point charges in some
scenarios and as force fields in other situations.
2. The tendency of a set of principles to be duplicated in sense by predictable analogies, as between inductance and capacitance, electrostatics
and magnetics, etc.
dual local oscillator See DOUBLE LOCAL OSCILLATOR.
dual meter A meter having two meter movements
and scales in a single case; the arrangement permits simultaneous monitoring of two quantities.
dual modulation The modulation of a single carrier or subcarrier by two different types of modulation—each carrying different information.
dual network A network that is the dual of another
network having complementary parameters. For
example, a common-emitter, current-sensitive,
bipolar-transistor circuit is the dual of a common-source, voltage-sensitive, field-effect-transistor (FET) circuit. Also see DUALITY.
dual operation In digital logic, the operation resulting from inverting all of the digits. Every 1 is
replaced with a 0, and vice versa.
dual-output power supply A power supply with
two outputs. Often, one output is positive and the
other is negative. In some cases, one output consists of alternating current (ac) and the other consists of direct current (dc).
dual pickup In disk reproduction, a pickup having
two styli, one for large-groove records and one for
fine-groove records.
dual potentiometer A ganged assembly of two potentiometers. The resistance values might or
might not be the same.
dual preset counter A preset counter that will set
alternately to two different numbers.
dual rail See DOUBLE RAIL.
dual resistor See DUAL POTENTIOMETER and
dual rheostat A ganged assembly of two rheostats. The resistance values might or might not
be the same.
dual stereo amplifier 1. A two-channel audio amplifier for stereophonic audio applications. 2. A
two-channel linear integrated circuit (IC) for
stereophonic audio applications.
loudspeaker See
dual trace In a cathode-ray oscilloscope, the use of
two separate electron beams, which can show two
different signals simultaneously on a single
dual-trace recorder See DOUBLE-TRACK RECORDER, 2.
dual-track recorder See DOUBLE-TRACK RECORDER.
dual recording In digital computer operations, updating two sets of master files simultaneously.
dual use The use of a communications system for
two modes of data transfer at the same time.
Duant electrometer See BINANT ELECTROMETER.
duct • dump check
Channel 1
Channel 2
dual trace
duct 1. A narrow propagation path, sometimes
traveled by microwaves, created by unusual atmospheric conditions. 2. A pipe or channel for cables and wires.
dubbing The adding of sound to a recorded magnetic tape, record disk, or film (e.g., replacing the
sound track of a film in one language with that of
another language).
dubnium Symbol, Db. Also clalled unnilpentium
(Unp) and hahnium (Ha). Atomic number, 105.
The most common isotope has atomic weight
262. Classified as a transition metal. It has a
half-life on the order of a few seconds to a few
tenths of a second (depending on the isotope), is
human-made, and is not known to occur in nature.
duct 1. A narrow propagation path, sometimes
traveled by microwaves, created by unusual atmospheric conditions. 2. A pipe or channel for cables and wires. 3. An opening, vent, or other
airway used for various purposes, such as cooling
and acoustic wave transmission.
ducted port An opening in a speaker cabinet that
has an airway (duct) extending several inches
into the cabinet. It improves the quality of sound
from a speaker system by equalizing the air pressure inside and outside the cabinet. Also provides
resonant audio effects at frequencies that depend
on the dimensions of the duct.
ductilimeter An instrument used for measuring
the ductility of metals.
ducting The confinement of a radio wave to a duct
(see DUCT, 1) between two layers of the atmosphere or between an atmospheric layer and the
Duddell arc A carbon copper arc circuit that produces audible continuous waves. Consists of a
series inductance-capacitance (LC) circuit shunting an electric arc.
Duerdoth’s multiple feedback system In an amplifier, feedback through several paths to improve
response over that afforded by single-path feed-
back. In a simple application of multiple feedback, a single external loop is augmented with
unbypassed emitter resistors in the amplifier
Duerdoth’s stability margin A feedback-amplifier
stability margin equal to a 6-dB increase in gain
at low and high frequencies over beta values between 0.3 and somewhat less than 2. For higher
beta values, Duerdoth adopts an angular margin
(for example, 15°); below β = 0.3, no danger of instability is present.
dummy 1. A nonoperative model of a piece of
equipment, usually assembled with dummy components (see DUMMY COMPONENT, 1) for the
purpose of developing a layout. 2. DUMMY ANTENNA, DUMMY COMPONENT, or DUMMY
LOAD. 3. Part of a computer program that, rather
than being useful for the problem at hand, only
serves to satisfy some other format or logic requirement.
dummy antenna 1. A nonradiating device that
serves as a load for a transmitter (i.e., it takes the
place of the regular antenna during tests and adjustments of the transmitter). 2. A device
containing a network of discrete inductive,
capacitive, and resistive elements, inserted between a radio-frequency signal generator and receiver to simulate a standard antenna.
dummy component 1. A nonoperative component used in developing a layout or package. 2.
A nonoperative component fraudulently included in a piece of equipment (e.g., an unwired
transistor in a receiver circuit, a common occurrence during the early days of the transistor,
when a 10-transistor radio brought more money
than an 8-transistor radio, without regard to the
circuit itself).
dummy instruction In a computer, a command
that serves no operational purpose, other than to
fill a format requirement.
dummy load 1. A load device, usually consisting of
resistance without reactance, used to terminate a
power generator or power amplifier during adjustments and tests. The load resistance is equal
to the output impedance of the generator or amplifier. 2. See DUMMY ANTENNA.
dummy resistor A power-type resistor used as a
dummy load.
dump 1. In digital-computer operations, to transfer, completely or partially, the contents of memory into a peripheral. 2. To switch off all power to
a computer, deliberately or accidentally, thereby
losing what is in the volatile memory.
dump and restart During a halt in a computer
program run, to backtrack to the last dump point
and use the data there to resume the run. Also
dump check In digital-computer operations, the
checking of all digits being transferred (see
DUMP, 1) to prevent errors when they are retransferred.
dumping • dust cover
duplexing assembly In a radar system, a device
that automatically makes the receiver unresponsive to the outgoing transmitted signal while allowing incoming signals to reach the receiver
duplex computer system An installation of two
computer systems, one standing by to take over
in case the other fails.
duplex operation The simultaneous operation of a
transmitter and receiver at a single location. This
becomes possible (without mutual interference)
through the use of two sufficiently separated carrier frequencies.
duplex system A system composed of two identical
equipment sets—either of which will perform the
intended function while the other stands by.
duplication check In digital-computer operations,
the checking of an operation by doing it twice, using different methods in each case, to ensure the
accuracy of results.
duplication house A professional person or company who makes high-quality copies of tape
recordings (either audio or video). Charges vary,
depending on the type and length of the recording.
duplicate To transfer data from one storage location to another. Compare DUMP, 1.
dural See DURALUMIN.
duralumin An alloy of aluminum, copper, magnesium, manganese, and silicon. It offers strength
with minimal weight.
duration control A potentiometer or variable capacitor for adjusting the duration of a pulse.
duration time The period during which a pulse is
sustained (i.e., the interval between turn-on and
turn-off time).
dumping To transfer the output at various stages
in a computer program run to an external storage
medium, so it will be available (in case of a failure) for the program’s resumption from a point
other than at the beginning.
dump point In writing a computer program, a point
at which instructions are given to transfer data
processed thus far to a storage medium that would
be unaffected by a software or hardware failure.
dumping resistor 1. See BLEEDER. 2. A resistor
having the minimum resistance permissible in a
given situation. Used to discharge a capacitor, it
acts to provide an alternative path to a potentially
destructive short circuit.
duo Any pair of matched components, usually in a
single package.
duodecal CRT base The 12-pin base of a cathoderay tube. Also see BIDECAL, DIHEPTAL, and
duodecal socket A 12-pin tube socket. Also see
duodecimal 1. Having 12 possibilities, states,
choices, etc. 2. Pertaining to the DUODECIMAL
NUMBER SYSTEM. 3. A number or numeral in
duodecimal number system A system of numbering in which the radix, also called the base or
modulus, is 12. The system uses the digits 0
through 9, plus two other characters (usually A
and B) to represent 10 and 11. Thus, counting
proceeds as 0, 1, 2, . . . , 9, A, B, 10, 11, 12, . . . , 19,
1A, 1B, 20, 21, 22, etc. At one time, some people
seriously proposed that this system replace the
DECIMAL NUMBER SYSTEM for general use.
duodiode See DUAL DIODE.
duolateral coil A multilayer, lattice-wound coil
(see UNIVERSAL WINDING) in which the turns in
successive layers are staggered slightly. Also
called honeycomb coil.
duopole A two-pole all-pass device.
duplex 1. A mode of communication in which two
channels are used so that either operator in a
conversation can interrupt the other at any time.
2. The transmission of two messages over a single
circuit, at the same time.
duplex artificial line In wire telephony, a balancing network that simulates the impedance of the
actual line and the remote terminal equipment; it
prevents an outgoing transmission from interfering with the local receiver.
duplex cable A cable consisting of a twisted pair of
insulated stranded-wire conductors.
duplex channel A channel used for wire or radio
duplex communication See DUPLEX OPERATION.
duplex diode See DUAL DIODE.
duplexer In radar operations, a device operated by
the transmitted pulse to automatically switch the
antenna from the receiver to the transmitter.
duration time
during cycle The interval during which a timer is
in operation.
durometer An instrument for measuring the hardness of a material.
dust collector See DUST PRECIPITATOR.
dust core A magnetic core for radio-frequency coils
consisting of very minute particles of iron or an
alloy, such as Permalloy.
dust cover A removable, usually plastic cover for
electronic and computer equipment, to protect
hardware during periods of nonuse.
dust-ignition-proof motor • dynamic debugging
dust-ignition-proof motor A motor whose housing completely prevents the entry of dust, virtually eliminating the danger of fine dust sparking
inside the machine.
dust precipitator An electrostatic device for removing dust, lint, and other particles from the
air. It consists essentially of a pair of screens or
wires through which the air passes; a potential of
several thousand volts is maintained between
them. The particles acquire a charge, then stick
to the oppositely charged screen.
Dutch metal A copper-zinc alloy.
duty cycle 1. The proportion or percentage of
time during which a device, circuit, or system is
operating or handling power. For example, when
a radiotelegraph transmitter is keyed on and off
to send Morse code, the duty cycle is approximately 50 percent; with frequency-shift keying,
the duty cycle is 100 percent. 2. The conditions
under which an electrochemical cell or battery
is used. In particular, the proportion or percentage of time during which current is drawn from
the cell or battery for the purpose of operating
an electrical or electronic circuit, device, or
duty cyclometer A direct-reading instrument for
measuring duty cycle.
duty factor 1. The ratio Pavg/Ppk, where Pavg is the
average power in a system and Ppk is the peak
power. 2. The product of the duration and the
repetition rate of regularly recurring pulses comprising a carrier.
duty ratio See DUTY FACTOR, 1.
dwell meter An instrument that shows the period
(or angle) during which contacts remain closed.
dwell switching Switching action in which the
contacts are held closed (or a circuit kept on) for
specified periods, as opposed to MOMENTARY
dwell tachometer A combination dwell meter/
tachometer for automobile engine testing and adjustment. The dwell meter allows observation and
adjustment of the ignition point cam angle; the
tachometer shows the motor speed in revolutions
per minute (rpm).
DX 1. Radiotelegraph abbreviation meaning long
distance or foreign country. 2. A communication
or broadcast station located far away and/or in a
foreign country. 3. Abbreviation of DUPLEX.
DXer An amateur radio operator who prefers to
communicate with stations far away and/or in
foreign countries.
Dy Symbol for DYSPROSIUM.
dyadic operation A binary operation (i.e., one using two operands).
dyn Abbreviation of DYNE.
dyna- A prefix (combined form) meaning power
(e.g., dynamometer and dynatron).
dynamic acceleration Acceleration whose magnitude and direction are constantly changing.
dynamic allocation In multiprogramming, a system in which a monitor program assigns peripherals and areas of memory to a program.
dynamic analogy A mathematical similarity between or among various phenomena involving the
motion of particles.
dynamic base current See AC BASE CURRENT.
dynamic base resistance See AC BASE RESISTANCE.
dynamic base voltage See AC BASE VOLTAGE.
dynamic behavior 1. The behavior of a component,
device, or system when signals are applied, as
opposed to static behavior under no-signal conditions. 2. The behavior of a device or system involving the motion of particles over a period of time.
dynamic braking A technique for stopping a motor
quickly using a resistor (the dynamic braking resistance) connected across the spinning armature. The resistor dissipates the energy generated
by the motor, producing a damping action that
results in braking.
dynamic characteristic The performance characteristic of a device or circuit under alternatingcurrent (ac) operating conditions, as opposed to
the static characteristic, when only direct current
(dc) flows.
dynamic check 1. A test made under actual operating conditions of a device or circuit. 2. A test
made with an alternating-current (ac) applied signal, rather than with direct-current (dc) quantities.
dynamic collector current See AC COLLECTOR
dynamic collector resistance See AC COLLECTOR RESISTANCE.
dynamic collector voltage See AC COLLECTOR
dynamic contact resistance In relay or switch
contacts, variation in the electrical resistance of
the closed contacts because of variations in contact pressure.
dynamic convergence In a color picture tube, the
meeting of the three beams at the aperture mask
during scanning.
dynamic current amplification Abbreviation,
DCA. An expression of gain in a bipolar transistor.
Specified as the ratio of the difference in collector
current IC to the difference in base current IB
Geometrically, the dynamic current amplification
at a given bias point is the slope of a line tangent
to the IC-versus-IB curve at that point.
dynamic curve A characteristic curve that accounts for the presence of resistance in series
with the device to which the curve applies.
dynamic debugging Any debugging operation performed on a computer system during a normalspeed program run.
dynamic decay • dynamic range
dynamic decay Decay resulting from such factors
as ion charging in a storage tube.
dynamic demonstrator A teaching aid consisting
of a board displaying an electronic circuit, behind
which is mounted the actual circuit. Various circuit components (especially adjustable ones) are
mounted on the front of the board, in clear view
at places where their circuit symbols appear. Pin
jacks at important test points in the circuit allow
connection of a meter, signal generator, and oscilloscope leads for testing or demonstrating the
dynamic deviation The difference between ideal
output and actual output of a circuit or device operating with a reference input that changes at a
constant rate and is free of transients.
dynamic diode tester An instrument that displays
the response curve (or family of curves) of a diode
on a calibrated oscilloscope screen. The horizontal axis of the screen indicates voltage, the vertical axis shows current, and zeros for both
quantities are at center screen. Also see DYNAMIC RECTIFIER TESTER.
dynamic drain current See AC DRAIN CURRENT.
dynamic drain resistance See AC DRAIN RESISTANCE.
dynamic drain voltage See AC DRAIN VOLTAGE.
dynamic dump A dump that occurs during a program run. See DUMPING.
dynamic electric field An electric field whose intensity is constantly changing, either periodically
or in a complex way.
dynamic emitter current See AC EMITTER CURRENT.
dynamic emitter resistance See AC EMITTER
dynamic emitter voltage See AC EMITTER VOLTAGE.
dynamic equilibrium 1. The state of balance between constantly varying quantities. 2. The tendency of two current-carrying circuits to maintain
at a maximum the magnetic flux linking them.
dynamic error In a periodic signal delivered by a
transducer, an error resulting from the restricted
dynamic response of the device.
dynamic flip-flop A flip-flop (bistable multivibrator) that is kept on by recirculating an alternating-current (ac) signal. The device can be
switched on or off by a single pulse. Compare
dynamic focus Compensation for defocusing,
caused by the electron beam sweeping in an arc
across a flat color picture-tube screen; the
method uses an alternating-current (ac) focusing-electrode voltage.
dynamic gate voltage See AC GATE VOLTAGE.
dynamic impedance The impedance of a device
(such as a transistor or diode) when it is operating with an applied alternating-current (ac) signal, as opposed to its static resistance with only
direct current (dc) applied.
dynamic limiter A limiter, such as is used in frequency-modulation (FM) receivers, that maintains the output-signal level, despite appreciable
excursions of input-signal amplitude.
dynamic loudspeaker See DYNAMIC SPEAKER.
dynamic magnetic field A magnetic field whose
intensity is constantly changing, either periodically or in a complex way.
dynamic memory A usually random-access data
storage method in which the memory cells must
be electrically refreshed periodically to avoid the
loss of held data.
dynamic microphone A microphone in which a
small coil attached to a vibrating diaphragm or
cone moves in a uniform magnetic field to generate the output signal.
Sound waves
dynamic microphone
dynamic mutual conductance See DYNAMIC
dynamic noise suppressor A noise limiter consisting of an audio filter whose bandwidth is directly
proportional to signal strength (i.e., it is varied
automatically by signal amplitude).
dynamic operating line A curve displaying the
control function of a device. For example, the
collector-current-versus-base-current curve of a
bipolar transistor is drawn between the limits of
saturation and cutoff.
dynamic output impedance The output impedance of a power supply, as “seen” by the load.
dynamic pickup A phonograph pickup whose stylus causes a small coil to vibrate in the field of a
permanent magnet. Works on the same principle
dynamic printout A printout that occurs as a single function, actuated by one command, and
completing itself in one operation.
dynamic problem checking A method of checking
the solution obtained by an analog computer, to
see that it makes sense (is not absurd).
dynamic programming A method of problem
solving in which continual checks are made to
ensure accuracy or conformance to a certain set
of rules.
dynamic range 1. In high-fidelity audio, the ratio
of the loudest sound to the faintest sound that
can be reproduced without significant distortion
dynamic range • dynatron
or noise. It is usually expressed in decibels. 2. In
a communications receiver, a measure of the
ability to receive both weak and strong signals
without excessive noise, distortion, desensitization or other undesirable effects. It is expressed
in various ways, typically in decibels. 3. The ratio
between the loudest and faintest sounds, or between the strongest and weakest signals, encountered in a given environment or situation. It is
usually expressed in decibels.
dynamic rectifier tester An instrument that displays the response curve of a rectifier on a calibrated oscilloscope screen. During the test, the
rectifier receives an alternating-current (ac)
voltage with a low positive peak and high negative peak, both corresponding to the rated forward and reverse voltages (respectively) of the
rectifier. The horizontal axis of the screen indicates voltage, the vertical axis indicates current,
and zeros for both quantities are at center
dynamic regulation In an automatically regulated
system, such as a voltage-regulated power supply, the transient response of the system. Dynamic regulation is determined from maximum
overshoot and recovery time when the load or line
value is suddenly changed.
dynamic regulator A circuit or device providing
dynamic regulation.
dynamic resistance See DYNAMIC IMPEDANCE.
dynamic run See DYNAMIC CHECK, 1. See also
dynamics The study of bodies, charges, fields,
forces, or pulses in motion. Compare STATICS.
dynamic sequential control In digital computer
operation, the computer’s changing the sequence
of instructions during a run.
dynamic source current See AC SOURCE CURRENT.
dynamic source resistance See AC SOURCE RESISTANCE.
dynamic source voltage See AC SOURCE VOLTAGE.
dynamic spatial reconstructor Abbreviation,
DSR. An advanced x-ray machine, developed at
the Mayo Clinic, that displays organs in threedimensional views in motion, and allows them to
be electronically dissected without actually
operating on the patient.
dynamic speaker A loudspeaker in which a small
coil (voice coil), attached to a diaphragm or cone
and carrying an audio-frequency signal current,
moves back and forth in a permanent magnetic
field and, accordingly, causes the diaphragm or
cone to vibrate (emit sound). Compare MAGNETIC SPEAKER.
dynamic stability A measure of the ability of a
robot to maintain its balance while in motion.
dynamic stop As caused by a computer program
instruction, a loop indicating the presence of an
dynamic storage See DYNAMIC MEMORY.
dynamic subroutine A form of computer subroutine that allows the derivation of other subroutines in various forms.
dynamic test See DYNAMIC CHECK.
transconductance Transconductance
determined from alternating-current (ac) signal
parameters, rather than from direct-current (dc)
dynamic transducer A coil-and-magnet device
that converts mechanical vibration into electric
currents, or vice versa. Common examples include most microphones, headphones, and loudspeakers.
dynamic transfer characteristic An input-output
characteristic determined, with respect to the
load of a transfer device. Also see DYNAMIC
dynamic transistor tester 1. An instrument for
checking the alternating-current (ac) gain of a
transistor, rather than its direct-current (dc)
beta. 2. An instrument for determining the condition of a transistor from its performance in a simple oscillator circuit. 3. An instrument that
displays a transistor response curve, or a family
of such curves, on a calibrated oscilloscope
screen. Also see DYNAMIC DIODE TESTER and
dynamo A mechanical generator of electricity; typically a rotating machine.
dynamoelectric machinery Rotating electric machinery. Examples: amplidynes, generators, dynamotors, rotary converters.
dynamometer 1. See ELECTRODYNAMOMETER.
2. A device for mechanically measuring the output power of a motor.
dynamometer ammeter See ELECTRODYNAMOMETER.
dynamometer voltmeter See ELECTRODYNAMOMETER.
dynamophone A dynamometer (see DYNAMOMETER, 2) that uses two telephone circuits to
measure the twist of a shaft.
dynamostatic machine A machine driven by alternating-current (ac) or direct-current (dc) power
for the generation of static electricity.
dynamotor A (usually small) self-contained
motor-generator. The motor and generator
portions are enclosed in a common housing,
giving the machine the appearance of a simple
dynaquad A pnpn four-layer semiconductor device
with three terminals, similar to the siliconcontrolled rectifier or thyristor.
dynatron A form of vacuum tube that displays a
negative-resistance characteristic, resulting in
oscillation at ultra-high and microwave frequencies.
dynatron frequency meter • dysprosium
dynatron frequency meter A heterodyne-type frequency meter using a dynatron oscillator.
dyne Abbreviation, d. A unit of force. One dyne
(10–5 newton) is the force that will give a mass of
1 gram an acceleration of 1 centimeter per second
per second. Compare NEWTON.
dyne-centimeter See ERG.
dyne-five In the Giorgi mks system, a unit of force
equal to 1 newton.
dyne per square centimeter Abbreviation, d/cm2.
A unit of pressure equal to 0.1 pascal (9.869 ×
10-7 atmosphere).
dyne-seven A unit of force equal to 107 dynes.
dynistor A semiconductor diode that continues to
conduct after the forward voltage is reduced below the normal threshold point. To stop the conduction, a reverse voltage must be applied, or
voltage must be entirely removed from the device.
It is used in switching applications.
dynode In a photomultiplier tube, any of several
slanting electrodes that receives a beam of electrons generated by the light-sensitive cathode
and reflects it, along with secondary electrons.
This amplifies the beam; the process is repeated
several times. Thus, the emission from the
cathode is greatly amplified when it reaches the
dysprosium Symbol, Dy. An element of the rareearth group. Atomic number, 66. Atomic weight,
162.50. Dysprosium is a highly magnetic substance.
1. Symbol for VOLTAGE. 2. Symbol for ELECTRIC FIELD STRENGTH. 3. Abbreviation of
EMITTER. 4. Symbol for prefix EXA. 5. Symbol
e 1. Symbol for VOLTAGE. 2. Abbreviation of
Symbol for the natural logarithm base (approximately equal to 2.71828). 5. Symbol for ECCENTRICITY. 6. Abbreviation of ERG.
EAM Abbreviation of electronic accounting machine.
E and M terminals The output and input leads in
some signaling systems. Also called E and M
early early sound Sound propagated through
solids and/or liquids that reaches a pickup device (such as a microphone) before the sound
propagated through the air. In general, sound
waves travel faster as the medium becomes more
early-failure period The period immediately after
manufacture of a device, during which the failure
rate (caused by defects in equipment or workmanship) is high.
early-warning radar Abbreviation, EWR. A radar
system that produces immediate warning when
enemy aircraft enter the monitored area.
earphone 1. Headphone (usually a single unit).
2. Telephone receiver. 3. A miniature acoustic
transducer that is small enough to be inserted
into the ear.
earpiece See EARPHONE, 3.
earth 1. The ground. 2. An electrical connection to
the earth (see GROUND CONNECTION, 2). 3. In
space communications, the planet Earth.
earth connection See GROUND CONNECTION, 2.
earth currents 1. Electric currents induced in the
earth by current flowing through underground or
underwater cables. 2. Electric currents flowing
through the earth between ground connections of
electrical equipment.
earth ground 1. A common connection to an electrode buried in the earth so that good conductivity is maintained between the common circuit
point and the earth itself. 2. A rod driven into the
surface of the earth for use as a common circuit
earth inductor A magnetometer consisting of a
coil that is rotated in the earth’s magnetic field. It
delivers an alternating-current (ac) voltage proportional to the field strength. Also called generating magnetometer.
earth-moon-earth See MOONBOUNCE.
earth resonance A resonant effect at extremely low
frequencies, caused by reflection of currents
within the earth. Resonant currents have been
tested as a means of communicating with submarines worldwide.
earth’s magnetic field Also called geomagnetic
field. The natural magnetic field whose lines of flux
extend from north to south. The earth’s magnetic
poles, also called the geomagnetic poles, do not exactly coincide with the geographic poles. The field
somewhat resembles that of a bar magnet.
Eastern Standard Time Abbreviation, EST. Local
mean time at the 75th meridian west of Greenwich.
east-west effect The phenomenon in which the
number of cosmic rays approaching earth near
the equator from the west is greater than that
from the east by 10 percent.
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Eavg • echo
Magnetic pole
Flux lines
Magnetic pole
earth’s magnetic field
Eavg Symbol for AVERAGE VOLTAGE.
E bend In a waveguide, a smooth change in the direction of the axis, which remains parallel to the
direction of polarization.
ebiconductivity Conductivity resulting from electron bombardment.
ebonite Hard rubber used as an insulant. Dielectric constant: 2.8. Dielectric strength: 30 to 110
EBS amplifier An amplifying device using an electron-bombarded semiconductor. The electron
beam is modulated by the input signal, and the
modulated resistance of the semiconductor target
modulates a relatively heavy current to provide
an amplified output. Current gains on the order
of 2000 are possible.
ec Abbreviation of ENAMEL-COVERED (in reference to wire).
eccentric circle See ECCENTRIC GROOVE.
eccentric groove On a phonograph record, an offcenter groove in which the stylus rides at the end
of the recording, where it causes the tone arm to
trip the record-changing mechanism.
eccentricity 1. The condition of being off center,
intentionally or not. It is often a consideration in
the behavior of dials, potentiometers, and servomechanisms. 2. On a phonograph record, the
condition in which the spiral recording groove
and the center hole of the disk are not concentric.
3. A quantitative expression for the extent to
which an ellipse is elongated.
eccentricity of orbit The extent to which the orbit
or path of a satellite differs from a circle. A
circular orbit has eccentricity zero. As the orbit
becomes elliptical and deviates more and more
from a perfect circle, the eccentricity increases.
When the eccentricity reaches 1, the object takes
a parabolic path through space. If the eccentricity
exceeds 1, the path is a hyperbola.
ECDC Abbreviation of electrochemical diffused collector.
ECG Abbreviation of electrocardiogram. (Also,
ECG telemetry Use of a radio telemetering system
to monitor the heart function of a person from a
echelon 1. A level of calibration accuracy, the
highest echelon being the national standard for
the particular measurement involved. 2. A level of
maintenance in which lower ordinal numbers refer to less-critical tasks, and higher ordinal numbers refer to tasks requiring progressively higher
skills and technological expertise.
echelon grating A diffraction grating with extremely high resolution. Generally useful only
over a small range of wavelengths.
echo 1. A signal that is reflected back to the point
of origin. 2. A reflected or delayed signal component that arrives at a given point behind the main
component. 3. A radar blip, indicating an object
or thundershower. 4. Reflection of the signal on a
telephone line, caused by improper impedance
matching, or by overload of the system by too
many subscribers attempting to use the system
at the same time. 5. In audio systems, a circuit
that causes sounds to repeat one or more times,
at intervals ranging from a fraction of a second to
several seconds. 6. The effect produced by a circuit, as defined in 5.
Short path
Long path (echo)
echo area • eddy-current loss
echo suppression In a telephone circuit, a device
that chokes off reflected waves, thereby minimizing audible echo.
echo suppressor See ECHO ELIMINATOR.
echo talk Echo in a telephone system that results
in distracting interference.
echo wave A reflected wave, such as a radio wave
reflected alternately between earth’s surface and
the ionosphere.
eclipse effect A decrease in the critical frequency
of the E and F1 layers of the ionosphere during a
solar eclipse.
ecliptic orbit Any orbit that lies in the same plane
as the orbit of the earth around the sun (the ecliptic plane). The ecliptic plane is slanted about
23.5° from the plane of the earth’s equator.
econometer An instrument for continuously monitoring the amount of carbon dioxide in (factory)
flue gases.
E core A transformer or transducer core having the
shape of an E. Coils can be wound on one, two, or
all three of the crosspieces.
echo area The area of a target that will return a
radar signal as an echo.
attenuation In a bidirectional wirecommunication circuit equipped with repeaters
or multiplexers, the attenuation of echo currents
set up by conventional operation.
echo box A resonant-cavity device used to test a
radar set. Part of the transmitted energy enters
the box, which retransmits it to the receiver. The
signal reaching the receiver is a slowly decaying
transient whose intensity eventually falls below
the level that can be displayed on the screen; the
time required to reach this level indicates radar
echo chamber A reverberation chamber, electronic
recording device, or room for acoustic tests or for
simulating sonic delays.
echo check In data communication, a means of
checking the accuracy of received data by sending it back to the transmitting station for comparison with the original data.
echo depth sounder See ACOUSTIC DEPTH
echo eliminator 1. A device that quiets a navigational instrument after receipt of a pulse, to prevent reception of a subsequent, delayed pulse. 2.
In a two-way telephone circuit, a voice-operated
device that suppresses echo currents caused by
conversation currents going in the opposite direction.
echoencephalograph An ultrasonic medical instrument that allows viewing of internal organs.
Used for diagnostic purposes in certain situations, instead of the X-ray machine.
echogram In acoustics, a graph of the sound
decrement in an enclosure. Time is plotted on
the horizontal axis; signal amplitude is plotted
on the vertical axis. An intense pulse is transmitted from a speaker; a microphone picks up the
echoes and sends them to a pen recorder or microprocessor.
echo intensifier A device used at a radar target to
boost the intensity of reflected energy.
echo interference Radio interference resulting
from a reflected signal arriving slightly later than
the direct signal.
echo matching In an echo-splitting radar system,
the trial-and-error orientation of the antenna to
find the direction from which the pulse indications are identical.
echo ranging An ultrasonic method of determining
the bearing and distance of an underwater object.
echo send In an audio mixer, an output for delivering signals to external systems, such as an
echo box (see ECHO, 5). It can also provide an
auxiliary output for a second set of speakers, a
tape recorder, etc.
echo splitting Separating a radar echo into two
parts so that a double indication appears on the
radar screen.
E core
ECPD Abbreviation of Engineer’s Council for Professional Development.
ECTL Abbreviation of emitter-coupled transistor logic.
eddy current A circulating current induced in a
conducting material by a varying magnetic field,
often parasitic in nature. Such a current can, for
example, flow in the iron core of a transformer.
eddy-current device A brake, coupling, clutch,
drag cup, drive unit, or similar device whose operation is based on the generation of torque, pull,
or opposition by the action of eddy currents.
eddy-current heating Heating caused by eddycurrent loss in a material.
eddy-current loss Power loss resulting from eddy
currents induced in nearby structures by an
eddy-current loss • effective acoustic center
electromagnetic field. Eddy currents in the core of
a transformer give rise to such loss.
edge connector A terminal block with a number of
contacts, attached to the edge of a printed-circuit
board for easy plugging into a foundation circuit.
edge control In the manufacture of paper, a
robotic system for maintaining the width of a
sheet by sensing the edges and correcting the
machine accordingly. Transducers that sense the
passing edges deliver output signals proportional
to variations from standard width.
edge detection The ability of a machine vision system to locate and follow boundaries. Used extensively in mobile robots.
edge effect The extension of electric lines of flux
between the outer edges of capacitor plates. This
portion of the interplate field contributes a small
amount of capacitance. Because the lines of flux
are not confined to the space between plates, they
can cause capacitive coupling with external
Positive plate of capacitor
Negative plate of capacitor
edge effect
edge-punched card In digital computer operations, a punched card whose edge is perforated in
a narrow column, the center being used for written annotation.
edgewise meter A meter having a curved horizontal scale; this arrangement allows mounting the
instrument edgewise in a panel.
edgewise-wound coil A coil made of a flat metal
strip cut in the shape of a coil spring. The design
allows the use of clips to vary the inductance, but
this advantage is often offset by the coil’s high
distributed capacitance.
edging In a color television picture, extraneous
color of a different hue than the objects around
whose edges it appears.
Edison base A threaded base on light bulbs, conetype heaters, and some pilot lamps.
Edison battery A group of Edison cells connected
in series, parallel, or both, and contained in a single package with two electrodes.
Edison cell A secondary (storage) cell in which the
active positive plate material consists of nickel
hydroxide held in steel tubes assembled into a
steel grid; the active negative plate material is
powdered iron oxide mixed with cadmium; the
electrolyte is potassium hydroxide. The open-
circuit voltage of the cell is typically 1.2 V at full
Edison distribution system A three-wire, 110- to
250-volt direct-current (dc) power-distribution
Edison effect Thermionic emission of negatively
charged particles (electrons) from a hot filament
sealed in an evacuated bulb; they are attracted by
a cold, positively charged metal plate in the bulb.
E display A radar display in which the horizontal
coordinate indicates distance, and the vertical coordinate indicates elevation.
edit 1. In tape recording, the modifying of the
recorded material by deleting (cutting out or erasing), adding (splicing or overrecording), or changing the sequence of the material by physically or
magnetically altering the tape. 2. In digital computer operations, to make data ready for processing.
edit decision list In the editing of a digital audio/video presentation, a record of every change
(cut and paste). The list is automatically made by
the computer and stored on disk for later reference if needed.
editing 1. Alteration of a magnetic-tape recording
by means of splicing. 2. Alteration of data stored
in memory, either by adding information, removing information, changing information, or (usually) a combination of these operations.
EDP Abbreviation of electronic data processing.
EDPC Abbreviation
EDPS Abbreviation
EDT 1. Abbreviation of ethylene diamine tartrate (a
synthetic piezoelectric material). 2. Abbreviation
of Eastern Daylight Time.
EDU Abbreviation of electronic display unit.
educational robot A robot that can be programmed
for the purpose of teaching its users something.
Popular as an educational toy for children.
EDVAC Acronym for Electronic Discrete Variable
Automatic Computer, a development of the University of Pennsylvania.
EEG Abbreviation
EEPROM Abbreviation
EES Abbreviation of EARLY EARLY SOUND.
effective acoustic center The apparent point of
propagation of spherically divergent sound waves
radiated by an acoustic generator.
effective actuation time • effective phase angle
effective actuation time The total actuation time
of a relay (i.e., the sum of the initial actuation
time and subsequent intervals of contact
effective address The address a computer uses in
implementing an instruction (i.e., one not necessarily coinciding with the address given in the instruction).
effective ampere An effective current of 1 ampere.
effective antenna length See ELECTRICAL
effective antenna resistance The radiation resistance of an antenna, as measured at the input
effective bandwidth The bandwidth of an ideal
bandpass filter, which, at a reference frequency,
has the same transfer ratio as an actual bandpass filter under consideration; it also has the
same current and voltage characteristics.
effective bandwidth
effective capacitance The actual capacitance between two points in a circuit resulting from the
combination of inherent, lumped, and stray capacitances.
effective conductivity Conductivity measured between the parallel faces of a unit cube of a material.
effective confusion area In a radar system, an
area in which interference makes it impossible to
see whether a target is present.
effective current Symbol, Ieff. The root-meansquare (rms) value of alternating current (see
EFFECTIVE VALUE). For a sinusoidal current,
Ieff = 0.707Imax, where Imax is the maximum value
of the current. Also called rms current.
effective cutoff frequency For a filter or similar
device operated between specified impedances,
the frequency at which insertion loss is higher
than the loss at a specified reference frequency in
the passband.
effective field intensity The root-mean-square
(rms) value of the field-strength voltage, averaged
for all points at a horizontal distance of one mile
from a transmitting antenna.
effective height The height of an antenna in terms
of its performance as a transmitter or receiver of
electromagnetic energy.
effective input capacitance The actual operative
capacitance present at the input terminals of a
circuit or device, caused by the shunt capacitance of the terminals themselves and the net
capacitance of the circuit connected to the
effective internal resistance In an electrochemical cell or battery, a resistance that originates
within the electrolyte and electrodes. This resistance is low when the current drain is low; it rises
as the current drain increases. It limits the maximum current that the cell or battery can deliver.
effective isolation The condition of components
or circuits being so well isolated or shielded that
no significant direct coupling, capacitive coupling, or inductive coupling exists between them.
effective instruction The machine-language version of an instruction given in a computer program, as produced by resident software.
effectively bonded The condition afforded by an
extremely low-resistance union between two conducting surfaces that are solidly fastened together.
effectively grounded The condition of being connected to earth or to the low-potential end of a
circuit by means of an extremely low-resistance
effective parallel capacitance Inherent capacitance that manifests itself in parallel with two circuit points in combination with any lumped
effective parallel resistance 1. The leakage resistance that manifests itself in parallel with a
dielectric (e.g., the leakage resistance of a
capacitor). 2. Parallel-resistance effects caused
by stray shunt-resistance components.
effective percentage of modulation For a complex waveform, an expression of the equivalent
percentage of modulation by a pure sine wave.
Given a certain proportion of power in the sidebands with modulation by a complex signal, the
effective percentage of modulation is that percentage which, when the modulating signal is sinusoidal, results in the same proportion of power
in the sidebands.
effective phase angle In alternating-current (ac)
circuits, the phase angle, with respect to waveforms for current and voltage. When both waveforms are sinusoidal, the effective phase angle is
effective phase angle • eight-level code
the actual phase angle. But when harmonics are
present in current or voltage, the angles differ,
the difference being greater in capacitive circuits
than in inductive circuits.
effective radiated power Abbreviation, ERP or
PER. 1. A measure of the performance of a wireless
transmitting antenna. Suppose a test antenna,
AT, is set up and the field strength in its favored
direction at a frequency f is measured at a distance d in free space. Let the field strength thus
measured be F watts per square meter. Suppose
AT is replaced with an isotropic radiator, AI, and
the field strength at the same frequency f is measured at the same distance d in free space. Let
the radio-frequency (RF) power at the feed point
of the isotropic radiator AI be varied until the field
strength is F, the same as it was with the test antenna AT. Let this RF power be symbolized P.
Then P is defined as the effective radiated power
(ERP or PER) of the test antenna, AT. 2. The figure
defined as in (1), measured in some direction
other than the favored direction of a test antenna.
effective resistance 1. In a coupled circuit, the
sum of the actual resistance of the circuit and the
reflected resistance of the load. 2. See EFFECTIVE ANTENNA RESISTANCE.
effective series inductance Inherent (distributed) inductance acting in series with other components in a circuit. The inherent inductance of
the wire in a wirewound resistor, for example,
manifests itself in series with the resistance of the
effective series resistance Inherent (distributed)
resistance acting in series with other components
in a circuit. Thus, the inherent resistance of the
wire in a coil appears in series with the inductance of the coil. Likewise, a capacitor has an effective series resistance because of the resistance
of the leads, plates, and connections.
effective shunt capacitance See EFFECTIVE
effective shunt resistance See EFFECTIVE PARALLEL RESISTANCE.
effective sound pressure The root-mean-square
(rms) value of instantaneous sound pressure at
one point in a sound cycle.
effective speed of transmission In telegraphy
(wire or radio) and in electronic data transmission, the transmission speed (characters per
minute, bits per second, etc.) that can be reliably
maintained for a given period.
effective thermal resistance The effective temperature rise (in degrees per watt of dissipation)
of a semiconductor junction above an external
reference temperature that is at equilibrium.
effective time For a computer, the time during
which useful work is performed.
effective transmission speed See EFFECTIVE
effective value The root-mean-square (rms) value
of an alternating-current (ac) quantity. The
effective value an alternating current produces in
a pure resistance has the same heating effect as
the equivalent direct current. See also ROOT
effective volt An effective potential of one rootmean-square (rms) volt. Also see EFFECTIVE
effective voltage Symbol, Eeff. The root-meansquare value of alternating-current (ac) voltage
(see EFFECTIVE VALUE). For a sinusoidal voltage, Eeff = 0.707Emax, where Emax is the maximum
value of the voltage. Also called rms voltage.
effective wavelength Wavelength in terms of measured frequency and effective propagation velocity.
effects processor In audio systems, a circuit that
produces various sound effects via digital signal
efficiency 1. The ratio of useful power or energy
output to total power or energy input to a device
or system. 2. The proportion of applied audiofrequency (AF) power that a loudspeaker converts
into acoustic energy. 3. See ELECTRICAL EFFICIENCY.
efficiency modulation A system of amplitude
modulation in which the efficiency of a radiofrequency (RF) power amplifier is varied at an audio-frequency (AF) rate.
efficiency of rectification For a rectifier, the ratio
of the direct-current (dc) output voltage to the
peak value of alternating-current (ac) input voltage. For percent efficiency, the ratio is multiplied
by 100.
efflorescence The giving up of water by a substance upon exposure to air. Some materials used
in electronics exhibit this property. Common efflorescent compounds are hydrated ferrous carbonate, ferrous sulfate, and sodium carbonate.
efflorescent material A material exhibiting efflorescence. Compare DELIQUESCENT MATERIAL.
E field 1. An electric field. 2. the electric-field component of an electromagnetic wave.
EFL Abbreviation of emitter-follower logic.
EHD Abbreviation of electrohydrodynamic(s).
EHP Abbreviation of effective horsepower.
E-H tee A waveguide junction in which E- and
H-plane tee junctions intersect the main waveguide at the same point. Also see WAVEGUIDE
E-H tuner An impedance-transforming E-H tee
with two arms that are terminated in tunable
plungers for critical adjustments. See WAVEGUIDE PLUNGER.
EHV Abbreviation of extra-h