Chapter 14.5 Dictionary of Audio Terms Jerry C. Whitaker, Editor-in-Chief 14.5.1 General Electronics Terms absolute delay The amount of time a signal is delayed. The delay may be expressed in time or number of pulse events. absolute zero The lowest temperature theoretically possible, –273.16°C. Absolute zero is equal to zero degrees Kelvin. absorption The transference of some or all of the energy contained in an electromagnetic wave to the substance or medium in which it is propagating or upon which it is incident. absorption auroral The loss of energy in a radio wave passing through an area affected by solar auroral activity. ac coupling A method of coupling one circuit to another through a capacitor or transformer so as to transmit the varying (ac) characteristics of the signal while blocking the static (dc) characteristics. ac/dc coupling Coupling between circuits that accommodates the passing of both ac and dc signals (may also be referred to as simply dc coupling). accelerated life test A special form of reliability testing performed by an equipment manufacturer. The unit under test is subjected to stresses that exceed those typically experienced in normal operation. The goal of an accelerated life test is to improve the reliability of products shipped by forcing latent failures in components to become evident before the unit leaves the factory. accelerating electrode The electrode that causes electrons emitted from an electron gun to accelerate in their journey to the screen of a cathode ray tube. accelerating voltage The voltage applied to an electrode that accelerates a beam of electrons or other charged particles. acceptable reliability level The maximum number of failures allowed per thousand operating hours of a given component or system. 14-89 14-90 Standards and Practices acceptance test The process of testing newly purchased equipment to ensure that it is fully compliant with contractual specifications. access The point at which entry is gained to a circuit or facility. acquisition time In a communication system, the amount of time required to attain synchronism. active Any device or circuit that introduces gain or uses a source of energy other than that inherent in the signal to perform its function. adapter A fitting or electrical connector that links equipment that cannot be connected directly. adaptive A device able to adjust or react to a condition or application, as an adaptive circuit. This term usually refers to filter circuits. adaptive system A general name for a system that is capable of reconfiguring itself to meet new requirements. adder A device whose output represents the sum of its inputs. adjacent channel interference Interference to communications caused by a transmitter operating on an adjacent radio channel. The sidebands of the transmitter mix with the carrier being received on the desired channel, resulting in noise. admittance A measure of how well alternating current flows in a conductor. It is the reciprocal of impedance and is expressed in siemens. The real part of admittance is conductance; the imaginary part is susceptance. AFC (automatic frequency control) A circuit that automatically keeps an oscillator on frequency by comparing the output of the oscillator with a standard frequency source or signal. air core An inductor with no magnetic material in its core. algorithm A prescribed finite set of well-defined rules or processes for the solution of a problem in a finite number of steps. alignment The adjustment of circuit components so that an entire system meets minimum performance values. For example, the stages in a radio are aligned to ensure proper reception. allocation The planned use of certain facilities and equipment to meet current, pending, and/or forecasted circuit- and carrier-system requirements. alternating current (ac) A continuously variable current, rising to a maximum in one direction, falling to zero, then reversing direction and rising to a maximum in the other direction, then falling to zero and repeating the cycle. Alternating current usually follows a sinusoidal growth and decay curve. Note that the correct usage of the term ac is lower case. alternator A generator that produces alternating current electric power. ambient electromagnetic environment The radiated or conducted electromagnetic signals and noise at a specific location and time. ambient level The magnitude of radiated or conducted electromagnetic signals and noise at a specific test location when equipment-under-test is not powered. Dictionary of Audio Terms 14-91 ambient temperature The temperature of the surrounding medium, typically air, that comes into contact with an apparatus. Ambient temperature may also refer simply to room temperature. American National Standards Institute (ANSI) A nonprofit organization that coordinates voluntary standards activities in the U.S. American Wire Gauge (AWG) The standard American method of classifying wire diameter. ammeter An instrument that measures and records the amount of current in amperes flowing in a circuit. amp (A) An abbreviation of the term ampere. ampacity A measure of the current carrying capacity of a power cable. Ampacity is determined by the maximum continuous-performance temperature of the insulation, by the heat generated in the cable (as a result of conductor and insulation losses), and by the heat-dissipating properties of the cable and its environment. ampere (amp) The standard unit of electric current. ampere per meter The standard unit of magnetic field strength. ampere-hour The energy that is consumed when a current of one ampere flows for a period of one hour. ampere-turns The product of the number of turns of a coil and the current in amperes flowing through the coil. amplification The process that results when the output of a circuit is an enlarged reproduction of the input signal. Amplifiers may be designed to provide amplification of voltage, current, or power, or a combination of these quantities. amplification factor In a vacuum tube, the ratio of the change in plate voltage to the change in grid voltage that causes a corresponding change in plate current. Amplification factor is expressed by the Greek letter µ (mu). amplifier (1—general) A device that receives an input signal and provides as an output a magnified replica of the input waveform. (2—audio) An amplifier designed to cover the normal audio frequency range (20 Hz to 20 kHz). (3—balanced) A circuit with two identical connected signal branches that operate in phase opposition, with input and output connections each balanced to ground. (4—bridging) An amplifying circuit featuring high input impedance to prevent loading of the source. (5—broadband) An amplifier capable of operating over a specified broad band of frequencies with acceptably small amplitude variations as a function of frequency. (6—buffer) An amplifier stage used to isolate a frequency-sensitive circuit from variations in the load presented by following stages. (7—linear) An amplifier in which the instantaneous output signal is a linear function of the corresponding input signal. (8—magnetic) An amplifier incorporating a control device dependent on magnetic saturation. A small dc signal applied to a control circuit triggers a large change in operating impedance and, hence, in the output of the circuit. (9—microphone) A circuit that amplifies the low level output from a microphone to make it sufficient to be used as an input signal to a power amplifier or another stage in a modulation circuit. Such a circuit is commonly known as a preamplifier. (10—push-pull) A balanced amplifier with two simi- 14-92 Standards and Practices lar amplifying units connected in phase opposition in order to cancel undesired harmonics and minimize distortion. (11—tuned radio frequency) An amplifier tuned to a particular radio frequency or band so that only selected frequencies are amplified. amplifier operating class (1—general) The operating point of an amplifying stage. The operating point, termed the operating class, determines the period during which current flows in the output. (2—class A) An amplifier in which output current flows during the whole of the input current cycle. (3—class AB) An amplifier in which the output current flows for more than half but less than the whole of the input cycle. (4—class B) An amplifier in which output current is cut off at zero input signal; a half-wave rectified output is produced. (5—class C) An amplifier in which output current flows for less than half the input cycle. (6—class D) An amplifier operating in a pulse-only mode. amplitude The magnitude of a signal in voltage or current, frequently expressed in terms of peak, peak-to-peak, or root-mean-square (RMS). The actual amplitude of a quantity at a particular instant often varies in a sinusoidal manner. amplitude distortion A distortion mechanism occurring in an amplifier or other device when the output amplitude is not a linear function of the input amplitude under specified conditions. amplitude equalizer A corrective network that is designed to modify the amplitude characteristics of a circuit or system over a desired frequency range. amplitude-versus-frequency distortion The distortion in a transmission system caused by the nonuniform attenuation or gain of the system with respect to frequency under specified conditions. analog carrier system A carrier system whose signal amplitude, frequency, or phase is varied continuously as a function of a modulating input. anode (1 — general) A positive pole or element. (2—vacuum tube) The outermost positive element in a vacuum tube, also called the plate. (3—battery) The positive element of a battery or cell. anodize The formation of a thin film of oxide on a metallic surface, usually to produce an insulating layer. antenna (1—general) A device used to transmit or receive a radio signal. An antenna is usually designed for a specified frequency range and serves to couple electromagnetic energy from a transmission line to and/or from the free space through which it travels. Directional antennas concentrate the energy in a particular horizontal or vertical direction. (2—aperiodic) An antenna that is not periodic or resonant at particular frequencies, and so can be used over a wide band of frequencies. (3—artificial) A device that behaves, so far as the transmitter is concerned, like a proper antenna, but does not radiate any power at radio frequencies. (4—broadband) An antenna that operates within specified performance limits over a wide band of frequencies, without requiring retuning for each individual frequency. (5—Cassegrain) A double reflecting antenna, often used for ground stations in satellite systems. (6—coaxial) A dipole antenna made by folding back on itself a quarter wavelength of the outer conductor of a coaxial line, leaving a quarter wavelength of the inner conductor exposed. (7—corner) An antenna within the angle formed by two plane-reflecting surfaces. (8—dipole) A center-fed antenna, one half-wavelength long. (9—direc- Dictionary of Audio Terms 14-93 tional) An antenna designed to receive or emit radiation more efficiently in a particular direction. (10—dummy) An artificial antenna, designed to accept power from the transmitter but not to radiate it. (11—ferrite) A common AM broadcast receive antenna that uses a small coil mounted on a short rod of ferrite material. (12—flat top) An antenna in which all the horizontal components are in the same horizontal plane. (13—folded dipole) A radiating device consisting of two ordinary half-wave dipoles joined at their outer ends and fed at the center of one of the dipoles. (14—horn reflector) A radiator in which the feed horn extends into a parabolic reflector, and the power is radiated through a window in the horn. (15—isotropic) A theoretical antenna in free space that transmits or receives with the same efficiency in all directions. (16—log-periodic) A broadband directional antenna incorporating an array of dipoles of different lengths, the length and spacing between dipoles increasing logarithmically away from the feeder element. (17—long wire) An antenna made up of one or more conductors in a straight line pointing in the required direction with a total length of several wavelengths at the operating frequency. (18—loop) An antenna consisting of one or more turns of wire in the same or parallel planes. (19—nested rhombic) An assembly of two rhombic antennas, one smaller than the other, so that the complete diamond-shaped antenna fits inside the area occupied by the larger unit. (20—omnidirectional) An antenna whose radiating or receiving properties are the same in all horizontal plane directions. (21—periodic) A resonant antenna designed for use at a particular frequency. (22—quarter-wave) A dipole antenna whose length is equal to one quarter of a wavelength at the operating frequency. (23—rhombic) A large diamond-shaped antenna, with sides of the diamond several wavelengths long. The rhombic antenna is fed at one of the corners, with directional efficiency in the direction of the diagonal. (24—series fed) A vertical antenna that is fed at its lower end. (25—shunt fed) A vertical antenna whose base is grounded, and is fed at a specified point above ground. The point at which the antenna is fed above ground determines the operating impedance. (26—steerable) An antenna so constructed that its major lobe may readily be changed in direction. (27—top-loaded) A vertical antenna capacitively loaded at its upper end, often by simple enlargement or the attachment of a disc or plate. (28—turnstile) An antenna with one or more tiers of horizontal dipoles, crossed at right angles to each other and with excitation of the dipoles in phase quadrature. (29—whip) An antenna constructed of a thin semiflexible metal rod or tube, fed at its base. (30—Yagi) A directional antenna constructed of a series of dipoles cut to specific lengths. Director elements are placed in front of the active dipole and reflector elements are placed behind the active element. antenna array A group of several antennas coupled together to yield a required degree of directivity. antenna beamwidth The angle between the half-power points (3 dB points) of the main lobe of the antenna pattern when referenced to the peak power point of the antenna pattern. Antenna beamwidth is measured in degrees and normally refers to the horizontal radiation pattern. antenna directivity factor The ratio of the power flux density in the desired direction to the average value of power flux density at crests in the antenna directivity pattern in the interference section. 14-94 Standards and Practices antenna factor A factor that, when applied to the voltage appearing at the terminals of measurement equipment, yields the electrical field strength at an antenna. The unit of antenna factor is volts per meter per measured volt. antenna gain The ratio of the power required at the input of a theoretically perfect omnidirectional reference antenna to the power supplied to the input of the given antenna to produce the same field at the same distance. When not specified otherwise, the figure expressing the gain of an antenna refers to the gain in the direction of the radiation main lobe. In services using scattering modes of propagation, the full gain of an antenna may not be realizable in practice and the apparent gain may vary with time. antenna gain-to-noise temperature For a satellite earth terminal receiving system, a figure of merit that equals G/T, where G is the gain in dB of the earth terminal antenna at the receive frequency, and T is the equivalent noise temperature of the receiving system in Kelvins. antenna matching The process of adjusting an antenna matching circuit (or the antenna itself) so that the input impedance of the antenna is equal to the characteristic impedance of the transmission line. antenna monitor A device used to measure the ratio and phase between the currents flowing in the towers of a directional AM broadcast station. antenna noise temperature The temperature of a resistor having an available noise power per unit bandwidth equal to that at the antenna output at a specified frequency. antenna pattern A diagram showing the efficiency of radiation in all directions from the antenna. antenna power rating The maximum continuous-wave power that can be applied to an antenna without degrading its performance. antenna preamplifier A small amplifier, usually mast-mounted, for amplifying weak signals to a level sufficient to compensate for down-lead losses. apparent power The product of the root-mean-square values of the voltage and current in an alternating-current circuit without a correction for the phase difference between the voltage and current. arc A sustained luminous discharge between two or more electrodes. arithmetic mean The sum of the values of several quantities divided by the number of quantities, also referred to as the average. armature winding The winding of an electrical machine, either a motor or generator, in which current is induced. array (1—antenna) An assembly of several directional antennas so placed and interconnected that directivity may be enhanced. (2—broadside) An antenna array whose elements are all in the same plane, producing a major lobe perpendicular to the plane. (3—colinear) An antenna array whose elements are in the same line, either horizontal or vertical. (4—endfire) An antenna array whose elements are in parallel rows, one behind the other, producing a major lobe perpendicular to the plane in which individual elements are placed. (5—linear) An antenna array whose elements are arranged end-to-end. (6—stacked) An antenna array whose elements are stacked, one above the other. Dictionary of Audio Terms 14-95 artificial line An assembly of resistors, inductors, and capacitors that simulates the electrical characteristics of a transmission line. assembly A manufactured part made by combining several other parts or subassemblies. assumed values A range of values, parameters, levels, and other elements assumed for a mathematical model, hypothetical circuit, or network, from which analysis, additional estimates, or calculations will be made. The range of values, while not measured, represents the best engineering judgment and is generally derived from values found or measured in real circuits or networks of the same generic type, and includes projected improvements. atmosphere The gaseous envelope surrounding the earth, composed largely of oxygen, carbon dioxide, and water vapor. The atmosphere is divided into four primary layers: troposphere, stratosphere, ionosphere, and exosphere. atmospheric noise Radio noise caused by natural atmospheric processes, such as lightning. attack time The time interval in seconds required for a device to respond to a control stimulus. attenuation The decrease in amplitude of an electrical signal traveling through a transmission medium caused by dielectric and conductor losses. attenuation coefficient The rate of decrease in the amplitude of an electrical signal caused by attenuation. The attenuation coefficient can be expressed in decibels or nepers per unit length. It may also be referred to as the attenuation constant. attenuation distortion The distortion caused by attenuation that varies over the frequency range of a signal. attenuation-limited operation The condition prevailing when the received signal amplitude (rather than distortion) limits overall system performance. attenuator A fixed or adjustable component that reduces the amplitude of an electrical signal without causing distortion. atto A prefix meaning one quintillionth. attraction The attractive force between two unlike magnetic poles (N/S) or electrically charged bodies (+/-). attributes The characteristics of equipment that aid planning and circuit design. automatic frequency control (AFC) A system designed to maintain the correct operating frequency of a receiver. Any drift in tuning results in the production of a control voltage, which is used to adjust the frequency of a local oscillator so as to minimize the tuning error. automatic gain control (AGC) An electronic circuit that compares the level of an incoming signal with a previously defined standard and automatically amplifies or attenuates the signal so it arrives at its destination at the correct level. autotransformer A transformer in which both the primary and secondary currents flow through one common part of the coil. auxiliary power An alternate source of electric power, serving as a back-up for the primary utility company ac power. 14-96 Standards and Practices availability A measure of the degree to which a system, subsystem, or equipment is operable and not in a stage of congestion or failure at any given point in time. avalanche effect The effect obtained when the electric field across a barrier region is sufficiently strong for electrons to collide with valence electrons, thereby releasing more electrons and giving a cumulative multiplication effect in a semiconductor. average life The mean value for a normal distribution of product or component lives, generally applied to mechanical failures resulting from “wear-out.” B back emf A voltage induced in the reverse direction when current flows through an inductance. Back emf is also known as counter-emf. back scattering A form of wave scattering in which at least one component of the scattered wave is deflected opposite to the direction of propagation of the incident wave. background noise The total system noise in the absence of information transmission, independent of the presence or absence of a signal. backscatter The deflection or reflection of radiant energy through angles greater than 90° with respect to the original angle of travel. backscatter range The maximum distance from which backscattered radiant energy can be measured. backup A circuit element or facility used to replace an element that has failed. backup supply A redundant power supply that takes over if the primary power supply fails. balance The process of equalizing the voltage, current, or other parameter between two or more circuits or systems. balanced A circuit having two sides (conductors) carrying voltages that are symmetrical about a common reference point, typically ground. balanced circuit A circuit whose two sides are electrically equal in all transmission respects. balanced line A transmission line consisting of two conductors in the presence of ground capable of being operated in such a way that when the voltages of the two conductors at all transverse planes are equal in magnitude and opposite in polarity with respect to ground, the currents in the two conductors are equal in magnitude and opposite in direction. balanced modulator A modulator that combines the information signal and the carrier so that the output contains the two sidebands without the carrier. balanced three-wire system A power distribution system using three conductors, one of which is balanced to have a potential midway between the potentials of the other two. balanced-to-ground The condition when the impedance to ground on one wire of a two-wire circuit is equal to the impedance to ground on the other wire. balun (balanced/unbalanced) A device used to connect balanced circuits with unbalanced circuits. band A range of frequencies between a specified upper and lower limit. Dictionary of Audio Terms 14-97 band elimination filter A filter having a single continuous attenuation band, with neither the upper nor lower cut-off frequencies being zero or infinite. A band elimination filter may also be referred to as a band-stop, notch, or band reject filter. bandpass filter A filter having a single continuous transmission band with neither the upper nor the lower cut-off frequencies being zero or infinite. A bandpass filter permits only a specific band of frequencies to pass; frequencies above or below are attenuated. bandwidth The range of signal frequencies that can be transmitted by a communications channel with a defined maximum loss or distortion. Bandwidth indicates the information-carrying capacity of a channel. bandwidth expansion ratio The ratio of the necessary bandwidth to the baseband bandwidth. bandwidth-limited operation The condition prevailing when the frequency spectrum or bandwidth, rather than the amplitude (or power) of the signal, is the limiting factor in communication capability. This condition is reached when the system distorts the shape of the waveform beyond tolerable limits. bank A group of similar items connected together in a specified manner and used in conjunction with one another. bare A wire conductor that is not enameled or enclosed in an insulating sheath. baseband The band of frequencies occupied by a signal before it modulates a carrier wave to form a transmitted radio or line signal. baseband channel A channel that carries a signal without modulation, in contrast to a passband channel. baseband signal The original form of a signal, unchanged by modulation. bath tub The shape of a typical graph of component failure rates: high during an initial period of operation, falling to an acceptable low level during the normal usage period, and then rising again as the components become time-expired. battery A group of several cells connected together to furnish current by conversion of chemical, thermal, solar, or nuclear energy into electrical energy. A single cell is itself sometimes also called a battery. bay A row or suite of racks on which transmission, switching, and/or processing equipment is mounted. Bel A unit of power measurement, named in honor of Alexander Graham Bell. The commonly used unit is one tenth of a Bel, or a decibel (dB). One Bel is defined as a tenfold increase in power. If an amplifier increases the power of a signal by 10 times, the power gain of the amplifier is equal to 1 Bel or 10 decibels (dB). If power is increased by 100 times, the power gain is 2 Bels or 20 decibels. bend A transition component between two elements of a transmission waveguide. bending radius The smallest bend that may be put into a cable under a stated pulling force. The bending radius is typically expressed in inches. 14-98 Standards and Practices bias A dc voltage difference applied between two elements of an active electronic device, such as a vacuum tube, transistor, or integrated circuit. Bias currents may or may not be drawn, depending on the device and circuit type. bidirectional An operational qualification which implies that the transmission of information occurs in both directions. bifilar winding A type of winding in which two insulated wires are placed side by side. In some components, bifilar winding is used to produce balanced circuits. bipolar A signal that contains both positive-going and negative-going amplitude components. A bipolar signal may also contain a zero amplitude state. bleeder A high resistance connected in parallel with one or more filter capacitors in a high voltage dc system. If the power supply load is disconnected, the capacitors discharge through the bleeder. block diagram An overview diagram that uses geometric figures to represent the principal divisions or sections of a circuit, and lines and arrows to show the path of a signal, or to show program functionalities. It is not a schematic, which provides greater detail. blocking capacitor A capacitor included in a circuit to stop the passage of direct current. BNC An abbreviation for bayonet Neill-Concelman, a type of cable connector used extensively in RF applications (named for its inventor). Boltzmann's constant 1.38 × 10–23 joules. bridge A type of network circuit used to match different circuits to each other, ensuring minimum transmission impairment. bridging The shunting or paralleling of one circuit with another. broadband The quality of a communications link having essentially uniform response over a given range of frequencies. A communications link is said to be broadband if it offers no perceptible degradation to the signal being transported. buffer A circuit or component that isolates one electrical circuit from another. burn-in The operation of a device, sometimes under extreme conditions, to stabilize its characteristics and identify latent component failures before bringing the device into normal service. bus A central conductor for the primary signal path. The term bus may also refer to a signal path to which a number of inputs may be connected for feed to one or more outputs. busbar A main dc power bus. bypass capacitor A capacitor that provides a signal path that effectively shunts or bypasses other components. bypass relay A switch used to bypass the normal electrical route of a signal or current in the event of power, signal, or equipment failure. C cable An electrically and/or optically conductive interconnecting device. Dictionary of Audio Terms 14-99 cable loss Signal loss caused by passing a signal through a coaxial cable. Losses are the result of resistance, capacitance, and inductance in the cable. cable splice The connection of two pieces of cable by joining them mechanically and closing the joint with a weather-tight case or sleeve. cabling The wiring used to interconnect electronic equipment. calibrate The process of checking, and adjusting if necessary, a test instrument against one known to be set correctly. calibration The process of identifying and measuring errors in instruments and/or procedures. capacitance The property of a device or component that enables it to store energy in an electrostatic field and to release it later. A capacitor consists of two conductors separated by an insulating material. When the conductors have a voltage difference between them, a charge will be stored in the electrostatic field between the conductors. capacitor A device that stores electrical energy. A capacitor allows the apparent flow of alternating current, while blocking the flow of direct current. The degree to which the device permits ac current flow depends on the frequency of the signal and the size of the capacitor. Capacitors are used in filters, delay-line components, couplers, frequency selectors, timing elements, voltage transient suppression, and other applications. carrier A single frequency wave that, prior to transmission, is modulated by another wave containing information. A carrier may be modulated by manipulating its amplitude and/or frequency in direct relation to one or more applied signals. carrier frequency The frequency of an unmodulated oscillator or transmitter. Also, the average frequency of a transmitter when a signal is frequency modulated by a symmetrical signal. cascade connection A tandem arrangement of two or more similar component devices or circuits, with the output of one connected to the input of the next. cascaded An arrangement of two or more circuits in which the output of one circuit is connected to the input of the next circuit. cathode ray tube (CRT) A vacuum tube device, usually glass, that is narrow at one end and widens at the other to create a surface onto which images can be projected. The narrow end contains the necessary circuits to generate and focus an electron beam on the luminescent screen at the other end. CRTs are used to display pictures in TV receivers, video monitors, oscilloscopes, computers, and other systems. cell An elementary unit of communication, of power supply, or of equipment. Celsius A temperature measurement scale, expressed in degrees C, in which water freezes at 0°C and boils at 100°C. To convert to degrees Fahrenheit, multiply by 0.555 and add 32. To convert to Kelvins add 273 (approximately). center frequency In frequency modulation, the resting frequency or initial frequency of the carrier before modulation. center tap A connection made at the electrical center of a coil. channel The smallest subdivision of a circuit that provides a single type of communication service. 14-100 Standards and Practices channel decoder A device that converts an incoming modulated signal on a given channel back into the source-encoded signal. channel encoder A device that takes a given signal and converts it into a form suitable for transmission over the communications channel. channel noise level The ratio of the channel noise at any point in a transmission system to some arbitrary amount of circuit noise chosen as a reference. This ratio is usually expressed in decibels above reference noise, abbreviated dBrn. channel reliability The percent of time a channel is available for use in a specific direction during a specified period. channelization The allocation of communication circuits to channels and the forming of these channels into groups for higher order multiplexing. characteristic The property of a circuit or component. characteristic impedance The impedance of a transmission line, as measured at the driving point, if the line were of infinite length. In such a line, there would be no standing waves. The characteristic impedance may also be referred to as the surge impedance. charge The process of replenishing or replacing the electrical charge in a secondary cell or storage battery. charger A device used to recharge a battery. Types of charging include: (1) constant voltage charge, (2) equalizing charge, and (3) trickle charge. chassis ground A connection to the metal frame of an electronic system that holds the components in a place. The chassis ground connection serves as the ground return or electrical common for the system. circuit Any closed path through which an electrical current can flow. In a parallel circuit, components are connected between common inputs and outputs such that all paths are parallel to each other. The same voltage appears across all paths. In a series circuit, the same current flows through all components. circuit noise level The ratio of the circuit noise at some given point in a transmission system to an established reference, usually expressed in decibels above the reference. circuit reliability The percentage of time a circuit is available to the user during a specified period of scheduled availability. circular mil The measurement unit of the cross-sectional area of a circular conductor. A circular mil is the area of a circle whose diameter is one mil, or 0.001 inch. clear channel A transmission path wherein the full bandwidth is available to the user, with no portions of the channel used for control, framing, or signaling. Can also refer to a classification of AM broadcast station. clipper A limiting circuit which ensures that a specified output level is not exceeded by restricting the output waveform to a maximum peak amplitude. clipping The distortion of a signal caused by removing a portion of the waveform through restriction of the amplitude of the signal by a circuit or device. Dictionary of Audio Terms 14-101 coax A short-hand expression for coaxial cable, which is used to transport high-frequency signals. coaxial cable A transmission line consisting of an inner conductor surrounded first by an insulating material and then by an outer conductor, either solid or braided.The mechanical dimensions of the cable determine its characteristic impedance. coherence The correlation between the phases of two or more waves. coherent The condition characterized by a fixed phase relationship among points on an electromagnetic wave. coherent pulse The condition in which a fixed phase relationship is maintained between consecutive pulses during pulse transmission. cold joint A soldered connection that was inadequately heated, with the result that the wire is held in place by rosin flux, not solder. A cold joint is sometimes referred to as a dry joint. comb filter An electrical filter circuit that passes a series of frequencies and rejects the frequencies in between, producing a frequency response similar to the teeth of a comb. common A point that acts as a reference for circuits, often equal in potential to the local ground. common mode Signals identical with respect to amplitude, frequency, and phase that are applied to both terminals of a cable and/or both the input and reference of an amplifier. common return A return path that is common to two or more circuits, and returns currents to their source or to ground. common return offset The dc common return potential difference of a line. communications system A collection of individual communications networks, transmission systems, relay stations, tributary stations, and terminal equipment capable of interconnection and interoperation to form an integral whole. The individual components must serve a common purpose, be technically compatible, employ common procedures, respond to some form of control, and, in general, operate in unison. commutation A successive switching process carried out by a commutator. commutator A circular assembly of contacts, insulated one from another, each leading to a different portion of the circuit or machine. compatibility The ability of diverse systems to exchange necessary information at appropriate levels of command directly and in usable form. Communications equipment items are compatible if signals can be exchanged between them without the addition of buffering or translation for the specific purpose of achieving workable interface connections, and if the equipment or systems being interconnected possess comparable performance characteristics, including the suppression of undesired radiation. complex wave A waveform consisting of two or more sinewave components. At any instant of time, a complex wave is the algebraic sum of all its sinewave components. compliance For mechanical systems, a property which is the reciprocal of stiffness. component An assembly, or part thereof, that is essential to the operation of some larger circuit or system. A component is an immediate subdivision of the assembly to which it belongs. 14-102 Standards and Practices COMSAT The Communications Satellite Corporation, an organization established by an act of Congress in 1962. COMSAT launches and operates the international satellites for the INTELSAT consortium of countries. concentricity A measure of the deviation of the center conductor position relative to its ideal location in the exact center of the dielectric cross-section of a coaxial cable. conditioning The adjustment of a channel in order to provide the appropriate transmission characteristics needed for data or other special services. conditioning equipment The equipment used to match transmission levels and impedances, and to provide equalization between facilities. conductance A measure of the capability of a material to conduct electricity. It is the reciprocal of resistance (ohm) and is expressed in siemens. (Formerly expressed as mho.) conducted emission An electromagnetic energy propagated along a conductor. conduction The transfer of energy through a medium, such as the conduction of electricity by a wire, or of heat by a metallic frame. conduction band A partially filled or empty atomic energy band in which electrons are free to move easily, allowing the material to carry an electric current. conductivity The conductance per unit length. conductor Any material that is capable of carrying an electric current. configuration A relative arrangement of parts. connection A point at which a junction of two or more conductors is made. connector A device mounted on the end of a wire or fiber optic cable that mates to a similar device on a specific piece of equipment or another cable. constant-current source A source with infinitely high output impedance so that output current is independent of voltage, for a specified range of output voltages. constant-voltage charge A method of charging a secondary cell or storage battery during which the terminal voltage is kept at a constant value. constant-voltage source A source with low, ideally zero, internal impedance, so that voltage will remain constant, independent of current supplied. contact The points that are brought together or separated to complete or break an electrical circuit. contact bounce The rebound of a contact, which temporarily opens the circuit after its initial make. contact form The configuration of a contact assembly on a relay. Many different configurations are possible from simple single-make contacts to complex arrangements involving breaks and makes. contact noise A noise resulting from current flow through an electrical contact that has a rapidly varying resistance, as when the contacts are corroded or dirty. contact resistance The resistance at the surface when two conductors make contact. Dictionary of Audio Terms 14-103 continuity A continuous path for the flow of current in an electrical circuit. continuous wave An electromagnetic signal in which successive oscillations of the waves are identical. control The supervision that an operator or device exercises over a circuit or system. control grid The grid in an electron tube that controls the flow of current from the cathode to the anode. convention A generally acceptable symbol, sign, or practice in a given industry. Coordinated Universal Time (UTC) The time scale, maintained by the BIH (Bureau International de l'Heure) that forms the basis of a coordinated dissemination of standard frequencies and time signals. copper loss The loss resulting from the heating effect of current. corona A bluish luminous discharge resulting from ionization of the air near a conductor carrying a voltage gradient above a certain critical level. corrective maintenance The necessary tests, measurements, and adjustments required to remove or correct a fault. cosmic noise The random noise originating outside the earth's atmosphere. coulomb The standard unit of electric quantity or charge. One coulomb is equal to the quantity of electricity transported in 1 second by a current of 1 ampere. Coulomb's Law The attraction and repulsion of electric charges act on a line between them. The charges are inversely proportional to the square of the distance between them, and proportional to the product of their magnitudes. (Named for the French physicist Charles-Augustine de Coulomb, 1736–1806.) counter-electromotive force The effective electromotive force within a system that opposes the passage of current in a specified direction. couple The process of linking two circuits by inductance, so that energy is transferred from one circuit to another. coupled mode The selection of either ac or dc coupling. coupling The relationship between two components that enables the transfer of energy between them. Included are direct coupling through a direct electrical connection, such as a wire; capacitive coupling through the capacitance formed by two adjacent conductors; and inductive coupling in which energy is transferred through a magnetic field. Capacitive coupling is also called electrostatic coupling. Inductive coupling is often referred to as electromagnetic coupling. coupling coefficient A measure of the electrical coupling that exists between two circuits. The coupling coefficient is equal to the ratio of the mutual impedance to the square root of the product of the self impedances of the coupled circuits. cross coupling The coupling of a signal from one channel, circuit, or conductor to another, where it becomes an undesired signal. 14-104 Standards and Practices crossover distortion A distortion that results in an amplifier when an irregularity is introduced into the signal as it crosses through a zero reference point. If an amplifier is properly designed and biased, the upper half cycle and lower half cycle of the signal coincide at the zero crossover reference. crossover frequency The frequency at which output signals pass from one channel to the other in a crossover network. At the crossover frequency itself, the outputs to each side are equal. crossover network A type of filter that divides an incoming signal into two or more outputs, with higher frequencies directed to one output, and lower frequencies to another. crosstalk Undesired transmission of signals from one circuit into another circuit in the same system. Crosstalk is usually caused by unintentional capacitive (ac) coupling. crosstalk coupling The ratio of the power in a disturbing circuit to the induced power in the disturbed circuit, observed at a particular point under specified conditions. Crosstalk coupling is typically expressed in dB. crowbar A short-circuit or low resistance path placed across the input to a circuit, usually for protective purposes. CRT (cathode ray tube) A vacuum tube device that produces light when energized by the electron beam generated inside the tube. A CRT includes an electron gun, deflection mechanism, and phosphor-covered faceplate. crystal A solidified form of a substance that has atoms and molecules arranged in a symmetrical pattern. crystal filter A filter that uses piezoelectric crystals to create resonant or antiresonant circuits. crystal oscillator An oscillator using a piezoelectric crystal as the tuned circuit that controls the resonant frequency. crystal-controlled oscillator An oscillator in which a piezoelectric-effect crystal is coupled to a tuned oscillator circuit in such a way that the crystal pulls the oscillator frequency to its own natural frequency and does not allow frequency drift. current (1—general) A general term for the transfer of electricity, or the movement of electrons or holes. (2—alternating) An electric current that is constantly varying in amplitude and periodically reversing direction. (3—average) The arithmetic mean of the instantaneous values of current, averaged over one complete half cycle. (4—charging) The current that flows in to charge a capacitor when it is first connected to a source of electric potential. (5—direct) Electric current that flows in one direction only. (6—eddy) A wasteful current that flows in the core of a transformer and produces heat. Eddy currents are largely eliminated through the use of laminated cores. (7—effective) The ac current that will produce the same effective heat in a resistor as is produced by dc. If the ac is sinusoidal, the effective current value is 0.707 times the peak ac value. (8—fault) The current that flows between conductors or to ground during a fault condition. (9—ground fault) A fault current that flows to ground. (10—ground return) A current that returns through the earth. (11—lagging) A phenomenon observed in an inductive circuit where alternating current lags behind the voltage that produces it. (12—leading) A phenomenon observed in a capacitive circuit where alternating current leads the voltage that produces it. (13—magnetizing) The current in a transformer primary winding that is just sufficient to magnetize the core and offset Dictionary of Audio Terms 14-105 iron losses. (14—neutral) The current that flows in the neutral conductor of an unbalanced polyphase power circuit. If correctly balanced, the neutral would carry no net current. (15—peak) The maximum value reached by a varying current during one cycle. (16— pick-up) The minimum current at which a relay just begins to operate. (17—plate) The anode current of an electron tube. (18—residual) The vector sum of the currents in the phase wires of an unbalanced polyphase power circuit. (19—space) The total current flowing through an electron tube. current amplifier A low output impedance amplifier capable of providing high current output. current probe A sensor, clamped around an electrical conductor, in which an induced current is developed from the magnetic field surrounding the conductor. For measurements, the current probe is connected to a suitable test instrument. current transformer A transformer-type of instrument in which the primary carries the current to be measured and the secondary is in series with a low current ammeter. A current transformer is used to measure high values of alternating current. current-carrying capacity A measure of the maximum current that can be carried continuously without damage to components or devices in a circuit. cut-off frequency The frequency above or below which the output current in a circuit is reduced to a specified level. cycle The interval of time or space required for a periodic signal to complete one period. cycles per second The standard unit of frequency, expressed in Hertz (one cycle per second). D damped oscillation An oscillation exhibiting a progressive diminution of amplitude with time. damping The dissipation and resultant reduction of any type of energy, such as electromagnetic waves. dB (decibel) A measure of voltage, current, or power gain equal to 0.1 Bel. Decibels are given by the equations 20 log Vout /Vin , 20 log Iout /Iin , or 10 log Pout /Pin. dBk A measure of power relative to 1 kilowatt. 0 dBk equals 1 kW. dBm (decibels above 1 milliwatt) A logarithmic measure of power with respect to a reference power of one milliwatt. dBmv A measure of voltage gain relative to 1 millivolt at 75 ohms. dBr The power difference expressed in dB between any point and a reference point selected as the zero relative transmission level point. A power expressed in dBr does not specify the absolute power; it is a relative measurement only. dBu A term that reflects comparison between a measured value of voltage and a reference value of 0.775 V, expressed under conditions in which the impedance at the point of measurement (and of the reference source) are not considered. dbV A measure of voltage gain relative to 1 V. dBW A measure of power relative to 1 watt. 0 dBW equals 1 W. 14-106 Standards and Practices dc An abbreviation for direct current. Note that the preferred usage of the term dc is lower case. dc amplifier A circuit capable of amplifying dc and slowly varying alternating current signals. dc component The portion of a signal that consists of direct current. This term may also refer to the average value of a signal. dc coupled A connection configured so that both the signal (ac component) and the constant voltage on which it is riding (dc component) are passed from one stage to the next. dc coupling A method of coupling one circuit to another so as to transmit the static (dc) characteristics of the signal as well as the varying (ac) characteristics. Any dc offset present on the input signal is maintained and will be present in the output. dc offset The amount that the dc component of a given signal has shifted from its correct level. dc signal bounce Overshoot of the proper dc voltage level resulting from multiple ac couplings in a signal path. de-energized A system from which sources of power have been disconnected. deca A prefix meaning ten. decay The reduction in amplitude of a signal on an exponential basis. decay time The time required for a signal to fall to a certain fraction of its original value. decibel (dB) One tenth of a Bel. The decibel is a logarithmic measure of the ratio between two powers. decode The process of recovering information from a signal into which the information has been encoded. decoder A device capable of deciphering encoded signals. A decoder interprets input instructions and initiates the appropriate control operations as a result. decoupling The reduction or removal of undesired coupling between two circuits or stages. deemphasis The reduction of the high-frequency components of a received signal to reverse the preemphasis that was placed on them to overcome attenuation and noise in the transmission process. defect An error made during initial planning that is normally detected and corrected during the development phase. Note that a fault is an error that occurs in an in-service system. deflection The control placed on electron direction and motion in CRTs and other vacuum tube devices by varying the strengths of electrostatic (electrical) or electromagnetic fields. degradation In susceptibility testing, any undesirable change in the operational performance of a test specimen. This term does not necessarily mean malfunction or catastrophic failure. degradation failure A failure that results from a gradual change in performance characteristics of a system or part with time. delay The amount of time by which a signal is delayed or an event is retarded. delay circuit A circuit designed to delay a signal passing through it by a specified amount. Dictionary of Audio Terms 14-107 delay distortion The distortion resulting from the difference in phase delays at two frequencies of interest. delay equalizer A network that adjusts the velocity of propagation of the frequency components of a complex signal to counteract the delay distortion characteristics of a transmission channel. delay line A transmission network that increases the propagation time of a signal traveling through it. delta connection A common method of joining together a three-phase power supply, with each phase across a different pair of the three wires used. delta-connected system A 3-phase power distribution system where a single-phase output can be derived from each of the adjacent pairs of an equilateral triangle formed by the service drop transformer secondary windings. demodulator Any device that recovers the original signal after it has modulated a high-frequency carrier. The output from the unit may be in baseband composite form. demultiplexer (demux) A device used to separate two or more signals that were previously combined by a compatible multiplexer and are transmitted over a single channel. derating factor An operating safety margin provided for a component or system to ensure reliable performance. A derating allowance also is typically provided for operation under extreme environmental conditions, or under stringent reliability requirements. desiccant A drying agent used for drying out cable splices or sensitive equipment. design A layout of all the necessary equipment and facilities required to make a special circuit, piece of equipment, or system work. design objective The desired electrical or mechanical performance characteristic for electronic circuits and equipment. detection The rectification process that results in the modulating signal being separated from a modulated wave. detectivity The reciprocal of noise equivalent power. detector A device that converts one type of energy into another. device A functional circuit, component, or network unit, such as a vacuum tube or transistor. dewpoint The temperature at which moisture will condense out. diagnosis The process of locating errors in software, or equipment faults in hardware. diagnostic routine A software program designed to trace errors in software, locate hardware faults, or identify the cause of a breakdown. dielectric An insulating material that separates the elements of various components, including capacitors and transmission lines. Dielectric materials include air, plastic, mica, ceramic, and Teflon. A dielectric material must be an insulator. (Teflon is a registered trademark of Du Pont.) 14-108 Standards and Practices dielectric constant The ratio of the capacitance of a capacitor with a certain dielectric material to the capacitance with a vacuum as the dielectric. The dielectric constant is considered a measure of the capability of a dielectric material to store an electrostatic charge. dielectric strength The potential gradient at which electrical breakdown occurs. differential amplifier An input circuit that rejects voltages that are the same at both input terminals but amplifies any voltage difference between the inputs. Use of a differential amplifier causes any signal present on both terminals, such as common mode hum, to cancel itself. differential dc The maximum dc voltage that can be applied between the differential inputs of an amplifier while maintaining linear operation. differential gain The difference in output amplitude (expressed in percent or dB) of a small high frequency sinewave signal at two stated levels of a low frequency signal on which it is superimposed. differential phase The difference in output phase of a small high frequency sinewave signal at two stated levels of a low frequency signal on which it is superimposed. differential-mode interference An interference source that causes a change in potential of one side of a signal transmission path relative to the other side. diffuse reflection The scattering effect that occurs when light, radio, or sound waves strike a rough surface. diffusion The spreading or scattering of a wave, such as a radio wave. diode A semiconductor or vacuum tube with two electrodes that passes electric current in one direction only. Diodes are used in rectifiers, gates, modulators, and detectors. direct coupling A coupling method between stages that permits dc current to flow between the stages. direct current An electrical signal in which the direction of current flow remains constant. discharge The conversion of stored energy, as in a battery or capacitor, into an electric current. discontinuity An abrupt nonuniform point of change in a transmission circuit that causes a disruption of normal operation. discrete An individual circuit component. discrete component A separately contained circuit element with its own external connections. discriminator A device or circuit whose output amplitude and polarity vary according to how much the input signal varies from a standard or from another signal. A discriminator can be used to recover the modulating waveform in a frequency modulated signal. dish An antenna system consisting of a parabolic shaped reflector with a signal feed element at the focal point. Dish antennas commonly are used for transmission and reception from microwave stations and communications satellites. dispersion The wavelength dependence of a parameter. display The representation of text and images on a cathode-ray tube, an array of light-emitting diodes, a liquid-crystal readout, or another similar device. Dictionary of Audio Terms 14-109 display device An output unit that provides a visual representation of data. distortion The difference between the wave shape of an original signal and the signal after it has traversed a transmission circuit. distortion-limited operation The condition prevailing when the shape of the signal, rather than the amplitude (or power), is the limiting factor in communication capability. This condition is reached when the system distorts the shape of the waveform beyond tolerable limits. For linear systems, distortion-limited operation is equivalent to bandwidth-limited operation. disturbance The interference with normal conditions and communications by some external energy source. disturbance current The unwanted current of any irregular phenomenon associated with transmission that tends to limit or interfere with the interchange of information. disturbance power The unwanted power of any irregular phenomenon associated with transmission that tends to limit or interfere with the interchange of information. disturbance voltage The unwanted voltage of any irregular phenomenon associated with transmission that tends to limit or interfere with the interchange of information. diversity receiver A receiver using two antennas connected through circuitry that senses which antenna is receiving the stronger signal. Electronic gating permits the stronger source to be routed to the receiving system. documentation A written description of a program. Documentation can be considered as any record that has permanence and can be read by humans or machines. down-lead A lead-in wire from an antenna to a receiver. downlink The portion of a communication link used for transmission of signals from a satellite or airborne platform to a surface terminal. downstream A specified signal modification occurring after other given devices in a signal path. downtime The time during which equipment is not capable of doing useful work because of malfunction. This does not include preventive maintenance time. In other words, downtime is measured from the occurrence of a malfunction to the correction of that malfunction. drift A slow change in a nominally constant signal characteristic, such as frequency. drift-space The area in a klystron tube in which electrons drift at their entering velocities and form electron bunches. drive The input signal to a circuit, particularly to an amplifier. driver An electronic circuit that supplies an isolated output to drive the input of another circuit. drop-out value The value of current or voltage at which a relay will cease to be operated. dropout The momentary loss of a signal. dropping resistor A resistor designed to carry current that will make a required voltage available. duplex separation The frequency spacing required in a communications system between the forward and return channels to maintain interference at an acceptably low level. 14-110 Standards and Practices duplex signaling A configuration permitting signaling in both transmission directions simultaneously. duty cycle The ratio of operating time to total elapsed time of a device that operates intermittently, expressed in percent. dynamic A situation in which the operating parameters and/or requirements of a given system are continually changing. dynamic range The maximum range or extremes in amplitude, from the lowest to the highest (noise floor to system clipping), that a system is capable of reproducing. The dynamic range is expressed in dB against a reference level. dynamo A rotating machine, normally a dc generator. dynamotor A rotating machine used to convert dc into ac. E earth A large conducting body with no electrical potential, also called ground. earth capacitance The capacitance between a given circuit or component and a point at ground potential. earth current A current that flows to earth/ground, especially one that follows from a fault in the system. Earth current may also refer to a current that flows in the earth, resulting from ionospheric disturbances, lightning, or faults on power lines. earth fault A fault that occurs when a conductor is accidentally grounded/earthed, or when the resistance to earth of an insulator falls below a specified value. earth ground A large conducting body that represents zero level in the scale of electrical potential. An earth ground is a connection made either accidentally or by design between a conductor and earth. earth potential The potential taken to be the arbitrary zero in a scale of electric potential. effective ground A connection to ground through a medium of sufficiently low impedance and adequate current-carrying capacity to prevent the buildup of voltages that might be hazardous to equipment or personnel. effective resistance The increased resistance of a conductor to an alternating current resulting from the skin effect, relative to the direct-current resistance of the conductor. Higher frequencies tend to travel only on the outer skin of the conductor, whereas dc flows uniformly through the entire area. efficiency The useful power output of an electrical device or circuit divided by the total power input, expressed in percent. electric Any device or circuit that produces, operates on, transmits, or uses electricity. electric charge An excess of either electrons or protons within a given space or material. electric field strength The magnitude, measured in volts per meter, of the electric field in an electromagnetic wave. Dictionary of Audio Terms 14-111 electric flux The amount of electric charge, measured in coulombs, across a dielectric of specified area. Electric flux may also refer simply to electric lines of force. electricity An energy force derived from the movement of negative and positive electric charges. electrode An electrical terminal that emits, collects, or controls an electric current. electrolysis A chemical change induced in a substance resulting from the passage of electric current through an electrolyte. electrolyte A nonmetallic conductor of electricity in which current is carried by the physical movement of ions. electromagnet An iron or steel core surrounded by a wire coil. The core becomes magnetized when current flows through the coil but loses its magnetism when the current flow is stopped. electromagnetic compatibility The capability of electronic equipment or systems to operate in a specific electromagnetic environment, at designated levels of efficiency and within a defined margin of safety, without interfering with itself or other systems. electromagnetic field The electric and magnetic fields associated with radio and light waves. electromagnetic induction An electromotive force created with a conductor by the relative motion between the conductor and a nearby magnetic field. electromagnetism The study of phenomena associated with varying magnetic fields, electromagnetic radiation, and moving electric charges. electromotive force (EMF) An electrical potential, measured in volts, that can produce the movement of electrical charges. electron A stable elementary particle with a negative charge that is mainly responsible for electrical conduction. Electrons move when under the influence of an electric field. This movement constitutes an electric current. electron beam A stream of emitted electrons, usually in a vacuum. electron gun A hot cathode that produces a finely focused stream of fast electrons, which are necessary for the operation of a vacuum tube, such as a cathode ray tube. The gun is made up of a hot cathode electron source, a control grid, accelerating anodes, and (usually) focusing electrodes. electron lens A device used for focusing an electron beam in a cathode ray tube. Such focusing can be accomplished by either magnetic forces, in which external coils are used to create the proper magnetic field within the tube, or electrostatic forces, where metallic plates within the tube are charged electrically in such a way as to control the movement of electrons in the beam. electron volt The energy acquired by an electron in passing through a potential difference of one volt in a vacuum. electronic A description of devices (or systems) that are dependent on the flow of electrons in electron tubes, semiconductors, and other devices, and not solely on electron flow in ordinary wires, inductors, capacitors, and similar passive components. 14-112 Standards and Practices Electronic Industries Association (EIA) A trade organization, based in Washington, DC, representing the manufacturers of electronic systems and parts, including communications systems. The association develops standards for electronic components and systems. electronic switch A transistor, semiconductor diode, or a vacuum tube used as an on/off switch in an electrical circuit. Electronic switches can be controlled manually, by other circuits, or by computers. electronics The field of science and engineering that deals with electron devices and their utilization. electroplate The process of coating a given material with a deposit of metal by electrolytic action. electrostatic The condition pertaining to electric charges that are at rest. electrostatic field The space in which there is electric stress produced by static electric charges. electrostatic induction The process of inducing static electric charges on a body by bringing it near other bodies that carry high electrostatic charges. element A substance that consists of atoms of the same atomic number. Elements are the basic units in all chemical changes other than those in which atomic changes, such as fusion and fission, are involved. EMI (electromagnetic interference) Undesirable electromagnetic waves that are radiated unintentionally from an electronic circuit or device into other circuits or devices, disrupting their operation. emission (1—radiation) The radiation produced, or the production of radiation by a radio transmitting system. The emission is considered to be a single emission if the modulating signal and other characteristics are the same for every transmitter of the radio transmitting system and the spacing between antennas is not more than a few wavelengths. (2—cathode) The release of electrons from the cathode of a vacuum tube. (3—parasitic) A spurious radio frequency emission unintentionally generated at frequencies that are independent of the carrier frequency being amplified or modulated. (4—secondary) In an electron tube, emission of electrons by a plate or grid because of bombardment by primary emission electrons from the cathode of the tube. (5—spurious) An emission outside the radio frequency band authorized for a transmitter. (6—thermonic) An emission from a cathode resulting from high temperature. emphasis The intentional alteration of the frequency-amplitude characteristics of a signal to reduce the adverse effects of noise in a communication system. empirical A conclusion not based on pure theory, but on practical and experimental work. emulation The use of one system to imitate the capabilities of another system. enable To prepare a circuit for operation or to allow an item to function. enabling signal A signal that permits the occurrence of a specified event. encode The conversion of information from one form into another to obtain characteristics required by a transmission or storage system. Dictionary of Audio Terms 14-113 encoder A device that processes one or more input signals into a specified form for transmission and/or storage. energized The condition when a circuit is switched on, or powered up. energy spectral density A frequency-domain description of the energy in each of the frequency components of a pulse. envelope The boundary of the family of curves obtained by varying a parameter of a wave. envelope delay The difference in absolute delay between the fastest and slowest propagating frequencies within a specified bandwidth. envelope delay distortion The maximum difference or deviation of the envelope-delay characteristic between any two specified frequencies. envelope detection A demodulation process that senses the shape of the modulated RF envelope. A diode detector is one type of envelop detection device. environmental An equipment specification category relating to temperature and humidity. EQ (equalization) network A network connected to a circuit to correct or control its transmission frequency characteristics. equalization (EQ) The reduction of frequency distortion and/or phase distortion of a circuit through the introduction of one or more networks to compensate for the difference in attenuation, time delay, or both, at the various frequencies in the transmission band. equalize The process of inserting in a line a network with complementary transmission characteristics to those of the line, so that when the loss or delay in the line and that in the equalizer are combined, the overall loss or delay is approximately equal at all frequencies. equalizer A network that corrects the transmission-frequency characteristics of a circuit to allow it to transmit selected frequencies in a uniform manner. equatorial orbit The plane of a satellite orbit which coincides with that of the equator of the primary body. equipment A general term for electrical apparatus and hardware, switching systems, and transmission components. equipment failure The condition when a hardware fault stops the successful completion of a task. equipment ground A protective ground consisting of a conducting path to ground of noncurrent carrying metal parts. equivalent circuit A simplified network that emulates the characteristics of the real circuit it replaces. An equivalent circuit is typically used for mathematical analysis. equivalent noise resistance A quantitative representation in resistance units of the spectral density of a noise voltage generator at a specified frequency. error A collective term that includes all types of inconsistencies, transmission deviations, and control failures. excitation The current that energizes field coils in a generator. 14-114 Standards and Practices expandor A device with a nonlinear gain characteristic that acts to increase the gain more on larger input signals than it does on smaller input signals. extremely high frequency (EHF) The band of microwave frequencies between the limits of 30 GHz and 300 GHz (wavelengths between 1 cm and 1 mm). extremely low frequency The radio signals with operating frequencies below 300 Hz (wavelengths longer than 1000 km). F fail-safe operation A type of control architecture for a system that prevents improper functioning in the event of circuit or operator failure. failure A detected cessation of ability to perform a specified function or functions within previously established limits. A failure is beyond adjustment by the operator by means of controls normally accessible during routine operation of the system. (This requires that measurable limits be established to define “satisfactory performance”.) failure effect The result of the malfunction or failure of a device or component. failure in time (FIT) A unit value that indicates the reliability of a component or device. One failure in time corresponds to a failure rate of 10–9 per hour. failure mode and effects analysis (FMEA) An iterative documented process performed to identify basic faults at the component level and determine their effects at higher levels of assembly. failure rate The ratio of the number of actual failures to the number of times each item has been subjected to a set of specified stress conditions. fall time The length of time during which a pulse decreases from 90 percent to 10 percent of its maximum amplitude. farad The standard unit of capacitance equal to the value of a capacitor with a potential of one volt between its plates when the charge on one plate is one coulomb and there is an equal and opposite charge on the other plate. The farad is a large value and is more commonly expressed in microfarads or picofarads. The farad is named for the English chemist and physicist Michael Faraday (179–1867). fast frequency shift keying (FFSK) A system of digital modulation where the digits are represented by different frequencies that are related to the baud rate, and where transitions occur at the zero crossings. fatigue The reduction in strength of a metal caused by the formation of crystals resulting from repeated flexing of the part in question. fault A condition that causes a device, a component, or an element to fail to perform in a required manner. Examples include a short-circuit, broken wire, or intermittent connection. fault to ground A fault caused by the failure of insulation and the consequent establishment of a direct path to ground from a part of the circuit that should not normally be grounded. Dictionary of Audio Terms 14-115 fault tree analysis (FTA) An iterative documented process of a systematic nature performed to identify basic faults, determine their causes and effects, and establish their probabilities of occurrence. feature A distinctive characteristic or part of a system or piece of equipment, usually visible to end users and designed for their convenience. Federal Communications Commission (FCC) The federal agency empowered by law to regulate all interstate radio and wireline communications services originating in the United States, including radio, television, facsimile, telegraph, data transmission, and telephone systems. The agency was established by the Communications Act of 1934. feedback The return of a portion of the output of a device to the input. Positive feedback adds to the input, negative feedback subtracts from the input. feedback amplifier An amplifier with the components required to feed a portion of the output back into the input to alter the characteristics of the output signal. feedline A transmission line, typically coaxial cable, that connects a high frequency energy source to its load. femto A prefix meaning one quadrillionth (10–15). ferrite A ceramic material made of powdered and compressed ferric oxide, plus other oxides (mainly cobalt, nickel, zinc, yttrium-iron, and manganese). These materials have low eddy current losses at high frequencies. ferromagnetic material A material with low relative permeability and high coercive force so that it is difficult to magnetize and demagnetize. Hard ferromagnetic materials retain magnetism well, and are commonly used in permanent magnets. fidelity The degree to which a system, or a portion of a system, accurately reproduces at its output the essential characteristics of the signal impressed upon its input. field strength The strength of an electric, magnetic, or electromagnetic field. filament A wire that becomes hot when current is passed through it, used either to emit light (for a light bulb) or to heat a cathode to enable it to emit electrons (for an electron tube). film resistor A type of resistor made by depositing a thin layer of resistive material on an insulating core. filter A network that passes desired frequencies but greatly attenuates other frequencies. filtered noise White noise that has been passed through a filter. The power spectral density of filtered white noise has the same shape as the transfer function of the filter. fitting A coupling or other mechanical device that joins one component with another. fixed A system or device that is not changeable or movable. flashover An arc or spark between two conductors. flashover voltage The voltage between conductors at which flashover just occurs. flat face tube The design of CRT tube with almost a flat face, giving improved legibility of text and reduced reflection of ambient light. 14-116 Standards and Practices flat level A signal that has an equal amplitude response for all frequencies within a stated range. flat loss A circuit, device, or channel that attenuates all frequencies of interest by the same amount, also called flat slope. flat noise A noise whose power per unit of frequency is essentially independent of frequency over a specified frequency range. flat response The performance parameter of a system in which the output signal amplitude of the system is a faithful reproduction of the input amplitude over some range of specified input frequencies. floating A circuit or device that is not connected to any source of potential or to ground. fluorescence The characteristic of a material to produce light when excited by an external energy source. Minimal or no heat results from the process. flux The electric or magnetic lines of force resulting from an applied energy source. flywheel effect The characteristic of an oscillator that enables it to sustain oscillations after removal of the control stimulus. This characteristic may be desirable, as in the case of a phase-locked loop employed in a synchronous system, or undesirable, as in the case of a voltage-controlled oscillator. focusing A method of making beams of radiation converge on a target, such as the face of a CRT. Fourier analysis A mathematical process for transforming values between the frequency domain and the time domain. This term also refers to the decomposition of a time-domain signal into its frequency components. Fourier transform An integral that performs an actual transformation between the frequency domain and the time domain in Fourier analysis. frame A segment of an analog or digital signal that has a repetitive characteristic, in that corresponding elements of successive frames represent the same things. free electron An electron that is not attached to an atom and is, thus, mobile when an electromotive force is applied. free running An oscillator that is not controlled by an external synchronizing signal. free-running oscillator An oscillator that is not synchronized with an external timing source. frequency The number of complete cycles of a periodic waveform that occur within a given length of time. Frequency is usually specified in cycles per second (Hertz). Frequency is the reciprocal of wavelength. The higher the frequency, the shorter the wavelength. In general, the higher the frequency of a signal, the more capacity it has to carry information, the smaller an antenna is required, and the more susceptible the signal is to absorption by the atmosphere and by physical structures. At microwave frequencies, radio signals take on a line-of-sight characteristic and require highly directional and focused antennas to be used successfully. frequency accuracy The degree of conformity of a given signal to the specified value of a frequency. Dictionary of Audio Terms 14-117 frequency allocation The designation of radio-frequency bands for use by specific radio services. frequency content The band of frequencies or specific frequency components contained in a signal. frequency converter A circuit or device used to change a signal of one frequency into another of a different frequency. frequency coordination The process of analyzing frequencies in use in various bands of the spectrum to achieve reliable performance for current and new services. frequency counter An instrument or test set used to measure the frequency of a radio signal or any other alternating waveform. frequency departure An unintentional deviation from the nominal frequency value. frequency difference The algebraic difference between two frequencies. The two frequencies can be of identical or different nominal values. frequency displacement The end-to-end shift in frequency that may result from independent frequency translation errors in a circuit. frequency distortion The distortion of a multifrequency signal caused by unequal attenuation or amplification at the different frequencies of the signal. This term may also be referred to as amplitude distortion. frequency domain A representation of signals as a function of frequency, rather than of time. frequency modulation (FM) The modulation of a carrier signal so that its instantaneous frequency is proportional to the instantaneous value of the modulating wave. frequency multiplier A circuit that provides as an output an exact multiple of the input frequency. frequency offset A frequency shift that occurs when a signal is sent over an analog transmission facility in which the modulating and demodulating frequencies are not identical. A channel with frequency offset does not preserve the waveform of a transmitted signal. frequency response The measure of system linearity in reproducing signals across a specified bandwidth. Frequency response is expressed as a frequency range with a specified amplitude tolerance in dB. frequency response characteristic The variation in the transmission performance (gain or loss) of a system with respect to variations in frequency. frequency reuse A technique used to expand the capacity of a given set of frequencies or channels by separating the signals either geographically or through the use of different polarization techniques. Frequency reuse is a common element of the frequency coordination process. frequency selectivity The ability of equipment to separate or differentiate between signals at different frequencies. frequency shift The difference between the frequency of a signal applied at the input of a circuit and the frequency of that signal at the output. 14-118 Standards and Practices frequency shift keying (FSK) A commonly-used method of digital modulation in which a one and a zero (the two possible states) are each transmitted as separate frequencies. frequency stability A measure of the variations of the frequency of an oscillator from its mean frequency over a specified period of time. frequency standard An oscillator with an output frequency sufficiently stable and accurate that it is used as a reference. frequency-division multiple access (FDMA) The provision of multiple access to a transmission facility, such as an earth satellite, by assigning each transmitter its own frequency band. frequency-division multiplexing (FDM) The process of transmitting multiple analog signals by an orderly assignment of frequency slots, that is, by dividing transmission bandwidth into several narrow bands, each of which carries a single communication and is sent simultaneously with others over a common transmission path. full duplex A communications system capable of transmission simultaneously in two directions. full-wave rectifier A circuit configuration in which both positive and negative half-cycles of the incoming ac signal are rectified to produce a unidirectional (dc) current through the load. functional block diagram A diagram illustrating the definition of a device, system, or problem on a logical and functional basis. functional unit An entity of hardware and/or software capable of accomplishing a given purpose. fundamental frequency The lowest frequency component of a complex signal. fuse A protective device used to limit current flow in a circuit to a specified level. The fuse consists of a metallic link that melts and opens the circuit at a specified current level. fuse wire A fine-gauge wire made of an alloy that overheats and melts at the relatively low temperatures produced when the wire carries overload currents. When used in a fuse, the wire is called a fuse (or fusible) link. G gain An increase or decrease in the level of an electrical signal. Gain is measured in terms of decibels or number-of-times of magnification. Strictly speaking, gain refers to an increase in level. Negative numbers, however, are commonly used to denote a decrease in level. gain-bandwidth The gain times the frequency of measurement when a device is biased for maximum obtainable gain. gain/frequency characteristic The gain-versus-frequency characteristic of a channel over the bandwidth provided, also referred to as frequency response. gain/frequency distortion A circuit defect in which a change in frequency causes a change in signal amplitude. galvanic A device that produces direct current by chemical action. gang The mechanical connection of two or more circuit devices so that they can all be adjusted simultaneously. Dictionary of Audio Terms 14-119 gang capacitor A variable capacitor with more than one set of moving plates linked together. gang tuning The simultaneous tuning of several different circuits by turning a single shaft on which ganged capacitors are mounted. ganged One or more devices that are mechanically coupled, normally through the use of a shared shaft. gas breakdown The ionization of a gas between two electrodes caused by the application of a voltage that exceeds a threshold value. The ionized path has a low impedance. Certain types of circuit and line protectors rely on gas breakdown to divert hazardous currents away from protected equipment. gas tube A protection device in which a sufficient voltage across two electrodes causes a gas to ionize, creating a low impedance path for the discharge of dangerous voltages. gas-discharge tube A gas-filled tube designed to carry current during gas breakdown. The gasdischarge tube is commonly used as a protective device, preventing high voltages from damaging sensitive equipment. gauge A measure of wire diameter. In measuring wire gauge, the lower the number, the thicker the wire. Gaussian distribution A statistical distribution, also called the normal distribution. The graph of a Gaussian distribution is a bell-shaped curve. Gaussian noise Noise in which the distribution of amplitude follows a Gaussian model, that is, the noise is random but distributed about a reference voltage of zero. Gaussian pulse A pulse that has the same form as its own Fourier transform. generator A machine that converts mechanical energy into electrical energy, or one form of electrical energy into another form. geosynchronous The attribute of a satellite in which the relative position of the satellite as viewed from the surface of a given planet is stationary. For earth, the geosynchronous position is 22,300 miles above the planet. getter A metal used in vaporized form to remove residual gas from inside an electron tube during manufacture. giga A prefix meaning one billion. gigahertz (GHz) A measure of frequency equal to one billion cycles per second. Signals operating above 1 gigahertz are commonly known as microwaves, and begin to take on the characteristics of visible light. glitch A general term used to describe a wide variety of momentary signal discontinuities. graceful degradation An equipment failure mode in which the system suffers reduced capability, but does not fail altogether. graticule A fixed pattern of reference markings used with oscilloscope CRTs to simplify measurements. The graticule may be etched on a transparent plate covering the front of the CRT or, for greater accuracy in readings, may be electrically generated within the CRT itself. 14-120 Standards and Practices grid (1—general) A mesh electrode within an electron tube that controls the flow of electrons between the cathode and plate of the tube. (2—bias) The potential applied to a grid in an electron tube to control its center operating point. (3—control) The grid in an electron tube to which the input signal is usually applied. (4—screen) The grid in an electron tube, typically held at a steady potential, that screens the control grid from changes in anode potential. (5—suppressor) The grid in an electron tube near the anode (plate) that suppresses the emission of secondary electrons from the plate. ground An electrical connection to earth or to a common conductor usually connected to earth. ground clamp A clamp used to connect a ground wire to a ground rod or system. ground loop An undesirable circulating ground current in a circuit grounded via multiple connections or at multiple points. ground plane A conducting material at ground potential, physically close to other equipment, so that connections may be made readily to ground the equipment at the required points. ground potential The point at zero electric potential. ground return A conductor used as a path for one or more circuits back to the ground plane or central facility ground point. ground rod A metal rod driven into the earth and connected into a mesh of interconnected rods so as to provide a low resistance link to ground. ground window A single-point interface between the integrated ground plane of a building and an isolated ground plane. ground wire A copper conductor used to extend a good low-resistance earth ground to protective devices in a facility. grounded The connection of a piece of equipment to earth via a low resistance path. grounding The act of connecting a device or circuit to ground or to a conductor that is grounded. group delay A condition where the different frequency elements of a given signal suffer differing propagation delays through a circuit or a system. The delay at a lower frequency is different from the delay at a higher frequency, resulting in a time-related distortion of the signal at the receiving point. group delay time The rate of change of the total phase shift of a waveform with angular frequency through a device or transmission facility. group velocity The speed of a pulse on a transmission line. guard band A narrow bandwidth between adjacent channels intended to reduce interference or crosstalk. H half-wave rectifier A circuit or device that changes only positive or negative half-cycle inputs of alternating current into direct current. Hall effect The phenomenon by which a voltage develops between the edges of a current-carrying metal strip whose faces are perpendicular to an external magnetic field. Dictionary of Audio Terms 14-121 hard-wired Electrical devices connected through physical wiring. harden The process of constructing military telecommunications facilities so as to protect them from damage by enemy action, especially electromagnetic pulse (EMP) radiation. hardware Physical equipment, such as mechanical, magnetic, electrical, or electronic devices or components. harmonic A periodic wave having a frequency that is an integral multiple of the fundamental frequency. For example, a wave with twice the frequency of the fundamental is called the second harmonic. harmonic analyzer A test set capable of identifying the frequencies of the individual signals that make up a complex wave. harmonic distortion The production of harmonics at the output of a circuit when a periodic wave is applied to its input. The level of the distortion is usually expressed as a percentage of the level of the input. hazard A condition that could lead to danger for operating personnel. headroom The difference, in decibels, between the typical operating signal level and a peak overload level. heat loss The loss of useful electrical energy resulting from conversion into unwanted heat. heat sink A device that conducts heat away from a heat-producing component so that it stays within a safe working temperature range. heater In an electron tube, the filament that heats the cathode to enable it to emit electrons. hecto A prefix meaning 100. henry The standard unit of electrical inductance, equal to the self-inductance of a circuit or the mutual inductance of two circuits when there is an induced electromotive force of one volt and a current change of one ampere per second. The symbol for inductance is H, named for the American physicist Joseph Henry (1797–1878). hertz (Hz) The unit of frequency that is equal to one cycle per second. Hertz is the reciprocal of the period, the interval after which the same portion of a periodic waveform recurs. Hertz was named for the German physicist Heinrich R. Hertz (1857–1894). heterodyne The mixing of two signals in a nonlinear device in order to produce two additional signals at frequencies that are the sum and difference of the original frequencies. heterodyne frequency The sum of, or the difference between, two frequencies, produced by combining the two signals together in a modulator or similar device. heterodyne wavemeter A test set that uses the heterodyne principle to measure the frequencies of incoming signals. high-frequency loss Loss of signal amplitude at higher frequencies through a given circuit or medium. For example, high frequency loss could be caused by passing a signal through a coaxial cable. high Q An inductance or capacitance whose ratio of reactance to resistance is high. 14-122 Standards and Practices high tension A high voltage circuit. high-pass filter A network that passes signals of higher than a specified frequency but attenuates signals of all lower frequencies. homochronous Signals whose corresponding significant instants have a constant but uncontrolled phase relationship with each other. horn gap A lightning arrester utilizing a gap between two horns. When lightning causes a discharge between the horns, the heat produced lengthens the arc and breaks it. horsepower The basic unit of mechanical power. One horsepower (hp) equals 550 foot-pounds per second or 746 watts. hot A charged electrical circuit or device. hot dip galvanized The process of galvanizing steel by dipping it into a bath of molten zinc. hot standby System equipment that is fully powered but not in service. A hot standby can rapidly replace a primary system in the event of a failure. hum Undesirable coupling of the 60 Hz power sine wave into other electrical signals and/or circuits. HVAC An abbreviation for heating, ventilation, and air conditioning system. hybrid system A communication system that accommodates both digital and analog signals. hydrometer A testing device used to measure specific gravity, particularly the specific gravity of the dilute sulphuric acid in a lead-acid storage battery, to learn the state of charge of the battery. hygrometer An instrument that measures the relative humidity of the atmosphere. hygroscopic The ability of a substance to absorb moisture from the air. hysteresis The property of an element evidenced by the dependence of the value of the output, for a given excursion of the input, upon the history of prior excursions and direction of the input. Originally, hysteresis was the name for magnetic phenomena only—the lagging of flux density behind the change in value of the magnetizing flux—but now, the term is also used to describe other inelastic behavior. hysteresis loop The plot of magnetizing current against magnetic flux density (or of other similarly related pairs of parameters), which appears as a loop. The area within the loop is proportional to the power loss resulting from hysteresis. hysteresis loss The loss in a magnetic core resulting from hysteresis. I I2R loss The power lost as a result of the heating effect of current passing through resistance. idling current The current drawn by a circuit, such as an amplifier, when no signal is present at its input. image frequency A frequency on which a carrier signal, when heterodyned with the local oscillator in a superheterodyne receiver, will cause a sum or difference frequency that is the Dictionary of Audio Terms 14-123 same as the intermediate frequency of the receiver. Thus, a signal on an image frequency will be demodulated along with the desired signal and will interfere with it. impact ionization The ionization of an atom or molecule as a result of a high energy collision. impedance The total passive opposition offered to the flow of an alternating current. Impedance consists of a combination of resistance, inductive reactance, and capacitive reactance. It is the vector sum of resistance and reactance (R + jX) or the vector of magnitude Z at an angle θ. impedance characteristic A graph of the impedance of a circuit showing how it varies with frequency. impedance irregularity A discontinuity in an impedance characteristic caused, for example, by the use of different coaxial cable types. impedance matching The adjustment of the impedances of adjoining circuit components to a common value so as to minimize reflected energy from the junction and to maximize energy transfer across it. Incorrect adjustment results in an impedance mismatch. impedance matching transformer A transformer used between two circuits of different impedances with a turns ratio that provides for maximum power transfer and minimum loss by reflection. impulse A short high energy surge of electrical current in a circuit or on a line. impulse current A current that rises rapidly to a peak then decays to zero without oscillating. impulse excitation The production of an oscillatory current in a circuit by impressing a voltage for a relatively short period compared with the duration of the current produced. impulse noise A noise signal consisting of random occurrences of energy spikes, having random amplitude and bandwidth. impulse response The amplitude-versus-time output of a transmission facility or device in response to an impulse. impulse voltage A unidirectional voltage that rises rapidly to a peak and then falls to zero, without any appreciable oscillation. in-phase The property of alternating current signals of the same frequency that achieve their peak positive, peak negative, and zero amplitude values simultaneously. incidence angle The angle between the perpendicular to a surface and the direction of arrival of a signal. increment A small change in the value of a quantity. induce To produce an electrical or magnetic effect in one conductor by changing the condition or position of another conductor. induced current The current that flows in a conductor because a voltage has been induced across two points in, or connected to, the conductor. induced voltage A voltage developed in a conductor when the conductor passes through magnetic lines of force. 14-124 Standards and Practices inductance The property of an inductor that opposes any change in a current that flows through it. The standard unit of inductance is the Henry. induction The electrical and magnetic interaction process by which a changing current in one circuit produces a voltage change not only in its own circuit (self inductance) but also in other circuits to which it is linked magnetically. inductive A circuit element exhibiting inductive reactance. inductive kick A voltage surge produced when a current flowing through an inductance is interrupted. inductive load A load that possesses a net inductive reactance. inductive reactance The reactance of a circuit resulting from the presence of inductance and the phenomenon of induction. inductor A coil of wire, usually wound on a core of high permeability, that provides high inductance without necessarily exhibiting high resistance. inert An inactive unit, or a unit that has no power requirements. infinite line A transmission line that appears to be of infinite length. There are no reflections back from the far end because it is terminated in its characteristic impedance. infra low frequency (ILF) The frequency band from 300 Hz to 3000 Hz. inhibit A control signal that prevents a device or circuit from operating. injection The application of a signal to an electronic device. input The waveform fed into a circuit, or the terminals that receive the input waveform. insertion gain The gain resulting from the insertion of a transducer in a transmission system, expressed as the ratio of the power delivered to that part of the system following the transducer to the power delivered to that same part before insertion. If more than one component is involved in the input or output, the particular component used must be specified. This ratio is usually expressed in decibels. If the resulting number is negative, an insertion loss is indicated. insertion loss The signal loss within a circuit, usually expressed in decibels as the ratio of input power to output power. insertion loss-vs.-frequency characteristic The amplitude transfer characteristic of a system or component as a function of frequency. The amplitude response may be stated as actual gain, loss, amplification, or attenuation, or as a ratio of any one of these quantities at a particular frequency, with respect to that at a specified reference frequency. inspection lot A collection of units of product from which a sample is drawn and inspected to determine conformance with acceptability criteria. instantaneous value The value of a varying waveform at a given instant of time. The value can be in volts, amperes, or phase angle. Institute of Electrical and Electronics Engineers (IEEE) The organization of electrical and electronics scientists and engineers formed in 1963 by the merger of the Institute of Radio Engineers (IRE) and the American Institute of Electrical Engineers (AIEE). Dictionary of Audio Terms 14-125 instrument multiplier A measuring device that enables a high voltage to be measured using a meter with only a low voltage range. instrument rating The range within which an instrument has been designed to operate without damage. insulate The process of separating one conducting body from another conductor. insulation The material that surrounds and insulates an electrical wire from other wires or circuits. Insulation may also refer to any material that does not ionize easily and thus presents a large impedance to the flow of electrical current. insulator A material or device used to separate one conducting body from another. intelligence signal A signal containing information. intensity The strength of a given signal under specified conditions. interconnect cable A short distance cable intended for use between equipment (generally less than 3 m in length). interface A device or circuit used to interconnect two pieces of electronic equipment. interface device A unit that joins two interconnecting systems. interference emission An emission that results in an electrical signal being propagated into and interfering with the proper operation of electrical or electronic equipment. interlock A protection device or system designed to remove all dangerous voltages from a machine or piece of equipment when access doors or panels are opened or removed. intermediate frequency A frequency that results from combining a signal of interest with a signal generated within a radio receiver. In superheterodyne receivers, all incoming signals are converted to a single intermediate frequency for which the amplifiers and filters of the receiver have been optimized. intermittent A noncontinuous recurring event, often used to denote a problem that is difficult to find because of its unpredictable nature. intermodulation The production, in a nonlinear transducer element, of frequencies corresponding to the sums and differences of the fundamentals and harmonics of two or more frequencies that are transmitted through the transducer. intermodulation distortion (IMD) The distortion that results from the mixing of two input signals in a nonlinear system. The resulting output contains new frequencies that represent the sum and difference of the input signals and the sums and differences of their harmonics. IMD is also called intermodulation noise. intermodulation noise In a transmission path or device, the noise signal that is contingent upon modulation and demodulation, resulting from nonlinear characteristics in the path or device. internal resistance The actual resistance of a source of electric power. The total electromotive force produced by a power source is not available for external use; some of the energy is used in driving current through the source itself. 14-126 Standards and Practices International Standards Organization (ISO) An international body concerned with worldwide standardization for a broad range of industrial products, including telecommunications equipment. Members are represented by national standards organizations, such as ANSI (American National Standards Institute) in the United States. ISO was established in 1947 as a specialized agency of the United Nations. International Telecommunications Union (ITU) A specialized agency of the United Nations established to maintain and extend international cooperation for the maintenance, development, and efficient use of telecommunications. The union does this through standards and recommended regulations, and through technical and telecommunications studies. International Telecommunications Satellite Consortium (Intelsat) A nonprofit cooperative of member nations that owns and operates a satellite system for international and, in many instances, domestic communications. interoperability The condition achieved among communications and electronics systems or equipment when information or services can be exchanged directly between them or their users, or both. interpolate The process of estimating unknown values based on a knowledge of comparable data that falls on both sides of the point in question. interrupting capacity The rating of a circuit breaker or fuse that specifies the maximum current the device is designed to interrupt at its rated voltage. interval The points or numbers lying between two specified endpoints. inverse voltage The effective value of voltage across a rectifying device, which conducts a current in one direction during one half cycle of the alternating input, during the half cycle when current is not flowing. inversion The change in the polarity of a pulse, such as from positive to negative. inverter A circuit or device that converts a direct current into an alternating current. ionizing radiation The form of electromagnetic radiation that can turn an atom into an ion by knocking one or more of its electrons loose. Examples of ionizing radiation include X rays, gamma rays, and cosmic rays IR drop A drop in voltage because of the flow of current (I) through a resistance (R), also called resistance drop. IR loss The conversion of electrical power to heat caused by the flow of electrical current through a resistance. isochronous A signal in which the time interval separating any two significant instants is theoretically equal to a specified unit interval or to an integral multiple of the unit interval. isolated ground A ground circuit that is isolated from all equipment framework and any other grounds, except for a single-point external connection. isolated ground plane A set of connected frames that are grounded through a single connection to a ground reference point. That point and all parts of the frames are insulated from any other ground system in a building. isolated pulse A pulse uninfluenced by other pulses in the same signal. Dictionary of Audio Terms 14-127 isophasing amplifier A timing device that corrects for small timing errors. isotropic A quantity exhibiting the same properties in all planes and directions. J jack A receptacle or connector that makes electrical contact with the mating contacts of a plug. In combination, the plug and jack provide a ready means for making connections in electrical circuits. jacket An insulating layer of material surrounding a wire in a cable. jitter Small, rapid variations in a waveform resulting from fluctuations in a supply voltage or other causes. joule The standard unit of work that is equal to the work done by one newton of force when the point at which the force is applied is displaced a distance of one meter in the direction of the force. The joule is named for the English physicist James Prescott Joule (1818-1889). Julian date A chronological date in which days of the year are numbered in sequence. For example, the first day is 001, the second is 002, and the last is 365 (or 366 in a leap year). K Kelvin (K) The standard unit of thermodynamic temperature. Zero degrees Kelvin represents absolute zero. Water freezes at 273 K and water boils at 373 K under standard pressure conditions. kilo A prefix meaning one thousand. kilohertz (kHz) A unit of measure of frequency equal to 1,000 Hz. kilovar A unit equal to one thousand volt-amperes. kilovolt (kV) A unit of measure of electrical voltage equal to 1,000 V. kilowatt A unit equal to one thousand watts. Kirchoff's Law At any point in a circuit, there is as much current flowing into the point as there is flowing away from it. klystron (1—general) A family of electron tubes that function as microwave amplifiers and oscillators. Simplest in form are two-cavity klystrons in which an electron beam passes through a cavity that is excited by a microwave input, producing a velocity-modulated beam which passes through a second cavity a precise distance away that is coupled to a tuned circuit, thereby producing an amplified output of the original input signal frequency. If part of the output is fed back to the input, an oscillator can be the result. (2—multi-cavity) An amplifier device for UHF and microwave signals based on velocity modulation of an electron beam. The beam is directed through an input cavity, where the input RF signal polarity initializes a bunching effect on electrons in the beam. The bunching effect excites subsequent cavities, which increase the bunching through an energy flywheel concept. Finally, the beam passes to an output cavity that couples the amplified signal to the load (antenna system). The beam falls onto a collector element that forms the return path for the current and dissipates the heat resulting from electron beam bombardment. (3—reflex) A 14-128 Standards and Practices klystron with only one cavity. The action is the same as in a two-cavity klystron but the beam is reflected back into the cavity in which it was first excited, after being sent out to a reflector. The one cavity, therefore, acts both as the original exciter (or buncher) and as the collector from which the output is taken. knee In a response curve, the region of maximum curvature. ku band Radio frequencies in the range of 15.35 GHz to 17.25 GHz, typically used for satellite telecommunications. L ladder network A type of filter with components alternately across the line and in the line. lag The difference in phase between a current and the voltage that produced it, expressed in electrical degrees. lagging current A current that lags behind the alternating electromotive force that produced it. A circuit that produces a lagging current is one containing inductance alone, or whose effective impedance is inductive. lagging load A load whose combined inductive reactance exceeds its capacitive reactance. When an alternating voltage is applied, the current lags behind the voltage. laminate A material consisting of layers of the same or different materials bonded together and built up to the required thickness. latitude An angular measurement of a point on the earth above or below the equator. The equator represents 0°, the north pole +90°, and the south pole –90°. layout A proposed or actual arrangement or allocation of equipment. LC circuit An electrical circuit with both inductance (L) and capacitance (C) that is resonant at a particular frequency. LC ratio The ratio of inductance to capacitance in a given circuit. lead An electrical wire, usually insulated. leading edge The initial portion of a pulse or wave in which voltage or current rise rapidly from zero to a final value. leading load A reactive load in which the reactance of capacitance is greater than that of inductance. Current through such a load leads the applied voltage causing the current. leakage The loss of energy resulting from the flow of electricity past an insulating material, the escape of electromagnetic radiation beyond its shielding, or the extension of magnetic lines of force beyond their intended working area. leakage resistance The resistance of a path through which leakage current flows. level The strength or intensity of a given signal. level alignment The adjustment of transmission levels of single links and links in tandem to prevent overloading of transmission subsystems. Dictionary of Audio Terms 14-129 life cycle The predicted useful life of a class of equipment, operating under normal (specified) working conditions. life safety system A system designed to protect life and property, such as emergency lighting, fire alarms, smoke exhaust and ventilating fans, and site security. life test A test in which random samples of a product are checked to see how long they can continue to perform their functions satisfactorily. A form of stress testing is used, including temperature, current, voltage, and/or vibration effects, cycled at many times the rate that would apply in normal usage. limiter An electronic device in which some characteristic of the output is automatically prevented from exceeding a predetermined value. limiter circuit A circuit of nonlinear elements that restricts the electrical excursion of a variable in accordance with some specified criteria. limiting A process by which some characteristic at the output of a device is prevented from exceeding a predetermined value. line loss The total end-to-end loss in decibels in a transmission line. line-up The process of adjusting transmission parameters to bring a circuit to its specified values. linear A circuit, device, or channel whose output is directly proportional to its input. linear distortion A distortion mechanism that is independent of signal amplitude. linearity A constant relationship, over a designated range, between the input and output characteristics of a circuit or device. lines of force A group of imaginary lines indicating the direction of the electric or magnetic field at all points along it. lissajous pattern The looping patterns generated by a CRT spot when the horizontal (X) and vertical (Y) deflection signals are sinusoids. The lissajous pattern is useful for evaluating the delay or phase of two sinusoids of the same frequency. live A device or system connected to a source of electric potential. load The work required of an electrical or mechanical system. load factor The ratio of the average load over a designated period of time to the peak load occurring during the same period. load line A straight line drawn across a grouping of plate current/plate voltage characteristic curves showing the relationship between grid voltage and plate current for a particular plate load resistance of an electron tube. logarithm The power to which a base must be raised to produce a given number. Common logarithms are to base 10. logarithmic scale A meter scale with displacement proportional to the logarithm of the quantity represented. 14-130 Standards and Practices long persistence The quality of a cathode ray tube that has phosphorescent compounds on its screen (in addition to fluorescent compounds) so that the image continues to glow after the original electron beam has ceased to create it by producing the usual fluorescence effect. Long persistence is often used in radar screens or where photographic evidence is needed of a display. Most such applications, however, have been superseded through the use of digital storage techniques. longitude The angular measurement of a point on the surface of the earth in relation to the meridian of Greenwich (London). The earth is divided into 360° of longitude, beginning at the Greenwich mean. As one travels west around the globe, the longitude increases. longitudinal current A current that travels in the same direction on both wires of a pair. The return current either flows in another pair or via a ground return path. loss The power dissipated in a circuit, usually expressed in decibels, that performs no useful work. loss deviation The change of actual loss in a circuit or system from a designed value. loss variation The change in actual measured loss over time. lossy The condition when the line loss per unit length is significantly greater than some defined normal parameter. lossy cable A coaxial cable constructed to have high transmission loss so it can be used as an artificial load or as an attenuator. lot size A specific quantity of similar material or a collection of similar units from a common source; in inspection work, the quantity offered for inspection and acceptance at any one time. The lot size may be a collection of raw material, parts, subassemblies inspected during production, or a consignment of finished products to be sent out for service. low tension A low voltage circuit. low-pass filter A filter network that passes all frequencies below a specified frequency with little or no loss, but that significantly attenuates higher frequencies. lug A tag or projecting terminal onto which a wire may be connected by wrapping, soldering, or crimping. lumped constant A resistance, inductance, or capacitance connected at a point, and not distributed uniformly throughout the length of a route or circuit. M mA An abbreviation for milliamperes (0.001 A). magnet A device that produces a magnetic field and can attract iron, and attract or repel other magnets. magnetic field An energy field that exists around magnetic materials and current-carrying conductors. Magnetic fields combine with electric fields in light and radio waves. magnetic flux The field produced in the area surrounding a magnet or electric current. The standard unit of flux is the Weber. Dictionary of Audio Terms 14-131 magnetic flux density A vector quantity measured by a standard unit called the Tesla. The magnetic flux density is the number of magnetic lines of force per unit area, at right angles to the lines. magnetic leakage The magnetic flux that does not follow a useful path. magnetic pole A point that appears from the outside to be the center of magnetic attraction or repulsion at or near one end of a magnet. magnetic storm A violent local variation in the earth's magnetic field, usually the result of sunspot activity. magnetism A property of iron and some other materials by which external magnetic fields are maintained, other magnets being thereby attracted or repelled. magnetization The exposure of a magnetic material to a magnetizing current, field, or force. magnetizing force The force producing magnetization. magnetomotive force The force that tends to produce lines of force in a magnetic circuit. The magnetomotive force bears the same relationship to a magnetic circuit that voltage does to an electrical circuit. magnetron A high-power, ultra high frequency electron tube oscillator that employs the interaction of a strong electric field between an anode and cathode with the field of a strong permanent magnet to cause oscillatory electron flow through multiple internal cavity resonators. The magnetron may operate in a continuous or pulsed mode. maintainability The probability that a failure will be repaired within a specified time after the failure occurs. maintenance Any activity intended to keep a functional unit in satisfactory working condition. The term includes the tests, measurements, replacements, adjustments, and repairs necessary to keep a device or system operating properly. malfunction An equipment failure or a fault. manometer A test device for measuring gas pressure. margin The difference between the value of an operating parameter and the value that would result in unsatisfactory operation. Typical margin parameters include signal level, signalto-noise ratio, distortion, crosstalk coupling, and/or undesired emission level. Markov model A statistical model of the behavior of a complex system over time in which the probabilities of the occurrence of various future states depend only on the present state of the system, and not on the path by which the present state was achieved. This term was named for the Russian mathematician Andrei Andreevich Markov (1856–1922). master clock An accurate timing device that generates a synchronous signal to control other clocks or equipment. master oscillator A stable oscillator that provides a standard frequency signal for other hardware and/or systems. matched termination A termination that absorbs all the incident power and so produces no reflected waves or mismatch loss. 14-132 Standards and Practices matching The connection of channels, circuits, or devices in a manner that results in minimal reflected energy. matrix A logical network configured in a rectangular array of intersections of input/output signals. Maxwell's equations Four differential equations that relate electric and magnetic fields to electromagnetic waves. The equations are a basis of electrical and electronic engineering. mean An arithmetic average in which values are added and divided by the number of such values. mean time between failures (MTBF) For a particular interval, the total functioning life of a population of an item divided by the total number of failures within the population during the measurement interval. mean time to failure (MTTF) The measured operating time of a single piece of equipment divided by the total number of failures during the measured period of time. This measurement is normally made during that period between early life and wear-out failures. mean time to repair (MTTR) The total corrective maintenance time on a component or system divided by the total number of corrective maintenance actions during a given period of time. measurement A procedure for determining the amount of a quantity. median A value in a series that has as many readings or values above it as below. medium An electronic pathway or mechanism for passing information from one point to another. mega A prefix meaning one million. megahertz (MHz) A quantity equal to one million Hertz (cycles per second). megohm A quantity equal to one million ohms. metric system A decimal system of measurement based on the meter, the kilogram, and the second. micro A prefix meaning one millionth. micron A unit of length equal to one millionth of a meter (1/25,000 of an inch). microphonic(s) Unintended noise introduced into an electronic system by mechanical vibration of electrical components. microsecond One millionth of a second (0.000001 s). microvolt A quantity equal to one-millionth of a volt. milli A prefix meaning one thousandth. milliammeter A test instrument for measuring electrical current, often part of a multimeter. millihenry A quantity equal to one-thousandth of a henry. milliwatt A quantity equal to one thousandth of a watt. Dictionary of Audio Terms 14-133 minimum discernible signal The smallest input that will produce a discernible change in the output of a circuit or device. mixer A circuit used to combine two or more signals to produce a third signal that is a function of the input waveforms. mixing ratio The ratio of the mass of water vapor to the mass of dry air in a given volume of air. The mixing ratio affects radio propagation. mode An electromagnetic field distribution that satisfies theoretical requirements for propagation in a waveguide or oscillation in a cavity. modified refractive index The sum of the refractive index of the air at a given height above sea level, and the ratio of this height to the radius of the earth. modular An equipment design in which major elements are readily separable, and which the user may replace, reducing the mean-time-to-repair. modulation The process whereby the amplitude, frequency, or phase of a single-frequency wave (the carrier) is varied in step with the instantaneous value of, or samples of, a complex wave (the modulating wave). modulator A device that enables the intelligence in an information-carrying modulating wave to be conveyed by a signal at a higher frequency. A modulator modifies a carrier wave by amplitude, phase, and/or frequency as a function of a control signal that carries intelligence. Signals are modulated in this way to permit more efficient and/or reliable transmission over any of several media. module An assembly replaceable as an entity, often as an interchangeable plug-in item. A module is not normally capable of being disassembled. monostable A device that is stable in one state only. An input pulse causes the device to change state, but it reverts immediately to its stable state. motor A machine that converts electrical energy into mechanical energy. motor effect The repulsion force exerted between adjacent conductors carrying currents in opposite directions. moving coil Any device that utilizes a coil of wire in a magnetic field in such a way that the coil is made to move by varying the applied current, or itself produces a varying voltage because of its movement. ms An abbreviation for millisecond (0.001 s). multimeter A test instrument fitted with several ranges for measuring voltage, resistance, and current, and equipped with an analog meter or digital display readout. The multimeter is also known as a volt-ohm-milliammeter, or VOM. multiplex (MUX) The use of a common channel to convey two or more channels. This is done either by splitting of the common channel frequency band into narrower bands, each of which is used to constitute a distinct channel (frequency division multiplex), or by allotting this common channel to multiple users in turn to constitute different intermittent channels (time division multiplex). multiplexer A device or circuit that combines several signals onto a single signal. 14-134 Standards and Practices multiplexing A technique that uses a single transmission path to carry multiple channels. In time division multiplexing (TDM), path time is shared. For frequency division multiplexing (FDM) or wavelength division multiplexing (WDM), signals are divided into individual channels sent along the same path but at different frequencies. multiplication Signal mixing that occurs within a multiplier circuit. multiplier A circuit in which one or more input signals are mixed under the direction of one or more control signals. The resulting output is a composite of the input signals, the characteristics of which are determined by the scaling specified for the circuit. mutual induction The property of the magnetic flux around a conductor that induces a voltage in a nearby conductor. The voltage generated in the secondary conductor in turn induces a voltage in the primary conductor. The inductance of two conductors so coupled is referred to as mutual inductance. mV An abbreviation for millivolt (0.001 V). mW An abbreviation for milliwatt (0.001 W). N nano A prefix meaning one billionth. nanometer 1 × 10–9 meter. nanosecond (ns) One billionth of a second (1 × 10–9 s). narrowband A communications channel of restricted bandwidth, often resulting in degradation of the transmitted signal. narrowband emission An emission having a spectrum exhibiting one or more sharp peaks that are narrow in width compared to the nominal bandwidth of the measuring instrument, and are far enough apart in frequency to be resolvable by the instrument. National Electrical Code (NEC) A document providing rules for the installation of electric wiring and equipment in public and private buildings, published by the National Fire Protection Association. The NEC has been adopted as law by many states and municipalities in the U.S. National Institute of Standards and Technology (NIST) A nonregulatory agency of the Department of Commerce that serves as a national reference and measurement laboratory for the physical and engineering sciences. Formerly called the National Bureau of Standards, the agency was renamed in 1988 and given the additional responsibility of aiding U.S. companies in adopting new technologies to increase their international competitiveness. negative In a conductor or semiconductor material, an excess of electrons or a deficiency of positive charge. negative feedback The return of a portion of the output signal from a circuit to the input but 180° out of phase. This type of feedback decreases signal amplitude but stabilizes the amplifier and reduces distortion and noise. Dictionary of Audio Terms 14-135 negative impedance An impedance characterized by a decrease in voltage drop across a device as the current through the device is increased, or a decrease in current through the device as the voltage across it is increased. neutral A device or object having no electrical charge. neutral conductor A conductor in a power distribution system connected to a point in the system that is designed to be at neutral potential. In a balanced system, the neutral conductor carries no current. neutral ground An intentional ground applied to the neutral conductor or neutral point of a circuit, transformer, machine, apparatus, or system. newton The standard unit of force. One newton is the force that, when applied to a body having a mass of 1 kg, gives it an acceleration of 1 m/s2. nitrogen A gas widely used to pressurize radio frequency transmission lines. If a small puncture occurs in the cable sheath, the nitrogen keeps moisture out so that service is not adversely affected. node The points at which the current is at minimum in a transmission system in which standing waves are present. noise Any random disturbance or unwanted signal in a communication system that tends to obscure the clarity or usefulness of a signal in relation to its intended use. noise factor (NF) The ratio of the noise power measured at the output of a receiver to the noise power that would be present at the output if the thermal noise resulting from the resistive component of the source impedance were the only source of noise in the system. noise figure A measure of the noise in dB generated at the input of an amplifier, compared with the noise generated by an impedance-method resistor at a specified temperature. noise filter A network that attenuates noise frequencies. noise generator A generator of wideband random noise. noise power ratio (NPR) The ratio, expressed in decibels, of signal power to intermodulation product power plus residual noise power, measured at the baseband level. noise suppressor A filter or digital signal processing circuit in a receiver or transmitter that automatically reduces or eliminates noise. noise temperature The temperature, expressed in Kelvin, at which a resistor will develop a particular noise voltage. The noise temperature of a radio receiver is the value by which the temperature of the resistive component of the source impedance should be increased—if it were the only source of noise in the system—to cause the noise power at the output of the receiver to be the same as in the real system. nominal The most common value for a component or parameter that falls between the maximum and minimum limits of a tolerance range. nominal value A specified or intended value independent of any uncertainty in its realization. nomogram A chart showing three or more scales across which a straight edge may be held in order to read off a graphical solution to a three-variable equation. 14-136 Standards and Practices nonionizing radiation Electromagnetic radiation that does not turn an atom into an ion. Examples of nonionizing radiation include visible light and radio waves. nonconductor A material that does not conduct energy, such as electricity, heat, or sound. noncritical technical load That part of the technical power load for a facility not required for minimum acceptable operation. noninductive A device or circuit without significant inductance. nonlinearity A distortion in which the output of a circuit or system does not rise or fall in direct proportion to the input. nontechnical load The part of the total operational load of a facility used for such purposes as general lighting, air conditioning, and ventilating equipment during normal operation. normal A line perpendicular to another line or to a surface. normal-mode noise Unwanted signals in the form of voltages appearing in line-to-line and lineto-neutral signals. normalized frequency The ratio between the actual frequency and its nominal value. normalized frequency departure The frequency departure divided by the nominal frequency value. normalized frequency difference The algebraic difference between two normalized frequencies. normalized frequency drift The frequency drift divided by the nominal frequency value. normally closed Switch contacts that are closed in their nonoperated state, or relay contacts that are closed when the relay is de-energized. normally open Switch contacts that are open in their nonoperated state, or relay contacts that are open when the relay is de-energized. north pole The pole of a magnet that seeks the north magnetic pole of the earth. notch filter A circuit designed to attenuate a specific frequency band; also known as a band stop filter. notched noise A noise signal in which a narrow band of frequencies has been removed. ns An abbreviation for nanosecond. null A zero or minimum amount or position. O octave Any frequency band in which the highest frequency is twice the lowest frequency. off-line A condition wherein devices or subsystems are not connected into, do not form a part of, and are not subject to the same controls as an operational system. offset An intentional difference between the realized value and the nominal value. Dictionary of Audio Terms 14-137 ohm The unit of electric resistance through which one ampere of current will flow when there is a difference of one volt. The quantity is named for the German physicist Georg Simon Ohm (1787–1854). Ohm's law A law that sets forth the relationship between voltage (E), current (I), and resistance (R). The law states that E = I 2 R. Ohm's Law is named for the German physicist Georg Simon Ohm (1787–1854). ohmic loss The power dissipation in a line or circuit caused by electrical resistance. ohmmeter A test instrument used for measuring resistance, often part of a multimeter. ohms-per-volt A measure of the sensitivity of a voltmeter. on-line A device or system that is energized and operational, and ready to perform useful work. open An interruption in the flow of electrical current, as caused by a broken wire or connection. open-circuit A defined loop or path that closes on itself and contains an infinite impedance. open-circuit impedance The input impedance of a circuit when its output terminals are open, that is, not terminated. open-circuit voltage The voltage measured at the terminals of a circuit when there is no load and, hence, no current flowing. operating lifetime The period of time during which the principal parameters of a component or system remain within a prescribed range. optimize The process of adjusting for the best output or maximum response from a circuit or system. orbit The path, relative to a specified frame of reference, described by the center of mass of a satellite or other object in space, subjected solely to natural forces (mainly gravitational attraction). order of diversity The number of independently fading propagation paths or frequencies, or both, used in a diversity reception system. original equipment manufacturer (OEM) A manufacturer of equipment that is used in systems assembled and sold by others. oscillation A variation with time of the magnitude of a quantity with respect to a specified reference when the magnitude is alternately greater than and smaller than the reference. oscillator A nonrotating device for producing alternating current, the output frequency of which is determined by the characteristics of the circuit. oscilloscope A test instrument that uses a display, usually a cathode-ray tube, to show the instantaneous values and waveforms of a signal that varies with time or some other parameter. out-of-band energy Energy emitted by a transmission system that falls outside the frequency spectrum of the intended transmission. outage duration The average elapsed time between the start and the end of an outage period. 14-138 Standards and Practices outage probability The probability that an outage state will occur within a specified time period. In the absence of specific known causes of outages, the outage probability is the sum of all outage durations divided by the time period of measurement. outage threshold A defined value for a supported performance parameter that establishes the minimum operational service performance level for that parameter. output impedance The impedance presented at the output terminals of a circuit, device, or channel. output stage The final driving circuit in a piece of electronic equipment. ovenized crystal oscillator (OXO) A crystal oscillator enclosed within a temperature regulated heater (oven) to maintain a stable frequency despite external temperature variations. overcoupling A degree of coupling greater than the critical coupling between two resonant circuits. Overcoupling results in a wide bandwidth circuit with two peaks in the response curve. overload In a transmission system, a power greater than the amount the system was designed to carry. In a power system, an overload could cause excessive heating. In a communications system, distortion of a signal could result. overshoot The first maximum excursion of a pulse beyond the 100% level. Overshoot is the portion of the pulse that exceeds its defined level temporarily before settling to the correct level. Overshoot amplitude is expressed as a percentage of the defined level. P pentode An electron tube with five electrodes, the cathode, control grid, screen grid, suppressor grid, and plate. photocathode An electrode in an electron tube that will emit electrons when bombarded by photons of light. picture tube A cathode-ray tube used to produce an image by variation of the intensity of a scanning beam on a phosphor screen. pin A terminal on the base of a component, such as an electron tube. plasma (1—arc) An ionized gas in an arc-discharge tube that provides a conducting path for the discharge. (2—solar) The ionized gas at extremely high temperature found in the sun. plate (1—electron tube) The anode of an electron tube. (2—battery) An electrode in a storage battery. (3—capacitor) One of the surfaces in a capacitor. (4—chassis) A mounting surface to which equipment may be fastened. propagation time delay The time required for a signal to travel from one point to another. protector A device or circuit that prevents damage to lines or equipment by conducting dangerously high voltages or currents to ground. Protector types include spark gaps, semiconductors, varistors, and gas tubes. proximity effect A nonuniform current distribution in a conductor, caused by current flow in a nearby conductor. Dictionary of Audio Terms 14-139 pseudonoise In a spread-spectrum system, a seemingly random series of pulses whose frequency spectrum resembles that of continuous noise. pseudorandom A sequence of signals that appears to be completely random but have, in fact, been carefully drawn up and repeat after a significant time interval. pseudorandom noise A noise signal that satisfies one or more of the standard tests for statistical randomness. Although it seems to lack any definite pattern, there is a sequence of pulses that repeats after a long time interval. pseudorandom number sequence A sequence of numbers that satisfies one or more of the standard tests for statistical randomness. Although it seems to lack any definite pattern, there is a sequence that repeats after a long time interval. pulsating direct current A current changing in value at regular or irregular intervals but which has the same direction at all times. pulse One of the elements of a repetitive signal characterized by the rise and decay in time of its magnitude. A pulse is usually short in relation to the time span of interest. pulse decay time The time required for the trailing edge of a pulse to decrease from 90 percent to 10 percent of its peak amplitude. pulse duration The time interval between the points on the leading and trailing edges of a pulse at which the instantaneous value bears a specified relation to the peak pulse amplitude. pulse duration modulation (PDM) The modulation of a pulse carrier by varying the width of the pulses according to the instantaneous values of the voltage samples of the modulating signal (also called pulse width modulation). pulse edge The leading or trailing edge of a pulse, defined as the 50 percent point of the pulse rise or fall time. pulse fall time The interval of time required for the edge of a pulse to fall from 90 percent to 10 percent of its peak amplitude. pulse interval The time between the start of one pulse and the start of the next. pulse length The duration of a pulse (also called pulse width). pulse level The voltage amplitude of a pulse. pulse period The time between the start of one pulse and the start of the next. pulse ratio The ratio of the length of any pulse to the total pulse period. pulse repetition period The time interval from the beginning of one pulse to the beginning of the next pulse. pulse repetition rate The number of times each second that pulses are transmitted. pulse rise time The time required for the leading edge of a pulse to rise from 10 percent to 90 percent of its peak amplitude. pulse train A series of pulses having similar characteristics. pulse width The measured interval between the 50 percent amplitude points of the leading and trailing edges of a pulse. 14-140 Standards and Practices puncture A breakdown of insulation or of a dielectric, such as in a cable sheath or in the insulant around a conductor. pW An abbreviation for picowatt, a unit of power equal to 10–12 W (–90 dBm). Q Q (quality factor) A figure of merit that defines how close a coil comes to functioning as a pure inductor. High Q describes an inductor with little energy loss resulting from resistance. Q is found by dividing the inductive reactance of a device by its resistance. quadrature A state of alternating current signals separated by one quarter of a cycle (90°). quadrature amplitude modulation (QAM) A process that allows two different signals to modulate a single carrier frequency. The two signals of interest amplitude modulate two samples of the carrier that are of the same frequency, but differ in phase by 90°. The two resultant signals can be added and transmitted. Both signals may be recovered at a decoder when they are demodulated 90° apart. quadrature component The component of a voltage or current at an angle of 90° to a reference signal, resulting from inductive or capacitive reactance. quadrature phase shift keying (QPSK) A type of phase shift keying using four phase states. quality The absence of objectionable distortion. quality assurance (QA) All those activities, including surveillance, inspection, control, and documentation, aimed at ensuring that a given product will meet its performance specifications. quality control (QC) A function whereby management exercises control over the quality of raw material or intermediate products in order to prevent the production of defective devices or systems. quantum noise Any noise attributable to the discrete nature of electromagnetic radiation. Examples include shot noise, photon noise, and recombination noise. quantum-limited operation An operation wherein the minimum detectable signal is limited by quantum noise. quartz A crystalline mineral that when electrically excited vibrates with a stable period. Quartz is typically used as the frequency-determining element in oscillators and filters. quasi-peak detector A detector that delivers an output voltage that is some fraction of the peak value of the regularly repeated pulses applied to it. The fraction increases toward unity as the pulse repetition rate increases. quick-break fuse A fuse in which the fusible link is under tension, providing for rapid operation. quiescent An inactive device, signal, or system. quiescent current The current that flows in a device in the absence of an applied signal. R rack An equipment rack, usually measuring 19 in (48.26 cm) wide at the front mounting rails. Dictionary of Audio Terms 14-141 rack unit (RU) A unit of measure of vertical space in an equipment enclosure. One rack unit is equal to 1.75 in (4.45 cm). radiate The process of emitting electromagnetic energy. radiation The emission and propagation of electromagnetic energy in the form of waves. Radiation is also called radiant energy. radiation scattering The diversion of thermal, electromagnetic, or nuclear radiation from its original path as a result of interactions or collisions with atoms, molecules, or large particles in the atmosphere or other media between the source of radiation and a point some distance away. As a result of scattering, radiation (especially gamma rays and neutrons) will be received at such a point from many directions, rather than only from the direction of the source. radio The transmission of signals over a distance by means of electromagnetic waves in the approximate frequency range of 150 kHz to 300 GHz. The term may also be used to describe the equipment used to transmit or receive electromagnetic waves. radio detection The detection of the presence of an object by radio location without precise determination of its position. radio frequency interference (RFI) The intrusion of unwanted signals or electromagnetic noise into various types of equipment resulting from radio frequency transmission equipment or other devices using radio frequencies. radio frequency spectrum Those frequency bands in the electromagnetic spectrum that range from several hundred thousand cycles per second (very low frequency) to several billion cycles per second (microwave frequencies). radio recognition In military communications, the determination by radio means of the “friendly” or “unfriendly” character of an aircraft or ship. random noise Electromagnetic signals that originate in transient electrical disturbances and have random time and amplitude patterns. Random noise is generally undesirable; however, it may also be generated for testing purposes. rated output power The power available from an amplifier or other device under specified conditions of operation. RC constant The time constant of a resistor-capacitor circuit. The RC constant is the time in seconds required for current in an RC circuit to rise to 63 percent of its final steady value or fall to 37 percent of its original steady value, obtained by multiplying the resistance value in ohms by the capacitance value in farads. RC network A circuit that contains resistors and capacitors, normally connected in series. reactance The part of the impedance of a network resulting from inductance or capacitance. The reactance of a component varies with the frequency of the applied signal. reactive power The power circulating in an ac circuit. It is delivered to the circuit during part of the cycle and is returned during the other half of the cycle. The reactive power is obtained by multiplying the voltage, current, and the sine of the phase angle between them. reactor A component with inductive reactance. 14-142 Standards and Practices received signal level (RSL) The value of a specified bandwidth of signals at the receiver input terminals relative to an established reference. receiver Any device for receiving electrical signals and converting them to audible sound, visible light, data, or some combination of these elements. receptacle An electrical socket designed to receive a mating plug. reception The act of receiving, listening to, or watching information-carrying signals. rectification The conversion of alternating current into direct current. rectifier A device for converting alternating current into direct current. A rectifier normally includes filters so that the output is, within specified limits, smooth and free of ac components. rectify The process of converting alternating current into direct current. redundancy A system design that provides a back-up for key circuits or components in the event of a failure. Redundancy improves the overall reliability of a system. redundant A configuration when two complete systems are available at one time. If the online system fails, the backup will take over with no loss of service. reference voltage A voltage used for control or comparison purposes. reflectance The ratio of reflected power to incident power. reflection An abrupt change, resulting from an impedance mismatch, in the direction of propagation of an electromagnetic wave. For light, at the interface of two dissimilar materials, the incident wave is returned to its medium of origin. reflection coefficient The ratio between the amplitude of a reflected wave and the amplitude of the incident wave. For large smooth surfaces, the reflection coefficient may be near unity. reflection gain The increase in signal strength that results when a reflected wave combines, in phase, with an incident wave. reflection loss The apparent loss of signal strength caused by an impedance mismatch in a transmission line or circuit. The loss results from the reflection of part of the signal back toward the source from the point of the impedance discontinuity. The greater the mismatch, the greater the loss. reflectometer A device that measures energy traveling in each direction in a waveguide, used in determining the standing wave ratio. refraction The bending of a sound, radio, or light wave as it passes obliquely from a medium of one density to a medium of another density that varies its speed. regulation The process of adjusting the level of some quantity, such as circuit gain, by means of an electronic system that monitors an output and feeds back a controlling signal to constantly maintain a desired level. regulator A device that maintains its output voltage at a constant level. relative envelope delay The difference in envelope delay at various frequencies when compared with a reference frequency that is chosen as having zero delay. Dictionary of Audio Terms 14-143 relative humidity The ratio of the quantity of water vapor in the atmosphere to the quantity that would cause saturation at the ambient temperature. relative transmission level The ratio of the signal power in a transmission system to the signal power at some point chosen as a reference. The ratio is usually determined by applying a standard test signal at the input to the system and measuring the gain or loss at the location of interest. relay A device by which current flowing in one circuit causes contacts to operate that control the flow of current in another circuit. relay armature The movable part of an electromechanical relay, usually coupled to spring sets on which contacts are mounted. relay bypass A device that, in the event of a loss of power or other failure, routes a critical signal around the equipment that has failed. release time The time required for a pulse to drop from steady-state level to zero, also referred to as the decay time. reliability The ability of a system or subsystem to perform within the prescribed parameters of quality of service. Reliability is often expressed as the probability that a system or subsystem will perform its intended function for a specified interval under stated conditions. reliability growth The action taken to move a hardware item toward its reliability potential, during development or subsequent manufacturing or operation. reliability predictions The compiled failure rates for parts, components, subassemblies, assemblies, and systems. These generic failure rates are used as basic data to predict the reliability of a given device or system. remote control A system used to control a device from a distance. remote station A station or terminal that is physically remote from a main station or center but can gain access through a communication channel. repeater The equipment between two circuits that receives a signal degraded by normal factors during transmission and amplifies the signal to its original level for retransmission. repetition rate The rate at which regularly recurring pulses are repeated. reply A transmitted message that is a direct response to an original message. repulsion The mechanical force that tends to separate like magnetic poles, like electric charges, or conductors carrying currents in opposite directions. reset The act of restoring a device to its default or original state. residual flux The magnetic flux that remains after a magnetomotive force has been removed. residual magnetism The magnetism or flux that remains in a core after current ceases to flow in the coil producing the magnetomotive force. residual voltage The vector sum of the voltages in all the phase wires of an unbalanced polyphase power system. 14-144 Standards and Practices resistance The opposition of a material to the flow of electrical current. Resistance is equal to the voltage drop through a given material divided by the current flow through it. The standard unit of resistance is the ohm, named for the German physicist Georg Simon Ohm (1787–1854). resistance drop The fall in potential (volts) between two points, the product of the current and resistance. resistance-grounded A circuit or system grounded for safety through a resistance, which limits the value of the current flowing through the circuit in the event of a fault. resistive load A load in which the voltage is in phase with the current. resistivity The resistance per unit volume or per unit area. resistor A device the primary function of which is to introduce a specified resistance into an electrical circuit. resonance A tuned condition conducive to oscillation, when the reactance resulting from capacitance in a circuit is equal in value to the reactance resulting from inductance. resonant frequency The frequency at which the inductive reactance and capacitive reactance of a circuit are equal. resonator A resonant cavity. return A return path for current, sometimes through ground. reversal A change in magnetic polarity, in the direction of current flow. reverse current A small current that flows through a diode when the voltage across it is such that normal forward current does not flow. reverse voltage A voltage in the reverse direction from that normally applied. rheostat A two-terminal variable resistor, usually constructed with a sliding or rotating shaft that can be used to vary the resistance value of the device. ripple An ac voltage superimposed on the output of a dc power supply, usually resulting from imperfect filtering. rise time The time required for a pulse to rise from 10 percent to 90 percent of its peak value. roll-off A gradual attenuation of gain-frequency response at either or both ends of a transmission pass band. root-mean-square (RMS) The square root of the average value of the squares of all the instantaneous values of current or voltage during one half-cycle of an alternating current. For an alternating current, the RMS voltage or current is equal to the amount of direct current or voltage that would produce the same heating effect in a purely resistive circuit. For a sinewave, the root-mean-square value is equal to 0.707 times the peak value. RMS is also called the effective value. rotor The rotating part of an electric generator or motor. RU An abbreviation for rack unit. Dictionary of Audio Terms 14-145 S scan One sweep of the target area in a camera tube, or of the screen in a picture tube. screen grid A grid in an electron tube that improves performance of the device by shielding the control grid from the plate. self-bias The provision of bias in an electron tube through a voltage drop in the cathode circuit. shot noise The noise developed in a vacuum tube or photoconductor resulting from the random number and velocity of emitted charge carriers. slope The rate of change, with respect to frequency, of transmission line attenuation over a given frequency spectrum. slope equalizer A device or circuit used to achieve a specified slope in a transmission line. smoothing circuit A filter designed to reduce the amount of ripple in a circuit, usually a dc power supply. snubber An electronic circuit used to suppress high frequency noise. solar wind Charged particles from the sun that continuously bombard the surface of the earth. solid A single wire conductor, as contrasted with a stranded, braided, or rope-type wire. solid-state The use of semiconductors rather than electron tubes in a circuit or system. source The part of a system from which signals or messages are considered to originate. source terminated A circuit whose output is terminated for correct impedance matching with standard cable. spare A system that is available but not presently in use. spark gap A gap between two electrodes designed to produce a spark under given conditions. specific gravity The ratio of the weight of a volume, liquid, or solid to the weight of the same volume of water at a specified temperature. spectrum A continuous band of frequencies within which waves have some common characteristics. spectrum analyzer A test instrument that presents a graphic display of signals over a selected frequency bandwidth. A cathode-ray tube is often used for the display. spectrum designation of frequency A method of referring to a range of communication frequencies. In American practice, the designation is a two or three letter acronym for the name. The ranges are: below 300 Hz, ELF (extremely low frequency); 300 Hz–3000 Hz, ILF (infra low frequency); 3 kHz–30 kHz, VLF (very low frequency); 30 kHz–300 kHz, LF (low frequency); 300 kHz–3000 kHz, MF (medium frequency); 3 MHz–30 MHz, HF (high frequency); 30 MHz–300 MHz, VHF (very high frequency); 300 MHz–3000 MHz, UHF (ultra high frequency); 3 GHz–30 GHz, SHF (super high frequency); 30 GHz–300 GHz, EHF (extremely high frequency); 300 GHz–3000 GHz, THF (tremendously high frequency). 14-146 Standards and Practices spherical antenna A type of satellite receiving antenna that permits more than one satellite to be accessed at any given time. A spherical antenna has a broader angle of acceptance than a parabolic antenna. spike A high amplitude, short duration pulse superimposed on an otherwise regular waveform. split-phase A device that derives a second phase from a single phase power supply by passing it through a capacitive or inductive reactor. splitter A circuit or device that accepts one input signal and distributes it to several outputs. splitting ratio The ratio of the power emerging from the output ports of a coupler. sporadic An event occurring at random and infrequent intervals. spread spectrum A communications technique in which the frequency components of a narrowband signal are spread over a wide band. The resulting signal resembles white noise. The technique is used to achieve signal security and privacy, and to enable the use of a common band by many users. spurious signal Any portion of a given signal that is not part of the fundamental waveform. Spurious signals include transients, noise, and hum. square wave A square or rectangular-shaped periodic wave that alternately assumes two fixed values for equal lengths of time, the transition being negligible in comparison with the duration of each fixed value. square wave testing The use of a square wave containing many odd harmonics of the fundamental frequency as an input signal to a device. Visual examination of the output signal on an oscilloscope indicates the amount of distortion introduced. stability The ability of a device or circuit to remain stable in frequency, power level, and/or other specified parameters. standard The specific signal configuration, reference pulses, voltage levels, and other parameters that describe the input/output requirements for a particular type of equipment. standard time and frequency signal A time-controlled radio signal broadcast at scheduled intervals on a number of different frequencies by government-operated radio stations to provide a method for calibrating instruments. standing wave ratio (SWR) The ratio of the maximum to the minimum value of a component of a wave in a transmission line or waveguide, such as the maximum voltage to the minimum voltage. static charge An electric charge on the surface of an object, particularly a dielectric. station One of the input or output points in a communications system. stator The stationary part of a rotating electric machine. status The present condition of a device. statute mile A unit of distance equal to 1,609 km or 5,280 ft. steady-state A condition in which circuit values remain essentially constant, occurring after all initial transients or fluctuating conditions have passed. Dictionary of Audio Terms 14-147 steady-state condition A condition occurring after all initial transient or fluctuating conditions have damped out in which currents, voltages, or fields remain essentially constant or oscillate uniformly without changes in characteristics such as amplitude, frequency, or wave shape. steep wavefront A rapid rise in voltage of a given signal, indicating the presence of high frequency odd harmonics of a fundamental wave frequency. step up (or down) The process of increasing (or decreasing) the voltage of an electrical signal, as in a step-up (or step-down) transformer. straight-line capacitance A capacitance employing a variable capacitor with plates so shaped that capacitance varies directly with the angle of rotation. stray capacitance An unintended—and usually undesired—capacitance between wires and components in a circuit or system. stray current A current through a path other than the intended one. stress The force per unit of cross-sectional area on a given object or structure. subassembly A functional unit of a system. subcarrier (SC) A carrier applied as modulation on another carrier, or on an intermediate subcarrier. subharmonic A frequency equal to the fundamental frequency of a given signal divided by a whole number. submodule A small circuit board or device that mounts on a larger module or device. subrefraction A refraction for which the refractivity gradient is greater than standard. subsystem A functional unit of a system. superheterodyne receiver A radio receiver in which all signals are first converted to a common frequency for which the intermediate stages of the receiver have been optimized, both for tuning and filtering. Signals are converted by mixing them with the output of a local oscillator whose output is varied in accordance with the frequency of the received signals so as to maintain the desired intermediate frequency. suppressor grid The fifth grid of a pentode electron tube, which provides screening between plate and screen grid. surface leakage A leakage current from line to ground over the face of an insulator supporting an open wire route. surface refractivity The refractive index, calculated from observations of pressure, temperature, and humidity at the surface of the earth. surge A rapid rise in current or voltage, usually followed by a fall back to the normal value. susceptance The reciprocal of reactance, and the imaginary component of admittance, expressed in siemens. sweep The process of varying the frequency of a signal over a specified bandwidth. 14-148 Standards and Practices sweep generator A test oscillator, the frequency of which is constantly varied over a specified bandwidth. switching The process of making and breaking (connecting and disconnecting) two or more electrical circuits. synchronization The process of adjusting the corresponding significant instants of signals—for example, the zero-crossings—to make them synchronous. The term synchronization is often abbreviated as sync. synchronize The process of causing two systems to operate at the same speed. synchronous In step or in phase, as applied to two or more devices; a system in which all events occur in a predetermined timed sequence. synchronous detection A demodulation process in which the original signal is recovered by multiplying the modulated signal by the output of a synchronous oscillator locked to the carrier. synchronous system A system in which the transmitter and receiver are operating in a fixed time relationship. system standards The minimum required electrical performance characteristics of a specific collection of hardware and/or software. systems analysis An analysis of a given activity to determine precisely what must be accomplished and how it is to be done. T tetrode A four element electron tube consisting of a cathode, control grid, screen grid, and plate. thyratron A gas-filled electron tube in which plate current flows when the grid voltage reaches a predetermined level. At that point, the grid has no further control over the current, which continues to flow until it is interrupted or reversed. tolerance The permissible variation from a standard. torque A moment of force acting on a body and tending to produce rotation about an axis. total harmonic distortion (THD) The ratio of the sum of the amplitudes of all signals harmonically related to the fundamental versus the amplitude of the fundamental signal. THD is expressed in percent. trace The pattern on an oscilloscope screen when displaying a signal. tracking The locking of tuned stages in a radio receiver so that all stages are changed appropriately as the receiver tuning is changed. trade-off The process of weighing conflicting requirements and reaching a compromise decision in the design of a component or a subsystem. transceiver Any circuit or device that receives and transmits signals. transconductance The mutual conductance of an electron tube expressed as the change in plate current divided by the change in control grid voltage that produced it. Dictionary of Audio Terms 14-149 transducer A device that converts energy from one form to another. transfer characteristics The intrinsic parameters of a system, subsystem, or unit of equipment which, when applied to the input of the system, subsystem, or unit of equipment, will fully describe its output. transformer A device consisting of two or more windings wrapped around a single core or linked by a common magnetic circuit. transformer ratio The ratio of the number of turns in the secondary winding of a transformer to the number of turns in the primary winding, also known as the turns ratio. transient A sudden variance of current or voltage from a steady-state value. A transient normally results from changes in load or effects related to switching action. transient disturbance A voltage pulse of high energy and short duration impressed upon the ac waveform. The overvoltage pulse can be one to 100 times the normal ac potential (or more) and can last up to 15 ms. Rise times measure in the nanosecond range. transient response The time response of a system under test to a stated input stimulus. transition A sequence of actions that occurs when a process changes from one state to another in response to an input. transmission The transfer of electrical power, signals, or an intelligence from one location to another by wire, fiber optic, or radio means. transmission facility A transmission medium and all the associated equipment required to transmit information. transmission loss The ratio, in decibels, of the power of a signal at a point along a transmission path to the power of the same signal at a more distant point along the same path. This value is often used as a measure of the quality of the transmission medium for conveying signals. Changes in power level are normally expressed in decibels by calculating ten times the logarithm (base 10) of the ratio of the two powers. transmission mode One of the field patterns in a waveguide in a plane transverse to the direction of propagation. transmission system The set of equipment that provides single or multichannel communications facilities capable of carrying audio, video, or data signals. transmitter The device or circuit that launches a signal into a passive medium, such as the atmosphere. transparency The property of a communications system that enables it to carry a signal without altering or otherwise affecting the electrical characteristics of the signal. tray The metal cabinet that holds circuit boards. tremendously high frequency (THF) The frequency band from 300 GHz to 3000 GHz. triangular wave An oscillation, the values of which rise and fall linearly, and immediately change upon reaching their peak maximum and minimum. A graphical representation of a triangular wave resembles a triangle. trim The process of making fine adjustments to a circuit or a circuit element. 14-150 Standards and Practices trimmer A small mechanically-adjustable component connected in parallel or series with a major component so that the net value of the two can be finely adjusted for tuning purposes. triode A three-element electron tube, consisting of a cathode, control grid, and plate. triple beat A third-order beat whose three beating carriers all have different frequencies, but are spaced at equal frequency separations. troposphere The layer of the earth's atmosphere, between the surface and the stratosphere, in which about 80 percent of the total mass of atmospheric air is concentrated and in which temperature normally decreases with altitude. trouble A failure or fault affecting the service provided by a system. troubleshoot The process of investigating, localizing, and (if possible) correcting a fault. tube (1—electron) An evacuated or gas-filled tube enclosed in a glass or metal case in which the electrodes are maintained at different voltages, giving rise to a controlled flow of electrons from the cathode to the anode. (2—cathode ray, CRT) An electron beam tube used for the display of changing electrical phenomena, generally similar to a television picture tube. (3—cold-cathode) An electron tube whose cathode emits electrons without the need of a heating filament. (4—gas) A gas-filled electron tube in which the gas plays an essential role in operation of the device. (5—mercury-vapor) A tube filled with mercury vapor at low pressure, used as a rectifying device. (6—metal) An electron tube enclosed in a metal case. (7—traveling wave, TWT) A wide band microwave amplifier in which a stream of electrons interacts with a guided electromagnetic wave moving substantially in synchronism with the electron stream, resulting in a net transfer of energy from the electron stream to the wave. (8—velocity-modulated) An electron tube in which the velocity of the electron stream is continually changing, as in a klystron. tune The process of adjusting the frequency of a device or circuit, such as for resonance or for maximum response to an input signal. tuned trap A series resonant network bridged across a circuit that eliminates (“traps”) the frequency of the resonant network. tuner The radio frequency and intermediate frequency parts of a radio receiver that produce a low level output signal. tuning The process of adjusting a given frequency; in particular, to adjust for resonance or for maximum response to a particular incoming signal. turns ratio In a transformer, the ratio of the number of turns on the secondary to the number of turns on the primary. tweaking The process of adjusting an electronic circuit to optimize its performance. twin-line A feeder cable with two parallel, insulated conductors. two-phase A source of alternating current circuit with two sinusoidal voltages that are 90° apart. U ultra high frequency (UHF) The frequency range from 300 MHz to 3000 MHz. Dictionary of Audio Terms 14-151 ultraviolet radiation Electromagnetic radiation in a frequency range between visible light and high-frequency X-rays. unattended A device or system designed to operate without a human attendant. unattended operation A system that permits a station to receive and transmit messages without the presence of an attendant or operator. unavailability A measure of the degree to which a system, subsystem, or piece of equipment is not operable and not in a committable state at the start of a mission, when the mission is called for at a random point in time. unbalanced circuit A two-wire circuit with legs that differ from one another in resistance, capacity to earth or to other conductors, leakage, or inductance. unbalanced line A transmission line in which the magnitudes of the voltages on the two conductors are not equal with respect to ground. A coaxial cable is an example of an unbalanced line. unbalanced modulator A modulator whose output includes the carrier signal. unbalanced output An output with one leg at ground potential. unbalanced wire circuit A circuit whose two sides are inherently electrically unlike. uncertainty An expression of the magnitude of a possible deviation of a measured value from the true value. Frequently, it is possible to distinguish two components: the systematic uncertainty and the random uncertainty. The random uncertainty is expressed by the standard deviation or by a multiple of the standard deviation. The systematic uncertainty is generally estimated on the basis of the parameter characteristics. undamped wave A signal with constant amplitude. underbunching A condition in a traveling wave tube wherein the tube is not operating at its optimum bunching rate. Underwriters Laboratories, Inc. A laboratory established by the National Board of Fire Underwriters which tests equipment, materials, and systems that may affect insurance risks, with special attention to fire dangers and other hazards to life. ungrounded A circuit or line not connected to ground. unicoupler A device used to couple a balanced circuit to an unbalanced circuit. unidirectional A signal or current flowing in one direction only. uniform transmission line A transmission line with electrical characteristics that are identical, per unit length, over its entire length. unit An assembly of equipment and associated wiring that together forms a complete system or independent subsystem. unity coupling In a theoretically perfect transformer, complete electromagnetic coupling between the primary and secondary windings with no loss of power. unity gain An amplifier or active circuit in which the output amplitude is the same as the input amplitude. 14-152 Standards and Practices unity power factor A power factor of 1.0, which means that the load is—in effect—a pure resistance, with ac voltage and current completely in phase. unterminated A device or system that is not terminated. up-converter A frequency translation device in which the frequency of the output signal is greater than that of the input signal. Such devices are commonly found in microwave radio and satellite systems. uplink A transmission system for sending radio signals from the ground to a satellite or aircraft. upstream A device or system placed ahead of other devices or systems in a signal path. useful life The period during which a low, constant failure rate can be expected for a given device or system. The useful life is the portion of a product life cycle between break-in and wear out. user A person, organization, or group that employs the services of a system for the transfer of information or other purposes. V VA An abbreviation for volt-amperes, volts times amperes. vacuum relay A relay whose contacts are enclosed in an evacuated space, usually to provide reliable long-term operation. vacuum switch A switch whose contacts are enclosed in an evacuated container so that spark formation is discouraged. vacuum tube An electron tube. The most common vacuum tubes include the diode, triode, tetrode, and pentode. validity check A test designed to ensure that the quality of transmission is maintained over a given system. varactor A semiconductor that behaves like a capacitor under the influence of an external control voltage. varactor diode A semiconductor device whose capacitance is a function of the applied voltage. A varactor diode, also called a variable reactance diode or simply a varactor, is often used to tune the operating frequency of a radio circuit. variable frequency oscillator (VFO) An oscillator whose frequency can be set to any required value in a given range of frequencies. variable impedance A capacitor, inductor, or resistor that is adjustable in value. variable-gain amplifier An amplifier whose gain can be controlled by an external signal source. variable-reluctance A transducer in which the input (usually a mechanical movement) varies the magnetic reluctance of a device. variation monitor A device used for sensing a deviation in voltage, current, or frequency, which is capable of providing an alarm and/or initiating transfer to another power source when programmed limits of voltage, frequency, current, or time are exceeded. Dictionary of Audio Terms 14-153 varicap A diode used as a variable capacitor. VCXO (voltage controlled crystal oscillator) A device whose output frequency is determined by an input control voltage. vector A quantity having both magnitude and direction. vector diagram A diagram using vectors to indicate the relationship between voltage and current in a circuit. vector sum The sum of two vectors which, when they are at right angles to each other, equal the length of the hypotenuse of the right triangle so formed. In the general case, the vector sum of the two vectors equals the diagonal of the parallelogram formed on the two vectors. velocity of light The speed of propagation of electromagnetic waves in a vacuum, equal to 299,792,458 m/s, or approximately 186,000 mi/s. For rough calculations, the figure of 300,000 km/s is used. velocity of propagation The velocity of signal transmission. In free space, electromagnetic waves travel at the speed of light. In a cable, the velocity is substantially lower. vernier A device that enables precision reading of a measuring set or gauge, or the setting of a dial with precision. very low frequency (VLF) A radio frequency in the band 3 kHz to 30 kHz. vestigial sideband A form of transmission in which one sideband is significantly attenuated. The carrier and the other sideband are transmitted without attenuation. vibration testing A testing procedure whereby subsystems are mounted on a test base that vibrates, thereby revealing any faults resulting from badly soldered joints or other poor mechanical design features. volt The standard unit of electromotive force, equal to the potential difference between two points on a conductor that is carrying a constant current of one ampere when the power dissipated between the two points is equal to one watt. One volt is equivalent to the potential difference across a resistance of one ohm when one ampere is flowing through it. The volt is named for the Italian physicist Alessandro Volta (1745–1827). volt-ampere (VA) The apparent power in an ac circuit (volts times amperes). volt-ohm-milliammeter (VOM) A general purpose multirange test meter used to measure voltage, resistance, and current. voltage The potential difference between two points. voltage drop A decrease in electrical potential resulting from current flow through a resistance. voltage gradient The continuous drop in electrical potential, per unit length, along a uniform conductor or thickness of a uniform dielectric. voltage level The ratio of the voltage at a given point to the voltage at an arbitrary reference point. voltage reference circuit A stable voltage reference source. 14-154 Standards and Practices voltage regulation The deviation from a nominal voltage, expressed as a percentage of the nominal voltage. voltage regulator A circuit used for controlling and maintaining a voltage at a constant level. voltage stabilizer A device that produces a constant or substantially constant output voltage despite variations in input voltage or output load current. voltage to ground The voltage between any given portion of a piece of equipment and the ground potential. voltmeter An instrument used to measure differences in electrical potential. vox A voice-operated relay circuit that permits the equivalent of push-to-talk operation of a transmitter by the operator. VSAT (very small aperture terminal) A satellite Ku-band earth station intended for fixed or portable use. The antenna diameter of a VSAT is on the order of 1.5 m or less. W watt The unit of power equal to the work done at one joule per second, or the rate of work measured as a current of one ampere under an electric potential of one volt. Designated by the symbol W, the watt is named after the Scottish inventor James Watt (1736–1819). watt meter A meter indicating in watts the rate of consumption of electrical energy. watt-hour The work performed by one watt over a one hour period. wave A disturbance that is a function of time or space, or both, and is propagated in a medium or through space. wave number The reciprocal of wavelength; the number of wave lengths per unit distance in the direction of propagation of a wave. waveband A band of wavelengths defined for some given purpose. waveform The characteristic shape of a periodic wave, determined by the frequencies present and their amplitudes and relative phases. wavefront A continuous surface that is a locus of points having the same phase at a given instant. A wavefront is a surface at right angles to rays that proceed from the wave source. The surface passes through those parts of the wave that are in the same phase and travel in the same direction. For parallel rays the wavefront is a plane; for rays that radiate from a point, the wavefront is spherical. waveguide Generally, a rectangular or circular pipe that constrains the propagation of an acoustic or electromagnetic wave along a path between two locations. The dimensions of a waveguide determine the frequencies for optimum transmission. wavelength For a sinusoidal wave, the distance between points of corresponding phase of two consecutive cycles. weber The unit of magnetic flux equal to the flux that, when linked to a circuit of one turn, produces an electromotive force of one volt as the flux is reduced at a uniform rate to zero in Dictionary of Audio Terms 14-155 one second. The weber is named for the German physicist Wilhelm Eduard Weber (1804– 1891). weighted The condition when a correction factor is applied to a measurement. weighting The adjustment of a measured value to account for conditions that would otherwise be different or appropriate during a measurement. weighting network A circuit, used with a test instrument, that has a specified amplitude-versusfrequency characteristic. wideband The passing or processing of a wide range of frequencies. The meaning varies with the context. Wien bridge An ac bridge used to measure capacitance or inductance. winding A coil of wire used to form an inductor. wire A single metallic conductor, usually solid-drawn and circular in cross section. working range The permitted range of values of an analog signal over which transmitting or other processing equipment can operate. working voltage The rated voltage that may safely be applied continuously to a given circuit or device. X x-band A microwave frequency band from 5.2 GHz to 10.9 GHz. x-cut A method of cutting a quartz plate for an oscillator, with the x-axis of the crystal perpendicular to the faces of the plate. X ray An electromagnetic radiation of approximately 100 nm to 0.1 nm, capable of penetrating nonmetallic materials. Y y-cut A method of cutting a quartz plate for an oscillator, with the y-axis of the crystal perpendicular to the faces of the plate. yield strength The magnitude of mechanical stress at which a material will begin to deform. Beyond the yield strength point, extension is no longer proportional to stress and rupture is possible. yoke A material that interconnects magnetic cores. Yoke can also refer to the deflection windings of a CRT. yttrium-iron garnet (YIG) A crystalline material used in microwave devices. 14-156 Standards and Practices 14.5.2 General Electronics Acronyms and Abbreviations1 A a atto (10–18) Å angstrom A ampere AAR automatic alternate routing AARTS automatic audio remote test set ac alternating current ACA automatic circuit assurance ACC automatic callback calling ACD automatic call distributor ac-dc alternating current - direct current ACK acknowledge character ACTS Advanced Communications Technology Satellite ACU automatic calling unit A-D analog-to-digital ADC analog-to-digital converter; analog-to-digital conversion ADCCP Advanced Data Communication Control Procedures ADH automatic data handling ADP automatic data processing ADPCM adaptive differential pulse-code modulation ADPE automatic data processing equipment ADU automatic dialing unit ADX automatic data exchange AECS Aeronautical Emergency Communications System [Plan] AF audio frequency AFC area frequency coordinator; automatic frequency control AFRS Armed Forces Radio Service 1. This section adapted from: General Services Administration, Information Technology Service, National Communications System: Glossary of Telecommunication Terms, Technology and Standards Division, Federal Standard 1037C, General Services Administration, Washington, D.C., August, 7, 1996. Dictionary of Audio Terms 14-157 AGC automatic gain control AGE aerospace ground equipment AI artificial intelligence AIG address indicator group; address indicating group AIM amplitude intensity modulation AIN advanced intelligent network AIOD automatic identified outward dialing AIS automated information system AJ anti-jamming ALC automatic level control; automatic load control ALE automatic link establishment ALU arithmetic and logic unit AM amplitude modulation AMA automatic message accounting AMC administrative management complex AME amplitude modulation equivalent; automatic message exchange AMI alternate mark inversion [signal] AM/PM/VSB amplitude modulation/phase modulation/vestigial sideband AMPS automatic message processing system AMPSSO automated message processing system security officer AMSC American Mobile Satellite Corporation AMTS automated maritime telecommunications system ANI automatic number identification ANL automatic noise limiter ANMCC Alternate National Military Command Center ANS American National Standard ANSI American National Standards Institute AP anomalous propagation APC adaptive predictive coding API application program interface APK amplitude phase-shift keying APL average picture level ARP address resolution protocol 14-158 Standards and Practices ARPA Advanced Research Projects Agency [now DARPA] ARPANET Advanced Research Projects Agency Network ARQ automatic repeat-request ARS automatic route selection ARSR air route surveillance radar ARU audio response unit ASCII American Standard Code for Information Interchange ASIC application-specific integrated circuits ASP Aggregated Switch Procurement; adjunct service point ASR automatic send and receive; airport surveillance radar AT access tandem ATACS Army Tactical Communications System ATB all trunks busy ATCRBS air traffic control radar beacon system ATDM asynchronous time-division multiplexing ATE automatic test equipment ATM asynchronous transfer mode ATV advanced television au astronomical unit AUI attachment unit interface AUTODIN Automatic Digital Network AUTOVON Automatic Voice Network AVD alternate voice/data AWG American wire gauge AWGN additive white Gaussian noise AZ azimuth B b bit B bel; byte balun balanced to unbalanced basecom base communications BASIC beginners’ all-purpose symbolic instruction code Dictionary of Audio Terms 14-159 BCC block check character BCD binary coded decimal; binary-coded decimal notation BCI bit-count integrity Bd baud B8ZS bipolar with eight-zero substitution bell BEL character BER bit error ratio BERT bit error ratio tester BETRS basic exchange telecommunications radio service BEX broadband exchange BIH International Time Bureau B-ISDN broadband ISDN bi-sync binary synchronous [communication] bit binary digit BIT built-in test BITE built-in test equipment BIU bus interface unit BNF Backus Naur form BOC Bell Operating Company bpi bits per inch; bytes per inch BPSK binary phase-shift keying b/s bits per second b/in bits per inch BPSK binary phase-shift keying BR bit rate BRI basic rate interface BSA basic serving arrangement BSE basic service element BSI British Standards Institution B6ZS bipolar with six-zero substitution B3ZS bipolar with three-zero substitution BTN billing telephone number BW bandwidth 14-160 Standards and Practices C c centi (10–2) CACS centralized alarm control system CAM computer-aided manufacturing CAMA centralized automatic message accounting CAN cancel character CAP competitive access provider; customer administration panel CARS cable television relay service [station] CAS centralized attendant services CASE computer-aided software engineering; computer aided system engineering; computer-assisted software engineering CATV cable TV; cable television; community antenna television CBX computer branch exchange C2 command and control C3 command, control, and communications C3CM C3 countermeasures C3I command, control, communications and intelligence CCA carrier-controlled approach CCD charge-coupled device CCH connections per circuit hour CCIF International Telephone Consultative Committee CCIR International Radio Consultative Committee CCIS common-channel interoffice signaling CCIT International Telegraph Consultative Committee CCITT International Telegraph and Telephone Consultative Committee CCL continuous communications link CCS hundred call-seconds CCSA common control switching arrangement CCTV closed-circuit television CCW cable cutoff wavelength cd candela CD collision detection; compact disk CDF combined distribution frame; cumulative distribution function Dictionary of Audio Terms 14-161 CDMA code-division multiple access CDPSK coherent differential phase-shift keying CDR call detail recording CD ROM compact disk read-only memory CDT control data terminal CDU central display unit C-E communications-electronics CEI comparably efficient interconnection CELP code-excited linear prediction CEP circular error probable CFE contractor-furnished equipment cgs centimeter-gram-second ChR channel reliability CIAS circuit inventory and analysis system CIC content indicator code CIF common intermediate format CIFAX ciphered facsimile CiR circuit reliability C/kT carrier-to-receiver noise density CLASS custom local area signaling service cm centimeter CMI coded mark inversion CMIP Common Management Information Protocol CMIS common management information service CMOS complementary metal oxide substrate CMRR common-mode rejection ratio CNR carrier-to-noise ratio; combat-net radio CNS complementary network service C.O. central office COAM customer owned and maintained equipment COBOL common business oriented language codec coder-decoder COG centralized ordering group 14-162 Standards and Practices COMINT communications intelligence COMJAM communications jamming compandor compressor-expander COMPUSEC computer security COMSAT Communications Satellite Corporation COMSEC communications security CONEX connectivity exchange CONUS Continental United States COP Committee of Principals COR Council of Representatives COT customer office terminal CPAS cellular priority access services CPE customer premises equipment cpi characters per inch cpm counts per minute cps characters per second CPU central processing unit; communications processor unit CR channel reliability; circuit reliability CRC cyclic redundancy check CRITICOM Critical Intelligence Communications CROM control read-only memory CRT cathode ray tube c/s cycles per second CSA Canadian Standards Association CSC circuit-switching center; common signaling channel CSMA carrier sense multiple access CSMA/CA carrier sense multiple access with collision avoidance CSMA/CD carrier sense multiple access with collision detection CSU channel service unit; circuit switching unit; customer service unit CTS clear to send CTX Centrex® [service]; clear to transmit CVD chemical vapor deposition CVSD continuously variable slope delta [modulation] Dictionary of Audio Terms 14-163 cw carrier wave; composite wave; continuous wave CX composite signaling cxr carrier D d deci (10–1) da deka (10) D-A digital-to-analog; digital-to-analog converter D/L downlink DACS digital access and cross-connect system DAMA demand assignment multiple access DARPA Defense Advanced Research Projects Agency dB decibel dBa decibels adjusted dBa0 noise power measured at zero transmission level point dBc dB relative to carrier power dBm dB referred to 1 milliwatt dBm(psoph) noise power in dBm measured by a set with psophometric weighting DBMS database management system dBmV dB referred to 1 millivolt across 75 ohms dBm0 noise power in dBm referred to or measured at 0TLP dBm0p noise power in dBm0 measured by a psophometric or noise measuring set having psophometric weighting dBr power difference in dB between any point and a reference point dBrn dB above reference noise dBrnC noise power in dBrn measured by a set with C-message weighting dBrnC0 noise power in dBrnC referred to or measured at 0TLP dBrn(f1–f2) flat noise power in dBrn dBrn(144) noise power in dBrn measured by a set with 144-line weighting dBv dB relative to 1 V (volt) peak-to-peak dBW dB referred to 1 W (watt) dBx dB above reference coupling dc direct current 14-164 Standards and Practices DCA Defense Communications Agency DCE data circuit-terminating equipment DCL direct communications link DCPSK differentially coherent phase-shift keying DCS Defense Communications System DCTN Defense Commercial Telecommunications Network DCWV direct-current working volts DDD direct distance dialing DDN Defense Data Network DDS digital data service DEL delete character demarc demarcation point demux demultiplex; demultiplexer; demultiplexing dequeue double-ended queue DES Data Encryption Standard detem detector/emitter DFSK double-frequency shift keying DIA Defense Intelligence Agency DID direct inward dialing DIN Deutsches Institut für Normung DIP dual in-line package DISA Defense Information Systems Agency DISC disconnect command DISN Defense Information System Network DISNET Defense Integrated Secure Network DLA Defense Logistic Agency DLC digital loop carrier DLE data link escape character DM delta modulation DMA Defense Mapping Agency; direct memory access DME distance measuring equipment DMS Defense Message System DNA Defense Nuclear Agency Dictionary of Audio Terms 14-165 DNIC data network identification code DNPA data numbering plan area DNS Domain Name System DO design objective DoC Department of Commerce DOD Department of Defense; direct outward dialing DODD Department of Defense Directive DODISS Department of Defense Index of Specifications and Standards DOD-STD Department of Defense Standard DOS Department of State DPCM differential pulse-code modulation DPSK differential phase-shift keying DQDB distributed-queue dual-bus [network] DRAM dynamic random access memory DRSI destination station routing indicator DS digital signal; direct support DS0 digital signal 0 DS1 digital signal 1 DS1C digital signal 1C DS2 digital signal 2 DS3 digital signal 3 DS4 digital signal 4 DSA dial service assistance DSB double sideband (transmission); Defense Science Board DSB-RC double-sideband reduced carrier transmission DSB-SC double-sideband suppressed-carrier transmission DSC digital selective calling DSCS Defense Satellite Communications System DSE data switching exchange DSI digital speech interpolation DSL digital subscriber line DSN Defense Switched Network DSR data signaling rate 14-166 Standards and Practices DSS direct station selection DSSCS Defense Special Service Communications System DSTE data subscriber terminal equipment DSU data service unit DTE data terminal equipment DTG date-time group DTMF dual-tone multifrequency (signaling) DTN data transmission network DTS Diplomatic Telecommunications Service DTU data transfer unit; data tape unit; digital transmission unit; direct to user DVL direct voice link DX signaling direct current signaling; duplex signaling E E exa (1018) E-MAIL electronic mail EAS extended area service EBCDIC extended binary coded decimal interchange code Eb/N0 signal energy per bit per hertz of thermal noise EBO embedded base organization EBS Emergency Broadcast System EBX electronic branch exchange EC Earth coverage; Earth curvature ECC electronically controlled coupling; enhance call completion ECCM electronic counter-countermeasures ECM electronic countermeasures EDC error detection and correction EDI electronic data interchange EDTV extended-definition television EHF extremely high frequency EIA Electronic Industries Association eirp effective isotropically radiated power; equivalent isotopically radiated power EIS Emergency Information System Dictionary of Audio Terms 14-167 el elevation ELF extremely low frequency ELINT electronics intelligence; electromagnetic intelligence ELSEC electronics security ELT emergency locator transmitter EMC electromagnetic compatibility EMCON emission control EMD equilibrium mode distribution EME electromagnetic environment emf electromotive force EMI electromagnetic interference; electromagnetic interference control EMP electromagnetic pulse EMR electromagnetic radiation e.m.r.p. effective monopole radiated power; equivalent monopole radiated power EMS electronic message system EMSEC emanations security emu electromagnetic unit EMV electromagnetic vulnerability EMW electromagnetic warfare; electromagnetic wave ENQ enquiry character EO end office E.O. Executive Order EOD end of data EOF end of file EOL end of line EOM end of message EOP end of program; end output EOS end-of-selection character EOT end-of-transmission character; end of tape EOW engineering orderwire EPROM erasable programmable read-only memory EPSCS enhanced private switched communications system ERL echo return loss 14-168 Standards and Practices ERLINK emergency response link ERP, e.r.p. effective radiated power ES end system; expert system ESC escape character; enhanced satellite capability ESF extended superframe ESM electronic warfare support measures ESP enhanced service provider ESS electronic switching system ETB end-of-transmission-block character ETX end-of-text character EW electronic warfare EXCSA Exchange Carriers Standards Association F f femto (10–15) f frequency FAA Federal Aviation Administration FAQ file Frequently Asked Questions file FAX facsimile FC functional component FCC Federal Communications Commission FCS frame check sequence FDDI fiber distributed data interface FDDI-2 fiber distributed data interface-2 FDHM full duration at half maximum FDM frequency-division multiplexing FDMA frequency-division multiple access FDX full duplex FEC forward error correction FECC Federal Emergency Communications Coordinators FED-STD Federal Standard FEMA Federal Emergency Management Agency FEP front-end processor Dictionary of Audio Terms 14-169 FET field effect transistor FIFO first-in first-out FIP Federal Information Processing FIPS Federal Information Processing Standards FIR finite impulse response FIRMR Federal Information Resources Management Regulations FISINT foreign instrumentation signals intelligence flops floating-point operations per second FM frequency modulation FO fiber optics FOC final operational capability; full operational capability FOT frequency of optimum traffic; frequency of optimum transmission FPIS forward propagation ionospheric scatter fps foot-pound-second FPS frames per second; focus projection and scanning FRP Federal Response Plan FSDPSK filtered symmetric differential phase-shift keying FSK frequency-shift keying FSS fully separate subsidiary FT fiber optic T-carrier FTAM file transfer, access, and management FTF Federal Telecommunications Fund ft/min feet per minute FTP file transfer protocol ft/s feet per second FTS Federal Telecommunications System FTS2000 Federal Telecommunications System 2000 FTSC Federal Telecommunications Standards Committee FWHM full width at half maximum FX fixed service; foreign exchange service FYDP Five Year Defense Plan 14-170 Standards and Practices G g profile parameter G giga (109) GBH group busy hour GCT Greenwich Civil Time GDF group distribution frame GETS Government Emergency Telecommunications Service GFE Government-furnished equipment GGCL government-to-government communications link GHz gigahertz GII Global Information Infrastructure GMT Greenwich Mean Time GOS grade of service GOSIP Government Open Systems Interconnection Profile GSA General Services Administration GSTN general switched telephone network G/T antenna gain-to-noise-temperature GTP Government Telecommunications Program GTS Government Telecommunications System GUI graphical user interface H h hecto (102); hour; Planck’s constant HCS hard clad silica (fiber) HDLC high-level data link control HDTV high-definition television HDX half-duplex (operation) HE11 mode the fundamental hybrid mode (of an optical fiber) HEMP high-altitude electromagnetic pulse HERF hazards of electromagnetic radiation to fuel HERO hazards of electromagnetic radiation to ordnance HERP hazards of electromagnetic radiation to personnel HF high frequency Dictionary of Audio Terms 14-171 HFDF high-frequency distribution frame HLL high-level language HPC high probability of completion HV high voltage Hz hertz I IA International Alphabet I&C installation and checkout IC integrated circuit ICI incoming call identification ICNI Integrated Communications, Navigation, and Identification ICW interrupted continuous wave IDDD International Direct Distance Dialing IDF intermediate distribution frame IDN integrated digital network IDTV improved-definition television IEC International Electrotechnical Commission IEEE Institute of Electrical and Electronics Engineers IES Industry Executive Subcommittee IF intermediate frequency I/F interface IFF identification, friend or foe IFRB International Frequency Registration Board IFS ionospheric forward scatter IIR infinite impulse response IITF Information Infrastructure Task Force ILD injection laser diode ILS instrument landing system IM intensity modulation; intermodulation I&M installation and maintenance IMD intermodulation distortion IMP interface message processor 14-172 Standards and Practices IN intelligent network INFOSEC information systems security INS inertial navigation system INTELSAT International Telecommunications Satellite Consortium INWATS Inward Wide-Area Telephone Service I/O input/output (device) IOC integrated optical circuit; initial operational capability; input-output controller IP Internet protocol; intelligent peripheral IPA intermediate power amplifier IPC information processing center IPM impulses per minute; interference prediction model; internal polarization modulation; interruptions per minute in/s inches per second ips interruptions per second IPX Internet Packet Exchange IQF intrinsic quality factor IR infrared IRAC Interdepartment Radio Advisory Committee IRC international record carrier; Interagency Radio Committee ISB independent-sideband (transmission) ISDN Integrated Services Digital Network ISM industrial, scientific, and medical (applications) ISO International Organization for Standardization ITA International Telegraph Alphabet ITA-5 International Telegraph Alphabet Number 5 ITC International Teletraffic Congress ITS Institute for Telecommunication Sciences ITSO International Telecommunications Satellite Organization ITU International Telecommunication Union IVDT integrated voice data terminal IXC interexchange carrier Dictionary of Audio Terms 14-173 J JANAP Joint Army-Navy-Air Force Publication(s) JCS Joint Chiefs of Staff JPL Jet Propulsion Laboratory JSC Joint Steering Committee; Joint Spectrum Center JTC3A Joint Tactical Command, Control and Communications Agency JTIDS Joint Tactical Information Distribution System JTRB Joint Telecommunications Resources Board JTSSG Joint Telecommunications Standards Steering Group JWID Joint Warrior Interoperability Demonstration K k kilo (103); Boltzmann’s constant K coefficient of absorption; kelvin KDC key distribution center KDR keyboard data recorder KDT keyboard display terminal kg kilogram kg·m·s kilogram-meter-second kHz kilohertz km kilometer kΩ, k kilohm KSR keyboard send/receive device kT noise power density KTS key telephone system KTU key telephone unit L LAN local area network LAP-B Data Link Layer protocol (CCITT Recommendation X.25 ) LAP-D link access procedure D laser light amplification by stimulated emission of radiation LASINT laser intelligence LATA local access and transport area 14-174 Standards and Practices LBO line buildout LC limited capability LCD liquid crystal display LD long distance LDM limited distance modem LEC local exchange carrier LED light-emitting diode LF low frequency LFB look-ahead-for-busy (information) LIFO last-in first-out LLC logical link control (sublayer) l/m lines per minute LMF language media format LMR land mobile radio LNA launch numerical aperture LOF lowest operating frequency loran long-range aid to navigation system; long-range radio navigation; long-range radio aid to navigation system LOS line of sight, loss of signal LP linearly polarized (mode); linear programming; linking protection; log-periodic (antenna); log-periodic (array) LPA linear power amplifier LPC linear predictive coding LPD low probability of detection LPI low probability of interception lpi lines per inch lpm lines per minute LP01 the fundamental mode (of an optical fiber) LQA link quality analysis LRC longitudinal redundancy check LSB lower sideband, least significant bit LSI large scale integrated (circuit); large scale integration; line status indication LTC line traffic coordinator Dictionary of Audio Terms 14-175 LUF lowest usable high frequency LULT line-unit-line termination LUNT line-unit-network termination LV low voltage M m meter M mega (106) MAC medium access control [sublayer] MACOM major command MAN metropolitan area network MAP manufacturers’ automation protocol maser microwave amplification by the stimulated emission of radiation MAU medium access unit MCC maintenance control circuit MCEB Military Communications-Electronics Board MCM multicarrier modulation MCS Master Control System MCW modulated continuous wave MCXO microcomputer compensated crystal oscillator MDF main distribution frame MDT mean downtime MEECN Minimum Essential Emergency Communications Network MERCAST merchant-ship broadcast system MF medium frequency; multifrequency (signaling) MFD mode field diameter MFJ Modification of Final Judgment MFSK multiple frequency-shift keying MHF medium high frequency MHS message handling service; message handling system MHz megahertz mi mile 14-176 Standards and Practices MIC medium interface connector; microphone; microwave integrated circuit; minimum ignition current; monolithic integrated circuit; mutual interface chart MILNET military network MIL-STD Military Standard min minute MIP medium interface point MIPS, mips million instructions per second MIS management information system MKS meter-kilogram-second MLPP multilevel precedence and preemption MMW millimeter wave modem modulator-demodulator mol mole ms millisecond (10–3 second) MSB most significant bit MSK minimum-shift keying MTBF mean time between failures MTBM mean time between maintenance MTBO mean time between outages MTBPM mean time between preventive maintenance MTF modulation transfer function MTSO mobile telephone switching office MTSR mean time to service restoration MTTR mean time to repair µ micro (10–6) µs microsecond MUF maximum usable frequency MUX multiplex; multiplexer MUXing multiplexing mw microwave MWI message waiting indicator MWV maximum working voltage Dictionary of Audio Terms 14-177 N n nano (10–9); refractive index N0 sea level refractivity; spectral noise density NA numerical aperture NACSEM National Communications Security Emanation Memorandum NACSIM National Communications Security Information Memorandum NAK negative-acknowledge character NASA National Aeronautics and Space Administration NATA North American Telecommunications Association NATO North Atlantic Treaty Organization NAVSTAR Navigational Satellite Timing and Ranging NBFM narrowband frequency modulation NBH network busy hour NBRVF narrowband radio voice frequency NBS National Bureau of Standards NBSV narrowband secure voice NCA National Command Authorities NCC National Coordinating Center for Telecommunications NCS National Communications System; net control station NCSC National Communications Security Committee NDCS network data control system NDER National Defense Executive Reserve NEACP National Emergency Airborne Command Post NEC National Electric Code® NEP noise equivalent power NES noise equivalent signal NF noise figure NFS Network File System NIC network interface card NICS NATO Integrated Communications System NID network interface device; network inward dialing; network information database NII National Information Infrastructure NIOD network inward/outward dialing 14-178 Standards and Practices NIST National Institute of Standards and Technology NIU network interface unit NLP National Level Program nm nanometer NMCS National Military Command System nmi nautical mile NOD network outward dialing Np neper NPA numbering plan area NPR noise power ratio NRI net radio interface NRM network resource manager NRRC Nuclear Risk Reduction Center NRZ non-return-to-zero NRZI non-return-to-zero inverted NRZ-M non-return-to-zero mark NRZ-S non-return-to-zero space NRZ1 non-return-to-zero, change on ones NRZ-1 non-return-to-zero mark ns nanosecond NSA National Security Agency NSC National Security Council NS/EP National Security or Emergency Preparedness telecommunications NSTAC National Security Telecommunications Advisory Committee NTCN National Telecommunications Coordinating Network NTDS Naval Tactical Data System NT1 Network termination 1 NT2 Network termination 2 NTI network terminating interface NTIA National Telecommunications and Information Administration NTMS National Telecommunications Management Structure NTN network terminal number Dictionary of Audio Terms 14-179 NTSC National Television Standards Committee; National Television Standards Committee (standard) NUL null character NVIS near vertical incidence skywave O O&M operations and maintenance OC operations center OCC other common carrier OCR optical character reader; optical character recognition OCU orderwire control unit OCVCXO oven controlled-voltage controlled crystal oscillator OCXO oven controlled crystal oscillator OD optical density; outside diameter OFC optical fiber, conductive OFCP optical fiber, conductive, plenum OFCR optical fiber, conductive, riser OFN optical fiber, nonconductive OFNP optical fiber, nonconductive, plenum OFNR optical fiber, nonconductive, riser OMB Office of Management and Budget ONA open network architecture opm operations per minute OPMODEL operations model OPSEC operations security OPX off-premises extension OR off-route service; off-route aeronautical mobile service OSHA Occupational Safety and Health Administration OSI open switching interval; Open Systems Interconnection OSI-RM Open Systems Interconnection—Reference Model OSRI originating stations routing indicator OSSN originating stations serial number OTAM over-the-air management of automated HF network nodes 14-180 Standards and Practices OTAR over-the-air rekeying OTDR optical time domain reflectometer; optical time domain reflectometry OW orderwire [circuit] P p pico (10–12) P peta (1015) PABX private automatic branch exchange PAD packet assembler/disassembler PAL phase alternation by line PAL-M phase alternation by line—modified PAM pulse-amplitude modulation PAMA pulse-address multiple access p/a r peak-to-average ratio PAR performance analysis and review PARAMP parametric amplifier par meter peak-to-average ratio meter PAX private automatic exchange PBER pseudo-bit-error-ratio PBX private branch exchange PC carrier power (of a radio transmitter); personal computer PCB power circuit breaker; printed circuit board PCM pulse-code modulation; plug compatible module; process control module PCS Personal Communications Services; personal communications system; plasticclad silica (fiber) PCSR parallel channels signaling rate PD photodetector PDM pulse delta modulation; pulse-duration modulation PDN public data network PDS protected distribution system; power distribution system; program data source PDT programmable data terminal PDU protocol data unit PE phase-encoded (recording) Dictionary of Audio Terms 14-181 PEP peak envelope power (of a radio transmitter) pF picofarad PF power factor PFM pulse-frequency modulation PI protection interval PIC plastic insulated cable ping packet Internet groper PIV peak inverse voltage PLA programmable logic array PL/I programming language 1 PLL phase-locked loop PLN private line network PLR pulse link repeater PLS physical signaling sublayer pm phase modulation PM mean power; polarization-maintaining (optical fiber); preventive maintenance; pulse modulation PMB pilot-make-busy (circuit) PMO program management office POI point of interface POP point of presence POSIX portable operating system interface for computer environments POTS plain old telephone service PP polarization-preserving (optical fiber) P-P peak-to-peak (value) P/P point-to-point PPM pulse-position modulation pps pulses per second PR pulse rate PRF pulse-repetition frequency PRI primary rate interface PRM pulse-rate modulation PROM programmable read-only memory 14-182 Standards and Practices PRR pulse repetition rate PRSL primary area switch locator PS permanent signal psi pounds (force) per square inch PSK phase-shift keying PSN public switched network p-static precipitation static PSTN public switched telephone network PTF patch and test facility PTM pulse-time modulation PTT postal, telephone, and telegraph; push-to-talk (operation) PTTC paper tape transmission code PTTI precise time and time interval PU power unit PUC public utility commission; public utilities commission PVC permanent virtual circuit; polyvinyl chloride (insulation) pW picowatt PWM pulse-width modulation PX private exchange Q QA quality assurance QAM quadrature amplitude modulation QC quality control QCIF quarter common intermediate format QMR qualitative material requirement QOS quality of service QPSK quadrature phase-shift keying QRC quick reaction capability R racon radar beacon rad radian; radiation absorbed dose radar radio detection and ranging Dictionary of Audio Terms 14-183 RADHAZ electromagnetic radiation hazards RADINT radar intelligence RAM random access memory; reliability, availability, and maintainability R&D research and development RATT radio teletypewriter system RBOC Regional Bell Operating Company RbXO rubidium-crystal oscillator RC reflection coefficient; resource controller RCC radio common carrier RCVR receiver RDF radio-direction finding REA Rural Electrification Administration REN ringer equivalency number RF radio frequency; range finder RFI radio frequency interference RFP request for proposal RFQ request for quotation RGB red-green-blue RH relative humidity RHR radio horizon range RI routing indicator RISC reduced instruction set chip RJ registered jack RJE remote job entry rms root-mean-square (deviation) RO read only; receive only ROA recognized operating agency ROC required operational capability ROM read-only memory ROSE remote operations service element protocol rpm revolutions per minute RPM rate per minute RPOA recognized private operating agency 14-184 Standards and Practices rps revolutions per second RQ repeat-request RR repetition rate RSL received signal level rss root-sum-square R/T real time RTA remote trunk arrangement RTS request to send RTTY radio teletypewriter RTU remote terminal unit RTX request to transmit RVA reactive volt-ampere RVWG Reliability and Vulnerability Working Group RWI radio and wire integration RX receive; receiver RZ return-to-zero S s second SCC specialized common carrier SCE service creation environment SCF service control facility SCP service control point SCPC single channel per carrier SCR semiconductor-controlled rectifier; silicon-controlled rectifier SCSR single channel signaling rate SDLC synchronous data link control SDM space-division multiplexing SDN software-defined network SECDEF Secretary of Defense SECORD secure voice cord board SECTEL secure telephone SETAMS systems engineering, technical assistance, and management services Dictionary of Audio Terms 14-185 SEVAS Secure Voice Access System S-F store-and-forward SF single-frequency (signaling) SGDF supergroup distribution frame S/H sample and hold SHA sidereal hour angle SHARES Shared Resources (SHARES) HF Radio Program SHF super high frequency SI International System of Units SID sudden ionospheric disturbance SIGINT signals intelligence SINAD signal-plus-noise-plus-distortion to noise-plus-distortion ratio SLD superluminescent diode SLI service logic interpreter SLP service logic program SMDR station message-detail recording SMSA standard metropolitan statistical area SNR signal-to-noise ratio SOH start-of-heading character SOM start of message sonar sound navigation and ranging SONET synchronous optical network SOP standard operating procedure SOR start of record SOW statement of work (S+N)/N signal-plus-noise-to-noise ratio sr steradian S/R send and receive SSB single-sideband (transmission) SSB-SC single-sideband suppressed carrier (transmission) SSN station serial number SSP service switching point SSUPS solid-state uninterruptible power system 14-186 Standards and Practices STALO stabilized local oscillator STD subscriber trunk dialing STFS standard time and frequency signal (service); standard time and frequency service STL standard telegraph level; studio-to-transmitter link STP standard temperature and pressure; signal transfer point STU secure telephone unit STX start-of-text character SUB substitute character SWR standing wave ratio SX simplex signaling SXS step-by-step switching system SYN synchronous idle character SYSGEN system generation T T tera (1012) TADIL tactical data information link TADIL-A tactical data information link-A TADIL-B tactical data information link-B TADS teletypewriter automatic dispatch system TADSS Tactical Automatic Digital Switching System TAI International Atomic Time TASI time-assignment speech interpolation TAT trans-Atlantic telecommunication (cable) TC toll center TCB trusted computing base TCC telecommunications center TCCF Tactical Communications Control Facility TCF technical control facility TCP transmission control protocol TCS trusted computer system TCU teletypewriter control unit TCVXO temperature compensated-voltage controlled crystal oscillator Dictionary of Audio Terms 14-187 TCXO temperature controlled crystal oscillator TD time delay; transmitter distributor TDD Telecommunications Device for the Deaf TDM time-division multiplexing TDMA time-division multiple access TE transverse electric [mode] TED trunk encryption device TEK traffic encryption key TEM transverse electric and magnetic [mode] TEMPEST compromising emanations TEMS telecommunications management system TGM trunk group multiplexer THD total harmonic distortion THF tremendously high frequency THz terahertz TIA Telecommunications Industry Association TIE time interval error TIFF tag image file format TIP terminal interface processor TK response timer TLP transmission level point TM transverse magnetic [mode] TP toll point TRANSEC transmission security TRC transverse redundancy check TRF tuned radio frequency TRI-TAC tri-services tactical [equipment] TSK transmission security key TSP Telecommunications Service Priority [system] TSPS traffic service position system TSR telecommunications service request; terminate and stay resident TTL transistor-transistor logic TTTN tandem tie trunk network 14-188 Standards and Practices TTY teletypewriter TTY/TDD Telecommunications Device for the Deaf TV television TW traveling wave TWT traveling wave tube TWTA traveling wave tube amplifier TWX® teletypewriter exchange service TX transmit; transmitter U UDP User Datagram Protocol UHF ultra high frequency U/L uplink ULF ultra low frequency UPS uninterruptible power supply UPT Universal Personal Telecommunications service USB upper sideband USDA U.S. Department of Agriculture USFJ U.S. Forces, Japan USFK U.S. Forces, Korea USNO U.S. Naval observatory USTA U.S. Telephone Association UT Universal Time UTC Coordinated Universal Time uv ultraviolet V V volt VA volt-ampere VAN value-added network VAR value added reseller VARISTAR variable resistor vars volt-amperes reactive VC virtual circuit Dictionary of Audio Terms 14-189 VCO voltage-controlled oscillator VCXO voltage-controlled crystal oscillator V/D voice/data Vdc volts direct current VDU video display unit; visual display unit VF voice frequency VFCT voice frequency carrier telegraph VFDF voice frequency distribution frame VFO variable-frequency oscillator VFTG voice-frequency telegraph VHF very high frequency VLF very low frequency V/m volts per meter VNL via net loss VNLF via net loss factor vocoder voice-coder vodas voice-operated device anti-sing vogad voice-operated gain-adjusting device volcas voice-operated loss control and echo/signaling suppression vox voice-operated relay circuit; voice operated transmit VRC vertical redundancy check VSAT very small aperture terminal VSB vestigial sideband [transmission] VSM vestigial sideband modulation VSWR voltage standing wave ratio VT virtual terminal VTU video teleconferencing unit vu volume unit W WADS wide area data service WAIS Wide Area Information Servers WAN wide area network 14-190 Standards and Practices WARC World Administrative Radio Conference WATS Wide Area Telecommunications Service; Wide Area Telephone Service WAWS Washington Area Wideband System WDM wavelength-division multiplexing WHSR White House Situation Room WIN WWMCCS Intercomputer Network WITS Washington Integrated Telecommunications System WORM write once, read many times wpm words per minute wps words per second wv working voltage WVDC working voltage direct current WWDSA worldwide digital system architecture WWMCCS Worldwide Military Command and Control System WWW World Wide Web X XMIT transmit XMSN transmission XMTD transmitted XMTR transmitter XO crystal oscillator XOFF transmitter off XON transmitter on XT crosstalk XTAL crystal Z Z Zulu time ZD zero defects Zo characteristic impedance 0TLP zero transmission level point Dictionary of Audio Terms 14-191 14.5.3 Bibliography Whitaker, Jerry C.: Power Vacuum Tubes Handbook, CRC Press, Boca Raton, Fla., 1999. General Services Administration, Information Technology Service, National Communications System: Glossary of Telecommunication Terms, Technology and Standards Division, Federal Standard 1037C, General Services Administration, Washington, D.C., August, 7, 1996.