Enqineerínq - American Radio History

Enqineerínq - American Radio History
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Enqineerínq
OCTOBER, 1936
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Thewww.americanradiohistory.com
Journal of World Communication
FROM
TRANSMITTER
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Complete Installation with
ISOLANTITE COAXIAL
TRANSMISSION LINE
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National Newark and Essex Bank Building. Showing location al transmitter and
antenna connected by ISOLANTITE COAXIAL TRANSMISSION LINE.
In the rapidly developing technique of radio communication engineers
the coaxial transmission line as the most efficient means of conducting
quency energy from point to point and from transmitter to antenna.
ISOLANTITE INC. has been closely identified with this development
announces A COMPLETE COAXIAL TRANSMISSION LINE SYSTEM
recognize
radio fre-
and now
for ultra
high frequency and broadcasting stations.
Write for our complete bulletin on this product. ISOLANTITE INC., 233 Broadway,
N. Y. C. Factory at Belleville, N. J.
Sold only through Graybar Electric Company and Manufacturers of transmitting equipment
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BROADCAST
CO MUNICATION
ENGINEERING
Registe ed U. S. Paten
Office
/
Member of Audit Bureau of Circulatio
Cp
GS
RAY D. RETTENMEYER
Editor
-
P.
F.
ENT oFFICE
VOLUME
OCTOBER, 1936
3
WALEN
Associate Editor
NUMBER
10
CONTENTS
FEATURES
Page
Editorial
2
A High- Frequency Pack Transmitter
A. Greer
5
Taylor
8
W. C. Eddy
12
of Instrument Landing and ColBy Henry W. Roberts
14
Albert Preisman
16
Chart Showing Attenuation of Resistance Pad vs. Ratio
of Termination to Input Resistance
26
By Palmer
COVER
ILLUSTRATION
THE
MODULATED
By John
Cold- Cathode Multipactors
By
The Simon System
lision Warning
Balanced Amplifiers, Part IV
AMPLI-
FIER TUBE CUBICLE IN THE
100 -KW SOTTENS (SWITZER-
LAND) BROADCASTING STATION. THIS PHOTOGRAPH
WAS FURNISHED THROUGH
THE COURTESY
Uni -Directional Microphone
By
P.
DEPARTMENTS
OF "ELEC-
TRICAL COMMUNICATION;
Telecommunication
18
The Market Place
20
Veteran Wireless Operators Association News
28
Over the Tape
30
Index of Advertisers
3I
Published Monthly by the
BRYAN DAVIS PUBLISHING CO., INC.
BRYAN S. DAVIS
President
47th Street
New York City
19 East
JAMES A. WALKER
Secretary
Chicago Office -608
S. Dearborn
Telephone: Wabash 1903.
New York Telephone: Plaza
St.-C. O.
Stimpson, Mgr.
Wellington. New Zealand -Te Aro Book Depot.
PAUL S. WEIL
Advertising Manager
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Circulation Manager
3 -0483
Ave.-J
Cleveland
Ohoce:
Melbourne,
C. Munn, Mgr
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act of March
at the Post Office at New York, N. Y., under the
Entered as second class matter October 17, 1934,
and Canada, $4.00 in foreion countries.
Yearly subscription ratet $3.00 in the United States
3, 1879.
cents in farrign countries.
fifty
Canada,
and
States
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cents
Single copies: thirtfive
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OCTOBER
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OCTOBER
1
9
3
6
EDTORIAL
BROADCAST ALLOCATIONS HEARING
representatives of broadcast stations, networks, educational and other
organizations were present at the recent
broadcast allocations hearing of the Federal
Communications Commission. This hearing
was held at the offices of the Commission in
Washington, D. C., beginning on October 5.
The many important recommendations
made at this gathering deserve much more
space than is available here. To mention a
few, however, the RMA urged maintenance
of clear channels, high power and the expansion of short-wave broadcasting ; NBC's
president, Lenox R. Lohr, discussed the economic and social aspects of broadcasting as
it appears in this country ; Arthur Van Dyck,
also representing the NBC, supplied facts
concerning the present performance of receivers in the home ; detailed engineering
data on receiver selectivity and fidelity, discussion of interference problems and a special recommendation for a protected i -f frequency were presented by L. C. F. Hoyle
who represented the RMA's Engineering
Committee : and I'aul M. Segal, counsel, and
Raymond M. Wilmotte, consulting engineer,
also appeared on behalf of the stations on
the 940-kc channel.
This hearing served to further emphasize
the fact that clear-channel stations do render a distinct service to the radio audience
of the United States. As a general rule,
they are high -power stations serving large
territories and providing good reception in
many communities remote from broadcast
stations. In this connection it is interesting
to note that a recent survey made by the
FCC showed that 75 percent of rural radio
listeners preferred programs from clear channel broadcasting stations rather than
from regional or local stations. Higher powers on clear channels will mean even better
service for this audience.
During the course of Mr. Lohr's testimony he recommended that the period of
broadcast licenses be extended to three years.
Mr. Lohr also recommended that the power
of regional stations be increased to 5 -kw for
both day and night, and he suggested power
increases for local stations "whenever the
engineering and economic factors warrant
the use of such power."
Mr. Wilmotte. in considering the limitations of and possibilities that may be provided
by regional broadcast stations, urged the
Commission that "in granting licenses, it
give careful consideration to the location of
the station, not only relative to other stations, but also relative to the nearest town
SEVERAL HUNDRED
2
so
....I
The October 5 broadcast allocations hearing was quite comprehensive in scope, and
the data presented should go far in helping
the Commission to determine future allocations.
ROCHESTER FALL MEETING
THE ANNUA1. RUl'11EsTER FALL MEETING, a
joint meeting of the Institute of Radio Engineers and the Engineering Division of the
Radio Manufacturers Association, is to be
held at the Sagamore Hotel, Rochester, New
York, from November 16 through 18.
The following are the technical articles
which will be presented at this gathering:
Equipment and Methods Used in Routine
Measurements of Loudspeaker Response, by
S. V. Perry (RCA) ; Current Measurements
at Ultra -High Frequencies, by J. H. Miller
(Weston) Acoustic Networks in Radio Receiver Cabinets, by H. S. Knowles ( Jensen)
Shot Effect in Space -Charge -Limited Vacuum Tubes, by B. J. Thompson and D. O.
North (RCA) Automatic Control of Selectivity by Feedback, by H. F. Mayer (General Electric) The Federal Communications
Commission and the Engineering Division of
RMA, by T. A. M. Craven (FCC) ; Radio
Tubes Today, by R. M. Wise (Hygrade Sylvania) ;Commercial Television and its Needs,
by A. N. Goldsmith (consulting engineer) ;
Latest Television Standards as Proposed by
the Engineering Division of the RMA, by A.
F. Murray (Philco) ; Survey of Receiver
Characteristics, by A. F. Van Dyck and D.
E. Foster (RCA License Lab.) Application of Nickel to Radio, by E. M. Wise
(Int'l. Nickel Co.) ; Partial Suppression of
One Sideband in Television Reception, by
W. J. Poch and D. W. Epstein (RCA) ; Improvements in Performance of Cabinet Type
Loudspeakers at Low Frequencies, by B.
Olney (Stromberg Carlson) ; Notes on
Feedback Amplifiers, by R. B. Dome (General Electric) and Improvements in High Frequency Receivers, by J. J. Lamp,
;
;
;
;
(ARRL).
The Rochester Fall Meetings have acquired an enviable reputation for their interesting technical sessions. This year's convention promises to be even more outstanding
than usual.
OCTOBER
19
3
that better synchronization, directional
effects, etc., may be used when wanted to
the best possible advantage
make a special plea that future engineering developments and the progress of broadcasting be
not endangered by freezing the space available on the basis of our present knowledge
and technical skill."
COMMUNICATION
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F
WCL
JAN ES VILLE, WISCONSI N
on die Giih.
teitA foStelot Elect4e4
)Ieeu 1OO-2SO/J'aIG
717441-611nélteAOther stations that
r
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23A's:
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WEXL
KABC
WFOY
WMBC
WBAX
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KFJB
WFBG
KlS
KGY
KRKO
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ti
WHOI
KDB
WSGN
WIBX
KYOS
WKOK
WLAP
WOCL
LISTENERS SAY: "Programs coming in clear as a
bell "... "I listened to your change from old to new,
and wish to say it was a great improvement ".. .
"WCLO comes to us the clearest of any station"...
"Reception so much better we will be among your
"Marvelous improvement. As
fans in future"
clear and fine as any high powered station."
-
...
WCLO SAYS: It took but 16 hours to set up the
transmitter and tune it. It has far fewer parts than
other new transmitters we investigated ... is simple
to tune and operate. As far as we have been able to
discover, it does everything Western Electric claims
for it."
WESTERN ELECTRIC SAYS: "The new 23A Trans-
mitter gives high fidelity performance at minimum
cost. You'll be interested in these features: high
overall efficiency... stabilized feedback... grid bias
modulation... complete AC operation... small tubes,
all radiation cooled." For full details, write Graybar
Electric, Graybar Building, New York.
Western Electric
Distributed by GRAYBAR Electric Co.
A D
R
I
O
T E L E P
H
O N
E
B
R
In
O A
Canada: Northern Electric Co., Ltd.
D C A
S T
I
N G
E
Q
U
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OCTOBER
COMMUNICATION
19
BROADCAST ENGINEERING
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N T
3
Rai 304a
laoil
INTRODUCING THE NEW
RCA UNI-DIRECTIONALR MICROPHONE
Type 77-A
-
Ingenious new type High Fidelity
Microphone...picks up sound coming only from
one direction...solves a problem that has
puzzled engineers for years
An achievement in the Microphone field featuring:
1.
2.
3.
4.
Uniform wide -angle response from the front.
Negligible response at ALL frequencies from the back.
Attenuates audience noises in theatres or large studios.
Can be placed closer to the wall in small studios without pick -up of reflected sound.
5. Can be tilted and rotated conveniently.
6. Can be used with all RCA Microphone Stands, or
suspended.
RCA's new Uni- Directional Microphone uses but a single
ribbon. The lower half of this new microphone is operated
on Velocity principles ... the upper half, Pressure. Ingenious labyrinth provides proper terminating impedance.
It practically kills all unwanted sounds. Wide pick -up
covers entire stage or studio where broadcasters are located,
thus eliminating the need for two or three ordinary microphones. Is ideal for small studio use, since it picks up a
much lower percentage of reflected sound.
Frequency response is uniform throughout the audio
range. The Type 77 -A affords reproduction as smooth and
pleasant as that provided by the standard Velocity Microphone, and can be used interchangeably, or can be mixed
with standard Velocity or Inductor type microphones.
Specifications: Output impedance, 250 ohms. Output
level (10 bar input), -69 db. Mountings, standard. Directional ratio, 10 -to-1.
Write us for complete descriptive literature concerning
this new broadcasting creation. The 77 -A -RCA Uni- Directional Microphone -is the one the experts demanded ...
Here it is!
'vamp
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that it can be placed close to the
back wall, with much less pick-up
of reflected sound from the back.
A
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The noise -discriminating feature
of this microphone is similarly
valuable if a large audience is
seated in
o
limited space.
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In small studios the Type 77 -A
Microphone has the advantage
a a
ìri:istt
Audience
Type 77 -A Microphone is uniquely adapted for pick -ups in auditoriums, theatres, night clubs
and the like, where audience
noise is always a problem. Because of the wide angle pick-up,
one microphone will usually suffice, even for large ensembles.
°
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P. M., E.'S.
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Listen to 'The Magic Key" every Sunday, a to
RCA MANUFACTURING CO., INC., CAMDEN, N. J.
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on NBC Blue Network
Service of the Radio Corporation of America
OCTOBER
COMMUNICATION
19
BROADCAST ENGINEERING
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COMM I\IICAI ON & BROA D CA ST
ENG II\IEIEIfII\\
FOR OCTOBER, 1936
A HICK -1: It EQUENCY
PACK TRANSMITTER
PALMER A. GREER
By
Transmitter Engineer
WHIO
YEAR there has been a
great deal of interest displayed, particularly in broadcasting circles, in the posFOR THE PAST
s
sibilities of portable high -frequency
transmitting equipment for use in locations where telephone lines are not
readily available. The networks and a
few independent stations have obtained
or built equipment for this purpose and
have rebroadcast programs picked up
on it with varied degrees of success.
M
To meet requirements a pack transmitter must, first of all, be as light and
SCHEMATIC
r
so that the person wearing it on his
small as possible and must be well balanced, so that it may be carried by an
announcer on location without putting
such a strain on him that he can not
keep his mind on his work. A good deal
of weight may be carried on a person's
back, provided it is well balanced. The
transmitter must have a good overall
frequency response, so that broadcast
quality is obtainable. The carrier must
be stable, as a signal that is shifting in
back may walk through confined spaces.
Design of the transmitter circuit must
be such that low voltages may be used
on the plates of all tubes and, at the
same time, current consumption kept at
a minimum.
The pack transmitter to be described
has been successfully used to broadcast
descriptions of circus parades and performances, "man -on-the-street" broadcasts from various downtown locations,
broadcasts from tall buildings, airplanes,
frequency means the difference between
a good rebroadcast and a poor one. The
antenna should be as short as possible
DIAGRAM OF
R. F.
THE
HIGH -FREQUENCY PACK
TRANSMITTER.
Unit
1
_ouoling Link
J
32
D.
Fig. 3
PSI Switch
E
+67.5V
-C, l9
-C,
-C,
30
32
-A
+A-fit C
WIOXGB 3f to 40 Mc. PACK
TRANSMITTER
19
AND
C
BROADCAST ENGINEERING
V1
COMMUNICATION
OCTOBER
3 6
www.americanradiohistory.com
etc.; stunt broadcasts of many types
have been carried out, most of them
with good results. However, on a few
occasions, unforeseen causes of interference or poor locations have marred
broadcasts.
When we first decided to try our luck
with some high- frequency rebroadcasts,
we were unable to decide on what type
of a circuit to use, so considerable experimenting was done, and the resulting
transmitter has, we believe, been worth
with antenna disconnected, is shown in
Fig. 2. The separation of the audio from
the r -f is very essential, as it was discovered that the r -f caused a feedback in the
audio amplifier when these units are
not isolated from each other. Shields
may be removed from either unit independently, thus facilitating servicing.
We shall first consider the r -f unit
(see Fig. 3). Two type 19 tubes are
used in this section, one as a push -pull
oscillator and the other as a Class C
circuits of both the oscillator and the
amplifier are tuned with variable condensers of 15 mmfds capacity. Grid and
plate inductances in both circuits are
coils of six turns, % inch in diameter
and wound from No. 12 tinned wire.
These coils are N inch in length. Condensers are mounted so as to permit all
controls to come flush with one side of
the case, where they may be easily tuned
by means of a non -metallic screwdriver. All inductances are mounted on
Isolantite stand -off or feedthru insulators, and are made quite rigid by ce-
menting thin strips of celluloid inside
the turns. Vibrationless inductances are
quite important, especially in the oscillator circuit, as any movement in these
coils, due to shocks or jars, will cause
the frequency to fluctuate. Neutralization of the r -f amplifier is accomplished
by means of two small thumb -nail trimmer condensers, and when properly adjusted, this stage shows no inclination
to break into oscillation. The r -f chokes
used consist of about 35 turns of No. 28
D. C. C. wire on a % -inch x 1%-inch
Isolantite form. The first ten turns are
slightly spaced.
It may seem that the use of two tubes
in the r -f section of this transmitter is
a waste of space and an additional drain
on the batteries, when possibly a modulated oscillator would be sufficient for
a transmitter of such low power. However, this point can be cleared up by
mentioning a few of the difficulties experienced when experimenting with
modulated oscillators. A unity- coupled
oscillator was tried and found to be very
unstable, even after trying every conceivable type of coupling to the antenna.
Any movement around this oscillator
caused a frequency change that was
noticeable even on a super -regenerative
receiver. A tuned-plate
tuned -grid
oscillator was also tried with about the
same amount of success, so we were
convinced that in spite of the extra
space necessary and the slightly additional current drain, the increased stability of operation more than offset
these disadvantages.
-
FIG. I.
SHOWING
THE
ASSEMBLY
all the time spent in its development.
This pack set is built in two separate
sections which are finally bolted together to form a single unit. The audio
amplifier, batteries, microphone receptacle, and battery switch are in one case
measuring 12 x 12 x 5 inches. The r -f
unit is in another case 5 x 5 x 8 inches.
Both cases are made of 1/16 inch sheet
aluminum, reinforced at necessary
points with duralumin angles, as may be
seen in Fig. 1. The complete assembly.
6
OF
THE
TRANSMITTER.
amplifier. This type of tube was used
for several reasons, .namely, low filament-current consumption, relatively
low plate voltage for normal operation,
and the ability to oscillate as well as
amplify at the ultra -high radio frequencies. These two stages are link coupled to each other, this method giving a very good transfer of excitation
from the oscillator to the grids of the
amplifier, and at the same time making
for ease of tuning. The plate 'Ind grid
.
An inductor microphone is used. It
works into a type 32 tube, which has a
fairly high amplification factor when
impedance coupled to the succeeding
stage. Resistance coupling was tried
but the gain obtained by this method
was not nearly as great as that of the
impedance coupling. A choke of about
1085 henries was used as a plate reactor.
The second stage consists of a type 30
tube, which is transformer coupled to
the grids of the 19 tube in the final
audio stage. This tube is operated as a
Class B amplifier and delivers plenty of
power to modulate tl-e ('lass C r -f am-
OCTOBER
COMMUNICATION
19
BROADCAST ENGINEERING
3
6
www.americanradiohistory.com
AND
r
plifier. A small amount of bias -about
-is used on the Class B amplifier and the resulting power output is
approximately 2 watts. The selection
of tubes was made with gain per tube
and battery drain being the major considerations, and a number of different
types were tried before being discarded
for one reason or another.
2 volts
One of the biggest problems encountered was the choice of a suitable antenna. Not much power is available in
the tank of the r -f amplifier, and hence
the necessity for an efficient antenna is
apparent-also a means of coupling the
antenna to the tank. After experimenting for days with about every type of
antenna applicable to a pack transmitter,
one was found that seemed to perform
better than the others. A piece of duralumin tubing % inch in diameter and
about four feet long was obtained, and
this was cut off about a foot from one
end. A small insulator 1 inch long and
of the same diameter as the tubing was
inserted between the two pieces. By
winding a coil around this insulator, a
sectionalized antenna, such as used by
a number of broadcast stations, was the
result. The coil was wound to load the
antenna to a quarter wave of the operating wavelength, and our four -foot
antenna worked as well as one cut to
a full quarter wavelength. Thus a saving of over two feet in the length of
the rod was effected when operating at
frequency of about 37.6 mc.
The antenna is inductively coupled to
the tank coil, one end of the coupling
coil being grounded and the other end
connected to the antenna through a
series variable condenser of 15 mmfds
capacity. This series condenser affords
a means of tuning the antenna circuit
to resonance with the tank. The antenna
is anchored to the chassis at the feed thru insulator and also to a stand -off
insulator 2% inches from the point at
which it is fed. Previous to the time the
sectionalized rod was adopted, the four foot rod was loaded at the bottom, and
also between the coupling coil and
ground, but in both cases the chassis
was hot with r -f and any movement
around the set seriously affected the
antenna current. Touching the microphone caused considerable drop in signal strength. Hence the search until the
sectionalized, loaded-top antenna was
tried and adopted.
The battery complement of the transmitter consists of two 1% -volt A bat teries, three 45 -volt batteries, and one
7% -volt C battery. Weight of the complete pack, including all batteries,
microphone, and antenna is about 30
pounds. A layer of sponge rubber on
the side that rests against the carrier's
back makes the load quite easy to bear.
Webbing straps bolted to the pack to
form a harness furnish the means of
strapping it on.
In the event that any of the readers
are contemplating the construction of a
pack transmitter, it might be well to
add a few remarks that will give an
idea as to what kind of performance to
expect. Consistently good broadcasts
over any great distance cannot be ob-
FIG.
2.
THE COMPLETE
ASSEMBLY
tamed, because of the low power available. A good rule to follow is to keep
the transmitter in sight of the receiving
point if possible. Very good results may
be had if too much is not expected of
the set. It is always a good policy to
test the locations of a proposed broadcast before actually putting it on the
air as a rebroadcast. In this manner,
dead spots can be located and avoided.
The receiving point should be as high
and as far from local interference, such
ignition, etc., as possible. A
good receiving antenna is, of course, as
important as a good transmitting antenna.
In order that the pack may be operated in one of the bands authorized by
the FCC for broadcast pickup, it is a
good idea to have some means of checking the operating frequency. This pack
is checked for frequency by means of a
simple wavemeter consisting of a pickup
coil, thermogalvanometer, and a 35as auto
WITH
ANTENNA
DISCONNECTED.
mmfd variable condenser. These parts
are mounted in a small aluminum case
about 4 inches square, the coil plugging
into pin jacks in the outside of the case.
The number of turns in the pickup coil
can easily be determined by experiment,
according to what frequency range is
desired, and the completed wavemeter
is calibrated by means of the Lecher
wire method, a description of which
may be found in most good radio handbooks.
COMMUNICATION
OCTOBER
I936
AND
BROADCAST ENGINEERING
www.americanradiohistory.com
DIRECTIONAL
By
JOHN
P.
MICROPHONE
TAYLOR
at least for the time being,
the opinion held by many station engineers -viz., that there is no such a thing
as an "all -purpose" microphone-the
new -model velocity microphones announced for production this fall and
winter include three quite different
types. First, there are the standard bidirectional models, intended primarily
for high -quality studio pickups-and
featuring, as an innovation, the use of
Alnico magnets. Second, there are
junior models which, with only a very
small sacrifice in response range, provide a saving of nearly two-thirds in
size and weight-qualities that, with
the lower cost (about half that of the
standard models), should do much to
advance the use of this type of microphone for remote pickups-particularly
those of the semi -fixed type. And, third,
there is a new uni- directional model
which is totally different from anything
heretofore available.
This uni-directional microphone, the
present model of which has been designed by Mr. L. J. Anderson, is based
on the idea originally developed by Dr.
H. F. Olson. The outstanding feature
which it incorporates-and the one
which gives it name
the property of
picking up sounds arriving from one
direction while rejecting, to all practical
purposes, those arriving from the opposite direction. This one -sided, or unidirectional, pickup is markedly different
from that of any of the various types
of microphones presently in use. In
order to fully comprehend the true extent of this difference, it is necessary to
recall briefly the meaning and importance of directional characteristics.
Experts in the sound engineering field
divide all microphones into two classifications -viz., directional and non directional. Unfortunately this perhaps-
CONSULTANT
CONFIRMING,
-is
too -simple division has led to some confusion. The difficulty being purely a
matter of the definition of directionalism, it is worthwhile to get the matter
straightened out. The directionalism of
some types of microphones is obvious.
For instance, the velocity microphone,
with its "figure -8" pattern, is responsive
from two sides and dead on the other
two sides, and this is true at all frequencies. Thus there can be no question
that it is a "directional" microphone.
Similarly, the "eight- ball" microphone,
and some types of crystal microphones -since they have an identical response all the way around -are definitely "non-directional" microphones.
However, after these are eliminated,
there remains the large group of microphones sometimes referred to as the
FIG.
2.
GRAPHICAL ILLUSTRATION
OF THE
OF
ADDITIVE ACTION OF THE TWO PARTS
THE UNI -DIRECTIONAL MICROPHONE.
limited angles. Since the condenser
microphone (as well as the other diaphragm types) responds to random
noises over more than two-thirds of the
audio range (speaking, of course, in
octaves), and even though the frequency
characteristic maintains no semblance of
uniformity at most angles, it is by this
definition, a "non-directional" microphone. Thus different definitions lead
to different conclusions. If the two
viewpoints are understood and kept in
mind there need be no confusion -however, this requires some practice. In
the meantime-and at the risk of introducing a third definition
is possible
to keep the matter straight by referring
to this class of microphones as "semi directional." Since these microphones
are in reality "non- directional" for
noise, whereas they are "directional"
for music, the in-between terms have a
connotation easy to remember.
With the meaning of directionalism
thus fixed in mind, the place which the
uni- directional microphone occupies
with respect to other types becomes
clear. Like the standard velocity microphone it has a limited angle of response
at all frequencies, and is, therefore, a
"directional" microphone by anyone's
-it
Response of upper
(pressure actuated)
half of
, ribbon
Response of lower
(velocity -actuated)
ho/f of ribbon
"diaphragm" types. These include condenser, dynamic, inductor and similar
types. It is in this classification that the
difficulty comes. To illustrate, an engineer using a condenser microphone in
the field, thinks in terms of its usefulness. It has a satisfactory pickup only
from one side -therefore, it is "directional." But the expert in the laboratory says -"not so !" For, according
to his definition, a "non-directional"
microphone is one which, in general,
responds to noises from random (all)
directions; a "directional" microphone,
one which responds only over certain
Combined response
of two halves of
ribbon (in series)
OCTOBER
COMMUNICATION
8 1936
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a.
f
definition. Unlike the standard model,
however, it is responsive on one side
only. The pickup pattern associated
with it might be likened to one of the
lobes of the "figure -8" pattern, with the
notable exception that the angle over
which substantial uniformity is obtained
is much greater. Thus, like the "semi directional" types, it is particularly
suited for those applications where the
desired sounds conic from one general
direction. However, while these earlier
types are "non- directional" to most frequencies -and particularly to the lower
frequencies which are most easily reflected-the uni- directional microphone
responds only to sounds coming from
the desired direction, no matter what
their frequency. Hence, the total pickup
of undesired sounds (extraneous and
reflected) is greatly reduced -theoretically fifty percent-and the possible
definition correspondingly increased.
Finally, like the "non -directional" types,
it has a frequency characteristic which
is essentially independent of angle-so
that artists may be arranged as desired
without fear of frequency discrimination. Thus, this new microphone may
be said to have adopted features of the
three earlier types-that is, the frequency response independent of angle
of the "non- directional," the single sidedness of the "semi- directional" and
the true directionalism of the "bidirectional." This does not mean that
these other types are obsolete. Quite
the contrary, the "non- directional" and
"bi- directional" will still be equal or
better for many (if not most) applications. And, too, the "semi- directional"
will still have a place, especially since
the higher price of the new microphone
will likely restrict its use to the more
critical applications.
TIONAL.
FIG.
FIG.
I.
FIG. I.
II -,EMI- DIRECTIONAL.
III -BI-DIRECTIONAL.
DIRECTIONAL CHARACTERISTICS
r
A more graphic (and, if correctly interpreted, more accurate) comparison
of the directional properties of the unidirectional microphone with those of
the three other types is provided by
Fig. 1. As the methods of portraying
directional characteristics are neither
standardized nor well -understood, some
explanation of these patterns is required.
First, it is obviously impossible to show
all frequencies-hence the question
which to choose to give an unbiased
comparison. Since the 1000 -cycle point
is widely used as a reference, a curve
for this frequency is obligatory. To
illustrate the low- frequency performance, the obvious choice is 100 cycles
chiefly because it is ordinarily the lowest frequency for which dependable in-
FIG.
I.
IV- UNI- DIRFCTIONAL.
-
COMMUNICATION
OCTOBER
19
3
formation is available (and, in any
event, curves below 100 cycles have, by
themselves, little real significance). For
a high- frequency point there is no obvious choice -for a variety of reasons.
The 5000-cycle point used in the accompanying curves is, admittedly, arbitrary. However, a careful consideration seems to indicate that for present day operating conditions it gives a fair
and quite representative picture.
In plotting these curves a slight departure from more -usual methods has
been made. Ordinarily the points of the
several frequency curves are all made
to pass through a zero point where they
cross the normal to the microphone
face. This is tantamount to assuming a
perfectly flat response along the normal -and the curves plotted can hence
only indicate the deviations from whatever the actual response is at the normal. Unless an additional curve of
response vs. frequency (along the normal) is given, this may lead to some
misconception. In the curves shown
here, only the 1000 -cycle (reference)
curve passes through zero at the normal -and the other two curves are
plotted to show the increase or decrease
in response at these frequencies. Thus
these curves show the actual frequency
characteristic at any angle, without
necessity of interpolating from another
curve. Of course, only three points of
any characteristic are available -however, the choice of the three frequencies
is such that a representative indication
is provided.
The radial ordinate, of all the curves
of Fig. 1, is decibels above or below the
1000 -cycle response on the normal. Such
a decibel scale has more practical meaning to the average station engineer than
does the more -usual percent- response
scale (which has a tendency to over accentuate the importance of deviations). In addition to showing quantitatively the performance at various angles, curves so plotted give, at a glance,
a general idea of the configuration of
artist placing. In the case of the curves
given here, the zero point has been
chosen so as to give the four patterns
size and shape of some comparative
value, although it is necessary to realize that factors independent of microphone characteristics have such a large
bearing on artist placing that comparisons of theoretical patterns are, at best,
only a beginning.
Curves of the kind shown in Fig. I
could be made to yield even more information by making the reference point
to actual measured output level of the
microphone for a given input (instead
of zero as here). However, the present
comparison is between the several
classifications of microphones. rather
than between individual models, and
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9
the fact that the various microphones
falling in any particular classification
may have widely- different output levels
rules out the use of absolute levels.
Similarly, it should be understood that
the curves of I, II and III of Fig. 1 arc
to be considered as typical of these gen-
eral classifications rather than as flic
actual values for any one make or model
of microphone. They may be thought of
as representing the mean of the outstanding types in each classification.
THE UNI- DIRECTIONAL
4.
: {Mie,'
PATTERN
The method by which uni- directional
pickup is obtained will seen[ complicated
to those who do not understand the
problem, surprisingly simple to those
who do. On first thought it might seem
that the directionalism of the diaphragm
microphones (at high frequencies) indicates tendency toward single sidedness.
However, on examination, it is found
that this effect is due to the distortion
of the sound field by the solid surface
of the microphone -more apparent at
high frequencies, of course, because the
dimensions of such surfaces are comparable to the wavelengths of high frequency sounds. Theoretically all diaphragm- type microphones arc "non directional" and would be in practice if
they could be made sufficiently small
that they did not seriously distort the
sound field, and if the cavity in front
of the diaphragm could be eliminated.
(In fact, miniature condenser microphones closely approaching these requirements have been made and used
for laboratory measurements.) Thus,
there are really only two kinds of char-
FIG.
Curves of equi - sensitivity
FIG. 6.
PHONE
IN SMALL STUDIOS THIS MICRO PROVIDES MAXIMUM SPACE FOR
ARTISTS.
acteristics -viz., the "non- directional"
characteristic of the pressure-actuated
microphones and the "bi- directional"
characteristic of the velocity-actuated
(pressure -gradient) microphones. All
other types must derive from these two.
The idea which Olson first called attention to-and which now seems so obvious -was simply to make a microphone
in two parts, so designed that one part
acted as a pressure- actuated microphone
while the other acted as a velocityactuated microphone. Combining the
responses of the two parts provided the
desired uni-di rectional characteristic.
This can be seen from inspection of
Fig. 2. The response of the "non directional" pressure-actuated part can
be represented by a circle with center
at the microphone ; that of the "bidirectional" velocity-actuated part by
two circles tangent to the microphone
faces. One of the latter is in phase
THE UNI- DIRECTIONAL MICROPHONE DISASSEMBLED
TO SHOW
LABYRINTH.
with, and hence adds to, the "nondirectional" circle, while the other is of
opposite phase and hence subtracts. The
resulting net response is represented by
a cardioid or revolution, providing a
very satisfactory degree of directionalism. These figures are, of course, the
idealized patterns. However, in practice
this theoretically predicted result is
closely approached -as can be seen by
IV of Fig. 1, which is the actual
measured response of the production
model. It is interesting to note that the
whole action is analogous to that of
"direction- finders" in which the non directional pickup of a vertical antenna
is combined with the two -sided pickup
of a loop antenna to give the required
directionalism.
TWO -IN -ONE CONSTRUCTION
The mechanical construction of the
uni- directional microphone is shown in
the several views (Figs. 3 and 4). The
relation of the constructional design to
the operation, deserves a short explanation. As can be seen, the moving elements of the two parts of the microphone are the respective halves of a corrugated ribbon identical in dimension
and mounting to that of the standard
velocity microphone, except that the
ribbon is fixed at the center so that the
two parts vibrate independently. The
lower half is free both in front and in
back, operates as a velocity microphone
and has a "bi- directional" pickup pattern similar to that of Fig. 1, III. The
upper half is enclosed in back, operates
as a pressure microphone and has a
"non- directional" pickup pattern similar
to that of Fig. 1, I. It might be well to
point out here that the widely- prevalent
idea that a ribbon microphone is, per
se, a velocity microphone is a misconception. In the standard velocity microphone the ribbon is open front and
back -hence the pressure which makes
it move is the difference between the
dynamic (i. e., varying) pressure in
front of it and the dynamic pressure in
back of it-or, in other words, the pressure gradient (i. e., change in pressure
with distance) in the sound wave itself.
This pressure gradient is proportional
to the velocity-hence the term, velocity
microphone. But the fact that the moving element is a ribbon is not the determining factor -and, a ribbon microphone is not necessarily a velocity
microphone. In the case of the upper
half of the ribbon of the uni -directional
microphone, it is strictly a pressure
microphone. This half of the ribbon is
enclosed in back by a closed labyrinth.
The pressure which causes it to move
is, therefore, the difference between the
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dynamic pressure in front of the ribbon and the static pressure behind it.
in other words, its movement is proportional only to the instantaneous pressure
in the sound wave-and it is, therefore,
a true pressure microphone.
The manner of enclosing the back of
the upper half of the ribbon is an essential element of the design. If this enclosure were simply a small closed
space, the trapped air would exercise
a damping effect dependent on frequency, the response would thus vary
with frequency as would also the directionalism. To avoid this it is necessary
to present an acoustic impedance to the
back of the ribbon. An infinitely long
open tube would be ideal -but this being
impractical, an equivalent effect has been
obtained by using a coiled labyrinth
lightly packed with absorbing material.
It is interesting to note that this upper
half of the uni- directional microphone
is not only a new type of pressure
microphone, but is, moreover, an unusually good one. Since it presents only very
small obstructing surfaces, it does not
distort the sound wave as do the diaphragm type microphones. Moreover,
the open structure removes possibility of
cavity resonance. Thus the pickup pattern it provides, instead of being "semidirectional" like other pressure microphones, is actually "non- directional"
like Fig. 1, I. This, together with the
"bi- directional" pattern of the lower
half of the ribbon, insures the action
illustrated in Fig. 2, and makes possible
the measured overall response indicated
by Fig. 1, IV.
APPLICATION AND USE
Front
(Fig.
.y
1,
this response characteristic
IV) the particular qualities of
the uni- directional microphone are immediately apparent. Specifically, they
are first, 20 db attenuation of back -side
pickup -that is, a 10 -to -1 ratio of desired to undesired signal ; second, a very
broad pickup angle-useful through 150
degrees, or more; third, a very uniform
frequency response throughout the
whole of this useful angle and, fourth,
response to extraneous noises (such as
reverberation) only fifty percent of that
of "non- directional" and "semi- directional" microphones.
The advantages of these unique qualities are so obvious as to hardly require
comment. They are particularly outstanding under certain special situations.
Primary of these, of course, is the condition met with in pickups from theatres, auditoriums and theatre or auditorium -type studios, where a large audience is present. In such cases the tinidirectional microphone furnishes the
only satisfactory method of cutting
FIG.
3.
THE
UNIDIRECTIONAL MICROPHONE
SHIELD REMOVED.
down audience noises. Placed as in Fig.
5, it is almost 100 percent efficient -and,
moreover, the angle of response is so
broad that for many, if not most, pickups, one microphone will suffice and will
replace several of other types. The
same advantage will, of course, obtain
in ordinary studios when an audience
is present in the studio itself.
In small studios, too, there will be at
least occasional times when this microphone will be advantageous- particularly when a more -than -normal number
of artists must be accommodated. This
statement is at first surprising. since it
FIG.
ETC..
5.
IN
THIS
AUDITORIUMS. THEATRES.
MICROPHONE CAN BE USED
TO ADVANTAGE.
3
OUTER
might be thought that "bi- directional"
or "non- directional" types would have
the advantage under such conditions. A
glance at Fig. 6 gives the answer. Because of its negligible back response the
uni- directional microphone can be placed
very much nearer to the back wall.
With even a small amount of "dead -end"
absorbing material it can be placed quite
close. Such back response as this microphone does have is practically all at the
higher frequencies-and, of course, even
relatively poor absorbing materials are
quite effective in this range. Thus it
allows a maximum number of artists to
be placed, means less deviation from
conventional seating arrangements and
does not require the leader to turn his
back on part of his orchestra.
In use the uni- directional microphone
should not require any special technique-and, in fact, should be less critical in most respects than other highquality types. The output level is of the
same order as that of the standard
velocity microphones -and impedances
and mountings are standard. Thus it
should not only he interchangeable with,
but also could, if desired, be mixed with
these. It provides sound and studio engineers with a new tool of considerable
possibilities, and while, at first, it will
be in the nature of a special instrument
for particularly critical jobs, it seems
reasonable to suppose that it will, before
long, be used as widely as other types.
COMMUNICATION AND
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OCTOBER
19
WITH
6
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COLD-CATHODE
DURING THE PAST IWO years, the Farns-
worth cold -cathode multipactors have
been repeatedly brought to the attention
of radio engineers through magazine
and newspaper articles, but now, with
the advent of this tube on the open market, particular interest is being shown
in its theory and application.
In view of this interest, a brief explanation of the fundamental principles
of operation of this type of tube should
be in order. The multipactor is, primarily, an electron multiplier in which
the principle of secondary emission produces both the high efficiency and the
rich harmonic content that makes this
type of tube adaptable to commercial
applications.
Electronic oscillation can occur
within the tube in several fundamental
modes dependent upon the physical arrangement and number of elements. One
type of oscillation will, of course, be
more suitable for a given application
than another, and for this reason we will
discuss the three general forms that
apply to present commercial practice.
The first mode considers a double cathode arrangement in which the electrons, under the influence of an external magnetic field, oscillate between the
two disc cathodes by reason of the
attraction set up by the ring-type anode
(see Figs. 1 -A and 1 -B). The second
mode considers a cylindrical cathode
surrounding an open grid -like anode,
the oscillation taking place between the
Anode
Cothode
inner diametrically- opposed surfaces
of the cathode (Figs. 2 -A and 2 -B) .
The third mode is similar to the second,
except for the addition of a third element erected in the center of the tube;
in this mode the oscillation depends
upon the effect of a negative field about
the third radius rather than the diameter of the tube.
In order to explain the theoretical
operation of the multipactor, let us consider a tube similar in construction to
the DM10, oscillating in the second
mode (Fig. 2). If the potential differ-
By
W. C. EDDY
(Lieut. U. S. N. Ret.)
tinue to oscillate about the central structure indefinitely. This theoretical condition, of course, will not produce sec-
ence between the anode and cathode is
properly established, the primary elec-
trons emitted from the cathode will be
accelerated toward the anode. Due to
the velocity acquired through this acceleration, they will continue on through
the central anode field toward the opposite cathode surface, being gradually
decelerated as they approach this cathode surface. If the acceleration is
equal and opposite to the deceleration,
the electrons will of course arrive at
the cathode with zero velocity. The
electrons will then repeat their travels
and under stable conditions would con-
Cathode
Cathode
-Anode
FIG.
I.S.
ondaries because an impact velocity has
not been furnished to "splash off" the
secondaries from the secondary emissive
surface. Some method must be employed to give these primaries a definite
impact velocity upon their arrival at the
second cathode surface.
Fig. 2 -A shows a circuit capable of
fulfilling these conditions. If the tank circuit frequency is of such order that
the electrons make five complete trips
per cycle (a purely arbitrary assumption) we can expect the conditions
.
i
ated, but the decelerative effect is now
only 680 volts, in that, at the time that
the electrons reach the opposite cathode
surface No. 1 and the deceleration taken
on between the anode and cathode surface No. 2, is 20 volts. The return trip
of the secondaries finds a similar difference existing upon their arrival at
cathode surface No. 1, and this condition will continue for five transits of
the tube. At this point the r -f voltage
of the tank has reached its maximum
and the electrons approaching the cathode will find the deceleration greater
NMI
Axial
non-emitting
cathode
Fig.4
12L
graphically illustrated in Fig. 3 to exist.
At the instant the initial electron leaves
the cathode the voltage curve of the r -f
circuit shows 200 volts negative, with
an anode voltage of 500 volts positive.
The electrons are, therefore, under the
accelerative effect of 700 volts. On leaving the axial anode field in its first
transit, the electron is gradually deceler-
OCTOBER
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19
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4.
MUJLTIPACTORS
FARNSWORTH TELEVISION
Incorporated
than the acceleration. From this point
on, these electrons will be unable to
impact upon the cathode and after a
FIG.
_w
2.B.
brief period of damped harmonic vibration about the anode they will be absorbed by this element, delivering their
energy to the circuit.
To briefly recapitulate this, on the
positive swing of the r -f cathode voltage
the deceleration is less than the acceleration and, therefore, on this half cycle
secondaries are produced by impact. On
the next half cycle, the deceleration being greater than the acceleration, electronic oscillation is damped, resulting in
the electrons being picked up on the
anode. The electron leaving the cathode
does not traverse its path without mishap. The wires forming the anode structure attract and collect about 10 percent
of the electrons attempting each passage.
This parasitic action of the anode and
the resultant deflection or absorption of
a portion of the electrons increases as
the square of the distance between anode
and cathode because as the distance is
increased, the projection of the width
of the wires on the cathode follows
optical equations.
There are two methods of limiting the
current taken up in the anode circuit.
First, it is evident that currents approaching infinity would build up in a
circuit in which the fundamental or
tank- circuit frequency was of such low
order that a great number of transits
and corresponding great multiplication
of currents were obtained. This is not
true, of course, because under low-
voltage and low-frequency conditions,
the anode's attraction will draw off such
a cloud of secondaries that their space
charge effect is of such order that no
further multiplication is probable. This
type of control can be termed "spacecharge suppression" and can be used in
all three modes at low and intermediate
frequencies and voltages.
The second method of suppressing
multiplication was illustrated in the explanation of the first mode of oscillation ; i. e., when the frequency is high
enough to limit the number of electron
transits and suppress further multiplication by reversing its polarity and collecting the energy. This effect will not
be encountered below 20 mc. With an
understanding of the fundamental principles of multipactor oscillation, the theory behind the other modes can be
briefly covered.
In the first mode, the double-cathode
ring, anode arrangement, the electrons
travel from cathode to cathode. An external magnetic field maintained axially
through the anode prevents the drift of
the electronic stream into the anode
until sufficient multiplication trips have
+200
+160
E,
!
ó
j
Electrons strike surface
I
+80
harmonics.
If we make an analysis of the electronic currents developed in a multi pactor we find that it is only during the
last few transits preceding suppression
that currents of any amount are developed. To all intents and purposes, then,
we can consider the power absorbed
and delivered to the circuit to be comparable to a current pulse of considerable magnitude. If the circuit's impedance is of such order that oscillation
is maintained under shock -excitation
conditions harmonic output comparable
in power to that of the fundamental can
be obtained.
Electrons strike surface
2
+413
o
Electrons strike surface I
-40
80
r_120
o -f60
cc
pull.
mode (Fig. 4), a metallic
out as a third element is
a negative potential that
the electrons are forced to oscillate over
a portion of the radius rather than the
diameter of the structure. In this type
of oscillation the production of harmonic frequencies will be intensified.
This is due to the fact that we have
approximately linear acceleration and
deceleration in the space between the
anode and outer cathode, but with much
larger deceleration near the small axial
cathode, producing both odd and even
modified push
In the third
pillar brought
held at such
Electrons strike surface 2
Electrons strike surface I
Electrons strike surface 2
+120
.e
ú
-
This type of multi pactor is particularly useful for highfrequency work where the half period
of the tank- circuit oscillation equals the
electron transit time. The tank -circuit
arrangement as shown in Fig. 1 -A is
been performed.
Electrons strike surface 2
Electrons return surface
Electrons strike surface
-200
I
2
Electron leaves cathode
Time
Electron Current Out of Cathode
Fig .3
Electron Current Picked
Up by Anode
AND
OCTOBER
COMMUNICATION
19
BROADCAST ENGINEERING
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1
n
3
- Cone of Silence
Safe
1
1
I,
Collision "warning
Loop
-''- -í
Transmitter*"
/
FIG.
4.
UTILIZATION
OF
í
i
Indicator automatically shows
zenithal bearing of obstruction
THE SIMON SYSTEM FOR COLLISION WARNING.
4.
THE SIMON SYSTEM
of
INSTRUMENT LANDING and COLLISION WARNING
THE NEED for a reliable method of locating a fog -bound airport, and then
making a safe landing within the airport limits without seeing the ground.
has long been realized in aviation. A
transportation system is valuable only
in proportion to the regularity of its
schedules. To maintain schedules, our
air liners must be able to operate under
all conditions of weather and visibility.
It is not an exaggeration to say that
radio makes commercial aviation possible. The array of dials on the instrument board can only tell the pilot how
he is flying; only radio can tell him
where he is. The invisible tentacles of
radio range beacons reach into the darkness and guide the invisible ships to
their invisible destinations. Radio direction finders, on the ground and in
the air, pick up wisps of song and code
and translate them into bearings and
position. The ubiquitous radio keeps
the pilot on his course, tells him of the
weather ahead, and brings him to his
FIG.
2.
THE
By
HENRY W. ROBERTS
destination -and if needs be, to a safe
landing.
The problem of instrument landing of
aircraft is extremely complex. Several
tons of metal, traveling at a minimum
safe speed of over a mile a minute
through an opaque void where there is
neither up nor down, must be gently
brought down to an invisible strip of
land less than a hundred feet wide and
but a few hundred feet long, and its
mode of travel transferred from three
dimensions to only two-from air -borne
wings to earth -borne wheels. Just as
"blind" flying instruments reproduce
for the pilot the invisible horizon, so
must the "blind" landing instruments
reproduce for him the invisible spatial
landing path from a point in space above
the ground to a point within the airport limits.
Reduced to elementals, the problem is
INDICATING INSTRUMENT AND RECEIVER.
to provide for the pilot automatic and
continuous information on his position
in space with respect to the airport.
This information must be three -fold: in
what direction the airport lies ; how
far down ; and how far away.
Not less than seven systems of instrument landing have so far been developed and successfully tested in flight,
each contributing something to this new
art, and although the ideal system has
not yet been devised, it is already possible to forsee the solution.
The problem of providing lateral guidance, i.e., indicating in what direction
the airport lies, is easily solved either
by the use of an equisignal zone type of
directional radio beacon or by the use
of a radio direction finder aboard the
airplane. The problem of longitudinal
guidance, i.e., indicating how far away
the airport lies, is likewise solved by
measuring the increase in the field intensity as the beacon is approached, for
approximate distance indications, and
using suitably located marker beacons
for definite position check.
The problem of vertical guidance, i.e.,
determination of the gliding path in a
vertical dimension, has, however, so far
presented difficulties. The solutions proposed by Diamond, Lorenz, Loth and
others, while extremely ingenious and
workable, cannot be regarded as final.
The solution described in this article,
proposed by Emil J. Simon, approaches
the matter from an entirely new angle
and has the paramount advantage in
that the pilot can approach the field
from any direction and at any altitude,
and bring his ship to the center of the
airport at any convenient gliding angle.
The Simon system of instrument
landing and collision warning is predicated on the use of a ratio -type radio
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direction finder. Such an instrument.
called the Simon Radioguide, was described in the August 1936 issue of
COMMUNICATION AND BROADCAST ENGINEERING and, for the benefit of those
who are not familiar with it, we will
briefly describe the principle of its
operation.
When used for radio direction finding, i.e., determination of position and
course in azimuth, the Radioguide consists of two small electrostatically
shielded loops fixedly mounted within
the airplane; a special twin- channel
superheterodyne receiver and an indicating instrument. The loops are disposed, in a vertical plane, at equal and
cpposite angles with respect to the
longitudinal axis of the airplane, each
feeding its corresponding channel of
the receiver ; and the indicating instrument measures the ratio of the outputs
of the two channels.
It is known that a vertical loop is
most receptive to signals emanating
from points lying within its plane and
least receptive to those at right angles
to it; between these two positions its
receptivity varies as the cosine of the
angle between the plane of the loop and
the source of signal. Therefore, given
two identical loops equally and oppositely disposed with respect to the longitudinal axis of the airplane, feeding two
identical channels of amplification having equal gain, and means of comparing
the output of the two channels, it is
possible to obtain constant and automatic measurement of the ratio of signal
intensities induced in the two loops and,
consequently, the direction and the angular bearing from which the received signal emanates.
Thus, in an airplane heading directly
at a transmitting station, the two loops
of the instrument are at equal (but opposite) angles to the source of the signal
and, consequently, the voltages induced
in the two loops are equal. If the airplane veers away from this heading,
there is an increase in signal strength
in one of the loops and a corresponding
;
y
r
r
FIG. 3.
FIG. I.
THE LOOP UNIT
decrease in the other loop. The ratio
of the signal intensities in the two
loops remains constant for a given angle
irrespective of the field strength or the
distance from the station. It is, therefore. possible to calibrate the indicating
instrument in degrees.
When used for obtaining vertical
guidance. i.e.. determination of position
and course in zenith. the two loops are
disposed. in a horizontal plane, at angles
equal and opposite with respect to the
horizontal axis of the airplane; and if
a suitable transmitter is provided on the
ground. the zenithal bearing of the
transmitter can be continuously and
automatically measured.
Such a transmitter is found in a horizontal loop antenna located underground
at the center of the airport (Fig. 3).
The field pattern of this antenna arrangement is shown in the drawing, and
its horizontal components, received by
the horizontally disposed loops, provide
vertical guidance and enable the pilot
to measure, in zenith, his bearing on the
center of the airport in degrees.
Perusal of Fig. 3 will disclose the
manner of making the "blind" approach
and "blind" landing. First, the pilot
approaches the airport at any convenient
altitude, taking his radio course on the
airport transmitter by means of a radio
APPROACHES MAY BE MADE FROM ANY DIRECTION.
OF THE SIMON
RADIOGUIDE.
direction tinder. When the airport is
near, he puts his Radioguide in operation and obtains a vertical bearing on
the airport. Knowing the flying characteristics of his airplane and the weight
it carries. the pilot is in a position to
select the optimum gliding angle to suit
his needs. He approaches the airport,
flying level, until the vertical-bearing
indicator shows that the airport lies
at that angle. whereupon he begins his
glide. Throughout his descent he has
a constant check on his bearings, in both
azimuth and zenith, and is immediately
warned by his instruments of any corrections needed in his course because of
wind drift or errors in piloting.
It is interesting to note that the
Radioguide permits such constant check
in both horizontal and vertical dimensions. Comparison of azimuthal radio
course with the directional gyro reading
gives the check for horizontal drift,
while comparison of zenithal radio
course with the inclinometer angle gives
information on whether the airplane is
descending along the correct landing
path, irrespective of the attitude of the
craft's axis with regard to the earth's
surface. In this manner the glide can
be made in either tail -low or tail -high
(Continued on page 27)
ALTITUDE AND ANGLE.
Cone
of
Silence
.
i
CC*
i
Optimum gliding ongle
Circular marker antenna around loop
OCTOBER
ii
Transm
COMMUNICATION
I936
L+*.
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BROADCAST ENGINEERING
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Balanced Amplifiers
PART
IV
By ALBERT PREISMAN
Head of The Department of Audio -Frequency Engineering
RCA INSTITUTES, INC.
XIV.
CONSTANT -MU PARABOLIC TUBES
for equation (27) of practical interest
ANOTHER FORM
is that where
A = 2VA,, A
which are exactly the assumptions niade in order that
equation (27) reduce to (28).
It is an experimental fact that in most triodes, the
tube surface is tangent to the eg
e, coordinate plane
(in which case the second-degree terms form a perfect
A.
Au,
of the tube. Under these two conditions equation (27)
becomes
(28)
A,, (µe + e,) + AO, (µe + ev )' = i,
rise
to
which is a parabolic cylinder, Fig. 19, and gives
a family of parabolas with equidistant spacing upon the
e,
i, and es i, coordinate planes, Fig. 20. If it
is remembered that the general definition of the amplification factor is
-
ai,
=--ae,
= Au:
/-
(29)
and that the A's of the power series are formed according to the law of a McLaurin Expansion, namely
;
v
(30)
ae,"
then, if µ is assumed constant, it can be shown that
A =µAu,
A
,,
=2µA.
=2ue,
=2
is zero, and (28) becomes
(32)
r
R,
(I,-I:) -+µE,.+µeJ
4
l'-g-
11
L
R,
=A E-(I,-I,)-+Ise. I
'
(33)
where E = (EB + SE,) is the equivalent diode voltage
for the d-c component and
rr
1.= Ann
LE+
(I,
-I,)
á -1.e.
R
(31)
(34)
From (33) and (34) we obtain
(I, -I,)
_
4AE
r
+ A. ER,,
ve,
= 2I,,
(35)
-
If we substitute the value of (I, I,) from (35)
(34), and set I, equal to zero, we obtain the value
pen
1
l'
4
of grid swing for cut-off of
:
-µ'= \
16
I=.\
in
A=µA
so that
in
This type of tube has some interesting properties. Referring to (32) we may write for the balanced -amplifier
circuit having a resistive load, RI,
1
aer,2
and
where
4
ae,
Al =
0
PROPERTIES OF SQUARE-LAW TUBE
XV.
òi,
a9.'
=
which is the well -known Van der Bijl's Equation.
a constant to be identified with the amplification factor
-
ae
(µe, + e,)'
ae,
i,
=µ
aiP
=
so that
and
)\
-
a
=E (1 + Ann ER,,)
I
namely:
(36)
If we substitute the latter value of µe, in either (33) or
(35) we obtain the value of I, where I, cuts off, to wit:
Au,
OCTOBER
COMMUNICATION
19
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AND
9
I,
=4AE'
(37)
At this point the plate voltage has dropped by the
amount (from (37) )
I,- =
R
(38)
Ap, E' R,,
4
and the effective voltage has been changed from E by
the amount of the corresponding grid swing given by
(36), or is now equal to E (2 + Ao_ ERL). Let the
remainder of the grid swing be designated by e,', then
beyond cut -off for I_, is
the equation for
I
rr
I, =A0,
(2
LE
+A.ER,,)
- -+µe:
I, R,,
=2 I,,
(39)
4
The reader can check. from this equation that I, equals
when µe,' is zero.
Equation (35) gives the relation between the load
current IL and µe, above cut-off of Iî (Class A operation), while (39) gives the relation below or beyond
cut -off of I2 (Class AB operation), for the particular
4A02 E2
tube given by (32).
The slope of IL above cut-off is evidently (differentiating (35) )
dI,
2
(µe,)
d
1
A. E
+
(40)
ER,,
The slope beyond cut -off, found by differentiating (39)
is
A(2E+µe,'+-a.E'R,
dI,
2
+- I2E +µe,' +AE-RL
A.
d(we;)
1
2
22
When µe,' equals zero, this becomes
2 A, E
dl,,
1.
d
r
1
+
.(41)
I,, R,,
(42)
Ao ERL
which is the same value given by (40). In other words,
the Class A characteristic blends smoothly into the
Class AB characteristic for this type of tube, and hence
the overall characteristic may be assumed to have less
higher harmonics than one exhibiting a sharp break at
this point. This matter may be conveniently represented
graphically by plotting one tube's characteristics inverted
with respect to the other, but so that their operating
I_) is tangent at
points line up. Thus in Fig. 21 (I,
-
cut -off to the I, and I, curves. The broken lines indicate the individual tube characteristics if they were parabolic beyond cut -off. It will be noted from (37) that
I, at cut-off is independent of RL: the smaller the latter
is, the faster I, increases, but also I2 to cut -off. Also
the blending shown in Fig. 21 is true regardless of the
value of R,, or E ( = EB + SE,.) the greater the bias,
or the smaller RL is, the sooner does cut -off begin, and
the sooner does the characteristic become I, alone and
continue parabolically as shown previously or given by
(39). The latter parabolic departure from linearity is
not great unless the grid swing is very much beyond
cut-off, and is moreover upward and in a direction to
offset the effects of grid current. Hence the relation
between load current IL and grid signal voltage e, may
be linear for quite a large value of the latter.
Equation (36) shows that the cut-off grid voltage is
smaller, the the smaller RL is, or E. The smaller E is,
the greater E, is relative to EB for a given A. The significance is that Class AB operation, namely operation up
to and beyond cut-off, is obtained either by means of
overbias or by using a low value of RL. At the same
time, the preceding paragraph has indicated that the
distortion products may nevertheless be small under these
conditions. The value of overbiasing is that a high
power- supply voltage EB may be used and yet the
quiescent d -c component Idc may be kept down to
where the plate dissipation at no- signal (equal to
Ids EB) is within safe limits. The possible increase,
thereby, of EB results in greater maximum power output.
The value of being able to use low values of RL is
that the latter can be chosen for maximum power output for a given EB without the restriction (so cramping
in single -side amplifiers) that the plate currents do not
approach too near cut-off and produce too much distortion.
:
OPTIMUM VALUE OF LOAD RESISTANCE
XVI.
The optimum value of RL for Class A operation is
easily formulated. Thus, for values of µe, below cut-off
(given by (36) ), and from (35), we have that the
power output is
R,,
2A' E' e.' RL
(I,
Po
-I,)'
=
_
8
(1
+ A. ER,,)'
(43)
The optimum value of RL occurs where
ap,
6R,,
= 0,
or
R,,= Ao,E =2r,
since the plate resistance, ro, is given by
r-
8
e,
- 2AE
(44)
1
(45)
It is to be noted that the above value of r, is that at the
operating point.
(Continued on page 22)
COMMUNICATION AND
BROADCAST ENGINEERING
OCTOBER
19
3 6
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17
TELEC:03iDiUNICATI /1N
PANORAMA OF PROGRESS IN THE
"MIRROPHONIC" SOUND SYSTEM
TILE NEW Western
Electric sound sys-
tem for theatres, known as the "Mirrophonic," was announced at a recent
ERPI sales convention held in New
York City. This system is said to
achieve a degree of naturalness exceeding anything heretofore heard by theatre
audiences
featuring higher quality,
increased volume range, and a speaker
system that provides uniform sound
over the entire theatre.
A new reproducer set is employed as
standard in the "Mirrophonic" system.
This unit employs a film -pulling mechanism known as the "Kinetic Scanner,"
in which a damped mechanical impedance is utilized to provide uniform film
velocity. It has also an improved optical
system in which the physical slit is replaced by a cylindrical lens combination.
The amplifier equipment is of advanced type. In addition to the excellent frequency characteristic and high
degree of reliability there is employed
a new device, termed a "Harmonic Suppressor." This may be compared to an
...
FIELDS OF
COMMUNICATION AND BROADCASTING
in the theatre may exceed the weakest
by more than 100,000,000 times.
The new amplifiers are very simple
to operate. They run entirely on a -c and'
all parts of the circuit requiring adjustment can be checked by means of a selector switch associated with a "Percentage Meter" -that is, a meter whose
scale is graduated to read percentages
of the normal or correct value, which is
taken as 100 percent.
The "Di- Phonic" speaker system employed forms part of the well -known
Stereophonic system. The term "DiPhonic" indicates that the sound is reproduced in two frequency ranges,
upper and lower. The upper range is
handled by cellular high- frequency
horns of the type employed in the
Philadelphia - Washington demonstration.* The low- frequency speakers are
of the dished -baffle type, in which the
principle of
cellular
sub -division
is
again employed to obtain proper low frequency distribution.
'See Bell Laboratories Record, May, 1933, p.
electrical governor which automatically.
and without any moving parts, causes
the amplifier to maintain constant quality, free from distortion, over an output
254.
range in which the loudest sounds heard
four southern states are now linked to-
-MIRROPHONIC"
THE
HIGHPOWER
TELETYPE FOR WEATHER BUREAUS
WEATHER BUREAUS in a dozen cities in
AMPLIFIER.
A
TYPICAL
gether by teletypewriters in an improved
hurricane warning service. Heretofore
it has often been difficult to find the
center, intensity, and direction of hurricanes in the Caribbean Ocean and Gulf
of Mexico because ships, upon whose
reports the weather bureau must rely,
naturally avoid the path of the storm.
Now these twelve weather bureaus are
organized into a connected series of reporting stations. Their reports, together
with reports received from vessels, give
accurate indication of where barometric
pressure is low, where it is rising or
falling, and other data which may be
interpreted into a general weather condition and into a forecast for a certain
period in advance. This information is
made instantly available, through the
24 -hour teletypewriter service, to the
cities linked in this weather- reporting
chain. These are: Jacksonville, Miami,
Key West, Tampa, and Pensacola, Fla.;
Mobile, Ala.; New Orleans, La.: Port
Arthur, Galveston, Houston, Corpus
Christi, and Brownsville, Tex. In case
of emergency, bulletins can be give' to
the newspapers for publication and to
radio stations for broadcasting by the
weather bureaus in any of these cities
which are in the path of a storm of
hurricane proportions.
"DI- PHONIC" SPEAKER INSTALLATION.
t
A,
18
OCTOBER
1
COMMUNICATION
936
AND
BROADCAST ENGINEERING
www.americanradiohistory.com
UTC
Linear Standard Audio Transformers are
of high
transquality audio show:
$8 to $25
Precise measurements
net price range of
formers in the
TRANSFORMER
LINE TO GRID
between
Measured deviation
cycles
30
and
1000
1.0 DB
beween
Measured deviation
cycles
1000 and 10,000
between
Measured deviation
cycle
15,000
and
1000
between
Measured deviation
cycles
20,000
and
1000
rox
DB rise at resonance shift)
(A
h
measure of phase ft)
Hum at maximum po
Hum at minimum position
Poorest
characteristics
el any high
lidelit units
1.5 DB
1.2DB
v
13DB
3 DB
2.8 DB
2.5 DB
2.8 DB
2.8 DB
42 DB
10DB
Critical organizations tan dard audios ms,
UTC oisaciA ... 01/1211.4
¿2O11DIV
FREQUENCY RANGE
Claims for wide frequency response are common today. UTC is the only organization that GUARAN± DB.
TEES its frequency response and it specifies the widest range of all: 30 to 20,000 CYCLES
1
lflililf
rt
PHASE SHIFT Ifs
UTC windLow distributed ccpacity is of paramount importance in audio components. The exclusive
makes 20,000 cycle response possible
ing method costs more but assures lowest possible capacity
and assures negligible phase shift.
...
...
1fß
HUM PICKUP
and cast ferrous
Most manufacturers have already adopted some form of humbucking coil structure UTC's hum balstaff. But
case. Both of these developments were pioneered by the UTC engineering
FIVE
anced coil structure is designed for POSITIVE SELF BALANCE and the UTC cast alloy has
TIMES THE PERMEABILITY OF ORDINARY CAST IRON.
llllllllll
TRI -ALLOY MAGNETIC FILTER
now incorporate TRI -ALLOY
In addition to their normal shielding, UTC low level input transformers
pickup tremendously. This
MAGNETIC FILTERING, a new method of shielding which reduces hum
methods. Rotation in
MAGNETIC FILTER was developed after a thorough analysis of hum reduction
while
much better, makes necone plane was found of practically no value. Orientation in two planes,
of its effect if the field plane is altered
essary unusual and unworkmanlike mounting and loses most(frequent
in remote pickup equipment).
or if stray flux from surrounding equipment is encountered
position has a hum
The MAGNETIC FILTER makes possible a transformer which in its worst pickup
available transformer on
level far lower than any other transformer in its best position. The nearest
in shieldadvancement
UTC
LS
-10.
This
the market under $25 shows 17 DB greater hum than the UTC
ing is the greatest forward step in ten years.
NEW YORK, N. Y.
72 SPRING STREET
EXPORT DIVISION
:
100
\+ARICK STREET
NEW YORK N.Y.
,
CABLES "ARLAB
:
"
COMMUNICATION
OCTOBER
1936
AND
BROADCAST ENGINEERING
www.americanradiohistory.com
/
yV
THE
MARKET PLACE
NEW PRODUCTS FOR THE COM MU NICATION AND BROADCAST FIELDS
VACUUM -TUBE, PEAK VOLTMETER
Clough -Brengle Co., of 2815 W.
19th St., Chicago, Ill., nave just announced
their Model 88 combination vacuum-tube
voltmeter and peak- voltage indicator.
As a vacuum -tube voltmeter, a range of
0 -1.2 volts rms is covered by direct connection to the tube (Type 6F5 metal) grid
without any shunts. Thus, a large deflection is secured by potentials as low as 0.1
volt on the 4% -inch fan -type meter. The
voltmeter tube is placed at the end of a 30inch extension cable, making possible direct
connection of the tube grid -cap in the circuit, the potential of which it is desired to
measure, and thus eliminating all capacity
effects.
As a peak voltmeter, ranges of 0 -10 and
0 -100 are provided without the necessity
of external power supply. These find wide
usage in measuring avc, c -bias, and other
potentials where no current drain is permitted and where the wave shape is other
than sinusoidal with the resultant lack of
fixed relationship between rms and peak
potentials.
the tube ..,, as to develop a 4 -inch image.
A power generator keeps the neon tube
ignited. This is made up with a 6L6 beam
power tube as a 100 kc radio -frequency
oscillator feeding directly into the neon
oscilloscope tube. This system keeps a constant glow on the tips of the electrodes.
The input potentials are amplified by a
6J7 and 6L6 high -gain audio amplifier
and impressed on the power generator.
The
VACUUMTUBE VOLTMETER.
GAMMATRON
the Type 154 Gammatron.
In physical appearance the 154 stands
approximately 6% inches from top to toe
and has a straight -sided glass envelope 2
inches in diameter. The base is of the
standard UX type. The grid and plate
leads are rigid tungsten rods extending
through opposite sides of the glass envelope. These form the double side -arm construction which has proved so satisfactory
at ultra -high frequencies.
Tantalum grid and plate, solidly supported, are incorporated in this tube. Ample
plate emission is also said to be obtained,
the actual safe rating of 175 milliamperes
being conservative.
The main feature of this tube is low
plate -voltage operation. Whereas 1,500
volts is safe, high outputs may also be
secured with 750 volts. This is said to
hold whether the tube is used in a -f or r -f
circuits at waves as low as 5 meters.
The general ratings of the Type 154 are
OAMMAT RON
154.
CRYSTAL COUPLER
:
Filament voltage....
Filament current....
Plate dissipation....
NEOBEAM
OSCILLOSCOPE
Plate voltage
Plate current
1
5.0 volts
6.5 amperes
50 watts
500 volts (max.)
175 ma
30 ma
Grid current
(max. aver.)
(max. aver.)
Plate resistance
1,750 ohms
constant
6.7
Complete information may be secured
from the above organization.
NEOBEAM OSCILLOSCOPE
20
154
Heintz & Kaufman, Ltd., South San
Francisco, Calif., have recently announced
a low- voltage transmitting tube, known as
The Radio Engineering and Manufacturing Co.. 26 Journal Square, Jersey City,
N. J., has just developed a preliminary
coupling amplifier for use with any type
crystal pickup.
The new unit is known as the R20 -A
Crystal Coupler and the entire unit, which
incorporates such features as low -and high .frequency compensation, complete a -c operation, and 50- 200 -ohm output terminations, is built within a round metal casing that may be mounted directly in the
top of transcription tables, or when independent floor -type turntables are used, the
coupler may be supplied with a special
floor stand and pickup bracket which fastens to the side of the coupler unit.
Bulletin 14A is now being prepared. It
fully describes this new equipment.
The Neobeam oscilloscope is an electronic measuring device using a gaseous
discharge tube to make sound visible. The
wave pattern is traced on a 4 -inch calibrated screen with clear definition between
amplitude and frequency.
The principle by which the gaseous oscilloscope tube operates is that the area of
the glow covering the elongated cathode is
proportional to the current passing through
the tube. On alternating current the electrodes glow alternately depending upon
the frequency of the impressed voltage.
This development, while new, is along the
line of experiments started by Mr. E.
Gherke in 1904.
The oscilloscope tube as now developed
measures 6 inches overall by % inch diameter and is filled with neon gas. The
two electrodes are 2 inches long by >'sinch diameter and set at each end of
This fluctuating power corresponds to the
vertical deflection of the wave pattern.
Complete information may be obtained
from Sundt Engineering Company, 4238
Lincoln Ave., Chicago, Ill.
Amplification
PORTABLE SOUND SYSTEM
The Clarion Model C -45 is a portable
sound system. The speaker, amplifier, microphone and desk stand are all
contained in a luggage case which meas5 -watt
PORTABLE
SOUND
SYSTEM.
ures 12% by 12% by 87A inches.
In operation the amplifier is removed
from the case, the case then acting as a
baffle for the speaker. Twenty -five feet of
rubber -covered cable is attached to the
speaker for connecting to the amplifier.
The amplifier is of the high -gain type and
the system can be used with any modern
type of microphone.
The Clarion Model C -45 is a product
of the Transformer Corporation of Amerka, 69 Wooster St., New York City.
OCTOBER
COMMUNICATION
19
BROADCAST ENGINEERING
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AND
t
for speech- amplifier filaments
in broadcast stations, motion- picture theatres, motion-picture studios, public -address and centralized radio systems.
An essential design feature of this unit
is the stabilized d -c output. A special circuit is used which holds the d -c output essentially constant regardless of the load
imposed on the RectiFilteR. The ripple
(a -c component) remaining in the d -c output is -80 db, and it is stated that this may
he reduced to -120 db through the use of
an auxiliary filter.
Further details may be obtained by requesting Bulletin DL48 -118 from the Raytheon Manufacturing Company, Electrical
Equipment Division, 102 Willow Street,
Waltham, Mass.
MYCALEX PRODUCTS
110 -volt a -c)
AMPERITE BOOM STAND
By merely a slight pressure of the hand,
the new Amperite boom stand is silently
adjustable in a vertical or horizontal position. The microphone can therefore be
placed at any height and at any angle desired. No adjusting screws are required.
This action is obtainable by using a ball
clutch for the vertical adjustment. Obtainable in chrome or gunmetal finish. Complete information may be obtained from
Amperite Corporation, 561 Broadway, New
York City.
The American Radio Hardware Co.,
Inc., 476 Broadway, New York. announce
a new line of Mycalex radio parts and accessories.
In addition to the extensive line of coil
forms, midget variable condensers, crystal
holders, and all the popular size glass -tube
sockets have been made available. Depicted
herewith are two of the more specialized
types of Mycalex sockets for use with the
RCA -803 and RK-28.
Write for Catalog No. 36A.
RECTIFILTER
The Raytheon RectiFilteR, shown in the
accompanying illustration, has been designed to supply d -c power (direct from
A "HIGH POWER"
STANDARD
SIGNAL GENERATOR
Suitable for
RESEARCH AND DESIGN
LABORATORY USE
Output up to TWO VOLTS available across LOW RESISTANCE
MODEL 14C STANDARD SIGNAL GENERATOR
Built in coils cover 75 to 30,000 kilocycles.
Operates on EITHER 115 volt, 60 cycle AC OR on batteries (without change in instrument)
Can be made for any reasonable line voltage and frequency
specified at additional charge of $10.00
Low radio frequency harmonics (Approx. %)
I
Price, $1,250.00 FOB Newark, N.
lUN /TE
J.
(Never over 20 ohms).
Accurate measurements can be made at
fractions of a microvolt, as smallest scale
division is for one -tenth microvolt.
WORM DRIVE TUNING CONDENSER
makes possible measurement of very small
differences. The 30 FOOT
total scale length provides 25 large divisions, approx. 3 inch scale length, for
each IO Kcs. in broadcast band, and corresponding spread at other frequencies.
frequency
FOR ILLUSTRATED CIRCULAR WITH FULL DETAILS
FERRIS INSTRUMENT CORPORATION,
BOONTON,
N.
AND
OCTOBER
COMMUNICATION
19
BROADCAST ENGINEERING
3
6
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J.
f1
L
BALANCED AMPLIFIERS
(Conh,nfed from page 17)
in audio frequency
transmission
control
ATTENUATION
w.
IMPEDANCE
D OuT
If the grid swing is greater than the cut -off value,
(Class AB1 or AB2) we must modify the above results,
since the two tubes are in the picture for only part
of the grid swing. A complete mathematical treatment
is involved and unnecessary, since actual tubes are only
approximately parabolic in their characteristics. If the
grid swing is sufficiently great (particularly if the grid
goes positive) the ep
i , curves are practically linear and
parallel near the peak swing (for a triode) and may be
considered as straight lines in this region. Thus, in Fig.
22 we have a plate family of curves, with the tube load
line AB superimposed. The line AC represents half
of the load line as it would appear to an equivalent tube
capable of conducting in either direction, or to a pair
of equivalent linear tubes in Class B (biased to cut -off).
It may also be regarded as the push -pull load line, since
the latter is usually practically straight and coincident
AD X DC
with it. The power output may be taken as
r
-
2
or the area of triangle ADC, since AD and DC represent the peak current and voltage, respectively, through
the load. It can be shown that where C is fixed, and A
is on one of a family of parallel lines ( (ep
ip) curves,
assumed linear in this region), then triangle ADC has
maximum area when AC forms an isosceles triangle
with the plate-current curve through A. This in turn
means that
-
R,
1.
Constant Impedance
2.. Uniform Attenuation
3. Uniform Frequency Response
4.
Long Life
Four good reasons for the ever
increasing popularity of Centralab
Sound Projection Controls
in
broadcast studios, remote control
stations, and P.A. Systems.
Centralab has issued an interesting
booklet. It is yours for the asking.
= 4r,
MILWAUKEE, WIS.
British Centralab, Ltd.
Canterbury Rd., Kilburn, London, N. W. 6, England
French Centralab Co.
118 Avenue Ledru-Rollin, Paris, France
VOLUME CONTROLS
FIXED RESISTORS
22
(46)
where rp is now the plate resistance at peak swing,
namely, the tangent to the plate- current curve through A.
This follows from the fact that AC represents RL /4 (as
shown in the previous article) and for AC at the same
angle as the plate- current curve through A, RL/4 must
equal rp.
The value of rp in this region is fairly constant, and
may at least be a guide for a subsequent graphical calculation. The latter, when corrected for self-rectification,
will give a load line higher than AB, and an operating
point farther to the right of C. A recalculation of RL
may result in a better optimum value.
The extent of grid swing e, is determined by how far
the grid may be swung positive. For the value of RL
determined as above, e, must not be so great that line
AD cuts through the grid -current curves where they are
rising steeply, otherwise the driver -tube requirements
will be excessive, and the plate- current curve will droop
off from linearity and thus produce a flat-topped output
wave. The grid swing may be increased if RL is decreased, and greater power output obtained, but usually
in Class AB operation this results in excessive plate
dissipation at full signal swings, and also in excessive
power -supply demands, particularly as regards filtering
and bypass requirements.
XVII.
PLATE DISSIPATION
The plate dissipation at nu- signal swing has been
given and it has been stated that it can be kept down
by using sufficient bias. The plate dissipation at full signal
swing wp,,, however, is a function of RL and
and is
not easily determined nor controlled. It is equal to the
product of the d -c component of the plate current Ide,
at full signal swing by the power -supply voltage, minus
e
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COMMUNICATION
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BROADCAST ENGINEERING
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AND
S
4
the a -c power output of the tube, which is half of the
total a -c power output, Po, or
Wn
=
flde. X Ea)
-
(47)
P,12
An analytical expression for Idea is very complicated,
and hence the best means of ascertaining it are from a
graphical analysis, including the correction for self rectification. Pa is also best calculated from the corrected load line. It will be noted from the graphical
analysis that the greater ea is, or the smaller RL, the
greater the peak current of each tube, and the greater the
d-c component. On the other hand, the greater the initial
bias (the closer to Class B operation), the smaller is
the d-c component. Hence, by varying these factors as
indicated above, the designer can obtain the maximum
power output of the tubes consistent with permissible
plate dissipation. In passing, it is worthy of note that
since the peak power demands are not continuous, it
may he desirable to rate vacuum tubes on an intermittent -duty basis similar to that of a railway motor.
The vacuum tube, however, has a smaller thermal capacity
and consequently a lower thermal overload capacity.
r
XVIII.
SELF -BIAS, SELF- RECTIFICATION
Where self -bias is employed, the change in d -c component must be small, otherwise the bias will be increased
with impress of ea, and this in turn means a lower operating point and decreased output. It is assumed, of course,
that the bias resistor is adequately bypassed, otherwise
as pointed out above, odd harmonics will be generated
too. Small change in d-c component is obtained by
using a higher value of RL than for fixed bias, since then
the cut-off grid voltage is prolonged, and the self- rectification in each tube is less. The grid swing generally
has to be decreased, too. to minimize the latter effect.
The result of increasing RL from its optimum value and
reducing ea is to decrease the power output, hence fixed
bias is preferable when available.
The matter of self -rectification requires some comments. In a single tube, employing inductive feed (paralleled by the load resistor RL), the load line for d -c
is vertical through Ea, and the quiescent point is determined by the intersection of this load line and the
plate-current curve whose parameter is E. It is then
assumed, as a first approximation, that the locus of the
plate current for ea is along the load line for RL. If
the time function for the plate current reveals an additional d -c component due to self -rectification, then this
component must flow through RL and produce a d-c
voltage drop across it. But this voltage cannot be supported by the parallel inductance, hence the load line for
RL must be shifted until it reveals no further d-c component. The corrected load line will in general intersect the E. plate- current curve' at some value, Es', diferent from Es. If the additional d-c component is positive (as in ordinary triodes) it will result in Es' being
greater than Ea. We may regard the tube as operating
at a higher supply voltage Es', but that the resistance to
the additional d -c component is the same as that to the
a-c components, namely RL. This is analogous to the
usual viewpoint of considering inductive feed as equivalent to ordinary resistance coupling at a higher supply
voltage.
' In the case of a balanced -amplifier stage we have a
similar state of affairs. The load line for either tube
reveals odd and even harmonics, including additional
7. See
Kilgour-IRE Proceedings, January, 1931.
(Continued on page 24)
AN elaborate radio program was auditioned for
a sponsor, who after hearing it, decided that
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MANUFACTURERS of the FAMOUS GREEN SEAL DISC
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123
BALANCED AMPLIFIERS
(Continued from page 23)
d -c component in the time function for the plate current. Since the output choke is assumed a linear device,
we may superimpose the effects of the two tubes upon
one another and RL. Thus each tube's current due to
ea may be regarded as flowing through a reflected resistance RL /4. The odd harmonics produce odd- harmonic
is-
voltage drops across this reflected resistance, that
across one -half of the output choke. Due to the mutual
inductance between the two halves of the choke, equal
odd -harmonic voltages are induced across the other half.
The other tube similarly develops odd- harmonic voltages
across its half of the choke, and induces equal voltages
across the other half. For the odd harmonics, these voltages are additively superimposed, so that there is twice
as much odd-harmonic voltage, plate -to-plate, as across
TflE
BLUE RIBBON
RADIO
either half.
In the case of the even harmonics, however, the voltages are subtractively superimposed, so that the voltages
across either half and from plate -to-plate are zero.
The even harmonics from each tube are in time phase,
but flow in opposite directions through halves of the
CATALOG,/
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All this checks with the physical analysis given in the
previous article, consequently the individual tube load
lines require no correction so far. When we come to the
case of the additional d-c components, however, we run
into an inconsistency. By hypothesis, these, too, flow
through RL /4 and develop d-c voltages across the two
halves of the choke. Since there is no mutual reactance
between the two halves at zero frequency (tacitly assumed even for an ideal choke) there can be no d-c
voltage induced in the one half by the other, hence no
such balance obtains, i.e., there are d-c voltages across
the two halves. These must be liquidated separately by
each tube, and hence the correction for each tube's load
line due to the effects of self-rectification.
It is of interest to show, analytically, how the individual tube's load line is straightened out by a mid branch resistance, Rb. The plate voltage can be written
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(IKi
+ipl)R1r
- -i,)-R,,7J
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4
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ATLANTA
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219 CI NYRA1
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AVE
Rb is
=[
equal to RL/4, (48) becomes
,ìH
-
S
R,,7
iP1
(49)
?
or the plate voltage of tube I is not dependent upon the
plate-current of tube II,
ip,. This means that that
particular value of Rb (= RL /4) has decoupled tube
I from tube II by introducing a coupling equal and
opposite to that of the two halves of the output transformer. The load line for either tube will therefore be
a straight line determined by the resistance RL/2, and
is tangent at the operating point to the curved load line
of either tube when there is no mid- branch resistance.
In the case of winding resistance in the output
transformer, the corrections as detailed in the previous
article give the individual tubes' currents. From these
the power output can be calculated, but it must be remembered that this is the output into the transformer.
To obtain the power output into the load resistance RL,
the losses in output transformer must be subtracted.
In this article there has been formulated some general
theorems on balanced -amplifier circuits.
Assuming
truly balanced conditions, it has been shown that
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(48)
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(1) The output contains odd- order, and no even order modulation products.
(2) The mid -branch current contains even- order, but
no odd -order modulation products.
(3) Mid -branch impedances produce voltages which
cross -modulate with the signal voltage to produce odd order modulation products in the output, in vector addition to those normally produced by the tubes themselves.
(4) Mid -branch voltages produce no output directly,
but do cross- modulate with the signal voltage to produce odd-order terms in the output.
(5) A tube whose power series contains no term
higher than the second will give distortionless output
in a balanced amplifier operating Class A. This is true
even if its amplification factor is variable subject to the
above restrictions.
(6) In the case where the above type of tube has a
constant amplification factor, it was shown that even
in Class AB a nearly distortionless output can be obtained. In particular, the square -law tube. (Van der
Bijl's equation) gives a smooth dynamic characteristic
for the above operation, which indicates a lack of high order modulation products. This is true for all reasonable values of load resistance, bias, and signal voltage.
(7) The above tube can give greater output in conjunction with a similar tube in balanced -amplifier operation than in single -side operation, because a higher supply
voltage can be used, with overbias to keep the no- signal
plate dissipation down. Also, an optimum value of load
resistance can be used, even though either tube cuts off
before the peak of the signal swing is reached. Thus,
for this tube operating Class A, when the load resistance
(plate -to- plate) is twice the tube resistance (at the
operating point), maximum power output is obtained.
If operation beyond Class A is desired, namely Class
AB, maximum power output is obtained when the load
resistance is four times the tube resistance at the point
of peak signal swing. The above results are approximately true for tubes of parabolic characteristics.
(8) Maximum grid swing is determined by the grid
current. The latter depends, however, upon the plate
voltage, which is at a minimum when the grid voltage
is at a maximum. The value to which the plate voltage
drops is determined by the load resistance, as well, hence
the peak grid swing is best determined graphically for
the value of load resistance determined previously.
(9) The full signal plate dissipation depends upon a
number of factors, so that it is best calculated after the
additional d-c component has been determined graphically. It can be reduced to within safe limits by reducing the grid swing, increasing the load resistance, or increasing the bias. The latter is often done, which results
in more nearly Class B operation. The advantage is better all -day operating economy ; the disadvantage is mainly
higher percentage of distortion products.
(10) For self -bias, the change in d-c component, hence
change in bias, must be minimized. This can be done
by operating more nearly Class A, which means generally
a higher value of load resistance and reduced signal voltage, for the same percentage of distortion products.
(11) The analytical method is theoretically correct,
and requires no corrections if a sufficient number of
terms have been used in the power series. The graphical
method is correct as far as determination of the a-c components is concerned, but requires a correction for the
change in d -c component. This correction, in turn,
changes the operating point, and thereby changes the
magnitude and phase of the a -c components.
(To be continued)
For the communication and
electronics engineer
the new version
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COMMUNICATION
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HAROLD PENDER, Ph.D., Editor -in -Chief
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JOHN WILEY & SONS, INC.,
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Kindly send me a copy of the "Communication and Electronics"
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condition, and at the correct drift angle
if a cross -wind approach is necessary.*
The Radioguide also provides approximate distance indication which iautomatically shown on the dial, in percent of distance traveled. This indication, however, is derived from the increase in the field strength as the transmitter is approached, and therefore may
not be sufficiently accurate for purpose
of instrument landing during the last
few critical feet: the field intensity may
vary with irregularities of transmitter
output or changes in the dielectric potential of the ground. For this reason, a provision is made for two suitably arranged marker beacons for definite position check : one to indicate the
immediate vicinity of the airport, tht
other to indicate when the center of the
airport is reached and the actual landing should be made.
For the sake of technical accuracy, it
should be noted that the theoretical path
so defined is not a straight line, but
rather one -half of a hyperbolic curve
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however, this can be considered :I
straight line as the sharp downward
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VETERAN WIRELESS OPERATORS
ASSOCIATION NEWS
W. J. McGonigle, Secretary,
VWOA CONSTITUTION AND BY -LAWS
II, SECTION 2. "At the December
ARTICLE
meeting the Board of Directors shall submit a list of nominees for Officers and
Board of Directors, of not more than three
(3) names for each office, President, VicePresident, Secretary and Treasurer, and
not more than twenty (20) names for
Board of Directors. Printed ballots shall
be prepared and mailed to each member
eligible to vote. These ballots shall be returned to the Secretary sealed, not later
than midnight prior to day of January
meeting."
ARTICLE III, SECTION I. "Following the November meeting the Board of Directors
will receive petitions in writing, signed by
not less than thirty (30) members entitled
to vote, setting forth the name of the candidate and the office for which it is desired
he be nominated. These petitions shall be
considered by the Board of Directors and
shall be included in the final list of nominees when submitted at the December
meeting."
The above two Sections quoted refer to
nominations for National Officers and
Directors and in no way do they affect the functioning of local chapters. They
are included at this time for the information of the membership at large.
CHICAGO
J. NECKER was recently elected treasurer
of the Chicago Chapter to fill the unexpired term of Sidney Winsberg, who, because of pressure of business, found it
necessary to resign. EJ has started an extremely active campaign to line up the
Mackay Radio personnel in Chicago. . .
EJ being associated with that organization.
The following are the members he has
signed up: L. E. Thiele, Louis Leeda, L.
O. Gorder, Irving R. Quay, and Henry
E. Wegner.
L. E. Thiele attended the Marconi Institute back in 1915 and was later associated with the Alaskan Steamship Company of Seattle, Wash., and the Canadian
Pacific Steamship Company of Vancouver,
B. C. Mr. Thiele's war experience included service in the Signal Corps and the
Artillery, being discharged as a Radio Sergeant in the 39th Artillery. At present,
he is Division Traffic Superintendent of
the Postal Telegraph-Cable Company.
Louis Leeda was transoceanic radio opE.
erator at Amsterdam, Holland, from 1925
to 1928. He then came to the United States
where, from 1929 to 1934, he was employed with the Bull Line. He is at present with the Mackay Radio Company as
operator at their Chicago terminus.
L. O. Gorder, who started professional
operating just after the war, includes among
his employers the Shipping Board, Goodrich Transit Company, Lykes Brothers and
several others in the marine field.
Irving R. Quay was employed by the
United Wireless Company at Chicago in
28v
112
Willoughby Avenue, Brooklyn, N. Y.
1914, then with Pershing expeditionary
forces in Mexico, and old "WUJ," Fort
Sam Houston, Texas, in 1915 and 1916,
continuing in the Signal Corps with the
AEF in charge of Third Army Headquarters Radio Station at Coblenz, Germany, during 1917 to 1919. At present he
is engaged as Division Testing and Regulating Inspector with the Postal Telegraph-Cable Company in Chicago.
Henry E. Wegner obtained his first
commercial license in March, 1924, and
subsequently operated for the Reiss Steamship Company, Intercity Wireless Telegraph Company, Southern Pacific and
Radiomarine Corporations and the Universal Wireless Company. Duty at the receiving station of the Mackay Radio Company at Merrillville, 'Indiana, keeps him
busy eight hours a day at present.
George I. Martin, Chicago Chapter Chairman, continues his efforts to make the Chicago Chapter one of our largest. He includes with a recent interesting communication the application of William H. Barlow,
who began operating on shipboard in 1921
with the Radiomarine Corporation and continued for a considerable period on board
various Great Lakes vessels. WHB served
in the Signal Corps of the Canadian Army
during the War. At present he is employed
as Instructor in the operating department
of the Coyne Radio School and in his spare
time operates amateur radio station
W9UEU.
Keep up the good work GIM and EJN,
and Chicago will soon have the largest of
the VWOA Chapters.
BOSTON
to learn that Harry Chet ham, Boston Chapter Secretary, is in the
WE ARE SORRY
Naval Hospital at Chelsea, Mass., with an
infected foot. Harry has quite a record
(not an enviable one to be sure) of successive hospitalizations. He has been in
the hospital on forty different occasions
since the war -in almost as many different
hospitals. We sincerely trust that Harry's
present visit will be a short, pleasant one.
(You know, Harry, you've got to be on
deck for the big affair on the 11th of February. It won't be a success without your
aid and attendance I) Despite his difficulties.
however, Harry has gone right ahead and
solicited new members in the Boston area.
Among those signed up recently are the
following: T. C. J. Prior, who operates
at WJAR in Providence, R. I., his home
town; Lawrence S. Bennett, who started
operating with the Marconi Company back
in 1913; J. Frank Sullivan, President of
the Rhode Island Radio School, who also
worked for the Marconi Company way
back in 1910; R. G. Webster, who is with
the Sam Curtis Radio School in Boston;
James E. Rigby, with the Radio Corporation from 1920 to the present; Walter S.
Rogers of the well known "Radio Shack"
OCTOBER
I
9
3
6
in Boston, who started operating in 1910;
J. A. Loyall, with RCA Communications
in Boston, who started in the United States
Navy in 1924 and then went with RCA;
and Edward F. Tierney, Chief Radio Operator of the Cambridge Police Department,
Cambridge, Mass.
Harry tells us in his notes -"Bill English, who now owns and operates a gas
station at West Hartford, Conn., was formerly at old 'BN' at 88 Broad St. Mark
:McAdam is very busy at the Ware Radio
plant in Brockton, Mass. Guy Entwistle,
our jovial Vice -Chairman, and his partner,
Raymond F. Trop, Treasurer of our Chapter, opened the fall season with large classes
in attendance at their Massachusetts Radio
and Telegraph School. Arthur Ericson
spends many enjoyable hours at his 'ham'
rig in Beverly, Mass., with which he has
worked all continents. Sam Curtis has
opened his new Communication Industrial
Electronic and Television School on Massa chussetts Avenue, Boston, and has engaged
Ted McElroy, world's fastest radio telegrapher, and a Boston Chapter member, as
one of his instructors. J. Frank Sullivan,
of the Rhode Island Radio School, reports
excellent registration for the fall term."
Then Harry adds -"Seems as tho' we
have a monopoly on the school business
up this way."
PERSONALS
-
:
Karl Baarslag writes
the Secretary as follows
"I called on
Doc and learned to my indignation that
none of his old friends or pals had been
to see him in a long time. I was his first
visitor in over a year. You know, Bill,
Doe's sight is none too good and failing
and he can no longer go out alone or visit
New York. It is, therefore, up to oldtimers to pay Doc a call for old times
sake. He is the only Radio Operator in
an institution of over 900 sea captains,
engineers and sailors. Old timers with
cars ought to pay Doc a visit and take
him out for a ride. It is but a short bus
ride to the door after leaving the Staten
Island Ferry at St. George. He can be
visited anytime of the day, but after 3 p.m.
is best for him. Doc asks old friends who
can't call to drop him an occasional post
card from foreign ports now that he can
no longer sail the seas and visit them him"LEST WE FORGET "
self.
-
e
"I think it a
shame the way fellows
have forgotten him so completely Nearly
blind-alone in the world-and forgotten
by all his old 'friends' ( ?). Not a pleasant
outlook."
On our visit to "Doc" James Forsythe
at Sailor's Snug Harbor, Staten Island,
N. Y., within the next few days. can we
assure him of your visit or letter ? A post
card, letter or personal visit will make life
for "Doc" immeasurably more pleasant.
Thank you.
!
.
COMMUNICATION
AND
BROADCAST ENGINEERING
www.americanradiohistory.com
44
r
air -ga
Type BC 46 Isolantite variabletempera
its
oven mounting maintains
at 50"C. Approved b
1`C.
within
ture
F. C. C.
t
r
'
Type BC 10 Isolantite
holder.
res. variable air-gap
roi
A precision mounting
Bey Crystals between
1
riar
p)
&TUN m
KAII
100 KC. and 5,000
Type VP 4 Steatite body
hol.
adjustable pressure
It
For all Bliley Crystals
300 KC. to 28 MC.
THIS MODEL D -2
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CRYSTAL MICROPHONE, WE MEAN
DIREC-
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Utilising
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Oat from 50 to 6000 e.p.s. Because of Its ruggedness, beauty and size (only
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FREQUENCIES
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TIONAL bimorph crystal microphone
FROM 20KC.
for Bulletin 62 will bring complete information.
Development Co. patents. Astatie patents pending.
Price $25.00. Your request
Licensed under Brush
Bliley Broadcast Crystals are approved by
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u
Write for complete Catalog. G-9.
BLILEY
ELECTRIC COMPANY
ERIE, PA.
UNION STATION BUILDING
TRANSFORMERS
MICROPHONE LABORATORtY,Inc.YOUNGS}nTOWNrO.
nASTATIC
lianect
f/W2UiÌQCfILAFh!
0 U[ay U2ak&
REMLER
Apr -29 BROADCAST
Line Amplifier
for Transmitting
Below -dmerTran aircooled transmitrint
rnent transformer.
Above-AmerTran air,,00led
trausestttlpt plate transformer
-sises
1
0
up to
7
kpa.
AmerTran's line of air -cooled transmitting
transformers are designed to meet the most
rigid broadcast station requirements. Units are
of the highest quality and standard types are
available to meet all usual requirements in
rectifiers utilizing either type '66 or '72 tubes.
The illustrations show our new improved
mountings and standard ratings are listed in
Bulletin No. 1002 ...Mag we send you a copy?
AMERICAN TRANSFORMER CO.
175
Emmet St., Newark, N. J.
Three stage push -pull line amplifier, gain 67 db. Undistorted output plus 20 db. Response within plus or minus 11/2 db. 30 to
12,000 cycles. Input and output impedance is 500 ohms balanced
to ground. Key provided to switch to auxiliary input. Tubes:
Shielded input
2 - 6A6 dual triode, and 2 - 89 triode connected.
former, cushioned in rubber. 100.000 ohm Ranier wire wound
potentiometer gain control. V.I. reference variable from minus 10 to
plus 20 db.
Operates from 118 volt SO to 60 cycle line: supplies 6.3 volts
AC- -180 volts DC for preamplifiers. Standard 19" x 14" attractive
brushed (lurid panel.
Preamplifiers, line and bridging
input systems. Attractive prices.
REMLER
CO., Ltd.
amplifiers
and
2101 Bryant Si., San Francisco
COMMUNICATION
OCTOBER
1936
complete speech
AND
BROADCAST ENGINEERING
www.americanradiohistory.com
OVER THE
NEWS
OF THE
TAPE...
RADIO, TELEGRAPH AND TELEPHONE INDUSTRIES
MARINE EXHIBITION
The Third Annual Marine Exhibition
will be held from November 12 -20 at the
Maritime Exchange Building, 80 Broad
Street, New York City. This exhibition
is under auspices of The Maritime Association of the Port of New York.
CORNELL-DUBILIER CATALOG
WALTER BIDDICK
SALES
The transcription service of the Walter
Biddick Co., Los Angeles, Calif., including
its own program productions and those
for which it has the sales rights, has been
extended to foreign countries. Fall sales
have included purchases by stations in
Panama, Mexico, Cuba, England, Canada,
Australia, New Zealand and other countries.
A special catalog has been issued
by
the Cornell -Dubilier Corporation covering
the new reduced prices recently announced
for their line of "Dwarf- Tiger" condensers.
This catalog lists the entire line of this
series, together with catalog numbers, and
shows both the old and new price schedules. The savings shown average over 30
percent. This catalog No. 132A will be
mailed to those requesting it from the
Cornell -Dubilier Corporation, 1000 Hamilton Boulevard, South Plainfield, New
Jersey.
PROGRESSIVE"
II
"Progressive" II, a supplement to the
"Progressive" Transmitter Guide for Amateurs, is now off the press. It covers a
simple plan to build a complete "rig" in
steps. Complete diagrams and parts lists
are included. This booklet may be obtained
from the Amateur Press, 1300 W. Harrison St., Chicago. The price is fifteen cents.
TURNER APPOINTMENT
The Turner Company of Cedar Rapids,
Iowa, have announced the appointment of
L. G. Cushing Company, 540 North Michigan Avenue, Chicago. Illinois, as their
new Illinois representative.
WILLIAM
BRAND
CATALOG
A new catalog, No. 11, listing the vari-
ous types of electrical insulating materials
produced by their organization, has just
been issued by William Brand & Company, 268 Fourth Avenue, New York,
N. Y. This catalog will be sent free upon
request.
"SOUND ENGINEERING MANUAL"
After many delays and corrections, due
to rapid advances in sound engineering,
Webster -Chicago has announced that the
first completed copies of the "Sound Engineering Manual" are expected off the press
within a few days.
Every dealer who has previously requested one of these manuals will receive
it free of charge, although due to the
magnitude of the book and consequent expense, it has been found necessary to
establish a price of 10 cents. As edited,
this manual now contains 18 diagrams
covering different phases of sound engineering from details of microphone construction to complete installations.
30
STUDIOS
FOR
WFIL
Station WFIL, Philadelphia, has completed plans for the construction of a suite
of modern, air -conditioned studios and
offices to be located on the eighteenth (top)
floor of the Widener Building, at Broad
and Chestnut Streets.
Work on construction is to be rushed
so that the new quarters will be ready
for occupancy early in 1937, in time to
commemorate the station's second anniversary. Horace Trumbauer, prominent
Philadelphia architect, and Frank V.
Becker, WFIL's chief engineer, who designed the general plans for the studios,
are supervising building operations.
BALLANTINE BULLETIN
Ballantine Laboratories, Inc., Boonton,
N. J.. have recently issued Bulletin 1 on
"Telephone Receiver Test Equipment."
Contained in this bulletin is a complete discussion of the artificial ear, Type 502. and
telephone receiver test equipment, Type
"KENYON ENGINEERING NEWS"
Vol. 1, No. 1 of Kenyon Engineering
News will make its appearance at an early
date. This monthly publication, which will
be edited by J. B. Carter, is to be devoted
entirely to the amateur, sound technician
and experimenter. The first issue will
feature, among other things, the following:
a new combination mixer and preamplifier;
tone equalization ; audio amplifiers ; modulation improvements in transmitters, and
four handy engineering data charts, known
as Ken -O- Grafs.
Kenyon Engineering News is published
by the Kenyon Transformer Company, 840
Barry Street, New York, N. Y.
RECTOX BOOKLET
A new
12 -page
booklet (B- 2078), describing the selection and application of
Rectox copper -oxide rectifiers for changing a -c to d -c without moving parts or
chemical reaction, is announced by Westinghouse Electric and Manufacturing Company, East Pittsburgh, Pa. The Rectox
is finding an increasing use for supplying
d -c power from an a -c source for industrial applications such as operating d -c
brakes, control elements, fire alarms and
signal and communication systems, battery
charging, electro-plating. metering and
many others. The booklet may be secured
without cost.
500A.
"PERPETUAL CATALOG"
AEROVOX CATALOG
An enlarged and revised catalog has just
been issued by Aerovox Corporation, 70
Washington St.. Brooklyn, N. Y., and is
now ready for distribution. Known as the
Second Edition 1936 Catalog, this literature covers an extensive line of condensers
and resistors for radio and allied applications.
Many new condensers are announced. A copy of the catalog may he
obtained from the local Aerovox jobber
or by writing the company direct.
CENTRALAB CATALOG
A new catalog on controls. resistors and
selector switches has lust been issued by
Centralab, 900 East Keefe Ave., Milwaukee, Wis. Of particular interest with re-
gard to selector switches are the Isolantite
switch sections for u'e in short -wave and
ultra- short -wave work. Also of interest
are the midget replacement controls for
auto -radio receivers. This catalog may he
obtained from the above organization.
ADAMS JOINS ASSOCIATED CINEMA
Larry Adams. Hollywood sound engi-
neer, this month became affiliated with the
technical staff of Associated Cinema, Hollywood transcription organization.
OCTOBER
A "Perpetual Catalog" on transformers
for sound engineers and radio amateurs has
recently been issued by the General Transformer Corporation, 500-532 S. Throop St.,
Chicago, Ill.
Upon request the above organization will
mail direct any additions and changes to
this catalog as issued
or send additional forms. These supplementary forms
may be easily inserted in the same binding.
Complete technical information on the
GTC line of transformers is contained in
this catalog. The price is 20 cents.
...
U.
S.
RUBBER
PRODUCTS MANUAL
The United States Rubber Products. Inc..
1790 Broadway, New York City, is issuing
a new handy manual -"Laytex, The New
Dielectric in Communication and Control
Wires and Cables" -for use by engineers,
contractors and designers when specifying
wire and cable installations for signal and
control service.
The manual gives detailed information,
graphs and tables indicating the characteristics and proper uses of the various types
and gauges of "U.S." Laytex insulated
communication cables, fire -alarm and police- signal cables, supervisory control cables, telephone cable, outside telephone
wire. inside telephone wire, and emergency
telephone wire.
COMMUNICATION
1936
AND
BROADCAST ENGINEERING
www.americanradiohistory.com
lf
r
I
ROTARY SWITCHES
\DEX TO
Yt,i
ADVERTISERS
A
PAGE
American Transformer Co..
Amperex Electronic Products, Inc.
Astatic Microphone Lab., Inc...
29
32
29
Ñ ,e1!
'71`
For switch applications where only the best can be used, yet where
test of our products will be definitely worth while.
ecenomy is imperative.
We have a switch for every purpose and with any desirable characteristics
such as Imo reactance to r.f., zero thermal e.m.l., low noise level. low contact
resistance, etc.
Ask for our new
resistance instruments.
catalogue
covering
switches,
attenuators
and
other
TECH LABORATORIES
705 NEWARK AVENUE
N. J.
JERSEY CITY,
B
Brush Development Co., The
29
32
Burstein -Applebee Co.
31
Bliley Elec. Co.
"THE CRYSTAL SPECIALISTS SINCE 1925"
PIEZO- ELECTRIC CRYSTALS
GUARANTEED Accurate to BETTER than .01%
C
Cardwell Mfg. Corp., The Alen D.
Centralab
Commercial Radio Equip. Co.
Cornell -Dubilier Corp.
SCIENTIFIC RADIO SERVICE
27
22
Send for FREE Booklet and Price List!
HYATTSVILLE, MD.
UNIVERSITY PARK
31
32
ENCLOSURES
METER
PROTECTIVE
Circular, rectangular, and special enclosures,
fitted with plate glass, for the protection of
personnel and transmitting equipment, at low
Write
cost, described in two -page bulletin 111t.
F
Ferranti Electric, Inc
Ferris Instrument Corp,
Fourth Cover
Third Cover
WE
,7
1
Second Cover
P
Presto Recording Corp.
23
ENGINEERING
,ca//ay
Radio Eng. &
Radiotone Recording Co.
Remler Co., Ltd.
CO.
a.
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£o n12í
-Grin&
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An 1&tardcadi xdhrfiu,2d a'nd _Alt edict Y./Ai ,E pz ow: c mr,.a .E C&.ta1o, TODAY !
(0
BURSTED- APPLEBEE
KARSASICITY. m0.
PRECISION FREQUENCY
MEASUREMENTS
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Mfg. Co.
MFG.
JERSEY CITE
.7u6sa a.rze
R
RCA Mfg. Co., Inc.
&
JOURNAL SQUARE
BROAOCA5TI11G EQUIPIYIEIIT
3
Isolantite, Inc.
it! Quotations given.
RADIO
26
G
General Radio Co.
Graybar Electric Co.
for
21
31
27
29
TRU -AXIS LOW DRIFT CRYSTALS
'
RADIO ENGINEERING
CONSULTANTS
e
Commercial
7205
Radio Equipment
Co.
BALTIMORE AVE.. KANSAS CITY. MO.
S
Scientific Radio Service
Shallcross Mfg. Co.
Sundt Eng. Co.
31
27
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Watch your QUALITY
T
Tech Labs
31
Triumph Mfg. Co.
31
U
United Transformer Corp
19
Wiley
& Sons, Inc., John
tions. Standard U. S. Government
Equipment. Write today and save
big moneyy. Ship. wt. 33 lbs. F. O. B.
Chicago. 25% down. Balance C.O.D.
Money Sect G
tee
We eland back of every purr of
testing equipment we sell direct.
W
Western Electric Co.
Wholesale Radio Service Co., Inc.
Triumph Top Operated Top scanned
Osclllograph. Protects your transmitter. Keeps you within F.C.C. regula-
' Your money cheerfully refunded
within
3
24
25
on merchandise returned
10 days in original condition.
"rtttGMnaH
Lake Sit.
Chicago. Ill.
4015 W.
3
Triumph Slashes Prices
New Factory -Direct Plan. No
middleman profits-no high
Interest rates -no long time
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Triumph. Send today for complete details. ACT NOW.
COMMUNICATION
OCTOBER
19
CO.
$63.60
AND
BROADCAST ENGINEERING
6
www.americanradiohistory.com
31
THE IDEAL
Transmitting Capacitor
T8 20.020
2
AMPEREX
CfIRBON ANODE
TANSMITTING TUBES
MICROFARAD
20,000 VOLTS, D.C.
11,000 Volts
R.M.S. Rect. A.C.
combination of six
of these capacitors, in a
A
phase full wave rectifier power supply circuit,
3
will help furnish
a
de-
pendable source of D.C.
voltage for stations employing up to 50,000
watts output.
Investigate the history making story of Dykanol, a
C -D
laboratory development, utilized in these
capacitors!
The full line of these and other high voltage oil and
mica transmitting capacitors listed in Catalog No. 127.
Stocked for immediate delivery for all emergency
requirements.
Wet & Dry Electrolytic
Mica
Dykanol
Paper
World's Largest Exclusive Manufacturer of Condensers
..
1005
..
..
CORNELL -DUBILIER
¡vs"-
CORPORATION
HAMILTON BLVD., SO. PLAINFIELD, N. J.
AMPE:1-E X
ELECTRONIC
WLLÎIIEL L
PRODUCTS,
Inc.
79 WASHINGTON ST., BROOKLYN, N. Y.
BRUSH
genera / »urpoie
MICROPHONE
STATEMENT OF THE OWNERSHIP, MANAGEMENT, CIRCULATION, ETC., REQUIRED BY THE ACTS OF CONGRESS OF
AUGUST 24, 1912 AND MARCH 3, 1933, OF COMMUNICATION &
BROADCAST ENGINEERING
Published monthly at New York, N. Y., for October
-
The Brush G2S2P sound cell microphone -an all
around general purpose microphone for program
remote pickup and announcing work. Widely used in
high grade public address installations. A typical sound
cell microphone built to Brush's traditionally high
mechanical and electrical standards. Non -directional.
No diaphragms. No distortion from close speaking.
Trouble-free operation. No button current or input
transformer to cause hum.
Beautifully finished in dull chromium. Output level
minus 70 D.B.
Size 3 inches by 1t /4z1t/a inches.
Furnished complete, at no extra cost, with a Brush S -1
socket that facilitates easy installation.
Full details
will be found in Data Sheet No. 4 Free. Send for one.
State of New York,
County of New York.
BRUSH
#ec%h on ¢.i
Meet every headphone requirement. Response 60
to 10,000 cycles. No magnets to cause diaphragm
chatter. Specially designed cases minimize breakage.
Light in weight. Only 6 oz, ,complete with headband
and cords. A quality product at a low price. Details,
Data Sheet No. 10. Copies on request. Send for one.
1,
1936.
/ ss
Before me, a Notary Public in and for the State and county aforesaid,
personally appeared B. S. Davis, who, having been duly sworn according
to law, deposes and says that he is the Business Manager of COMMUNICATION AND BROADCAST ENGINEERING, and that the following is,
to the best of his knowledge and belief, a true statement of the ownership,
management, etc., of the aforesaid publication for the date shown in the
above caption, required by the Act of August 24, 1912. as amended by
the Act of March 3, 1933, embodied in section 537, Postal Laws and
Regulations, to wit: I. That the names and addresses of the publisher, editor,
managing editor, and business manager are: Publisher, Bryan Davis Publishing Co., Inc., 19 East 47th Street, New York. Editor, Ray D. Rettenmeyer,
Madison. N. J. Managing Editor, None. Business Manager, B. S. Davis,
Ghent, N. Y. 2. That the owners are: Bryan Davis Pub. Co., Inc., 19East47th
St., New York, N. Y.; B. S. Davis, Ghent, N. Y.; J. C. Munn, Union City,
Pa.; T. A. Walker, Richmond Hill, N. Y.; A. B. Goodenough, New
Rochelle, N. Y. 3. That the known bondholders, mortgagees, and other
security holders owning or holding 1% or more of the total amount of
bonds, mortgages, or other securities are: None. 4. That the two paragraphs next above. giving the names of the owners, stockholders, and
security holders, if any, contain not only the list of stockholders and
security holders as they appear upon the books of the company but also,
in cases where a stockholder or security holder appears upon the books
of the company as trustee or in any other fiduciary relation, the name
of the person Or corporation for whom such trustee is acting, is given:
also, that the said two paragraph's contain statements embracing affiant's
full knowledge and belief as to the circumstances and conditions under
which stockholders and security holders who do not appear upon the
books of the company as trustee, hold stock and securities in capacity
other than that of a bona fide owner; and this alliant has no reason to
believe that any other person, association. or corporation has any
interest direct or indirect in the said stock, bonds. or other securities than
as so stated by him.
(Signed) B. S. DAVIS, Business Manager.
1894
E.
40th
PIE
E IC
EEC"
St.
MICROPHONES
32
DEVELOPMENT
COMPANY
MIKE STANDS
TWEETERS
CLEVELAND, O.
HEAD PHONES
LOUD SPEAKERS
Sworn to and subscribed before me this 26th day of September. 1936.
(Seal)
J. A. WALKER, Notary Public.
Queens Co. CIk's No. 3149, Reg. No. 7476.
New York Co. Clk's No. 831, Reg. No. 7 -W -514.
Commission expires March 30, 1937.
AND
OCTOBER
COMMUNICATION
19
BROADCAST ENGINEERING
3
6
www.americanradiohistory.com
4
4
r
Power -Level Indicators
E
RECTIFIER -TYPE METERS as power -level indicators were developed and introduced
by General Radio Company several years ago. General Radio now announces its
latest line of improved power -level indicators which have been developed after an
extensive survey of the requirements of the broadcast, motion picture and public
address system fields.
Features of these new indicators include:
High Accuracy -error
less than 0.2 db.
Ruggedness -simplified construction -ceramic insulated resistors.
Compactness-rack model requires only three and one -half inches.
High -Speed Meters-on the -DM and -DR models.
Attractiveness -designed to match other station and studio equipment in neatness.
Enclosed Multiplier Switch-contacts protected -multiplier adjustable in 2 db steps
over range of 20 db.
One, the DR and DM, has a power-level
These indicators are available in two models.
model, equipped with a normal speed
EM
26 db. The ER and
range of
0 to
16
db.
to
of
a
range
meter, has
1
20
Type
Type
Type
Type
586 -DR -Relay-Rack Model
586 -DM- Cabinet Model
586 -ER -Relay -Rack Model
586 -EM- Cabinet Model
$55.00*
55.00
60.00*
60.00
*These can be supplied with panel finish to match Western
Electric or RCA gray, or RCA flat black, $4.00 additional.
Standard models are G -R black crackle finish.
WRITE FOR BULLETIN
70 -K
FOR COMPLETE DATA
GENERAL RADIO COMPANY
30 State Street
Cambridge, Massachusetts
www.americanradiohistory.com
N W
TRANSFO MERS
FR
Sertes B .1At db. 30 to 16,000 cycles
Cass 2sÿ" alij"a34í"h.
Mntg 2
Series
A
db. 30 to 12,000
Cass 2s,, "a2!s "a3
hint.. 2!,¡' 14" "h.
1
"a
1
sÿ"
cycles
FEATURES
I
1.
90 New Transformers
All
in
2. New Low Prices
3.
New Designs Throughout
4. Latest
High Fidelity Standards
5. New Self Shielding Core Type Construction
6. Free from Hum and Pickup
New Reversible Through -Type Mountings
No Waste Space for Mounting Flanges or Feet
9. Electrostatic Shields Between Windings
7.
8.
10.
11.
12.
13.
14.
15.
The
Small in Size
Light in Weight
Exceptionally Low Insertion. Loss
Moisture -Proof Construction
Available for Immediate Shipment from Stock
Designed and Manufactured in the United States
"A"
Series is the lowest priced self -shielding transformer
New straight -through mounting on both series,
plus self -shielding enables units to be actually mounted against
each other
no waste space
every unit designed for
available
.
.
.
.
either top or subpanel mounting.
SEND FOR COMPLETE LISTING.
FERRANTI ELECTRIC, INC.
Mirror illustrate
30 Rockefeller Plaza, New York, N. Y.
SubPane1
Mounting
New
www.americanradiohistory.com
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