operators handbook - American Radio History

operators handbook - American Radio History
BROADCAST
OPERATORS
HANDBOOK
By
HAROLD E. ENNES
Staff Engineer
Indianapolis Broadcasting, Inc.
JOHN F. RIDER PUBLISHER, INC.
480 CANAL STREET, NEW YORK 13, N.Y.
COPYRIGHT 1947 BY
JOHN F. RIDER
of translation
into the Scandinavian and other foreign languages
All rights reserved including that
FIRST PRINTING; NOVEMBER, 1947
SECOND PRINTING; FEBRUARY, 1949
THIRD PRINTING; SEPTEMBER, 1949
PRINTED IN THE UNITED STATES OF AMERICA
TO
BARBARA JEAN
INTRODUCTION
has been called one of the great giants of
our age. Actually, its strides into virgin territory have been almost beyond prophecy. Since 1921, when the beginnings of
broadcast stations as a specialized field of radio were realized, this industry has undergone a convulsion of changes that would take thousands of volumes to record. Transmitting and receiving equipment have
been made to realize a state of fidelity of tone that the comparison to
"canned music" is no longer descriptive of the art. Studios have
reached a state of development that has almost hopelessly antiquated
those of a few years back. Production of complex musical and dramatic shows has reached a peak that marks a transition from an old
era into a brilliant new one. And still the upheaval goes on, all eyes
are still ahead, all energies still expended in further development.
All this is not surprising. Development of almost flawless equipment
seems taken for granted by this scientific generation of young and old
alike. The surprising aspect is the obvious gap in literature that
exists between this field of radio engineering and design, and the practical operation of their products under actual use. This is especially
true in the field of broadcasting. Probably this is due to the somewhat
limited circle of engineers who are concerned with broadcast operations; yet there is no subject of interest more expansible or inexhaustible.
Part 1 of this book is thus intended primarily to be a comprehensive
treatise of control -room operation for broadcast technicians, endeavoring to collect enough coordinated facts to result in a general set of
rules to serve as standards of good operation practice. An attempt
is made to bring forth a new approach to modern operating technique, and to discuss and clarify existing facts that should lead to a
better understanding between studio and transmitter personnel. The
discussion necessarily includes an analysis of different types of indicating meters used in practice, in order that their functions may be more
clearly interpreted and understood in relation to the work which they
are intended to perform. Related subjects, such as loudness sensation
THE RADIO INDUSTRY
vii
viii
INTRODUCTION
for a given meter reading, waveform, and phase shift in studios, are
analyzed.
The subject and content of this book are intended not only for the
many newcomers to control rooms and transmitters, but also for the
"old timers," familiar with all the problems peculiar to their work.
The first four parts cover the operating practice in control rooms, the
master control, remote controls, and the transmitter, and the fifth and
sixth parts are concerned with technical data for operators and technicians.
Station setups must inevitably fall into two general classifications:
the "smaller station" design, where control room and master control
are combined on one centralized console with studios grouped about it,
and the "larger station" setup, with individual control rooms for each
studio, and master control as the central switching unit.
The book has been so arranged in order to present the material on
each subject in as thorough a manner as possible, and will be equally
applicable to either type of technical setup.
ACKNOWLEDGMENTS
The author wishes to thank the editors of Radio -Electronic Engineering for permission to use some of the material of his articles appearing in that publication as follows: portions of Chapter 1 from
"Program Metering Circuits," April 1945; portions of Chapters 7, 8,
and 9 from "Remote Control Broadcasting," October 1946; portions
of Chapter 16 from "Heat Dissipation In Broadcast Transmitter
Tubes," May 1944; and Chapter 19 from "Broadcast Studio Design,"
October 1944.
Chapter 20 contains in part material appearing in articles by this
author in RADIO during January, February and March of 1945, and
is reproduced herein through the courtesy of Radio Magazines Inc.
The entire book is based on the authors' original article "Some Suggestions for Standards of Good Operating Practice in Broadcasting,"
RADIO, August, September and October, 1943. Part 4 contains some
data from the author's "Operational Engineering for Broadcast Transmitters" in COMMUNICATIONS.
The author is also indebted to Mr. Joseph Kaufman, Director of
Education at the National Radio Institute for his sincere desire to see
such a book as this published, and his courtesy in allowing the use of
part of the material herein that was written by the author for the new
broadcast section of NRI home study courses.
Many thanks also to Bert H. Koeblitz for his invaluable contributions to the book, namely Chapters 5 and 11, and his information on
technical equipment at WHK.
The author is also indebted to the editors of the John F. Ride.
Publisher, Inc., for their many helpful suggestions and aid over the
rough spots in this, the writers' first book attempt.
HAROLD
November
22, 1947
ix
E.
ENNES
Mr
TABLE OF CONTENTS
PART
1
OPERATING IN THE CONTROL ROOM AND STUDIO
CHAPTER 1. WHAT YOU'RE UP AGAINST
1
Control Operator -2. Studio and Transmitter Installation -3. Transmitter Operating Technique-7. Loudness -7. Details of Control Room
Metering Circuits-10. Volume Indicator Interpretations -12. Dynamic
Range Indication-13.
CHAPTER 2. ARE MECHANICAL OPERATIONS
CHAPTER 3.
APPARENT?
KEEPING SOUND "OUT OF THE MUD"
.
.
.
.
15
.
.
19
CHAPTER 4. YOU'RE OFTEN A PRODUCER TOO
25
Importance of Rehearsals -30. Musical Setups -33. Sound Effects -35.
Importance of Control Room Maintenance -40. Transcription Turn-
tables -40. Turntable Operation -42. Instantaneous Recording Department -43. The Influence of FM -43.
PUT THAT MIKE THERE! (by Bert H. Koeblitz)
45
Large Orchestra -45. Keep It Simple -47. Choral Pickup -48. Drama
and Novelty Pickups 49. Small and Hotel Orchestras -50. Novelty and
Vocal Groups -51. Piano Pickup-52. Organ Pickup -54.
CHAPTER 5.
.
PART
.
2
OPERATING THE MASTER CONTROL
WHERE SPLIT SECONDS COUNT
57
Master Control of United Broadcasting Co. -58. Function of Master
Control Operations-59. Master Control Procedure -59. Studio Procedure 62. Field Procedure -67. Glossary-68.
CHAPTER 6.
PART
3
OPERATING OUTSIDE THE STUDIO
-
CHAPTER 7. REMOTE CONTROL PROBLEMS
71
CHAPTER 8. REMOTE VERSUS STUDIO PICKUPS
General Comparisons of Studio and Remote Pickups -78.
xi
77
Remote Control Amplifiers-72. Simplex Control of Remote Amplifiers
74. General Remote Operating Problems-75.
TABLE OF CONTENTS
xii
CHAPTER 9. REMOTE MUSICAL
PICKUPS
.
.
.
..
.
.
Brass Bands-81. Salon Orchestra Remotes-81. Symphonic Pickups
82. Church Remotes-83.
EYE -WITNESS PICKUPS AND MOBILE TRANSMITTERS
Frequency Assignments 87. Operation-88.
-
80
CHAPTER 10.
THE LIVE SYMPHONY PICKUP (by Bert H.
Pre-Broadcast Problems-91. Physical Arrangement of
Microphone Placement-95. Other Problems-96. The
phone-98. Transporting Equipment-99. Problems of
toriums -101.
CHAPTER 11.
85
Koeblitz)
90
Orchestra -93.
Soloist MicroStrange Audi-
PART 4
OPERATING THE TRANSMITTER
OPERATOR'S DUTIES
104
Outline of Responsibilities-104. Typical Presign on Procedures -105.
Pre-Program Level Checks -106.
CHAPTER 12
CHAPTER 13. PROGRAMS ARE ENTERTAINMENT
108
Coorelation of Meter Readings-109. 100% Modulation-111. Operation
of Limiter Amplifiers-113.
CHAPTER 14. MEASURING NOISE AND DISTORTION
.
.
.
.
116
Excerpts From Standards -118.
PART
5
WE'RE OFF THE AIR
CHAPTER 15.
EMERGENCY SHUTDOWNS
CHAPTER 16. WHY
PREVENTIVE MAINTENANCE
121
124
Proposed Transmitter Maintenance Schedule-125. Maintenance of
Water -Cooling Systems -129. Forced -Air Systems -131. Station WIRE
Preventive Maintenance Schedule-132.
PREVENTIVE MAINTENANCE INSTRUCTIONS . 136
Preventive Maintenance Operations-136. Suggested List of Tools for
Rely and Commutator Maintenance -138. Construction for Relay and
Commutator Tools-139. Use and Care of Tools-141. Vacuum Tubes
142. Maintenance Procedures-143. Capacitors -147. Resistors -149.
Fuses-150. Bushings and Insulators -151. Relays -152. Relay Servicing Tools and Their Use-157. Switches-158. Generators and Motors
159. Transformers and Choke Coils-160. Variacs-161. Rheostats and
Potentiometers-161. Terminal Boards and Connecting Panels-162. Air
Filters-163. Cabinets-163. Meters-164. Pilot Lights -165. Plugs
and Receptacles -166.
CHAPTER 17.
-
TABLE OF CONTENTS
PART
xiii
6
TECHNICALLY SPEAKING
169
CONTROL ROOM AND STUDIO EQUIPMENT
Broadcast Microphones-174. Microphone Fundamentals -175. The
Ribbon Microphone-178. Variable Pattern Microphones-179. Output
Circuits and Line Equalization-181. Frequency Runs of Studio Equipment -184. Noise and Distortion Measurements-185. Telephone Company Line Services -185.
CHAPTER 18.
.
.
187
THE BROADCAST STUDIO
Problems in Studio Design-189. Early Studio Design -190. Advances
in Studio Design-193.
CHAPTER 19.
SELECTING THE BROADCAST TRANSMITTER LO197
CATION
Service Area -197. Required Field Strength -198. Ground Wave Propagation Data-201. Using the Propagation Data-203. Other Factors
204. Broadcast Antenna Systems -211. Considerations in Antenna System Design -213. Outline of Transmitter Installations-214. Antenna
Tuning-215. Circuit Tests -217. Factors Affecting Hum and Noise -219.
CHAPTER 20.
-
BIBLIOGRAPHY
220
APPENDIX
221
RCA 96-A Limiter Amplifier -221. RCA DISTORTION AND NOISE
METER-221. Installation-224. Noise Level Measurements -227. Distortion Measurements-228. Maintenance -231. RCA PHASE MONITOR-233. Measuring Phase Shift in Television I -F Circuits-234. Description-234. Phase Measuring Circuit -236. The Blanking Stages
238. The Phase Shifter Stage-239. Installation-240. Preliminary Adjustments-241. Operation-241. REMOTE ANTENNA-CURRENT
INDICATOR-243. Installation-244. Sampling Adjustment-245. Use
of Tuned Circuits-246. Use of Sampling Kit-247. Nonresonant Shielded
Loop -249. Location-250. Sampling Feeder at Tower Base -250. Sampling on Tower Structure -251. Sampling from an Adjacent Mast-252.
Sampling Lines-252. RCA LIMITING AMPLIFIER-255. Description
-255. Connections-257. Maintenance -259. Time Constant Changes
-
262.
-
.ir
BROADCAST OPERATORS
HANDBOOK
II.
Part
1
OPERATING IN THE CONTROL ROOM
AND STUDIO
Chapter
1
WHAT YOU'RE UP AGAINST
there are three kinds of pickups which concern
the control-room operatór; namely, studio, remote controls, and
incoming network programs where the station is affiliated with
a particular network.
Studio programs are all programs that originate at the regular station studios. All the most popular shows, such as Jack Benny, Bing
Crosby, and Fred Allen, are studio programs at the main network
studios. These same shows, of course, are handled as incoming network programs at the affiliated stations.
A remote control, or "nemo" in radio language, is a pickup originating somewhere other than the stations' regular studios, such as a sporting event or night club. Remote controls will be discussed in Part 3
of this book.
For studio programs, microphones must be set up or "spotted" in the
studio in such a manner that all musical instruments and performers
that are part of the production will be adequately covered. Sound
waves striking the movable element of the microphone causes a vibration in the magnetic field in which the element is suspended, which in
turn results in an electric potential on the element varying in accordance with the sound waves. The mechanical construction of various
types of microphones used for broadcasting is explained in Part 6 of
this handbook. The electric energy thus generated is very weak and
must be amplified to an amount sufficient to be carried by wire lines
to the transmitting plant. (This is true in all cases except in some of
the lowest powered installations where the transmitter and control
rooms are installed together. Even when this is true, the signal must be
amplified considerably to drive the speech input stages of the transmitter.) Control of the various microphones is provided by grouping
individual switches and volume controls for each microphone on a
panel known as the control console. A volume indicator must be used
to indicate the relative magnitude of the program signals and is
mounted in a convenient visual area on the control console.
BROADLY SPEAKING,
1
BROADCAST OPERATORS HANDBOOK
2
Control Operator
One duty of the control operator is to place the microphones in the
studio where the production director wants them for a particular program. Where no production director is employed, the control operator
must determine the positions of the microphones, or, perhaps more
correctly stated, he must determine the positioning of the performers
in the microphone pickup area. The best positions are usually determined only by rehearsing the show before air time, and alternating the
respective positions until the proper pickup is achieved.
During the progress of a studio show, the studio operator's position is at the control console. It is his function to operate the various
microphone controls so that their respective outputs properly "blend"
into the effect desired. When a production director is employed at a
station, he will assist the operator by telling him which sound or sections of sound to "bring up" or "lower." Since, in any transmission
system, definite limits exist as to maximum volume that can be han -
0 0©
O 0
O 0
O 0
©
©
©
IC El IM
o
©M
o
El
ZS
©
©
©
©
Fig. 1-1(A). Block diagram of a typical broadcast station installation,
showing various setups for switching to different studios and remote and
network lines, monitoring, etc.
WHAT YOU'RE UP AGAINST
3
died and minimum volume that is adequate for transmission, the overall volume must be monitored and controlled by the operator. This
is the purpose of the volume indicator. The operator must also operate
the switching system to choose the proper studio or incoming program
lines. Technical features of typical control consoles and switching
systems are considered in Part 6 of this handbook.
A good studio operator must not only be familiar with the technical
equipment, but also be very sensitive to art as well as science in broadcasting service.
Studio and Transmitter Installation
In order to visualize more clearly some of the discussion to follow,
it will be helpful to refer to the block diagram of a typical broadcast
installation as shown in Fig. 1-1(A). Most of the illustration is selfexplanatory, showing in simplified form the setup necessary for mixing
Fig. 1-1(B). The control console of Fig. 1-1(A). The master panel is in the
middle with studio panels on either side.
and blending of voice and music from a specified studio, switching of
studios, "remote" and network lines, visual and aural monitoring
facilities, wire transmission to the transmitter, and associated equipment. A photograph of this centralized control installation is shown
in Fig. 1-1(B).
BROADCAST OPERATORS HANDBOOK
4
The pad P shown in the master control panel circuit before the
111-C repeater coil is inserted to provide a constant load at all times
for the channel amplifier, and is necessary since the equipment sometimes operates at a higher level than is deemed advisable to feed into
program lines of the telephone company. The new standard vu meter
bridged across the monitoring points are supposedly indicators of 1
milliwatt of power (sine -wave) in 600 ohms. Actually, the meter indicates 0 vu with a sine -wave power at 1000 cycles of between +4 vu
and +26 vu, depending on the external resistance used in series with
the meter to allow greater bridging characteristics, and to facilitate
adjustments to correlate readings of the meters used at slightly different volume levels in the circuit. Rms meters of greater sensitivity
have not proved practical to date. It should be kept in mind that this
calibration assumes a sine -wave signal, and that under actual program material of energy sufficient for 0 vu deflection, instantaneous
peaks will exist of several times 1 milliwatt energy, and average power
will be a fraction of 1 milliwatt.1
As may be observed from the block diagram, visual indication of
the program in progress is provided on the studio panel, the outgoing
channel amplifier, the line amplifier at the transmitter, and the final
result, monitoring of percentage modulation of the transmitter. The
duties of the control operator include not only the "spotting" of microphones for musical and dramatic pickups, switching of studios and
lines on scheduled time or cue words, and proper mixing of voice and
music on studio setups; but also making certain that his "reference
volume" or zero volume level does not exceed that point to which
100% modulation of the transmitter is referred.
"Zero volume" level is simply an arbitrary point, and is not to be
thought of as rigid fundamental electrical units of power, current, or
voltage. It is necessary that it be understood only in relation to the
electrical and dynamic characteristics of the meter used and the technique of reading its response. Perhaps this will be clarified by Fig.
1-2, showing the response of two typical volume indicators on a sudden
applied signal. This difference in dynamic characteristics of the new
and old type volume indicators (Fig. 1-3) shows the need for a difference of technique in using the interpretation of the meters. The
standardization of the new type indicator is a great step forward in
broadcasting and most stations are equipped with these meters today.
'Chinn, Gannett, and Morris, "A New Standard Volume Indicator and ReferProceedings, IRE, January 1940.
ence Level,"
WHAT YOU'RE UP AGAINST
5
It must be remembered, however, that modulation monitors at the
transmitter must necessarily be of the semi-peak reading type since
this is specified by the FCC (Federal Communications Commission)
whereas, the vu meter used at studios is meant to integrate whole syl;
lables or words. This meter is slightly underdamped, which tends to
cause the pointer to pause for a moment on the maximum swing, then
start downward more slowly than in the case of the previous indicators. Therefore the meter appears to "float" on the peaks without
any erratic jumps. The psychological effect is excellent and the meter
160
140
OLD
TYPE
120
1'100
z
0
F
J4 80
L.)
o
ó 60
NEW
TYPE
40
20
o
01
02
03
0 4
0.5
SECONDS
1
0 6
07
08
09
1.0
Fig. 1-2. The response of old and new types of volume indicators to a
suddenly applied signal indicates a need for a different technique in the
interpretation of the readings. Courtesy Proc. IRE
appears to show the audio wave as it sounds to the ear from a monitoring speaker. A typical transmitter modulation meter reaches 100
on the scale in approximately 0.09 second when a 1000 -cycle voltage
of the required amplitude is applied to the equipment; whereas the
vu indicator reaches 99 in 0.3 second, as indicated in Fig. 1-2.
Coupled with this difference of dynamic characteristics of the two
meters is the conventional habit of monitoring at the transmitter on a
single positive or negative peak. By studying Fig. 1-4, which is a
BROADCAST OPERATORS HANDBOOK
6
graph drawn from a typical oscillograph of a speech wave, it is noted
that the energy in positive and negative peaks is far from equal. This
is typical of speech waves at the output of a microphone regardless of
the type or make of microphone used. Since the vu meter works from
-3-2
_g
2
EA)
00
-I
80
áo
i00
(B)
Fig. 1-3. The old type of volume indicator is shown at (A) and the new
type at (B).
a balanced full -wave rectifier, its reading is not dependent on the pole
of operation, and thus the comparison of the indication at the transmitter modulation meter position with that at the studio cannot be
expected to agree even with perfectly matched circuits between.
This one fact is probably the most universal reason for friction between transmitter and studio personnel. It is not possible, for instance,
Fig. 1-4. This representation of a typical speech wave shows that the energy
in the positive and negative peaks are unequal.
to obtain the same polarity of maximum energy from the two sides of
a bidirectional microphone. An interviewer may show an indication
at the transmitter of 100% modulation and the interviewee on the
opposite side of the microphone (therefore oppositely poled at the
WHAT YOU'RE UP AGAINST
7
microphone transformer) may show only 50% (or less), yet the indicator at the studio (full-wave rectification) will show exactly the
same peak level. It is perfectly plausible then that the transmitter
operator unfamiliar with speech-wave characteristics through a microphone should conclude from his monitor reading that the two
voices are not balanced at the studio end. This belief is sometimes
further encouraged by the extreme difference of "loudness sensation"
between two voices of different timbre that are peaked the same
amount on a full -wave rectifier indicator. This discrepancy between
level indication on a meter and the aural "on air level" is one of the
most perplexing problems of broadcasting and will be taken up in more
detail presently.
Transmitter Operating Technique
The foregoing discussion brings to mind several questions as to
transmitter operating technique. Is there any true indication at the
transmitter of comparative levels from the studio? Which pole of the
modulation envelope should be monitored continuously and why?
These problems, together with detailed suggestions of pre-program
level checks will be discussed in Part 4 on transmitter operating practice.
As will be discussed under the transmitter section, it is highly desirable to have all the undirectional microphones in use at the studio
poled so that the maximum energy pole of operation will coincide
with the positive side of the modulation envelope at the transmitter.
The ratio of peak energy difference varies with type and make of microphone, but is apparently most pronounced in pressure type microphones, such as the RCA type 88-A. This type microphone, due to
its light weight and rugged construction, is often used for remote pickups, and in studios, such as transcription booths, used mainly for
announcements. The operator should always take advantage of this
characteristic when this type microphone is used, as the results of
proper polarization at the studio are very much worth while.
Loudness
As to the problem of difference in "loudness sensation" for a given
meter reading between two or more voices, a brief perusal of the situation will emphasize the magnitude of its importance, and should constitute a challenge to operators and engineers to correlate existing
facts with operational procedure.
BROADCAST OPERATORS HANDBOOK
8
Fig. 1-5 is a graph of loudness level curves as adopted by the American Standards Association. The derivation of these curves is explained
in most standard textbooks on sound and will not be duplicated here.
An example will suffice to enable the reader to use this graph correctly.
It will be noted, for example, that a tone of 300 cycles, 40 db above
the reference level (0 db) corresponds to a point on the curve marked
120
120
IIo
loo
80
80
60
60
50
70
m
o
Z
J
>
J
Lai
40
40
20
o
-1020
50
100
500 1000
FREQUENCY
5000
10
000
Fig. 1-5. Family of loudness level curves as adopted by the
American Standards Association.
30. This is then the loudness level. It means that the intensity level
of a 1000 -cycle tone (reference frequency) would be only 30 db in
order to sound equally loud as the 40 -db 300 -cycle tone.
Now assuming a fundamental of 392 cycles (G-string of a violin)
with an actual intensity of 40 db above reference level, it would be
noted from the curve that the loudness level is approximately 36 db.
It was determined in Bell Laboratories that the addition of the overtones or harmonics of the fundamental raised the intensity from 40 to
40.9 db, whereas the loudness level was raised from 36 to 44 db. In
other words, the addition of the harmonics raises the actual meter
reading only 0.9 db, while the loudness level increases 8 db. For the
complex tone, the reference level of 1000 cycles would be 44 db to
sound equally loud.
When it is realized that the vocal organs of human beings are all
exceedingly different, and are associated with a particular resonating
WHAT YOU'RE UP AGAINST
9
apparatus that gives to the voice its individual timbre, it becomes
clear why it often occurs that two voices peaked at a given meter
reading will sound far different in loudness. Certain harmonics of the
voice are emphasized while others are suppressed in an infinite variety
of degrees. A study of Fig. 1-6, which illustrates a graphical integration of two male voices intoning the same vowe will reveal a decided
,
I
I
III
IV
Fig. 1-6. Graphical integration of two male voices intoning the same
vowel that discloses a great difference in the peak factor of each.
difference in peak factor (ratio of peak to average content), which in
turn depends to a large extent on harmonic content and phase relationship of the harmonics to the fundamental.
At the present time only one solution suggests itself. When it becomes necessary to transmit two voices of such difference in timbre as
to be decidedly unequal in loudness for a given reference level, the
good taste and judgment of the operator at the control panel must
govern their respective levels. The author fully realizes the many and
varied complications that arise from this condition, since loudness is
not only a physical, but also a psychological reaction. The level at
which the receiver in the home is operated will determine the extent
to which changes in loudness intensity are noticeable, since at low
volumes greater change of intensity is required to be noticeable to the
ear than is the case at higher volumes. Acoustics of the studio and
the room in which the home receiver is operated will influence the
ear's appreciation of level intensity changes. However, the control
man with good taste, a critical ear, and keen appreciation of values
can find the "happy medium" between aesthetics and conventional
transmission operations. This is of prime importance when voice
and music are to be blended, as will be discussed later.
10
BROADCAST OPERATORS HANDBOOK
Details of Control Room Metering Circuits
A few of the fundamental characteristics of broadcast metering circuits have been discussed in relation to the proper understanding of
their functions by both control room and transmitter personnel. The
operator employed in broadcasting is confronted with the handling and
measuring of the quantity known as the "volume" of sound. His conception of volume must necessarily be influenced by other than precise mathematical relationships of electrical units such as power, voltage, or current. At the same time, his means of measuring the complex
and nonperiodic speech and program waves must be based primarily
on a -c theory in terms of the related values of sine -wave currents.
The correlation of data on program metering circuits to serve definite
performance characteristics for various parts of a transmission system
is a most important subject and yet perhaps the least understood
among the operators and technicians concerned with their use.
Since the earliest days of electrical program transmission, about
1921, when it became apparent that distortion due to overloading of
an amplifier was far more noticeable in a loudspeaker than in the or -
L___
/
39001L
ATTENUATOR
COPPER -OXIDE
RECT FIER
AND
METER
390011
390011.
Fig. 1-7. Circuit that is used to bridge the new vu meter across program
lines or individual studio output lines.
dinary telephone receiver, various schemes for measuring the magnitude of program waves have been developed. The first device was a
d -c milliammeter connected in the output of a triode detector, with an
input potentiometer to adjust the sensitivity in 2 -db steps. Thus, by
adjustment of the sensitivity control so that peaks of program waves
caused an indication of approximately mid -scale on the meter at intervals, and by operating the telephone repeaters at about 10 db
lower on peaks than the point of overload, a visually monitored program circuit became a reality.
From this early start, there developed a long series of devices, some
with tube rectifiers, others with dry rectifiers (peak and rms indicat-
WHAT YOU'RE UP AGAINST
11
, full- and half-wave rectification, all degrees of damped movements, and calibrated with reference levels of 10-9, 1, 6, 10, 121/2, or
50 milliwatts, in 500 or 600 ohms impedance. It was not until 1938
that the Bell Telephone Laboratories, the Columbia Broadcasting
System, and the National Broadcasting Company pooled their knowledge and problems in a joint effort to develop a standardized volume
indicator with the reference level implied in the definition of volume
units.
The outcome of this concentrated study was the new standard vu
meter such as those on the control panel of Fig. 1-1 (B) . The schematic diagram of Fig. 1-7 shows the circuit used to bridge the meter
across program lines or individual studio output lines. It is seen that
the total impedance presented to the line is about 7500 ohms; 3900
ohms in the meter and about 3600 ohms supplied externally to the
meter. The dynamic characteristic is also standardized as mentioned
earlier, being such that, if a 1000 -cycle voltage of such amplitude as to
give a steady indication of 100 on the voltage scale or 0 db on the
decibel scale, is suddenly applied, the pointer will reach 99 in 0.3
seconds and overswing the 100 mark by not more than 1.5%. This
meter is a great improvement over previous volume indicators where
large amounts of overswing often occurred.
The graph of Fig. 1-4 is a representation of a speech wave taking
place in the time interval of 1/100 second. It is obvious that due to
mechanical inertia of meter movements, true "peak reading" indicators are impossible in the strict sense of the term. Since the copper oxide instrument, indicating rms values, is sufficiently sensitive without the use of vacuum tubes, and since in the final analysis, the
indication on the meter should follow as nearly as possible the psychological effect of hearing, this type indicator has been standardized for
control room and line transmission use. Although peak -reading indicators are much faster than rms instruments, in actual practice their
accuracy is limited to about 100 cycles per second. At the higher
frequencies their function is to integrate the speech occurring over
a period of time.
As will be discussed in detail in the transmitter section of this handbook, the FCC specifies some form of semi -peak indicating meter to
measure modulation percentage at the transmitter. This is necessary
since the peak factor (ratio of peak to rms values) of program waves
may be 10 db or more, and when these peaks occur in rapid succession, danger of breakdown in circuit components exists as well as the
ing)
12
BROADCAST OPERATORS HANDBOOK
occurrence of adjacent channel interference. Means must also be
provided to check positive or negative peaks of the modulated carrier.
Thus the modulation monitor is essentially a half -wave rectifier indicator. These differences between studio and transmitter meter characteristics must always be borne in mind by the operators.
Volume Indicator Interpretations
For the purpose of discussing the problems relating to use and interpretation of volume indicator readings, the well-known fact that
any wave, no matter how complex, may be reproduced exactly by a
number of sources of pure tones will be employed.
Fig. 1-8(A) shows two simple harmonic motions of the same frequency, differing slightly in phase; that is, tone b is lagging behind
(A)
a
TOTAL -O
b
(B)
Fig. 1-8. When two harmonic motions of the same frequency, waves a and
b, are out of phase by less than 180°, their total is greater than either, as
shown by the vector at right of (A). When a and b are 180° out of phase,
they cancel as shown in (B).
tone a by a certain number of degrees. The vector addition at the right
shows how the total amplitude is influenced by the reinforcement of the
two tones, causing an addition to the total magnitude over either one by
itself. Fig. 1-8 (B) illustrates what happens when the same tones of
similar frequency are differing in phase by exactly 180°. The vector at
the right shows complete cancellation of the total energy, since the
tones are now opposing each other resulting in zero amplitude. Keeping this clearly in mind, it is seen that the total amplitude will be
larger for smaller angles of phase difference, and if the two tones are
exactly in phase, the parallelogram at the right collapses and becomes
WHAT YOU'RE UP AGAINST
13
a straight line that is the sum of the individual amplitudes. As the
angle of phase displacement becomes larger, the total amplitude becomes less, until at 180° it becomes zero.
In actual practice, it is realized that under program conditions a
large number of different frequencies with varying phase displacements
are being covered, and the loudness sensation produced in the ear for
a given meter reading is dependent on the number of harmonics present and the phase relationships of these harmonics. It then becomes
obvious that acoustical treatment of studios and type of program
content will influence the correct interpretation of a volume indicator
reading. It is, of course, apparent that the volume indicator performs
its duty in respect to showing the magnitude of the waveform,
whether it be "distortion peaks," noise, or musical sound, that must be
kept within the dynamic range of the transmission system. But when
correlating the reading of the volume indicator with the effect produced
on the hearing sense of the listener, these problems must be met and
analyzed. The loudness sensation for a given meter swing indication
has already been discussed in regard to voices of different persons.
The same characteristic is noted between individual musical instruments where the number of harmonics and their phase relationships
may vary in wide degrees.
Dynamic Range Indication
The volume indicator is used as a means of visually monitoring the
magnitude of the program waves for two primary reasons: (a) to
compress the original wide dynamic range to an amount consistent
with good engineering practice of the broadcast transmission system,
and (b) for locating the upper part of the dynamic range below the
overload point of associated equipment. For the latter purpose, a
scale of 10 db would be adequate; for the former purpose, a much
wider decibel range is desirable. Since the instrument is used for both
applications, it was decided that a compromise on a scale length of 20
db would be desirable. It appears that as the art and appreciation of
higher fidelity service advances, not only the frequency range but also
the dynamic range of transmission will be extended, particularly for
certain types of program material. This feature becomes a very important one for f -m service. With present-day meters, it is left to the
experience and judgment of the operator as to how far the volume
should be allowed to drop below the visual indication of the vu meter.
It would appear then that, in the interest of good operating practice,
14
BROADCAST OPERATORS HANDBOOK
some form of auxiliary monitoring of passages below the present-day
meter indication point on types of programs requiring wide dynamic
range, might be worth while. A suitable oscilloscope used in conjunction with the meter might be one solution. The practicability of this
method would be doubtful due to the fact that the operator's attention must be divided between the monitoring device and the studio
action. The same drawback would exist for an indicating meter of
such wide scale that the entire meter action does not fall readily into
the operator's line of vision. A meter of, say, 270 -degree scale would
have the same disadvantage of having either the low-passage or max-
imum-passage indication fall at an awkward position.
Perhaps the most practical solution would be a device consisting
essentially of two indicating pointers, one immediately below the
other. The lower pointer would indicate the first 50% of channel
utilization, with automatic overload protection built into the movement (by limiting tube or network) to prevent overload of this movement when the volume is such that the upper movement is indicating
the final 50% of channel utilization. The design should be such that
either indicator is in a practical plane of vision for the operator.
Chapter
2
ARE MECHANICAL OPERATIONS APPARENT?
THE REALM of the physical, mental, and psychological faculties
of the control -room operator lies the success or failure of the
broadcaster's daily schedule. A script -writer's masterpiece or a
composer's dream can amount to no more than the original worth of
N
his work, plus the ability of the control man to interpret that work on
the technical equipment at his command. Yet, perhaps paradoxically,
the best qualified operators are the least conspicuous to the listener
at home.
An ideal job of switching and blending of microphones for the various performers of a given show is such that the listener -in is entirely
unconscious of mechanical operations necessary to their performance.
The operator who "cuts" Lis program at its conclusion, instead of
fading out (even though because of time limitations it must be a
"quick fade"), not only makes mechanical operations apparent to the
listener, but marks himself as a man not entirely a master of his equipment. Exceptions to this rule exist, such as "stunts" of a technical
nature that are sometimes aired to impart a technical flavor to the
layman. In such programs, technical operations should be accentuated,
of course, rather than subdued, but it is well to remember that, as a
general rule, the test of the operating technique should be, "Are me-
chanical operations apparent?"
This primary rule should govern the entire operating technique of
the control man. Music, speech, or background accompaniment that
is too high or too low in level should be gradually adjusted to normal
in a manner cognizant of musical and dramatic values. It might appear at first that this prime requisite for good operating practice
would conflict seriously with good engineering practice. When levels
are too high, overloading of associated equipment at the transmitter
occurs. When compression amplifiers are used, as is commonly the
case, the distortion arises from excessive compression rather than from
overmodulation of the transmitter. It has been proved from extensive
tests, however, that distortion caused by momentary overloads simply
15
BROADCAST OPERATORS HANDBOOK
16
is not noticeable even to highly trained ears. This appears to be due
to physiological and psychological factors that determine the ears'
appreciation of aural distortion, resulting in a lack of response to overload distortion occurring at rare intervals and of short duration.
The level of the speaking voice can be least obviously adjusted by
correcting the fader setting between words or sentences where slight
pauses occur, rather than increasing or decreasing the volume during
PROGRAM TITLE
t
DATE OF BROADCAST
Musical Clock
FOR
Thursday Aug.19
t
MEDIUMt
Books
t
FROM
7,15 am
t
TOt
ET and Recordings
8,15 am
RECORD OR TRANSCRIPTION
TITLE OF COMPOSITION
BRAND
SERIAL NUMBER
Got the Moon In My Pocket
W
How About You
Vi
Ferry Boat Serenade
11
Back Home Again in Indiana' De
Blueberry Hill
*
America, I Love You
Co
x
Chinese Lullaby
PERFORMING SOC.OR LICENSING AGT.
ASCAP
ASCAP
ASCAP
ASCAP
ASCAP
ASCAP
ASCAP
5163
27749
3921
3786
3829
35865
6690
LEGEND,
W
-
Vi
De
Co
Th
-
-
World
Victor
Decca
Columbia
Thesaurus
Fig. 2-1. Typical music sheet for a program of recordings supplied to the
announcer operating the turntable and the control-room operator. Brand
names enable operator to anticipate volume level.
actual excitation of the microphone by the sound waves. A comparison
of these two methods by the operator on his audition channel will reveal the striking difference in the obviousness of level control.
Anticipation can play a major part in smooth level control when
circumstances permit. The operator soon becomes familiar with the
approximate fader setting of each announcer as he takes over to relieve the preceding announcer. It is obvious here, of course, that ample
opportunity is given to adjust the mixer gain before actual air time.
This is also possible in some instances with transcribed and recorded
shows, when the operator is aware of the brand of recording to be
played next.
Fig. 2-1 is a reproduction of a musical sheet for a given program
as used at Station WIRE in Indianapolis. The announcer, who operates the turntables, and the operator in the control room each has a
copy on hand for reference. It will be noted that the brand of each
number, such as World, Victor, Decca, is clearly indicated. This en-
ARE MECHANICAL OPERATIONS APPARENT?
17
ables the operator to anticipate the level to a certain extent, since, for
example, World transcriptions are several vu lower in level than
Victor recordings, requiring a higher fader setting. This will also be
influenced to a great extent by the type of filter used on the turntable
for various recordings, since a different filter is used in many instances
for different brands or conditions of recordings and transcriptions.
This is discussed more fully in the section on turntable operation appearing at the end of Chapter 4. The gain settings for a given brand
will usually be fairly consistent. Thus when the operator has become
familiar with the necessary fader adjustment for each brand of trancription or recording, he will be able to use the art of anticipation to
good advantage. When the level to be anticipated is uncertain, it is
well to remember that from an aesthetic point of view as well as a
technical point of view, it is far better to be able to "fade in" the
speech or music rather than to experience the shock of excessive volume which must be quickly lowered to normal values.
The foregoing discussion is likely to lead to an erroneous point of
view to a newcomer in a control room. It might be well to point out
at this time that one of the greatest errors of new men in this field
is to "ride gain" to the point of exasperation to a critical listener. The
operator should endeavor at all times to give musical and dramatic
values a free rein insofar as is practically possible. Remember that
from the listener's point of view, the business and purpose of broadcasting is to provide entertainment through the medium of bringing
music and dramatics into the home. The technical setup necessary for
this purpose has been engineered to a point of perfection; it is only
necessary that this equipment be operated in a manner that will
promote these musical and dramatic values in their original intent.
The fundamental rule of good operating technique is probably the
most abused by innocent operators during the transmission of symphony broadcasts. Suppose that an orchestra of some 40 to 80 members has just finished a number which for the past few minutes has
been very pianissimo, say -15 to -20 vu. It is safe to say that the
average listener to a symphony program will have his receiver volume adjusted so that comparatively high power exists in the speaker
when the studio level hits 0 vu. It is obvious then, what will occur if
the announcer suddenly pops in at 0 -vu level. The listener may not
be actually raised from his chair by this sudden human roar, but the
experience, to say the least, is a shock to all five senses, including
smell. Sudden crescendos in music are expected, welcomed, and ap-
18
BROADCAST OPERATORS HANDBOOK
preciated, but a single announcer, exploiting the glorious qualities of
Joe Glotz's Super Zoot Suits at an apparently greater volume than all
80 men with everything in their possession from a piccolo to kettle
drums, simply is not only unwelcome, but extremely obnoxious.
It is a safe rule to remember that after such musical numbers as
this, the announcer should be held down to about
maximum. The
difference to be maintained between levels of voice and music will
depend not only upon the type of program aired, but also upon the
acoustical treatment of the studio and will be mentioned in chapter 3.
The inadequacy of present-day broadcasting to the field of symphony music transmission is quite apparent to most engineers. The
discrepancy between the usual 70 -db dynamic range of a full orchestra and the actual 30 to 35 db allowed by broadcast equipment is all
too obvious to the control man handling such pickups. It has been the
practice of some operators who do not appreciate the symphonic form,
to bring all low passages up to around -4, then "crank down" on the
gain as the orchestra increases its power according to the continuity
of the musical score. The fault in this technique should be apparent.
If the very lowest passages are brought up to just "jiggle" the meter,
and care is taken to use good taste in suppression of the crescendos,
a very satisfactory dynamic range may be experienced, since even a
range of 25 db will vary the output at the receiving point from 25
milliwatts to nearly 18 watts on peaks.
Needless to say the technician on a symphony program, or any
musical program, should possess a good ear for music. Rules and regulations will never help a man with a pair of "tin ears" to handle a
musical show properly. There are, of course, many competent technicians who do not like or appreciate music, and these men should be
assigned to the performance of technical maintenance or transmitter
duty. It is nevertheless important that the transmitter technician
understand that a great amount of modulation during classical music
will be below 20% even with compression line amplifiers.
Recordings and transcriptions of symphony music have already been
compressed into broadcast dynamic range, since the recording engineer has essentially the same problem to contend with in relation to
this difficulty. Usually all that is necessary for the control technician
to do is to set the level on the peaks of the music to correspond with
0 vu or 100 on the scale, and "let it ride."
Specific symphony pickup will be discussed in chapter 11 since this
type of program is often handled as a remote program.
-6
Chapter
3
KEEPING SOUND "OUT OF THE MUD"
correlating volume levels with comparative
loudness of speech and music has appeared as an item of major importance and should no longer be ignored by broadcast
station personnel. Table 1 was compiled as a result of "group tests" of
comparative loudness of different types of music with that of speech.1
The "peak factor" (ratio of peak to rms values) of speech waveform
is very great in comparison to that of music waveform, as emphasized
by Fig. 3-1. It is apparent, therefore, that 2 to 3 db more power may
exist in speech waves in a circuit monitored by an rms meter than is
indicated by the meter itself. This will explain the results shown in
Table 2, which as well as Table 1, was taken from the aforementioned
article. It is apparent then that when speech and music levels are
THE PROBLEM of
TABLE
1
Volume Indicator (RMS) Reading
for Same Loudness as Speech
Type of Program
Male speech
Female speech
Dance orchestra
Symphony orchestra
Male singing
0
0.1
2.8
2.7
2.0
Showing importance of peaking music 2 to 3 db higher than male speech for equal
loudness sensation. (See text.)
adjusted in correct ratio to avoid overloading, the loudness will be
approximately the same.
Table 1 contains a discrepancy with the author's personal experience, and is mentioned with the hope of further research and clarification. It will be noticed that results of the tests on this particular
group of listeners dictated the need for a 2.8 -db higher level for a
' Chinn, Gannett, and Morris, "A New Standard Volume Indicator and Reference Level"; Proceedings, IRE, January 1940.
19
BROADCAST OPERATORS HANDBOOK
20
dance orchestra, and a 2.7 -db higher level for a symphony orchestra
over that of male speech. If the author was to compile a similar table
of equal loudness from several years experience of watching volume
indicators (VI's) on various types of programs, he would choose approximately 3 db higher level for a dance orchestra, and 4 to 6 db
;nigher for a symphony orchestra over that of male speech. The author
(A)
Fig. 3-1. The "peak factor" (ratio of
peak to rms values) of music waveform
(A) is not as great as the peak factor
of voice waveform (B).
(8)
that this is not caused by a different physical response of the ear
itself, but rather to a possible difference of acoustical factors involved,
plus the fact that certain psychological factors were not considered
in the original tests. By this is meant the important difference in
feels
TABLE 2
Total No.
Type of Program
No. of
of
RMS
Volume
Tests
Observations
Indicator
Male speech
Female speech
Piano
Brass band
Dance orchestra
Violin
8
8
81
82
5
5
40
25
42
1
15
22.1
22.8
24.1
24.1
24.7
25.8
Average speech
Average music
16
15
163
122
22.4
24.5
4
The final column shows average overload points of different types of programs,
measùred at the output of a W.E. 94B amplifier. The important fact of this table
is the revelation that the point of overload for average speech is about 2 db lower
than the point of overload for average music (rms volume indicator).
KEEPING SOUND "OUT OF THE MUD"
21
listening technique between the symphony audience and the dance music listener.
As was mentioned before, because of the nature of the classical type
of music, the symphony fan at home will operate his receiver on the
average a great deal higher in level than he would for ordinary programs. Five minutes of symphony music will have perhaps 3 to 4
minutes of low to very low levels; the average intensity level over a
period of time is far lower than the average intensity level of a dance
orchestra in the same time interval. It should then be obvious that a
greater difference should exist in the ratio of music to speech levels
for symphony programs than for those of dance music. Perhaps if
tests were carried out with this difference in receiver volume considered, as well as the type of music on the program, the results would
be more nearly in agreement with the foregoing argument.
The acoustical treatment of the studio in which the program originates will affect to a great degree the loudness of voice and music, and
in a different ratio. A studio that is overtreated with absorbent material deadens the sound because of high -frequency absorption, and is
an outstanding enemy to musical programs. Music from "dead" studios is "down in the mud," lacking in brilliance, and generally dull to
hear. The effect on speech, however, is not so pronounced as that on
music. Speech originates within a few feet of the microphone and requires much less reverberation to assure naturalness, whereas the space
10
20
.
30
40
50
60 70
OPTIMUM REVERBERATION
80 90 100
150
200
TIME
Fig. 3-2. Graph showing the influence of acoustical conditions on ratio
of peaking voice and music assuming a necessary 2 -db difference for
optimum acoustical conditions.
between the source of the music and the microphone is greater, and
many things happen to the musical waveforms that must eventually
be translated into perceptions of loudness.
Fig. 3-2 is a graph drawn on the assumption of a necessary 2-db
BROADCAST OPERATORS HANDBOOK
22
difference of voice and music level readings on an rms meter under
normal acoustical conditions. The optimum reverberation time will
vary according to the size of the studio, as shown by the curve of Fig.
3-3. The curve of Fig. 3-2 is drawn on a probability basis, correlating
known facts concerning reverberation time with loudness sensation of
voice and music. This graph shows the necessity of a lower peaking
of voice in relation to music for less reverberation time than normal,
2.5
2.0
Fig. 3-3. The optimum reverberation time varies with the
size of the studio, as is evident
from these curves. See also Fig.
128 CYCLES
1.5
512
1.0
2048 CYCLES
3-2.
After Knudsen
0.5
6.25
200
100
50
25
CUBIC FEET-THOUSANDS
12.5
400
and at the same time shows that for 1.5 times the optimum reverberation time, where a great amount of reinforcement of the original musical waves takes place, the voice and music should be peaked the same.
It should be pointed out here that so called "optimum reverberation
time" really is an expression of what constitutes pleasing sound, and
this conception is still changing with experience. It may well be that
near future standards of optimum reverberation time will see a condition which will decidedly alter the above discussion of ratio in peaking voice and music. The point that is important to keep in mind is
that a great majority of present-day studios throughout the country
are below even up-to-date standards of correct reverberation characteristics; hence the need for the discussion.
The newer "live end, dead-end" studios, with musical instruments
placed in the live end and microphones spotted in the dead end, present one solution for properly controlled reverberation. In these studios, voice and music peaked at the same level will appear the same
in loudness sensation. In fact, the advancing state of studio development points to all indications that the present day is experiencing a
transitional era in which, from some of the most modern studios using
reflecting panels for musical pickups, the brilliance of the music is so
great that, when peaked an amount on the meter equal to that of
KEEPING SOUND "OUT OF THE MUD"
Courtesy National Broadcasting Co.
Figs. 3-4(A) above, 3-4(B). The live end of a "live -end, dead-end" studio
designed to provide properly controlled reverberation. Slanted wooden
sound-dispersing panels are suspended against the side walls, forming a
series of resonance diaphragms, shown in (A). The walls of this studio are
slanted (B) to eliminate standing waves that cause flutter.
23
BROADCAST OPERATORS HANDBOOK
24
TeBzE 3
Instrument
Bass viol
Bass saxophone
Trombone
Trumpet
Trumpet (muted)
French horn
Clarinet
Flute
Violin
Piano
Electric organ
Pipe organ
Studios of Optimum
Reverberation Time,
Distance in Feet
6
6
Studios of 25% Optimum
Reverberation Time,
Distance in Feet
4
4-5
12
5
7
8
5-6
8
8
6
5
5
3-4
5
15
3
10
15-20
20-25
8-10
10-15
7
voice, the voices sound much lower in loudness than the music. This
brings to mind again the importance of using judgment in aural perspective when "riding gain" on productions with the intent of achieving a properly balanced effect in the listener's home.
The use of wood in broadcasting in accordance with exact acoustical
specifications for controlled reverberation was apparently introduced
by CBS in New York about 1935. The entire "live end" of the studio
was constructed as a series of resonance diaphragms of seasoned wood,
held in suspension with air chambers behind them, as shown in Fig.
3-4(A). The wood panels that cover about one-third of the side walls
are placed on slanted surfaces so that the side walls form shallow
"V's" running from ceiling to floor. These are so placed that the wall
surfaces are not parallel to one another, as shown in Fig. 3-4(B).
This eliminates standing waves which would normally produce "flutter." However, because of the highly reflective surfaces of the wood,
a certain amount of reverberation is achieved, a quality which adds
life and brilliance to the speech and music originating in this type
studio.
This is essentially the same principal used by WBBM (CBS) in
Chicago and other key points, as well as by the other major networks
irl their key stations. A number of smaller independent stations have
since utilized this type of construction in their studios, and it is
hoped that others who contemplate new studios or remodeling of old
ones will recognize the tremendous importance of a degree of liveness
in broadcast studios.
Chapter
4
YOU'RE OFTEN A PRODUCER TOO
the control room is called upon many times to
set up complex musical and dramatic shows. This is especially true in smaller stations that have no production man,
and is sometimes true of important key network stations where the
control man must achieve the desired results of the production man
assigned to a particular show. The responsibility of setups of studio
shows is not a simple one. Many years of research and much thought
have gone into production, and a knowledge of at least the fundamentals of the art, as they affect the technical duties, will help the control
technician over many difficult situations that will arise in the course
THE OPERATOR of
of his work.
',
In determining the proper use and placement of microphones for
any given setup, it is important that the operator becomes familiar
with the pickup patterns of the microphones used. These patterns illustrate completely the function as to amplitude and frequency response for varying degrees of placement about the face of the microphone. Fig. 4-1(A) shows the pattern of the RCA 44-BX velocity
microphone, and Fig. 4-1(B) is the pattern of a RCA 77-B combina-
30°30°
50°,é ,
10° 0
45°
°
:::
45°
50°
d-!e
-:..-:-.I
60°,'.,
1
45°
o
10°
60°
30°
45°
0
Courtesy RCA Mfg. Co.
Fig. 4-1. The pickup response pattern of the ribbon or velocity microphone
(A) is bidirectional and that of the combination ribbon and pressure type
(B) is unidirectional.
25
26
BROADCAST OPERATORS HANDBOOK
tion ribbon and pressure type instrument. There are several important
points of interest relating to these patterns which show great differences in characteristics aside from the most apparent one, that of bidirectional and unidirectional pickup.
An analysis of the patterns reveals a much wider range of amplitude
response for the combination pressure gradient (ribbon) and pressure
type microphone [Fig. 4-1 (B) ] than for the ribbon type alone. See
Fig. 4-2. Take for example the 1000 -cycle curve for the 44-BX ve -
90°
Fig. 4-2. The amplitude response of the 77B
combination type microphone (solid curve)
has a wider range than the 44BX velocity
microphone (dotted curve). Such patterns are
useful for making setups and eliminating unwanted sounds.
locity microphone. It is noted from Fig. 4-1 (A) that at an angle of
70 degrees, the amplitude response is down about 10 db in respect to
its response at a given distance at 0 degrees. Now note on the 1000cycle response curve of the 77-B combination type in Fig. 4-1 (B) that
the amplitude response at 70 degrees is down only approximately 3
db from 0 degrees reference. These patterns are useful for determining the setups necessary for discriminating against unwanted sources
of sound, and for obtaining a particular relation between sounds of
different sources. It can be seen that as a performer is moved around
the microphone, loss of sensitivity may be compensated for by moving
closer to the instrument.
It is clear then that characteristics of the type or types of microphone in use should be thoroughly understood. Fig. 4-2 is presented
as a basic principal in using patterns of a unidirectional microphone
of the combination ribbon and pressure type. It is a well-known fact
that, because of the pressure gradient characteristic of the ribbon microphone, the instrument will favor the lower frequencies of longer
wavelength under close talking conditions. For this reason announcers
on such microphones must be at least 1.5 to 2 feet from the microphone. When close talking becomes necessary, however, the combination type instrument may be utilized by the engineer, who can then
safely instruct the announcer to approach an angle of 90 degrees with
YOU'RE OFTEN A PRODUCER TOO
27
the face of the microp_lione as shown in Fig. 4-3, and work as closely
as desired. In this position the ribbon element will contribute practically no energy to be output, leaving the pickup to the pressure
element, which is not afected by the spherical character of close talking sound waves.
It may be seen that the "fading zone," where sensitivity falls off
rapidly for increasing angles, is just as useful as the ordinary pickup
zone, since the quality k just as good and a fine degree of shading may
be realized by understanding its proper use.
As will be described :and illustrated in the technical explanation of
microphones in Part 6, a number of modern ribbon and combination
microphones have an as ociated equalizing feature known as a "speech
strap." In the "speech" position, close talking into the ribbon element
will not result in excess:7e bass response. When the same microphone,
however, is used both r the musical pickup and the announcer, the
strap is placed in the "music" position, and the announcer must work
the mike as explained above.
As far as is practicE ily possible, only one microphone should be
used for a given pickup. When two or more instruments are used,
serious frequency and delay distortion is likely to result, since each
f
ANNOUNCERS
ZONE
PICK-UP
ZONE
60°^,
00
Fig. 4-3. When close talkinª into the combination type microphone is Iecessary, it can
be approached as closely a: desired in the
zone between 60 and 90 degr 2es. The lower
response of the "fading" zone between 90
and 120 degrees, does not af'ect the quality.
L.:o%.1
11W«,5,4
120°
120°
Courtesy Western Elec`ric Co.
DEAD
FADING
ZONE
microphone will be a dr_fferent distance from a given sound source.
It can be seen that soutd waves would not reach the instruments at
the same time, and their combined outputs will result in partial reinforcements or cancellation, depending on their phase relationship.
When it is absolutely necessary to use two microphones very close
BROADCAST OPERATORS HANDBOOK
28
together, they may be poled so that their outputs are additive rather
than subtractive, either by rotating a bidirectional microphone
through 180 degrees, or by reversing the connections on a unidirectional microphone when the outputs are subtractive. This may be accomplished by using a patchcord between any two terminations of the
circuit on the jack panel, and reversing one end at a time during the
test. The proper phasing of the two instruments is accomplished by
watching the vu indicator when the two inputs are switched to the
first one, then both together, and noting whether the combined outputs are additive or subtractive. Usually one connection will give
greater additive effect than the other connection, and this effect someORCH.
7
\
/
`
\
,
00001
O
\ `/
-.0j
l
M
(
)
/00000\
O
NULL
NULL
\
/
\
\
_./
)
Fig. 4-4. A good basic arrangement of ribbon type microphones, M, for
proper pickup of sounds from two sources. The dotted circles indicate
the microphones' response areas.
times changes with a change of frequency; although for complex
waves where we are not concerned with pure tones of a single frequency, a good average additive effect can be obtained. Fig. 4-4 shows
the basic idea in proper placement of microphones when two are necessary for proper pickup of two separate sound sources.
As a rule, the most common error of newcomers to control rooms is
the placement of the microphone too close to the sound source. As has
been discussed before, loudness sensation for a given meter reading
YOU'RE OFTEN A PRODUCER TOO
29
depends largely on the harmonic content of the waveform. Placement
of the microphone extremely close to the musical instruments results
in peaks on the vu meter that are almost inaudible to the listener, and
since the intensity of these peaks must be kept below 0 vu, the resultant music is completely "down in the mud" and lacking in brilliance. Smooth control under these conditions is impossible, and harmonic content is very low.
For pickup of piano music, a distance of at least 15 feet between
microphone and piano should be observed in studios of optimum reverberation time. More intimate pickups are necessary for dead studios, since no reinforcement of the sound waves takes place. Too great
distance in such studios results in a thin sound, lacking in body.
For the purpose of presenting a basic rule for distance in microphone placement for certain instrumental solos, Table 3 is presented.
This table is not meant to be an infallible rule of exact distances in
microphone placement. It is intended to convey an idea of the minimum distance to start from on rehearsals before air time. Any change
to be made then would be toward greater distances rather than less.
It is imperative, of course, that the operator experiment with microphone placement in his own studios to get the best results from its
particular acoustical condition.
The effect of phase shift in studios on the quality of musical sounds
is important even though the human ear is not essentially a "form
Fig. 4-5. The energy
arriving at the microphone M is the sum
of the initial energy
W1 of the direct sound
from the source S together with the reflected wave trains W2
and
W3.
analyzer." Phase shift causes trouble in both live and dead studios.
"Dead spots" nearly always exist in studios because of cancellation
of large amounts of the complex wave frequencies caused by phase
shift. Fig. 4-5 illustrates the basic theory of wave -train travel from
its source to the microphone spot. The energy at M, the microphone,
30
BROADCAST OPERATORS HANDBOOK
is the energy of the initial direct wave train WI from the sources,
plus the energy of the reflected wave trains W3 and W3. The amount
of energy of the reflected waves is governed by the characteristics of
the reflecting surface, which in turn determines the reverberation time
of the studio. It may be observed here how phase shift, because of the
different distances over which the waves travel, could cause reinforcement or cancellation of certain frequencies at the microphone spot.
Complete dead spots are more likely to occur in live studios, since
reflection from a perfectly hard surface causes no change in phase
of the individual frequencies of the complex wave, creating a condition in which, theoretically, complete cancellation of the entire spectrum at a particular spot in the studio might occur. In dead studios,
absorption of the higher frequencies is greater than at lower frequencies, thus making complete cancellation of the complex wave unlikely.
If this phenomenon is fully understood, it will be realized that microphone placement is much more critical in dead than in live studios,
since dead spots are easily avoided in live -end studios where reinforcement of the musical tones is smooth and even over the entire spectrum
of frequencies for a given microphone spot; whereas the placement
is only a compromise of the greatest possible frequency range for a
given pickup spot in dead studios. Construction of the new live-end
studios with sidewalls arranged in "V's" so that no surface is parallel,
results in a dispersion of sound that helps to overcome the occurrence
of dead spots in this type of studio. The contribution of the reflected
waves in a live -end studio to the loudness intensity, resulting from the
reinforcement and sustaining of the overtones of the musical instruments, gives these studios a decided advantage over the older type
"general purpose" studios.
Importance of Rehearsals
The co-ordination of hand, ear, sight, and sound for the purpose of
blending the component parts of a studio performance is best gained
by the operator through the medium of rehearsals. Fading in or out
of various microphones, turning them off and on, is the procedure
which enables the engineer to play upon the sound of voice and orchestra much as if the control panel itself were a musical instrument.
Indeed, in a sense, this is just what it is. The ratio of fader adjustments will determine the apparent distance of a singer from the audience; the voice may be smothered with music or may be made to
stand alone with only a suggestion of background accompaniment. A
YOU'RE OFTEN A PRODUCER TOO
31
proper blend of voice and music, or of dramatics and sound effects,
can only be properly created through careful and detailed rehearsals.
This is the one and only method of preventing the "on air" show from
becoming only a caricature of the original idea.
Many "c:1 timers" are familiar with the coloratura soprano who
is nicely "adjusted" on rehearsal, then hits +20 vu on the air without
batting an eyelash. This condition simply emphasizes one important
point: the operator must be apt at diplomacy as well as technically
conscious. Talent must be made cognizant of the importance of treating rehearsals just the same as "on air" performances. If the performers are instructed in "mike technique" from the point of view
of making their performance sound just the way they desire to the
listener, the operator will find ready and willing co-operation. Do
not be shy of temperament. The more temperamental the performer,
the more he likes to be "fussed over" at rehearsals to gain emphasis
of his best talents. Ask any operator or producer of big time shows
out of New York, Hollywood, or Chicago; they are in a position to
know.
The distance to be maintained between vocalist and microphone
will depend on the type or style of vocal form used by the singer. In
general there are two commonly encountered types of vocalists, the
"crooner" and the "operatic" singer. Whereas the crooner will employ
a dynamic range of around 15 vu, the "operatic" singer will use a
much wider dynamic range. For the former type, where the sound
waves are garnered principally from activation of the upper larynx
and throat muscles with comparatively low-pressure waves resulting,
it is usually necessary to work close to very close into the microphone.
The vocalist who "sings out" by bringing the chest muscles into action must be placed a minimum of 4 feet, preferably 6 to 8 feet, from
the microphone. This may appear to be an excessive distance, but
actually a much greater dynamic range and brilliancy of voice may be
realized by using this distance for singers who range from extremely
low to very high air pressures to excite the microphone element.
There are of course a number of "in between" singers, such as some
of those who sing with dance orchestras, and they are usually placed
from 2 to 3 feet from the microphone.
Microphone technique for actors in a dramatic program spells success or failure in creating the desired illusion in the loudspeaker.
,Usually one microphone only is used for the entire cast, with a separate microphone for sound effects. As each actor plays his part, he
BROADCAST OPERATORS HANDBOOK
32
steps up to the microphone, sometimes approaching from the fading
zone into the announce zone to create the illusion of approaching the
scene of action, sometimes leaving in the same manner. In some cases
"board fades" are marked on the script [Fig. 4-5 (A) ]. The operator
fades the entire studio setup including sound effects by fading out
with the "master gain" control. Shouts or screams must be performed
in the shading area "off mike" to avoid excessive pressure on the microphone element which would require an excessive gain adjustment
by the operator, losing the effectiveness of the illusion.
While studio rehearsals are in progress, it is imperative that the
engineer and production director be able to talk to the cast for the
purpose of instruction in positions, microphone technique, etc. This
is accomplished by means of a "talk -back," which consists of a microphone in the control room connected to an amplifier feeding a loud -
1.
OPENING SOUND.
2.
NARRATOR.
(ORCHESTRA)
Have
Le
ever been
to Hell?... Well I have ... and nov I have to go back...
3.
4.
to
stay:
MUSICAL CRESCENDO
5.
SOUND.
6.
NARRATOR.
-
THEN SILENCE FOR 3 SECONDS...
She had everything a man could want, topped off with
7.
a beautiful name ... Clarissa.
8.
that first night I saw her,
9.
had been for hours,.. -and..
I'll never forget
it vas raining...
10. SOUND.
PADE IN RAIN ON PAVEMENT.
11.
CAR SWIFTLY PASSINO..SPLASHINO WATER..
12. CLARISSA.
(STARTLED) (OPP MINE)
13. NARRATOR.
Oh Miss:
as it
STREET NOISES..AUTO HORNS.
Oh:
That's a tough break... Better get back here..
14.
farther from the curb.. Motorists don't think you know.
15.
Here-share my umbrella.
X16.
í
SOMBER, DRAMATIC STRAINS
(LOW MONOTONE, VERY CLOSE TO MIRE).
CLARISSA.
i*17.
xa18.
(DRY LAUGH).
yours?
I
shan't get any wetter nov..
(PAUSE)
My name's Clarissa, What's
I'm afraid
Thank you anyway.
(START BOARD FADE HERE)" 3 SECOND PAUSE.
Just like that... and she vas young..
19. NARRATOR.
(REMINISCENTLY).
20.
and so sweet... and beautiful:
Fig. 4-5(A). Sample of script which an engineer has marked so that he can
"cue" himself for what is coming. The "board fade" is done by fading the
master gain control. Note that in line 10 the "fade in" might be done by
the turntable operator if sound is on records; it rain and street sounds
originate in studio, control man fades in associated microphone.
YOU'RE OFTEN A PRODUCER TOO
33
speaker in the studio. Switches on the control console and perhaps
also on the production director's console where such is used, are provided for the talk -back mike. The control man is sometimes provided
with a foot-switch to free his hands for the controls. When this mike
is turned on, the control -room speaker is cut off by a relay interlocked
4.1)
Z
ula
CC
TROMBONES
3 RD. SAXOPHONE
1ST. SAXOPHONE
TENOR SAXOPHONE
4TH.SAXOPHONE
Fig. 4-6. Microphone arrangement for musical show often necessary in a
"dead" studio.
with the switch to prevent acoustic feedback. This microphone is also
electrically interlocked with the "on -air" position of the output switch
so that it may not be operated during the time a show is actually being broadcast.
Musical Setups
Figs. 4-6 and 4-7 illustrate specific setups for musical shows. Acoustical conditions are so varied that no specific rules can be drawn up
for instrumental placement about the microphones. The most important rule is to be thoroughly familiar with the pickup patterns of
the microphones used, as outlined previously. One microphone is to
be preferred in a sufficiently live studio for a complete musical aggregation, whereas dead studios requiring more intricate pickups, may
require two or more microphones to cover all the musical instruments.
Network practice in the pickup of twin pianos is illustrated in Fig.
4-8. The lids of the pianos are removed and the microphone raised
slightly higher than for single -piano setups. When an audience is pres-
34
BROADCAST OPERATORS HANDBOOK
TRIANGLE
BASS
SNARE
XYLOPHONE
CHIMES
TYMPANI
TRUMPETS
TROMBONES
NN
FRENCH HORNS
2ND.VIOLINS
VIOLAS
BASS
VIOLS.
iST.VIOLINS
3
Fig. 4-7. Orchestra and choral arrangement for a "live" studio, mike 1 for
main orchestra; mike 2, soloist; 3, announcer; 4 and 5 for choir, when clarity
of diction is needed. Mike 2 used for over-all choral effect.
ent in a studio, "applause" and "laugh" mikes are swung out over the
audience on booms or suspended from the ceiling so that the "presence" of the audience may be "boosted" in gain by the control engineer when necessary.
When obtaining a check on the "balance" of the various instruments
on a musical program, the monitor speaker volume in the control
room should not be run at excessively high levels. There is a tendency
on the part of many control men to run their monitor speakers at
Fig. 4-8. A microphone M for a twopiano pickup is placed between and
slightly higher than the pianos from
which the lids have been removed.
levels that are almost never maintained in the home. Fig. 4-9 illustrates the relative response of the "average" ear to different frequencies at a given level. It may be observed that the threshold of
hearing at 32 cycles is 60 db, whereas for a frequency of approximately
YOU'RE OFTEN A PRODUCER TOO
35
-8
2500 cycles the threshold of hearing starts at about
db. When
control -room speakers are run at excessive levels, bass response is
much greater than it would be at normal levels, which is likely to
result in the placement of the bass instruments in a lower sensitivity
area of the microphone. When this occurs, bass response is almost
140
i
m
O
120
U
á
/
100
1`
z
Fig. 4-9. The lower curve
á 80
shows how the average
human ear responds rela- wQ 60
tively to different frequencies at a given level.
40
See text.
z b
0
cr
FEELING
//
N
N
.
N
THRESHOLD
OF
HEARING
i
1
I
20
0
-20
10
20 40
100 200 400
1000 2K 4K
10K
20K
601'.
inaudible in the receiver at home. This characteristic of the human ear
has resulted in the development of the "bass boost" circuit in modern
receivers which is intended to accentuate the bass response in receivers
operating at low levels.
Sound Effects
Major network practices in the art of sound effects has developed
over the years into one of the most highly specialized fields of broadcasting. A sound effects technician can take the lowly strawberry box
and create illusions ranging from the squeak of a wooden gate or the
squeak of a ship moored to a dock, to the terrible rending crashes and
splintering cf wood for collisions of any description. A bow of a bass
viol is drawn in a particular manner over the edges of the box for the
first effects, while the box is crumbled between the hands close to the
microphone for the collision effect. Rainfall is simulated by the pouring of birdseed or buckshot on a sheet of parchment or by a rain machine, consisting of perforated pipes through which water pours onto
brushes in a tub, as shown in Fig. 4-10. Of course, actual objects are
also used to produce certain sound effects as illustrated in Figs.
4-11 (A) and (B), which show the contents falling out of Fibber Mc Gee's famous closet on the NBC "Fibber McGee and Molly" program.
36
BROADCAST OPERATORS HANDBOOK
YOU'RE OFTEN A PRODUCER TOO
37
BB shot rolled back and forth with skillful timing over a copper
screen can simulate either a lazy palm -bordered beach or a veritable
turmoil of angry waves in an ocean storm. Cellophane crackled
gently between the hands close to the microphone can create the illusion of the most terrible forest fire imaginable.
The sound technicians' heterogeneous collection as shown in Fig.
4-12, consists of all sorts of weird machines, hail and wind machines,
boxes in which glass is shattered, thunder drums, hurricane machines,
NBC
Photo
Fig. 4-10. Sound effects for a good night for a murder.
The noise of the howling wind comes from the electrically revolved reeds in the circular shield at the right,
controlled by the operator's foot, and the heavy rain-
storm results from the rain machine on the left, being
turned on full force.
heavy doors on frames, keys, and a thousand items entirely beyond
the scope of this book to reveal. In addition he has a console on which
a number of turntables are mounted with their individual pickup
38
BROADCAST OPERATORS HANDBOOK
arms and dials which automatically "count" the number of grooves
set in from the edge for proper "cuing" sound effects. These turntables may be varied from 0 to about 150 rpm to make still more flexible the number of weird and uncanny effects that can be obtained
from recordings.
NBG'Photo
Fig. 4-12. The sound equipment storage room in the Chicago studios of the
National Broadcasting Co.
The voice can be made to sound as though it were coming over a
telephone by means of a "filter mike," which is simply a microphone
run through a filter amplifier, clipping high and low frequencies so
that the quality is similar to that heard in the telephone receiver.
Reverberation may be added by feeding the signal to be so treated into
e
PK.
Fig. 4-13. The further a microphone is placed from the speaker
in a "reverberation chamber,"
the larger seems the hall or cavern in which the action occurs.
a speaker at one end of a "reverberation chamber" as illustrated in
Fig. 4-13. The farther away the microphone is placed, the larger be-
YOU'RE OFTEN A PRODUCER TOO
39
comes the hall or cavern meant to be simulated in the drama. The
illusion of talking in close quarters such as that of a telephone booth
is created by placing a microphone in a sound absorbent booth, as
shown in Fig. 4-14.
Although the average broadcast station is much more limited in
elaborate equipment utilized by the major network key stations, there
f:,:
Fig. 4-14. When a microphone is placed in
a booth with walls lined with sound -absorbent material, the resulting speech seems to
be coming from a telephone booth.
. :s:
:.\i,
L:..:r:K:. .:\:,
.\
MIKE
BOOTH
is no limit to the possibilities of using what equipment is available
to the ingenious technician. A good telephone effect can be achieved
by feeding a microphone signal through a separate amplifier and exciting a pair of cheap headphones (the cheaper, the better) that may
O PERFORMER
Fig. 4-15. Conversation
over a telephone can also
be simulated by feeding the amplified output
of one microphone into
headphones and broadcasting their sound.
MIKE
AMPLIFIER
ICROPHONE
'ON AIR""
M
be held immediately adjacent to another microphone in the studio.
This circuit is illustrated schematically in Fig. 4-15.
A slight reverberation effect may be obtained by placing a microphone immediately above the sounding board holes of a piano, and
directing the voice by means of a megaphone or tube over the strings
of the piano. The sustaining pedal is held down to allow the strings
to vibrate freely when the voice waves are impinged upon them.
Several good textbooks exist on sound effects and will provide more
detailed information.
-}(I
BROADCAST OPERATORS HANDBOOK
Importance of Control -Room Maintenance
There is no time allowed in a broadcaster's daily schedule for trouble in equipment. There is no allowance made by advertising agencies
and producers for bad quality of a studio show due to weak tubes,
faulty patch -cords, dirty jacks, or fader controls. Complete failure of
equipment is apt to occur in even the best maintained control room
due to a defective tube or power supply failure, but when all is simmered down to actual fact, there is never an excuse for fuzzy sounds
or any kinds of distortion arising from dirt collected in jack strips or on
contacts of fader controls. A detailed, well -performed maintenance
schedule is mandatory to trouble -free operation.
All tubes should be checked at regular intervals, preferably once
a month. Weak and questionable tubes should be immediately replaced. Visual inspection of all rectifier tubes should be made every
morning before sign -on, and any such tube showing an undue amount
of blue glow should be replaced. Jacks, since they constitute both
series and parallel connections in the path of the signal, must be kept
free of dust and dirt. They should be frequently vacuum cleaned, and
the jack contacts kept clean by regular insertions and removals of
patch-cord plugs. The outside cover of fader controls should be removed about once a week and the contacts cleaned with a small brush
and carbon tetrachloride. A very thin coating of white vaseline after
this cleaning helps to prevent wear. All relay contacts in the installation should be regularly cleaned with crocus cloth or strip of glazed
paper. Smooth trouble -free operation of control -room equipment rests
largely on this maintenance schedule and the technicians responsible
for carrying it out to the letter. (A detailed discussion of preventive
maintenance will be found in Part 5.)
Transcription Turntables
The practice of playing recordings and transcriptions varies considerably with different stations. In many of the smaller stations, the
control man operates the turntables as well as running the control
console. In the majority, of the stations of 5 kw or more, either the
announcer runs the tables, or an especially trained person is used to
run the turntables, which may be in a separate room just for this
purpose, as shown in Fig. 4-16.
Recorded and transcribed shows constitute a most important part of
a broadcaster's daily schedule. "Transcriptions" are recordings made
YOU'RE OFTEN A PRODUCER TOO
41
especially for broadcasting purposes; they are usually 16 inches in
diameter and use a turntable speed of 33% rpm to enable recording
a full 15 minutes of program time.
WOR Photo
Fig. 4-16. The transcription studio at Station WOR, New York.
A transcription "platter" may also consist of a number of separate
musical or voice selections on a single disk, in which case they are
numbered on the label with the titles of each number listed. Also on
this label will be the information as to lateral or vertical cut, start on
inside or outside groove, and reproduction speed (33% or 78 rpm) .
This is enough to keep any operator "on his toes," especially when a
program consists of both recordings and transcriptions which may require change of turntable speed, lateral or vertical switch placement,
and noting whether the cut is started on the inside or outside groove.
Then too, a filter selector switch is employed to select a suitable frequency compensation for the particular disk used. For example, RCA
lists typical switch positions for the 70 -CI turntable as follows:
Lateral
#1. Transcriptions, Orthacoustic, Columbia.
#2. Home records and worn transcriptions.
BROADCAST OPERATORS HANDBOOK
42
#3. Home records, World, Decca, and AMP.
#4. Test records and special recordings (wide
open at highs)
.
Vertical
#1. World and AMP transcriptions.
#2. Worn transcriptions.
All records, and some transcriptions, are played at 78 rpm (same
as the record player at home), are "laterally" cut, and played from
outside groove toward the inside. Most transcriptions, however, play
at 33% rpm. In addition to this, some transcriptions are cut "vertically," that is, the groove variations that comprise the signal are
varied up and down instead of side to side, using the depth on the
coating of the disk. Also, some of them play from inside-out, and require the starting of the pickup arm on the inside groove.
Turntable Operation
In operating a turntable, it is necessary to be sure that the pickup
selector switch is on the proper setting for the pickup arm used (lateral
or vertical) that the turntable speed switch is on the correct speed
adjustment for the particular recording used (33% or 78 rpm), and
that the disk has been properly "cued." This means that the pickup
arm must be at the spot on the groove where the announcement or
music begins, so that no time is lost in waiting for the arm to reach
that point on the disk. This is usually accomplished by using headphones on an auxiliary amplifier so that each disk may be "cued in"
preparatory to going on the air.
When the disk has been properly "cued in," most experienced operators find it advantageous to start the turntable moving while holding the disk (on the outside edge so as not to touch the grooves) to
keep it from turning until start is desired. This practice eliminates
"wows" that are apt to occur on the starting due to time taken for
the turntable to gain proper running speed. When this trick of operation is not followed, the disk should be "cued back" at least one full
revolution of the turntable so that the proper speed will be reached
before start of the signal.
The art of smooth turntable operation on the air takes considerable
practice by the operator. Familiarity with the operating procedure
can be gained only by practice, and most stations demand a thorough
"break in" training before entrusting the operator with an air show
comprised of recordings and transcriptions.
;
YOU'RE CFTEN A PRODUCER TOO
43
The music library of a broadcast station may contain files of thousands of recordings and transcriptions, and their proper care in storing
and handling is an important factor in "on the air" quality of reproduction. Excessive heat ar_d dust in the air are major enemies to be
considered in the storage room. The library should be well air-conditioned, with an efficient dust-filtering system. In any case, the disk
should be cleaned with a soft dry cloth before playing. Static electricity causes dust to cling tightly to records, and all precautions such
as use of linoleum floors in library and turntable room to reduce static
electricity should be taken. Finger marks cause noisy reproduction
due to the oil and grease from the hands causing foreign matter to
cling close to the walls of the grooves. Platters should be handled on
the edge only.
For this same reason, tie permanent type pickup needle should
not be "swiped-off" with the fingers in an attempt to clear it of dust.
A small soft brush should be used.
Instantaneous Recording Department
All large stations, and many of the smaller stations have a recording department where acetate -coated disks may be cut for immediate
playback if necessary. Such equipment is used for recording programs
such as delayed broadcasts, rehearsals, auditions, or the reference file.
A reference file is kept by same large stations of the entire broadcast
day, or of portions thereof. The art of recording, including equipment
and stylus adjustment, is a complex field of its own, and an entire textbook is necessary to do it justice. There are several good manuals
of recording technique published today, and any technician who may
be concerned with this depanment of a broadcast station should obtain
and study them.
The Influence of F.M.
The influence of f.m. (frecuency modulation) on future operational
practices is not to be denied, whether or not f.m. will ever entirely replace or simply supplement the present a -m stations is indeed an
abstruse problem. However, it is a certainty that this new type of service, with static -free reception, greater frequency and dynamic range,
and freedom from interchannel interference, will find a highly important niche in the future of radiobroadcasting. It is entirely possible that local and shared -channel broadcast stations will gradually
44
BROADCAST OPERATORS HANDBOOK
transfer to f.m. for the purpose of providing better interference-free
coverage both night and day for its primary area.
The great difference in dynamic range between a.m. and f.m. will
a
undoubtedly call for new types of visual indicators in level and
by
hoped
is
It
practice.
slightly new technique in general operating
the author that as the art of f.m. advances, the new technique can be
analyzed and presented in a possible future edition of this handbook.
The complex operating practices in relation to television will also be
are
included as the state of the art advances and operating standards
more definitely stabilized.
Chapter
5
PUT THAT MIKE THERE!
BY BERT
H. KOEBLITZ
THE PROBLEM of studio pickups or setups is a little difficult to
approach because conditions vary so widely between one station and another. In a small local station, the technician may
have full control of what goes where and why; whereas in a network
center the technician may find himself surrounded by a superabundance of production men to take care of this. In the first case, knowledge is essential to success. In the latter instance the technician can be
of real help to the production man. Production men, unless they have
been recruited from the technical department, rarely know anything
about microphone patterns. Instead, they pursue a series of superstitions and grandma's tales about what a certain type of microphone
will or will not do. Therefore a technician with thorough knowledge
can help the production man over many difficult spots, and in the
case of important programs, frequently finds himself the recipient
of slight remembrances now and then.
But that is only one conditional variation. Another is studio construction. What may be good practice at one station may not do at
all somewhere else. To describe a specific setup at WHK or anywhere else would accomplish little of value. The important thing is
that the same fundamentals can be used to determine whether a given
practice is good or bad in your own particular studios. However, certain specific examples will be given, not to demonstrate what is done
at WHK, but to illustrate principles which can be applied in any station.
Large Orchestra
The first program which comes to mind is one involving about as
many things at one time as will ever be encountered outside a network center. It is a so-called "variety" program, although "hodgepodge" would be far more accurate. It consists of a 25 -piece orchestra
which is really ten miscellaneous additions to a 15 -piece dance band
which in its turn further degenerates into a "gut bucket" four. Then
45
46
BROADCAST OPERATORS HANDBOOK
there is a 20 -voice chorus, a drama cast, a novelty group, a guest artist,
went
a master of ceremonies, and an announcer. Before the program
section
on the air, the production man tried the orchestra in a straight
"V"
in-front -of -section style, sections side by side, sections in little
formations, lengthwise, sideways, and diagonally in the studio, but to
it.
no avail. He knew what he wanted but he did not know how to get
The problem was turned over to the technician, who eventually straightened things out. That illustrates fundamental No. 1: be prepared with
a full knowledge of what can be done in your studios with your microphones.
The setup finally used for the orchestra was the section -in-front -ofsection type. The section nearest the microphone consisted of four
violins and two violas. Between them and the saxophone section were a
cello and harp. Brass was in the last section with the trombone in front
of the trumpets. The trumpets were put on high risers and the trombones on low risers, not for setup purposes but so the men could see
the director without difficulty. Piano, drums, bass, and guitar were
placed so they could hear each other.
Now let's go back to the perspiring production man for a moment.
He failed to get a satisfactory pickup with the orchestra in the positions described because he was unable to put his finger on the true difficulty. When one section was too soft, he made the all too common
assumption that that section was too far from the microphone. A
moment's thought will reveal that when two things are of different
volumes, there are two possibilities involved: one may be too soft or
the other may be too loud. It is necessary to make sure which is
which before making changes in a setup. Making such changes is
really no different from making an original setup; you must be sure
this
of everything you do. In starting from scratch, an orchestra of
a
will
be
It
percussion.
and
size is bound to have strings, reeds, brass,
A
order.
in
that
the
microphone
logical start to place them before
couple of numbers should suffice to set roughly the relative distances
for sections.
Here enters a theoretical point that is sometimes helpful in practice. Assume for a moment that we have a perfect studio and that
we have found that the strings should be 4 feet from the microphone,
the reeds 8 feet, and the brass 12 feet. This yields a ratio of two to
one and three to one for the other sections as referred to the strings.
This means that in our imaginary perfect studio, there would be an
infinite number of good setups; that is, the absolute distance is unim-
PUT THAT MIKE THERE!
47
portant as long as these ratios are maintained. There would be no detectable difference between spacings of 4, 8, 12; 5, 10, 15; 6, 12, 18; etc.
Within restricted reasonable limits this will hold true in our imperfect
studios. This fact can sometimes be used to advantage and was in the
case of this orchestra. The section distances had been established but
the cello and harp were too weak because they were both considerably
off side. The sections were redistributed but the distance ratios were
maintained. This made sufficient room between strings and reeds to
bring harp and cello into center.
Another factor too often overlooked is section "presence." Having
section volumes equal is only half the battle; section presences must
also be equal. The ratio procedure can be applied here too. Assume
that the sections have again been established at 4, 8, and 12 feet for
equal volume but that the strings sound "closer" to the microphone
than reeds or brass. The "presence" problem can be ironed out by increasing the distances while maintaining the ratios. The general
axiom to be drawn from al] this is: do not do anything in making or
changing a setup unless or until you have a logical reason for doing it.
We will call this fundamental No. 3, because No. 2 is closely allied to
No. 1 but involves the chorus which will be discussed farther along.
Keep It Simple
All of the original attempts at a setup, both the straight-line and
side -by -side types were discarded for a variety of reasons. All of them
had one common fault, which, however, was not the cause of their
failure. It must be borne in mind that some numbers were played by
the full orchestra, some by the dance-band portion of the orchestra,
and some by the four -piece jive outfit. In the side -by -side setups two
microphones were picking up the orchestra and there was a third one,
to and from which the hapless four were supposed to dash madly for
their numbers. Aside from any other considerations, the show began
to look like a track meet to the studio audience. In the production
man's straight -on setup a microphone was in front of each section.
There lay the common fault: three microphones. A multi-mike pickup
is never quite as clean as a single mike, probably because of the several paths each sound can take. Also, more than one microphone puts
the burden of instantaneous balance on the shoulders of the technician. Granted, there are many technicians who can be depended on to
do this correctly. Also granted, there are many who cannot. This is
not stated in derision of the latter group. It is one of those things that
BROADCAST OPERATORS HANDBOOK
paint, some can't;
you either have or you haven't. Some people can
case there is no
any
In
on.
so
and
some people can repair watches
when the large
harm in eliminating microphones. As it turned out,
48
volume and presorchestra sections were properly balanced for both
was principally
which
band,
ence on the one microphone, the dance
by having
Further,
up.
the two rear sections, also was well picked
the jump
for
saxophones
the
the muted trumpet step down behind
so
without
outfit
-piece
four
numbers, a good pickup was had on the
simplicity
for
strive
4:
No.
much hundred -yard dash. Fundamental
error as possible.
in setups and eliminate as many possibilities of
Choral Pickup
of four standThe 20 -voice chorus contained five members for each
consideration
first
The
ard voices: soprano, alto, tenor, and bass.
and the
tried
were
was what microphone to use. All different types
This
used.
finally
was
dynamic section of a Western Electric cardioid
Howresponse.
is a nondirectional unit with excellent high -frequency
have done as well;
ever, any other unit with equivalent highs would
cardioid.
it just happened that the only tall stand was fitted to take a
about a
The important thing is that the most common complaint
human
the
to
chorus is indistinct diction. Diction is distinguishable
are
Sibilants
ear by virtue of the sibilants in the consonant sounds.
a
hence,
the high -frequency components of the consonant sounds;
used.
be
microphone with adequate high -frequency response should
that the microResult: impression of good diction. Care must be taken
is needed. One
phone also has lows; in other words, a wide range
choral effects.
which has only highs will give good diction but poor
its placement can
Once the particular microphone has been selected,
be considered.
of the
To begin with, it should go on a line through dead center
not promigroup, and back far enough so that individual voices are
moving
by
adjusted
be
should
sections
in
nent. Any inequalities
the micropeople. Actually as far as choral effect alone is concerned,
As usual
phone can go as far back as studio space will permit.
without acthough, circumstances alter cases. If the chorus sings
how far back the
companiment, then there is practically no limit to
accompaniments,
microphone can be placed. If there is orchestral
have to be
probably
will
microphone
as there was in this case, then the
voices. When
placed as close in as it can be without getting individual
too much oralways
was
there
the series of programs first started
PUT THAT MIKE THERE!
49
chestra behind the chorus. No type or placement of microphone or
separation of chorus effected a solution, simply because none of these
things was the cause of the trouble. The arranger insisted on writing
full orchestra accompaniments, and any time there are eight brass
blowing they are going to be heard above the chorus. The arranger
was prevailed upon to use strings and clarinets only, which cleared up
the trouble. Fundamental No. 2 which is closely allied to No. 1:
know what can't be done in your studios with your microphones.
Drama and Novelty Pickups
The drama cast does not offer anything unusual in the matter of setups. If more than two persons are concerned in any one scene, at WHK
it is preferred to use a nondirectional microphone so that it may be
approached from any direction. This is also convenient for balancing
players since it is only necessary to establish a correct distance for
each one. Likewise the novelty group treatment will depend on the
novelty group. In our case there were five men who played a dozen
instruments at different times besides singing at other times. They
were also provided with a nondirectional microphone (as a matter of
fact it was the same one the drama cast used since they were never
on concurrQntly) so that their only worry was distance. A distance
was established for each instrument so that whoever played it had
only to move in wherever he could find an opening. To finish up this
program, the guest artists, announcer, and master of ceremonies all
used the same microphone. Result: Three orchestra groups, a novelty
group, a chorus, a drama cast, vocalists, announcer, and master of
ceremonies were all picked up on four microphones. With the exception of vocal solos, there was only one microphone open at any one
time.
To recapitulate, the following fundamentals can be gleaned from this
particular program set up:
prepared with a full knowledge of what can be done in your
studios with your microphones.
2. Know what can't be done in your studios with your microphones.
3. Don't do anything in making or changing a setup unless or until
you have a logical reason for doing it.
4. Strive for simplicity in setups and eliminate as many possibilities
of human error as you can.
1. Be
r,o
BROADCAST OPERATORS HANDBOOK
Small Orchestra
For the sake of definition, consider anything under ten men a small
orchestra. Setups for these groups will depend largely on the groups
themselves. There is rarely any problem of sectional balance, because
it is unlikely that there is more than one section. Usually such a small
combination depends greatly on one player. It may be a pianist who is
exceptionally good at "noodling," a hot guitar, trumpet, or almost anything else. The type of microphone is moderately unimportant. The
best procedure is to place the musician of the type previously mentioned at the best possible advantage with respect to the microphone
and then adjust the rest of the group until everyone can be heard. In
the case where piano is the mainstay, a separate piano mike is nearly
always needed, since it is usually impossible to get the piano close
enough to the orchestra mike and still keep it close enough to the rest
of the rhythm instruments. One other possible pitfall is the bass fiddle.
If it does not seem to be loud enough, it can usually be helped by moving the orchestra mike farther from the group without changing the
position of any of the musicians. In small groups, one is likely to run
into musicians who double on more than one instrument. Very often
both instruments will not pick up equally well from the same position.
About all that can be done, short of giving each man an individual
mike, is to arrange for him to step forward with the weaker instrument.
Hotel Orchestras
The hotel orchestra is another matter entirely. There is usually no
possibility of a logical solution of problems but rather there is a selection of what seems to be the best group of compromises. Except in the
more lavish hotels, the band stand, being a place which provides no
revenue, is almost sure to be too small and the wrong shape. Because
of this the orchestra can hardly be disposed either the way it should be
or the way the leader wants it. Since the orchestra geometry will
necessarily be side by side, at least two mikes are generally needed for
a good pickup. However, the announcer and vocalists can usually use
one of these.
It is to be greatly decried that so many stations give these pickups
practically no attention. A man comes in and plunks a mike down
somewhere in front of the orchestra and that is that. Frequently, a
technician is not even sent out, the amplifier being turned on from the
PUT THAT MIKE THERE!
51
studio and the orchestra -leader depended upon to place the microphone.
All this when a little care will provide a fairly decent pickup. Perhaps this leads us to another fundamental: whatever is worth doing is
worth doing well.
Novelty Groups
Somewhat like the small orchestra, the novelty group setup will depend on the group itself. Few if any are strictly instrumental and
moving people in for vocals introduces most of the problems encountered. In a group where lie members play the same instruments all
the time, there is rarely any difficulty either as to choice of microphone
or placement. However, when four or five men play ten or twelve instruments and come in for vocal besides, then you are likely to have
your hands full.
One such group at WHK was set up with a ribbon mike, because
it was thought that the two live sides would afford ample room for
four vocalists. This assumption alone was correct, but other considerations made the ribbon unsatisfactory. The man who played bass fiddle
most of the time (all of them played it at some time) felt he had to
stand in a certain place when he sang. In this position, the bass fiddle
was exactly on the dead side of the mike. It was suggested that someone else take the bass fiddle during the singing, but no one else could
play it and sing at the same time.
In addition, there was another complication. There were a half
dozen other instruments spread around the studio, some of them large
(piano, vibraharp, marimba, electric organ, etc.) . The effective pickup
angle of a ribbon is very little more than 90 degrees for each face. I
was difficult to get enough instruments close enough to it and still leave
room for the track meet during each number.
The obvious and actual solution was to use a nondirectional microphone which solved the bass fiddle problem and furnished a full 360
degrees in which to deploy all the instruments. It could be argued
that more mikes could be ised. They could, but the total effect will
never be as clean as with a single microphone.
Vocal Groups
The treatment of vocal groups is almost the same regardless of their
size. The primary concern is to get a blend so that it sounds like a
group rather than a collection of individual voices, which cannot be
done with the microphone in too close. In general, the larger the
52
BROADCAST OPERATORS HANDBOOK
group, the more separation can be tolerated. In smaller groups such as
quartets, you may sometimes encounter the rare case where the accompanist plays quite softly. If there is a separate microphone for
the accompanying instrument, it may be noticed on loud vocal passages
that the voices can be "heard" on the other mike. When this effect is
noticed, it will also be noticed that the fader setting on the vocal mike
is less than that on the accompaniment mike. Anything which will
allow the vocal fader to be higher than the other one will correct the
condition. The accompanist can be asked to play louder and thus
cause that fader to be reduced. This is not always satisfactory because
the accompanist is usually playing softly because that is his or her
normal procedure and it will be reverted to after a number or two.
The better solution is to move the vocal mike away from the group
sufficiently to allow that fader setting always to be higher than the
other.
The choice of a microphone should be one with a good high -frequency response. At the same time it should be emphasized that the
microphone should have neither highs nor lows; it should be a wide range instrument. The intelligibility of human diction is centered
mostly in the high -frequency consonant sounds. A wide -range microphone is indicated to reproduce adequately the vocalists' words.
Piano Pickup
The subject of piano pickups, if not the most controversial, is at
least the most varied problem in the business. Microphones have been
placed under the piano, in it, beside it, across the studio from it, over
it, in fact everywhere but in the performer's pocket. The lid has been
opened, closed, and off. Correct piano pickup follows a series of logical principles, so that if any trick procedures have been successful,
they have also been illusions. In other words, somebody's ears are defective, some studio equipment is defective, or an accident has occurred which compensated for a studio deficiency.
Let us start off with a little theory. We need concern ourselves only
with grand pianos, because few if any studios use any other kind.
The grand piano was designed with two things in mind. If all conditions are perfect the maximum efficiency should be expected (1) with
the lid on full stick and (2) at some position on an imaginary extension of the hammer line. That is all there is to the theory.
Next, the problems likely to be encountered. All pianos are not built
with equal care, so you may find that your particular one has a more
PUT THAT MIKE THERE!
53
brilliant bass than treble or vice versa. Pianos which were originally
good may have become tonally lopsided through age, lack of care, or
misuse. Regardless of the condition of the piano, each pianist is also
a separate problem. Some play softly, some loud, some have a heavy
right hand and some a heavy left. Finally, we have to deal with the
characteristics of the studio in which the piano is located.
There are two adjustments of microphone position which will handle
any or all of these variables. Going back to the theory for a moment
and assuming a perfect piano, perfect pianist, and perfect studio conditions, the microphone should be on the imaginary extension of the
hammer line about 8 to IO feet from the piano. The first adjustment,
if necessary, will be on account of studio acoustics. If the studio is
very live, the 10 -foot distance may give more reverberation than is
pleasant. The microphone should be moved straight in on this imaginary line until the noticeable reverberation is reduced to a pleasing
amount. The second adjustment is for bass-treble balance. This one
will work regardless of the reason for the unbalance, whether piano
or pianist is at fault. If the treble needs to be increased, the microphone will have to be moved in still farther on the afore-mentioned
imaginary line. In extreme cases it has been necessary to move the
microphone all the way up to the piano case, lower it, and tilt it toward the treble strings. Now, mentally restoring yourself to the
microphone position where reverberation was just right, assume the
bass is weak. While maintaining the proper reverberation distance
from the piano, move the microphone toward the tail of the piano.
This will increase the pickup from the bass strings and decrease the
pickup from the treble strings.
With the above procedure in mind, it should never be necessary to
use a grand piano any other way than with the lid on full stick. That
is the way the piano was designed to be used and that is the only way
the piano sounds normal. Taking the lid off, putting it on the half
stick, or closing it only seems to do something which could be done
better some other way. For instance, putting the lid on the half stick
does not reduce volume appreciably but it will muffle the tone considerably.
A two -piano pickup involves the same principles as with one piano.
It is usually more convenient to make adjustments in this case by
holding the microphone position constant and moving the pianos.
There is one added problem: temperament of the pianists. Assuming
perfect conditions again, the hammer lines of both pianos should be on
"
54
BROADCAST OPERATORS HANDBOOK
the same imaginary contiguous line. The pianos should be about 15
feet apart with open lids toward each other. The microphone should
go half way between them on the imaginary line. The two principles
mentioned for one piano apply equally well to two pianos. In addition, if one pianist plays more heavily than the other, the microphone
can be moved closer to the weak one.
Now another problem: the temperament of the pianists. Many two piano teams like to be closer together than 15 feet. If they cannot
be talked out of it, some of the clarity and brilliance of the pickup
will have to be sacrificed by moving them closer together. If you refuse to do so, the pianists will play either badly or not at all, so you
will not have anything anyway. Sometimes the players will insist upon having the pianos right together and side by side. This very
nearly prevents a first-class pickup. There is some hope, however, if
the same pianist always plays the lead part. In this case the lead
piano should be closer to the microphone, which is placed as if for one
piano only high enough to clear the top of the lead piano lid. Balance
between the two pianos can usually be accomplished by raising or
lowering the microphone. Raising it helps the second piano.
In picking up piano with a small orchestra, clarity and brilliance
are mostly buried in the sound of the orchestra so the preceding practices can be more or less ignored. It will be found that the microphone
has to go very close to the piano. Also, if possible, the piano should
be oriented so that the open lid physically masks from the microphone
most of the orchestra, or at least the loudest instruments.
Piano with symphony orchestra is entirely another matter. Referring to the setup described for the symphony orchestra broadcasts at
Severance Hall in Cleveland, the place normally occupied by the conductor is occupied with the piano. An additional microphone is used
for the piano a sufficient distance away so that the presences of the
orchestra and piano are the same. The piano microphone is opened
only enough to provide a little definition. Many piano -with -symphony
programs are ruined on the air by making the piano too loud. Much
of the time in this type of composition the piano has a supporting
rather than solo part.
Organ Pickup
There is little that can be said about pickup of pipe organ. The type
and make of organ and studio size all vary so widely that there probably are not two identical setups in the whole country. It simply
PUT THAT MIKE THERE!
55
remains for each technician faced with such a problem to use horse
sense and ingenuity to secure a satisfactory pickup.
Electric organs present somewhat less difficulty. The older type
speaker with openings on both top and side were pretty much a headache. There was not much that could be done to get a really good
pickup. The newer type speakers with opening on the side only are
duck soup. Just place a microphone straight out in front at whatever
distance gives the desired amount of reverberation.
BROADCAST OPERATORS HANDBOOK
56
11!
h
id
P,
g
III
"Ct
cl
C.)
CI,
C.)
Q
:z1
-cs
-cs
t
o
itC
o
u
I. -
1
It,
51
2
.1
3
sus
tt 1
----1
o
L- _J
o
z
o
a)
C.)
r)
4
CL)
C.)
WC)
o
.-.
de
-
63
5
4
O
CO
t
Part
2
OPERATING THE MASTER CONTROL
Chapter
6
WHERE SPLIT. SECONDS COUNT
N STATION SETUPS where a comparatively large number of individual studios are involved, a central switching point known as
"master control" is employed. Fig. 6-1 shows a simplified schematic of the NBC technical layout. This illustration shows how indi-
vidual studios are connected through the switchbank selectors to the
master control position, where the program or programs may be routed
in any way desired. Fig. 6-2 is an illustration of NBC's Chicago master control.
The NBC program switching system is a standardized layout for
all key stations of the network. Since more than one program is being handled at any one time, the setup must be as flexible and foolproof as technically possible. This calls for operation on a preset basis,
eliminating as far as practicable confusion of switching a number of
program sources in the split seconds allowed.
In the NBC system, the switchbank selector is a group of relays
associated with outgoing channels, arranged for a single connecting
means between any group desired and any single program input. A
brief description of operation of the program switching system is as
follows.
The program sheets or schedule sheets prepared in advance by the
program and traffic departments indicate the program sources such as
studio (and the particular studio number), for a remote point, or incoming network line. Also indicated are the outgoing channels feeding various points with the programs. At the start of operations, the
channels required for each separate program are preset by operating
numbered key switches in master control which are connected to separate switchbanks. Any switchbank is then connected to any program
source at the proper time by operating the associated key switch on
the switchbank selector panel, one panel being associated with each
studio or other program source. This operation actuates the "carrier"
lights at both the announcer's control desk in the studio and on the
engineer's console in the control room, and is the signal for the pro 57
BROADCAST OPERATORS HANDBOOK
NBC
Fig. 6-2. The master control at the NBC studio in Chicago.
Photo
gram to begin. In this way, programs are routed to the station's own
transmitter and to the various other sources such as network, f.m., or
special circuits such as international short wave.
Master Control of United Broadcasting Company
WHK master control is definitely not standard; it has grown
through the years from the personal preferences of master control operators. From the foregoing statement it might seem to some that it
would be a most glorious hodge-podge of gadgets by now. Actually it
is the most simple and flexible system that could be imagined.
All program sources, each studio, the network, and four remote positions go to individual 12 -tube repeater amplifiers. This provides
twelve copies of each program source to be used for local station, network feed, f.m., monitor systems, etc. On the master control console
are six banks of mechanically interlocking switches which route any
program source to any or all of six line amplifiers. The interlocking
is to prevent more than one key being depressed at any one time. The
switchbank for WHK's line amplifier is different from the rest. Here,
any program source can be put on any one of three faders, and interlocking prevents getting more than one program on any one fader.
The faders in turn feed the line amplifier. The faders are considered
WHERE SPLIT SECONDS COUNT
59
necessary to smooth operation for getting in or out of programs late
or early. There are no relays in any program circuit. One line amplifier feeds WHK's transmitter, one for the Mutual Network, one for
an Ohio network, and three spares which can be used for anything.
Also on the console itself are two switching panels which route any of
30 remote lines to any of the four remote positions. These same panels have facilities for line reversal and private telephone to each remote.
In addition to the console there are three banks of double depth
relay racks which house (1) power supplies, (2) all program amplifiers, and (3) monitor amplifiers. Every piece of audio equipment is
brought out to normal through jacks so each one may be replaced or
removed from circuit in a few seconds in case of failure. All amplifiers have pads connected to their input jacks to take plus 8 vu down to
whatever is necessary for that amplifier. This makes it possible to
have every input and output plus 8 vu at 600 ohms. Even a shoemaker
couldn't hurt anything by patching them all in series.
Function of Master Control Operations
Every individual station employing a master control has, of course,
slightly different "rules and regulations" of procedure to suit their
individual requirements and to satisfy the technical executives who
are responsible for the co-ordination of all operations. The following
rules of studio procedure that were compiled by the engineering supervisors of WBBM for guidance of their technical staff is presented
here to acquaint the reader with general master control operations.
The rules are divided into three sections: (1) master control, (2)
studios, (3) field. The letters M, S, and F have been used respectively
to differentiate between these sections in numbering. Since all are
closely tied in with the duties of the master control operator, they are
presented here in their entirety.
MASTER CONTROL PROCEDURE
Checking of New York Daily Operations Sheet
The Master Control engineer is required to check the routings of all
network originations with the New York Daily Operations Sheet, and
to compare the routings listed with those on the WBBM Daily Operations Sheet.
Ml
60
BROADCAST OPERATORS HANDBOOK
M2
Booth Check-in
For procedure to be used on a booth check-in, see S5. In addition,
the Master Control engineer is to record on the WBBM Daily Operations Sheet, above the engineer's name, the time of the check-in.
Should the studio engineer report someone as absent, Master Control
should immediately notify the Program Department.
M3
Time of Making Preset
All relay presetups should be made approximately four (4) minutes
before each regular switching period (see Glossary).
M4
Use of Switching Light
The signal for Master Control to switch from one studio (excepting
studio M7) to another, on all local originations, will be the switching
light.
M5
Checking Equipment
All equipment is to be carefully checked for gain settings, tube
currents, etc., before being placed in service.
M6
Filling During Network Failures
For procedure see S18. In addition, on all scheduled stand-bys and
all emergency fills to the network, Master Control is to patch the
stand-by studio's cue speaker to the incoming network line.
M7
Cutting of Local Programs Running into Network
Commercials or into Synchronization
All local programs running into synchronization or into network
"musts" which are to be carried by WBBM, will be cut by Master
Control only.
M8
Relieving of Engineers
a. A relief engineer is not to take over the Master Control if only
(5) minutes or less remain before a switch. The engineer being relieved is to make the switch and see that the program or programs
start properly.
b. An engineer is not to be relieved of duty until he has cleared the
patching bays of all unnecessary cords.
WHERE SPLIT SECONDS COUNT
61
Checking Program Level
Master Control engineers are to keep a close check on the level of
all programs, and to see that the proper level is maintained at all
times. See also S9.
M9
Remote Check-in to Master Control
The Master Control should see that all remote engineers check in
by twenty-eight (28) minutes before air time. If the remote has not
been heard from by twenty (20) minutes before air time, provision
should be made for a stand-by.
M10
Mll
Testing of Field Equipment
Remote engineers, before leaving the building for "pickups," are to
give Master Control an audio test of their equipment. This equipment
is not to be O.K.'d other than in good condition. The time of these
tests is to be recorded on the W BBM Daily Operations Sheet, opposite the particular pickup, with the Master Control engineer's initials.
Patching Up Remote Talk-Lines
Remote talk -lines are to be patched up only after the scheduled
Studio engineer arrives in the booth and requests them.
M12
Recording of Inability of Studio Engineers to Get
Program Procedure
All reports by Studio engineers of inability to ascertain the procedure on a particular program are to be recorded in the "penciled"
comments, with the reasons and name or names of persons concerned.
M13
Making Setup for Following Morning
The engineer signing off each evening is to make the necessary setup
in Master Control for the following morning, in order that the Studio
engineer can put the station on the air should the Master Control engineer fail to arrive.
M14
Changes to the WBBM Daily Operations Sheet
All changes and notations to the WBBM Daily Operations Sheet
are to be made in ink and initialed by the Master Control engineer.
M15
62
BROADCAST OPERATORS HANDBOOK
M16
Signing of Engineering Department Copy of WBBM
Daily Operations Sheet
Engineers must sign on the Engineering Department copy of the
WBBM Daily Operations Sheet the time "ON" and the time "OFF"
duty.
STUDIO PROCEDURE
SI
Ascertaining of Program Procedure
The engineer is required to acquaint himself with the procedure of
all programs on which he is assigned. This is required regardless of
the number of times the engineer may have been assigned to the show.
If at any time it is impossible to secure this information, Master Control is to be notified in order that it may be entered in the "penciled"
comments.
S2
Time of Check-in to Master Control
Studio engineers are to check in to Master Control not later than
seven (7) minutes before air time.
S3
Remaining in Booth
Engineers are to remain in the booth between the time of checking
in to Master Control and two (2) minutes after the program. It is,
however, permissible to leave for the purpose of making a necessary
last-minute change in the studio setup.
Checking In for Rehearsals
84
Engineers scheduled on rehearsals are to report to the studio ten
(10) minutes early, and have all equipment tests completed by rehearsal time. The failure of producer or talent to arrive does not relieve the engineer of this responsibility.
S5
The Check-in to Master Control
The check-in to Master Control is to be made as follows:
"John Doe checking in from studio three, T -H -R -E -E, for Columbia's School of the Air, 2:30-2:591/2i to SRR-NW-TC (give complete
routing).
"The time is 2:20 and 40 seconds. Woof !"
If it is a local program only, the engineer is to add after the routing
WHERE SPLIT SECONDS COUNT
63
that there is, or is not, a spot announcement following his program,
and, if so, the studio in which it is scheduled.
It is the responsibility of both the Master Control and Studio engineer to make these check -ins carefully. The Master Control will repeat and spell out the studio number.
When making check -ins it will be understood that, unless Master
Control is informed otherwise, all tests have been completed and all
talent, including the announcer, is present.
Time of Arrival in Booth on Remote Programs
Engineers are to arrive in the studio at least thirty (30) minutes
before air time, if schedule permits, on all remote commercials and
special events; on all other remote programs the minimum time is fifteen (15) minutes.
S6
Patching Up Remote Talk-Lines
Remote talk -lines are to be patched up only after the scheduled
Studio engineer arrives in the booth and requests them.
S7
Studio Line-up with Remotes
The studio line-up with remotes should include the following, and
preferably in the order shown:
1. Line and equipment test.
2. Level check (the Field engineer will call peaks) .
3. Name and sequence of musical selections (if it is an orchestra).
4. Corroboration of air time.
5. Time check.
88
89
A Proper Level to Be Maintained
It is the duty of the Studio engineer assigned to a program to maintain a proper level at all times. If the level from a remote is abnormal, correct it and then ask the Remote engineer to either raise or
lower it.
810
The One -Minute Warning
One minute before air time Studio engineers are required, first, to
"kill" all microphones and give a one -minute warning over the "talk back" mike to studio talent; and second, if a remote is scheduled, to
give a one -minute warning over the telephone to the Remote engineer
(see F5, a). After these warnings, the "talk -back" mike is to be dis-
connected.
64
BROADCAST OPERATORS HANDBOOK
Remaining in Booth After Air Program
Engineers are to remain in the booth, and equipment must be left
turned on for at least two (2) minutes after each air program.
811
S12
Use of Switching Light
The signal for Master Control to switch from one studio to another
on all originations for WBBM only is the switching light. Hold the
switch on until the channel light is removed.
813
Turning On Cue Speaker
The WBBM cue speaker is to be turned on immediately after the
one -minute warning preceding the start of the program for the purpose of ascertaining the time the channel will be received.
814
Reporting of Trouble on Tests
All trouble encountered on tests preceding an air program must be
reported to Master Control immediately.
S15
Filling Out of Program Report
An Engineering Program Report is to be filled out in full by the
Studio engineer after each air program where there has been an interruption to the normal routine. This report is to be deposited in Master Control reasonably soon after the program.
Disposition of Mikes and Cords After Each Program
After the completion of each program or a succession of programs
from the same studio, all mike cords are to be rolled up and placed in
a corner, and microphones are to be returned to their designated places
in the Maintenance Department.
S16
Network Breaks: Length and Level of Sustaining
Background
a. All regular closing network breaks and breaks used for split network switching are of thirty (30) seconds duration, with the sustaining background faded out after fifteen (15) seconds.
b. All network breaks during a program which are used for station
identification only are of twenty (20) seconds duration, with the sustaining background supplied for the entire period.
S17
WHERE SPLIT SECONDS COUNT
65
c. The level of the sustaining background during all CBS breaks
is to be lowered to 30 (-10 vu).
818
"Filling" During Network Failures
When standing by for the network or any portion thereof, should a
failure occur or trouble develop which renders the program unintelligible, the "fill" should be made as follows:
First: In order to know when the trouble has cleared, turn on the
CBS cue speaker, which Master Control has patched across
the incoming line.
.Second: Wait forty-five (45) seconds, and if by then the trouble has
not cleared, fade off the incoming line and signal the stand-by
announcer to make a courtesy; the "stand-by" should then be
supplied.
Third: Immediately after the trouble has cleared on the cue speaker,
the announcer should be signaled to make a second courtesy
announcement rejoining the program.
Fourth: Fade out the "stand-by" and fade up the program.
In connection with the second and third items above, it should be
understood that should a situation arise whereby an announcer is not
available, the procedure remains the same with the exception that the
courtesies are deleted.
Procedure in Remote Program Line Failure
The following procedure is to be followed should a remote program line develop trouble:
If the trouble develops before air time, Master Control is to be notified, and both points (Master Control and Field) will then reverse
lines. The remote engineer should then feed a test as usual. One
minute before air time Master Control will disconnect the remote feed
to the studio (to guard against a feedback), and supply "cue" over the
substitute program line. The remote should then start the program
five (5) seconds after the proper cue, which will be heard on the monitoring phones. This five seconds will be used by Master Control in
normaling the feed to the studio. If the remote program consists of
an orchestra which is to be announced from the studio, five (5) seconds will be allotted between musical selections.
The foregoing procedure is formulated, of course, on the assumption that the regular program line cannot be used even for cue purS19
poses.
66
BROADCAST OPERATORS HANDBOOK
Channel Lights: Taking Away of
Unless Master Control directs otherwise, the channel light or lights
on each network origination will be taken away fifteen (15) seconds
after a, the middle CBS cue (if any), which is used for split-network
switching only, and b, the closing CBS cue. In the case of a, the channel light or lights will be returned in the regular manner (see S21) .
S20
Signal Used to Begin Network and Local Originations
a. All regular network originations will start five (5) seconds after
the channel light or lights are received..
b. All regular local originations will start immediately upon receipt
of channel light or lights.
S21
Network and WBBM Remote Originations: Opening
"Go -Ahead"
All originations for both the network and WBBM which open from
local remotes will start by a verbal "go-ahead" from the Studio en-
S22
gineer.
The Cutting of Local Runovers
On local "runovers," all cuts which are made necessary because of
synchronization or network "musts" to be carried by WBBM, will be
made by Master Control.
823
Nonrelief Period of Engineers
When programs originate consecutively in the same studio, engineers are not to relieve each other during the last three minutes of a
program and the first two (2) minutes of the following program, and
then only after the relief engineer has familiarized himself with the
routine of the program or programs.
S24
Turning Off of Equipment
With the exception of studio three (3) after 6:00 p.m., all equipment is to be turned off when it is not being operated by a member
of the Engineering Staff.
S25
Studio Engineer Should Be Able to Put Station on the Air
Should the Master Control engineer fail to arrive for a "sign -on,"
the Studio engineer should be able to put the station on the air. For
S26
WHERE SPLIT SECONDS COUNT
67
this reason, he should acquaint himself with the operation and setup
of the following equipment:
1. Battery supply, and associated switches.
2. Local relay channel
3. Patching of phonograph to studio.
See also M14.
827
Use of Telautograph
Corrections to the WBBM Daily Operations Sheet will be written
on the Telautograph. The engineer upon arriving in a booth should
note all corrections affecting him, and change his own schedule ac-
cordingly.
The Daily Work Sheet and Weekly Time Sheet
a. A Daily Work Sheet is to be filled out in full each day and deposited in the box provided in the Maintenance Department.
b. The Weekly Time Sheet, which is posted on the bulletin board
in the Maintenance Department, is to be filled out each day showing
the number of hours worked. This sheet is to be initialed by the engineer at the end of the week.
828
FIELD PROCEDURE
Fl
Returning of Field Equipment
Field engineers are required to return equipment to the Maintenance
Department after the engineer's last pickup for the day, and place it
in its proper location.
F2 Doors That May Be Used When Taking Equipment In or Out
of Building
Field equipment may be carried in or out of the Wrigley Building
through any door except the front door up to 6:00 p.m. After this
time, call for a building watchman to open a side door.
F3
Guests on Pickups
Engineers are not to take guests to remote pickups at any time.
F4
Testing Remote Equipment
Engineers before leaving for the field must give their equipment an
audio and mechanical test as follows:
BROADCAST OPERATORS HANDBOOK
Check 1) microphones and cords for defects; 2) quality; 3)
First:
output level; 4) microphonics; 5) tube shields, observing that
they are in properly, etc.; and 6) volume indicator.
Second: Recheck the first four foregoing items with Master Control.
68
Check-in and Line-up from Field
a. Remote engineers are to check in to Master Control with an equipment test at least one-half hour before air time on all programs (see
also M10) . Leave a test on the line until the one -minute warning,
which will be given over the telephone by the Studio engineer, and
then fade out the equipment.
b. The line-up to the Studio engineer should include the following,
and preferably in the order shown:
1. Line and equipment test.
2. Level check by calling peaks.
.
3. Name and sequence of musical selections (if it is an orchestra)
4. Corroboration of air time.
5. Time check.
careOn "3" above it is the duty of the Remote engineer to check
orchestra
the
with
fully the name and sequence of musical selections
leader.
F5
Lowering of Sustaining Music
the
On all remote orchestras which are announced from the studio,
mubetween
Remote engineer is to lower the level of the sustaining
sical selections to 30 (-10 vu).
F6
F7
Procedure in Remote Program Line Failure
See S19.
F8
The Daily Work Sheet and Weekly Time Sheet
See S28.
GLOSSARY
each
Channel Lights. The small circle of lights found in the center of
an
is
feeding
booth console and used as the signal which that studio
"outgoing" line. Each light represents a separate line.
the Master
Check-in. The verbal report by the Studio engineer to
for
Control that he or she (i.e., the Studio engineer) is in the booth
his or her next program (see S5 and M2) .
WHERE SPLIT SECONDS COUNT
69
Cue Speaker. The small speaker located in the booth console which
can be patched by Master Control to either the local or the network
program.
Daily Log. See Master Control Log.
Daily Operations Sheet. See New York Daily Operations Sheet.
Daily Schedule Sheet. The schedule which shows the rehearsal time,
air time, studio number, destination (i.e., network or local), and the
name of the engineer assigned to each program. This schedule is
posted on the bulletin board in the Maintenance Department each
evening for the following day's operations.
Daily Work Sheet. A form which is to be filled out by each Studio and
Remote engineer every day showing the name and time of all rehearsals and air programs worked.
Engineering Program Report. A report filled out by Studio engineers
for the information of Master Control, and which explains any and
all interruptions to the normal routine of an air program.
Master Control Log. The daily record of all abnormal operations kept
by Master Control.
Network. The entire Columbia Broadcasting System or any portion
thereof.
Network Break; CBS Break. The 30- or 20 -second period at the end
or in the middle of each program which is used for station identification. It always follows the words, "this is the Columbia Broadcasting System."
New York Daily Operations Sheet. The New York Daily Schedule
which shows the exact network routing of each program.
One -Minute Warning. The warning that everyone should remain
quiet, given to talent in the studio and/or a remote one minute before a program is scheduled to take the air.
"Penciled" Comments. The log kept by Master Control in which is
recorded only material of a purely engineering nature.
Regular Program Schedule. See WBBM Daily Operations Sheet.
Remote. Any program originating at a point outside of the studio
from which that program is controlled.
Split Network. A broadcast period during which time the Columbia
Network is divided into two or more sections; i.e., more than one
program is being originated at the same time.
Switching Light. A light located in Master Control and turned on by
a switch on each booth console. It is used to signal the Master Control engineer to switch to the following studio or program,
BROADCAST OPERATORS HANDBOOK
Switching Period. Each quarter hour, i.e., the 15-, 30-, 45-, and 60 70
minute period.
Synchronization. The period after sundown each day during which
time radio stations KFAB and WBBM broadcast simultaneously on
the same frequency.
Talent. The person or persons associated with a program and who
will be heard on the air during that program. This includes the announcer.
Talk -Back. The equipment used in speaking from the booth to the
talent in the studio during rehearsals.
Trouble-Report Form. The report filled out by each engineer and filed
with the Maintenance Department for each piece of equipment
found defective.
WBBM Break; Local Break. The station identification.
WBBM Daily Operations Sheet. The official schedule of program operations for the day for WBBM.
Part
3
OPERATING OUTSIDE THE STUDIO
Chapter
7
REMOTE-CONTROL PROBLEMS
the development of radiobroadcasting since its
earliest days, when the mere broadcasting of actual sound was
miracle enough to create unbounded interest, has witnessed an
almost fantastic evolution of technical equipment and technique of
operation. Even during the earlier period when amplifier response and
the old magnetic loudspeakers so limited the possible fidelity capabilities, broadcast engineers recognized the troublesome problems associated with the room or "studio" in which the program originated.
Ordinary architectural construction did not satisfy the requirements
for smooth control and faithful reproduction. This led to a detailed
study and development of both architectural design and acoustical
treatment to suit the needs of broadcasting. Although many experts
believe that the final answer to this problem has not yet been found,
they all concede that modern broadcast studios have spelled the difference between the success and the utter uselessness of high-fidelity
amplifiers, microphones, and line or relay links.
Broadcast programs, however, are as varied as the interests of the
more than twelve -million people who comprise the listening audience. It is inevitable that a great number of programs. must originate
at some point other than in a carefully designed studio with a permanent and complex studio control console and amplifier racks. Such
programs as speeches and political rallies, news commentators "on
the spot," audience participation shows from theatres or auditoriums,
sports, religious programs from churches, popular music from night
clubs, classical music from concert halls, and novelty and variety
shows from theatre stages necessitate a special department at each
broadcast station to handle such events adequately.
There are certain exacting requirements for remote -control equipment. The remote operator will encounter conditions that will be far
from favorable for the type of program to be broadcast. If the specific location produces very decided effects, he must either use them to
his advantage or avoid them. It is the purpose of Part 3 of this hand THE HISTORY of
71
72
BROADCAST OPERATORS HANDBOOK
book to outline the general type of remote -control equipment, and to
discuss comprehensively the problems encountered in the best utilization of this equipment to achieve the desired results.
REMOTE-CONTROL AMPLIFIERS
Equipment used for remote -control broadcasts must provide the
same means of mixing the outputs of the microphones and sufficient
amplifier gain for use of low -output high -quality microphones as does
the main studio equipment. It is obvious, however, that the equipment must be conveniently portable and therefore limited in size and
weight. For this reason, nearly all amplifiers of this type use low-level
mixing circuits requiring only one preamplifier tube for all microphone
inputs. Since mixing potentiometers are in the extremely low-level
position, frequent cleaning is mandatory. Power for remote equipment
is supplied either by batteries or power line current where available,
or by dynamotor supply in some cases of mobile equipment.
Fig. 7-1 is a panel view of one type of remote amplifier with selfcontained batteries and provision for four microphone inputs. The
RCA
Photo
Fig. 7-1. One type of battery-operated remote -control
amplifier with provision for four microphones.
RCA OP -5 weighs only 36 pounds when completely loaded with batteries and is a convenient size to carry. The line key switches shown
REMOTE-CONTROL PROBLEMS
73
at the upper right in Fig. 7-1 enable either of two lines to be connected to the output of the amplifier, or to a socket on the rear of the
chassis where an interphone may be plugged in for a talk and cue
line. Specially developed nonmicrophonic tubes are used, which have
high gain and low battery drain. Tubes may quickly be reached
through the door on the front panel which mounts the V.I. meter, and
the entire chassis may be removed from the case by simply loosening
the four corner thumb screws shown in the illustration.
Since the level requirements for remote -control lines will vary with
conditions, provisions are made for a multiplier arrangement on the
V.I. meter so that zero reference may actually range from minus 6
to plus 6 db. On some long open wire lines, for example, it may be advisable to feed a higher level to override line noise.
One example where this was found necessary occurred on a field
broadcast handled from the Indianapolis Municipal Airport which
consisted of interviews of incoming passengers from the planes. The
remote amplifier was battery operated, but the signal from the control
tower transmitter was feeding through so strongly on the broadcast
line that the tower operator completely swamped the announcer when
feeding a "zero level" to the line. By adjusting the V.I. multiplier
switch to +6, and peaking zero on the V.I., the tower operator was
down far enough below the program level that, when he came on with
instructions to the pilots, he simply provided an "on -the -spot" atmosphere to the program without spoiling it entirely.
Equipment used for remote -control purposes is largely an outgrowth
of the personal preference of the particular station, and therefore
varies considerably from one station to another. Remote -control fa.silities are more apt to be built up by a station to meet individual
requirements than any other type of the station's equipment, such as
control consoles and transmitters. Fig. 7-2 illustrates the series of
amplifiers built up by the staff of WHK (United Broadcasting Company), tailored to meet their preference in remote equipment. Remotes may require anything from one microphone to a dozen. It is
undesirable to carry a big amplifier to a one -microphone remote, and
it is confusing from a maintenance standpoint to have a great many
different kinds of amplifiers. With this thought in mind, WHK engineers designed this series of amplifiers which are all essentially the
same. There are three types of amplifiers in the series, all of which
have the same physical dimensions and the same internal circuits. All
types have the following common characteristics:
BROADCAST OPERATORS HANDBOOK
74
(1) 15 x 7 x 6 inches made from two standard 15 x 7 x 3 -inch chassis pans.
(2) Preamplifier for each input which the staff felt necessary to im-
prove the signal-to-noise ratio.
(3) Facilities to feed two separate 600 -ohm outputs with +8 vu
level.
(4) High impedance output with separate gain control for feeding
a p -a amplifier.
(5) High level earphone jacks with separate gain control.
Courtesy of Station
WHK
Fig. 7-2. Amplifiers for remote -control work must be portable and compact.
Details of these illustrated are listed above.
basic unit has four inputs, uses 6 -volt tubes, and has an a -c
supply and emergency batteries in another case the same size
amplifier. This type is used on dance band and night spot reThe subbasic unit has two inputs, uses 1.5 -volt tubes, and the
batteries are in the same case. This type is used for the one- and two microphone pickups. The superbasic unit has eight microphone inputs
plus a high level input, uses 6 -volt tubes, and the same power supply
as the basic unit. The high-level input allows two or more amplifiers
to be connected in series so that any number of microphones can be
handled.
The
power
as the
motes.
Simplex Control of Remote Amplifiers
Many times it is highly desirable from an efficiency point of view to
allow turning the remote amplifier on and off from the studio. This is
REMOTE -CONTROL PROBLEMS
75
desirable for a regularly scheduled broadcast from a point requiring
only one microphone where no "mixing" adjustments are necessary.
This may be accomplished by means of a "simplex" installation as
shown in Fig. 7-3. The simplex coil "in" and "out" appears on the
jack panel at the studio. When the remote line is patched into the
STUDIO
REMOTE
f
ö
-LINE
POINT
TO LINE TERMINALS
ON REMOTE AMPLIFIER
O
22.5
r
I
AC
SWITCH
REMOTE
TO
AMPLIFIER
O
Fig. 7-3. A simplified schematic of a "simplex" installation which is used to
switch on and off a remote amplifier from the studio.
equipment through this coil, it may be seen that the battery circuit
will be completed to activate the relay at the remote point which is in
the power-supply circuit of the remote amplifier. This procedure
eliminates the necessity of sending an operator to this point each day.
General Remote Operating Problems
The remote operator is faced with conditions so varied and complex
that any discussion of a specific type of pickup must necessarily present only general principles involved.
A singer's voice is given a certain recognized timbre by the breath
which carries the sound from vibrating vocal chords into the modifying air cavities of the head. As these sound waves emerge they disturb
the air in the place of origin in all directions, but principally in the
direction which the singer is facing. The microphone will pick up the
sound anywhere in the room. Good transmission will depend upon
76
BROADCAST OPERATORS HANDBOOK
the relationship of the position between performer and microphone, and
also upon the relationship of position with the walls, floor, and ceiling
of the room. The air cavities and acoustical condition of the air boundaries will affect the character or "timbre" of the sound just as do the
air cavities of the singer's head which determines his original voice
quality.
Thus it becomes apparent that the varied acoustical conditions encountered will place considerable importance on the type of microphone to be used and method of placement of the microphone. For
example, the operator may find the surfaces bounding the point of pickup to be highly reflecting in character to sound waves, causing distinct
"slaps" and echoes to be prevalent. This condition is caused by deflecting surfaces parallel to each other, and is the reason why "live end" broadcast studios are constructed with no parallel surfaces
existing. Under this kind of handicap, the operator must use the directional characteristics of the microphone to the best advantage. He
could not, for example, use a bidirectional microphone with one live
side toward the pickup and the other live side toward a highly reflecting wall.
Due to the nature of remote -control pickups, the microphones used
are nearly always of the unidirectional type. This permits much better
discrimination between wanted and unwanted sound, since the noise
level at any remote point is quite high compared with a broadcast studio. The unidirectional characteristic is convenient to aid in preventing large amounts of reflected sound -wave energy from actuating the
microphone elements. Since the intensity of a sound wave decreases
as the square of the distance, increasing the distance between the
sound source and the reflecting surfaces (where this is possible) will
decrease the amount of reflected sound -wave energy at the microphone.
By experimenting with the distance between sound source and microphone it may be observed that the relationship between origina!_
and reflected sound will vary over a considerable range. Thus by decreasing this distance a greater proportion of original sound is obtained, and by increasing the distance (between wanted sound source
and microphone) a greater proportion of reflected sound is obtained.
Music in particular needs a certain amount of reflected sound for brilliance and color. Too much reflected sound will cause a "hollow" tone
and uncomfortable overlapping of succeeding musical passages. If the
amount of reflected sound is too small, such as in many studios over treated with sound absorbent material, the music will be lifeless.
Chapter
8
REMOTE VERSUS STUDIO PICKUPS
broadcasting concerns the transmission and reception of voice and music with the preservation of all the
original values. This precludes that any effect should be added
to or withdrawn from the original intent. In radio, sound can play on
the emotions of the listener only as effectively as the transmitter and
receiver equipment, studio conditions, and the skill of the engineers
will permit. Microphones and amplifiers are today of such good quality that no practical limitations to true fidelity exist from mechanical
or electrical characteristics. Modern broadcast studios are such that
only slight limitations exist ,for faithful transmission of sound. This
emphasizes, insofar as remote -control broadcasting is concerned, that
the skill of the engineer or producer responsible for microphone setups
and operating technique, is of utmost importance. This becomes
doubly important when it is realized that each orchestra of any type
has its own identifying qualities resulting from instrumentation, musical technique, and conductor's interpretations, all under the influencing factor of microphone placement and acoustical conditions of the
point of origin.
The effects desired by the orchestra conductor may be achieved only
by proper relationship of the microphones to the musical instruments.
This "proper relationship" is directly influenced by the acoustical condition of the pickup area. For transmission of pure musical tones of
a violin, the microphone must be far enough away from the sound
holes of the violin that the reflected sounds may be caught in all their
beauty denoting rich and true harmonic content. Conversely, when
special effects are desired such as in many instrumentations of rumbas in dance orchestras, the microphone should be so near the violin as
to bring out the harshnessof the resined bow drawn across the strings
of the instrument.
THE PROBLEM of
77
78
BROADCAST OPERATORS HANDBOOK
General Comparisons of Studio and Remote Pickups
Perhaps the most striking difference between studio and field pickups is the complete lack of permanent facilities of any kind in the field.
The Bell Telephone System installs a "broadcast loop" upon order
from the program or traffic department of the station. Sometimes two
loops are installed, one to be used as a "talk" line direct to the control room at the studio, or for emergency broadcast service in case of
trouble with the regular broadcast line. These lines, however, must
be installed as conveniently as possible to the source of the broadcast,
yet as inconspicuously as can be arranged. For this reason, it is often
a matter of a "line hunt" on behalf of the field engineer, and this is
one reason why he arrives at the remote point a long time in advance
of broadcast time. The line or lines may be found under tables, behind
chairs, piano, organ console, or what -have -you on the stage, or it may
be in a room off from the main room where the broadcast is to take
place. It is usually tagged with an identifying card such as "WIRE
Broadcast."
Since the problem of good transmission of talks or speeches at remote points is not nearly so difficult as that of musical pickups, the
discussion to follow will concern music. Musical programs may originate at such places as ballrooms, restaurants, night clubs, and cafes
featuring dinner music, and music for dancing and floor shows. The
situation calls for a decided difference in technique of technical production between studio and remote broadcasts.
In the ideal studio musical setup, only one microphone is used at
sufficient distance, with the musical instruments grouped and positioned so as to blend into the proper balance at the microphone position. This procedure not only simplifies the problem of control, which
always makes for a better effect, but also leaves the problem of orchestral balance in the conductor's hands where it rightfully belongs.
Multiple microphone arrangement will place the maximum responsibility for balance of the various sections in the hands of the operator
mixing the outputs of the various microphones.
At remote points, however, where so much activity such as dining
or dancing occurs, microphones must be placed close to the musicians.
This is inevitable since otherwise the background noise would result
in a disagreeable hodge-podge of confusion. This close microphone
arrangement calls for the use of more than one microphone to achieve
the desired balance; otherwise the instruments closest to the micro-
REMOTE VERSUS STUDIO PICKUPS
79
phone would dwarf the rest of the orchestra. Then the setup is divided into units of like instruments or combination of instruments,
each unit being covered by a separate microphone so that the volume
from each unit may be adjusted at the mixing panel to achieve the
desired balance.
The practice has some advantages for remote -control pickups other
than avoiding background noise. Acoustical conditions that might
severely affect the broadcast are minimized to the fullest extent, since
the ratio of any reflected sound to the original sound is small. Then
too, although some loss of tonal brilliance results from close microphone arrangement, good instrumental definition is gained, which is
important for dance broadcasts.
Symphony music and church broadcasts are different in this respect
in that the audience is comparatively quiet, and the pickup may be
treated more as a studio show by studying the acoustical conditions
existing at the point of origin. This is discussed in a following chapter.
Chapter
9
REMOTE MUSICAL PICKUPS
of Fig. 9-1 will reveal the principles involved for
a typical dance orchestra broadcast. Insofar as the operator is
N OBSERVATION
concerned, this setup divides the orchestra into three separate
units: microphone #1 for saxophone and clarinets; #2 for trumpets,
trombones, and soloist; and #3 for string bass and piano. Microphone #3 is very handy for special emphasis of the rhythm section, or
piano or string bass solo passages. It will be noted that when the trumpets are open, they are behind the trombones and caught on microphone #2; when muted, they step down ahead of the trombones and
immediately in front of the microphone. Muted trumpets or trombones must be played with the muted bells very close to the face of
the microphone. The same is true of any wind instrument upon which
the player is producing subtones. The subtones of any wind instrument are just as low in volume, even though open -belled, as the softest
muted instrument. This, then, calls for close co-operation between
the conductor and his musicians and the engineer responsible for
proper pickup. Many times, important solo "licks" of a particular passage may be lost by lack of co-ordination.
TRUMPETS
OPEN)
0
Q
°lQ
00
PIANO
TRAPS
\\\
O
STRING
BASS
\\\ TROMBONES
4 #3
MIKE
TRUMPETS (MUTED)
0
4
0 0 0
SAXOPHONES
0
AND/OR
CLARINETS
#2
MIKE
ALSO ANNOUNCER
AND SOLOIST
MIKE #1
Fig. 9-1. Seating arrangement of dance orchestra and placement of microphones for a typical remote pickup.
80
REMOTE MUSICAL PICKUPS
81
Brass Bands
Although the 4/4 type bands share comparatively small time in
radio, their particular peculiarities pose special problems in pickup.
A number of community organizations, fraternal societies, and, of
course, the armed services participate in radio through presentation of
brass bands. These pickups very often must be made out of doors,
the least favorable spot for broadcasting. With no outdoor shell or
walls of any kind, no reflection of sound can occur to create the ideal
polyphased sound dispersion so important to broadcasting technique.
Under these conditions it is again necessary to use multiple microphone pickups, grouping the units by means of spotting separate microphones where needed as determined by trial.
For a fair-sized band organization, the units are usually as follows:
one microphone for the clarinets, piccolos, and flutes; one for the English horns, bassoons, bass clarinets, saxophones, and tubas; and one
for the French horns, trombones, and trumpets. The tympani, traps,
and chimes are usually placed in the lower sensitivity zone of one of
the microphones which prevents the use of excessive distance for
proper balance. Indeed, the sensitivity pattern characteristics of the
particular microphones used must be thoroughly understood for any
kind of musical pickup. Tympani, when used with brass, are very
predominate in character when placed in an equal sensitivity zone to
the rest of the instruments. Just the opposite is true when they are
used with strings, since the masking effect due to the characteristics of
the musical instruments themselves tends to subordinate the tympani
sound.
When well -designed outdoor shells are used, the ideal condition exists for brass -band broadcast. Usually only one microphone is used,
suspended some 15 feet out and above the front-line musicians. As
before, predominate instruments, such as tympani, traps, and chimes,
are placed at the side in a lower sensitivity area of the microphone.
Salon Orchestra Remotes
Some dining places have salon or chamber music organizations
which are picked up for broadcasting during the noon or early evening hours. Since a salon orchestra's library concerns the more serious
type of music with many low passages, precautions must be taken to
subdue as much as possible the noise of the patrons. An intimate
microphone placement is therefore indicated.
BROADCAST OPERATORS HANDBOOK
82
Usually the salon group is small, ranging from string trios and
quartets to about ten members. For the smaller groups, one microphone raised quite high and slanted down at an angle of about 35 to
45 degrees with the floor will be adequate. A hard floor with no covering will aid in obtaining just the amount of brilliance necessary for
this type of pickup. A salon orchestra requires more definition than
brilliance in musical tones.
Symphonic Pickups
Symphony orchestra programs have become a regular feature on the
air each season and quite often must be broadcast from a remote point
rather than from a regular broadcast studio. Thus far, musical setups
have been discussed involving a comparatively small number of musicians and a specific type of instrumental structure. The symphony
orchestra, however, is many orchestras in one. The engineer is concerned with the proper grouping of four distinct instrumental sections:
1.
Strings: violins, violas, cellos, string basses.
2. Woodwinds: clarinets, bassoons, English horns, flutes.
3. Brasses: trumpets, trombones, French horns, tubas, euphonium.
4. Percussions: snare drums, bass drums, tambourines, triangles,
cymbals, piano, harp, xylophones, marimbas, tympani.
To this instrumental setup, vocal soloists and choirs are often added,
as for Beethoven's "Ninth Symphony" or Verdi's "Requiem." The musical score itself will influence many times the necessary spotting of
microphones. For such numbers as the delicate "Clair de Lune" of
Debussy, the perspective of the violin passages should be distant, with
a rich and brilliant tonal quality. In numbers such as the Strauss
waltzes, the perspective of the strings should be closer and more strident in character. This problem will be outlined in more detail presently.
As a general rule, the arrangement of the symphony orchestra for
broadcast is the same as for a regular audience performance. The
instruments vary in volume of sound produced and therefore in penetrative quality. Strings produce the least volume, then flutes, clarinets, horns, trumpets, and percussion instruments.
The acoustical situation for symphony broadcasts is generally better than for most other remote controls since the auditorium is usually
designed for such large groups and made compatible with good listening for the audience, although not always ideal for broadcasting.
REMOTE MUSICAL PICKUPS
83
It is easier from a good transmission standpoint to encounter an auditorium that is too "live" and reverberant so that wall, ceiling, and
floor treatments may be added, than to start from one that is too
"dead" to sound reflection.
The correct setup for a symphony orchestra is always arrived at on
the first rehearsal by trial and error. A number of microphones are
spotted at the most likely points so that each may be tried without
the commotion of continually moving one microphone. The most likely
setup is one microphone suspended at a height of about 15 feet about
20 feet in front of the violins. A separate microphone must be used
for vocal solos, since a closer relationship of vocalist to microphone
must prevail for proper balance.
A typical setup for a full symphony orchestra was shown in Fig. 4-7
and no difference need occur for remotes. Some deviations occur in
practice with various symphony orchestras. Toscanini's NBC pickup,
which originates in a regular studio, uses two microphones for the main
orchestra. Due to the directional characteristics and angle of placement (one for each side section) , the orchestra is effectively divided
into two microphone fields with little overlapping. Sometimes another
microphone is suspended directly over the violin section for special
effects on certain compositions as mentioned before. The Ford Sunday
Evening Hour, broadcasted over CBS on Sunday evenings, used two
microphones on the choir for clarity and definition of diction.
In chapter 11 is a complete description of a specific symphony setup.
Church Remotes
Programs from churches usually involve both music and the sermon.
Fig. 9-2. The usual positions of a choir as shown
here, results in too strong
soprano response and insufficient alto and bass.
Compare Fig. 9-3.
BARITONES
AND
TENORS
AND
SECOND
FIRST
BASSES
ALTOS
SOPRANOS
SOPRANOS
AUDITORIUM
This ordinarily requires only one microphone when the minister's po-
BROADCAST OPERATORS HANDBOOK
84
dium is directly in front of the choir as is the most common church
arrangement. When vocal solos occur during the choral rendition, a
separate microphone is necessary for proper pickup and balance. It
will be noted in nearly all instances that, during solos being picked up
by a microphone very close to the choir loft, organ accompaniment
must be brought up to the proper background level by use of the rostrum microphone or microphone farther out in the congregation. This
is due to the acoustical properties which are evident in nearly all
churches causing the organ tones to be much more predominant out
in the congregation than up near the choir.
Conventional choir arrangements are often not practical for broadcasting whether in a regular studio or at a remote point. Fig. 9-2 illustrates the usual arrangement of a choir as used for auditorium or
church presentation. On a broadcast, this arrangement nearly always
results in a predominance of soprano voices with very little alto or
bass. Fig. 9-3 shows an arrangement much more satisfactory for
broadcast purposes, resulting in a better all-around balance of voices.
cr
O
z
oF
.\
Fig. 9-3. By placing a microphone in this
relationship to the rows of singers, a better all-around balance of voices is obtained over the arrangement shown in
Fig. 9-2.
MICROPHONE
Although it would be impossible to cover all the details and complexities of remote -control pickups in a single discussion, it is hoped
that the picture here presented has set forth the fundamental procedures that would help in a general way to approach a remote -control
problem properly. To present an absolutely complete picture would
be impossible, since acoustical conditions and orchestral intent varies
as the number of places from which a broadcast can originate, and
the number of different musical combinations existing. A good understanding of equipment and acoustical variations, however, will enable
any engineer to achieve good results on this type broadcast.
Chapter
10
EYE -WITNESS PICKUPS AND MOBILE
TRANSMITTERS
many types of events of wide public appeal that cannot be adequately covered by the usual methods of remote -control pickups using wire lines for links of communication. Among
these are various kinds of sports such as boat racing, cross-country
events, and golf matches. Aside from these events, there are the inevitable times of disaster such as floods, fires, earthquakes, and the
myriad types of catastrophes that wreck ordinary communication
services for many miles around the point of trouble. In order to be
prepared to bring eye -witness accounts of happenings of these kinds to
THERE ARE
111
PACK
TRANSMITTER
RECEIVER FOR
PACK
TRANSMITTER
RECEIVER
FOR
STUDIO
(CUING)
PACK
13 TRANSMITTER
MOBILE
TRANSMITTER
RECEIVER
AT STUDIO
LINE OR
INPUT TO
STUDIO
CONSOLE
OR REMOTE
POINT
U
POWER
SUPPLY
GENERATOR
TRANSMITTER AT
MAIN
TRANSMITTER FOR
CUING OR TALK BACK
DSTUDIO OR
MOBILE TRUCK
LOCATION
Fig. 10-1. Block diagram of equipment for pack-to -truck and truck -to-main
transmitter relay transmissions.
85
86
BROADCAST OPERATORS HANDBOOK
NBC Photo
Fig. 10-2. Broadcasting an eye -witness account of the burning of the S.S.
Normandie from an adjacent pier by means of a pack transmitter.
the thousands of interested listeners, most stations are equipped with
portable and mobile relay facilities that utilize power supplies independent of utility companies, and also independent of any necessary
wire lines, for relaying the signal to the studio or main transmitter.
There is probably no other division of radiobroadcasting that differs so radically from one station to another as the mobile -relay
department. Fundamentally, however, the necessary inventory of
equipment includes small portable transmitters known as "pack transmitters," a mobile transmitter and antenna mounted in a truck, receivers for cuing and pickup of pack transmitters, and power supplies
for the equipment used.
Fig. 10-1 shows the fundamental layout of equipment used to broadcast any event as mentioned in the beginning of this chapter. Pack
transmitters are low -output transmitters (usually about 2 watts) such
as illustrated in Fig. 10-2. These transmitters are usually good for
line -of-sight transmission only and therefore are picked up on a re-
EYE -WITNESS PICKUPS AND MOBILE TRANSMITTERS
87
ceiver in the mobile truck and fed to the main mobile transmitter.
Mobile transmitters with their associated antenna systems are mounted
in trucks or cars, such as that illustrated in Fig. 10-3.
Frequency Assignments
A license issued to a broadcasting station for mobile relay purposes
covers a group of four frequencies as follows:
Group A (Kilocycles)
1622
2058
2150
2790
Group B (Kilocycles)
1606
2074
2102
2758
Group C (Kilocycles)
Group F (Kilocycles)
31,620
35,260
37,340
39,620
Group G (Kilocycles)
33,380
35,020
37,620
39,820
Group H (Kilocycles)
1646
2090
2190
2830
156,075
157, 575
Group D (Kilocycles)
Group I (Kilocycles)
30,820
33,740
35,820
39,980
156,750
158,400
159,300
161,100
Group E (Kilocycles)
Group J
Any 4 frequencies above
300,000 kc excluding band
400,000 to 401,000 kc.
31,220
35,620
37,020
39,260
159,975
161,925
Only one of any of these groups is assigned to each station. In
order to avoid interference problems insofar as is practically possible,
the FCC (Federal Communications Commission) has ordered that
the first application from any particular metropolitan area in groups
A, B, or C shall specify group A, the second shall specify group B,
the third group C, the fourth group A again, etc. The same is true of
groups D, E, F, or G.
88
BROADCAST OPERATORS HANDBOOK
Group H is assigned only when need for these frequencies may be
shown. Group I is for frequency modulation only. Group J is issued
only to stations capable of carrying out research and experimental
work for advancement of relay broadcast services.
Operation
Relay stations in groups A, B, C, and J are licensed to operate with
a power output no more than is necessary to receive the signal satisfactorily. Those in groups D, E, F, and G are not licensed for an out-
WOR Photo
Fig. 10-3. The second link in an on -the -spot broadcast
is often a mobile short-wave transmitter installed in a
truck.
put power in excess of 100 watts. The FCC also stipulates that before
any power in excess of 25 watts is used, tests shall be run to insure
that no interference will occur to the service of any government station.
A station with only one license may use only one of the four authorized frequencies at any one time. When it is desired to transmit the
program on one of these frequencies and maintain contact with the
studio on one or more of the other authorized frequencies at the same
time (such as for cuing purposes and instructions), two or more licenses must be obtained by the station.
The operator of a relay broadcast station must maintain the frequency of the transmitter within the following limits:
EYE-WITNESS PICKUPS AND MOBILE TRANSMITTERS
89
(a) 1622 to 2830 kc: within 0.04%
(b) 30,000 to 40,000 kc and above: 10 watts or less within 0.1%, over
10 watts within 0.05%
The operator must also be certain that the call letters of the relay
station are announced at the beginning and end of each period of operation (whether rebroadcast on the main station transmitter or not)
and at least once every hour during the operating period.
Chapter
11
THE LIVE SYMPHONY PICKUP
BY BERT H. KOSBLITZ
M
will probably never be called upon to handle a
live symphony program. This is because the proportion of
symphony programs to all the programs broadcasted is very
small, and when a technician has handled such an event well he is
likely to be used over and over again for this work. In other words,
such a job is not "passed around" to give everyone a chance at it as is
the case with many other things. No one knows, however, when he
may be given a chance to handle such a program, in which case a
little inside knowledge will be of great value. The information is not
lost in any case, because almost every fundamental point in symphony
handling is applicable to other types of programs. A great deal of
symphony technique can be used to advantage in recorded symphony
OST OPERATORS
programs.
Making a symphony pickup involves numerous problems, some of
which are technical and some which are not. Some of these problems
are psychological, some social, others political. Hence, not only the
technician, but representatives from all departments of the station
staff may be called upon at times to effect a solution. You are probably wondering why this should be mentioned in an operators' handbook. At WHK it is standard practice to have the technician attend
all rehearsals to get a reading on various orchestral numbers. Usually he is the only station representative present and so may be called
upon to handle details outside his own department; therefore it is
well for him to know the activities of all departments.
The symphony management perhaps has to be convinced that the
broadcasts will be beneficial to it and that they will be properly
handled by the radio station and its staff. The attitude of the conductor and the assistant conductor to the broadcast will make the
situation easier or more difficult, as the case may be. The acoustical
characteristics of the hall in which the orchestra plays will govern the
limits of what the technician can do to make a good pickup. The
type of microphone, the number of them used, the associated equip 90
THE LIVE SYMPHONY PICKUP
91
ment, especially the monitoring facilities, will all affect the pickup.
Finally, the technician who handles the faders can make or break
the program. Perhaps the best method of getting detail on all these
things would be to describe how these problems were handled by WHK
in its broadcasts of the Cleveland Symphony Orchestra to the Mutual
Network.
Pre-Broadcast Problems
Early in 1943, Mutual decided to furnish its listeners with a complete season of Cleveland Symphony broadcasts, if suitable arrangements could be made with the orchestra management. These arrangements, for the most part, were made by WHK personnel with the
cooperation and guidance of Mutual's president. The first and probably the greatest obstacle which had to be overcome was the symphony
management's fear of hurting box office receipts, which fear seems to
have been quite common in the past. A symphony orchestra has a
great many musicians in it. If the orchestra is to be really good, there
must be a fair proportion of the country's better musicians in it. This
costs money. It was feared that a weekly radiobroadcast would tend
to keep people from coming to the regular concerts, which would result in a smaller income and eventually would reduce the caliber of
men in the orchestra.
WHK was firmly convinced that such an impression was erroneous
and was finally able to get the symphony management to agree to let
Mutual hire the orchestra for a one -hour program each week. It was
agreed that the major work presented on the broadcast would never be
the same as the one performed at the Thursday and Saturday evening
regular concerts. Thus no one could hear a major work played over
the radio which someone else had to pay to hear. Before the season
was half over, the box office had exceeded its record for any previous
year since the orchestra had started. WHK feels, therefore, that the
broadcasts not only did not hurt the box office receipts, but actually
increased them to these unheard of proportions.
Once the business arrangements with the symphony management
had been completed there remained about a month's work to co-ordinate all the other factors before the first program was broadcasted.
Those factors included orchestra conductor, associate conductor,
radio script, orchestra seating, auditorium acoustics, announcer, technicians, microphone types and placement, and monitoring facilities.
The conductor during the first season of broadcasts was Erich
92
BROADCAST OPERATORS HANDBOOK
Leinsdorf who had been conducting Wagner for the Metropolitan
Opera Company. Despite his comparative youth, Mr. Leinsdorf had
a wealth of conducting experience and was a most thorough all-around
musician. He was extremely conscientious about respecting the composer's wishes rather than giving his own interpretation of the composer's ideas. He was enthusiastic about the broadcasts and helped
greatly with accurate timing and correcting minor unbalances in the
orchestra. The associate conductor was Dr. Rudolph Ringwall, who
also is a first-rate musician and conductor. Dr. Ringwall was not only
enthusiastic about the broadcasts, but was experienced in these matters
and therefore understood most of the problems. His experience in
both music and radio proved to be of inestimable value in making the
original setup and in properly presenting the orchestral works later.
On every program which he did not conduct he was in the monitoring
room with a score, telling the technicians in advance what they might
expect at various places.
The orchestra management was somewhat concerned over the program notes to be used on the broadcasts. It was certain that the notes
should be written by someone with a good knowledge of orchestras and
classic works, and it was equally certain that the broadcast had to be
timed out properly. This was worked out by two people. There was
no doubt that the person best qualified to write the program notes was
the program annotator of the Cleveland Orchestra. There was also no
doubt that the radio production man should control the timing. So,
early in the week, the orchestra would rehearse the radio numbers
so that they could be timed. Once the total music time was known,
the program annotator could be told how much script to write. This
would not give the desired effect, however, because the announcer
might have read at a different speed than the annotator had expected
and musicians and conductors vary their tempos with weather, auditorium acoustics, audience reaction, and their personal feelings.
To overcome this difficulty, articulated copy was used. The annotator wrote solid copy which would last two minutes less than the time
at his disposal. Then he would add to the middle and closing announcements several paragraphs of 15 or 20 seconds duration which
could be used or not. The closing announcement was written in four
parts in such a way that any part or any combination of parts made
a complete sign -off. These four parts were 11/2 minutes, 1 minute, 30
seconds, and 15 seconds long so that the announcer could adjust the
THE EYE SYMPHONY PICKUP
93
closing to take anywhere from 15 seconds to 31/4 minutes. This system
was highly successful because no deletion or padding was ever apparent to the listening audience, and hurrying or slowing down the
talking speed was never necessary.
Physical Arrangement of Orchestra
The physical arrangement of the orchestra is a matter over which
the radio státion has little control. Each conductor has his own preferred way of placing the men, and if there are to be any guest conductors, the radio people are faced with the problem of constantly
changing setups. At least so it would seem. As it worked out in practice with the Cleveland Orchestra broadcasts, no change of microphone position was necessary with rearrangement of orchestra personnel. The seating arrangement used by the regular conductor of
the Cleveland Orchestra was highly recommended from both practical
and theoretical points of view.
The strings were placed in rows which radiated like spokes from
the conductor's podium back to the last riser. As the conductor faced
the orchestra, the first few rows to his left were first violins and the
next few rows were second violins. The principal sound from a stringed
instrument radiates on a perpendicular to the belly. With the microphone placed above and directly behind the conductor, the violins were
in perfect position for optimum results. To the conductor's right were
violas and cellos in rows like the violins. Here it might be argued that
in theory the violas and cellos were in a poor position, since their
sound holes would point away from the microphone. In practice this
arrangement proved to be satisfactory because these instruments have
a slightly more robust tone than the violins and normally are a supporting rather than a lead voice. The cellos, which are often a weak
section, had a direct line to the microphone and picked up beautifully.
The strings mentioned so far roughly form a shallow letter "V" with
the conductor at the vertex. The front part of the remaining empty
space seats the woodwinds, not in spoke -like rows but as arcs of circles
with the conductor at the center. Behind them were trumpets and
trombones. Still farther back and constituting the last row were the
bass viols. To the left of the basses were the French horns and tuba
and to the right were tympani and percussion. The harps were on the
top riser back of the violas. When the guest conductors changed everything around, it was discovered that, within reasonable limits, there
94
BROADCAST OPERATORS HANDBOOK
was no difference in the pickup no matter how the orchestra was placed.
This possibly was because of the excellently designed shell around
the stage at Severance Hall.
The acoustics of the hall in which the orchestra plays will have
much to do with the microphone setup. A "live" hall is preferred by
a good many symphony listeners. Such a place need not be of undue
concern to the technician unless there is a bad reflective path coming
back to the stage. This can be tested initially by clapping the hands
while standing on the stage. If the noise reverberates but dies off, you
have nothing to worry about. If a second hard slap comes back, then
you have troubles. There is one hall in the United States that is so
poor acoustically that a curtain has to be hung between the stage and
the auditorium when the orchestra rehearses in order to keep reflected
notes from interfering. Severance Hall in Cleveland has excellent
acoustics. A person speaking with ordinary volume on the stage can
be heard in every seat in the house without the use of a public address
system. Another striking fact about this auditorium is that the
acoustics are the same whether it is empty or full. This is because the
seats are upholstered and covered with plush, thereby absorbing
sound just the same as clothing does.
The selection of a suitable announcer does not concern the technical
department except that the technician should exert whatever influence
he can to see that this man has a moderately deep and pleasing voice
and has a little knowledge of what he is talking about. The selection
of technicians for a symphony broadcast should be made carefully.
At WHK, there are several different groups in the technical department. Men are not specifically assigned to any one group, but each
more or less gravitates toward his major ability and preference. There
are studio control men, master control men, remote pickup men (usually studio men with extra ingenuity) , maintenance men (who also
build new equipment) , transmitter operators, and development engineers. It was decided by the executives to send two technicians out,
since all the equipment was in duplicate. It so happened that the best
studio control man, who was also the best remote man, liked symphony music, so he was selected to make the setup and push faders
on the program. One of the maintenance men, who was an excellent
mechanic and trouble shooter, also liked symphony music, so he was
sent along to provide whatever facilities the other man might require.
Selection of microphones is a matter of station facilities, individual
auditorium characteristics, and personal preference. Monitoring equip-
THE LIVE SYMPHONY PICKUP
95
ment should be the best obtainable and in no case inferior to the line
you are feeding.
Microphone Placement
It is perhaps just as important to know what not to do as to know
what to do in certain instalces. Therefore the whole process of arriving
at a microphone placement will be described. In some auditorium
other than Severance Hal_, the things discarded might have been retained. An all-around picture will give a clue to procedures possible
in any hall. To begin w=th, the two technicians agreed beforehand
that the pickup should be made with a single microphone. To use
more than one would take the problem of orchestral balance from the
conductor, where it prope-ly belongs, and make it the responsibility
of the technician, who nine times out of ten would garble it. The
conductor and the associate conductor were persuaded on this basis
that one microphone woulc be best and that it should be placed somewhere on the direct-center stage line. Three 1 -inch brass angle
brackets were made up to suspend three microphones each. Armed
with these brackets, nine microphones, and a bushel of clothes line, in
addition to the regular remote equipment, the two technicians arrived
at Severance Hall three hours before rehearsal time.
Before anything else was done, a height of 15 feet above stage
level was agreed on for the position of the microphone. The first
bracket was hung 15 feet high and about six feet into the orchestra from the conductor's position. It supported a Western Electric
618-A dynamic microphone, an RCA ribbon strapped for voice, and a
Western Electric cardioid set on cardioid. The second bracket was
directly over the conductor and supported an unbaf led eight -ball
microphone, a ribbon strapped for music, and a cardioid. The third
bracket was about six fee, behind the conductor and contained an
unbaffled salt -shaker microphone, a ribbon strapped for voice, and a
cardioid. Extension cords were run into a monitoring room and arrangements made to listen to each microphone separately.
By this time the stage began to look as though we were preparing
for a circus performance. The conductor went through his rehearsal
just as if nothing were amiss, while the associate conductor and technicians selected a microphone. It is useless to recount the endless discussions and ladder climbing; therefore only the results will be given.
First it was determined that the first and second bracket arrangements were too far forward to give sectional balance to the orchestra.
96
BROADCAST OPERATORS HANDBOOK
In either of these positions some group of musicians dominated beyond
all proportion over the volume of the rest. The third bracket arrangement was shifted back and forth until all were satisfied that the orchestra sections were balanced. This satisfactory position was 12
feet from a line drawn across the stage just touching the chairs of
the musicians closest to the audience. During intermission, all three
bracket arrangements were clustered together so that all the microphones could be tried.
The results of this experiment were as follows. The 618-A dynamic microphone had sufficient "highs" but not enough bass. Also,
the "highs" were spotty, certain high frequencies being accentuated
more than others. Both the unbaffied eight -ball and the unbaffied saltshaker microphones gave excellent reproduction and were thought by
the technicians to be satisfactory. However, the "highs" were reproduced so well that a considerable amount of extraneous noise such as
bowing rasp and reed sizzle were noticed. While this was faithful
reproduction, it was not pleasant reproduction. The ribbon strapped
either way did not even approach satisfactory fidelity. Since the cardioid gave splendid reproduction without accentuating the extraneous
noises, it was selected and it also had the virtue of wide-angle frontal
pickup and was electrically "dead" toward the audience. In practice,
a stand was used instead of the trapeze, two units being mounted side
by side with one for regular use and one for emergency use. This may
be summarized as follows: the pickup should be made with a single
microphone. That microphone should be somewhere on a line at the
direct center of the stage. In Severance Hall a Western Electric cardioid set on cardioid was used, 12 feet toward the audience from the
nearest musician, 15 feet above stage level, and tilted to point approximately at the center of the orchestra.
Other Problems
The amplifier following the microphone was flat to plus or minus 0.75
db from 30 to 15,000 cycles. One of its 500 -ohm outputs was fed to a
111-C coil strapped 1 -to -1, which in turn fed the phonograph input of
a speaker amplifier. The speaker amplifier was a high-fidelity type
with separate bass and treble tone controls arranged so that in the
middle position for each one the amplifier was flat. This in turn fed a
high-fidelity speaker. The room containing this equipment was about
20 by 30 feet and was furnished much like a living room. Those are
important considerations-the size of the room and the furnishings.
THE LIVE SYMPHONY PICKUP
97
The best speaker in the world is ineffectual in a small room, and a
room that is too live will tend to cause the technician to reduce the
"highs." The speaker was placed at one end of the room and the technician at the other so that the tones had a chance to develop and blend
before he heard them.
The next step was to set the speaker volume properly. It is well
known that the efficiency of the ear varies with volume intensity;
therefore some standard had to be set up which could always be usedin this case something in the nature of a hike. The two technicians
and the associate conductor tried seats in every section of the auditorium and finally agreed that the orchestra sounded best in the middle
seats of the 8th, 9th, and 10th rows of the middle section on the main
floor. These seats are directly in line with the microphone. After a
multitude of trips from the seats to the monitoring room, the volume
on the speaker was fixed so that the same level came to the control
position as was noticed in the referenced seats. Fortunately, the
speaker amplifier had a volume indicator on it so that this volume
could always be maintained regardless of tube wear.
Once the mechanical equipment is properly arranged, there remains
the problem of properly broadcasting the program. A psychological
reaction is strongly involved in this procedure. The most common
complaint from musicians and conductors is that the technician raises
the soft passages and reduces the loud passages, thereby defeating the
function of the conductor and destroying the symphonic intent of
the music. It is therefore mandatory that some procedure be used
which will insure at least the approximate dynamic range of the orchestra in the hall. The upper limit is, of course, the maximum operating level of the particular station involved. The lower limit is the
signal-to-noise ratio at the receiver location. Inside the primary service area of a station there is normally no difficulty with signal-to-noise
ratio. If the soft passages are raised to help the listeners outside the
primary service area, the loud passages, of necessity, will have to be
reduced. In that case no listeners in either area are able to enjoy the
full dynamic range. If the soft passages are not raised, the listeners
inside the primary service area can be given the full dynamic range of
the orchestra.
At WHK it was decided that it was better to serve some listeners
well, even at the expense of others, than to serve no listeners well. One
of the technicians assigned to the symphony was sent to all rehearsals.
He set up the equipment just as he would for the actual broadcast.
98
BROADCAST OPERATORS HANDBOOK
Then he would arrive at a fader setting for each number or movement
which would cause the vu meter to peak no more than the maximum
allowed. These settings were carefully written down so that on the
evening of the broadcast the orchestra fader was always set at the
correct place before each number started and was never moved during
the number. Thus listeners were furnished with the full dynamic range
of the symphony orchestra.
This proved to be only part of the total problem. Using the method
just described will mean that the listener has to increase the setting of
the volume control on his set if he desires to hear the softest passages.
If the listener does this (and he will if he is a symphony enthusiast),
the level normally permitted announcers will drive him out of the
room. Therefore it is necessary to keep the announcer's level somewhat
below standard.
The easiest way to state the comparative readings is in per cent.
If the maximum peak allowed the orchestra is 100%, then the maximum peak allowed the announcer should be 40%. Later in the season
it was discovered that this procedure resulted in a sort of automatic
set tuning action. The symphony programs from WHK always were
introduced by the announcer. Normally, the listener already had his
set turned on listening to some other program. When the symphony
announcer came on peaking only 40%, his voice would sound much
too soft so that the listener would increase the volume until the announcer's voice sounded normal. This usually proved to be approximately the correct volume for symphony listening.
The Soloist Microphone
The last important consideration in symphonic pickups is the presentation of soloists. In a way, the term "soloist" is erroneously
interpreted, especially where it pertains to instruments. Most of the
compositions written for this type of presentation are either concertos
or in concerto form. In a concerto, the solo instrument is no more important than any other voice in the orchestra. One has only to listen
to air presentations of such performances to realize that this fact is
generally ignored. About half of the time in an ordinary concerto
the orchestra is supposed to take precedence over the so-called soloist.
It is not only a matter of relative volume but also includes the delicate
distinction of relative auditory presence.
For example, a trumpeter three feet from the microphone can blow
softly enough so that he will produce a tone of the same electrical
THE LIVE SYMPHONY PICKUP
99
volume as a trumpeter ten feet from the microphone blowing a little
louder. Yet the two tones will not sound the same. Why? Actually
there are two reasons; the first of which is that a trumpet does not
sound the same when it is blown softly as when it is blown loudly.
That variable can be eliminated. Let the two trumpeters keep the
same distances mentioned and both blow at exactly the same volume.
Then the technician can adjust his fader so that they will both register
the same electrical volume; however, they still will not sound alike.
That is because their auditory presences are different. Therefore, to
present a soloist properly with an orchestra in a concerto, it is necessary to place the solo microphone far enough away so that the auditory
presence of the soloist regardless of volume is the same as that of the
orchestra.
There is no rule of thumb on how to accomplish this since the relative distances will vary with auditoriums. It has to be done by trial
and error during rehearsal; also, the distance will rarely be the same
for two different performers. Once the distance is established for a
given performer, the microphone fader must be carried only high
enough to give a small amount of definition to the instrument. If the
solo volume is allowed to go to 100%, it has the same effect as allowing
the announcer to peak 100%.
Transporting Equipment
There is one other consideration peculiar to the Cleveland Orchestra
that may not obtain in other cities. The experience gained, however,
has sufficient application in ordinary remote work to bear relating.
The Cleveland Orchestra makes three concert tours each year, which
means that five broadcasts will be in some city other than Cleveland.
Since so much care had been taken to insure a good pickup locally,
and since so much depended on the particular technicians assigned
and on the particular equipment used, WHK decided to take precautionary measures and send those men and that equipment along.
Transportation for the men was no problem, but there were 800
pounds of equipment that could not be condensed into a small shipping
case. Like Noah, it was decided to take two of everything.
There were no standard trunks, sample cases, piano boxes, etc.,
which would satisfactorily hold the equipment. An old trunkmaker
was found who agreed to build trunks especially for the equipment.
Accordingly, he was provided with a complete duplicate set of equipment. Two months later it was returned to WHK enclosed in two
100
BROADCAST OPERATORS HANDBOOK
THE LIVE SYMPHONY PICKUP
101
trunks, as shown in Fig. 11-1-trunks an expressman would consider
ideal to handle. The trunkmaker had done an ideal piece of work on
them because not a single piece of equipment has been damaged in two
years of travel, and on more than one occasion the trunks were delivered in a distant city by one man, which meant they were dropped
off the truck and rolled end over end into the auditorium.
The larger trunk is for microphones and stands. The microphone
heads are removed and placed in drawers which have compartments
lined with two inches of sponge rubber and fitted with tops, so that
when the drawers are closed nothing can move. The other half of the
trunk is devoted to an arrangement for solidly holding microphone
stand bases and shanks. There are two extra drawers for extension
cords and tools. The smaller is arranged to accommodate two remote
amplifiers and two battery boxes. One set fits into each side in sponge rubber -lined compartments. There are also two extra drawers for miscellaneous use.
To assure its delivery for the orchestra broadcasts on Sunday, the equipment is sent to the distant city on the previous Monday. The technicians arrive there either Thursday evening or Friday
morning apparently early for a Sunday broadcast, but for a good reason. The telephone companies usually terminate the lines somewhere
on the stage unless a specific place is requested; however, the technicians prefer to work in a separate room beyond the stage. Because
most auditoriums are devoid of help from Friday night until concert
time on Sunday, the technicians, by arriving at that earlier date, are
assured of having their individual room.
Problems of Strange Auditoriums
Another interesting problem arises in working in a strange auditorium. All auditoriums are different and there is no possibility of rehearsal because the orchestra does not usually arrive in the broadcast
city until two or three hours before concert time. First, the technician
should stand on the stage and clap his hands in a hopeful effort to ascertain the acoustics of the hall. From what he hears, he tries to determine how much that will change with an audience; however, he
does not have to be too particular. If the original clap echoes but dies
away, the pickup will be live but not distorted. If the sound of the
original clap is returned as though the hands were clapped twice, then
something has to be done. If a cardioid microphone is used, it can be
placed with no tilt and lowered about three feet from its normal posi-
BROADCAST OPERATORS HANDBOOK
102
tion. This places the dead side directly toward the clap and the reduced height partially restores any loss of balance resulting from no
tilt. Sectional balance would be difficult in such a live hall anyway.
The main problem is to get whatever sound is reproduced as clear as
possible.
Another problem is presented by the variety of stage sizes and shapes
in different auditoriums. In some the stage will be very wide but very
shallow, making it necessary for the orchestra to be in a long narrow
rectangular arrangement instead of a semicircular arrangement. In
such a case the microphone can be tilted almost to a horizontal position in order to diminish the pickup of wind instruments. The strings
will be physically farther from the microphone in this instance so it will
be necessary to keep the wind instruments down. Another type of stage
which gives trouble is one without any shell where a great deal of
the sound is not projected forward. The solution is to leave the microphone at normal tilt but lowered a couple of feet and moved in closer
to the conductor.
The final consideration on road trips is difference in level from the
home auditorium. A fader setting noted at rehearsal in the regular hall
will not necessarily pertain in some other hall. A live hall with a shell
is likely to give more deflection than expected, and a hall with no
shell is likely to give less. Unfortunately no indication can be had
from the announcer's voice since he is working so close to the microphone that acoustics have little if any bearing on his level. The
safest way is for the orchestra fader to be set where it would be in the
home auditorium. If the level is too high, the fader should be reduced
one notch after each group of excessive peaks. By the time that particular number or movement is completed, the normal level should be
determined for that auditorium. The amount reduced can then be
subtracted from all fader settings marked down for the other numbers,
eliminating any further guesswork. If the level is too low, as compared
to the local hall, the fader should be increased one point each time
a climax, remembered from rehearsal, fails to peak 100%. The difference thus arrived at can then be added to the other settings.
To sum up the symphony broadcast,
single microphone should be used behind the conductor on a
line with center stage and uplifted in the air (usually about half
1. A
the height of the proscenium arch) .
THE LIVE SYMPHONY PICKUP
103
Auditory presence should be adjusted for soloists without giving
them too much volume.
3. Fader settings should be determined at rehearsal and not changed
on the broadcast. Where this is impossible, faders should be
moved very gradually to obtain proper setting.
4. The best possible equipment should be used. The setup depends
upon what is heard through that equipment.
5. The symphony broadcast technician should be prepared to argue
with his fellow workers and A. T. & T. about low level. But be
firm, because they will give up in five or six weeks.
2.
Part
4
OPERATING THE TRANSMITTER
Chapter
12
OPERATOR'S DUTIES
and students familiar with the technical characteristics of transmitting equipment in general, and broadcast equipment in particular, are cognizant of the greatly advanced state of technical design and transmission fidelity. It will not
be the purpose of this section to duplicate the already published data
on broadcast transmitter circuit theory and relationships. A workable knowledge of this field is assumed in this text.
The discussion to follow will pertain to the all-important operation
of the broadcast transmitting installation in order to achieve the best
results possible from the finely engineered equipment available and
in use today. Operating practice at the transmitter is just as important in the final result of over-all performance as it is at the broadcast studio. The science of operating the transmitter and associated
speech input equipment may be shown to be a highly specialized art,
and we have chosen the term "operational engineering" to define the
content of the special study undertaken in this part of the handbook.
ALLENGINEERS
Outline of Responsibilities
It is true that the primary purpose of the transmitter operator
is to keep the station on the air. But with the rapidly progressing
demands for higher -fidelity program transmission, the day when the
typical "ship operator" of thorough technical understanding could step
into a broadcast installation, has passed forever. The operator of a
broadcast transmitting plant has a specialized range of duties requiring a technical education, plus a thorough understanding and appreciation of the more intangible values of program material.
A number of his fundamental duties are, of course, strictly technical
in nature and, since this is meant to be an analysis of an operator's
duties, the technical functions will be described from an operational
point of view. In brief, his technical duties consist in turning the
transmitter on ahead of the beginning of the daily program schedule,
checking all meter readings to make proper adjustments, checking
104
OPERATOR'S DUTIES
105
level with the studio, shutting down the transmitter after sign -off,
repairing and maintaining equipment, and testing for noise and distortion levels. During the daily operating schedule he consistently
monitors the program from a monitoring amplifier and loudspeaker,
adjusts line amplifier gain _n accordance with good engineering practice pertaining to percentage modulation (the transmitter operator
does not normally "ride gain" as does the studio operator), maintains
correct tuning of transmitter, logs all meter readings every 30 minutes
required by the FCC, and corrects any trouble that develops in the
shortest possible time. Useful hints for meeting technical emergencies
will be given later.
Typical Pre -Sign-on Prccedures
The transmitter operator in all but the lowest power local stations
is usually scheduled to be on duty at least 30 minutes prior to air
time for the purpose of getting the equipment ready for the broadcast
day. The start of an operatpr's day may be outlined as follows:
Audio rack power applied (including such measuring equipment as the frequency monitor and modulation monitor)
Audio line used as program loop opened by inserting patch cord
into the line jacks. This removes the line from the input to the
line amplifier and prevents any test program that might be on
the line from the studio from being applied to the transmitter
when turned on.
2. Visual inspection of all relays in antenna -phasing cabinets
(where used) and in coupling houses at the antennas. Relay
armatures manually operated to ascertain freedom of movement. Observation of pointers on all r -f meters for bent hands
or zero set.
3. Inspection of all safety gaps including antenna and transmission -line lightning gaps for approximate correct spacings.
4. Water pumps started (where used) and rate -of -flow meters
observed for correct rate of water flow. Water flow must be
normal before filament voltage is applied. Air-cooling systems
usually start the blower motors when "filament-on" switches
are operated. Transmitter filaments now turned on and filament voltages checked. In large power tubes using tungsten
type filaments, minimum voltage should first be applied, then
run up to normal filament voltage after about 3 or 5 minutes.
1.
.
106
BROADCAST OPERATORS HANDBOOK
This is a means of lengthening the usable life of such power
tubes but it is not observed in some stations. Tubes of the
thoriated-tungsten or oxide -coated filaments such as used in
the low -power stages, are always operated at normal filament
voltage for maximum tube life.
5. Plate voltage then applied to low -power units or exciter unit
(in power installations of 1 kw or more) to check for proper
excitation to final stage.
6. Low power then applied to final stage. All meter readings
checked for normal low -power operation. If everything is
normal, high power applied and meter readings checked.
7. Filament and line voltages checked and adjusted for high power operation. Final adjustment made on final stage for
optimum meter readings regarding resonance condition and
power input.
S. Since the control -room operator sometimes has circuits "hot"
with his own testing procedure, the transmitter operator plugs
patch cord from program line to monitor amplifier to ascertain
continuity of program line. Then notifies control operator to
stand by for over-all circuit test. When this has been done,
transmitter operator removes patch cord from jacks which
automatically restores line connection to input of line amplifier. A test tone may then be fed from studio to check over-all
continuity of circuits from studio to transmitter modulators.
Pre -Program Level Checks
Level checks with the studio are not required as a daily procedure
after an initial installation has been made, tested, and operated for
some time, since with properly operating equipment the level remains
very nearly the same over a period of time. At regular intervals, however, it is desirable to use a signal generator to check the frequency
characteristics of the line and transmitting equipment. In this connection it is well for the transmitter operator to understand the difference in modulator power requirements for sine wave and speech or
music program content.
It will be remembered from circuit theory that for a class C modulated amplifier, the power requirement for complete sinusoidal modulation is 50% of the d -c power input to the modulated tube or tubes.
Fig. 12-1, however, shows how the "peak -factor" of speech or music
waves varies greatly from that of a pure sine wave. This peak factor
OPERATOR'S DUTIES
107
of program waves is 10 to 15 db more than that of a sine wave. That
is, the ratio of peak to rms voltage is far greater for complex waveforms than that of a sine-wave form. In other words, the average
power for complete modulation of a transmitter over a period of time
is far less than the average power required for complete modulation by
means of a signal generator. It is a well-known fact that for program
Fig. 12-1. The "peak factor" of a
speech or music wave is 10 or 15 db
greater than that of a sine wave; i.e.
the ratio of peak to rms value is
greater for complex waves than for
sine waves.
signal waves the modulator power required may be 25% or less of the
d -c power input to a class C stage. Therefore, if a signal generator is
used at the studio for frequency runs or level checks, the transmitter
operator must realize that if he '-has adjusted the gain on the line
amplifier to give 100% modulation on sine wave, the same adjustment
will be 10 to 15 db high for program signals. Thus the gain adjustment must be lowered to the point that experience has dictated for
program modulation before -the actual program schedule starts. In the
past this has led to seme confusion among transmitter operators.
This difference in peak factor between program and sine waves is
also noticed when comparing the per cent of antenna -current increase
with 100% modulation. It is true that the antenna -current increase
should be approximately 22.5% over no modulation when a sine wave
is applied to the transmitter at 100% modulation value. Antenna current increases for 100% program modulation, however, will be much
less, due not only to the difference in peak factor, but also the sluggishness of the thermocouple r -f meter action. This slowness of action
is due to the heating effect of the two dissimilar metals upon which the
action of the meter depends.
Chapter
13
PROGRAMS ARE ENTERTAINMENT
broadcast day the transmitter operator
keeps the circuits properly tuned, maintains correct power input to the final stage, logs meter readings each 30 minutes
(which also aids in forestalling trouble), maintains frequency of operation within plus or minus 10 cycles, and maintains the program level
at a point consistent with good engineering practice and the type of
program in progress.
It is only natural that the program level being sent via wire line
from the studio be the most concern from a strictly operational point
of view to the transmitter operator. With competent studio personnel,
the line amplifier gain adjustment may be set for 100% modulation
on program peaks at the start of the day and left at that adjustment.
Many times, however, the transmitter operator who does not appreciate musical and dramatic values will become piqued with the control
operator when program level is very low. He should realize that broadcast stations are not strictly "communications," but intended to bring
entertainment into the home with as much of, the original intent as
possible consistent with the state of the art. Certain types of programs,
symphony concerts in particular, are meant for those listeners in the
primary service area and not intended to override the noise level at
some secondary service point. If the monitor speaker is turned up in
volume consistent with that of the interested listener at home for these
types of programs, the transmitter operator will be able to use
good judgment as to whether the signal is entirely too low to be usable.
In relation to the study of program levels, it is of prime importance
to understand the characteristics of indicating meters used at both ends
of the transmission system. These meters differ in characteristics because of the different function which they are intended to perform.
The standard vu meter used in most broadcast studios today is an
rms-indicating full -wave rectifier device intended to give a close
approximation visually of the sound waves emanating from the loud DURING THE REGULAR
108
PROGRAMS ARE ENTERTAINMENT
109
speaker. We are concerned, however, with modulating voltages at the
transmitter, and a semipeak indicating device is necessary and is required by the FCC. If peaks of the program signal content should be
excessive and occur in rapid succession, danger of circuit component
breakdowns would exist as well as severe adjacent channel interference. Theiefore, since the peak factor of program waves is high as
discussed earlier, the modulation meter is a "peak" indicating device.
It is also necessary that a phase reverse switch be incorporated in the
modulation meter circuit which switches the polarity of the input to
the vacuum-tube voltmeter so that either the positive or negative side
of the modulated envelope may be monitored separately. Thus it is
obvious that we are confronted with two distinct types of level meters;
namely, a full -wave rms meter at the studio and a half-wave peak
meter at the transmitter. In addition to these meters, we usually have
a limiting type amplifier (in most modern installations) which is used
at the transmitter as a line amplifier. This has a meter which measures the amount of compression (full -wave peak meter) and output
level in vu (full -wave rms meter) .
Correlation of Meter Readings
The number of different types of indicating meters used should not
confuse the operator as long as the proper interpretation is given to
the readings. Fig. 13-1 is a representation of the indication of a proTRANSMITTER
MODULATION
MONITOR
100
STUDIO
OUTPU'r
r...".100
STUDIO
VU
LINE
TRANSMITTER
LINE AMPLIFIER
3
+
5db+100
COMPRESSION
METER
VU
PEAK
100
OUTPUT
METER
\
PEAKS
/
MODULATION
PEAK
INDICATOR
Fig. 13-1. A representation of the indications on the various meters of a
program peak at any given instant.
gram peak at a given instant on the various meters involved. The
studio vu meter has registered 100, the compression meter on the trans-
BROADCAST OPERATORS HANDBOOK
110
amount of limiting, the line amplifier output
meter shows 100, and the modulation meter would show either 100%
modulation on positive peaks, or, if set to monitor negative peaks,
might show only 60% modulation. This, of course, could be just reversed with a change in polarity of the microphone output or any
connection in between.
It is a well-known fact that speech waves are not equal in positive
and negative peaks regardless of type of microphone used. This may
be observed from the graph of the speech wave shown in Fig. 12-1.
Two speakers working from opposite sides of a bidirectional microphone and "peaked" the same amount on the studio vu meter will not
give equal indication at the modulation meter when set to indicate a
certain peak (either positive or negative).
Assume, for example, that the modulation monitor switch is set
to monitor the negative peaks, and the indication of one voice is close
to 100%. The indication of the voice on the other side of the microphone (therefore oppositely poled at the microphone output transformer) may indicate only 40% or 50%, with the amplitude of the
studio vu meter remaining the same. For this' reason it is obvious why
misunderstandings sometimes arise between studio and transmitter
personnel regarding comparative level of two or more voices.
The question then arises as to what indication, if any, exists at the
transmitter plant to show a true indication of comparative levels from
the studio. It has been shown that the half -wave reading of the modulation meter, which depends upon the polarity of operation, is not a
mitter shows normal
5 db
POSITIVE
NEGATIVE
Figs. 13-2, left, 13-3. A drawing (left) of an oscillogram showing a sine -wave
carrier that is 100% modulated and one that is over -modulated is shown on
the right.
s
PROGRAMS ARE ENTERTAINMENT
111
true indication of comparative levels from the studios. The vu meter
on the output of a limiting amplifier would not be a true indication
since the output level is limited by the compression taking place in
the amplifier for signals over a predetermined level. The compression
meter, although a full -wave indicating device, is a peak reading instrument and, since the peak factor of program waves varies considerably, it is not an absolutely accurate indication of comparative levels.
It is, however, the most reliable indication (within limits) existing at
the transmitter, since it is full -wave rectified and is limited by only
wire line characteristics. If two voices, for example, show about the
same amount of compression, the comparative levels may be considered
very nearly the same.
100% Modulation
Fig. 13-2 is a drawing of an oscillographic pattern of a 100% modulated (sine tone) carrier, stowing what constitutes positive and negative modulation of the carrier. It may be seen that negative or
"trough" modulation cannon attain more than 100% of the available
range, whereas positive or "peak" modulation may go over 100%.
When a carrier is thus modLlated with a pure tone, the degree of modulation m is
m
average envelope amplitude-minimum envelope amplitude
average envelope amplitude
and the peaks' and troughs of the envelope will be equal. When the
minimum envelope amplitude (negative peak modulation) is zero in
the foregoing equation, the degree of modulation is 1.0 and the degree
of modulation is complete, or 100% expressed in percentage modulation.
When the envelope variation is not sinusoidal, such as is true for
program signals, the positive and negative peaks will not be equal as
explained earlier, and the degree of modulation differs for peaks and
troughs of modulation as folbws:
Positive peak modulation
Negative peak modulation
-
Emax
-Eat,
- Em:n X 100
Eat,
-
Em;n X
100
Eav
Thus it is possible to unde,stand the mathematical analysis of why
the trough modulation cannot exceed 100%, since the minimum
voltage cannot be less than zero. It may be seen, however, that the
positive peak voltage may be more than twice the average (or carrier)
BROADCAST OPERATORS HANDBOOK
voltage (Ea.,,) in which case positive peak modulation will exceed 100%
modulation. What important information does this hold for the
transmitter operator?
First, it should be clarified in the operator's mind that "overmodulation" can take place on the negative (trough) modulation as weil
as on the positive (peak) modulation. It is true that the degree of
modulation can never exceed unity on the negative peaks, but can
exceed unity on the positive peaks. Complete modulation (of a class
C stage) however, requires that the peak value of the modulating voltage equal the d-c plate voltage of the modulated stage. Fig. 13-3
shows a drawing of an oscillographic pattern of a carrier wave with
modulating voltage exceeding the d -c plate voltage causing overmodulation of the carrier. It is true that the positive modulation peaks exceed unity while the negative peaks are "cut off" by the excessive
negative modulating voltage and cannot exceed unity. This excess
energy, however, which allows the negative peak voltage to result in
a voltage applied to the r -f amplifier plate circuit to become negative
with respect to ground, causes a radiation of this excess energy in the
form of spurious frequencies, resulting in "splatter" and adjacent
channel interference.
This actually is "overmodulation" in its severest form, since positive peaks may extend beyond 100% modulation without amplitude
distortion, whereas negative peak "overmodulation" will cause severe
amplitude distortion. It will be remembered that the bandwidth occupied by the carrier and sidebands depends (for amplitude modulation) not upon the degree of modulation, but upon the highest frequency being transmitted. Amplitude distortion, however, resulting
from negative peak overmodulation, generates a number of distortion
frequencies at harmonics that may well extend high enough to spread
the sidebands into channels adjacent to the assigned frequency of the
transmitter in question.
This discussion has been presented in order to show the transmitter
operator that the negative side of the modulation is the most important peak to monitor on the modulation meter, and to hold under
100% at all times. It is well to remember that the modulation meter
of the vacuum-tube voltmeter type will not be able to indicate over
100% (negative) on the meter because the peaks cannot attain more
than this value as shown before. This is the reason why a cathode-ray
oscilloscope is invaluable at a broadcast transmitter to show negative
peak "overmodulation," since the negative peak "clipping" shows up
112
PROGRAMS ARE ENTERTAINMENT
113
as white lines across the center of the modulated pattern. When the
usual vacuum -tube voltmeter type of modulation indicator is used, the
flasher should be set to flash at 90% or 95% modulation so that when
observing negative peaks, the warning is given when the peaks go up
to 100% modulating value.
Operation of Limiter Amplifiers
The limiting amplifier, also known as a compression amplifier (see
panel view in Fig. 13-4) is a very important link in a broadcast installation. However, its effect may be small and detrimental, if the
RCA Plwto
Fig. 13-4. Panel view of a limiting or compression amplifier for preventing overloading transmitter components
and adjacent channel interference.
wrong operational interpretation is given to the main purpose for
which it is designed and intended. This type of amplifier, as designed
for use in a broadcast installation, is intended as a peak limiting device, the amount of gain reduction being a function of the program
peak amplitude. In order to prevent material reduction in the dynamic
range of the signal, the peak gain reduction is not intended to be more
than 3 to 5 db. A broadcast limiting amplifier, therefore, should
not be considered as a volume limiter, but as a peak limiter intended
to prevent overloading of transmitter components and adjacent channel interference.
114
BROADCAST OPERATORS HANDBOOK
The original advertising claims of manufacturers offering this type
of equipment proved misleading from an operational point of view. It is
true that doubling the output power of a transmitter raises the signal
intensity 3 db. It is also true that the limiter amplifier also raises the
signal level about 3 db on program peaks. To those familiar with
watching volume indicators on program circuits, however, this 3 -db
increase on speech or music is of small consequence. As far as the
transmitter operator is concerned, he should think of this amplifier as
a protective device to limit peaks caused by wire line transmission and
those program peaks that escape the action of the control -room
operator.1
That the primary purpose of a limiting amplifier may be defeated
by erroneous operation is a very important fact for the broadcast
operator to know. Seriously detrimental effects will result if this amplifier is operated as an actual "volume compression" device to attempt to prove a coverage area greater than a given power and transmitter location warrants. The "attack" time of peak limiting (about
0.001 second) is determined by a resistor -capacitor charging circuit
with the inherent characteristics of a low pass filter. At high frequencies, and where the duration of the peak is short compared to
this operating time, a portion of the peak energy will escape limiting
action. If the average signal level is so high that a great amount
of compress;( , takes place at all times, a larger amount of adj acentchannel interference will result, thus defeating one of the main purposes of the amplifier.
This has been quite noticeable in practice when the program content consists of music from dance orchestras of brass instruments
where high peak powers at high frequencies are very prevalent. A
limiting amplifier operated properly for broadcast service will show
about 3 to 5 db of intermittent gain reduction as indicated by the
peak reading meter used to show the amount of program peak compression. The operator must realize that for certain types of programs
such as symphonies, liturgical music, and operas, the average audio
signal may be very low over a period of time even with limiting amplifiers in use. Dynamic range is just as important to high-fidelity transmission of these types of programs as is the frequency range.
Another consideration is the recovery time value, or time required
to restore the gain to normal after a peak has momentarily reduced
the gain. Optimum recovery time may well be different for different
-1
'See Appendix for important adjustment of the
96 -AX limiting amplifier.
PROGRAMS ARE ENTERTAINMENT
115
types of program material. Piano music, for example, sounds unnatural when recovery time is too short, because the effect is similar
to inadequate damping of the strings after they are struck or to holding the sustaining pedal too long on the loud notes. The longer the
recovery time is made, however, reduced gain will be in effect a larger
proportion of the total time, and will result in unnatural transmission
of certain passages in specific musical compositions. When operated
properly in accordance with good operating practice, and not subjected
to more than the specified amount of peak load, very satisfactory results may be obtained?
When thinking of a compression amplifier as a means of increasing
the service area of a transmitter, it is well to keep in mind the known
facts concerning the psychological differences that exist in listening
habits for various types of programs. A lower relative signal level is
tolerable for dance music, news broadcasts, etc., where the average
audio level is high over a period of time. In this case where listeners
well outside the "primary service area" of the station may be numerous, the maximum amount of peak limiting may be used to help
raise the signal-to-noise ratio at the receiving point. It is realized,
however, that symphony broadcasts, choral music, certain liturgical
music, opera, etc., where the average audio signal may be very low
over a period of time, will appeal only to those listeners who are very
adequately served with strong carrier signals. In the interests of preserving the original dramatic effects of this type of program, it simply
is not technically feasible for a broadcaster to attempt to set a fixed
value of coverage area for all types of program material. Similarly,
the operator responsible for the transmission of programs should not
attempt to operate all equipment in the same manner regardless of
type of programs being transmitted.
2W. L. Black and N. C. Norman, "Program -Operated Level-Governing Amplifier," IRE Proc., Nov. 1941.
Chapter
14
MEASURING NOISE AND DISTORTION
any modern broadcast installation are adequate frequency range to convey as much of
the original sound as possible, low noise and distortion levels
necessary for required dynamic range, and dependability of performance. One of the most important pieces of auxiliary equipment about
a transmitting plant is the instrument for determining noise and/or
distortion over the usable frequency range to facilitate proper adjustment of the over-all installation. Several manufacturers are supplying such equipment for broadcast frequencies, and most stations are
equipped with means of checking noise and distortion. Definite instructions accompany all such equipment, but a typical description of
procedure for using one type of noise and distortion test equipment is
given here in outline form as a matter of general interest. This outline conveys the general principles of all noise and distortion measuring equipment.
Fig. 14-1 is an illustration of the RCA 69-C Distortion and Noise
meter, which may be used to measure distortion in transmitters or
audio equipment at any frequency from 50 to 7500 cycles, providing
THE IMPORTANT CHARACTERISTICS Of
RCA Photo
Fig. 14-1. Meter for measuring distortion in transmitters
or a-f amplifiers from 0.3% to 100% and noise levels
down to -85 db below 12.5 milliwatts.
116
MEASURING NOISE AND DISTORTION
117
measurements of rms total distortion from 0.3% to 100% and noise
levels down to minus 85 db below 12.5 milliwatts. This instrument
consists essentially of a diode detector which is used when taking
measurements on a transmitter to demodulate the modulated r -f signal,
047R.
PICKUP
COIL
DISTORTED
WAVE
F.
DIODE
DISTORTION
COMPONENT
Jr.,'"
ATTENUATOfÿ MIXER
AMPL.
ATTENUÁTOR METER
PURE
SINE -WAVE.,
V
-
TO
TRANSMITTER
INPUT
-WAVE
OSCILLATOR
S NE
Fig. 14-2. Functional block diagram
of the distortion and noise meter on
the opposite page.
TO
DISTORTION
METER
PHASE
SHIFTER
an attenuator to adjust the audio output of this detector, a phase -shifting network, a mixer stage to combine the output of the attenuator
with that of the phase shifter, an amplifier, a range attenuator to adjust amplifier gain, and the meter which measures the amplifier output.1 A functional diagram is shown in Fig. 14-2.
In operation, a sine wave from a stable oscillator is applied both to
the transmitter and the phase shifter of the RCA 69-C meter. The
phase -shifting network is adjusted until the signal is exactly in phase
with that derived from the output of the transmitter. The output
signal from the transmitter is adjusted in amplitude by the attenuator
so that its fundamental -frequency component is exactly equal to the
output of the phase shifter. In other words, the amplitude and phase
controls are adjusted until a minimum meter reading is obtained.
Each of these two signals is impressed on the grid of one of two mixer
tubes, whose plates are connected in push-pull by means of a transformer. The difference voltage of the two input signals appears
across the secondary of this transformer and is at minimum value
when the distorted and undistorted signals are adjusted in phase and
amplitude to have minimum difference. With this adjustment, the
3
For schematic and other data, see Appendix.
118
BROADCAST OPERATORS HANDBOOK
fundamental -frequency component of the distorted signal is canceled
out by the sine -wave signal, the difference voltage containing the distortion components. This difference voltage is amplified and the meter
reads the total rms distortion directly.
Noise and distortion measurements should be run on broadcast
transmitters at least every six months, as well as a complete frequency
run to determine frequency response of the equipment. For the guidance of the transmitter operator, the following excerpts from the "FCC
Standards of Good Engineering Practice" that directly affect his
duties, are presented.
Excerpts From Standards
Section 3.46 requires that the transmitter proper and associated
transmitting equipment of each broadcast station shall be designed,
constructed, and operated in accordance with the "Standards of Good
Engineering Practice" in addition to the specific requirements of the
"Rules and Regulations of the Commission."
The specifications deemed necessary to meet the requirements of
the "Rules and Regulations" and "Good Engineering Practice" with
respect to design, construction, and operation of standard broadcast
stations are set forth in the following text. These specifications will
be changed from time to time as the state of the art and the need
arises for modified or additional specifications.
A. Design. The general design of standard broadcast transmitting
equipment [main studio microphone (including telephone lines, if
used, as to performance only) to antenna output] shall be in accordance with the following specifications. For the points not specifically
covered, the principles set out shall be followed.
The equipment shall be so designed that:
(1) The maximum rated carrier power (determined by section 3.42)
is in accordance with the requirements of section 3.41.
(2) The equipment is capable of satisfactory operation at the
authorized operating power or the proposed operating power with
modulation of at least 85 to 95 per cent with no more distortion than
given in (3).
(3) The total audio -frequency distortion from microphone terminals, including microphone amplifier, to antenna output does not
exceed 5% harmonics (voltage measurements of arithmetical sum or
r.s.s.) when modulated from 0 to 84%, and not over 7.5% harmonics
(voltage measurements of arithmetical sum or r.s.s.) when modulating
MEASURING NOISE AND DISTORTION
119
85% to 95%. (Distorticn shall be measured with modulating frequencies of 50,100, 400, 1000, 5000, and 7500 cycles up to the tenth harmonic or 16,000 cycles, or any intermediate frequency that readings
on these frequencies indicate is desirable.)
(4) The audio -frequency transmitting characteristics of the equipment from the microphone terminals (including microphone amplifier
unless microphone frequency correction is included, in which event
proper allowance shall be made accordingly) to the antenna output
does not depart more than 2 db from that at 1000 cycles between 100
and 5000 cycles.
(5) The carrier shift (current) at any percentage of modulation
does not exceed 5%.
(6) The carrier hum and extraneous noise (exclusive of microphone
and studio noises) level (unweighted r.s.s.) is at least 50 db below
100% modulation for the frequency band of 150 to 5000 cycles and at
least 40 db down outside this range.
B. Operation. In addition to the specific requirements of the rules
governing standard broadcast stations, the following operating requirements shall be observed:
(1) The maximum percentage of modulation shall be maintained at
as high a level as practicable without causing undue audio -frequency
harmonics, which shall not be in excess of 10% when operating with
85% modulation.
(2) Spurious emissions, including radio -frequency harmonics and
audio -frequency harmonics, shall be maintained at as low a level as
practicable at all times in accordance with good engineering practice.
(3) In the event interference is caused to other stations by modulating frequencies in excess of 7500 cycles or spurious emissions, including radio -frequency harmonics and audio -frequency harmonics outside the band plus or minus 7500 cycles of the authorized carrier
frequency, the licensee shall install equipment or make adjustments
which limit the emissions to within this band or to such an extent
above 7500 cycles as to reduce the interference to where it is no longer
objectionable.
(4) The operating power shall be maintained within the limits of
5% above and 10% below the authorized operating power and shall
be maintained as near aE. practicable to the authorized operating
power.
(5) Licensees of broadcast stations employing directional antenna
systems shall maintain the ratio of the currents in the elements of the
BROADCAST OPERATORS HANDBOOK
array within 5% of that specified by the terms of the license or other
instrument of authorization.
(6) In case of excessive shift in operating frequency during warmup periods, the crystal oscillator shall be operated continuously.
The automatic -temperature -control circuits should be operated continuously under all circumstances.
120
Part
5
WE'RE OFF THE AIR
Chapter
15
EMERGENCY SHUTDOWNS
the situation that invariably causes a state of panic in
the newcomer to a transmitter operating job. In nearly all instances he is alone, with the responsibility of correcting the
trouble as quickly as possible to avoid loss of revenue by his employer.
The highest efficiency in correcting trouble will come with more experience at the particular installation. The operator, however, who
can visualize general circuit theory in relation to the particular circuits
with which he is concerned will find a logical and natural sequence of
looking for the fault. The main requirement quite naturally is to become thoroughly acquainted with the circuits used. He should be able
to draw from memory a good general functional picture of all circuits,
and be able to draw a block diagram of the sequence of operation of
starting relays and protective relays in the power -control circuits.
It is obvious that confidence and peace of mind can be achieved only
by a complete familiarity with all circuits and their relation to the
over-all performance of the transmitter.
It is, of course, impossible to set down a definite method of locating
and clearing specific troubles of any kind or description. We hope,
however, to be ableto set forth a clear concise approach to procedures
in general; that is, a logical and straightforward means of meeting
emergencies.
There is one piece of equipment at the transmitter installation that
should be the central focusing point for the operator's first attention
when trouble occurs. This is the modulation meter which has an r -f
input indication meter that reads a definite place on the scale 'for
normal operation, and, of course, the percentage modulation indicator.
The purpose of this will be evident in the following discussions.
At the first interruption of the program, or the occurrence of noise
or distortion in the monitoring loudspeaker, this modulation monitor
should be observed. Let us assume that the r -f input meter is at normal scale which assures us that the trouble is not in the r -f section
THIS Is
121
BROADCAST OPERATORS HANDBOOK
122
because any trouble there would cause some deviation in the r -f input
to the meter.
The following is a procedure to follow when the program suddenly
stops from the loudspeaker:
R -f input meter shows normal, modulation meter shows modulation taking place. Trouble obviously in monitoring line or amplifier and we are not off the air.
2. R -f input normal, no modulation as shown on meter.
Trouble either in audio section of transmitter, line amplifier,
program line from studio to transmitter, or at studio.
Call studio control to ascertain condition at that point. If everything there is normal, check line by patching line into monitor
amplifier or spare amplifier to see if program is coming into the
transmitter from line. If not, notify control to feed program on
spare line and call local test board of Bell Telephone Co. If
coming in satisfactorily from line, use spare line amplifier to feed
transmitter. If the regular line amplifier is working normally,
then the trouble obviously lies in the audio section of the transmitter itself. Usually any trouble here will be indicated by abnormal plate -current meter readings, and, of course, tube trouble
is the most common source of program interruption.
1.
The same procedure should be used where noise or distortion occurs,
first checking with studio, then line, line amplifier, and audio section
of transmitter. If all speech input tube currents are zero, then the
trouble is in the associated power supply. Most likely trouble again
is due to a tube, and it should be changed upon indication of abnormal plate current. Next in line comes bleeder resistors, resistor taps
from bleeder supply, and line -to -plate circuits of tubes. Power -supply
component parts usually show a visual indication of damage, such as
a smoking part, unless opened up.
If, at the first indication of trouble, a glance at the modulation
monitor position shows zero or low r -f input, then the trouble lies in the
r -f stages of the transmitter. The operator must accordingly proceed
to check for the trouble in the r -f section by observing all r -f circuit
meter indications. Observation of plate and grid current meters
aid in quickly determining the faulty stage.
When the transmitter is shut down by relay operation in the control
circuits, the cause of the failure is quickly traced if the operator is
EMERGENCY SHUTDOWNS
123
familiar with relay sequence and functions. Control circuits are divided into two functional purposes: (1) those which control circuits to
the primaries of power supplies, and (2) those of protective functions.
Pilot lights are often associated with the various relays to show when
open or closed. As stated before, the sequence of operation should
be committed to memory. The filament power supply, for example,
will not operate until the cooling motor contactors have functioned
to supply the cooling medium (water or air) to the tubes. After the
filament contactor has applied filament voltage, the plate -voltage contactor will not operate until the time delay relay has functioned, etc.
Rectifier tubes of the mercury-vapor type nearly always arc -back
several times before expiring. When arc -back indicators are used, the
faulty tube may be quickly observed and changed immediately.
Other troubles in high -voltage power supplies nearly always show
signs of physical deterioration as stated before.
Short circuits which cause a quick tripping of overload relays are
always the most difficult troubles to locate. In some difficult troubles
of this kind, overload relays have been strapped out of the circuits,
and limiting resistors put in the lower current fuse box to limit the
amount of current flowing. The circuits were then visually observed
for arc-overs with doors open and interlock switches short-circuited.
This is a dangerous procedure, however, and should be left to the more
experienced operators. More than one man should carry out any
unusual procedure of this kind.
This all may be summarized into the most important factor. Be
familiar with the transmitter, and know what indications would be
for the most common sources of trouble such as tubes and power supplies for the various circuits.
Chapter
16
WHY PREVENTIVE MAINTENANCE
any preventive maintenance schedule,
of course, is to reduce as much as possible the likelihood of
failure during the broadcast day of any component part of the
broadcasting installation. Regular maintenance schedules are in force
at most broadcast stations, and do much to increase their useful life
THE PRIMARY PURPOSE of
and anticipate and prevent many tube and parts failures that would
occur if neglected.
Preventive maintenance of any sort of equipment may be defined
as a systematic series of operations performed periodically on the
equipment in order to prevent breakdowns. This type of maintenance
may be divided into two phases: work performed while the equipment
is functioning and work performed during the normal shutdown periods. Here we are concerned only with the shutdown period preventive
maintenance.
The importance of preventive maintenance cannot be overestimated.
The owners of a broadcast station depend upon its being on the air
every second of its scheduled periods of transmission. It is of the
utmost importance that the personnel of radio stations properly maintain their equipment so that lapses in the transmission will be kept to
a minimum.
Cleanliness of equipment is of utmost importance since colleetion
of dust and dirt has been known to cause a number of troubles. This
is particularly true in the higher power stages of transmitters, since
accumulation of foreign matter over a period of time reduces the voltage insulation to a point where leakage currents and arc-overs are
common. High -voltage contacts have an extreme tendency to collect
dirt (this is the principle used in electronic smoke eliminators) , and
the higher relative humidity existing in summertime or southern locations tends to aggravate this characteristic. A dusting and clean-up
procedure, then, is a desirable nightly procedure at a transmitter plant.
A source of dry air under pressure is a common means of blowing out
dirt, dead insects, and the like from inaccessible corners and variable
124
WHY PREVENTIVE MAINTENANCE
125
tuning capacitors. Insulators, safety gaps, etc. should be polished
with a dry cloth or carbon tetrachloride used to loosen excessive dirt
and grime.
Proposed Transmitter Maintenance Schedule
In order that preventive maintenance be effective, it is essential that
it be performed at regular intervals; that is, certain portions of the
equipment must be inspected for certain things every day while other
parts of the equipment need only be inspected weekly or monthly in
addition, of course, to those things which are inspected daily. Below
will be found a comprehensive maintenance scheduler which may be
considered as a guide to anyone desiring to set up such a means of
preventing breakdowns. Naturally, items may be included in this
schedule which may be felt to be unnecessary at some particular transmitter, but it has been compiled with the thought that every precaution should be taken.
Later on in this chapter will be found the actual preventive
maintenance schedule which is followed at Station WIRE.
TRANSMITTER MAINTENANCE
A. DAILY
1. Hourly read all meters and check power tube filament voltages.
temperatures. Check water temperature of water-cooled tubes.
3. Check for correct cabinet temperature of air around high -voltage rectifiers.
4. After shutdown make a general inspection for overheated
components, such as capacitors, inductors, transformers, relays,
and blowers.
5. Investigate any peculiarities of meter readings.
6. In the event of overloads, examine safety gaps and transmitter
components for arc pits, etc. Clean and repolish surfaces
where arcs have occurred. Reset gaps if necessary. Investigate cause of outages.
7. In the event of lightning or heavy static discharges, inspect
the transmission line, terminating equipment, and antenna including gaps. Polish pitted surfaces.
8. If gas filled co -ax is used, check pressure.
2. Check air-cooled anode
1
By courtesy of RCA Mfg. Co.
BROADCAST OPERATORS HANDBOOK
126
B. WEEKLY (In addition to above)
1. Immediately after shutdown, check antenna terminating components for signs of overheating.
2. Clean antenna tuning apparatus. Check for arc pits, etc.
Clean and polish gaps and adjust if necessary.
3. Test antenna monitor rectifier tubes.
4. Calibrate remote antenna meters against meters in the antenna.
5. Clean transmitter with vacuum.
6. Clean component parts of transmitter.
a. Brush terminal boards,
b. Clean insulators with carbon tet,
c. Clean power tubes and high voltage rectifiers with tissue
and alcohol (or distilled water).
7. Check filament voltages and d-c voltages at the tube socket
of all tubes which are not completely metered by panel meters.
8. Check air flow interlocks for proper operation. Check all door
interlocks for proper operation.
9. Check operation of grounding switches. Examine mechanical
10.
operation and electrical contacts.
Inspect blowers for loose impellers, free rotation, and sufficient
oil.
11.
12.
13.
14.
15.
16.
17.
18.
Inspect relays for proper mechanical and electrical operation.
If necessary, clean and adjust components.
Inspect air filters; clean if excessive dirt has accumulated.
Check all sphere and needle gaps. Clean any pits or dirt.
Check gap spacings.
Check filter bank surge resistors with ohmmeter.
Check any power tube series resistors with ohmmeter.
Check power change switches if used; check for no serious
arcing during day -night antenna change -over if used.
Make general performance check-up. Distortion, noise, and
frequency response. Observe modulated wave form on CRO.
Check neutralization by cutting crystal oscillator and observing grid currents. Observe overmodulation waveform envelope on CRO.
proper operating voltage for pure tungsten filament
tubes. Operate at lowest voltage permissible as indicated by:
a. AM transmitters-distortion and carrier shift checks.
b. FM transmitters-decrease filament voltage until output
begins to drop.
19. Check
WHY PREVENTIVE MAINTENANCE
127
c. Operate filaments approximately 1% above filament voltage determined in a or b.
20. If water cooling is employed check entire system for any signs
of leakage and for electrical leakage.
21. Check pressure of any gas -filled capacitors.
C. MONTHLY (In addition to above)
1. Make detailed inspection of all transmitter components with
whatever tests of parts that may seem advisable.
2. Clean and inspect all vacuum and rectifier tube socket con-
tacts, and the tube pins.
3. Clean air filter or replace. Brush dust from blower impellers,
canvas boots, etc.
4. Clean and adjust all relay contacts. Clean pole faces on con-
tactors. Replace badly worn contacts.
5. Oil blower motors (carefully).
6. Operate all spare vacuum tubes for a minimum of two hours
under normal operating conditions. Clean up any gassy tubes.
7. Operate all spare mercury vapor rectifiers normally, after first
applying filament only for a minimum of 30 minutes. Store
S.
tubes upright.
Inspect all variable inductor contacts for tension, signs of
overheating, and dirt. Clean and adjust as required. Carbon
tet or crocus cloth may be used for cleaning. Do not use emery
cloth.
9. Check for proper operation of time delays, notching relays
and any automatic control systems.
attenuator and low
level switching contacts with cleaner; wipe off excess.
11. Check tubes in station monitor equipment, such as frequency
monitor, modulation monitor, etc.
12. Clean switches in monitoring equipment with cleaner.
10. Clean audio equipment (console, etc.)
D. QUARTERLY (In addition to above)
1. Lubricate tuning motors and inspect for ease of rotation.
2. Check all indicating meters (a -c, d-c, r -f) . Check a -c filament voltmeters with an accurate dynameter type of meter.
3. Check all connections and terminals for tightness.
4. Inspect any flexible cables to door connections.
5. Inspect and lubricate if necessary any flexible drive cables.
6. Inspect, clean, and service (if necessary), all switches. Volt-
BROADCAST OPERATORS HANDBOOK
128
meter selector switches, push button switches, control switches,
etc.
Clean transmission line insulators and take up slack if open
wire lines are used.
8. Check oil circuit breakers, if used, for sufficient oil and loose
or defective parts.
E. SEMIANNUALLY (In addition to above)
1. Test transformer oil for breakdown and filter it if necessary
(power company).
2. Check protective overload relays or circuit breakers for correct operation.
a. A -c overload relays may be checked by shorting the
high -voltage transformer secondary.
b. D -c overload relays may be checked by shorting the d.c.
through the relay in the circuit protected by the relay.
MAINTENANCE SUGGESTIONS
A. CONTACTORS GENERAL
1. Inspect all parts at regular intervals.
2. Parts should be kept free of dirt, grease, and gum.
3. Replace contact tips as needed (keep spares on hand).
4. Keep all contacts and interlocks clean and free from burrs
and pits.
5. Main copper contacts should not be lubricated. Darkened
tips due to overheating, or copper beads should be dressed with
a fine file. (Do not use emery cloth.)
7.
B. CONTACTORS-HUM
Clean off rust, dirt, or grease from pole piece and armature
and apply a small quantity of light machine oil to prevent
rusting.
2. Check pole shader and its circuit. Armature contact surfaces
above and below shader should be approximately equal.
3. Armature to pole piece contact should be made over a large
area; gaps should not be over 1/1000 to 2/1000 inch. If the
contact area is small or the gap too wide, the pole face may be
ground or filed down to a FLAT surface.
C. CONTACTS SILVER
1. If not burned or pitted they may be cleaned with a contact
burnishing tool.
2. If burned and pitted, dress with a small fine file and polish
with crocus cloth.
1.
WHY PREVENTIVE MAINTENANCE
129
Maintenance of Water -Cooling Systems
As has been stated before, it is not the purpose of this section to
duplicate otherwise available data on the engineering aspects of transmitting equipment. However, since cooling systems of transmitters
of more than 1 -kw rating are so highly important to the problem of
keeping the station on the air, some factors of operating and maintaining these cooling systems that have not been emphasized before will
be presented here for the operator's convenience.
Fundamentally, the power rating of a tube in free air is determined
by three characteristics, namely:
1. Plate voltage that may be safely applied (dependent on physical
parameters) .
2. Electron emission of filament.
3. Amount of heat that can be dissipated at anode without causing
overheating (dependent on physical and electrical parameters).
Thus it becomes apparent that insofar as the operator is concerned,
the third characteristic is the only variable in the problem of heat
dissipation, since electrical parameters such as operating angle in electrical degrees, bias voltage, etc. are more or less under the direct supervision of the operator.
In water-cooled systems, the temperature of the water at the outlet
of the tube jacket should never exceed 70° C. (158° F.) as indicated
by the water thermometer at that point. The rate of flow should be
approximately 15 gallons per minute; 20 gallons per minute is more
beneficial in retarding accumulation of foreign matter in the jacket
and the prevention of steam bubbles along the anode surface. The effect
of increasing the flow of water is to increase the turbulency of flow.
This increased turbulency breaks down the layer of steam present at
the anode wall and increases the heat exchange between the wall and
the water. The turbulency of the flow may be increased by mechanical
means, such as baffles.
Extraordinary precautions must be taken in the installation of the
tube in the water jacket. The movable metal parts of the jacket should
be coated with a light film of oil to help prevent corrosion. The tube
should then be placed gently in the jacket, and after it is correctly
seated the retaining studs or jacket clamping device is fastened firmly
into place to force the flange of the plate into solid contact with the
watertight gasket. The electrical connections may then be made. Care
should be taken that the wires are not near ôr do not touch the glass
130
BROADCAST OPERATORS HANDBOOK
bulb. Should this precaution be neglected, puncture of the glass from
corona discharge is likely to occur. Particular care should also be
observed in making the connection between hose and jacket tight and
clean. Because of electrolysis, trouble is likely to develop at this point,
and close inspection every two or three weeks is advisable.
A reasonably rigid maintenance schedule should be observed on the
entire system to forestall trouble from water leakage, scale formation,
or the formation of steam bubbles with resultant transmitter shutdown
and loss of time on the air. Leaks, of course, may be temporarily
sealed to a certain extent by using friction tape until permanent repairs can be made after sign -off. In some instances, it is possible to
cover the radiator used to cool the water with a blanket until the inlet
temperature of the water rises to around 104° F., resulting in a slight
expansion of the parts which will aid in sealing a minor leak.
Scale formation, if and when it occurs, will prevent adequate transfer of heat from anode to water. If it becomes necessary to remove
the tube for this or any other reason, the tube should be lifted carefully from the jacket after the clamping device has been released.
Sticking of the tube often occurs, and in this case a gentle twisting
back and forth while lifting will free the tube. Immersion of the plate
in a 10% solution of hydrochloric acid is usually recommended to dissolve scale formation. The anode should then be rinsed thoroughly
in distilled water.
The formation of steam bubbles may be checked periodically by
using a good insulating rod at least six feet long. This should be moved
along the jacket while aural observations are made. Precautions
should be taken to assure the operator's safety, including grounding
the testing tube between water jacket and the observer by a "hot
stick" or similar arrangement.
A convenient way for the operator to keep an approximate check on
the heat dissipation of the tube is by use of the formula:
P(KW)
- n (t04 ti)
where:
t; = known initial temperature of water in degrees C
to = temperature of water at jacket outlet in degrees C
n = rate of flow in gallons per minute.
It should be remembered here that the filament heat is also being
dissipated into the watet. It is recommended that the operator read
WHY PREVENTIVE MAINTENANCE
131
the manufacturer's instructions that come packed with transmitting
tubes. Some of the foregoing information is from RCA tube instruction sheets.
Forced -Air Systems
Although the problems of deteriorating hose, leaky hose connections,
electrolysis, and troublesome flow -interlocks have been largely overcome by porcelain reels, reliable flow -interlocks and completely nonferrous circulating systems (all -copper tank and pipes), the familiar
problems have remained of scale formation, gradual water evaporation,
and relatively large time consumption in changing tubes.
In recent years, the elimination of the water-cooling system has been
accomplished for transmitters up to and including 50 -kw rating by the
development of forced -air cooling systems. Control circuits for this
system are greatly simplified, consisting as they do of an air -interlock
damper on top of the blower motor, which prevents application of
filament and plate voltages until normal air -flow pressure is present,
and a blower motor "keep -alive" relay, which is a time -delay relay
keeping blower motors functioning 4 to 7 minutes after filament voltage is removed.
Maintenance of forced -air systems is simpler than that of water
systems but is just as important for trouble -free operation.
The canvas air ducts should be cleaned about once a month by removing them, turning them inside out, and using a vacuum cleaner
to remove accumulated dirt. While these ducts are removed, a cloth
may be used to slide between the fins of the tube, especially in against
the tube anode, to remove dust. Care should be taken not to damage
the mercury air -flow switches which are mounted on the blower housing. These switches prevent the application of filament and plate voltages until proper air flow is present. Both sides of the air -flow vanes
(half -circle disks used to operate the mercury switch) should be wiped
clean with a cloth or chamois and a small wire brush may be used
to clean the corners of the °an blades. A vacuum cleaner then should
be used to pick up any dust from inside the bottom of the blower
frames.
After this cleaning procedure has been carried out, the blowers
should be started to check ,he air-flow vanes for proper operation of
the mercury switches, canvas ducts replaced, and over-all operation
checked.
132
BROADCAST OPERATORS HANDBOOK
STATION WIRE PREVENTIVE MAINTENANCE SCHEDULE
The following preventive maintenance schedule has been in use at
Station WIRE and as may be seen from designations, it is planned to
have this work done on each Thursday night after the transmitter goes
off the air. This arrangement is different from the general schedule
presented earlier in this chapter inasmuch as some of the maintenance operations are performed weekly, others monthly, and the last
group is performed five or six times per year.
First Thursday Night of Month Maintenance Schedule
Before turning main transmitter off, after conclusion of program
from studio, read both North and South Tower Antenna Current
meters. Check and adjust Remote -Reading Antenna meters, on the
operating console, to read with their respective Tower meters. Turn
main transmitter off in accordance with the usual sign-off procedure.
Shift antenna change -over switch to the Auxiliary Transmitter side.
Turn on Auxiliary Transmitter for one-half hour check. Make regular
transmitter log on this half-hour operation. Also, enter the readings
of both the Antenna Current and Remote-Reading Antenna meters on
this log sheet.
In addition to the daily sign -off procedure, carefully remove the
two oscillator tubes and wipe them free of dust.
Clean both sides of plate glass partitions in front of the three large
tubes. Use damp cloth on this and dry with paper hand towel.
Open all glass meter partition doors at top of transmitter and clean
glass on both sides. Clean all glass meter faces including those on the
power panel and Audio racks.
After Auxiliary Transmitter has been tested, turned off and log completed, BE SURE TO RETURN ANTENNA CHANGE-OVER
SWITCH TO THE 5-D OPERATING SIDE.
Vacuum-clean the top of transmitter cabinets.
Wipe off all insulators on top of transmitter and insulators holding
copper bus bar to rear wall, and all insulators on top of phasing cabinet (to transmission line), and all insulators on modulation transformer and reactor.
Wipe off all insulators and all components on the filter rack (filter
condensers, reactors, resistors, relays, etc.) .
Remove all rectifier tubes (remember to keep them upright in case
of mercury-vapor rectifiers) from their sockets. Remove the shields
and clean the sockets and other components under shields.
WHY PREVENTIVE MAINTENANCE
]
23
Open all front interlock doors. Use vacuum to clean all reachable
space from the front, behind center panels, tube shelves, and floor
plates.
Wipe off the four high -voltage insulators between modulator blower
motors and the insulator above each of the high -voltage rectifiers.
Also the insulators above the first and second audio stage tubes. Wipe
off insulators on condenser above power-amplifier blower motor. Also
the rectifier and oscillator feed-thru insulators in bottom of Exciter
Unit.
Clean all components in modulator section ABOVE the final -tube
holders. Inspect and tighten all connections in this half section.
Open rear doors on modulation and final stage. Wipe off floor of
both from the rear. Wipe off all three blower frames. BE VERY
CAREFUL OF ALL INSULATORS, ESPECIALLY MICALEX.
Take and record reading of "Filament Elapsed Hours Clock."
REPORTS: Make Transmitter Operating Room Report, as shown
in Fig. 16-1, that this schedule was completed or any deviations from
it. Also any other observations made.
TRANSMITTER OPERATING ROOM REPORT
DATE
7-15-1947
PROGRAM
TIME
Melody Billboard
ANNOUNCER
5134 ym
o
(Musical ET)
Fisher
CONTROL OPERATOR
ORIGINATED
I3n5ort
TRANSMITTER OPERATOR
STU
C
(BT)
Ennes
REMARKS:
Carrier
off thirty seconds due electrical
Picteil lead on directional
burned open.
storm.
antenna relay in phasing'unit
Replaced with temporary clip jumper.
BY
(PILE IN
011.,112T
AT
MI TM
.jL,
OMI
I.OINE
)
transmitter operating-room report as used by
the author at Station WIRE.
Fig. 16-1. An example of a
FINAL CHECK: Turn on transmitter in usual manner, first on low
power of 1000 watts. If everything is normal then check the 5000 watt operation.
134
BROADCAST OPERATORS HANDBOOK
Second Thursday Night of Month Maintenance Schedule
Remove canvas air ducts beneath modulator and final tubes and
place paper or cloth cover over blower openings. Carefully clean between fins of all three large tubes by sliding cloth between fins especially in against tube anodes.
Clean all components in lower half of modulator section. Check all
components in this section including terminal blocks. .
Remove temporary cover over blower openings. Wipe off both sides
of air flow vanes. Check for free movement.
Brush corners of fan blades with small brush, then vacuum.
Some dust usually remains in bottom of blowers and should be removed by running each blower and using a deflector over blower opening on top to direct air away from tube bases. After all three are
cleaned, and with blowers running, check to see that the air -flow vanes
are operating mercury switches properly.
Replace canvas air ducts, and double-check for proper cond.
Run regular Auxiliary Transmitter test.
REPORTS: Make Transmitter Room Report that this schedule was
completed or any deviations from it. Also report if conditions of
air filters on back doors necessitates replacement.
FINAL CHECK: Check for low power and high power operation in
usual manner.
Third Thursday Night Maintenance Schedule
Regular Auxiliary Transmitter check.
Clean relay contacts in phasing unit.
Inspect and clean lightning gaps on transmission line above phasing
unit.
Tighten and clean all connection and chassis of tuning assemblies
in tower houses. Clean relay contacts.
Check relay operation for Directional and Non -Directional operation by turning transmitter on as outlined for previous maintenance
schedules.
Fourth Thursday Night Maintenance Schedule
Regular Auxiliary Transmitter check.
Clean input and output attenuators on 96-A line amplifier, also
monitor attenuator. (Use Lubriplate and clean cloth.)
Vacuum jack strips on speech input panel.
WHY PREVENTIVE MAINTENANCE
135
Inspect for tightness connections on relays in power -control panel.
Clean the above relay contacts.
Wipe off filament rheostats on power control panel.
Wipe off all accessible places on power control panel.
Clean "modulator bias" relay contacts.
Clean the contacts of the two overload relays and time -delay relay
in exciter unit.
Clean and inspect all components in exciter unit not covered in
previous schedules.
Vacuum inside of power -control console, tighten all connections.
Regular transmitter check for normal operation.
Fifth Thursday Night Maintenance Schedule
(where this occurs)
Regular Auxiliary Transmitter check.
Check all tubes (with tube checker) of 96-A line amplifier and associated power supply, modulation monitor, frequency monitor, program
monitor, and speech input tubes.
Check 6K7 balance in 96-A line amplifier.
Check spare line amplifier for proper operation.
Check lubrication of all motors including toilet and shower water
pumps and exhaust fans.
Take inventory of new transmitter log sheets, transmitter -room report sheets, spare tubes, spare fuses, indicator lamps, and illuminating
lamps for building and towers.
Chapter
17
PREVENTIVE MAINTENANCE INSTRUCTIONS
N THE PRECEDING chapter some general facts about preventive
maintenance were presented together with schedules showing when
the different operations should be performed. Inasmuch as some
of these operations deal with apparatus that can easily be damaged
unless proper care is exercised, certain procedures should be followed
so that no damage does result from the periodical inspections and so
that if repairs to the apparatus are necessary, they can be effected
properly. It should be borne in mind that the data in the following
pages are general for the most part and it may be that some manufacturers recommend specific procedures for their products, which, of
course, should be followed.
The reasons why preventive maintenance operations are followed
seem obvious with no further comment. It might be well, however, for
the men who are responsible for this maintenance work to keep in
mind that the procedures discussed in the following pages have been
designed to
Combat the detrimental effects of dirt, dust, moisture, water, and
the ravages of weather on the equipment.
2. Keep the equipment in condition to insure uninterrupted operation for the longest period of time possible.
3. Maintain the equipment so that it always operates at the maximum possible efficiency.
4. Prolong the useful life of the equipment.
1.
Preventive Maintenance Operations
The actual work performed during the application of the preventive
maintenance schedule items is divided into six types of operations.
Throughout this section, the lettering system for the six operations is
as follows:
136
PREVENTIVE MAINTENANCE INSTRUCTIONS
F-Feel
I-Inspect
T-Tighten
137
C-Clean
A-Adjust
L-Lubricate
The "Feel" operation is used most extensively to check
rotating machinery (such as blower motors, drive motors, and generators) for over -heated bearings. "Feeling" indicates the need for lubrication or the existence of some other type of defect requiring correction.
Normal operating temperature is that which will permit the bare hand
in contact with the motor -bearing cover for a period of 5 seconds
without feeling any discomfort. The "Feel" operation also is applied
to a few items other than rotating machinery; the "Feel" operation
for these items is explained in the discussion of each specific item.
Note: It is important that the feel operation be performed as soon
as possible after the shutdown, and always before any other maintenance is done.
b. Inspect (I). "Inspection" is probably the most important of all
the preventive maintenance operations. If more than one man is available to do this work, choose the most observant, for careful observation is required to detect defects in the functioning of moving parts
and any other abnormal conditions. To carry out the "Inspection"
operation most effectively, make every effort to become thoroughly
familiar with normal operating conditions and to learn to recognize
and identify abnormal conditions readily.
"Inspection" consists of carefully observing all parts in the equipment. Notice such characteristics as their color, placement, and state
of cleanliness. Inspect for the following conditions:
(a) Overheating, as indicated by discoloration, blistering or bulging
of the part or surface of the container; leakage of insulating compounds; and oxidation of metal contact surfaces.
(b) Placement, by observing that all leads and cabling are in their
original positions.
(c) Cleanliness, by carefully examining all recesses in the units for
accumulation of dust, especially between connecting terminals. Parts,
connections, and joints should be free of dust, corrosion, and other foreign matter. In tropical and high -humidity locations, look for fungus
growth and mildew.
(d) Tightness, by testing any connection or mounting which appears
to be loose, by slightly pulling on the wire or feeling the lug or terminal screw.
a.
Feel (F).
138
BROADCAST OPERATORS HANDBOOK
c. Tighten (T). Any movement of the equipment caused by transportation or by vibration from moving machinery may result in loose
connections which are likely to impair the operation of the set. The
importance of firm mountings and connections cannot be overemphasized; however, never tighten screws, bolts, and nuts unless it is definitely known that they are loose. Fittings that are tightened beyond
the pressure for which they were designed will be damaged or broken.
When tightening, always be certain to use the correct tool in the
proper size.
d. Clean (C). When the schedule calls for a "Cleaning" operation,
it does not mean that every item which bears that identifying letter
must be cleaned each time it is inspected. Clean parts only when inspection shows that it is necessary. The "Cleaning" operation to be
performed on each part is described later on.
e. Adjust (A). Adjustments are made only when necessary to restore
normal operating conditions. Specific types of adjustment are described later.
f. Lubricate (L).
Lubrication means the addition of oil or grease
to form a film between two surfaces that slide against each other, in
order to prevent mechanical wear from friction. Generally, lubrication
is performed only on motors and bearings.
Note: When a part is suspected of impending failure, even after
protective maintenance operations have been performed, immediately
notify the person in charge who will see that the condition is corrected
by repair or replacement before a breakdown occurs.
Suggested List of Tools Necessary for Relay and
Commutator Maintenance
A number of items on the preventive maintenance schedule require
work of a special and somewhat delicate nature. This work includes
cleaning and repairing relay contacts, cleaning plugs and receptacles,
polishing commutators, and adjusting motor and generator brushes.
To do the work properly, special supplies and specially constructed
tools are needed. A suggested list is given below:
Nonmagnifying dental mirror.
Cleaning brush, 2 -inch.
Canvas-cloth strip.
Sandpaper strip, fine.
Sandpaper strip, semifine.
PREVENTIVE MAINTENANCE INSTRUCTIONS
139
Crocus -cloth strip.
Small relay crocus -cloth stick.
Relay -contact burnishing tool.
Fine-cut file.
Brush seating stone.
Commutator polishing stone.
Canvas -cloth stick.
Crocus-cloth stick.
Sandpaper stick.
1 Brush, cleaning, 1 -inch.
1 Brush, cleaning, 2 -inch (2) .
1 Carbon tetrachloride, quart can.
2 Cement, household, tube.
1 Cloth, canvas, 2 x 4-feet.
1 Cloth or canvas, strip, 2 x 6 -inch, cut from sheet (3).
1 Cloth, lint -free, package.
6 Crocus -cloth, sheets.
1 Crocus -cloth, strip, 3/4 x 6 -inch, cut from sheet (6) .
1 File, small, fine cut.
1 Lubricant, Vaseline, container.
1 Mirror, nonmagnifying dental.
6 Sandpaper sheets, #0000.
6 Sandpaper sheets, #00.
1 Sandpaper, #0000, 3/4 x 6 -inch, cut from sheet.
1 Sandpaper strip, #00, 3/4 x 6 -inch, cut from sheet.
1 Stick, crocus -cloth, large.
1 Stick, special, canvas -covered.
1 Stick, special, crocus -cloth stick for relays, small.
1 Stick, special, sandpaper covered.
1 Stone, commutator polishing stone.
1 Stone, brush seating stone.
50 Tags, small marker.
1 Tool, relay contact burnishing.
Construction for Relay and Commutator Tools
Crocus -cloth, canvas -cloth, and sandpaper sticks are constructed in
the following manner:
1. First prepare a length of wood 33/4 inches long, % inch wide,
and 1/16 inch thick or less. Cut one piece of crocus cloth 21/2 inches
long and 1 inch wide.
140
BROADCAST OPERATORS HANDBOOK
2. Fold the crocus cloth as in Fig. 17-1 (A) and cement it to the
stick. Note that both sides of the stick are covered. Place the stick
in the vise, press it and wait until the cement hardens. Cut off the
piece of crocus cloth which extends over the edge of the stick.
CROCUS CLOTH
"
2'4"
OR LESS
11-12
-
GLUE HERE
END VIEW
CROCUS CLOTH
GLUE HERE
6
GLUE HERE
'
U
SUITABLE
WIDTH
SANDPAPER
OR
CROCUS CLOTH
GLUE HERE
Fig. 17-1. The crocus -cloth stick (A) is used for cleaning
relay contacts and the one in (B) is for cleaning motor
or generator commutators.
3. Obtain three pieces of wood which measure 8 inches long, 1 inch
wide, and approximately 1/4 inch thick. Cut one piece of crocus cloth,
one piece of #0000 sandpaper, and one piece of canvas cloth, each
51/4 inches long and 1 inch wide.
4. Fold the long, narrow pieces of crocus cloth, sandpaper, and canvas cloth as shown in Fig. 17-1 (B) and cement one of them to each
of the three sticks. Note that in this case the fold is over one end of
the stick rather than over the sides. Place the sticks in the vise, press,
and wait until the cement hardens.
PREVENTIVE MAINTENANCE INSTRUCTIONS
141
Use and Care of Tools
Proper care of tools is as necessary as proper care of radio equipment. Any effort or time spent in caring for tools is worth while. Clean
them when necessary and always replace them so that they are easily
accessible. The following information will be helpful in using and caring for the tools listed below.
a. Crocus -Cloth Stick. The crocus -cloth sticks are used to clean contacts of relays in the radio equipment.
b. Large Commutator Sticks. Commutator sticks with covering of
sandpaper or canvas are used for cleaning commutators of electric
motors and generator sets.
c. Commutator Dressing Stone. The dressing stone is used only in
case of emergency to dress a commutator or motor generator.
d. Brush Seating Stone. The seating stone is used when a set of new
brushes is installed in alternators or exciters. Only a very limited
application of the seating stone is required to seat the average set of
brushes.
e. Electric Soldering Iron. The use of the soldering iron is generally
known. Remember to keep the tip properly tinned and shaped.
the
f. Allen Wrenches. Allen wrenches are used to tighten or remove
small
are
These
Allen setscrews on fan pulleys, motor pulleys, etc.
wrenches and should be kept in the cloth bag provided for that purpose. After use, wipe them off with an oily rag, replace them in the
bag, and restore them to the tool box.
g. Diagonal -Cutting Pliers. Diagonal pliers are used to cut copper
wire (no larger than No. 14) when working in small places. Do not
cut iron wire with the diagonals.
h. Gas Pliers. Gas pliers are used to hold round tubing, round studs,
or any other round metal objects that do not have screw driver slots
or flat sides for wrenches.
i. Long -Nose Pliers. Long-nose pliers are used to hold and dent
small wires and to grip very small parts. They are generally used
around delicate apparatus.
j. Adjustable End -Wrenches. Adjustable end -wrenches are designed
to remove or hold bolts, studs, and nuts of various sizes. Keep the
adjusting -nut free from dirt and sand and oil them frequently.
k. Nut -Driver Wrenches. Nut -driver wrenches are used to remove
nuts of various sizes. Choose a wrench that fits the nut snugly.
1. Screw Drivers. Screw drivers of different sizes are important tools
and must be kept in good condition. Select the proper size for the job
142
BROADCAST OPERATORS HANDBOOK
to be done. Never force a screw; if undue resistance is felt, examine
the threads for damage and replace the screw if necessary.
m. Shorting Bar. The shorting bar must be constructed at the station. Obtain a piece of wood about 15 inches long and 1 inch thick.
Fasten a piece of copper or brass rod or tubing securely to one end of
the stick in such a manner that the rod extends 12 inches beyond the
end of the stick. Solder a piece of heavy flexible wire about 18 inches
long to the metal rod at the point where it is fastened to the stick
and attach a heavy clip to the free end of the wire. When using the
shorting bar, always attach the clip to a good ground connection BEFORE making contact with the terminal to be grounded.
Vacuum Tubes
The purpose of tube maintenance is to prevent tube failures caused
by loose or dirty connections and to maintain the tubes in a clean
operating condition at all times. Certain types of vacuum tubes, especially those used in high -voltage circuits, operate at high temperatures.
Careless contact with the bare hands or arms causes severe burns.
Sufficient time must be allowed for the tubes to cool before handling.
Maintenance of vacuum tubes involves making minor adjustments
and cleaning. Tubes requiring the most frequent maintenance are
those used in high -voltage circuits. Because of their high operating
potentials, these tubes require more frequent inspection and cleaning
than tubes used in low -voltage circuits. Loose coupling at the terminals of high -voltage tubes will result in the terminals becoming
pitted and corroded. Loose connections cause poor electrical contact
and lower the operational efficiency of the unit in which they are employed.
Maintenance of vacuum tubes should be applied onlÿ when necessary. Too frequent handling may result in damage to the tube terminals and connections. As a rule, vacuum tubes need little maintenance;
therefore, when the program calls for maintenance, but inspection
shows that the tubes do not require it, the operation should be omitted.
It is advisable, however, to clean the glass envelopes of the tubes and
remove dust or dirt accumulations surrounding their immediate areas.
The object of the maintenance program is to maintain the tubes free
from dirt, oil deposits, and corrosion.
Vacuum tubes for maintenance purposes are divided into two groups:
(1) Transmitting -type tubes.
(2) Receiving -type tubes.
PREVENTIVE MAINTENANCE INSTRUCTIONS
143
Maintenance procedures required for vacuum tubes differ according
to types. Certain maintenance operations that must be performed
on transmitting -type tubes may be omitted in the maintenance of receiving -type tubes. Transmitting -type tubes are those used in transmitters, modulators, and h:gh-voltage rectifier units. Because of their
physical construction they require careful inspection and cleaning during maintenance.
Five procedures are reqLired to the performance of maintenance of
vacuum tubes: feel, inspect, tighten, clean, and adjust. The procedures
involved depend on the type of tube being maintained. Transmitting
tubes may require the application of the above -mentioned procedures,
while the procedures requized for receiving tubes are limited by tube
types.
Maintenance Procedures
The following procedures should be employed for the maintenance of
vacuum tubes:
Caution: Discharge all high -voltage capacitors before performing
any maintenance operations. Avoid burns by allowing sufficient time
for tubes to cool before har_dling.
Feel (F). (1) This operation should be applied only to high -voltage
tubes, such as those used in transmitters, modulators, and high-voltage
rectifier units.
Note: The following operations should be performed 5 to 10 minutes
after power has been removed from the tubes.
(2) Feel the grid, plate, and filament terminals of the tubes for excessive heat. Practice will determine the temperature to be accepted
as normal. For example, when two grid terminals are felt, one should
not be warmer than the other. Excessive heat at terminals indicates
poor connections.
Inspect (I). This maintenance operation is applicable to all types
of vacuum tubes and should be performed after the tubes have had
sufficient time to cool.
'1) Inspect the glass or metal envelopes of tubes for accumulation3 of dust, dirt, and grease. Inspect the tube caps and connector
clips for dirt and corrosion. Inspect the complete tube assembly and
socket for dirt and corrosion. Check the tube caps to determine
whether any are loose. On glass tubes, check the glass envelope to
determine whether or not it has become loosened from the tube base.
Replace tubes which have loose grid caps or envelopes when these
144
BROADCAST OPERATORS HANDBOOK
faults are discovered. If replacement is impossible, do not attempt to
clean or handle the tube, operate the tube as it is, providing that its
operation is normal. Enter the tube condition in the log so that replacement can be made at the earliest possible time.
(2) Examine the spring clips that connect to the grid plate, and
filament caps for looseness. Also examine all leads connected to these
clips for poorly soldered or loose connections. These leads should be
free of frayed insulation and broken strands. When removing clips
from loosened grid caps, extreme care must be exercised, particularly
if corrosion exists. Never try to force or pry a grid clip from the grid
cap of a tube as damage to the tube or grid cap may result. If the
grid cap is loose and it is necessary to remove the grid clip, first loosen
the tension of the clip by spreading it open; then gently remove (do
not force) the clip from the tube cap.
(3) Inspect the tubes to be sure they are secure in their sockets.
Certain types of receiving tubes used are mechanically fastened with
tube spring locks; others have sockets in which the tube itself is locked
in place. Inspect by turning the tube in clockwise direction in its
socket until it is locked in place. This type of socket is generally used
for the transmitting-type tubes. However, the firmness with which the
tube is held in place depends upon the tension of the terminals in the
socket. These terminals are of the spring type (contact springs) and
must have sufficient tension to make good contact against the tube
prongs. The tension can be tested by grasping the tube and turning it
first counterclockwise and then clockwise to its original position. If
the tube seems to snap into place as it is turned, the spring tension
of the socket terminals is firm enough; however, if the tension seems
weak, they may be tightened or adjusted as explained in the tube
maintenance procedure under "Adjust."
(4) Inspect all metal tubes for signs of corrosion and looseness of
mounting. Many receiving -type tubes have keyways in the center
of the tube bases. These keyways sometimes become broken, and have
a tendency to loosen the tube in the socket. Do not attempt to replace
tubes that have broken keyways unless it is absolutely necessary tr do
so, and it is possible to replace the tube correctly in its proper position. Inspect the tube sockets of metal tubes for cracks or breaks. Do
not force metal tubes into their sockets. If they are hard to replace,
examine the tube pins for signs of corrosion or solder deposits.
Tighten (T). (1) In performing this operation, take care not to
overtighten tube sockets, tube clamps, and tube socket insulators.
PREVENTIVE MAINTENANCE INSTRUCTIONS
145
Porcelain sockets and stand-off insulators crack due to heat expansion
if they are excessively tightened. Do not overtighten them. Care
should be taken when tightening the tube caps of high -voltage tubes.
Use the proper screw driver or tool; if the tool should slip it may fall
against the glass envelope of the tube and ruin a perfect tube.
(2) Tighten all tube connections, terminals, sockets, and stand-off
insulators which were found loose during the inspection procedure.
When tightening tube sockets having stand-off insulators, determine
before tightening whether the fiber washers between the socket and
the stand-off insulators are intact. If these fiber spacers are cracked
or missing, replace them before tightening the tube socket. Tightening
the socket without these spacer washers breaks or cracks the porcelain -tube socket.
Clean (C). In the performance of this item, clean only where necessary. Do not remove tubes for cleaning purposes unless it is impossible
to clean them in their original positions. If the tube must be removed,
exercise care in doing so. Do not attempt to clean the envelopes if
they are located in an out-of-the-way place; in this case remove them
for cleaning. When tubes are removed for cleaning, replace them
immediately afterward. Do not leave them where they may be
broken.
(1) Clean the entire tube assemblies with a clean dry cloth if the
glass envelope is excessively dirty. Wipe the glass envelope with a
damp cloth moistened in water. Polish after cleaning with a clean
dry cloth. Do not wipe me _,al tubes with a cloth moistened in water,
as this causes the metal body of the tube to rust. Use a cleaning agent
if the tube is excessively dirty because of oil deposits. Generally, metal
tubes with oil deposits on their envelopes can be cleaned successfully
by polishing dry with a clean dry cloth. The oil film remaining on the
metal body of the tube prevents the tube from rusting. To remove oiliness, corrosion, or rust from tube envelopes, moisten a clean cloth with
cleaning agent and clean the area affected until it is clean. Wipe dry
with a clean dry cloth.
(2) Clean the grid and -plate caps, if necessary, with a piece of
#0000 sandpaper, or crocus cloth. The paper should be wrapped
around the cap and gently run along the surface. Excessive pressure
is not needed; neither is it necessary to grip the cap tightly. Clean
the caps completely before replacing them on the tube terminals if
corrosion is noted on the grid or plate caps.
(3) When the tube sockets are cleaned and the contacts are acces-
146
BROADCAST OPERATORS HANDBOOK
sible, fine sandpaper should be used if corrosion is present on the contacts. Clean the contacts thoroughly after sandpapering. Clean all
areas surrounding tube sockets with a brush and a clean dry cloth; this
prevents dust and dirt from being blown back on the tube envelopes
when the unit is put back into operation.
Adjust (A). When performing this operation, care must be taken
to arrange all leads and terminals to correspond as closely as possible
with their original positions.
(1) Adjust all leads and tube connections. Check to determine if
the leads are resting on the glass envelope of the high -voltage tubes;
if they are, redress the leads so that proper spacing is obtained.
Examine all leads connecting to the tube caps. These should not be
so tight that they barely reach the caps of the tubes. If this condition is found, redress these leads so that enough "play" is obtained.
Adjust all grid clamps so that the proper tension is obtained. To increase the tension of tube clamps, close the spring clamps slightly
with a pair of long -nose pliers until the proper tension is obtained. Do
not flatten the clamps.
(2) Tube sockets used for transmitting -type tubes should be adjusted if the tube is found loose in its mounting. The terminals of
these sockets are spring -tensioned so that they may be adjusted
to increase the pressure against the tube pins. To adjust these contacts, simply bend them toward the center on the socket until the correct tension is obtained. Do not apply too much pressure to the spring
contacts; they may be broken from their mountings in the porcelain
socket.
(3) Any difficulty in removing or inserting metal tubes can be remedied easily. Remove the metal tube and examine the tube pins to
determine if solder or corrosion has accumulated on the pins. Remove
solder deposits with a penknife; then polish the pins with fine sandpaper. Do not use a soldering iron to remove solder deposits; this
makes them worse, as the solder is built up on the pins rather than
removed. To remove corrosion, use fine sandpaper, but never use it
unless it is absolutely necessary. Saturate a small piece of cleaning
cloth with light lubricating oil or petroleum jelly, and wipe the tube
pins. Remove the excess oil from the pins by wiping them almost dry
with a clean dry cloth. If these procedures are followed, no difficulty
will be experienced in removing or reinserting the metal tube into its
socket.
Caution: Do not force metal tubes into their sockets. Do not pry or
PREVENTIVE MAINTENANCE INSTRUCTIONS
147
"wiggle" them loose, since this damages the prongs of the socket and
results in intermittent operation of the unit in which they are located.
Capacitors
High -Voltage Capacitors. High -voltage capacitors, because of their
high operating potentials, must be kept clean at all times to prevent
losses and arcing. Dirt, oil deposits, or any other foreign matter must
not be allowed to accumulate on the high -voltage terminals of these
capacitors. All leads and terminal connections must be inspected periodically for signs of looseness and corrosion, and the porcelain insulators inspected for cracks or breaks.
Low-Voltage Capacitors, Oil -Filled. Low -voltage oil -filled capacitors require the same care as those of the high -voltage type, although
the frequency of the maintenance operation is not so critical. The
terminals and connections of these capacitors should be given the
same careful inspection as those of the high -voltage types. The leads
of these capacitors are not as rugged as those used on the high -voltage
capacitors and should be inspected more closely for poorly soldered
connections.
Tubular Capacitors. These capacitors are of the low-voltage paper
type and are generally used in low -voltage circuits for coupling and
bypassing. They should be inspected and cleaned whenever the chassis
in which they are located is removed for maintenance. The only maintenance requirement for these capacitors is inspection of the tubular
body of the capacitor for bulging, excessive swelling of the capacitors,
and for signs of wax leakage. The terminal leads (pigtail type) of
the capacitors are inspected for firmness of contact at their respective points of connection. Never use a cloth to clean this type of capacitor, as damage to the surrounding circuits may result. These capacitors are easily cleaned with a small, soft brush. All dirt and dust are
brushed from the body of the capacitor and the surrounding area.
Mica Capacitors. Mica capacitors require very little maintenance
other than being kept free from dust and oil. Two types of mica capacitors are generally used the high -voltage and the low -voltage type.
The low-voltage types are inspected whenever the chassis of the unit
in which they are located is being maintained. The capacitors are inspected for cracked body conditions caused by excessive heat, while
their leads (pigtail type) are inspected for firmness of contact at their
respective points of connection. The high -voltage types, however, require terminals because of their high operating potentials. These ter-
148
BROADCAST OPERATORS HANDBOOK
minais must be inspected for tightness and corrosion, firmness of
mounting, and body conditions. The body of these capacitors is of a
ceramic material and care must be exercised when tightening the
mountings of these capacitors. The bodies of the capacitors are easily
kept clean with a dry clean cloth. For satisfactory operation the terminals must be free from dirt and corrosion at all times. Take care
when tightening the terminals of these capacitors, as excessive pressure
damages or cracks the ceramic case where the terminals are coupled
to the body of the capacitors.
Trimmer Capacitors. In very damp climates, trimmer capacitors
must be inspected often. Dampness, if allowed to accumulate on the
plates of the capacitors, results in erratic operation of the unit in which
the capacitors are used. In certain cases where high voltage is used,
serious damage to the capacitors results. A minute amount of moisture or a tiny bead of water is all that is necessary to short-circuit the
plates of the capacitor and cause abnormal operation. When such
conditions are encountered, the capacitor must be thoroughly dried by
the heat process which requires the use of a small portable heater.
A cleaning cloth used to dry the plates of the capacitors may throw the
plates out of alignment when the cloth is inserted between them. In
extreme cases where the plates of the capacitors are very closely
spaced, use a magnifying glass to locate the exact position of the moisture beads existing between the plates. Due to the sheen of the capacitor plates, very minute particles of moisture cannot always be detected by the naked eye.
Maintenance Procedures for Capacitors.
Caution: To avoid severe electrical shock in case of bleeder failures,
discharge all high -voltage capacitors before maintenance.
Feel (F). Feel the terminals of the high -voltage filter capacitors.
These should be fairly cool. Excessive heat probably indicates losses
due to loose, dirty, or corroded terminal connections. Feel the sides of
oil -filled and electrolytic capacitors. These should be cool or slightly
warm. If they are very warm or hot, the condition indicates excessive
internal leakage. Capacitors in this condition are subject to failure at
any time and should be reported for immediate replacement.
Inspect (I). Inspect the general condition of all capacitors regardless of type. Inspect for broken, frayed, or loose terminals, leads, and
connections. Inspect the condition of the terminals of the high -voltage
capacitors. Check these for dirt, corrosion, and looseness. Inspect the
body of the capacitors for excessive signs of bulging and oil leakage.
PREVENTIVE MAINTENANCE INSTRUCTIONS
149
Inspect the plates of the tuning capacitors for dirt and corrosion.
Check all capacitor shafts, bushings, bearings, and couplings for loose-
ness or binding.
Tighten (T). Tighten all loose terminals, connections, and terminal
leads on all types of capacitors. Tighten all capacitor mountings and
stand-off insulators. Tighten all loose shaft couplings and bushings.
Clean (C). Special at-ention should be given to all high -voltage
capacitors to insure that they are not only kept clean, but are free
from moisture. Thoroughly clean the insulators, terminals, and leads
of high -voltage capacitors. When extremely damp, due to high humidity, these capacitors frequently have to be wiped dry with a
clean, absorbent cloth to prevent arc-overs and breakdown of insulation. Remove terminals that appear to be either corroded or dirty; also
remove those causing power losses due to high -resistance connections.
Clean them with a crocus cloth which is either dry or moistened with
cleaning fluid. Polish the terminals dry after cleaning with a clean,
dry cloth. Replace all connections after cleaning, making certain that
good electrical contact is cbtained. The low-voltage capacitors require
little attention. However, all insulated bushings and supports should
be kept clean and free frcm foreign matter.
Adjust (A). Adjust all :eads if necessary. This requires the redressing of leads which may hive been dislocated during the maintenance
procedure. If capacitor leads are stretched too tightly, redress or replace them until the correct lead placement is obtained.
Resistors
Resistors may be divided for maintenance purposes into two groups:
the first group consists of those resistors easily detachable and known
as ferrule -type resistors; ;he second group includes those whose terminals are soldered and are known as pigtail-type resistors.
a. Ferrule-Type Resistors.
Caution: Do not touch power resistors immediately after the power
has been shut off. They are usually hot, and severe burns may result.
Feel (F). The springinss of ferrule clips may be ascertained when
removing the ferrule -type resistor. Insufficient pull at the clip may be
an indication of a loose connection and poor electrical contact.
Inspect (I). It is important to inspect all types of resistors for blistering or discoloration, fo: these are indications of overheating. Inspect the leads, clips, and :netalized ends of the resistors and adjacent
150
BROADCAST OPERATORS HANDBOOK
connections for corrosion, dirt, dust, looseness, and broken strands in
the connecting wires; also inspect the firmness of mounting.
Tighten (T). Tighten all resistor mountings and connections found
loose. If the tension at the end clips has decreased, it is common practice to press the clip ends together by hand or with a pair of pliers.
The hand method is preferred because the pliers may bend the clip or
damage the contact surface.
Clean (C). Dirty or corroded connections of ferrule -type resistors
can be cleaned by using a brush or cloth dipped in cleaning fluid. If
the condition persists, use crocus cloth moistened with cleaning fluid.
It may be necessary to sandpaper the resistors lightly with fine grade
sandpaper, such as #0000. Always wipe clean with a dry cloth before
replacing them. Vitreous resistors connected across high voltage should
be kept clean at all times to prevent leakage or flashovers between
terminals. They should be wiped clean with a dry cloth or a cloth
moistened with cleaning fluid. If cleaning fluid is used, the resistors
must be polished with a dry clean cloth.
Pigtail -Type Resistors. Maintenance of pigtail -type resistors is
limited to an inspection of soldered connections. Such connections
may break if the soldering is faulty or if the resistors are located in a
place subject to vibration. The recommended practice is to slide a
small insulated stick lightly over the connections and to inspect them
visually for solidity. If connections are noticeably weak or loose,
they should be re -soldered immediately. Discolored or chipped resistors indicate possible overloads. Although replacement is recommended, resistors in this condition have been known to last indefinitely. The pigtail -type connections should be dusted with a brush or
with an air blower if available.
Fuses
A fuse consists of a strip of fusible metal inserted in an electric circuit. When the current increases beyond a safe value, the metal melts,
thus interrupting the current. Fuses vary in size and rating depending
upon the circuits at which they are used. Some are designed to carry
currents in milliamperes. Being very rapid in action, they protect the
equipment from overloads and damage. Two types of fuses are used:
renewable and nonrenewable. The first type is designed so that the
fuse link, or element contained within the fuse cartridge, may be removed and replaced when blown. The second type, however, is constructed so that the fuse element is permanently sealed within the fuse
PREVENTIVE MAINTENANCE INSTRUCTIONS
151
housing. When a fuse blows, an attempt must be made to determine
the reason for its failure, and to make corrections, if possible, before a
new fuse is installed; then the complete fuse assembly must be replaced.
Renewable Type. The renewable type fuse assembly consists of a
housing or cartridge of insulating material with a threaded metal cap
(ferrule) at each end. The fuse element or link, as a precaution
against damage, is placed inside the cartridge or housing and it is held
in position by the two end caps, or ferrules. When a fuse is placed in
service, the two ends of the fuse cartridge are slid into spring contacts
mounted on the fuse block. This places the fuse in the circuit to be
protected.
Nonrenewable Type. When nonrenewable fuses are blown, they
must be discarded. Certain types of nonrenewable fuses are removed
by unscrewing and withdrawing the cap screws that hold them in place.
When removed, the fuse and cap screw are separated by pulling apart.
The glass fuses are easily removed for inspection. Care must be taken
to see that the fuse end and holding clips are kept clean and tight . If
they are not, overheating will result arid make replacement necessary.
Inspect (I). Inspect the fuse caps for evidence of overheating and
corrosion. Inspect the fuse clips for dirt, loose connections, and proper
tension.
Tighten (T). Tighten the end caps, the fuse clips, and connections
to the clips on replaceable fuses if they are found to be loose. The
tension of the fuse clips may be increased by pressing the sides closer
together. Fuse caps should be hand -tightened only. Excessive tightening results in difficulty in removing them when required.
Clean (C). Clean all fuse ends and fuse clips with fine sandpaper
when needed; wipe with a clean cloth after cleaning. If it becomes
necessary to use a file to remove deep pits in the clips, fuse ends, or
contacts, always finish up with fine sandpaper in order to leave a
smooth contact surface. As a final step, wipe the surface clean with a
clean dry cloth.
Bushings and Insulators
Bushings and insulators are extremely important elements in electric
circuits, especially when located in high -voltage circuits where insulation breakdown is most common. Most of the high -voltage insulators
are constructed of ceramic material with highly glazed surfaces.
BROADCAST OPERATORS HANDBOOK
Caution: Exercise extreme care when working near these insulators.
They are easily chipped or broken.
Inspect (I). Thoroughly inspect all high -voltage insulators and
bushings for moisture, dust, and other accumulated foreign matter.
Unless they are both clean and dry, leakage or arc-overs will occur
and damage them permanently. Check the chipped surfaces, hair line
cracks, carbonized arc -over paths, and other surface defects that may
make the insulator unserviceable. Insulators in this condition should
be reported to the person in charge for replacement.
Tighten (T). Feed -through bushings, stand-off and other insulators
should be tightened if found to have loose mountings or supports.
Tighten these insulators with care because gaskets absorb only a small
amount of pressure before breaking.
Clean (C). Cleaning operations are similar to those outlined for
tubes. Use a clean cloth (dampened with cleaning fluid if necessary)
to remove dust, dirt, or other foreign matter. Always polish with a
dry, absorbent cloth after cleaning.
152
Relays
The various types of relays may be classified as follows: overload
relays, time delay relays, and magnetic contactors. Relays require a
certain amount of preventive maintenance, which must never be performed except when absolutely necessary. Certain types will be
found to be completely encased in dustproof and moistureproof cases.
These require little maintenance other than a periodic inspection.
Maintenance of relays requires that they be inspected periodically
and preventive maintenance measures performed if necessary. The
inspection procedure requires that the terminals be inspected for
looseness, dirt, and corrosion. Contacts may have become loosened because of the jarring of the equipment during shipment. The contacts
may become dirty or corroded due to climatic conditions where the
equipment is being operated. Relay contacts must never be sandpapered or filed unless the operation is absolutely necessary for the
normal operation of the relay unit. A relay is considered normal if:
(1) The relay assembly is free from dirt, dust, and other foreign
matter.
(2) The contacts are not burned, pitted, or corroded.
(3) The contacts are properly lined up and correctly spaced.
(4) The contact springs are in good condition.
PREVENTIVE MAINTENANCE INSTRUCTIONS
153
(5) The moving parts travel freely and function in a satisfactory
manner. The solenoids of plunger type relays must be free
(6)
(7)
(8)
(9)
from obstructions.
The connections tc the relay are tight.
The wire insulation is not frayed or torn.
The relay assembly is securely mounted.
The coil shows no sign of overheating.
A relay is considered abnormal if it fails to meet any of the above -
mentioned requirements. The following are the maintenance procedures used in the maintenance of relay units.
Inspect (I). Inspect the relays, to determine abnormal conditions
using the check list given above. If the contacts are not readily accessible, they may be examined with the aid of a flashlight and mirror.
Many of the relays can be inspected and cleaned without being removed from their mountings or without being taken apart. Mechanical action of the relays should be checked to make certain that the
moving and stationary contacts come together in a positive manner
and that they are directly in line with each other. The armature or
plunger mechanism should move freely without binding or dragging.
Care should be taken during inspection not to damage or misalign the
relay mechanism. Relays that require the removal of the cover for
complete inspection may be found enclosed in glass, Bakelite, or metal
cases. Relays must never be taken apart unless it is absolutely necessary. If they must be taken apart for maintenance purposes, care
should be exercised in doing so. When disassembling relays, tag all
leads as they are being removed. This insures that the proper leads
are returned to their proper terminals after the maintenance procedure
is completed.
Tighten (T). Tighten all loose connections and mounting screws
found loose, but do not apply enough force to damage the screw or to
break the part which it holds. Do not start screws with their threads
crossed. If a screw does not turn easily, remove it and start again.
Relay coils can be tightened by inserting, if possible, a small wooden
or paper wedge between the coil and the core of the relay. This prevents chatter of the relay. Tighten any and all loose connections.
Tighten also the mounting of the relay assembly, if it is found loose.
When replacing glass or Bakelite covers over relay cases, take care
not to overtighten the screw cap holding the glass or Bakelite cover
over the relay assembly.
154
BROADCAST OPERATORS HANDBOOK
Clean (C). Clean the exterior of the relay with a dry cloth, if it is
very dirty; clean with a cloth or brush dipped in cleaning fluid; then
wipe the surface with a dry cloth. If loose connections are found,
they should be inspected. If inspection reveals that the connections
are either dirty or corroded, they should be removed and cleaned before tightening.
The relay service aid is a narrow piece of folded cloth or canvas. It
serves a twofold purpose: it is suitable for polishing a clean surface,
and it is used as a follow-up to a crocus cloth. It is also intended to remove grains of pumice which came off the crocus cloth and adhere to
the contact surface. The cloth is used as shown in Fig. 17-2.
Fig. 17-2.
faces are
row strip
as shown
Relay contact surpolished by a narof cloth or canvas
in the sketch.
Cleaning Relay Contacts. The following information should be carefully studied. It instructs how relay contacts of various types should
be cleaned.
Hard contacts. Hard alloy contacts are cleaned by drawing a strip
of clean wrapping paper between them while holding them together.
It may be necessary in some cases to moisten the paper with cleaning
fluid. Corroded, burned, or pitted contacts must be cleaned with the
crocus cloth strip or the burnishing tool as shown in Fig. 17-3.
Solid silver contacts. Dirty contacts. Dirty solid silver contacts are
easily cleaned with a brush dipped in cleaning fluid. After being
cleaned, the contacts are polished with a clean dry cloth.
Note: The brown discoloration that is found on silver and silverplated relay contacts is silver oxide and is a good conductor. It should
PREVENTIVE MAINTENANCE INSTRUCTIONS
155
be left alone unless the contacts must be cleaned for some other reason.
may be removed at any time with a cloth moistened in cleaning
fluid.
Corroded contacts: Dress the contacts first with crocus cloth, using
either the stick or the strip of crocus material. When all of the corrosion has been removed, wipe with a clean cloth moistened in cleaning
fluid and polish with a piece of folded cloth. Make certain that the
shape of the contacts has not been altered from the original.
It
FINGERS PRESSING
CONTACTS TOGETHER
TOOL BETWEEN
CONTACTS
Fig. 17-3. Hard alloy contacts of
a relay are cleaned by pulling a
strip of clean wrapping paper between them while pressing the
contacts together.
Burned or pitted contacts: Resurface the contacts, if necessary, with
#0000 sandpaper, making certain that the original shape of the contacts is not changed. Next, smooth the surface of the contacts with
crocus cloth until a high polish has been obtained. Wipe thoroughly
with a clean cloth to remove the abrasive remaining on the contacts.
When contacts are very badly burned or pitted and replacement is
not available, the small fine-cut file and #0000 sandpaper should be
used in keeping with instructions given later.
Silver-plated contacts. Dirty contacts: Dirty silver-plated contacts
are cleaned with a cloth or brush dipped in cleaning fluid. After being
cleaned, the contacts are polished with a dry cloth.
Corroded contacts: Dress first with crocus cloth, using either the
stick or strip of crocus material. The work must be done very carefully
not to remove an excessive amount of silver plating. When all of the
corrosion has been removed, polish with a clean dry cloth. Make
certain that the shape of the contacts has not been altered.
Burned or pitted contacts: Dress the contacts with crocus cloth
until the burned or pitted spots are removed. This may require an
appreciable amount of time and energy, but it is preferable to using
156
BROADCAST OPERATORS HANDBOOK
a file or sandpaper. If it is found that the crocus cloth does not remove
the burns or the pits, use the sandpaper tool very carefully. When
sandpaper is used, it must be followed with crocus cloth to polish the
contacts, and then wiped thoroughly with a cloth moistened in cleaning fluid. The contacts are then polished with a clean dry cloth.
Warning: Never use highly abrasive materials, such as emery cloth,
coarse sandpaper, or carborundum paper for servicing relay contacts,
as damage to the contacts will result.
Adjust (A). Adjust relay contacts after cleaning if necessary. The
contacts should close properly when the plunger is hand operated. Adjust the relay springs if necessary. Do not tamper with the relay
springs unless it is absolutely necessary. These springs are factory
adjusted and maintain a certain given tension and rarely get out of
adjustment. If the spring tension must be changed, exercise care when
doing so. The adjustment of the current control relays is accomplished
by setting calibrated knobs to the desired setting, or by turning a
knurled adjustment sleeve which has a calibrated scale mounted adjacent to it. The adjustments should not be changed from their original
factory setting except in cases of emergency. Overload relays must
never be adjusted unless the person in charge has been notified, and
has sanctioned the adjustment.
Shapes of Relay Contacts. Relay contacts are of varied shapes, as
shown in Fig. 17-4 depending upon their size and application. In some
I
FLAT CONTACT
r
Fig. 17-4. The original shape of
the contacts must be retained.
This shape may be either flat or
convex, as shown at the left.
CONVEX CONTACT
instances, both contacts are flat; in others, one contact is convex while
its mate is flat. The original shape of a contact must be retained during cleaning. If burning or pitting has distorted the contact so that
it must be reshaped, the original shape must be restored. It is essential that the maintenance personnel familiarize themselves with all
details of the relays by examining them while the relays are in good
condition. In this way, they will be better prepared to do their work
well.
PREVENTIVE MAINTENANCE INSTRUCTIONS
157
Relay Servicing Tools and Their Use
To service the relay contacts, several types of tools are needed.
Each of these has a special function, as described below.
The Burnishing Tool. This tool is used on relays which have extremely hard contacts made of palladium or elkonium. This tool is
not a file. A contact should not be burnished unless it is found to be
pitted or oxidized, and then not more than is necessary to restore a
clean smooth surface. The original shape of the contact must be retained.
Small Fine -Cut File. This file is to be used only on the larger contacts when they have becDme very badly burned or pitted, and a replacement is not available. This tool is not to be used on silver-plated
contacts, or on the contacts of the telephone-type relays. The file
should not be used more than is necessary to remove the pit. The
original shape of the contact must be preserved. After filing, #0000
sandpaper should be applied to the contact, and followed with crocus
cloth to obtain a smooth finish on the contact surface. A clean dry
cloth serves for final polishing.
The #0000 Sandpaper stick. This tool is made in the same way as
the crocus -cloth stick, except that sandpaper is used instead of crocus
cloth. The use of sandpaper is limited, as is the use of the fine-cut file,
to the treatment of badly burned or pitted contacts on the larger relays.
Sandpaper is not used on silver-plated contacts, except under extreme
circumstances, and when used should be followed with crocus cloth.
All contacts should be po:ished after sanding, with a clean dry cloth.
Crocus Cloth. This maintenance aid is available in two forms-as
a tool and as a strip of material. It serves a twofold purpose: it may
be used to remove corrosion from all relay contacts, or it may be applied to the contacts following the use of the fine-cut file and #0000
sandpaper. Neither the file nor sandpaper leaves a finish smooth
enough for proper relay operations. Use crocus cloth to polish the
surface of the contact. The choice between the stick and the piece of
cloth depends upon accessibility. If the location of the relay and the
position of the contacts permit the use of the crocus -cloth stick, it
should be used; otherwise, the strip of crocus cloth must serve. The
crocus cloth and tool are used as illustrated in Figs. 17-2 and 17-3. In
both cases the maintenance aid is inserted between the contacts and is
drawn through them while the contacts are pressed together with the
fingers.
15S
BROADCAST OPERATORS HANDBOOK
Switches
For the purpose of maintenance, switches may be classified into two
general groups: those whose contacts are readily accessible, and those
whose contacts are completely encased. The basic maintenance operations of "Inspection," "Cleaning," "Adjusting," and "Lubrication" are
applicable only to the first group. Because of the enclosed construction
of the second group, no maintenance can be applied. The work is
limited to a mechanical test of their operations.
Accessible Contact Switches. This group consists of knifeblade
switches, start-stop push-button switches, and high -voltage shorting
bars. With the exception of the shorting bars, all of these switches consist of blades which are mechanically inserted into spring contacts.
Inspect (I). Inspect all the terminal connections of each individual
switch for tightness and cleanliness. The mounting of the switch
should be checked for firmness. Operate the mechanism of the switch
and see if the parts move freely. Observe the stationary spring contacts to determine whether they have lost tension and whether they
are making good electrical contact.
Tighten (T). All loose mountings and connections should be tightened properly. If inspection shows that the fixed contacts have lost
tension, tighten them with the fingers or pliers. Tighten every connection or terminal found loose.
Clean (C). If inspection shows that any terminal, connection, or
section of the switch is dry, dusty, corroded, or pitted, clean the part
by using a dry clean cloth. If the condition is more serious, moisten
the cloth with cleaning fluid and rub vigorously. Surfaces which have
been touched with the bare hands must be thoroughly cleaned with
a cloth moistened in cleaning fluid, and then polished with a clean
cloth. The points of contact with the moving blade are naturally
those which most often show signs of wear. Examine these points very
carefully to insure that both sides of each blade, as well as the contact
surfaces of the clips, are spotlessly clean at all times. Crocus cloth
moistened with cleaning fluid should correct this condition; however, if
it is not corrected, #0000 or #000 sandpaper may be used. Always
polish clean after the sandpapering operation.
Adjust (A). Some of the switches have a tendency to fall out of
alignment because of loosening of the pivot. In most cases, tightening
the screw on the axis of motion corrects this condition.
Lubricate (L). If binding is noted during inspection of the opera-
PREVENTIVE MAINTENANCE INSTRUCTIONS
159
tion of the switch, apply a drop of instrument oil with a toothpick to
the point of motion or rotation. Do not allow oil to run into the electrical contacts, as a film of oil may cause serious damage or a poor
contact. Lubrication of switches is not recommended unless serious
binding is noticed.
Nonaccessible Contact Switches. Under this heading are included
all the remaining switches not discussed in the previous paragraph.
Interlock switches, toggle switches, meter protective push buttons, and
selector switches have been designed so that it is impossible to get
at the contact without breaking the switch assemblies. The only maintenance possible is to check the operation of the switch assemblies
and, if something abnormal is detected, to notify the person in charge
immediately so that a spare may be obtained and a replacement made
as soon as possible. Do not lubricate any of these switches under any
circumstances.
Generators and Motors
Certain preventive maintenance procedures must be applied to these
components if proper functioning and dependable performance are to
be obtained. There are three principal cases that contribute to faulty
operation of this type of equipment: accumulation of dirt, dust, or
other foreign matter on the windings and moving parts of the equipment; lack of sufficient lubrication on bearings and other moving parts;
and improper adjustments or damaged parts. Given proper maintenance care, motors and generators give long and efficient service. In
addition to the techniques given in the following paragraphs, additional
maintenance instructions covering certain motors or generators will be
found in various items of the manufacturer's instruction books. Unless specifically mentioned, the maintenance techniques that follow
apply to the motors and generators used in the transmitter.
Feel (F). The bearing and the housings should be tested by feeling
them to determine overheated conditions. An accepted test, except in
very hot climates, is to hold the bare hand in contact with the bearing
or housing for a period of at least 5 seconds. If the temperature can be
tolerated this length of time, the bearing temperature may be considered normal. Overheating may indicate lack of sufficient lubrication, a damaged bearing surface, or, in rare situations, an excessive
accumulation of dirt within the field windings.
Inspect (I). Each motor and generator exterior, and any other visible parts, must be inspected for dirt and signs of mechanical loose-
160
BROADCAST OPERATORS HANDBOOK
ness or defects. Wherever wires are exposed, see that all connections
are tight and in good condition and that the insulation is not frayed.
Inspect the motor ends for excess oil and the mounting for loose bolts.
Wherever possible and practicable, feel the pulleys, belts, and mechanical couplings to insure that the proper tension or tightness is
present.
Tighten (T). Any mounting, connection, or part found loose must
be properly tightened. If any internal part such as a commutator segment or an armature coil appears loose, notify the person in charge
and repair the part immediately or replace it at the first opportunity.
Operation under these conditions will cause considerable damage in a
very short period of time.
Clean (C). Carefully wipe the exterior, base, and mountings of
each motor and generator with an oiled cloth in order to leave a thin,
protective film of oil on the surfaces. If available, use an air blower, or
hand bellows to blow the dust and dirt out when inspection shows that
the windings are dusty or dirty.
If inspection of the commutator and brushes shows that cleaning
is necessary, the accepted cleaning practice is as follows: lift or remove the most accessible brush assembly and press a piece of canvas
cloth folded to the exact width of the commutator against the commutator; then run the motor for about 1 minute, exerting the necessary
pressure. If the condition still persists because the commutator has
been burned or pitted, use a piece of fine sandpaper (#0000), preferably mounted on the commutator cleaning stick, and, exerting the
necessary pressure, rotate the motor for approximately 1 minute.
Stop the motor and wipe around the commutator bars with a clean
cloth. It may be necessary to polish the commutator with a piece of
canvas, as explained in the first procedure. Identical maintenance procedures apply to slip rings.
Transformers and Choke Coils
Some transformers are enclosed in metal housings, others are external, but in all cases they are impregnated with insulating compound.
As a result, similar maintenance techniques are applicable to all of
them.
Inspect (I). Carefully inspect each transformer and choke for
general cleanliness, for tightness in connections of mounting brackets
and rivets, for solid terminal connections, and for secure connecting
lugs. The presence of dust, dirt, and moisture between terminals of
PREVENTIVE MAINTENANCE INSTRUCTIONS
161
the high -voltage transformers and chokes may cause flashovers. In
general, overheating in wax- or tar -impregnated transformers or coils,
is indicated by the presence of insulating compound on the outside
or around the base of each transformer or coil. If this condition is encountered, immediately notify the person in charge.
Tighten (T). Properly tighten mounting lugs, terminals, and rivets
found loose.
Clean (C). All metal -encased transformers can be cleaned easily
by wiping the outer casings with a cloth moistened with cleaning fluid.
Clean the casing and the immediate area surrounding the transformer
base. Clean any connections that are dirty or corroded. This operation
is especially important 071 high -voltage transformers and coils. It is
very important that transformer terminals and bushings on all types
of transformers be examined and kept clean at all times.
Variacs
Variacs, as a rule, are built sturdily and are protected so that very
little maintenance other than regular inspection is required.
Inspect (I). Carefully inspect the exteriors of the variacs for
signs of dirt and rust. Inspect the mounting of each variac to determine whether it is securely mounted. Inspect all connections for looseness, corrosion, and dirt. Ycheck the slip rings for signs of corrosion or
dirt.
Clean (C). The perforated casing of each variac as well as the area
surrounding the base must be cleaned regularly. If the slip rings need
cleaning, dismount the variac and clean with a cloth moistened in
cleaning fluid and then po_ish with a clean dry cloth. If the dirty condition persists, use crocus cloth and rub vigorously. Again polish with
a clean cloth. Reassemble the variac; then reinstall it, reconnecting all
terminals carefully.
Lubricate (L). If the variac shaft shows signs of binding or if it
squeaks, apply a few drops of household oil to the front and rear bearings. Rotate the control shaft back and forth several times to insure
equal distribution of the lubricant in the front and rear bearings.
Rheostats and Potentiometers
Rheostats and potentiometers fall into two main groups for maintenance purposes; those which have the resistance winding and the
sliding contact open and accessible, and those which, by construction,
have their inner parts totally enclosed. In the latter group, very little
162
BROADCAST OPERATORS HANDBOOK
maintenance can be performed, since opening and removing the metal
case may damage the unit.
Inspect (I). The mechanical condition of each rheostat must be inspected regularly. The control knob should be tight on the shaft.
Inspect the contact arm and resistor winding for cleanliness and good
electrical contact. Check the rheostat assembly and mounting screws
for firmness; the sliding arm for proper spring tension; and the insulating body of the rheostat for cracks, chipped places, and dirt.
Tighten (T). Tighten carefully any part of the rheostat or potentiometer assembly found loose.
Clean (C). The rheostat or potentiometer assembly is easily cleaned
by using a soft brush and then polishing with a soft clean cloth. If
additional cleaning is needed, or if the windings show signs of corrosion or grease, the brush may be dipped in cleaning fluid and brushed
over the winding and contacts. With a clean cloth, remove the film
that remains after the cleaning fluid has evaporated. If the contact
point of the sliding arm is found burned or pitted, it is good practice to
place a piece of folded crocus cloth between the contact and the winding and then to slide the arm a number of times over the crocus cloth.
When cleaning the winding, do not exert excess pressure, or damage
will result.
Adjust (A). If the tension of the sliding contact is insufficient, an
adjustment can be made with the long -nose pliers. Slight bending of
the rotating piece in the proper direction restores the original tension.
Lubricate (L). Apply lubrication only when necessary; that is, when
binding or squeaking is noticed. One or two drops of instrument oil
applied to the bearings with a toothpick is sufficient. Since the slightest
flow of oil into the winding or the sliding-arm contact may cause
serious damage, lubrication should be applied very carefully and only
on the bearings. Wipe off all excess oil.
Terminal Boards and Connecting Panels
Little preventive maintenance is required on terminal boards and
connecting panels.
Inspect (I). Carefully inspect terminal boards for cracks, breaks,
dirt, loose connections, and loose mountings. Examine each connection
for mechanical defects, dirt, corrosion, or breakage.
Tighten (T). All clean terminals, screws, lugs, and mounting bolts
found loose should be tightened properly. Use the proper rods for the
PREVENTIVE MAINTENANCE INSTRUCTIONS
163
tightening procedure and do not overtighten or the assembly may become cracked or broken.
Clean (C). If a connection is corroded or rusty, it is necessary to
disconnect it completely. Clean each part individually and thoroughly
with cloth or crocus cloth moistened with cleaning fluid. All contact
surfaces should be immaculate for good electrical contact. Replace
and tighten the connection after it has been thoroughly cleaned.
Air Filters
Air filters are placed in blowers and ventilating ducts to remove
dust from the air drawn into and circulated through the ventilating
system. Some filters are impregnated with oil and some are filled
with cut strands of glass to facilitate the filtering action. The following procedures cover their maintenance:
Inspect (I). The filter should be inspected for any large accumulation of dirt and for lack of oil. Note whether the filter is mounted
correctly and whether the retaining clips are in place. Improperly
assembled filter elements or wall frames, allow unfiltered air to leak
around the edges and thus permit dust to enter the ventilating system.
Tighten (T). Tighten the retaining clips if they are found loose, and
readjust the filter in its mounting.
Clean (C). The filters are easily accessible and may be taken out
after removal of the cover plate. The general procedure is, as follows:
mark the outside of the filter before removing it from the air duct.
Before washing it, tap its edges against the wall or on the ground to
remove as much dirt as possible. Wash the filter in gasoline, using a
brush to remove dirt from the steel wool. After the filter has been
washed, place it face down on two supports. Allow it to drain and dry
thoroughly before lubricating.
Lubricate (L). Lubricate or recharge the filter element by dipping
it in a bath of oil. In temperatures about 20 F., use SAE -10 oil.
Allow the filter to drain thoroughly, intake side down, before it is put
into use. While the filter is draining, keep the filter away from places
where sand or dirt is being blown through the air. Always replace a
filter with its intake side facing the incoming air flow.
Cabinets
The cabinets which house the various components of the set are
generally constructed of sheet steel.
Inspect (I). The outside and inside of each cabinet must be in-
164
BROADCAST OPERATORS HANDBOOK
spected. Check the door hinges (if any), the ventilator mountings, the
panel screws, and the zero -setting of the meters. Examine the pilot
light covers for cracks and breaks. Occasionally remove the covers and
see whether the pilot light bulbs are secure in their sockets. Inspect
the control panels for loose knobs and switches.
Adjust (A). Adjust the zero -setting of meters if found to be incorrect. Follow the specific instructions given below.
Clean (C). Clean each cabinet including the control panel, outside
and in, with a clean dry cloth. Clean the meter glasses and control
knobs with a clean dry cloth.
Lubricate (L). Door hinges and latches need little lubrication, but
if inspection reveals that they are becoming dry, apply a small amount
of instrument oil. All excess oil should be removed with a clean dry
cloth.
Meters
Meters are extremely delicate instruments and must be handled very
carefully. They require very little maintenance, but, because they
are precision instruments, they cannot be repaired in the field. A
damaged meter should be replaced with a spare; a defective meter returned to the maker for repair.
Inspect (I). Inspect the leads and connections to the meter. Check
for loose, dirty, and corroded connections. Also check for cracked or
broken cases and meter glasses. Since the movement of a meter is extremely delicate, its accuracy is seriously affected if the case or glass
is broken, and dirt and water filter through. If the climate is damp,
it is only a matter of time until enough moisture seeps through a crack
to ruin the meter movement.
Tighten (T). Tighten all loose connections and screws. Any loose
meter wires should be inspected for dirt or corrosion before they are
tightened. The tightening of meter connections requires a special
technique because careless handling can easily crack the meter case.
To prevent breakage, firmly hold the hexagonal nuts beneath the connecting lugs while the outside nut is being tightened. This permits the
tightening of the connection without increasing the pressure of the
head of the stud against the inside of the meter case.
Clean (C). Meter cases are usually made of hard highly polished
Bakelite, and can be cleaned with a dry cloth. If cleaning is difficult,
the cloth should be dampened with cleaning fluid. Dirty connections
may be cleaned with a small stiff brush dipped in the cleaning fluid
PREVENTIVE MAINTENANCE INSTRUCTIONS
165
or with a small piece of cloth dipped in the solvent. It should be emphasized that solvents do not remove dirt entirely from hard surfaces.
Some of the dirt remains in a softened state and must be removed with
a damp cloth. Corroded connections are cleaned by sanding them
lightly with a very fine grate of sandpaper, such as #0000. After they
are cleaned, the connections should be wiped carefully with a clean
cloth.
Adjust (A). Normally, all meters should indicate zero when the
equipment is turned off. The procedure for setting a meter to zero
is not difficult. The tool required is a thin -blade screw driver. Before
deciding that a meter needs adjusting, tap the meter case lightly with
the tip of one finger. This helps the needle overcome the slight friction
that sometimes exists at the pointer bearings and prevents an otherwise normal unit from coming to rest at zero. If adjustment is needed,
insert the tip of the screw driver in the slotted screwhead located below
the meter glass and slowly turn the adjusting screw until the pointer
rests at zero. Observe following precautions: View the meter face
and pointer full on and not from either side. Avoid turning the zero adjust screw too far, as the meter pointer may be bent against the stop
peg or the spring may be damaged. Zero adjustments should not be
made for several minutes after shutdown.
Pilot Lights
Pilot lights are used to indicate that power has been applied to a
circuit or that a circuit is ready for power to be applied. They are
easily removed and replaced. The colored pilot light covers should
be removed carefully, lest they be dropped and broken. The maintenance of pilot lights presents no special difficulty, but the following
instructions are given for general guidance.
Inspect (I). Inspect the pilot light assembly for broken or cracked
pilot light shields; loose bulbs; bulbs with loose bases; loose mounting
screws; and loose, dirty, or corroded connections.
Tighten (T). Tighten al_ mounting screws, and resolder any loose
connections. If the connections are dirty or corroded, they should be
cleaned before they are soldered. Loose bulbs should be screwed
tightly into their bases. Broken or cracked pilot light shields may
sometimes be temporarily repaired by joining the broken or cracked
pieces with a narrow piece of friction tape. Replace them as soon as
possible; also replace broken or burned -out pilot light bulbs as soon as
possible. While the remova= of a bulb may sometimes be difficult, the
166
BROADCAST OPERATORS HANDBOOK
process is made simple by folding a small piece of friction tape over
the top of the bulb and pressing firmly from the two sides. After the
tape is attached, the bulb can be unscrewed and removed from the
socket. The socket connections are, of course, inspected while the bulb
is out. A new bulb can be replaced with the fingers, but if difficulty
is experienced, use friction tape to grip the glass envelope of the bulb.
Clean (C). The pilot light shield, the base assembly, and the glass
envelope of the light bulb should be cleaned with a clean dry cloth.
Clean accumulated dust or dirt from the interior of the socket base
with a small brush. Corroded socket contacts or connections can be
cleaned with a piece of cloth or a brush dipped in cleaning fluid. The
surfaces are then polished with a dry cloth. Clean contacts and connections are important.
Plugs and Receptacles
There are two main types of plugs and receptacles used to interconnect the various components. The first type of plug is used with a
coaxial line and consists of a metal shell with a single pin in the center
insulated from the shell. When the plug is inserted into the receptacle,
this pin is gripped firmly by a spring connector. There is a knurled
metal ring around the plug which is screwed onto the corresponding
threads on the receptacle; while the female part is in the plug. The
insulation in these plugs is much heavier in order to withstand the
voltage. The second type of plug is used for connecting multiconductor
cables. The plug usually consists of a number of pins insulated from
the shell which are inserted into a corresponding number of female
connectors in the receptacle, although in some cases the plug has the
female connectors in it and the male connectors are in the receptacle.
This type of plug usually has two small pins or buttons which are
mounted on a spring inside the shell and protrude through the shell.
When the shell is properly oriented and placed in the receptacle, one
of these pins springs up through a hole in the receptacle, firmly locking the plug and receptacle together. When it becomes necessary to
remove the plug, the other pin is simply depressed and the plug
removed. Connections between all plugs and their cables are made inside the plug shell. The cable conductor may either be soldered to the
pin or there may be a screw holding the wire to the pin. Remove the
shell if it is necessary to get at these connections for repair or inspection. Loosen the screws if there is a clamp holding the cable to the
shell. In some cases, it is found that the shell and plug body are both
PREVENTIVE MAINTENANCE INSTRUCTIONS
167
threaded; then the shell may simply be unscrewed. Usually there are
several screws holding the shell. These are removed and the shell is
pulled off.
Inspect (I). (1) The part of the cable that was inside the shell
for dirt and cracked or burned insulation.
(2) The conductor or conductors and their connection to the pins for
broken wires; bad insulation; and for dirty, corroded, broken, or loose
connections.
(3) The male or female connectors in the plug for looseness in the
insulation, damage, and for dirt or corrosion.
(4) The plug body for damage to the insulation and for dirt or corrosion.
(5) The shell for damage such as dents or cracks and for dirt or
corrosion.
(6) The receptacle for damaged or corroded connectors, cracked insulation, and proper electrical connection between the connectors and
the leads.
Tighten (T). (1) Any looseness of the connectors in the insulation,
if possible; if not, replace the plug.
(2) Any loose electrical connections. Resolder if necessary.
Clean (C). (1) The cable, using a cloth and cleaning fluid.
(2) The connectors and connections using a cloth and cleaning
fluid. Use crocus cloth to remove corrosion.
(3) The plug body and shell using a cloth and cleaning fluid, and
crocus cloth to remove corrosion.
(4) The receptacle with a cloth and cleaning fluid if necessary. Corrosion should be removed with crocus cloth.
Adjust (A). The connectors for proper contact if they are of the
spring type.
Lubricate (L). The plug and receptacle with a thin coat of Vaseline
if they are difficult to connect or remove. The type of plug with the
threaded ring may especially require this.
Part
6
TECHNICALLY SPEAKING
INTRODUCTION
As has been mentioned several times in this handbook, it is not
our purpose to duplicate or rewrite any of the already excellently
presented technical phases of radio in other books. The content of
this section is technical in nature, but is slanted primarily to allow
a clearer insight of the why and wherefore of operating procedures
as presented in the first four sections. In addition to this, there are
a number of technical matters of outstanding interest to broadcast
operators that have not previously been written in the language of the
average technician who need not necessarily be a mathematical wizard.
It is hoped that the following pages will prove helpful in presenting
an understandable picture of the field of broadcast engineering to the
operating personnel and to students of the broadcasting arts.
168
Chapter
18
CONTROL ROOM AND STUDIO EQUIPMENT
may become very complex in number
of circuits and control functions, but is designed and installed
to achieve a practical easily operated setup that allows foolproof switching and flexibility of functions. Briefly, the general requirements are as follows:
CONTEOL-ROOM EQUIPMENT
(a) Amplifiers for stepping up the minute electric energy produced in the microphone by the program sound waves.
(b) Switching and mixing arrangements to allow selection of proper
program source and blending of microphone outputs for desired
program "balance."
(c) Facilities for "auditioning" or rehearsing a program to follow.
(d) Terminations of inputs and outputs of all amplifiers on jack
panels to allow rapic "rerouting" of the signal in case of trouble
in any one amplifier or channel.
(e) Incoming and outgoing line terminations on jack panels to permit flexibility in receiving or transmitting the signal in any way
desired.
Fig. 18-1 illustrates one type of commercial control -room console which
contains all amplifiers and relays within the cabinet. The power supply comes in an external wall mounting unit. This console provides
amplifiers, control circuits, and monitoring equipment necessary to
handle two studios, announce booth microphone, two transcription
turntables, control-room announce microphone, and six remote lines.
In addition to this, means are provided for simultaneously auditioning
or broadcasting from any combination of studios, turntables, or remote
lines. The volume indicator is a standard vu meter which has an adjustable attenuator mounted on the panel to the right of the instrument allowing a 100% deflection of the pointer on the scale to be
calibrated for +4, +8, +12, and +16 vu.
The technical layout of this speech input equipment is as follows:
169
170
BROADCAST OPERATORS HANDBOOK
Four preamplifiers connected to four of the six mixers on the panel
in center position serve to amplify the outputs of the microphones.
A 3 -position key switch is in the input of the fourth preamplifier to
allow its operation from a microphone in the studio, announce booth,
Fig. 18-1. One type of commercial control -room console
containing all amplifiers and relays within the cabinet.
or control room. The outputs of the mixers connect to lever keys to
provide switching to the regular program amplifier for broadcasting
or to the monitor amplifier for auditioning. When these key switches
are operated they also serve to disconnect the studio loudspeaker to
prevent feedback, and operate "on -air" light relays. The fifth and
sixth mixers may be connected by means of push keys to any of six
remote lines or the two turntables. Other push keys on the panel provide circuits for feeding the cue to remote lines and for bringing in
monitoring circuits such as transmitter or master -control (where used)
outputs. The monitoring amplifier may be used for the program amplifier in emergencies by operating the proper key. Means are also
provided to supply power to the preamplifiers from the monitoring
amplifier in case of power supply failure to the preamplifiers.
This is an example of the extreme flexibility and emergency provisions designed into control -room equipment. Fig. 18-2 is a simplified
schematic diagram of a typical installation. The "Override -Record"
switch permits a remote operator to call in from any of the six remote
lines and override the program on the control -room speaker. The
CONTROL ROOM AND STUDIO EQUIPMENT
171
woad 9Y1WJ
¡
O,gÁe
L-
i
`
,..rN
m
FY
p.-
¢
P..
..
2
¢i..
rO O
O
RR
*Si
s,
Y00110
90.0015
111009
'NW
I
'
o
-L
1. -p.
P--Pn n
ra
<
'
t
172
BROADCAST OPERATORS HANDBOOK
"Record" position of this switch furnishes a signal source for an external recording amplifier or other destination.
Control -room equipment and layout vary over a considerable range
and variety from composite setups through regular commercial consoles and custom-built equipment. Fig. 18-3 illustrates the type of studio control consoles at WHK in Cleveland..
At WHK, each studio has its own control room. The consoles for
all the studios are identical and were built by the WHK engineering
staff. This was not done for economic reasons, but because none of the
commercially available consoles were suitable for the particular needs
at hand. Each console is set up to handle six microphones normally,
with provision to patch in as many more as needed. Each input has a
preamplifier and mixing is done at high level. All mixers in studio
control and master control at WHK are the vertical type, which may
be a surprise to some readers.
Fig. 18-3. The handles of the faders on the studio consoles at Station WHK
are vertical, making them easier to handle than rotary faders.
Vertical faders have several advantages wherever space is no consideration. More vertical faders can be handled competently with one
hand than rotary faders. The amount which a vertical fader is opened
is instantly and graphically apparent; that is, the eye can tell whether
it is 1/2, %, or 34. Regardless of how a rotary fader is marked, it takes
some concentration to determine how far open it is, provided the
knob has not turned on the shaft. Every man who ever worked at
WHK and then worked somewhere else, has agreed that the vertical
type is much easier to use, especially on large programs.
CONTROL ROOM AND STUDIO EQUIPMENT
173
In addition to the micrcphone inputs there is a high level input into
which master control can patch any desired program source. This allows smooth handling of multisource programs. As a matter of fact,
any fader may be used as a high level input by patching the program
in after the preamplifier. It is standard practice at WHK to have
every piece of equipment come out on jacks. All equipment which is
normally used together is connected through normal through jacks.
Then there is a master fader which controls the console output. The
fader system is a completa unit hooked up between the preamplifiers
and the line amplifier, and has some interesting possibilities in case
of trouble. Fig. 18-4 illus=rates the basic mixing circuit.
FROM
HIGH
PRE-AMPLS.
LEVEL
1
5
'S
'S
îi
FADER CIRCUIT
s
TO LINE
AMPLIFIER
5
Fig. 18-4. The basic mixing circuit of the fader system used in the console
shown on the opposite pagre.
K1 faders whether used for high level, microphone, or master, are
exactly alike, so that anyone can be used for any purpose. When the
top of the fader is used as an input, it deposits the program onto a bus,
minus the vu loss of the fader setting. By using the top of the fader
for an output, the program on the bus is fed to any desired place minus
the vu loss of the fader setting. The faders are all 600 ohms in and
600 ohms out. If the maser fader in the diagram of Fig. 18-4 went
out of order, any of the microphone faders not in use, or the high level
mixer, could be patched to the line amplifier and would become the
new master fader.
There are two line ampl_fiers in each console, one of which is wired
through normal jacks and one which may be patched to replace the
regular. There are two power supplies, either one of which can be
selected by a change -over switch. There is also a monitor amplifier, a
p -a amplifier with separate gain control, and a communications amplifier for talking to studio or master control. The microphone and
speaker of the communication system are mounted flush in the surface
of the console. All ampliLers are vertically mounted in the console
174
BROADCAST OPERATORS HANDBOOK
with doors which expose the tubes on one side or the bottom of the
amplifier on the other. This makes for easy servicing. Characteristics
of all equipment except the communications portion, is plus or minus
0.5 db from 30 to 15,000 cycles. For the convenience of the operator
there are six monitor buttons by means of which he can select his own
console output, master control output, final station monitor, network,
Western Electric Photo
Fig. 18-5. This type of control-room console is more
usual than that illustrated in Fig. 18-3.
and two spares into which anything else may be patched. None of
these buttons affect the on -the -air program. There is also a pilot light
system which indicates to the studio operator every place his program
is going, local station, network, audition room, executive's office, etc.
Fig. 18-5 illustrates another type of control -room console.
BROADCAST MICROPHONES
The microphone, first gateway through which all sounds are passed
on to the "mixing" network of the control console, is the most important instrument under the direct supervision of the control operator
or producer.
Much depends on the characteristics and operational interpretation
of this first link. First, it must have a wide frequency range. Highfidelity amplifiers would be useless without high-fidelity microphones.
Second, it must have very low internal noise level for the wide dynamic range necessary to please exacting listeners, and to meet engineering standards of broadcast quality transmitters and receivers.
CONTROL ROOM AND STUDIO EQUIPMENT
175
Next, it must possess a definite and dependable response pattern in
relation to angle of incidence of the sound waves so that pickup areas
may be properly defined. In broadcasting, we are concerned with
wanted and unwanted sounds, and all shades in between. Aurally
correct blending of musical and vocal sounds involves correct usage of
the microphone characteristics as much as the proper manipulation of
the mixing controls on the control panel.
Since, in nearly all installations of broadcast studios it is necessary
for the microphone to be placed a considerable distance from the preamplifier, a low output impedance is desirable. This is important since
the microphone cable possesses distributed capacitance which would seriously affect the higher frequencies if a high impedance were used. The
most common preamplifier input impedances for broadcast use are
30, 50, and 250 ohms. All microphones, regardless of type, are of the
same impedance at any given broadcast station. A ribbon microphone,
condenser, dynamic, or combination type may be plugged into the
microphone inlet without adjustment of impedance values. Output
level is very low in most high -quality microphones, ranging from about
minus 55 db to minus 90 db where the reference level is one milliwatt
for a sound pressure of 10 dynes per square centimeter. Frequency response is comparatively good over a range of 30 to 15,000 cycles. Internal noise level is well under 50 db below no signal conditions.
Microphone Fundamentals
Fig. 18-6 shows the primary function of a "pressure" type microphone such as the dynamic, condenser, or crystal type. Sound waves
SOUND FROM REAR
/
/
SOUND EFOM
FRONT
180°
CASE
Fig. 18-6. The diaphraim of the "pressure" type microphone always moves
in the same direction w,ether the sound comes from the front or rear.
BROADCAST OPERATORS HANDBOOK
176
of alternate condensations and rarefactions of air entering the microphone cause the pressure variations of the diaphragm to actuate the
moving element between the magnetic pole pieces, which in turn generates a small electric current in accordance with the sound waves.
The diaphragm always moves in the same direction regardless of the
initial direction of the sound.
Fig. 18-7 illustrates the function of the "ribbon" or "velocity" microphone. This instrument consists essentially of a thin metallic ribbon
tee
o°
DIRECTION OF
RIBBON MOVEMENT
DIRECTION OF
RIBBON MOVEMENT
Fig. 18-7. Sound coming from the front or rear (0° or 180°) of the "velocity" microphone actuates the diaphragm, but sound coming from the side
(90°) does not cause the diaphragm to vibrate.
suspended between two magnetic pole pieces without a diaphragm or
associated cavity. As the sound waves strike the ribbon from one direction, the element is caused to move since a pressure difference exists
in any sound field between any two given points. Since this differential pressure exists between the front and back of the ribbon, tie
ribbon will naturally move in the direction of diminishing prese .re.
This rate of change of pressure with distance is called "pessure
gradient" and is the principle upon which the ribbon microphone
operates. As observed from Fig. 18-7, sound approachi,'ig from the
opposite direction causes the element to move in the opposite direction
according to the pressure gradient principle. The ribbon can move only
along the axis perpendicular to its surface, and sound waves entering
from the side 90° from either "face" of the microphone cause an equal
pressure on both sides, hence zero response. ..'hus this microphone
gives the conventional "figure eight" response rattern, in comparison
CONTROL ROOM AND STUDIO EQUIPMENT
177
to the nondirectional response pattern of the strictly "pressure" type
microphone.
Fundamentally, then, we have two distinct primary principles of
microphone operation, the "pressure," or nondirectional type, and the
"pressure gradient," or bidirectional type. These two functions may
be combined to achieve a third kind of response pattern, the unidirectional microphone.
The unidirectional, or one -direction response microphone is a very
important instrument in broadcasting pickup technique. This microphone consists essentially of a dynamic and ribbon element in one
assembly. The coil and ribbon are connected in series with the wires
poled so that the outputs of the two elements cancel for sound coming
from one direction, and augment one another for sound from the other
direction. Remember that the ribbon moves in the opposite direction
from that of the coil when sound waves impinge from one direction
Fig. 18-9, below. The family of response
curves for the ribbon microphone showing how the response varies for three frequencies at different angles.
Courtesy RCA
50°
50°
60°
60°
70°
80°
90°
70°
80°
90°
RCA Photo
Fig. 18-8, above. The ribbon or velocity type of microphone.
-------
10,000
6,000
1,000
cps
cps
cps
BROADCAST OPERATORS HANDBOOK
178
which causes an equal and opposite voltage to be generated in the
output (hence zero voltage) , whereas the movements are in the same
direction for sound waves on the opposite side of the microphone.
The Ribbon Microphone
The ribbon or "velocity" microphone is one of the most popular
types of microphone used in broadcast studios. Fig. 18-8 shows a
ribbon microphone, the associated response curve is shown in Fig. 18-9.
This type of microphone is free from effects of cavity resonance, diaphragm resonance, or pressure -doubling effects since the moving element is a metallic ribbon suspended so as to vibrate freely between
the pole pieces of the magnet. This microphone, as are most modern
microphones, has a "voice" and "music" connection to achieve the
best possible frequency characteristic for either vocal or musical
pickups. The frequency -response curves for both connections are
shown in Fig. 18-10.
+15
+10
+5
V1
0
r
W'
u
5
CI
to
W
t
VOICE CONNECTION
15
\--MUSIC
20
CONNECTION
25
20
50
200
500 1000
2000
FREQUENCY-CYCLES PER SECOND
100
5000
tOK
20K
Courtesy RCA
Fig. 18-10. The ribbon microphone has a "voice" connection and one for
"music" to obtain the best response for either type. The frequency response
curves for either connection are reproduced above.
As was mentioned in the section on studio setup technique, the ribbon microphone tends to accentuate the low frequencies under close
talking conditions due to the pressure -gradient characteristic. This is
because, although the pressure is independent of frequency, the pressure gradient is not and it becomes comparatively large for points close
to the source in relation to the wavelength. For this reason, the speech
"strap" is used to equalize the low-frequency "boom" under close talk-
CONTROL ROOM AND STUDIO EQUIPMENT
179
ing conditions. When the same microphone is used for musical pickup
and announcer, the "music" connection should be used and the announcer should work two feet or more away from the face of the microphone.
Variable Pattern Microphones
Fig. 18-11 illustrates the structure of the Western Electric 639B
cardioid microphone which has provisions to provide a number of re -
Fig. 18-11. The internal structure of the
cardioid microphone which provides a
number of response patterns by means of
a six-position switch in the rear.
Courtesy Western Electric Co.
sponse patterns by a six -position switch. It consists of a spec'al ribbon
and magnet structure in combination with a dynamic unit. The housing of the dynamic structure encloses the ribbon transformer, electrical
equalizer, and selector switch. In the "cardioid" position, the ribbon
and dynamic element are used together to obtain the familiar "cardioid" or unidirectional pattern, as described in a previous paragraph. It
may also be used as a ribbon microphone only with bidirectional characteristics, and dynamic only with nondirectional response, as well as
three other combinations of response patterns.
The new RCA polydirectional microphone Type 77-D consists of a
single ribbon element and a variable acoustic network. One side of
180
BROADCAST OPERATORS HANDBOOK
the ribbon is completely closed by a connector tube coupled to what
is known as a damped pipe or labyrinth. In the connector tube directly behind the ribbon is a variable aperture which adjusts the directional characteristics of the microphone. When this opening is large,
the back of the ribbon is exposed, as is the ordinary velocity microphone, and a bidirectional response pattern is obtained. When the
aperture is completely closed, the acoustic impedance of the network
is infinite and a nondirectional pattern is achieved similar to a dynamic microphone. The opening is continuously variable thus enabling
the operator to achieve a large variety of response patterns. Fig. 18-12
is a rear view showing the slotted shaft -control adjustment, Fig. 18-13
is a front view of the ribbon assembly, and Fig. 18-14 is a rear view
of the same assembly.
RCA Photo
Figs. 18-12, 18-13, 18-14, left to right. Rear external view of the polydirectional microphone. The middle view is the front of the ribbon assembly
and the rear view is at the right.
The plate of the slotted adjustment is marked "U," "N," and "B"
for "unidirectional," "nondirectional" and "bidirectional" designations,
and three other markings are used to provide reference points for other
obtainable patterns. Fig. 18-15 gives the reader an idea of the number
of different patterns that may be obtained by the aperture adjustment
of this instrument. The bidirectional pattern is approximately that of
C, the unidirectional pattern that of G, and the nondirectional that
of J or K.
CONTROL ROOM AND STUDIO EQUIPMENT
181
The lower half of the case of the 77-D contains the associated acoustical labyrinth, the output transformer tapped at 50/250/600 ohms,
99cP
OCDCD
t
Courtesy RCA
Fig. 18-15. Various response patterns obtainable with the polydirectional
microphone.
and a selector switch for voice or music. The frequency response
curves for either connection and for "U," "N" and "B" patterns are
illustrated in Fig. 18-16 on the next page.
OUTPUT CIRCUITS AND LINE EQUALIZATION
The line amplifier at the studio is always "isolated" from the line by
a pad and a repeater coil. The necessity for this becomes apparent if
the reader visualizes what would occur if such a means of coupling was
not employed. An amplifier with an output of 600 ohms to match a
600 -ohm line, if connected directly to the line, would have its fre-
quency response materially affected by the length and characteristics
of the line itself. Due to the distributed inductance and capacitance
of the line, a different impedance would exist at every different frequency. For this reason, a pad of at least 10 -db attenuation is always
used to load the output of the amplifier, followed by what is known as
a "repeating" coil. The control -room equipment is nearly always "balanced to ground" to prevent hum pickup and cross talk, in which case
the repeat coil has a center tap to ground on both primary and secondary. When the equipment is single ended (one side grounded),
the repeat coil is single ended on the primary side and balanced on
the secondary or line side in order to provide a suitable connection of
unbalanced to balanced conditions.
BROADCAST OPERATORS HANDBOOK
182
+10
+5
i
M
V1
\v2
20
50
100
200
400 600
1000
2000
4000
FREQUENCY- CYCLES PER SECOND
6000
15K
10K
(A)
+10
+5
s
M
O
lo
15
V2
-20
50
100
200
400
600
FREQUENCY
000
- CYCLES
4000 8000
2000
PER
10K
15K
SECOND
(B1
+ so
+5
V1
15
V2
20
50
100
200
400
800
FREQUENCY
-
2000
1000
CYCLES
(
l
PER
4000 8000
10K
15K
SECOND
Courtesy RCA
Fig. 18-16. When the switch of the polydirectional microphone is set
at "U," the response curve of (A) is obtained. Response curves for
bidirectional "B" and nondirectional "N" switch settings are shown in
(B) and (C) respectively.
CONTROL ROOM AND STUDIO EQUIPMENT
183
Operators and technicians are frequently confused when looking at
the schematic diagram of the control -room installation to find a 600 ohm to 150 -ohm output pad which is intended to feed a 600 -ohm line.
This arrangement is often used, however, where the line to be fed is
comparatively short and unequalized. It should be remembered that
the capacitive effect along the line attenuates the higher frequencies.
Using a mismatch of this kind provides a beneficial equalizing effect
which tends to compensate for the characteristics of the line. This arrangement is also often used on lines that are equalized, the amount
of equalization necessary being less, with less insertion loss due to a
great amount of equalization.
Line Equalization
Although the telephone company usually equalizes the incoming network lines and regular broadcast lines from studio to transmitter, it is
many times beneficial to equalize lines from remote pickup points
where the cost of high-class line service is not practical to the station.
For this purpose most stations have an equalizer of adjustable characteristics in the control room which may be used for this purpose.
Fig. 18-17 illustrates a typical setup for equalizing a broadcast line.
The signal source is a steady tone from an audio oscillator which is
vu
V
METER
METuER
LINE
600 A
COIL
TEL. LINE
OSC.
I
LOAD
LINE
AMPL
ISOLATION
PAD
Fig. 18-17. Block diagram for a typical setup for equalizing a broadcast line.
terminated in an isolation pad. The same load at any frequency must
be presented to the volume indicator and this instrument should therefore be bridged on the oscillator side of the pad. The equalizer must
be on the line side of the coil at the receiving point, as shown in Fig.
18-17.
A 1000 -cycle tone is usually used as the reference frequency. The
BROADCAST OPERATORS HANDBOOK
184
oscillator is set at this frequency and fed to the line at 0 -vu level.
The gain of the receiving amplifier is adjusted to give 0 -vu reading
at that point. The oscillator is then adjusted to 100 cycles, 1000, 3000,
and 5000 cycles with constant level maintained at each frequency,
and the equalizer adjustment made at the receiving point to compensate as much as possible for the line characteristics at each frequency.
This will determine the approximate setting of the equalizer, after
which finer adjustments may be made over the entire frequency range.
FREQUENCY RUNS OF STUDIO EQUIPMENT
Fig. 18-18 is a simplified block diagram of a studio control-room
setup for purposes of illustrating a convenient method of running
V U
METER
LOAD
MIC
JACKS
JACKS
PR
E-AMPL
JACKS
LOW
LEVEL
AMPL.
JACKS
HIGH LEVEL
AMPL.
PROGRAM
AMPL.
VU
METER
PA
DD
/\/\./.\/
AUDIO
OSC
^^^_
Iv
.
TO
EQUIPMENT
V
Fig. 18-18. Block diagram of a studio control-room setup for running fre-
quency-response curves on the equipment.
frequency -response curves on such equipment. The over-all frequency
response is first dctermined by plugging the output pad of the audio
oscillator into the input of the preamplifier and noting the final vu
meter reading at 1000-cycles reference point. On this initial reading,
both meters are driven to 0 -vu deflection. The oscillator output level
is now held constant over the entire frequency run and the number of
vu deviation from 1000 -cycle reference jotted down on paper or plotted
on a graph. Should the frequency response not be up to par over the
entire run, the frequency run of the main program amplifier may be
made, then going back down the line until the faulty stage is made apparent by noting where the frequency response begins to deviate from
normal.
CONTROL ROOM AND STUDIO EQUIPMENT
185
NOISE AND DISTORTION MEASUREMENTS
A typical noise and distortion meter is described in Part 4 and the
appendix for use on broadcast transmitters. This equipment may be
also used on control -room equipment. The diode detector is removed
from the circuit by a switch providing a connection through a balanced
input transformer for measurements on balanced audio equipment, or
for connection to the input attenuator for use with unbalanced circuits.
The rest of the procedure is then the same as that described for transmitter measurement. The same method of isolating noise or distortionintroducing stages may be used here as described above on frequency
runs.
TELEPHONE COMPANY LINE SERVICES
Line services offered by Bell Telephone and American Telephone
and Telegraph (AT&T) are divided into two general categories:
Metropolitan Area Circuits (Bell Telephone) which provide service
for remote pickup points and studio -to -transmitter loops.
Toll Circuits (AT&T) composing the national network of circuits
and long lines outside the metropolitan area.
The metropolitan area circuits are divided into services of the following general limitations:
(a) Frequency range of 35 to 8000 cycles per second within plus
or minus 1 db of 1000 -cycle reference, and a volume range of
40 db. This service is sometimes used for studio -to-transmitter
program loops.
(b) Frequency range of 100 to 5000 cycles per second within plus
or minus 2 db and a volume range of 40 db. This is the more
common studio -to -transmitter service, and sometimes used for
remote pickup points.
(c) Nonloaded commercial telephone service and unequalized, for
use of remote pickup points.
Toll circuits are divided into general classifications such as high quality, medium -quality, and speech -only services as follows:
(a) Frequency range of 100 to 5000 cycles and volume range of
30 db. This is the normal service of national network hookups.
BROADCAST OPERATORS HANDBOOK
(b) 150 to 3700 cycles, sometimes used where not enough time was
available to install the higher quality service.
(c) Speech -only service of about 250 to 2750 cycles. Also often
used for intercommunication between long-distance points and
emergencies.
186
Chapter
19
THE BROADCAST STUDIO
high-fidelity transmission of broadcast
programs is definitely not new; it has been the goal of at least
some engineers since the earliest days of broadcasting. The
realization of over-all high-fidelity service, however, includes the receiving set in the home and it has not been until very recently that
the "average" set in the medium price market was worthy of the extraordinary efforts of some broadcasters to render high-fidelity service.
Conversely, it is apparer_t at the present time that with a good receiver,
noticeable differences in fidelity characteristics of different stations
within the range of the receiving position are observed by the critical
listener.
If the present state of development in broadcast amplifier equipment
is taken as the sole criterion, then high-fidelity transmission is truly
here. Frequency response is within 2 db of 1000-cycle reference from
30 to 15,000 cycles, and is limited only by wire -line connecting links
in amplitude -modulation (a -m) installations, or not at all in frequency -modulation (f -m) installations. Noise level at the antenna
of the transmitter is at least 60 db below 100% modulation, and dynamic range capability :s at least 40 db for a.m. and 70 db for f.m.
Unfortunately, however, the actual existence of high-fidelity depends
on many factors other than the a -f and r -f amplifiers associated with
the installation. These amplifiers, according to the ideas of some, form
the "heart" of the transmission system insofar as high fidelity is concerned. Actually, they are merely a link in the chain of necessary
functions of broadcasting a program, and are no more important to
fidelity than the other links, as Fig. 19-1 demonstrates.
In order to focus attention on the possible weak links, by eliminating the amplifiers, as such, there remain: program and talent, production technicians respons:ble for pickup technique, the studio itself,
program producers and announcers, microphones, mixing and switching
circuits, control -room, master -control and transmitter operators, wire lines, feeder systems and matching units, antennas, and the limitations
THE ENDEAVOR to realize
.
187
BROADCAST OPERATORS HANDBOOK
188
PROGRAM
&
TALENT
-0-
CONTROL
ROOM
PRODUCTION
TECHNICIAN & PICKUP TECHNIQUE
STUDIO PRODUCER
& ANNOUNCER
-0-
OPERATOR
MASTER
CONTROL
EQUIPMENT
MIXING
-0-
MICROPHONES
INPUT
MASTER
CONTROL
OPERATOR
TRANSMITTER
PHASING EQUIPMENT
MATCHING UNITS
&
ANTENNA
AND/
FEEDING
OR
SYSTEM
a.
STUDIO
SPEECH
TRANSMITTER
INPUT
SPEECH
-.-
CIRCUITS
OPERATOR
--0-
WIRE LINES
OR
R.F. LINK
RADIO
TRANSMITTER
LIMITS SET BY
CHANNEL
BANDWIDTHS
Fig. 19-1. Various links in the chain of putting a program on the air, all of
which are important in high-fidelity broadcasting.
set by channel bandwidths subject to government regulations. This
presents quite a formidable list, and each item is recognizably inferior
to the modern amplifier associated with the broadcast installation in
performance. To those familiar with broadcasting, however, it may
be shown that the weakest links and those which cause most concern
at the present time, are the studio itself, operating personnel, wirelines, and bandwidth limitations in a -m stations.
The limitations set by wire -line transmission are not serious if considered in relation to the allowable 10-kc channel of the standard
broadcast installation. Most lines are equalized to 5000 cycles which
is, theoretically, the highest frequency tolerable of any effective
strength to prevent adjacent -channel interference. On the other hand,
insofar as the relatively small primary coverage area is concerned,
the frequency range of modern a -m transmitters (10,000 cycles) if
utilized, would allow a marked improvement over present fidelity
THE BROADCAST STUDIO
189
realization, with class B and C service areas suffering from increased
cross talk and interference. Although this situation is a deplorable
one, it requires little discussion, in that the problem is primarily one
to be solved in the future actions of the FCC.
Thus, there remain two factors to be considered, studio design and
operating personnel. It is obvious that the broadcaster could possess
high-fidelity equipment from microphone to antenna and still not
provide high-fidelity service. In the final analysis, the outcome of
any program for a given equipment installation depends entirely on
thé ability of the technical staff responsible for the operating technique of the equipment. Realizable dynamic range, for instance, which
is a highly important factor in high-fidelity transmission, is rarely
utilized by station operators. It should be stated here, however, that
this is not entirely the fault of operators, but is due rather to a combination of factors including an incomplete correlation between the
philosophy of dynamic range and compression amplifiers, inadequate
visual monitoring indicators for wide dynamic range, and a confusion
of ideas existent among personnel as to the amount of dynamic range
tolerable in the home receiver for various types of program content.
With the advent of f -m transmission, this problem will become more
and more important.
Problems in Studio Design
It is often surprising to discover from
a detailed study of the sequence of steps in the development of a certain product, that an indication of a definite direction exists which might well be given the term
evolution, and which inevitably indicates a trend that reveals to the
searcher an insight into future design of that product. The history
of broadcast studio development is interesting not only from this point
of view, but also from the viewpoint of establishing the present state
of the art as it affects high-fidelity possibilities.
In general the broadcast studio must meet the following requirements:
1.
Freedom from noise, internal or external
2. Freedom from echoes
3. Diffusion of sound, providing a uniform distribution of sound
energy throughout the microphone pickup area
4. Freedom from resonance effects
5. Reverberation reduction such that excessive overlapping of suc-
190
BROADCAST OPERATORS HANDBOOK
cessive sound energy of speech articulation or music does not
occur
6. Sufficient reverberation such that emphasis of speech and musical
overtones is provided to establish a pleasing effect as judged by
the listener.
Early Studio Design
In the earliest days of broadcasting, the foremost problems encountered were quite naturally noise and echoes, since "studios" were
simply rooms of rectangular shape, with windows of conventional type
and walls of ordinary architectural construction. The first steps in
1"
J -M
SOUND
ISOLATION FELT
FURRING CHANNEL
PLASTER
J
-M
WALL ISOLATER
METAL LATHE
WOOD GROUND
WOOD SLEEPER
J
-M FLOOR CHAIR
CONCRETE FLOOR
Courtesy
Johns Manville Corp.
Fig. 19-2. The "floating studio" type of wall and floor construction.
design procedure were then taken to treat the walls acoustically to prevent echoes and "flutter," and to cover the windows with the same
acoustical material. This sufficed for a certain era in broadcasting,
provided the operator with control over echoes, and practically isolated the microphone from factory whistles, fire sirens, etc. At that
THE BROADCAST STUDIO
191
time, this type of studio was entirely adequate to satisfy the fidelity
requirements of the program transmission possible with associated
transmitting and receiving equipment; indeed the electronic amplification of broadcast programs was so much better than the acoustic model
phonograph that the general public thought of the radio as a realization of true high-fidelity reproduction.
With the advent of the dynamic loudspeaker, microphone improvements, higher power and wider band amplifiers, the scope of fidelity
possibilities began to broEden considerably. Signal-to-noise ratio was
improved, and higher volumes could be handled in the receiver without distortion, resulting in a greater dynamic-range capability, but at
the same time adding to the burden of studio design, since extraneous
noises picked up at the studio were now more noticeable in the home receiver. This fact led to the "floating studio" type of construction,
shown in Fig. 19-2.
The period following saw many phenomenal improvements in broadcast equipment in general, such as 100% modulation of the transmitter
with greatly reduced distortion, improvement in syllabic transmission
characterstics, reduction of spurious frequencies and ripple level,
greatly reduced noise levels in switching and mixing circuits, and
nonmicrophonic tubes. Yet, strangely enough, studio design remained
nearly stagnant over a period of six or seven years except in isolated
cases. Indeed, the rectargular shaped, acoustically deadened studio
may be recognized by those familiar with the state of the art today
as being the most common type of studio among independent stations,
even of very recent installation.
The broadcast engineer found himself faced with many apparent
difficulties in studios of this type of construction. The big factor, in a
room with parallel walls, is the excessive acoustical treatment necessary to overcome the effect of echoes as mentioned previously. This
has resulted, in the past, in extreme high -frequency attenuation and a
lack of "liveness" such that the brilliancy of musical programs was
completely lacking. The loudness intensity for a given meter reading
on the volume indicator is very low for a studio of this type in comparison with that obtained from a modern studio.
The effect on speech, while not satisfactory, is not so pronounced
as that on music since speech originates within a few feet of the microphone and requires less reverberation to assure naturalness, whereas
the space between the scurce of the music and the microphone is
greater, and many things happen to the musical waveforms that must
e
192
BROADCAST OPERATORS HANDBOOK
eventually be translated into perceptions of loudness. This effect obviously leads into complex operational difficulties, requiring a lower
"peaking" of voice in relation to music on the volume indicator to obtain a comparative loudness intensity in the receiver at home. Furthermore, microphone placement technique for this type studio is such
that a number of microphones must be used for a group of performers,
since, if a single microphone is employed, a lack of reinforcement
of harmonics and overtones of the instruments results in a thin sound,
lacking in body.
Another difficulty resulting from parallel -wall construction is shown
in Fig. 19-3, where it may be observed that the angle of incidence of
Fig. 19-3. The effect on a sound
wave train of parallel -wall construction resulting in undesired
resonance effects.
(M. Rettinger: Acoustics in Studios,
Proc. IRE, July, 1940. By permission of the Proc. IRE.)
the wave-fronts remains the same no matter how many such reflections
occur. Due to the acoustical treatment this reflection (to any great
extent) occurs only at the lower frequencies and it may be seen that
the nodes would have marked regions of coincident reinforcement, resulting in resonance effects at the lower frequencies, and conditions
that would result in diffuse sound distribution are reduced. Thus it
becomes obvious that items 3, 4, and 6, as given earlier in requirements for good acoustics, are lacking in studios of this design. In addition, high -frequency response so necessary to brilliancy is reduced,
effective dynamic range is inadequate, and operational difficulties are
numerous. Thus, it is apparent that the studio becomes the weakest
link in the high-fidelity chain in the great majority of broadcast installations today. Exceptions, of course, are the main network studios,
and a few independent stations more "production conscious" than the
main body of independent broadcasters. It is certainly obvious that
the contemplated large scale expansion of f -m service will bring
about the need for a revolutionary education in studio requirements
for the independent station operator.
e
THE BROADCAST STUDIO
193
Advances in Studio Design
From the foregoing discussion the difficulties to be overcome may
be listed as follows:
1. Lack of diffusion of sound
2. Resonance conditions at low frequencies
3. Insufficient reverberation for music
4. High -frequency absorption
5.
Critical and multiple microphone placement
6. Operational complexities.
The size and dimensions of the studio comprise a certain problem
in studio design since an optimum volume per musician in the studio
exists. Reduced to practice, however, this problem becomes one of
9
8
7
6
5
4
3
2
40
120
80 90 100 110
20
30 40
50 60 70
DISTANCE FROM SOUND SOURCE (FEET)
Courtesy Johns Manville Corp.
Fig. 19-4. The absorption by the air of high -frequency sound
waves varies with the frequency and the distance from the source.
simply proportioning the studio for a certain maximum number of
musicians expected. This is possible because no difficulty exists in obtaining a good pickup of a smaller group in a studio designed for a
greater number of musicians; whereas, due to the fact that a small
room cannot conveniently be "aurally" enlarged, a large band in a
small studio presents a difficult problem. Portable hard "flats" Tire
BROADCAST OPERATORS HANDBOOK
often used in large studios to enclose a small group of musicians, thus
providing the optimum dimensions required for good pickup of a given
number of performers.
High -frequency absorption, particularly frequencies of over 5000
cycles, is relatively great as indicated in Fig. 19-4. The absorption
of sound by air at these frequencies is actually greater than the surface absorptivity of the studio even under normal temperature and
relative humidity conditions. It is not possible to construct a studio
having a reverberation time of over 1.2 seconds at 10,000 cycles even
with theoretical zero absorptivity in acoustical treatment.1 This, then,
makes obvious the fact brought out before concerning optimum volume
per musician in studio design. By distributing the reflector surfaces
in proximity to the musical instruments, a maximum of diffused, poly phased high -frequency sound will exist at the microphone without
being attenuated injuriously by space in back of the instruments. A
minimum number of microphones for adequate pickup is necessary
under these conditions.
In general, modern studios are of two types. First is the live -end,
dead-end type in which the talent is placed in the live -end and microphones placed in the "microphone area" in the dead-end, thus achieving the correct reverberation of sound waves striking the microphone
without bothersome reflections from side and rear walls. This type
of studio, as shown in Fig. 19-5, has the advantage of retaining a defi194
NBC Photo
Fig. 19-5. An example of a live -end, dead-end studio.
M. Rettinger, "Acoustics in Studios," Proc. IRE, July, 1940.
THE BROADCAST STUDIO
195
nite reverberation time not influenced by the size of the studio audience in the dead-end of the studio. It has the disadvantage of limiting
the pickup to a definite area in the studio. Second is the generalpurpose type studio, consisting of uniformly distributed acoustic treatment, or panels of different type of acoustical elements to achieve a
desired condition.
Fig. 19-6 shows graphically the sound -absorbing characteristics of
three materials developed by the research department of Johns -Manville in their acoustical _aboratory. By proportioning the amount or
adjusting the orientation of these three materials in a studio, the time frequency curve will achieve any desired contour. This type of studio
90
Z 80
u
aW
70
z
z
60
\
..
1
r'
50
0
¢
§
40
g30
20
10
o
I
'
/¡
80
i
ELEMENT
ú
ó
/-****"........../a.
...,/».---.
J.M.TRIPLE TUNED
/ /Ì
/
¡
,,
. .'
J M.HIGH FREQUENCY
ELEMENT
//
./.41';"----J M.LOW FREQUENCY
E_EMENT
I
100
200
300
I
500
700 1000
200
FREQUENCY IN CYCLES PER SECOND
2.0
Fig. 19-6, above. The sound absorbing characteristics of three
acoustical materials.
After Knudsen
iiiiiï
RIMMIUMMt
S5 MMMIIIMMZ
o.--mamma
Courtesy Johns Manville Corp.
Fig. 19-7, right. Optimum reverberation time for studios cf
various sizes.
400
0.5
51 2
10000
imimmumman
...mm\I
mumumr.-e
=I¡
Tp 2048(.miGii
.BBiiCMMMMMM
m»MOM
OiiGiiiiiiiiiiiiiiiiiiiiiiiiii
INIMMIIMUMMIMMIMIUMIMME
MOIMMOMMBIRMIM
BBBBB ZWZMOM
iiiiiiiiiiiiiiiiiiiiiiiiiiiiï
MMMMMMMMMMMMMMMMMIRMIMMIMBUMMIN
N
N
t0
in
ni
.-,
N
N
oIn
O
O
O
,-I
N
e
o
o
VOLUME IN THOU SANDS
OF CUBIC
FEET
o
BROADCAST OPERATORS HANDBOOK
has the advantage of unlimited pickup area, but has the disadvantage
of being affected by size of the studio audience, since a great difference
exists in reverberation time when the studio is vacant and when it is
occupied by a large group of performers and a large studio audience.
Optimum studio reverberation time is shown in the graph of Fig. 19-7.
196
Chapter 20
SELECTING THE BROADCAST TRANSMITTER
LOCATION
CHOICE
of the broadcast transmitter site is a highly specialized
field
that usually comes under the supervision of a consulting
engineering firm. A brief outline of the factors affecting the
proper location, however, is of prime importance to thé serious broadcast employee who likes to have a comprehensive picture of operation
and engineering.
In the discussion to follow, it is necessary to keep in mind that
field -strength of a radio wave is expressed in "millivolts" or "microvolts per meter." This is a measurement of the stress produced in the
ether by the carrier wave that is equivalent to the voltage induced in
a conductor one meter in length due to the magnetic flux of the wave
sweeping across the conductor at the velocity of light. This field
strength is greatly affected by the conductivity of the soil over which
it travels. The soil conductivity is expressed in "electromagnetic units,"
abbreviated emu. This value of soil conductivity varies over a considerable range with the type of soil concerned. Values will be around
3 x 10-13 emu for most loam (good conductivity) and about 1 x 10-14
emu for dry, sandy, or rocky ground which has relatively poor conductivity.
Service Area
The "primary coverage area" of a broadcast transmitter is that area
around the towers which provides a distortionless and interference free signal. This is provided by the ground wave, which must have a
carrer -to -noise ratio of at least 18 db, and a field strength of at least
several times the strength of the sky wave at the point measured.
The so-called "secondary coverage area" is that area outside the
primary area which is supplied primarily by the sky wave. The sky
wave, of course, is subject to selective fading (due to changing heights
of the Heaviside layer) with resulting distortion effects. The sky wave
at broadcast frequencies is almost completely absorbed in the daytime,
thus a secondary service area of any appreciable extent appears only
197
BROADCAST OPERATORS HANDBOOK
198
at night. Fig. 20-1 shows how the attenuation of the sky wave varies
through the sunset period.
t
05
0.2
0.1
0.05
Fig. 20-1. The relative field intensity
increases sharply after sunset. Measurements taken at 800 kc over 560 miles
during spring.
0.02
0.01
After FCC
0.005
0.002
0.0014
3 2
BEFORE
1
0
2
3 4
AFTER
HOURS FROM SUNSET
Required Field Strength
Since the required field strength for satisfactory coverage depends
on the existing interference level, the value will vary with location. It
may be assumed in general that the interference level is greatest in
the industrial and business sections of metropolitan areas, less in the
residential areas, and still less in rural areas.
TABLE
1
PRIMARY SERVICE
Field Intensity
Ground-Wave
Area:
City business or factory areas
City residential areas
Rural-all areas during winter or northern areas during
summer
Rural-southern areas during summer
10 to 50 my/m
2 to 10 mv/rn
0.1 to 0.5 my/m
0.25 to 1.0 my/m
-From FCC Standards
Table 1 shows the approxmate field strengths necessary to render
adequate service (for primary area) under various conditions. In
SELECTING THE TRANSMITTER LOCATION
199
some locations where conditions are more favorable than average,
primary service may be obtained with somewhat weaker field strength
than those indicated, and, of course, coverage of an intermittent na MILES FROM ANTENNA
.5
.1
1,000
.7
2
1
3
5
7
10
500
300
100
50
30
5000
WATER
10
30
10
6
3
ce
w
r
w
î
¢
a
.5
.3
a
1-
J
O
>
-
I
1
.05
.03
.01
.005
.003
.001
.0005
.0003
.000110
20
30
50
70
100
MILES
FROM
200 300
ANTENNA
500 700 1000
After FCC
The conductivity of the soil has
tion of the broadcast signal.
I+ig. 20-2.
a
great effect on the attenua-
BROADCAST OPERATORS HANDBOOK
200
TABLE 2
PROTECTED SERVICE CONTOURS AND PERMISSIBLE INTERFERENCE
SIGNALS FOR BROADCAST STATIONS
Class of
class of Channel
Used
Station
Signal Intensity Contour of
Area Protected From ObPermissible
jectionable Interference'
Power
Day3
Ia
Clear
50 kw
lb
Clear
10 kw
II
Clear
0.25 kw to
50 kw
500
kw to
5 kw
500
to
50 kw
SC 100
AC 500
SC 100
AC 500
uv/m
Regional
III-B
Regional 0.5 to 1 kw 500 uv/m
night and
5 kw
day
500 uv/m
Locale
0.1 kw to
0.25 kw
IV
wave)
2500 uv/me
Day3
2500
uv/m
Night'
5
uv/m Not du -
5
uv/m
plicated
25
uv/m
25 uv/m 125 uv/me
(ground
wave)
III-A
1
Night
uv/m Not duplicated
uv/m
uv/m 500 uv/m
uv/m
(50% sky
uv/m
Permissible Interfering Signal on
Same Channels
25
uv/m
125
uv/m
25
uv/m
200
uv/m
25 uv/m 200
uv/m
(ground
wave)
4000 uv/m
(ground
wave)
400
uv/m
(ground
wave)
1 When it is shown that primary service is rendered by any of the above classes
of stations, beyond the normally protected contour, and when primary service to
approximately 90 per cent of the population (population served with adequate signal)
of the area between the normally protected contour and the contour to which such
station actually serves, is not supplied by any other station or stations, the contour
to which protection may be afforded in such cases will be determined from the individual merits of the case under consideration. When a station is already limited
by interference from other stations to a contour of higher value than that normally
protected for its class, this contour shall be the established standard for such station
with respect to interference from all other stations.
2 For
adjacent channels see Table 3.
' Ground wave.
' Sky wave field intensity for 10 percent or more of the time.
6 These
values are with respect to interference from all stations except Class Ib,
which stations may cause interference to a field intensity contour of higher value.
However, it is recommended that Class II stations be so located that the interference received from Class Ib stations will not exceed these values. If the Class II
stations are limited by Class Ib stations to higher values, then such values shall be
the established standard with respect to protection from all other stations.
e Class IV stations may also be assigned to regional channels according to section 3.29.
SC = Same channel.
AC = Adjacent channel.
SELECTING THE TRANSMITTER LOCATION
201
ture prevails at times in localities where an hour -to -hour variation of
interference intensity occurs.
Approval of a transmitter site by the FCC must entail an application which includes a map showing the 250-, 25-, and 5-mv/m contours and the population residing in the 250-mv/m contour (the socalled "blanket area") . This map also indicates by symbols the
character of each area (business, manufacturing, residential, etc.),
heights of tallest buildings or other obstructions, density and distribution of population, and location of airports and airways. The field strength contours which would be produced by a transmitter at any
particular location, the population within each contour, and the areas
where the signal might be subject to nighttime fading and interference,
are the determining factors in choosing the most favorable site. For
this reason, propagation data that permit prediction of signal attenuation in all directions from a proposed location are of prime importance
to the engineer.
TABLE 3
ADJACENT CHANNEL INTERFERENCE
Maximum Ground Wave
Field Intensity of
Undesired Station
Channel separation between desired and undesired
stations:
10 kc.
20 kc.
30 kc.
0.25 my/m
5.0 my/m
25.0 my/m
-From FCC
Standards
Ground Wave Propagation Data
The primary service area resulting from a transmitter of given
frequency and power depends upon earth conductivity and directivity
of the antenna system. The graph of Fig. 20-2 illustrates the effect of
soil conductivity on signal attenuation. This type of graph is published by the FCC in blocks of frequencies as shown, some 20 graphs
being required to cover the broadcast -band assignments. They show
the ground -wave field intensity curve plotted against distance for
various conductivity values.
Fig. 20-3 is a map of the approximate and average soil conductivity
values for the United States. The protected service contours and permis'ihle interference signals on the same channel for various classes
BROADCAST
OPERATORS
HANDBOOK
By
HAROLD E. ENNES
Staff Engineer
Indianapolis Broadcasting, Inc.
JOHN F. RIDER PUBLISHER, INC.
480 CANAL STREET, NEW YORK 13, N.Y.
COPYRIGHT 1947 BY
JOHN F. RIDER
of translation
into the Scandinavian and other foreign languages
All rights reserved including that
FIRST PRINTING; NOVEMBER, 1947
SECOND PRINTING; FEBRUARY, 1949
THIRD PRINTING; SEPTEMBER, 1949
PRINTED IN THE UNITED STATES OF AMERICA
TO
BARBARA JEAN
INTRODUCTION
has been called one of the great giants of
our age. Actually, its strides into virgin territory have been almost beyond prophecy. Since 1921, when the beginnings of
broadcast stations as a specialized field of radio were realized, this industry has undergone a convulsion of changes that would take thousands of volumes to record. Transmitting and receiving equipment have
been made to realize a state of fidelity of tone that the comparison to
"canned music" is no longer descriptive of the art. Studios have
reached a state of development that has almost hopelessly antiquated
those of a few years back. Production of complex musical and dramatic shows has reached a peak that marks a transition from an old
era into a brilliant new one. And still the upheaval goes on, all eyes
are still ahead, all energies still expended in further development.
All this is not surprising. Development of almost flawless equipment
seems taken for granted by this scientific generation of young and old
alike. The surprising aspect is the obvious gap in literature that
exists between this field of radio engineering and design, and the practical operation of their products under actual use. This is especially
true in the field of broadcasting. Probably this is due to the somewhat
limited circle of engineers who are concerned with broadcast operations; yet there is no subject of interest more expansible or inexhaustible.
Part 1 of this book is thus intended primarily to be a comprehensive
treatise of control -room operation for broadcast technicians, endeavoring to collect enough coordinated facts to result in a general set of
rules to serve as standards of good operation practice. An attempt
is made to bring forth a new approach to modern operating technique, and to discuss and clarify existing facts that should lead to a
better understanding between studio and transmitter personnel. The
discussion necessarily includes an analysis of different types of indicating meters used in practice, in order that their functions may be more
clearly interpreted and understood in relation to the work which they
are intended to perform. Related subjects, such as loudness sensation
THE RADIO INDUSTRY
vii
viii
INTRODUCTION
for a given meter reading, waveform, and phase shift in studios, are
analyzed.
The subject and content of this book are intended not only for the
many newcomers to control rooms and transmitters, but also for the
"old timers," familiar with all the problems peculiar to their work.
The first four parts cover the operating practice in control rooms, the
master control, remote controls, and the transmitter, and the fifth and
sixth parts are concerned with technical data for operators and technicians.
Station setups must inevitably fall into two general classifications:
the "smaller station" design, where control room and master control
are combined on one centralized console with studios grouped about it,
and the "larger station" setup, with individual control rooms for each
studio, and master control as the central switching unit.
The book has been so arranged in order to present the material on
each subject in as thorough a manner as possible, and will be equally
applicable to either type of technical setup.
ACKNOWLEDGMENTS
The author wishes to thank the editors of Radio -Electronic Engineering for permission to use some of the material of his articles appearing in that publication as follows: portions of Chapter 1 from
"Program Metering Circuits," April 1945; portions of Chapters 7, 8,
and 9 from "Remote Control Broadcasting," October 1946; portions
of Chapter 16 from "Heat Dissipation In Broadcast Transmitter
Tubes," May 1944; and Chapter 19 from "Broadcast Studio Design,"
October 1944.
Chapter 20 contains in part material appearing in articles by this
author in RADIO during January, February and March of 1945, and
is reproduced herein through the courtesy of Radio Magazines Inc.
The entire book is based on the authors' original article "Some Suggestions for Standards of Good Operating Practice in Broadcasting,"
RADIO, August, September and October, 1943. Part 4 contains some
data from the author's "Operational Engineering for Broadcast Transmitters" in COMMUNICATIONS.
The author is also indebted to Mr. Joseph Kaufman, Director of
Education at the National Radio Institute for his sincere desire to see
such a book as this published, and his courtesy in allowing the use of
part of the material herein that was written by the author for the new
broadcast section of NRI home study courses.
Many thanks also to Bert H. Koeblitz for his invaluable contributions to the book, namely Chapters 5 and 11, and his information on
technical equipment at WHK.
The author is also indebted to the editors of the John F. Ride.
Publisher, Inc., for their many helpful suggestions and aid over the
rough spots in this, the writers' first book attempt.
HAROLD
November
22, 1947
ix
E.
ENNES
Mr
TABLE OF CONTENTS
PART
1
OPERATING IN THE CONTROL ROOM AND STUDIO
CHAPTER 1. WHAT YOU'RE UP AGAINST
1
Control Operator -2. Studio and Transmitter Installation -3. Transmitter Operating Technique-7. Loudness -7. Details of Control Room
Metering Circuits-10. Volume Indicator Interpretations -12. Dynamic
Range Indication-13.
CHAPTER 2. ARE MECHANICAL OPERATIONS
CHAPTER 3.
APPARENT?
KEEPING SOUND "OUT OF THE MUD"
.
.
.
.
15
.
.
19
CHAPTER 4. YOU'RE OFTEN A PRODUCER TOO
25
Importance of Rehearsals -30. Musical Setups -33. Sound Effects -35.
Importance of Control Room Maintenance -40. Transcription Turn-
tables -40. Turntable Operation -42. Instantaneous Recording Department -43. The Influence of FM -43.
PUT THAT MIKE THERE! (by Bert H. Koeblitz)
45
Large Orchestra -45. Keep It Simple -47. Choral Pickup -48. Drama
and Novelty Pickups 49. Small and Hotel Orchestras -50. Novelty and
Vocal Groups -51. Piano Pickup-52. Organ Pickup -54.
CHAPTER 5.
.
PART
.
2
OPERATING THE MASTER CONTROL
WHERE SPLIT SECONDS COUNT
57
Master Control of United Broadcasting Co. -58. Function of Master
Control Operations-59. Master Control Procedure -59. Studio Procedure 62. Field Procedure -67. Glossary-68.
CHAPTER 6.
PART
3
OPERATING OUTSIDE THE STUDIO
-
CHAPTER 7. REMOTE CONTROL PROBLEMS
71
CHAPTER 8. REMOTE VERSUS STUDIO PICKUPS
General Comparisons of Studio and Remote Pickups -78.
xi
77
Remote Control Amplifiers-72. Simplex Control of Remote Amplifiers
74. General Remote Operating Problems-75.
TABLE OF CONTENTS
xii
CHAPTER 9. REMOTE MUSICAL
PICKUPS
.
.
.
..
.
.
Brass Bands-81. Salon Orchestra Remotes-81. Symphonic Pickups
82. Church Remotes-83.
EYE -WITNESS PICKUPS AND MOBILE TRANSMITTERS
Frequency Assignments 87. Operation-88.
-
80
CHAPTER 10.
THE LIVE SYMPHONY PICKUP (by Bert H.
Pre-Broadcast Problems-91. Physical Arrangement of
Microphone Placement-95. Other Problems-96. The
phone-98. Transporting Equipment-99. Problems of
toriums -101.
CHAPTER 11.
85
Koeblitz)
90
Orchestra -93.
Soloist MicroStrange Audi-
PART 4
OPERATING THE TRANSMITTER
OPERATOR'S DUTIES
104
Outline of Responsibilities-104. Typical Presign on Procedures -105.
Pre-Program Level Checks -106.
CHAPTER 12
CHAPTER 13. PROGRAMS ARE ENTERTAINMENT
108
Coorelation of Meter Readings-109. 100% Modulation-111. Operation
of Limiter Amplifiers-113.
CHAPTER 14. MEASURING NOISE AND DISTORTION
.
.
.
.
116
Excerpts From Standards -118.
PART
5
WE'RE OFF THE AIR
CHAPTER 15.
EMERGENCY SHUTDOWNS
CHAPTER 16. WHY
PREVENTIVE MAINTENANCE
121
124
Proposed Transmitter Maintenance Schedule-125. Maintenance of
Water -Cooling Systems -129. Forced -Air Systems -131. Station WIRE
Preventive Maintenance Schedule-132.
PREVENTIVE MAINTENANCE INSTRUCTIONS . 136
Preventive Maintenance Operations-136. Suggested List of Tools for
Rely and Commutator Maintenance -138. Construction for Relay and
Commutator Tools-139. Use and Care of Tools-141. Vacuum Tubes
142. Maintenance Procedures-143. Capacitors -147. Resistors -149.
Fuses-150. Bushings and Insulators -151. Relays -152. Relay Servicing Tools and Their Use-157. Switches-158. Generators and Motors
159. Transformers and Choke Coils-160. Variacs-161. Rheostats and
Potentiometers-161. Terminal Boards and Connecting Panels-162. Air
Filters-163. Cabinets-163. Meters-164. Pilot Lights -165. Plugs
and Receptacles -166.
CHAPTER 17.
-
TABLE OF CONTENTS
PART
xiii
6
TECHNICALLY SPEAKING
169
CONTROL ROOM AND STUDIO EQUIPMENT
Broadcast Microphones-174. Microphone Fundamentals -175. The
Ribbon Microphone-178. Variable Pattern Microphones-179. Output
Circuits and Line Equalization-181. Frequency Runs of Studio Equipment -184. Noise and Distortion Measurements-185. Telephone Company Line Services -185.
CHAPTER 18.
.
.
187
THE BROADCAST STUDIO
Problems in Studio Design-189. Early Studio Design -190. Advances
in Studio Design-193.
CHAPTER 19.
SELECTING THE BROADCAST TRANSMITTER LO197
CATION
Service Area -197. Required Field Strength -198. Ground Wave Propagation Data-201. Using the Propagation Data-203. Other Factors
204. Broadcast Antenna Systems -211. Considerations in Antenna System Design -213. Outline of Transmitter Installations-214. Antenna
Tuning-215. Circuit Tests -217. Factors Affecting Hum and Noise -219.
CHAPTER 20.
-
BIBLIOGRAPHY
220
APPENDIX
221
RCA 96-A Limiter Amplifier -221. RCA DISTORTION AND NOISE
METER-221. Installation-224. Noise Level Measurements -227. Distortion Measurements-228. Maintenance -231. RCA PHASE MONITOR-233. Measuring Phase Shift in Television I -F Circuits-234. Description-234. Phase Measuring Circuit -236. The Blanking Stages
238. The Phase Shifter Stage-239. Installation-240. Preliminary Adjustments-241. Operation-241. REMOTE ANTENNA-CURRENT
INDICATOR-243. Installation-244. Sampling Adjustment-245. Use
of Tuned Circuits-246. Use of Sampling Kit-247. Nonresonant Shielded
Loop -249. Location-250. Sampling Feeder at Tower Base -250. Sampling on Tower Structure -251. Sampling from an Adjacent Mast-252.
Sampling Lines-252. RCA LIMITING AMPLIFIER-255. Description
-255. Connections-257. Maintenance -259. Time Constant Changes
-
262.
-
.ir
BROADCAST OPERATORS
HANDBOOK
II.
Part
1
OPERATING IN THE CONTROL ROOM
AND STUDIO
Chapter
1
WHAT YOU'RE UP AGAINST
there are three kinds of pickups which concern
the control-room operatór; namely, studio, remote controls, and
incoming network programs where the station is affiliated with
a particular network.
Studio programs are all programs that originate at the regular station studios. All the most popular shows, such as Jack Benny, Bing
Crosby, and Fred Allen, are studio programs at the main network
studios. These same shows, of course, are handled as incoming network programs at the affiliated stations.
A remote control, or "nemo" in radio language, is a pickup originating somewhere other than the stations' regular studios, such as a sporting event or night club. Remote controls will be discussed in Part 3
of this book.
For studio programs, microphones must be set up or "spotted" in the
studio in such a manner that all musical instruments and performers
that are part of the production will be adequately covered. Sound
waves striking the movable element of the microphone causes a vibration in the magnetic field in which the element is suspended, which in
turn results in an electric potential on the element varying in accordance with the sound waves. The mechanical construction of various
types of microphones used for broadcasting is explained in Part 6 of
this handbook. The electric energy thus generated is very weak and
must be amplified to an amount sufficient to be carried by wire lines
to the transmitting plant. (This is true in all cases except in some of
the lowest powered installations where the transmitter and control
rooms are installed together. Even when this is true, the signal must be
amplified considerably to drive the speech input stages of the transmitter.) Control of the various microphones is provided by grouping
individual switches and volume controls for each microphone on a
panel known as the control console. A volume indicator must be used
to indicate the relative magnitude of the program signals and is
mounted in a convenient visual area on the control console.
BROADLY SPEAKING,
1
BROADCAST OPERATORS HANDBOOK
2
Control Operator
One duty of the control operator is to place the microphones in the
studio where the production director wants them for a particular program. Where no production director is employed, the control operator
must determine the positions of the microphones, or, perhaps more
correctly stated, he must determine the positioning of the performers
in the microphone pickup area. The best positions are usually determined only by rehearsing the show before air time, and alternating the
respective positions until the proper pickup is achieved.
During the progress of a studio show, the studio operator's position is at the control console. It is his function to operate the various
microphone controls so that their respective outputs properly "blend"
into the effect desired. When a production director is employed at a
station, he will assist the operator by telling him which sound or sections of sound to "bring up" or "lower." Since, in any transmission
system, definite limits exist as to maximum volume that can be han -
0 0©
O 0
O 0
O 0
©
©
©
IC El IM
o
©M
o
El
ZS
©
©
©
©
Fig. 1-1(A). Block diagram of a typical broadcast station installation,
showing various setups for switching to different studios and remote and
network lines, monitoring, etc.
WHAT YOU'RE UP AGAINST
3
died and minimum volume that is adequate for transmission, the overall volume must be monitored and controlled by the operator. This
is the purpose of the volume indicator. The operator must also operate
the switching system to choose the proper studio or incoming program
lines. Technical features of typical control consoles and switching
systems are considered in Part 6 of this handbook.
A good studio operator must not only be familiar with the technical
equipment, but also be very sensitive to art as well as science in broadcasting service.
Studio and Transmitter Installation
In order to visualize more clearly some of the discussion to follow,
it will be helpful to refer to the block diagram of a typical broadcast
installation as shown in Fig. 1-1(A). Most of the illustration is selfexplanatory, showing in simplified form the setup necessary for mixing
Fig. 1-1(B). The control console of Fig. 1-1(A). The master panel is in the
middle with studio panels on either side.
and blending of voice and music from a specified studio, switching of
studios, "remote" and network lines, visual and aural monitoring
facilities, wire transmission to the transmitter, and associated equipment. A photograph of this centralized control installation is shown
in Fig. 1-1(B).
BROADCAST OPERATORS HANDBOOK
4
The pad P shown in the master control panel circuit before the
111-C repeater coil is inserted to provide a constant load at all times
for the channel amplifier, and is necessary since the equipment sometimes operates at a higher level than is deemed advisable to feed into
program lines of the telephone company. The new standard vu meter
bridged across the monitoring points are supposedly indicators of 1
milliwatt of power (sine -wave) in 600 ohms. Actually, the meter indicates 0 vu with a sine -wave power at 1000 cycles of between +4 vu
and +26 vu, depending on the external resistance used in series with
the meter to allow greater bridging characteristics, and to facilitate
adjustments to correlate readings of the meters used at slightly different volume levels in the circuit. Rms meters of greater sensitivity
have not proved practical to date. It should be kept in mind that this
calibration assumes a sine -wave signal, and that under actual program material of energy sufficient for 0 vu deflection, instantaneous
peaks will exist of several times 1 milliwatt energy, and average power
will be a fraction of 1 milliwatt.1
As may be observed from the block diagram, visual indication of
the program in progress is provided on the studio panel, the outgoing
channel amplifier, the line amplifier at the transmitter, and the final
result, monitoring of percentage modulation of the transmitter. The
duties of the control operator include not only the "spotting" of microphones for musical and dramatic pickups, switching of studios and
lines on scheduled time or cue words, and proper mixing of voice and
music on studio setups; but also making certain that his "reference
volume" or zero volume level does not exceed that point to which
100% modulation of the transmitter is referred.
"Zero volume" level is simply an arbitrary point, and is not to be
thought of as rigid fundamental electrical units of power, current, or
voltage. It is necessary that it be understood only in relation to the
electrical and dynamic characteristics of the meter used and the technique of reading its response. Perhaps this will be clarified by Fig.
1-2, showing the response of two typical volume indicators on a sudden
applied signal. This difference in dynamic characteristics of the new
and old type volume indicators (Fig. 1-3) shows the need for a difference of technique in using the interpretation of the meters. The
standardization of the new type indicator is a great step forward in
broadcasting and most stations are equipped with these meters today.
'Chinn, Gannett, and Morris, "A New Standard Volume Indicator and ReferProceedings, IRE, January 1940.
ence Level,"
WHAT YOU'RE UP AGAINST
5
It must be remembered, however, that modulation monitors at the
transmitter must necessarily be of the semi-peak reading type since
this is specified by the FCC (Federal Communications Commission)
whereas, the vu meter used at studios is meant to integrate whole syl;
lables or words. This meter is slightly underdamped, which tends to
cause the pointer to pause for a moment on the maximum swing, then
start downward more slowly than in the case of the previous indicators. Therefore the meter appears to "float" on the peaks without
any erratic jumps. The psychological effect is excellent and the meter
160
140
OLD
TYPE
120
1'100
z
0
F
J4 80
L.)
o
ó 60
NEW
TYPE
40
20
o
01
02
03
0 4
0.5
SECONDS
1
0 6
07
08
09
1.0
Fig. 1-2. The response of old and new types of volume indicators to a
suddenly applied signal indicates a need for a different technique in the
interpretation of the readings. Courtesy Proc. IRE
appears to show the audio wave as it sounds to the ear from a monitoring speaker. A typical transmitter modulation meter reaches 100
on the scale in approximately 0.09 second when a 1000 -cycle voltage
of the required amplitude is applied to the equipment; whereas the
vu indicator reaches 99 in 0.3 second, as indicated in Fig. 1-2.
Coupled with this difference of dynamic characteristics of the two
meters is the conventional habit of monitoring at the transmitter on a
single positive or negative peak. By studying Fig. 1-4, which is a
BROADCAST OPERATORS HANDBOOK
6
graph drawn from a typical oscillograph of a speech wave, it is noted
that the energy in positive and negative peaks is far from equal. This
is typical of speech waves at the output of a microphone regardless of
the type or make of microphone used. Since the vu meter works from
-3-2
_g
2
EA)
00
-I
80
áo
i00
(B)
Fig. 1-3. The old type of volume indicator is shown at (A) and the new
type at (B).
a balanced full -wave rectifier, its reading is not dependent on the pole
of operation, and thus the comparison of the indication at the transmitter modulation meter position with that at the studio cannot be
expected to agree even with perfectly matched circuits between.
This one fact is probably the most universal reason for friction between transmitter and studio personnel. It is not possible, for instance,
Fig. 1-4. This representation of a typical speech wave shows that the energy
in the positive and negative peaks are unequal.
to obtain the same polarity of maximum energy from the two sides of
a bidirectional microphone. An interviewer may show an indication
at the transmitter of 100% modulation and the interviewee on the
opposite side of the microphone (therefore oppositely poled at the
WHAT YOU'RE UP AGAINST
7
microphone transformer) may show only 50% (or less), yet the indicator at the studio (full-wave rectification) will show exactly the
same peak level. It is perfectly plausible then that the transmitter
operator unfamiliar with speech-wave characteristics through a microphone should conclude from his monitor reading that the two
voices are not balanced at the studio end. This belief is sometimes
further encouraged by the extreme difference of "loudness sensation"
between two voices of different timbre that are peaked the same
amount on a full -wave rectifier indicator. This discrepancy between
level indication on a meter and the aural "on air level" is one of the
most perplexing problems of broadcasting and will be taken up in more
detail presently.
Transmitter Operating Technique
The foregoing discussion brings to mind several questions as to
transmitter operating technique. Is there any true indication at the
transmitter of comparative levels from the studio? Which pole of the
modulation envelope should be monitored continuously and why?
These problems, together with detailed suggestions of pre-program
level checks will be discussed in Part 4 on transmitter operating practice.
As will be discussed under the transmitter section, it is highly desirable to have all the undirectional microphones in use at the studio
poled so that the maximum energy pole of operation will coincide
with the positive side of the modulation envelope at the transmitter.
The ratio of peak energy difference varies with type and make of microphone, but is apparently most pronounced in pressure type microphones, such as the RCA type 88-A. This type microphone, due to
its light weight and rugged construction, is often used for remote pickups, and in studios, such as transcription booths, used mainly for
announcements. The operator should always take advantage of this
characteristic when this type microphone is used, as the results of
proper polarization at the studio are very much worth while.
Loudness
As to the problem of difference in "loudness sensation" for a given
meter reading between two or more voices, a brief perusal of the situation will emphasize the magnitude of its importance, and should constitute a challenge to operators and engineers to correlate existing
facts with operational procedure.
BROADCAST OPERATORS HANDBOOK
8
Fig. 1-5 is a graph of loudness level curves as adopted by the American Standards Association. The derivation of these curves is explained
in most standard textbooks on sound and will not be duplicated here.
An example will suffice to enable the reader to use this graph correctly.
It will be noted, for example, that a tone of 300 cycles, 40 db above
the reference level (0 db) corresponds to a point on the curve marked
120
120
IIo
loo
80
80
60
60
50
70
m
o
Z
J
>
J
Lai
40
40
20
o
-1020
50
100
500 1000
FREQUENCY
5000
10
000
Fig. 1-5. Family of loudness level curves as adopted by the
American Standards Association.
30. This is then the loudness level. It means that the intensity level
of a 1000 -cycle tone (reference frequency) would be only 30 db in
order to sound equally loud as the 40 -db 300 -cycle tone.
Now assuming a fundamental of 392 cycles (G-string of a violin)
with an actual intensity of 40 db above reference level, it would be
noted from the curve that the loudness level is approximately 36 db.
It was determined in Bell Laboratories that the addition of the overtones or harmonics of the fundamental raised the intensity from 40 to
40.9 db, whereas the loudness level was raised from 36 to 44 db. In
other words, the addition of the harmonics raises the actual meter
reading only 0.9 db, while the loudness level increases 8 db. For the
complex tone, the reference level of 1000 cycles would be 44 db to
sound equally loud.
When it is realized that the vocal organs of human beings are all
exceedingly different, and are associated with a particular resonating
WHAT YOU'RE UP AGAINST
9
apparatus that gives to the voice its individual timbre, it becomes
clear why it often occurs that two voices peaked at a given meter
reading will sound far different in loudness. Certain harmonics of the
voice are emphasized while others are suppressed in an infinite variety
of degrees. A study of Fig. 1-6, which illustrates a graphical integration of two male voices intoning the same vowe will reveal a decided
,
I
I
III
IV
Fig. 1-6. Graphical integration of two male voices intoning the same
vowel that discloses a great difference in the peak factor of each.
difference in peak factor (ratio of peak to average content), which in
turn depends to a large extent on harmonic content and phase relationship of the harmonics to the fundamental.
At the present time only one solution suggests itself. When it becomes necessary to transmit two voices of such difference in timbre as
to be decidedly unequal in loudness for a given reference level, the
good taste and judgment of the operator at the control panel must
govern their respective levels. The author fully realizes the many and
varied complications that arise from this condition, since loudness is
not only a physical, but also a psychological reaction. The level at
which the receiver in the home is operated will determine the extent
to which changes in loudness intensity are noticeable, since at low
volumes greater change of intensity is required to be noticeable to the
ear than is the case at higher volumes. Acoustics of the studio and
the room in which the home receiver is operated will influence the
ear's appreciation of level intensity changes. However, the control
man with good taste, a critical ear, and keen appreciation of values
can find the "happy medium" between aesthetics and conventional
transmission operations. This is of prime importance when voice
and music are to be blended, as will be discussed later.
10
BROADCAST OPERATORS HANDBOOK
Details of Control Room Metering Circuits
A few of the fundamental characteristics of broadcast metering circuits have been discussed in relation to the proper understanding of
their functions by both control room and transmitter personnel. The
operator employed in broadcasting is confronted with the handling and
measuring of the quantity known as the "volume" of sound. His conception of volume must necessarily be influenced by other than precise mathematical relationships of electrical units such as power, voltage, or current. At the same time, his means of measuring the complex
and nonperiodic speech and program waves must be based primarily
on a -c theory in terms of the related values of sine -wave currents.
The correlation of data on program metering circuits to serve definite
performance characteristics for various parts of a transmission system
is a most important subject and yet perhaps the least understood
among the operators and technicians concerned with their use.
Since the earliest days of electrical program transmission, about
1921, when it became apparent that distortion due to overloading of
an amplifier was far more noticeable in a loudspeaker than in the or -
L___
/
39001L
ATTENUATOR
COPPER -OXIDE
RECT FIER
AND
METER
390011
390011.
Fig. 1-7. Circuit that is used to bridge the new vu meter across program
lines or individual studio output lines.
dinary telephone receiver, various schemes for measuring the magnitude of program waves have been developed. The first device was a
d -c milliammeter connected in the output of a triode detector, with an
input potentiometer to adjust the sensitivity in 2 -db steps. Thus, by
adjustment of the sensitivity control so that peaks of program waves
caused an indication of approximately mid -scale on the meter at intervals, and by operating the telephone repeaters at about 10 db
lower on peaks than the point of overload, a visually monitored program circuit became a reality.
From this early start, there developed a long series of devices, some
with tube rectifiers, others with dry rectifiers (peak and rms indicat-
WHAT YOU'RE UP AGAINST
11
, full- and half-wave rectification, all degrees of damped movements, and calibrated with reference levels of 10-9, 1, 6, 10, 121/2, or
50 milliwatts, in 500 or 600 ohms impedance. It was not until 1938
that the Bell Telephone Laboratories, the Columbia Broadcasting
System, and the National Broadcasting Company pooled their knowledge and problems in a joint effort to develop a standardized volume
indicator with the reference level implied in the definition of volume
units.
The outcome of this concentrated study was the new standard vu
meter such as those on the control panel of Fig. 1-1 (B) . The schematic diagram of Fig. 1-7 shows the circuit used to bridge the meter
across program lines or individual studio output lines. It is seen that
the total impedance presented to the line is about 7500 ohms; 3900
ohms in the meter and about 3600 ohms supplied externally to the
meter. The dynamic characteristic is also standardized as mentioned
earlier, being such that, if a 1000 -cycle voltage of such amplitude as to
give a steady indication of 100 on the voltage scale or 0 db on the
decibel scale, is suddenly applied, the pointer will reach 99 in 0.3
seconds and overswing the 100 mark by not more than 1.5%. This
meter is a great improvement over previous volume indicators where
large amounts of overswing often occurred.
The graph of Fig. 1-4 is a representation of a speech wave taking
place in the time interval of 1/100 second. It is obvious that due to
mechanical inertia of meter movements, true "peak reading" indicators are impossible in the strict sense of the term. Since the copper oxide instrument, indicating rms values, is sufficiently sensitive without the use of vacuum tubes, and since in the final analysis, the
indication on the meter should follow as nearly as possible the psychological effect of hearing, this type indicator has been standardized for
control room and line transmission use. Although peak -reading indicators are much faster than rms instruments, in actual practice their
accuracy is limited to about 100 cycles per second. At the higher
frequencies their function is to integrate the speech occurring over
a period of time.
As will be discussed in detail in the transmitter section of this handbook, the FCC specifies some form of semi -peak indicating meter to
measure modulation percentage at the transmitter. This is necessary
since the peak factor (ratio of peak to rms values) of program waves
may be 10 db or more, and when these peaks occur in rapid succession, danger of breakdown in circuit components exists as well as the
ing)
12
BROADCAST OPERATORS HANDBOOK
occurrence of adjacent channel interference. Means must also be
provided to check positive or negative peaks of the modulated carrier.
Thus the modulation monitor is essentially a half -wave rectifier indicator. These differences between studio and transmitter meter characteristics must always be borne in mind by the operators.
Volume Indicator Interpretations
For the purpose of discussing the problems relating to use and interpretation of volume indicator readings, the well-known fact that
any wave, no matter how complex, may be reproduced exactly by a
number of sources of pure tones will be employed.
Fig. 1-8(A) shows two simple harmonic motions of the same frequency, differing slightly in phase; that is, tone b is lagging behind
(A)
a
TOTAL -O
b
(B)
Fig. 1-8. When two harmonic motions of the same frequency, waves a and
b, are out of phase by less than 180°, their total is greater than either, as
shown by the vector at right of (A). When a and b are 180° out of phase,
they cancel as shown in (B).
tone a by a certain number of degrees. The vector addition at the right
shows how the total amplitude is influenced by the reinforcement of the
two tones, causing an addition to the total magnitude over either one by
itself. Fig. 1-8 (B) illustrates what happens when the same tones of
similar frequency are differing in phase by exactly 180°. The vector at
the right shows complete cancellation of the total energy, since the
tones are now opposing each other resulting in zero amplitude. Keeping this clearly in mind, it is seen that the total amplitude will be
larger for smaller angles of phase difference, and if the two tones are
exactly in phase, the parallelogram at the right collapses and becomes
WHAT YOU'RE UP AGAINST
13
a straight line that is the sum of the individual amplitudes. As the
angle of phase displacement becomes larger, the total amplitude becomes less, until at 180° it becomes zero.
In actual practice, it is realized that under program conditions a
large number of different frequencies with varying phase displacements
are being covered, and the loudness sensation produced in the ear for
a given meter reading is dependent on the number of harmonics present and the phase relationships of these harmonics. It then becomes
obvious that acoustical treatment of studios and type of program
content will influence the correct interpretation of a volume indicator
reading. It is, of course, apparent that the volume indicator performs
its duty in respect to showing the magnitude of the waveform,
whether it be "distortion peaks," noise, or musical sound, that must be
kept within the dynamic range of the transmission system. But when
correlating the reading of the volume indicator with the effect produced
on the hearing sense of the listener, these problems must be met and
analyzed. The loudness sensation for a given meter swing indication
has already been discussed in regard to voices of different persons.
The same characteristic is noted between individual musical instruments where the number of harmonics and their phase relationships
may vary in wide degrees.
Dynamic Range Indication
The volume indicator is used as a means of visually monitoring the
magnitude of the program waves for two primary reasons: (a) to
compress the original wide dynamic range to an amount consistent
with good engineering practice of the broadcast transmission system,
and (b) for locating the upper part of the dynamic range below the
overload point of associated equipment. For the latter purpose, a
scale of 10 db would be adequate; for the former purpose, a much
wider decibel range is desirable. Since the instrument is used for both
applications, it was decided that a compromise on a scale length of 20
db would be desirable. It appears that as the art and appreciation of
higher fidelity service advances, not only the frequency range but also
the dynamic range of transmission will be extended, particularly for
certain types of program material. This feature becomes a very important one for f -m service. With present-day meters, it is left to the
experience and judgment of the operator as to how far the volume
should be allowed to drop below the visual indication of the vu meter.
It would appear then that, in the interest of good operating practice,
14
BROADCAST OPERATORS HANDBOOK
some form of auxiliary monitoring of passages below the present-day
meter indication point on types of programs requiring wide dynamic
range, might be worth while. A suitable oscilloscope used in conjunction with the meter might be one solution. The practicability of this
method would be doubtful due to the fact that the operator's attention must be divided between the monitoring device and the studio
action. The same drawback would exist for an indicating meter of
such wide scale that the entire meter action does not fall readily into
the operator's line of vision. A meter of, say, 270 -degree scale would
have the same disadvantage of having either the low-passage or max-
imum-passage indication fall at an awkward position.
Perhaps the most practical solution would be a device consisting
essentially of two indicating pointers, one immediately below the
other. The lower pointer would indicate the first 50% of channel
utilization, with automatic overload protection built into the movement (by limiting tube or network) to prevent overload of this movement when the volume is such that the upper movement is indicating
the final 50% of channel utilization. The design should be such that
either indicator is in a practical plane of vision for the operator.
Chapter
2
ARE MECHANICAL OPERATIONS APPARENT?
THE REALM of the physical, mental, and psychological faculties
of the control -room operator lies the success or failure of the
broadcaster's daily schedule. A script -writer's masterpiece or a
composer's dream can amount to no more than the original worth of
N
his work, plus the ability of the control man to interpret that work on
the technical equipment at his command. Yet, perhaps paradoxically,
the best qualified operators are the least conspicuous to the listener
at home.
An ideal job of switching and blending of microphones for the various performers of a given show is such that the listener -in is entirely
unconscious of mechanical operations necessary to their performance.
The operator who "cuts" Lis program at its conclusion, instead of
fading out (even though because of time limitations it must be a
"quick fade"), not only makes mechanical operations apparent to the
listener, but marks himself as a man not entirely a master of his equipment. Exceptions to this rule exist, such as "stunts" of a technical
nature that are sometimes aired to impart a technical flavor to the
layman. In such programs, technical operations should be accentuated,
of course, rather than subdued, but it is well to remember that, as a
general rule, the test of the operating technique should be, "Are me-
chanical operations apparent?"
This primary rule should govern the entire operating technique of
the control man. Music, speech, or background accompaniment that
is too high or too low in level should be gradually adjusted to normal
in a manner cognizant of musical and dramatic values. It might appear at first that this prime requisite for good operating practice
would conflict seriously with good engineering practice. When levels
are too high, overloading of associated equipment at the transmitter
occurs. When compression amplifiers are used, as is commonly the
case, the distortion arises from excessive compression rather than from
overmodulation of the transmitter. It has been proved from extensive
tests, however, that distortion caused by momentary overloads simply
15
BROADCAST OPERATORS HANDBOOK
16
is not noticeable even to highly trained ears. This appears to be due
to physiological and psychological factors that determine the ears'
appreciation of aural distortion, resulting in a lack of response to overload distortion occurring at rare intervals and of short duration.
The level of the speaking voice can be least obviously adjusted by
correcting the fader setting between words or sentences where slight
pauses occur, rather than increasing or decreasing the volume during
PROGRAM TITLE
t
DATE OF BROADCAST
Musical Clock
FOR
Thursday Aug.19
t
MEDIUMt
Books
t
FROM
7,15 am
t
TOt
ET and Recordings
8,15 am
RECORD OR TRANSCRIPTION
TITLE OF COMPOSITION
BRAND
SERIAL NUMBER
Got the Moon In My Pocket
W
How About You
Vi
Ferry Boat Serenade
11
Back Home Again in Indiana' De
Blueberry Hill
*
America, I Love You
Co
x
Chinese Lullaby
PERFORMING SOC.OR LICENSING AGT.
ASCAP
ASCAP
ASCAP
ASCAP
ASCAP
ASCAP
ASCAP
5163
27749
3921
3786
3829
35865
6690
LEGEND,
W
-
Vi
De
Co
Th
-
-
World
Victor
Decca
Columbia
Thesaurus
Fig. 2-1. Typical music sheet for a program of recordings supplied to the
announcer operating the turntable and the control-room operator. Brand
names enable operator to anticipate volume level.
actual excitation of the microphone by the sound waves. A comparison
of these two methods by the operator on his audition channel will reveal the striking difference in the obviousness of level control.
Anticipation can play a major part in smooth level control when
circumstances permit. The operator soon becomes familiar with the
approximate fader setting of each announcer as he takes over to relieve the preceding announcer. It is obvious here, of course, that ample
opportunity is given to adjust the mixer gain before actual air time.
This is also possible in some instances with transcribed and recorded
shows, when the operator is aware of the brand of recording to be
played next.
Fig. 2-1 is a reproduction of a musical sheet for a given program
as used at Station WIRE in Indianapolis. The announcer, who operates the turntables, and the operator in the control room each has a
copy on hand for reference. It will be noted that the brand of each
number, such as World, Victor, Decca, is clearly indicated. This en-
ARE MECHANICAL OPERATIONS APPARENT?
17
ables the operator to anticipate the level to a certain extent, since, for
example, World transcriptions are several vu lower in level than
Victor recordings, requiring a higher fader setting. This will also be
influenced to a great extent by the type of filter used on the turntable
for various recordings, since a different filter is used in many instances
for different brands or conditions of recordings and transcriptions.
This is discussed more fully in the section on turntable operation appearing at the end of Chapter 4. The gain settings for a given brand
will usually be fairly consistent. Thus when the operator has become
familiar with the necessary fader adjustment for each brand of trancription or recording, he will be able to use the art of anticipation to
good advantage. When the level to be anticipated is uncertain, it is
well to remember that from an aesthetic point of view as well as a
technical point of view, it is far better to be able to "fade in" the
speech or music rather than to experience the shock of excessive volume which must be quickly lowered to normal values.
The foregoing discussion is likely to lead to an erroneous point of
view to a newcomer in a control room. It might be well to point out
at this time that one of the greatest errors of new men in this field
is to "ride gain" to the point of exasperation to a critical listener. The
operator should endeavor at all times to give musical and dramatic
values a free rein insofar as is practically possible. Remember that
from the listener's point of view, the business and purpose of broadcasting is to provide entertainment through the medium of bringing
music and dramatics into the home. The technical setup necessary for
this purpose has been engineered to a point of perfection; it is only
necessary that this equipment be operated in a manner that will
promote these musical and dramatic values in their original intent.
The fundamental rule of good operating technique is probably the
most abused by innocent operators during the transmission of symphony broadcasts. Suppose that an orchestra of some 40 to 80 members has just finished a number which for the past few minutes has
been very pianissimo, say -15 to -20 vu. It is safe to say that the
average listener to a symphony program will have his receiver volume adjusted so that comparatively high power exists in the speaker
when the studio level hits 0 vu. It is obvious then, what will occur if
the announcer suddenly pops in at 0 -vu level. The listener may not
be actually raised from his chair by this sudden human roar, but the
experience, to say the least, is a shock to all five senses, including
smell. Sudden crescendos in music are expected, welcomed, and ap-
18
BROADCAST OPERATORS HANDBOOK
preciated, but a single announcer, exploiting the glorious qualities of
Joe Glotz's Super Zoot Suits at an apparently greater volume than all
80 men with everything in their possession from a piccolo to kettle
drums, simply is not only unwelcome, but extremely obnoxious.
It is a safe rule to remember that after such musical numbers as
this, the announcer should be held down to about
maximum. The
difference to be maintained between levels of voice and music will
depend not only upon the type of program aired, but also upon the
acoustical treatment of the studio and will be mentioned in chapter 3.
The inadequacy of present-day broadcasting to the field of symphony music transmission is quite apparent to most engineers. The
discrepancy between the usual 70 -db dynamic range of a full orchestra and the actual 30 to 35 db allowed by broadcast equipment is all
too obvious to the control man handling such pickups. It has been the
practice of some operators who do not appreciate the symphonic form,
to bring all low passages up to around -4, then "crank down" on the
gain as the orchestra increases its power according to the continuity
of the musical score. The fault in this technique should be apparent.
If the very lowest passages are brought up to just "jiggle" the meter,
and care is taken to use good taste in suppression of the crescendos,
a very satisfactory dynamic range may be experienced, since even a
range of 25 db will vary the output at the receiving point from 25
milliwatts to nearly 18 watts on peaks.
Needless to say the technician on a symphony program, or any
musical program, should possess a good ear for music. Rules and regulations will never help a man with a pair of "tin ears" to handle a
musical show properly. There are, of course, many competent technicians who do not like or appreciate music, and these men should be
assigned to the performance of technical maintenance or transmitter
duty. It is nevertheless important that the transmitter technician
understand that a great amount of modulation during classical music
will be below 20% even with compression line amplifiers.
Recordings and transcriptions of symphony music have already been
compressed into broadcast dynamic range, since the recording engineer has essentially the same problem to contend with in relation to
this difficulty. Usually all that is necessary for the control technician
to do is to set the level on the peaks of the music to correspond with
0 vu or 100 on the scale, and "let it ride."
Specific symphony pickup will be discussed in chapter 11 since this
type of program is often handled as a remote program.
-6
Chapter
3
KEEPING SOUND "OUT OF THE MUD"
correlating volume levels with comparative
loudness of speech and music has appeared as an item of major importance and should no longer be ignored by broadcast
station personnel. Table 1 was compiled as a result of "group tests" of
comparative loudness of different types of music with that of speech.1
The "peak factor" (ratio of peak to rms values) of speech waveform
is very great in comparison to that of music waveform, as emphasized
by Fig. 3-1. It is apparent, therefore, that 2 to 3 db more power may
exist in speech waves in a circuit monitored by an rms meter than is
indicated by the meter itself. This will explain the results shown in
Table 2, which as well as Table 1, was taken from the aforementioned
article. It is apparent then that when speech and music levels are
THE PROBLEM of
TABLE
1
Volume Indicator (RMS) Reading
for Same Loudness as Speech
Type of Program
Male speech
Female speech
Dance orchestra
Symphony orchestra
Male singing
0
0.1
2.8
2.7
2.0
Showing importance of peaking music 2 to 3 db higher than male speech for equal
loudness sensation. (See text.)
adjusted in correct ratio to avoid overloading, the loudness will be
approximately the same.
Table 1 contains a discrepancy with the author's personal experience, and is mentioned with the hope of further research and clarification. It will be noticed that results of the tests on this particular
group of listeners dictated the need for a 2.8 -db higher level for a
' Chinn, Gannett, and Morris, "A New Standard Volume Indicator and Reference Level"; Proceedings, IRE, January 1940.
19
BROADCAST OPERATORS HANDBOOK
20
dance orchestra, and a 2.7 -db higher level for a symphony orchestra
over that of male speech. If the author was to compile a similar table
of equal loudness from several years experience of watching volume
indicators (VI's) on various types of programs, he would choose approximately 3 db higher level for a dance orchestra, and 4 to 6 db
;nigher for a symphony orchestra over that of male speech. The author
(A)
Fig. 3-1. The "peak factor" (ratio of
peak to rms values) of music waveform
(A) is not as great as the peak factor
of voice waveform (B).
(8)
that this is not caused by a different physical response of the ear
itself, but rather to a possible difference of acoustical factors involved,
plus the fact that certain psychological factors were not considered
in the original tests. By this is meant the important difference in
feels
TABLE 2
Total No.
Type of Program
No. of
of
RMS
Volume
Tests
Observations
Indicator
Male speech
Female speech
Piano
Brass band
Dance orchestra
Violin
8
8
81
82
5
5
40
25
42
1
15
22.1
22.8
24.1
24.1
24.7
25.8
Average speech
Average music
16
15
163
122
22.4
24.5
4
The final column shows average overload points of different types of programs,
measùred at the output of a W.E. 94B amplifier. The important fact of this table
is the revelation that the point of overload for average speech is about 2 db lower
than the point of overload for average music (rms volume indicator).
KEEPING SOUND "OUT OF THE MUD"
21
listening technique between the symphony audience and the dance music listener.
As was mentioned before, because of the nature of the classical type
of music, the symphony fan at home will operate his receiver on the
average a great deal higher in level than he would for ordinary programs. Five minutes of symphony music will have perhaps 3 to 4
minutes of low to very low levels; the average intensity level over a
period of time is far lower than the average intensity level of a dance
orchestra in the same time interval. It should then be obvious that a
greater difference should exist in the ratio of music to speech levels
for symphony programs than for those of dance music. Perhaps if
tests were carried out with this difference in receiver volume considered, as well as the type of music on the program, the results would
be more nearly in agreement with the foregoing argument.
The acoustical treatment of the studio in which the program originates will affect to a great degree the loudness of voice and music, and
in a different ratio. A studio that is overtreated with absorbent material deadens the sound because of high -frequency absorption, and is
an outstanding enemy to musical programs. Music from "dead" studios is "down in the mud," lacking in brilliance, and generally dull to
hear. The effect on speech, however, is not so pronounced as that on
music. Speech originates within a few feet of the microphone and requires much less reverberation to assure naturalness, whereas the space
10
20
.
30
40
50
60 70
OPTIMUM REVERBERATION
80 90 100
150
200
TIME
Fig. 3-2. Graph showing the influence of acoustical conditions on ratio
of peaking voice and music assuming a necessary 2 -db difference for
optimum acoustical conditions.
between the source of the music and the microphone is greater, and
many things happen to the musical waveforms that must eventually
be translated into perceptions of loudness.
Fig. 3-2 is a graph drawn on the assumption of a necessary 2-db
BROADCAST OPERATORS HANDBOOK
22
difference of voice and music level readings on an rms meter under
normal acoustical conditions. The optimum reverberation time will
vary according to the size of the studio, as shown by the curve of Fig.
3-3. The curve of Fig. 3-2 is drawn on a probability basis, correlating
known facts concerning reverberation time with loudness sensation of
voice and music. This graph shows the necessity of a lower peaking
of voice in relation to music for less reverberation time than normal,
2.5
2.0
Fig. 3-3. The optimum reverberation time varies with the
size of the studio, as is evident
from these curves. See also Fig.
128 CYCLES
1.5
512
1.0
2048 CYCLES
3-2.
After Knudsen
0.5
6.25
200
100
50
25
CUBIC FEET-THOUSANDS
12.5
400
and at the same time shows that for 1.5 times the optimum reverberation time, where a great amount of reinforcement of the original musical waves takes place, the voice and music should be peaked the same.
It should be pointed out here that so called "optimum reverberation
time" really is an expression of what constitutes pleasing sound, and
this conception is still changing with experience. It may well be that
near future standards of optimum reverberation time will see a condition which will decidedly alter the above discussion of ratio in peaking voice and music. The point that is important to keep in mind is
that a great majority of present-day studios throughout the country
are below even up-to-date standards of correct reverberation characteristics; hence the need for the discussion.
The newer "live end, dead-end" studios, with musical instruments
placed in the live end and microphones spotted in the dead end, present one solution for properly controlled reverberation. In these studios, voice and music peaked at the same level will appear the same
in loudness sensation. In fact, the advancing state of studio development points to all indications that the present day is experiencing a
transitional era in which, from some of the most modern studios using
reflecting panels for musical pickups, the brilliance of the music is so
great that, when peaked an amount on the meter equal to that of
KEEPING SOUND "OUT OF THE MUD"
Courtesy National Broadcasting Co.
Figs. 3-4(A) above, 3-4(B). The live end of a "live -end, dead-end" studio
designed to provide properly controlled reverberation. Slanted wooden
sound-dispersing panels are suspended against the side walls, forming a
series of resonance diaphragms, shown in (A). The walls of this studio are
slanted (B) to eliminate standing waves that cause flutter.
23
BROADCAST OPERATORS HANDBOOK
24
TeBzE 3
Instrument
Bass viol
Bass saxophone
Trombone
Trumpet
Trumpet (muted)
French horn
Clarinet
Flute
Violin
Piano
Electric organ
Pipe organ
Studios of Optimum
Reverberation Time,
Distance in Feet
6
6
Studios of 25% Optimum
Reverberation Time,
Distance in Feet
4
4-5
12
5
7
8
5-6
8
8
6
5
5
3-4
5
15
3
10
15-20
20-25
8-10
10-15
7
voice, the voices sound much lower in loudness than the music. This
brings to mind again the importance of using judgment in aural perspective when "riding gain" on productions with the intent of achieving a properly balanced effect in the listener's home.
The use of wood in broadcasting in accordance with exact acoustical
specifications for controlled reverberation was apparently introduced
by CBS in New York about 1935. The entire "live end" of the studio
was constructed as a series of resonance diaphragms of seasoned wood,
held in suspension with air chambers behind them, as shown in Fig.
3-4(A). The wood panels that cover about one-third of the side walls
are placed on slanted surfaces so that the side walls form shallow
"V's" running from ceiling to floor. These are so placed that the wall
surfaces are not parallel to one another, as shown in Fig. 3-4(B).
This eliminates standing waves which would normally produce "flutter." However, because of the highly reflective surfaces of the wood,
a certain amount of reverberation is achieved, a quality which adds
life and brilliance to the speech and music originating in this type
studio.
This is essentially the same principal used by WBBM (CBS) in
Chicago and other key points, as well as by the other major networks
irl their key stations. A number of smaller independent stations have
since utilized this type of construction in their studios, and it is
hoped that others who contemplate new studios or remodeling of old
ones will recognize the tremendous importance of a degree of liveness
in broadcast studios.
Chapter
4
YOU'RE OFTEN A PRODUCER TOO
the control room is called upon many times to
set up complex musical and dramatic shows. This is especially true in smaller stations that have no production man,
and is sometimes true of important key network stations where the
control man must achieve the desired results of the production man
assigned to a particular show. The responsibility of setups of studio
shows is not a simple one. Many years of research and much thought
have gone into production, and a knowledge of at least the fundamentals of the art, as they affect the technical duties, will help the control
technician over many difficult situations that will arise in the course
THE OPERATOR of
of his work.
',
In determining the proper use and placement of microphones for
any given setup, it is important that the operator becomes familiar
with the pickup patterns of the microphones used. These patterns illustrate completely the function as to amplitude and frequency response for varying degrees of placement about the face of the microphone. Fig. 4-1(A) shows the pattern of the RCA 44-BX velocity
microphone, and Fig. 4-1(B) is the pattern of a RCA 77-B combina-
30°30°
50°,é ,
10° 0
45°
°
:::
45°
50°
d-!e
-:..-:-.I
60°,'.,
1
45°
o
10°
60°
30°
45°
0
Courtesy RCA Mfg. Co.
Fig. 4-1. The pickup response pattern of the ribbon or velocity microphone
(A) is bidirectional and that of the combination ribbon and pressure type
(B) is unidirectional.
25
26
BROADCAST OPERATORS HANDBOOK
tion ribbon and pressure type instrument. There are several important
points of interest relating to these patterns which show great differences in characteristics aside from the most apparent one, that of bidirectional and unidirectional pickup.
An analysis of the patterns reveals a much wider range of amplitude
response for the combination pressure gradient (ribbon) and pressure
type microphone [Fig. 4-1 (B) ] than for the ribbon type alone. See
Fig. 4-2. Take for example the 1000 -cycle curve for the 44-BX ve -
90°
Fig. 4-2. The amplitude response of the 77B
combination type microphone (solid curve)
has a wider range than the 44BX velocity
microphone (dotted curve). Such patterns are
useful for making setups and eliminating unwanted sounds.
locity microphone. It is noted from Fig. 4-1 (A) that at an angle of
70 degrees, the amplitude response is down about 10 db in respect to
its response at a given distance at 0 degrees. Now note on the 1000cycle response curve of the 77-B combination type in Fig. 4-1 (B) that
the amplitude response at 70 degrees is down only approximately 3
db from 0 degrees reference. These patterns are useful for determining the setups necessary for discriminating against unwanted sources
of sound, and for obtaining a particular relation between sounds of
different sources. It can be seen that as a performer is moved around
the microphone, loss of sensitivity may be compensated for by moving
closer to the instrument.
It is clear then that characteristics of the type or types of microphone in use should be thoroughly understood. Fig. 4-2 is presented
as a basic principal in using patterns of a unidirectional microphone
of the combination ribbon and pressure type. It is a well-known fact
that, because of the pressure gradient characteristic of the ribbon microphone, the instrument will favor the lower frequencies of longer
wavelength under close talking conditions. For this reason announcers
on such microphones must be at least 1.5 to 2 feet from the microphone. When close talking becomes necessary, however, the combination type instrument may be utilized by the engineer, who can then
safely instruct the announcer to approach an angle of 90 degrees with
YOU'RE OFTEN A PRODUCER TOO
27
the face of the microp_lione as shown in Fig. 4-3, and work as closely
as desired. In this position the ribbon element will contribute practically no energy to be output, leaving the pickup to the pressure
element, which is not afected by the spherical character of close talking sound waves.
It may be seen that the "fading zone," where sensitivity falls off
rapidly for increasing angles, is just as useful as the ordinary pickup
zone, since the quality k just as good and a fine degree of shading may
be realized by understanding its proper use.
As will be described :and illustrated in the technical explanation of
microphones in Part 6, a number of modern ribbon and combination
microphones have an as ociated equalizing feature known as a "speech
strap." In the "speech" position, close talking into the ribbon element
will not result in excess:7e bass response. When the same microphone,
however, is used both r the musical pickup and the announcer, the
strap is placed in the "music" position, and the announcer must work
the mike as explained above.
As far as is practicE ily possible, only one microphone should be
used for a given pickup. When two or more instruments are used,
serious frequency and delay distortion is likely to result, since each
f
ANNOUNCERS
ZONE
PICK-UP
ZONE
60°^,
00
Fig. 4-3. When close talkinª into the combination type microphone is Iecessary, it can
be approached as closely a: desired in the
zone between 60 and 90 degr 2es. The lower
response of the "fading" zone between 90
and 120 degrees, does not af'ect the quality.
L.:o%.1
11W«,5,4
120°
120°
Courtesy Western Elec`ric Co.
DEAD
FADING
ZONE
microphone will be a dr_fferent distance from a given sound source.
It can be seen that soutd waves would not reach the instruments at
the same time, and their combined outputs will result in partial reinforcements or cancellation, depending on their phase relationship.
When it is absolutely necessary to use two microphones very close
BROADCAST OPERATORS HANDBOOK
28
together, they may be poled so that their outputs are additive rather
than subtractive, either by rotating a bidirectional microphone
through 180 degrees, or by reversing the connections on a unidirectional microphone when the outputs are subtractive. This may be accomplished by using a patchcord between any two terminations of the
circuit on the jack panel, and reversing one end at a time during the
test. The proper phasing of the two instruments is accomplished by
watching the vu indicator when the two inputs are switched to the
first one, then both together, and noting whether the combined outputs are additive or subtractive. Usually one connection will give
greater additive effect than the other connection, and this effect someORCH.
7
\
/
`
\
,
00001
O
\ `/
-.0j
l
M
(
)
/00000\
O
NULL
NULL
\
/
\
\
_./
)
Fig. 4-4. A good basic arrangement of ribbon type microphones, M, for
proper pickup of sounds from two sources. The dotted circles indicate
the microphones' response areas.
times changes with a change of frequency; although for complex
waves where we are not concerned with pure tones of a single frequency, a good average additive effect can be obtained. Fig. 4-4 shows
the basic idea in proper placement of microphones when two are necessary for proper pickup of two separate sound sources.
As a rule, the most common error of newcomers to control rooms is
the placement of the microphone too close to the sound source. As has
been discussed before, loudness sensation for a given meter reading
YOU'RE OFTEN A PRODUCER TOO
29
depends largely on the harmonic content of the waveform. Placement
of the microphone extremely close to the musical instruments results
in peaks on the vu meter that are almost inaudible to the listener, and
since the intensity of these peaks must be kept below 0 vu, the resultant music is completely "down in the mud" and lacking in brilliance. Smooth control under these conditions is impossible, and harmonic content is very low.
For pickup of piano music, a distance of at least 15 feet between
microphone and piano should be observed in studios of optimum reverberation time. More intimate pickups are necessary for dead studios, since no reinforcement of the sound waves takes place. Too great
distance in such studios results in a thin sound, lacking in body.
For the purpose of presenting a basic rule for distance in microphone placement for certain instrumental solos, Table 3 is presented.
This table is not meant to be an infallible rule of exact distances in
microphone placement. It is intended to convey an idea of the minimum distance to start from on rehearsals before air time. Any change
to be made then would be toward greater distances rather than less.
It is imperative, of course, that the operator experiment with microphone placement in his own studios to get the best results from its
particular acoustical condition.
The effect of phase shift in studios on the quality of musical sounds
is important even though the human ear is not essentially a "form
Fig. 4-5. The energy
arriving at the microphone M is the sum
of the initial energy
W1 of the direct sound
from the source S together with the reflected wave trains W2
and
W3.
analyzer." Phase shift causes trouble in both live and dead studios.
"Dead spots" nearly always exist in studios because of cancellation
of large amounts of the complex wave frequencies caused by phase
shift. Fig. 4-5 illustrates the basic theory of wave -train travel from
its source to the microphone spot. The energy at M, the microphone,
30
BROADCAST OPERATORS HANDBOOK
is the energy of the initial direct wave train WI from the sources,
plus the energy of the reflected wave trains W3 and W3. The amount
of energy of the reflected waves is governed by the characteristics of
the reflecting surface, which in turn determines the reverberation time
of the studio. It may be observed here how phase shift, because of the
different distances over which the waves travel, could cause reinforcement or cancellation of certain frequencies at the microphone spot.
Complete dead spots are more likely to occur in live studios, since
reflection from a perfectly hard surface causes no change in phase
of the individual frequencies of the complex wave, creating a condition in which, theoretically, complete cancellation of the entire spectrum at a particular spot in the studio might occur. In dead studios,
absorption of the higher frequencies is greater than at lower frequencies, thus making complete cancellation of the complex wave unlikely.
If this phenomenon is fully understood, it will be realized that microphone placement is much more critical in dead than in live studios,
since dead spots are easily avoided in live -end studios where reinforcement of the musical tones is smooth and even over the entire spectrum
of frequencies for a given microphone spot; whereas the placement
is only a compromise of the greatest possible frequency range for a
given pickup spot in dead studios. Construction of the new live-end
studios with sidewalls arranged in "V's" so that no surface is parallel,
results in a dispersion of sound that helps to overcome the occurrence
of dead spots in this type of studio. The contribution of the reflected
waves in a live -end studio to the loudness intensity, resulting from the
reinforcement and sustaining of the overtones of the musical instruments, gives these studios a decided advantage over the older type
"general purpose" studios.
Importance of Rehearsals
The co-ordination of hand, ear, sight, and sound for the purpose of
blending the component parts of a studio performance is best gained
by the operator through the medium of rehearsals. Fading in or out
of various microphones, turning them off and on, is the procedure
which enables the engineer to play upon the sound of voice and orchestra much as if the control panel itself were a musical instrument.
Indeed, in a sense, this is just what it is. The ratio of fader adjustments will determine the apparent distance of a singer from the audience; the voice may be smothered with music or may be made to
stand alone with only a suggestion of background accompaniment. A
YOU'RE OFTEN A PRODUCER TOO
31
proper blend of voice and music, or of dramatics and sound effects,
can only be properly created through careful and detailed rehearsals.
This is the one and only method of preventing the "on air" show from
becoming only a caricature of the original idea.
Many "c:1 timers" are familiar with the coloratura soprano who
is nicely "adjusted" on rehearsal, then hits +20 vu on the air without
batting an eyelash. This condition simply emphasizes one important
point: the operator must be apt at diplomacy as well as technically
conscious. Talent must be made cognizant of the importance of treating rehearsals just the same as "on air" performances. If the performers are instructed in "mike technique" from the point of view
of making their performance sound just the way they desire to the
listener, the operator will find ready and willing co-operation. Do
not be shy of temperament. The more temperamental the performer,
the more he likes to be "fussed over" at rehearsals to gain emphasis
of his best talents. Ask any operator or producer of big time shows
out of New York, Hollywood, or Chicago; they are in a position to
know.
The distance to be maintained between vocalist and microphone
will depend on the type or style of vocal form used by the singer. In
general there are two commonly encountered types of vocalists, the
"crooner" and the "operatic" singer. Whereas the crooner will employ
a dynamic range of around 15 vu, the "operatic" singer will use a
much wider dynamic range. For the former type, where the sound
waves are garnered principally from activation of the upper larynx
and throat muscles with comparatively low-pressure waves resulting,
it is usually necessary to work close to very close into the microphone.
The vocalist who "sings out" by bringing the chest muscles into action must be placed a minimum of 4 feet, preferably 6 to 8 feet, from
the microphone. This may appear to be an excessive distance, but
actually a much greater dynamic range and brilliancy of voice may be
realized by using this distance for singers who range from extremely
low to very high air pressures to excite the microphone element.
There are of course a number of "in between" singers, such as some
of those who sing with dance orchestras, and they are usually placed
from 2 to 3 feet from the microphone.
Microphone technique for actors in a dramatic program spells success or failure in creating the desired illusion in the loudspeaker.
,Usually one microphone only is used for the entire cast, with a separate microphone for sound effects. As each actor plays his part, he
BROADCAST OPERATORS HANDBOOK
32
steps up to the microphone, sometimes approaching from the fading
zone into the announce zone to create the illusion of approaching the
scene of action, sometimes leaving in the same manner. In some cases
"board fades" are marked on the script [Fig. 4-5 (A) ]. The operator
fades the entire studio setup including sound effects by fading out
with the "master gain" control. Shouts or screams must be performed
in the shading area "off mike" to avoid excessive pressure on the microphone element which would require an excessive gain adjustment
by the operator, losing the effectiveness of the illusion.
While studio rehearsals are in progress, it is imperative that the
engineer and production director be able to talk to the cast for the
purpose of instruction in positions, microphone technique, etc. This
is accomplished by means of a "talk -back," which consists of a microphone in the control room connected to an amplifier feeding a loud -
1.
OPENING SOUND.
2.
NARRATOR.
(ORCHESTRA)
Have
Le
ever been
to Hell?... Well I have ... and nov I have to go back...
3.
4.
to
stay:
MUSICAL CRESCENDO
5.
SOUND.
6.
NARRATOR.
-
THEN SILENCE FOR 3 SECONDS...
She had everything a man could want, topped off with
7.
a beautiful name ... Clarissa.
8.
that first night I saw her,
9.
had been for hours,.. -and..
I'll never forget
it vas raining...
10. SOUND.
PADE IN RAIN ON PAVEMENT.
11.
CAR SWIFTLY PASSINO..SPLASHINO WATER..
12. CLARISSA.
(STARTLED) (OPP MINE)
13. NARRATOR.
Oh Miss:
as it
STREET NOISES..AUTO HORNS.
Oh:
That's a tough break... Better get back here..
14.
farther from the curb.. Motorists don't think you know.
15.
Here-share my umbrella.
X16.
í
SOMBER, DRAMATIC STRAINS
(LOW MONOTONE, VERY CLOSE TO MIRE).
CLARISSA.
i*17.
xa18.
(DRY LAUGH).
yours?
I
shan't get any wetter nov..
(PAUSE)
My name's Clarissa, What's
I'm afraid
Thank you anyway.
(START BOARD FADE HERE)" 3 SECOND PAUSE.
Just like that... and she vas young..
19. NARRATOR.
(REMINISCENTLY).
20.
and so sweet... and beautiful:
Fig. 4-5(A). Sample of script which an engineer has marked so that he can
"cue" himself for what is coming. The "board fade" is done by fading the
master gain control. Note that in line 10 the "fade in" might be done by
the turntable operator if sound is on records; it rain and street sounds
originate in studio, control man fades in associated microphone.
YOU'RE OFTEN A PRODUCER TOO
33
speaker in the studio. Switches on the control console and perhaps
also on the production director's console where such is used, are provided for the talk -back mike. The control man is sometimes provided
with a foot-switch to free his hands for the controls. When this mike
is turned on, the control -room speaker is cut off by a relay interlocked
4.1)
Z
ula
CC
TROMBONES
3 RD. SAXOPHONE
1ST. SAXOPHONE
TENOR SAXOPHONE
4TH.SAXOPHONE
Fig. 4-6. Microphone arrangement for musical show often necessary in a
"dead" studio.
with the switch to prevent acoustic feedback. This microphone is also
electrically interlocked with the "on -air" position of the output switch
so that it may not be operated during the time a show is actually being broadcast.
Musical Setups
Figs. 4-6 and 4-7 illustrate specific setups for musical shows. Acoustical conditions are so varied that no specific rules can be drawn up
for instrumental placement about the microphones. The most important rule is to be thoroughly familiar with the pickup patterns of
the microphones used, as outlined previously. One microphone is to
be preferred in a sufficiently live studio for a complete musical aggregation, whereas dead studios requiring more intricate pickups, may
require two or more microphones to cover all the musical instruments.
Network practice in the pickup of twin pianos is illustrated in Fig.
4-8. The lids of the pianos are removed and the microphone raised
slightly higher than for single -piano setups. When an audience is pres-
34
BROADCAST OPERATORS HANDBOOK
TRIANGLE
BASS
SNARE
XYLOPHONE
CHIMES
TYMPANI
TRUMPETS
TROMBONES
NN
FRENCH HORNS
2ND.VIOLINS
VIOLAS
BASS
VIOLS.
iST.VIOLINS
3
Fig. 4-7. Orchestra and choral arrangement for a "live" studio, mike 1 for
main orchestra; mike 2, soloist; 3, announcer; 4 and 5 for choir, when clarity
of diction is needed. Mike 2 used for over-all choral effect.
ent in a studio, "applause" and "laugh" mikes are swung out over the
audience on booms or suspended from the ceiling so that the "presence" of the audience may be "boosted" in gain by the control engineer when necessary.
When obtaining a check on the "balance" of the various instruments
on a musical program, the monitor speaker volume in the control
room should not be run at excessively high levels. There is a tendency
on the part of many control men to run their monitor speakers at
Fig. 4-8. A microphone M for a twopiano pickup is placed between and
slightly higher than the pianos from
which the lids have been removed.
levels that are almost never maintained in the home. Fig. 4-9 illustrates the relative response of the "average" ear to different frequencies at a given level. It may be observed that the threshold of
hearing at 32 cycles is 60 db, whereas for a frequency of approximately
YOU'RE OFTEN A PRODUCER TOO
35
-8
2500 cycles the threshold of hearing starts at about
db. When
control -room speakers are run at excessive levels, bass response is
much greater than it would be at normal levels, which is likely to
result in the placement of the bass instruments in a lower sensitivity
area of the microphone. When this occurs, bass response is almost
140
i
m
O
120
U
á
/
100
1`
z
Fig. 4-9. The lower curve
á 80
shows how the average
human ear responds rela- wQ 60
tively to different frequencies at a given level.
40
See text.
z b
0
cr
FEELING
//
N
N
.
N
THRESHOLD
OF
HEARING
i
1
I
20
0
-20
10
20 40
100 200 400
1000 2K 4K
10K
20K
601'.
inaudible in the receiver at home. This characteristic of the human ear
has resulted in the development of the "bass boost" circuit in modern
receivers which is intended to accentuate the bass response in receivers
operating at low levels.
Sound Effects
Major network practices in the art of sound effects has developed
over the years into one of the most highly specialized fields of broadcasting. A sound effects technician can take the lowly strawberry box
and create illusions ranging from the squeak of a wooden gate or the
squeak of a ship moored to a dock, to the terrible rending crashes and
splintering cf wood for collisions of any description. A bow of a bass
viol is drawn in a particular manner over the edges of the box for the
first effects, while the box is crumbled between the hands close to the
microphone for the collision effect. Rainfall is simulated by the pouring of birdseed or buckshot on a sheet of parchment or by a rain machine, consisting of perforated pipes through which water pours onto
brushes in a tub, as shown in Fig. 4-10. Of course, actual objects are
also used to produce certain sound effects as illustrated in Figs.
4-11 (A) and (B), which show the contents falling out of Fibber Mc Gee's famous closet on the NBC "Fibber McGee and Molly" program.
36
BROADCAST OPERATORS HANDBOOK
YOU'RE OFTEN A PRODUCER TOO
37
BB shot rolled back and forth with skillful timing over a copper
screen can simulate either a lazy palm -bordered beach or a veritable
turmoil of angry waves in an ocean storm. Cellophane crackled
gently between the hands close to the microphone can create the illusion of the most terrible forest fire imaginable.
The sound technicians' heterogeneous collection as shown in Fig.
4-12, consists of all sorts of weird machines, hail and wind machines,
boxes in which glass is shattered, thunder drums, hurricane machines,
NBC
Photo
Fig. 4-10. Sound effects for a good night for a murder.
The noise of the howling wind comes from the electrically revolved reeds in the circular shield at the right,
controlled by the operator's foot, and the heavy rain-
storm results from the rain machine on the left, being
turned on full force.
heavy doors on frames, keys, and a thousand items entirely beyond
the scope of this book to reveal. In addition he has a console on which
a number of turntables are mounted with their individual pickup
38
BROADCAST OPERATORS HANDBOOK
arms and dials which automatically "count" the number of grooves
set in from the edge for proper "cuing" sound effects. These turntables may be varied from 0 to about 150 rpm to make still more flexible the number of weird and uncanny effects that can be obtained
from recordings.
NBG'Photo
Fig. 4-12. The sound equipment storage room in the Chicago studios of the
National Broadcasting Co.
The voice can be made to sound as though it were coming over a
telephone by means of a "filter mike," which is simply a microphone
run through a filter amplifier, clipping high and low frequencies so
that the quality is similar to that heard in the telephone receiver.
Reverberation may be added by feeding the signal to be so treated into
e
PK.
Fig. 4-13. The further a microphone is placed from the speaker
in a "reverberation chamber,"
the larger seems the hall or cavern in which the action occurs.
a speaker at one end of a "reverberation chamber" as illustrated in
Fig. 4-13. The farther away the microphone is placed, the larger be-
YOU'RE OFTEN A PRODUCER TOO
39
comes the hall or cavern meant to be simulated in the drama. The
illusion of talking in close quarters such as that of a telephone booth
is created by placing a microphone in a sound absorbent booth, as
shown in Fig. 4-14.
Although the average broadcast station is much more limited in
elaborate equipment utilized by the major network key stations, there
f:,:
Fig. 4-14. When a microphone is placed in
a booth with walls lined with sound -absorbent material, the resulting speech seems to
be coming from a telephone booth.
. :s:
:.\i,
L:..:r:K:. .:\:,
.\
MIKE
BOOTH
is no limit to the possibilities of using what equipment is available
to the ingenious technician. A good telephone effect can be achieved
by feeding a microphone signal through a separate amplifier and exciting a pair of cheap headphones (the cheaper, the better) that may
O PERFORMER
Fig. 4-15. Conversation
over a telephone can also
be simulated by feeding the amplified output
of one microphone into
headphones and broadcasting their sound.
MIKE
AMPLIFIER
ICROPHONE
'ON AIR""
M
be held immediately adjacent to another microphone in the studio.
This circuit is illustrated schematically in Fig. 4-15.
A slight reverberation effect may be obtained by placing a microphone immediately above the sounding board holes of a piano, and
directing the voice by means of a megaphone or tube over the strings
of the piano. The sustaining pedal is held down to allow the strings
to vibrate freely when the voice waves are impinged upon them.
Several good textbooks exist on sound effects and will provide more
detailed information.
-}(I
BROADCAST OPERATORS HANDBOOK
Importance of Control -Room Maintenance
There is no time allowed in a broadcaster's daily schedule for trouble in equipment. There is no allowance made by advertising agencies
and producers for bad quality of a studio show due to weak tubes,
faulty patch -cords, dirty jacks, or fader controls. Complete failure of
equipment is apt to occur in even the best maintained control room
due to a defective tube or power supply failure, but when all is simmered down to actual fact, there is never an excuse for fuzzy sounds
or any kinds of distortion arising from dirt collected in jack strips or on
contacts of fader controls. A detailed, well -performed maintenance
schedule is mandatory to trouble -free operation.
All tubes should be checked at regular intervals, preferably once
a month. Weak and questionable tubes should be immediately replaced. Visual inspection of all rectifier tubes should be made every
morning before sign -on, and any such tube showing an undue amount
of blue glow should be replaced. Jacks, since they constitute both
series and parallel connections in the path of the signal, must be kept
free of dust and dirt. They should be frequently vacuum cleaned, and
the jack contacts kept clean by regular insertions and removals of
patch-cord plugs. The outside cover of fader controls should be removed about once a week and the contacts cleaned with a small brush
and carbon tetrachloride. A very thin coating of white vaseline after
this cleaning helps to prevent wear. All relay contacts in the installation should be regularly cleaned with crocus cloth or strip of glazed
paper. Smooth trouble -free operation of control -room equipment rests
largely on this maintenance schedule and the technicians responsible
for carrying it out to the letter. (A detailed discussion of preventive
maintenance will be found in Part 5.)
Transcription Turntables
The practice of playing recordings and transcriptions varies considerably with different stations. In many of the smaller stations, the
control man operates the turntables as well as running the control
console. In the majority, of the stations of 5 kw or more, either the
announcer runs the tables, or an especially trained person is used to
run the turntables, which may be in a separate room just for this
purpose, as shown in Fig. 4-16.
Recorded and transcribed shows constitute a most important part of
a broadcaster's daily schedule. "Transcriptions" are recordings made
YOU'RE OFTEN A PRODUCER TOO
41
especially for broadcasting purposes; they are usually 16 inches in
diameter and use a turntable speed of 33% rpm to enable recording
a full 15 minutes of program time.
WOR Photo
Fig. 4-16. The transcription studio at Station WOR, New York.
A transcription "platter" may also consist of a number of separate
musical or voice selections on a single disk, in which case they are
numbered on the label with the titles of each number listed. Also on
this label will be the information as to lateral or vertical cut, start on
inside or outside groove, and reproduction speed (33% or 78 rpm) .
This is enough to keep any operator "on his toes," especially when a
program consists of both recordings and transcriptions which may require change of turntable speed, lateral or vertical switch placement,
and noting whether the cut is started on the inside or outside groove.
Then too, a filter selector switch is employed to select a suitable frequency compensation for the particular disk used. For example, RCA
lists typical switch positions for the 70 -CI turntable as follows:
Lateral
#1. Transcriptions, Orthacoustic, Columbia.
#2. Home records and worn transcriptions.
BROADCAST OPERATORS HANDBOOK
42
#3. Home records, World, Decca, and AMP.
#4. Test records and special recordings (wide
open at highs)
.
Vertical
#1. World and AMP transcriptions.
#2. Worn transcriptions.
All records, and some transcriptions, are played at 78 rpm (same
as the record player at home), are "laterally" cut, and played from
outside groove toward the inside. Most transcriptions, however, play
at 33% rpm. In addition to this, some transcriptions are cut "vertically," that is, the groove variations that comprise the signal are
varied up and down instead of side to side, using the depth on the
coating of the disk. Also, some of them play from inside-out, and require the starting of the pickup arm on the inside groove.
Turntable Operation
In operating a turntable, it is necessary to be sure that the pickup
selector switch is on the proper setting for the pickup arm used (lateral
or vertical) that the turntable speed switch is on the correct speed
adjustment for the particular recording used (33% or 78 rpm), and
that the disk has been properly "cued." This means that the pickup
arm must be at the spot on the groove where the announcement or
music begins, so that no time is lost in waiting for the arm to reach
that point on the disk. This is usually accomplished by using headphones on an auxiliary amplifier so that each disk may be "cued in"
preparatory to going on the air.
When the disk has been properly "cued in," most experienced operators find it advantageous to start the turntable moving while holding the disk (on the outside edge so as not to touch the grooves) to
keep it from turning until start is desired. This practice eliminates
"wows" that are apt to occur on the starting due to time taken for
the turntable to gain proper running speed. When this trick of operation is not followed, the disk should be "cued back" at least one full
revolution of the turntable so that the proper speed will be reached
before start of the signal.
The art of smooth turntable operation on the air takes considerable
practice by the operator. Familiarity with the operating procedure
can be gained only by practice, and most stations demand a thorough
"break in" training before entrusting the operator with an air show
comprised of recordings and transcriptions.
;
YOU'RE CFTEN A PRODUCER TOO
43
The music library of a broadcast station may contain files of thousands of recordings and transcriptions, and their proper care in storing
and handling is an important factor in "on the air" quality of reproduction. Excessive heat ar_d dust in the air are major enemies to be
considered in the storage room. The library should be well air-conditioned, with an efficient dust-filtering system. In any case, the disk
should be cleaned with a soft dry cloth before playing. Static electricity causes dust to cling tightly to records, and all precautions such
as use of linoleum floors in library and turntable room to reduce static
electricity should be taken. Finger marks cause noisy reproduction
due to the oil and grease from the hands causing foreign matter to
cling close to the walls of the grooves. Platters should be handled on
the edge only.
For this same reason, tie permanent type pickup needle should
not be "swiped-off" with the fingers in an attempt to clear it of dust.
A small soft brush should be used.
Instantaneous Recording Department
All large stations, and many of the smaller stations have a recording department where acetate -coated disks may be cut for immediate
playback if necessary. Such equipment is used for recording programs
such as delayed broadcasts, rehearsals, auditions, or the reference file.
A reference file is kept by same large stations of the entire broadcast
day, or of portions thereof. The art of recording, including equipment
and stylus adjustment, is a complex field of its own, and an entire textbook is necessary to do it justice. There are several good manuals
of recording technique published today, and any technician who may
be concerned with this depanment of a broadcast station should obtain
and study them.
The Influence of F.M.
The influence of f.m. (frecuency modulation) on future operational
practices is not to be denied, whether or not f.m. will ever entirely replace or simply supplement the present a -m stations is indeed an
abstruse problem. However, it is a certainty that this new type of service, with static -free reception, greater frequency and dynamic range,
and freedom from interchannel interference, will find a highly important niche in the future of radiobroadcasting. It is entirely possible that local and shared -channel broadcast stations will gradually
44
BROADCAST OPERATORS HANDBOOK
transfer to f.m. for the purpose of providing better interference-free
coverage both night and day for its primary area.
The great difference in dynamic range between a.m. and f.m. will
a
undoubtedly call for new types of visual indicators in level and
by
hoped
is
It
practice.
slightly new technique in general operating
the author that as the art of f.m. advances, the new technique can be
analyzed and presented in a possible future edition of this handbook.
The complex operating practices in relation to television will also be
are
included as the state of the art advances and operating standards
more definitely stabilized.
Chapter
5
PUT THAT MIKE THERE!
BY BERT
H. KOEBLITZ
THE PROBLEM of studio pickups or setups is a little difficult to
approach because conditions vary so widely between one station and another. In a small local station, the technician may
have full control of what goes where and why; whereas in a network
center the technician may find himself surrounded by a superabundance of production men to take care of this. In the first case, knowledge is essential to success. In the latter instance the technician can be
of real help to the production man. Production men, unless they have
been recruited from the technical department, rarely know anything
about microphone patterns. Instead, they pursue a series of superstitions and grandma's tales about what a certain type of microphone
will or will not do. Therefore a technician with thorough knowledge
can help the production man over many difficult spots, and in the
case of important programs, frequently finds himself the recipient
of slight remembrances now and then.
But that is only one conditional variation. Another is studio construction. What may be good practice at one station may not do at
all somewhere else. To describe a specific setup at WHK or anywhere else would accomplish little of value. The important thing is
that the same fundamentals can be used to determine whether a given
practice is good or bad in your own particular studios. However, certain specific examples will be given, not to demonstrate what is done
at WHK, but to illustrate principles which can be applied in any station.
Large Orchestra
The first program which comes to mind is one involving about as
many things at one time as will ever be encountered outside a network center. It is a so-called "variety" program, although "hodgepodge" would be far more accurate. It consists of a 25 -piece orchestra
which is really ten miscellaneous additions to a 15 -piece dance band
which in its turn further degenerates into a "gut bucket" four. Then
45
46
BROADCAST OPERATORS HANDBOOK
there is a 20 -voice chorus, a drama cast, a novelty group, a guest artist,
went
a master of ceremonies, and an announcer. Before the program
section
on the air, the production man tried the orchestra in a straight
"V"
in-front -of -section style, sections side by side, sections in little
formations, lengthwise, sideways, and diagonally in the studio, but to
it.
no avail. He knew what he wanted but he did not know how to get
The problem was turned over to the technician, who eventually straightened things out. That illustrates fundamental No. 1: be prepared with
a full knowledge of what can be done in your studios with your microphones.
The setup finally used for the orchestra was the section -in-front -ofsection type. The section nearest the microphone consisted of four
violins and two violas. Between them and the saxophone section were a
cello and harp. Brass was in the last section with the trombone in front
of the trumpets. The trumpets were put on high risers and the trombones on low risers, not for setup purposes but so the men could see
the director without difficulty. Piano, drums, bass, and guitar were
placed so they could hear each other.
Now let's go back to the perspiring production man for a moment.
He failed to get a satisfactory pickup with the orchestra in the positions described because he was unable to put his finger on the true difficulty. When one section was too soft, he made the all too common
assumption that that section was too far from the microphone. A
moment's thought will reveal that when two things are of different
volumes, there are two possibilities involved: one may be too soft or
the other may be too loud. It is necessary to make sure which is
which before making changes in a setup. Making such changes is
really no different from making an original setup; you must be sure
this
of everything you do. In starting from scratch, an orchestra of
a
will
be
It
percussion.
and
size is bound to have strings, reeds, brass,
A
order.
in
that
the
microphone
logical start to place them before
couple of numbers should suffice to set roughly the relative distances
for sections.
Here enters a theoretical point that is sometimes helpful in practice. Assume for a moment that we have a perfect studio and that
we have found that the strings should be 4 feet from the microphone,
the reeds 8 feet, and the brass 12 feet. This yields a ratio of two to
one and three to one for the other sections as referred to the strings.
This means that in our imaginary perfect studio, there would be an
infinite number of good setups; that is, the absolute distance is unim-
PUT THAT MIKE THERE!
47
portant as long as these ratios are maintained. There would be no detectable difference between spacings of 4, 8, 12; 5, 10, 15; 6, 12, 18; etc.
Within restricted reasonable limits this will hold true in our imperfect
studios. This fact can sometimes be used to advantage and was in the
case of this orchestra. The section distances had been established but
the cello and harp were too weak because they were both considerably
off side. The sections were redistributed but the distance ratios were
maintained. This made sufficient room between strings and reeds to
bring harp and cello into center.
Another factor too often overlooked is section "presence." Having
section volumes equal is only half the battle; section presences must
also be equal. The ratio procedure can be applied here too. Assume
that the sections have again been established at 4, 8, and 12 feet for
equal volume but that the strings sound "closer" to the microphone
than reeds or brass. The "presence" problem can be ironed out by increasing the distances while maintaining the ratios. The general
axiom to be drawn from al] this is: do not do anything in making or
changing a setup unless or until you have a logical reason for doing it.
We will call this fundamental No. 3, because No. 2 is closely allied to
No. 1 but involves the chorus which will be discussed farther along.
Keep It Simple
All of the original attempts at a setup, both the straight-line and
side -by -side types were discarded for a variety of reasons. All of them
had one common fault, which, however, was not the cause of their
failure. It must be borne in mind that some numbers were played by
the full orchestra, some by the dance-band portion of the orchestra,
and some by the four -piece jive outfit. In the side -by -side setups two
microphones were picking up the orchestra and there was a third one,
to and from which the hapless four were supposed to dash madly for
their numbers. Aside from any other considerations, the show began
to look like a track meet to the studio audience. In the production
man's straight -on setup a microphone was in front of each section.
There lay the common fault: three microphones. A multi-mike pickup
is never quite as clean as a single mike, probably because of the several paths each sound can take. Also, more than one microphone puts
the burden of instantaneous balance on the shoulders of the technician. Granted, there are many technicians who can be depended on to
do this correctly. Also granted, there are many who cannot. This is
not stated in derision of the latter group. It is one of those things that
BROADCAST OPERATORS HANDBOOK
paint, some can't;
you either have or you haven't. Some people can
case there is no
any
In
on.
so
and
some people can repair watches
when the large
harm in eliminating microphones. As it turned out,
48
volume and presorchestra sections were properly balanced for both
was principally
which
band,
ence on the one microphone, the dance
by having
Further,
up.
the two rear sections, also was well picked
the jump
for
saxophones
the
the muted trumpet step down behind
so
without
outfit
-piece
four
numbers, a good pickup was had on the
simplicity
for
strive
4:
No.
much hundred -yard dash. Fundamental
error as possible.
in setups and eliminate as many possibilities of
Choral Pickup
of four standThe 20 -voice chorus contained five members for each
consideration
first
The
ard voices: soprano, alto, tenor, and bass.
and the
tried
were
was what microphone to use. All different types
This
used.
finally
was
dynamic section of a Western Electric cardioid
Howresponse.
is a nondirectional unit with excellent high -frequency
have done as well;
ever, any other unit with equivalent highs would
cardioid.
it just happened that the only tall stand was fitted to take a
about a
The important thing is that the most common complaint
human
the
to
chorus is indistinct diction. Diction is distinguishable
are
Sibilants
ear by virtue of the sibilants in the consonant sounds.
a
hence,
the high -frequency components of the consonant sounds;
used.
be
microphone with adequate high -frequency response should
that the microResult: impression of good diction. Care must be taken
is needed. One
phone also has lows; in other words, a wide range
choral effects.
which has only highs will give good diction but poor
its placement can
Once the particular microphone has been selected,
be considered.
of the
To begin with, it should go on a line through dead center
not promigroup, and back far enough so that individual voices are
moving
by
adjusted
be
should
sections
in
nent. Any inequalities
the micropeople. Actually as far as choral effect alone is concerned,
As usual
phone can go as far back as studio space will permit.
without acthough, circumstances alter cases. If the chorus sings
how far back the
companiment, then there is practically no limit to
accompaniments,
microphone can be placed. If there is orchestral
have to be
probably
will
microphone
as there was in this case, then the
voices. When
placed as close in as it can be without getting individual
too much oralways
was
there
the series of programs first started
PUT THAT MIKE THERE!
49
chestra behind the chorus. No type or placement of microphone or
separation of chorus effected a solution, simply because none of these
things was the cause of the trouble. The arranger insisted on writing
full orchestra accompaniments, and any time there are eight brass
blowing they are going to be heard above the chorus. The arranger
was prevailed upon to use strings and clarinets only, which cleared up
the trouble. Fundamental No. 2 which is closely allied to No. 1:
know what can't be done in your studios with your microphones.
Drama and Novelty Pickups
The drama cast does not offer anything unusual in the matter of setups. If more than two persons are concerned in any one scene, at WHK
it is preferred to use a nondirectional microphone so that it may be
approached from any direction. This is also convenient for balancing
players since it is only necessary to establish a correct distance for
each one. Likewise the novelty group treatment will depend on the
novelty group. In our case there were five men who played a dozen
instruments at different times besides singing at other times. They
were also provided with a nondirectional microphone (as a matter of
fact it was the same one the drama cast used since they were never
on concurrQntly) so that their only worry was distance. A distance
was established for each instrument so that whoever played it had
only to move in wherever he could find an opening. To finish up this
program, the guest artists, announcer, and master of ceremonies all
used the same microphone. Result: Three orchestra groups, a novelty
group, a chorus, a drama cast, vocalists, announcer, and master of
ceremonies were all picked up on four microphones. With the exception of vocal solos, there was only one microphone open at any one
time.
To recapitulate, the following fundamentals can be gleaned from this
particular program set up:
prepared with a full knowledge of what can be done in your
studios with your microphones.
2. Know what can't be done in your studios with your microphones.
3. Don't do anything in making or changing a setup unless or until
you have a logical reason for doing it.
4. Strive for simplicity in setups and eliminate as many possibilities
of human error as you can.
1. Be
r,o
BROADCAST OPERATORS HANDBOOK
Small Orchestra
For the sake of definition, consider anything under ten men a small
orchestra. Setups for these groups will depend largely on the groups
themselves. There is rarely any problem of sectional balance, because
it is unlikely that there is more than one section. Usually such a small
combination depends greatly on one player. It may be a pianist who is
exceptionally good at "noodling," a hot guitar, trumpet, or almost anything else. The type of microphone is moderately unimportant. The
best procedure is to place the musician of the type previously mentioned at the best possible advantage with respect to the microphone
and then adjust the rest of the group until everyone can be heard. In
the case where piano is the mainstay, a separate piano mike is nearly
always needed, since it is usually impossible to get the piano close
enough to the orchestra mike and still keep it close enough to the rest
of the rhythm instruments. One other possible pitfall is the bass fiddle.
If it does not seem to be loud enough, it can usually be helped by moving the orchestra mike farther from the group without changing the
position of any of the musicians. In small groups, one is likely to run
into musicians who double on more than one instrument. Very often
both instruments will not pick up equally well from the same position.
About all that can be done, short of giving each man an individual
mike, is to arrange for him to step forward with the weaker instrument.
Hotel Orchestras
The hotel orchestra is another matter entirely. There is usually no
possibility of a logical solution of problems but rather there is a selection of what seems to be the best group of compromises. Except in the
more lavish hotels, the band stand, being a place which provides no
revenue, is almost sure to be too small and the wrong shape. Because
of this the orchestra can hardly be disposed either the way it should be
or the way the leader wants it. Since the orchestra geometry will
necessarily be side by side, at least two mikes are generally needed for
a good pickup. However, the announcer and vocalists can usually use
one of these.
It is to be greatly decried that so many stations give these pickups
practically no attention. A man comes in and plunks a mike down
somewhere in front of the orchestra and that is that. Frequently, a
technician is not even sent out, the amplifier being turned on from the
PUT THAT MIKE THERE!
51
studio and the orchestra -leader depended upon to place the microphone.
All this when a little care will provide a fairly decent pickup. Perhaps this leads us to another fundamental: whatever is worth doing is
worth doing well.
Novelty Groups
Somewhat like the small orchestra, the novelty group setup will depend on the group itself. Few if any are strictly instrumental and
moving people in for vocals introduces most of the problems encountered. In a group where lie members play the same instruments all
the time, there is rarely any difficulty either as to choice of microphone
or placement. However, when four or five men play ten or twelve instruments and come in for vocal besides, then you are likely to have
your hands full.
One such group at WHK was set up with a ribbon mike, because
it was thought that the two live sides would afford ample room for
four vocalists. This assumption alone was correct, but other considerations made the ribbon unsatisfactory. The man who played bass fiddle
most of the time (all of them played it at some time) felt he had to
stand in a certain place when he sang. In this position, the bass fiddle
was exactly on the dead side of the mike. It was suggested that someone else take the bass fiddle during the singing, but no one else could
play it and sing at the same time.
In addition, there was another complication. There were a half
dozen other instruments spread around the studio, some of them large
(piano, vibraharp, marimba, electric organ, etc.) . The effective pickup
angle of a ribbon is very little more than 90 degrees for each face. I
was difficult to get enough instruments close enough to it and still leave
room for the track meet during each number.
The obvious and actual solution was to use a nondirectional microphone which solved the bass fiddle problem and furnished a full 360
degrees in which to deploy all the instruments. It could be argued
that more mikes could be ised. They could, but the total effect will
never be as clean as with a single microphone.
Vocal Groups
The treatment of vocal groups is almost the same regardless of their
size. The primary concern is to get a blend so that it sounds like a
group rather than a collection of individual voices, which cannot be
done with the microphone in too close. In general, the larger the
52
BROADCAST OPERATORS HANDBOOK
group, the more separation can be tolerated. In smaller groups such as
quartets, you may sometimes encounter the rare case where the accompanist plays quite softly. If there is a separate microphone for
the accompanying instrument, it may be noticed on loud vocal passages
that the voices can be "heard" on the other mike. When this effect is
noticed, it will also be noticed that the fader setting on the vocal mike
is less than that on the accompaniment mike. Anything which will
allow the vocal fader to be higher than the other one will correct the
condition. The accompanist can be asked to play louder and thus
cause that fader to be reduced. This is not always satisfactory because
the accompanist is usually playing softly because that is his or her
normal procedure and it will be reverted to after a number or two.
The better solution is to move the vocal mike away from the group
sufficiently to allow that fader setting always to be higher than the
other.
The choice of a microphone should be one with a good high -frequency response. At the same time it should be emphasized that the
microphone should have neither highs nor lows; it should be a wide range instrument. The intelligibility of human diction is centered
mostly in the high -frequency consonant sounds. A wide -range microphone is indicated to reproduce adequately the vocalists' words.
Piano Pickup
The subject of piano pickups, if not the most controversial, is at
least the most varied problem in the business. Microphones have been
placed under the piano, in it, beside it, across the studio from it, over
it, in fact everywhere but in the performer's pocket. The lid has been
opened, closed, and off. Correct piano pickup follows a series of logical principles, so that if any trick procedures have been successful,
they have also been illusions. In other words, somebody's ears are defective, some studio equipment is defective, or an accident has occurred which compensated for a studio deficiency.
Let us start off with a little theory. We need concern ourselves only
with grand pianos, because few if any studios use any other kind.
The grand piano was designed with two things in mind. If all conditions are perfect the maximum efficiency should be expected (1) with
the lid on full stick and (2) at some position on an imaginary extension of the hammer line. That is all there is to the theory.
Next, the problems likely to be encountered. All pianos are not built
with equal care, so you may find that your particular one has a more
PUT THAT MIKE THERE!
53
brilliant bass than treble or vice versa. Pianos which were originally
good may have become tonally lopsided through age, lack of care, or
misuse. Regardless of the condition of the piano, each pianist is also
a separate problem. Some play softly, some loud, some have a heavy
right hand and some a heavy left. Finally, we have to deal with the
characteristics of the studio in which the piano is located.
There are two adjustments of microphone position which will handle
any or all of these variables. Going back to the theory for a moment
and assuming a perfect piano, perfect pianist, and perfect studio conditions, the microphone should be on the imaginary extension of the
hammer line about 8 to IO feet from the piano. The first adjustment,
if necessary, will be on account of studio acoustics. If the studio is
very live, the 10 -foot distance may give more reverberation than is
pleasant. The microphone should be moved straight in on this imaginary line until the noticeable reverberation is reduced to a pleasing
amount. The second adjustment is for bass-treble balance. This one
will work regardless of the reason for the unbalance, whether piano
or pianist is at fault. If the treble needs to be increased, the microphone will have to be moved in still farther on the afore-mentioned
imaginary line. In extreme cases it has been necessary to move the
microphone all the way up to the piano case, lower it, and tilt it toward the treble strings. Now, mentally restoring yourself to the
microphone position where reverberation was just right, assume the
bass is weak. While maintaining the proper reverberation distance
from the piano, move the microphone toward the tail of the piano.
This will increase the pickup from the bass strings and decrease the
pickup from the treble strings.
With the above procedure in mind, it should never be necessary to
use a grand piano any other way than with the lid on full stick. That
is the way the piano was designed to be used and that is the only way
the piano sounds normal. Taking the lid off, putting it on the half
stick, or closing it only seems to do something which could be done
better some other way. For instance, putting the lid on the half stick
does not reduce volume appreciably but it will muffle the tone considerably.
A two -piano pickup involves the same principles as with one piano.
It is usually more convenient to make adjustments in this case by
holding the microphone position constant and moving the pianos.
There is one added problem: temperament of the pianists. Assuming
perfect conditions again, the hammer lines of both pianos should be on
"
54
BROADCAST OPERATORS HANDBOOK
the same imaginary contiguous line. The pianos should be about 15
feet apart with open lids toward each other. The microphone should
go half way between them on the imaginary line. The two principles
mentioned for one piano apply equally well to two pianos. In addition, if one pianist plays more heavily than the other, the microphone
can be moved closer to the weak one.
Now another problem: the temperament of the pianists. Many two piano teams like to be closer together than 15 feet. If they cannot
be talked out of it, some of the clarity and brilliance of the pickup
will have to be sacrificed by moving them closer together. If you refuse to do so, the pianists will play either badly or not at all, so you
will not have anything anyway. Sometimes the players will insist upon having the pianos right together and side by side. This very
nearly prevents a first-class pickup. There is some hope, however, if
the same pianist always plays the lead part. In this case the lead
piano should be closer to the microphone, which is placed as if for one
piano only high enough to clear the top of the lead piano lid. Balance
between the two pianos can usually be accomplished by raising or
lowering the microphone. Raising it helps the second piano.
In picking up piano with a small orchestra, clarity and brilliance
are mostly buried in the sound of the orchestra so the preceding practices can be more or less ignored. It will be found that the microphone
has to go very close to the piano. Also, if possible, the piano should
be oriented so that the open lid physically masks from the microphone
most of the orchestra, or at least the loudest instruments.
Piano with symphony orchestra is entirely another matter. Referring to the setup described for the symphony orchestra broadcasts at
Severance Hall in Cleveland, the place normally occupied by the conductor is occupied with the piano. An additional microphone is used
for the piano a sufficient distance away so that the presences of the
orchestra and piano are the same. The piano microphone is opened
only enough to provide a little definition. Many piano -with -symphony
programs are ruined on the air by making the piano too loud. Much
of the time in this type of composition the piano has a supporting
rather than solo part.
Organ Pickup
There is little that can be said about pickup of pipe organ. The type
and make of organ and studio size all vary so widely that there probably are not two identical setups in the whole country. It simply
PUT THAT MIKE THERE!
55
remains for each technician faced with such a problem to use horse
sense and ingenuity to secure a satisfactory pickup.
Electric organs present somewhat less difficulty. The older type
speaker with openings on both top and side were pretty much a headache. There was not much that could be done to get a really good
pickup. The newer type speakers with opening on the side only are
duck soup. Just place a microphone straight out in front at whatever
distance gives the desired amount of reverberation.
BROADCAST OPERATORS HANDBOOK
56
11!
h
id
P,
g
III
"Ct
cl
C.)
CI,
C.)
Q
:z1
-cs
-cs
t
o
itC
o
u
I. -
1
It,
51
2
.1
3
sus
tt 1
----1
o
L- _J
o
z
o
a)
C.)
r)
4
CL)
C.)
WC)
o
.-.
de
-
63
5
4
O
CO
t
Part
2
OPERATING THE MASTER CONTROL
Chapter
6
WHERE SPLIT. SECONDS COUNT
N STATION SETUPS where a comparatively large number of individual studios are involved, a central switching point known as
"master control" is employed. Fig. 6-1 shows a simplified schematic of the NBC technical layout. This illustration shows how indi-
vidual studios are connected through the switchbank selectors to the
master control position, where the program or programs may be routed
in any way desired. Fig. 6-2 is an illustration of NBC's Chicago master control.
The NBC program switching system is a standardized layout for
all key stations of the network. Since more than one program is being handled at any one time, the setup must be as flexible and foolproof as technically possible. This calls for operation on a preset basis,
eliminating as far as practicable confusion of switching a number of
program sources in the split seconds allowed.
In the NBC system, the switchbank selector is a group of relays
associated with outgoing channels, arranged for a single connecting
means between any group desired and any single program input. A
brief description of operation of the program switching system is as
follows.
The program sheets or schedule sheets prepared in advance by the
program and traffic departments indicate the program sources such as
studio (and the particular studio number), for a remote point, or incoming network line. Also indicated are the outgoing channels feeding various points with the programs. At the start of operations, the
channels required for each separate program are preset by operating
numbered key switches in master control which are connected to separate switchbanks. Any switchbank is then connected to any program
source at the proper time by operating the associated key switch on
the switchbank selector panel, one panel being associated with each
studio or other program source. This operation actuates the "carrier"
lights at both the announcer's control desk in the studio and on the
engineer's console in the control room, and is the signal for the pro 57
BROADCAST OPERATORS HANDBOOK
NBC
Fig. 6-2. The master control at the NBC studio in Chicago.
Photo
gram to begin. In this way, programs are routed to the station's own
transmitter and to the various other sources such as network, f.m., or
special circuits such as international short wave.
Master Control of United Broadcasting Company
WHK master control is definitely not standard; it has grown
through the years from the personal preferences of master control operators. From the foregoing statement it might seem to some that it
would be a most glorious hodge-podge of gadgets by now. Actually it
is the most simple and flexible system that could be imagined.
All program sources, each studio, the network, and four remote positions go to individual 12 -tube repeater amplifiers. This provides
twelve copies of each program source to be used for local station, network feed, f.m., monitor systems, etc. On the master control console
are six banks of mechanically interlocking switches which route any
program source to any or all of six line amplifiers. The interlocking
is to prevent more than one key being depressed at any one time. The
switchbank for WHK's line amplifier is different from the rest. Here,
any program source can be put on any one of three faders, and interlocking prevents getting more than one program on any one fader.
The faders in turn feed the line amplifier. The faders are considered
WHERE SPLIT SECONDS COUNT
59
necessary to smooth operation for getting in or out of programs late
or early. There are no relays in any program circuit. One line amplifier feeds WHK's transmitter, one for the Mutual Network, one for
an Ohio network, and three spares which can be used for anything.
Also on the console itself are two switching panels which route any of
30 remote lines to any of the four remote positions. These same panels have facilities for line reversal and private telephone to each remote.
In addition to the console there are three banks of double depth
relay racks which house (1) power supplies, (2) all program amplifiers, and (3) monitor amplifiers. Every piece of audio equipment is
brought out to normal through jacks so each one may be replaced or
removed from circuit in a few seconds in case of failure. All amplifiers have pads connected to their input jacks to take plus 8 vu down to
whatever is necessary for that amplifier. This makes it possible to
have every input and output plus 8 vu at 600 ohms. Even a shoemaker
couldn't hurt anything by patching them all in series.
Function of Master Control Operations
Every individual station employing a master control has, of course,
slightly different "rules and regulations" of procedure to suit their
individual requirements and to satisfy the technical executives who
are responsible for the co-ordination of all operations. The following
rules of studio procedure that were compiled by the engineering supervisors of WBBM for guidance of their technical staff is presented
here to acquaint the reader with general master control operations.
The rules are divided into three sections: (1) master control, (2)
studios, (3) field. The letters M, S, and F have been used respectively
to differentiate between these sections in numbering. Since all are
closely tied in with the duties of the master control operator, they are
presented here in their entirety.
MASTER CONTROL PROCEDURE
Checking of New York Daily Operations Sheet
The Master Control engineer is required to check the routings of all
network originations with the New York Daily Operations Sheet, and
to compare the routings listed with those on the WBBM Daily Operations Sheet.
Ml
60
BROADCAST OPERATORS HANDBOOK
M2
Booth Check-in
For procedure to be used on a booth check-in, see S5. In addition,
the Master Control engineer is to record on the WBBM Daily Operations Sheet, above the engineer's name, the time of the check-in.
Should the studio engineer report someone as absent, Master Control
should immediately notify the Program Department.
M3
Time of Making Preset
All relay presetups should be made approximately four (4) minutes
before each regular switching period (see Glossary).
M4
Use of Switching Light
The signal for Master Control to switch from one studio (excepting
studio M7) to another, on all local originations, will be the switching
light.
M5
Checking Equipment
All equipment is to be carefully checked for gain settings, tube
currents, etc., before being placed in service.
M6
Filling During Network Failures
For procedure see S18. In addition, on all scheduled stand-bys and
all emergency fills to the network, Master Control is to patch the
stand-by studio's cue speaker to the incoming network line.
M7
Cutting of Local Programs Running into Network
Commercials or into Synchronization
All local programs running into synchronization or into network
"musts" which are to be carried by WBBM, will be cut by Master
Control only.
M8
Relieving of Engineers
a. A relief engineer is not to take over the Master Control if only
(5) minutes or less remain before a switch. The engineer being relieved is to make the switch and see that the program or programs
start properly.
b. An engineer is not to be relieved of duty until he has cleared the
patching bays of all unnecessary cords.
WHERE SPLIT SECONDS COUNT
61
Checking Program Level
Master Control engineers are to keep a close check on the level of
all programs, and to see that the proper level is maintained at all
times. See also S9.
M9
Remote Check-in to Master Control
The Master Control should see that all remote engineers check in
by twenty-eight (28) minutes before air time. If the remote has not
been heard from by twenty (20) minutes before air time, provision
should be made for a stand-by.
M10
Mll
Testing of Field Equipment
Remote engineers, before leaving the building for "pickups," are to
give Master Control an audio test of their equipment. This equipment
is not to be O.K.'d other than in good condition. The time of these
tests is to be recorded on the W BBM Daily Operations Sheet, opposite the particular pickup, with the Master Control engineer's initials.
Patching Up Remote Talk-Lines
Remote talk -lines are to be patched up only after the scheduled
Studio engineer arrives in the booth and requests them.
M12
Recording of Inability of Studio Engineers to Get
Program Procedure
All reports by Studio engineers of inability to ascertain the procedure on a particular program are to be recorded in the "penciled"
comments, with the reasons and name or names of persons concerned.
M13
Making Setup for Following Morning
The engineer signing off each evening is to make the necessary setup
in Master Control for the following morning, in order that the Studio
engineer can put the station on the air should the Master Control engineer fail to arrive.
M14
Changes to the WBBM Daily Operations Sheet
All changes and notations to the WBBM Daily Operations Sheet
are to be made in ink and initialed by the Master Control engineer.
M15
62
BROADCAST OPERATORS HANDBOOK
M16
Signing of Engineering Department Copy of WBBM
Daily Operations Sheet
Engineers must sign on the Engineering Department copy of the
WBBM Daily Operations Sheet the time "ON" and the time "OFF"
duty.
STUDIO PROCEDURE
SI
Ascertaining of Program Procedure
The engineer is required to acquaint himself with the procedure of
all programs on which he is assigned. This is required regardless of
the number of times the engineer may have been assigned to the show.
If at any time it is impossible to secure this information, Master Control is to be notified in order that it may be entered in the "penciled"
comments.
S2
Time of Check-in to Master Control
Studio engineers are to check in to Master Control not later than
seven (7) minutes before air time.
S3
Remaining in Booth
Engineers are to remain in the booth between the time of checking
in to Master Control and two (2) minutes after the program. It is,
however, permissible to leave for the purpose of making a necessary
last-minute change in the studio setup.
Checking In for Rehearsals
84
Engineers scheduled on rehearsals are to report to the studio ten
(10) minutes early, and have all equipment tests completed by rehearsal time. The failure of producer or talent to arrive does not relieve the engineer of this responsibility.
S5
The Check-in to Master Control
The check-in to Master Control is to be made as follows:
"John Doe checking in from studio three, T -H -R -E -E, for Columbia's School of the Air, 2:30-2:591/2i to SRR-NW-TC (give complete
routing).
"The time is 2:20 and 40 seconds. Woof !"
If it is a local program only, the engineer is to add after the routing
WHERE SPLIT SECONDS COUNT
63
that there is, or is not, a spot announcement following his program,
and, if so, the studio in which it is scheduled.
It is the responsibility of both the Master Control and Studio engineer to make these check -ins carefully. The Master Control will repeat and spell out the studio number.
When making check -ins it will be understood that, unless Master
Control is informed otherwise, all tests have been completed and all
talent, including the announcer, is present.
Time of Arrival in Booth on Remote Programs
Engineers are to arrive in the studio at least thirty (30) minutes
before air time, if schedule permits, on all remote commercials and
special events; on all other remote programs the minimum time is fifteen (15) minutes.
S6
Patching Up Remote Talk-Lines
Remote talk -lines are to be patched up only after the scheduled
Studio engineer arrives in the booth and requests them.
S7
Studio Line-up with Remotes
The studio line-up with remotes should include the following, and
preferably in the order shown:
1. Line and equipment test.
2. Level check (the Field engineer will call peaks) .
3. Name and sequence of musical selections (if it is an orchestra).
4. Corroboration of air time.
5. Time check.
88
89
A Proper Level to Be Maintained
It is the duty of the Studio engineer assigned to a program to maintain a proper level at all times. If the level from a remote is abnormal, correct it and then ask the Remote engineer to either raise or
lower it.
810
The One -Minute Warning
One minute before air time Studio engineers are required, first, to
"kill" all microphones and give a one -minute warning over the "talk back" mike to studio talent; and second, if a remote is scheduled, to
give a one -minute warning over the telephone to the Remote engineer
(see F5, a). After these warnings, the "talk -back" mike is to be dis-
connected.
64
BROADCAST OPERATORS HANDBOOK
Remaining in Booth After Air Program
Engineers are to remain in the booth, and equipment must be left
turned on for at least two (2) minutes after each air program.
811
S12
Use of Switching Light
The signal for Master Control to switch from one studio to another
on all originations for WBBM only is the switching light. Hold the
switch on until the channel light is removed.
813
Turning On Cue Speaker
The WBBM cue speaker is to be turned on immediately after the
one -minute warning preceding the start of the program for the purpose of ascertaining the time the channel will be received.
814
Reporting of Trouble on Tests
All trouble encountered on tests preceding an air program must be
reported to Master Control immediately.
S15
Filling Out of Program Report
An Engineering Program Report is to be filled out in full by the
Studio engineer after each air program where there has been an interruption to the normal routine. This report is to be deposited in Master Control reasonably soon after the program.
Disposition of Mikes and Cords After Each Program
After the completion of each program or a succession of programs
from the same studio, all mike cords are to be rolled up and placed in
a corner, and microphones are to be returned to their designated places
in the Maintenance Department.
S16
Network Breaks: Length and Level of Sustaining
Background
a. All regular closing network breaks and breaks used for split network switching are of thirty (30) seconds duration, with the sustaining background faded out after fifteen (15) seconds.
b. All network breaks during a program which are used for station
identification only are of twenty (20) seconds duration, with the sustaining background supplied for the entire period.
S17
WHERE SPLIT SECONDS COUNT
65
c. The level of the sustaining background during all CBS breaks
is to be lowered to 30 (-10 vu).
818
"Filling" During Network Failures
When standing by for the network or any portion thereof, should a
failure occur or trouble develop which renders the program unintelligible, the "fill" should be made as follows:
First: In order to know when the trouble has cleared, turn on the
CBS cue speaker, which Master Control has patched across
the incoming line.
.Second: Wait forty-five (45) seconds, and if by then the trouble has
not cleared, fade off the incoming line and signal the stand-by
announcer to make a courtesy; the "stand-by" should then be
supplied.
Third: Immediately after the trouble has cleared on the cue speaker,
the announcer should be signaled to make a second courtesy
announcement rejoining the program.
Fourth: Fade out the "stand-by" and fade up the program.
In connection with the second and third items above, it should be
understood that should a situation arise whereby an announcer is not
available, the procedure remains the same with the exception that the
courtesies are deleted.
Procedure in Remote Program Line Failure
The following procedure is to be followed should a remote program line develop trouble:
If the trouble develops before air time, Master Control is to be notified, and both points (Master Control and Field) will then reverse
lines. The remote engineer should then feed a test as usual. One
minute before air time Master Control will disconnect the remote feed
to the studio (to guard against a feedback), and supply "cue" over the
substitute program line. The remote should then start the program
five (5) seconds after the proper cue, which will be heard on the monitoring phones. This five seconds will be used by Master Control in
normaling the feed to the studio. If the remote program consists of
an orchestra which is to be announced from the studio, five (5) seconds will be allotted between musical selections.
The foregoing procedure is formulated, of course, on the assumption that the regular program line cannot be used even for cue purS19
poses.
66
BROADCAST OPERATORS HANDBOOK
Channel Lights: Taking Away of
Unless Master Control directs otherwise, the channel light or lights
on each network origination will be taken away fifteen (15) seconds
after a, the middle CBS cue (if any), which is used for split-network
switching only, and b, the closing CBS cue. In the case of a, the channel light or lights will be returned in the regular manner (see S21) .
S20
Signal Used to Begin Network and Local Originations
a. All regular network originations will start five (5) seconds after
the channel light or lights are received..
b. All regular local originations will start immediately upon receipt
of channel light or lights.
S21
Network and WBBM Remote Originations: Opening
"Go -Ahead"
All originations for both the network and WBBM which open from
local remotes will start by a verbal "go-ahead" from the Studio en-
S22
gineer.
The Cutting of Local Runovers
On local "runovers," all cuts which are made necessary because of
synchronization or network "musts" to be carried by WBBM, will be
made by Master Control.
823
Nonrelief Period of Engineers
When programs originate consecutively in the same studio, engineers are not to relieve each other during the last three minutes of a
program and the first two (2) minutes of the following program, and
then only after the relief engineer has familiarized himself with the
routine of the program or programs.
S24
Turning Off of Equipment
With the exception of studio three (3) after 6:00 p.m., all equipment is to be turned off when it is not being operated by a member
of the Engineering Staff.
S25
Studio Engineer Should Be Able to Put Station on the Air
Should the Master Control engineer fail to arrive for a "sign -on,"
the Studio engineer should be able to put the station on the air. For
S26
WHERE SPLIT SECONDS COUNT
67
this reason, he should acquaint himself with the operation and setup
of the following equipment:
1. Battery supply, and associated switches.
2. Local relay channel
3. Patching of phonograph to studio.
See also M14.
827
Use of Telautograph
Corrections to the WBBM Daily Operations Sheet will be written
on the Telautograph. The engineer upon arriving in a booth should
note all corrections affecting him, and change his own schedule ac-
cordingly.
The Daily Work Sheet and Weekly Time Sheet
a. A Daily Work Sheet is to be filled out in full each day and deposited in the box provided in the Maintenance Department.
b. The Weekly Time Sheet, which is posted on the bulletin board
in the Maintenance Department, is to be filled out each day showing
the number of hours worked. This sheet is to be initialed by the engineer at the end of the week.
828
FIELD PROCEDURE
Fl
Returning of Field Equipment
Field engineers are required to return equipment to the Maintenance
Department after the engineer's last pickup for the day, and place it
in its proper location.
F2 Doors That May Be Used When Taking Equipment In or Out
of Building
Field equipment may be carried in or out of the Wrigley Building
through any door except the front door up to 6:00 p.m. After this
time, call for a building watchman to open a side door.
F3
Guests on Pickups
Engineers are not to take guests to remote pickups at any time.
F4
Testing Remote Equipment
Engineers before leaving for the field must give their equipment an
audio and mechanical test as follows:
BROADCAST OPERATORS HANDBOOK
Check 1) microphones and cords for defects; 2) quality; 3)
First:
output level; 4) microphonics; 5) tube shields, observing that
they are in properly, etc.; and 6) volume indicator.
Second: Recheck the first four foregoing items with Master Control.
68
Check-in and Line-up from Field
a. Remote engineers are to check in to Master Control with an equipment test at least one-half hour before air time on all programs (see
also M10) . Leave a test on the line until the one -minute warning,
which will be given over the telephone by the Studio engineer, and
then fade out the equipment.
b. The line-up to the Studio engineer should include the following,
and preferably in the order shown:
1. Line and equipment test.
2. Level check by calling peaks.
.
3. Name and sequence of musical selections (if it is an orchestra)
4. Corroboration of air time.
5. Time check.
careOn "3" above it is the duty of the Remote engineer to check
orchestra
the
with
fully the name and sequence of musical selections
leader.
F5
Lowering of Sustaining Music
the
On all remote orchestras which are announced from the studio,
mubetween
Remote engineer is to lower the level of the sustaining
sical selections to 30 (-10 vu).
F6
F7
Procedure in Remote Program Line Failure
See S19.
F8
The Daily Work Sheet and Weekly Time Sheet
See S28.
GLOSSARY
each
Channel Lights. The small circle of lights found in the center of
an
is
feeding
booth console and used as the signal which that studio
"outgoing" line. Each light represents a separate line.
the Master
Check-in. The verbal report by the Studio engineer to
for
Control that he or she (i.e., the Studio engineer) is in the booth
his or her next program (see S5 and M2) .
WHERE SPLIT SECONDS COUNT
69
Cue Speaker. The small speaker located in the booth console which
can be patched by Master Control to either the local or the network
program.
Daily Log. See Master Control Log.
Daily Operations Sheet. See New York Daily Operations Sheet.
Daily Schedule Sheet. The schedule which shows the rehearsal time,
air time, studio number, destination (i.e., network or local), and the
name of the engineer assigned to each program. This schedule is
posted on the bulletin board in the Maintenance Department each
evening for the following day's operations.
Daily Work Sheet. A form which is to be filled out by each Studio and
Remote engineer every day showing the name and time of all rehearsals and air programs worked.
Engineering Program Report. A report filled out by Studio engineers
for the information of Master Control, and which explains any and
all interruptions to the normal routine of an air program.
Master Control Log. The daily record of all abnormal operations kept
by Master Control.
Network. The entire Columbia Broadcasting System or any portion
thereof.
Network Break; CBS Break. The 30- or 20 -second period at the end
or in the middle of each program which is used for station identification. It always follows the words, "this is the Columbia Broadcasting System."
New York Daily Operations Sheet. The New York Daily Schedule
which shows the exact network routing of each program.
One -Minute Warning. The warning that everyone should remain
quiet, given to talent in the studio and/or a remote one minute before a program is scheduled to take the air.
"Penciled" Comments. The log kept by Master Control in which is
recorded only material of a purely engineering nature.
Regular Program Schedule. See WBBM Daily Operations Sheet.
Remote. Any program originating at a point outside of the studio
from which that program is controlled.
Split Network. A broadcast period during which time the Columbia
Network is divided into two or more sections; i.e., more than one
program is being originated at the same time.
Switching Light. A light located in Master Control and turned on by
a switch on each booth console. It is used to signal the Master Control engineer to switch to the following studio or program,
BROADCAST OPERATORS HANDBOOK
Switching Period. Each quarter hour, i.e., the 15-, 30-, 45-, and 60 70
minute period.
Synchronization. The period after sundown each day during which
time radio stations KFAB and WBBM broadcast simultaneously on
the same frequency.
Talent. The person or persons associated with a program and who
will be heard on the air during that program. This includes the announcer.
Talk -Back. The equipment used in speaking from the booth to the
talent in the studio during rehearsals.
Trouble-Report Form. The report filled out by each engineer and filed
with the Maintenance Department for each piece of equipment
found defective.
WBBM Break; Local Break. The station identification.
WBBM Daily Operations Sheet. The official schedule of program operations for the day for WBBM.
Part
3
OPERATING OUTSIDE THE STUDIO
Chapter
7
REMOTE-CONTROL PROBLEMS
the development of radiobroadcasting since its
earliest days, when the mere broadcasting of actual sound was
miracle enough to create unbounded interest, has witnessed an
almost fantastic evolution of technical equipment and technique of
operation. Even during the earlier period when amplifier response and
the old magnetic loudspeakers so limited the possible fidelity capabilities, broadcast engineers recognized the troublesome problems associated with the room or "studio" in which the program originated.
Ordinary architectural construction did not satisfy the requirements
for smooth control and faithful reproduction. This led to a detailed
study and development of both architectural design and acoustical
treatment to suit the needs of broadcasting. Although many experts
believe that the final answer to this problem has not yet been found,
they all concede that modern broadcast studios have spelled the difference between the success and the utter uselessness of high-fidelity
amplifiers, microphones, and line or relay links.
Broadcast programs, however, are as varied as the interests of the
more than twelve -million people who comprise the listening audience. It is inevitable that a great number of programs. must originate
at some point other than in a carefully designed studio with a permanent and complex studio control console and amplifier racks. Such
programs as speeches and political rallies, news commentators "on
the spot," audience participation shows from theatres or auditoriums,
sports, religious programs from churches, popular music from night
clubs, classical music from concert halls, and novelty and variety
shows from theatre stages necessitate a special department at each
broadcast station to handle such events adequately.
There are certain exacting requirements for remote -control equipment. The remote operator will encounter conditions that will be far
from favorable for the type of program to be broadcast. If the specific location produces very decided effects, he must either use them to
his advantage or avoid them. It is the purpose of Part 3 of this hand THE HISTORY of
71
72
BROADCAST OPERATORS HANDBOOK
book to outline the general type of remote -control equipment, and to
discuss comprehensively the problems encountered in the best utilization of this equipment to achieve the desired results.
REMOTE-CONTROL AMPLIFIERS
Equipment used for remote -control broadcasts must provide the
same means of mixing the outputs of the microphones and sufficient
amplifier gain for use of low -output high -quality microphones as does
the main studio equipment. It is obvious, however, that the equipment must be conveniently portable and therefore limited in size and
weight. For this reason, nearly all amplifiers of this type use low-level
mixing circuits requiring only one preamplifier tube for all microphone
inputs. Since mixing potentiometers are in the extremely low-level
position, frequent cleaning is mandatory. Power for remote equipment
is supplied either by batteries or power line current where available,
or by dynamotor supply in some cases of mobile equipment.
Fig. 7-1 is a panel view of one type of remote amplifier with selfcontained batteries and provision for four microphone inputs. The
RCA
Photo
Fig. 7-1. One type of battery-operated remote -control
amplifier with provision for four microphones.
RCA OP -5 weighs only 36 pounds when completely loaded with batteries and is a convenient size to carry. The line key switches shown
REMOTE-CONTROL PROBLEMS
73
at the upper right in Fig. 7-1 enable either of two lines to be connected to the output of the amplifier, or to a socket on the rear of the
chassis where an interphone may be plugged in for a talk and cue
line. Specially developed nonmicrophonic tubes are used, which have
high gain and low battery drain. Tubes may quickly be reached
through the door on the front panel which mounts the V.I. meter, and
the entire chassis may be removed from the case by simply loosening
the four corner thumb screws shown in the illustration.
Since the level requirements for remote -control lines will vary with
conditions, provisions are made for a multiplier arrangement on the
V.I. meter so that zero reference may actually range from minus 6
to plus 6 db. On some long open wire lines, for example, it may be advisable to feed a higher level to override line noise.
One example where this was found necessary occurred on a field
broadcast handled from the Indianapolis Municipal Airport which
consisted of interviews of incoming passengers from the planes. The
remote amplifier was battery operated, but the signal from the control
tower transmitter was feeding through so strongly on the broadcast
line that the tower operator completely swamped the announcer when
feeding a "zero level" to the line. By adjusting the V.I. multiplier
switch to +6, and peaking zero on the V.I., the tower operator was
down far enough below the program level that, when he came on with
instructions to the pilots, he simply provided an "on -the -spot" atmosphere to the program without spoiling it entirely.
Equipment used for remote -control purposes is largely an outgrowth
of the personal preference of the particular station, and therefore
varies considerably from one station to another. Remote -control fa.silities are more apt to be built up by a station to meet individual
requirements than any other type of the station's equipment, such as
control consoles and transmitters. Fig. 7-2 illustrates the series of
amplifiers built up by the staff of WHK (United Broadcasting Company), tailored to meet their preference in remote equipment. Remotes may require anything from one microphone to a dozen. It is
undesirable to carry a big amplifier to a one -microphone remote, and
it is confusing from a maintenance standpoint to have a great many
different kinds of amplifiers. With this thought in mind, WHK engineers designed this series of amplifiers which are all essentially the
same. There are three types of amplifiers in the series, all of which
have the same physical dimensions and the same internal circuits. All
types have the following common characteristics:
BROADCAST OPERATORS HANDBOOK
74
(1) 15 x 7 x 6 inches made from two standard 15 x 7 x 3 -inch chassis pans.
(2) Preamplifier for each input which the staff felt necessary to im-
prove the signal-to-noise ratio.
(3) Facilities to feed two separate 600 -ohm outputs with +8 vu
level.
(4) High impedance output with separate gain control for feeding
a p -a amplifier.
(5) High level earphone jacks with separate gain control.
Courtesy of Station
WHK
Fig. 7-2. Amplifiers for remote -control work must be portable and compact.
Details of these illustrated are listed above.
basic unit has four inputs, uses 6 -volt tubes, and has an a -c
supply and emergency batteries in another case the same size
amplifier. This type is used on dance band and night spot reThe subbasic unit has two inputs, uses 1.5 -volt tubes, and the
batteries are in the same case. This type is used for the one- and two microphone pickups. The superbasic unit has eight microphone inputs
plus a high level input, uses 6 -volt tubes, and the same power supply
as the basic unit. The high-level input allows two or more amplifiers
to be connected in series so that any number of microphones can be
handled.
The
power
as the
motes.
Simplex Control of Remote Amplifiers
Many times it is highly desirable from an efficiency point of view to
allow turning the remote amplifier on and off from the studio. This is
REMOTE -CONTROL PROBLEMS
75
desirable for a regularly scheduled broadcast from a point requiring
only one microphone where no "mixing" adjustments are necessary.
This may be accomplished by means of a "simplex" installation as
shown in Fig. 7-3. The simplex coil "in" and "out" appears on the
jack panel at the studio. When the remote line is patched into the
STUDIO
REMOTE
f
ö
-LINE
POINT
TO LINE TERMINALS
ON REMOTE AMPLIFIER
O
22.5
r
I
AC
SWITCH
REMOTE
TO
AMPLIFIER
O
Fig. 7-3. A simplified schematic of a "simplex" installation which is used to
switch on and off a remote amplifier from the studio.
equipment through this coil, it may be seen that the battery circuit
will be completed to activate the relay at the remote point which is in
the power-supply circuit of the remote amplifier. This procedure
eliminates the necessity of sending an operator to this point each day.
General Remote Operating Problems
The remote operator is faced with conditions so varied and complex
that any discussion of a specific type of pickup must necessarily present only general principles involved.
A singer's voice is given a certain recognized timbre by the breath
which carries the sound from vibrating vocal chords into the modifying air cavities of the head. As these sound waves emerge they disturb
the air in the place of origin in all directions, but principally in the
direction which the singer is facing. The microphone will pick up the
sound anywhere in the room. Good transmission will depend upon
76
BROADCAST OPERATORS HANDBOOK
the relationship of the position between performer and microphone, and
also upon the relationship of position with the walls, floor, and ceiling
of the room. The air cavities and acoustical condition of the air boundaries will affect the character or "timbre" of the sound just as do the
air cavities of the singer's head which determines his original voice
quality.
Thus it becomes apparent that the varied acoustical conditions encountered will place considerable importance on the type of microphone to be used and method of placement of the microphone. For
example, the operator may find the surfaces bounding the point of pickup to be highly reflecting in character to sound waves, causing distinct
"slaps" and echoes to be prevalent. This condition is caused by deflecting surfaces parallel to each other, and is the reason why "live end" broadcast studios are constructed with no parallel surfaces
existing. Under this kind of handicap, the operator must use the directional characteristics of the microphone to the best advantage. He
could not, for example, use a bidirectional microphone with one live
side toward the pickup and the other live side toward a highly reflecting wall.
Due to the nature of remote -control pickups, the microphones used
are nearly always of the unidirectional type. This permits much better
discrimination between wanted and unwanted sound, since the noise
level at any remote point is quite high compared with a broadcast studio. The unidirectional characteristic is convenient to aid in preventing large amounts of reflected sound -wave energy from actuating the
microphone elements. Since the intensity of a sound wave decreases
as the square of the distance, increasing the distance between the
sound source and the reflecting surfaces (where this is possible) will
decrease the amount of reflected sound -wave energy at the microphone.
By experimenting with the distance between sound source and microphone it may be observed that the relationship between origina!_
and reflected sound will vary over a considerable range. Thus by decreasing this distance a greater proportion of original sound is obtained, and by increasing the distance (between wanted sound source
and microphone) a greater proportion of reflected sound is obtained.
Music in particular needs a certain amount of reflected sound for brilliance and color. Too much reflected sound will cause a "hollow" tone
and uncomfortable overlapping of succeeding musical passages. If the
amount of reflected sound is too small, such as in many studios over treated with sound absorbent material, the music will be lifeless.
Chapter
8
REMOTE VERSUS STUDIO PICKUPS
broadcasting concerns the transmission and reception of voice and music with the preservation of all the
original values. This precludes that any effect should be added
to or withdrawn from the original intent. In radio, sound can play on
the emotions of the listener only as effectively as the transmitter and
receiver equipment, studio conditions, and the skill of the engineers
will permit. Microphones and amplifiers are today of such good quality that no practical limitations to true fidelity exist from mechanical
or electrical characteristics. Modern broadcast studios are such that
only slight limitations exist ,for faithful transmission of sound. This
emphasizes, insofar as remote -control broadcasting is concerned, that
the skill of the engineer or producer responsible for microphone setups
and operating technique, is of utmost importance. This becomes
doubly important when it is realized that each orchestra of any type
has its own identifying qualities resulting from instrumentation, musical technique, and conductor's interpretations, all under the influencing factor of microphone placement and acoustical conditions of the
point of origin.
The effects desired by the orchestra conductor may be achieved only
by proper relationship of the microphones to the musical instruments.
This "proper relationship" is directly influenced by the acoustical condition of the pickup area. For transmission of pure musical tones of
a violin, the microphone must be far enough away from the sound
holes of the violin that the reflected sounds may be caught in all their
beauty denoting rich and true harmonic content. Conversely, when
special effects are desired such as in many instrumentations of rumbas in dance orchestras, the microphone should be so near the violin as
to bring out the harshnessof the resined bow drawn across the strings
of the instrument.
THE PROBLEM of
77
78
BROADCAST OPERATORS HANDBOOK
General Comparisons of Studio and Remote Pickups
Perhaps the most striking difference between studio and field pickups is the complete lack of permanent facilities of any kind in the field.
The Bell Telephone System installs a "broadcast loop" upon order
from the program or traffic department of the station. Sometimes two
loops are installed, one to be used as a "talk" line direct to the control room at the studio, or for emergency broadcast service in case of
trouble with the regular broadcast line. These lines, however, must
be installed as conveniently as possible to the source of the broadcast,
yet as inconspicuously as can be arranged. For this reason, it is often
a matter of a "line hunt" on behalf of the field engineer, and this is
one reason why he arrives at the remote point a long time in advance
of broadcast time. The line or lines may be found under tables, behind
chairs, piano, organ console, or what -have -you on the stage, or it may
be in a room off from the main room where the broadcast is to take
place. It is usually tagged with an identifying card such as "WIRE
Broadcast."
Since the problem of good transmission of talks or speeches at remote points is not nearly so difficult as that of musical pickups, the
discussion to follow will concern music. Musical programs may originate at such places as ballrooms, restaurants, night clubs, and cafes
featuring dinner music, and music for dancing and floor shows. The
situation calls for a decided difference in technique of technical production between studio and remote broadcasts.
In the ideal studio musical setup, only one microphone is used at
sufficient distance, with the musical instruments grouped and positioned so as to blend into the proper balance at the microphone position. This procedure not only simplifies the problem of control, which
always makes for a better effect, but also leaves the problem of orchestral balance in the conductor's hands where it rightfully belongs.
Multiple microphone arrangement will place the maximum responsibility for balance of the various sections in the hands of the operator
mixing the outputs of the various microphones.
At remote points, however, where so much activity such as dining
or dancing occurs, microphones must be placed close to the musicians.
This is inevitable since otherwise the background noise would result
in a disagreeable hodge-podge of confusion. This close microphone
arrangement calls for the use of more than one microphone to achieve
the desired balance; otherwise the instruments closest to the micro-
REMOTE VERSUS STUDIO PICKUPS
79
phone would dwarf the rest of the orchestra. Then the setup is divided into units of like instruments or combination of instruments,
each unit being covered by a separate microphone so that the volume
from each unit may be adjusted at the mixing panel to achieve the
desired balance.
The practice has some advantages for remote -control pickups other
than avoiding background noise. Acoustical conditions that might
severely affect the broadcast are minimized to the fullest extent, since
the ratio of any reflected sound to the original sound is small. Then
too, although some loss of tonal brilliance results from close microphone arrangement, good instrumental definition is gained, which is
important for dance broadcasts.
Symphony music and church broadcasts are different in this respect
in that the audience is comparatively quiet, and the pickup may be
treated more as a studio show by studying the acoustical conditions
existing at the point of origin. This is discussed in a following chapter.
Chapter
9
REMOTE MUSICAL PICKUPS
of Fig. 9-1 will reveal the principles involved for
a typical dance orchestra broadcast. Insofar as the operator is
N OBSERVATION
concerned, this setup divides the orchestra into three separate
units: microphone #1 for saxophone and clarinets; #2 for trumpets,
trombones, and soloist; and #3 for string bass and piano. Microphone #3 is very handy for special emphasis of the rhythm section, or
piano or string bass solo passages. It will be noted that when the trumpets are open, they are behind the trombones and caught on microphone #2; when muted, they step down ahead of the trombones and
immediately in front of the microphone. Muted trumpets or trombones must be played with the muted bells very close to the face of
the microphone. The same is true of any wind instrument upon which
the player is producing subtones. The subtones of any wind instrument are just as low in volume, even though open -belled, as the softest
muted instrument. This, then, calls for close co-operation between
the conductor and his musicians and the engineer responsible for
proper pickup. Many times, important solo "licks" of a particular passage may be lost by lack of co-ordination.
TRUMPETS
OPEN)
0
Q
°lQ
00
PIANO
TRAPS
\\\
O
STRING
BASS
\\\ TROMBONES
4 #3
MIKE
TRUMPETS (MUTED)
0
4
0 0 0
SAXOPHONES
0
AND/OR
CLARINETS
#2
MIKE
ALSO ANNOUNCER
AND SOLOIST
MIKE #1
Fig. 9-1. Seating arrangement of dance orchestra and placement of microphones for a typical remote pickup.
80
REMOTE MUSICAL PICKUPS
81
Brass Bands
Although the 4/4 type bands share comparatively small time in
radio, their particular peculiarities pose special problems in pickup.
A number of community organizations, fraternal societies, and, of
course, the armed services participate in radio through presentation of
brass bands. These pickups very often must be made out of doors,
the least favorable spot for broadcasting. With no outdoor shell or
walls of any kind, no reflection of sound can occur to create the ideal
polyphased sound dispersion so important to broadcasting technique.
Under these conditions it is again necessary to use multiple microphone pickups, grouping the units by means of spotting separate microphones where needed as determined by trial.
For a fair-sized band organization, the units are usually as follows:
one microphone for the clarinets, piccolos, and flutes; one for the English horns, bassoons, bass clarinets, saxophones, and tubas; and one
for the French horns, trombones, and trumpets. The tympani, traps,
and chimes are usually placed in the lower sensitivity zone of one of
the microphones which prevents the use of excessive distance for
proper balance. Indeed, the sensitivity pattern characteristics of the
particular microphones used must be thoroughly understood for any
kind of musical pickup. Tympani, when used with brass, are very
predominate in character when placed in an equal sensitivity zone to
the rest of the instruments. Just the opposite is true when they are
used with strings, since the masking effect due to the characteristics of
the musical instruments themselves tends to subordinate the tympani
sound.
When well -designed outdoor shells are used, the ideal condition exists for brass -band broadcast. Usually only one microphone is used,
suspended some 15 feet out and above the front-line musicians. As
before, predominate instruments, such as tympani, traps, and chimes,
are placed at the side in a lower sensitivity area of the microphone.
Salon Orchestra Remotes
Some dining places have salon or chamber music organizations
which are picked up for broadcasting during the noon or early evening hours. Since a salon orchestra's library concerns the more serious
type of music with many low passages, precautions must be taken to
subdue as much as possible the noise of the patrons. An intimate
microphone placement is therefore indicated.
BROADCAST OPERATORS HANDBOOK
82
Usually the salon group is small, ranging from string trios and
quartets to about ten members. For the smaller groups, one microphone raised quite high and slanted down at an angle of about 35 to
45 degrees with the floor will be adequate. A hard floor with no covering will aid in obtaining just the amount of brilliance necessary for
this type of pickup. A salon orchestra requires more definition than
brilliance in musical tones.
Symphonic Pickups
Symphony orchestra programs have become a regular feature on the
air each season and quite often must be broadcast from a remote point
rather than from a regular broadcast studio. Thus far, musical setups
have been discussed involving a comparatively small number of musicians and a specific type of instrumental structure. The symphony
orchestra, however, is many orchestras in one. The engineer is concerned with the proper grouping of four distinct instrumental sections:
1.
Strings: violins, violas, cellos, string basses.
2. Woodwinds: clarinets, bassoons, English horns, flutes.
3. Brasses: trumpets, trombones, French horns, tubas, euphonium.
4. Percussions: snare drums, bass drums, tambourines, triangles,
cymbals, piano, harp, xylophones, marimbas, tympani.
To this instrumental setup, vocal soloists and choirs are often added,
as for Beethoven's "Ninth Symphony" or Verdi's "Requiem." The musical score itself will influence many times the necessary spotting of
microphones. For such numbers as the delicate "Clair de Lune" of
Debussy, the perspective of the violin passages should be distant, with
a rich and brilliant tonal quality. In numbers such as the Strauss
waltzes, the perspective of the strings should be closer and more strident in character. This problem will be outlined in more detail presently.
As a general rule, the arrangement of the symphony orchestra for
broadcast is the same as for a regular audience performance. The
instruments vary in volume of sound produced and therefore in penetrative quality. Strings produce the least volume, then flutes, clarinets, horns, trumpets, and percussion instruments.
The acoustical situation for symphony broadcasts is generally better than for most other remote controls since the auditorium is usually
designed for such large groups and made compatible with good listening for the audience, although not always ideal for broadcasting.
REMOTE MUSICAL PICKUPS
83
It is easier from a good transmission standpoint to encounter an auditorium that is too "live" and reverberant so that wall, ceiling, and
floor treatments may be added, than to start from one that is too
"dead" to sound reflection.
The correct setup for a symphony orchestra is always arrived at on
the first rehearsal by trial and error. A number of microphones are
spotted at the most likely points so that each may be tried without
the commotion of continually moving one microphone. The most likely
setup is one microphone suspended at a height of about 15 feet about
20 feet in front of the violins. A separate microphone must be used
for vocal solos, since a closer relationship of vocalist to microphone
must prevail for proper balance.
A typical setup for a full symphony orchestra was shown in Fig. 4-7
and no difference need occur for remotes. Some deviations occur in
practice with various symphony orchestras. Toscanini's NBC pickup,
which originates in a regular studio, uses two microphones for the main
orchestra. Due to the directional characteristics and angle of placement (one for each side section) , the orchestra is effectively divided
into two microphone fields with little overlapping. Sometimes another
microphone is suspended directly over the violin section for special
effects on certain compositions as mentioned before. The Ford Sunday
Evening Hour, broadcasted over CBS on Sunday evenings, used two
microphones on the choir for clarity and definition of diction.
In chapter 11 is a complete description of a specific symphony setup.
Church Remotes
Programs from churches usually involve both music and the sermon.
Fig. 9-2. The usual positions of a choir as shown
here, results in too strong
soprano response and insufficient alto and bass.
Compare Fig. 9-3.
BARITONES
AND
TENORS
AND
SECOND
FIRST
BASSES
ALTOS
SOPRANOS
SOPRANOS
AUDITORIUM
This ordinarily requires only one microphone when the minister's po-
BROADCAST OPERATORS HANDBOOK
84
dium is directly in front of the choir as is the most common church
arrangement. When vocal solos occur during the choral rendition, a
separate microphone is necessary for proper pickup and balance. It
will be noted in nearly all instances that, during solos being picked up
by a microphone very close to the choir loft, organ accompaniment
must be brought up to the proper background level by use of the rostrum microphone or microphone farther out in the congregation. This
is due to the acoustical properties which are evident in nearly all
churches causing the organ tones to be much more predominant out
in the congregation than up near the choir.
Conventional choir arrangements are often not practical for broadcasting whether in a regular studio or at a remote point. Fig. 9-2 illustrates the usual arrangement of a choir as used for auditorium or
church presentation. On a broadcast, this arrangement nearly always
results in a predominance of soprano voices with very little alto or
bass. Fig. 9-3 shows an arrangement much more satisfactory for
broadcast purposes, resulting in a better all-around balance of voices.
cr
O
z
oF
.\
Fig. 9-3. By placing a microphone in this
relationship to the rows of singers, a better all-around balance of voices is obtained over the arrangement shown in
Fig. 9-2.
MICROPHONE
Although it would be impossible to cover all the details and complexities of remote -control pickups in a single discussion, it is hoped
that the picture here presented has set forth the fundamental procedures that would help in a general way to approach a remote -control
problem properly. To present an absolutely complete picture would
be impossible, since acoustical conditions and orchestral intent varies
as the number of places from which a broadcast can originate, and
the number of different musical combinations existing. A good understanding of equipment and acoustical variations, however, will enable
any engineer to achieve good results on this type broadcast.
Chapter
10
EYE -WITNESS PICKUPS AND MOBILE
TRANSMITTERS
many types of events of wide public appeal that cannot be adequately covered by the usual methods of remote -control pickups using wire lines for links of communication. Among
these are various kinds of sports such as boat racing, cross-country
events, and golf matches. Aside from these events, there are the inevitable times of disaster such as floods, fires, earthquakes, and the
myriad types of catastrophes that wreck ordinary communication
services for many miles around the point of trouble. In order to be
prepared to bring eye -witness accounts of happenings of these kinds to
THERE ARE
111
PACK
TRANSMITTER
RECEIVER FOR
PACK
TRANSMITTER
RECEIVER
FOR
STUDIO
(CUING)
PACK
13 TRANSMITTER
MOBILE
TRANSMITTER
RECEIVER
AT STUDIO
LINE OR
INPUT TO
STUDIO
CONSOLE
OR REMOTE
POINT
U
POWER
SUPPLY
GENERATOR
TRANSMITTER AT
MAIN
TRANSMITTER FOR
CUING OR TALK BACK
DSTUDIO OR
MOBILE TRUCK
LOCATION
Fig. 10-1. Block diagram of equipment for pack-to -truck and truck -to-main
transmitter relay transmissions.
85
86
BROADCAST OPERATORS HANDBOOK
NBC Photo
Fig. 10-2. Broadcasting an eye -witness account of the burning of the S.S.
Normandie from an adjacent pier by means of a pack transmitter.
the thousands of interested listeners, most stations are equipped with
portable and mobile relay facilities that utilize power supplies independent of utility companies, and also independent of any necessary
wire lines, for relaying the signal to the studio or main transmitter.
There is probably no other division of radiobroadcasting that differs so radically from one station to another as the mobile -relay
department. Fundamentally, however, the necessary inventory of
equipment includes small portable transmitters known as "pack transmitters," a mobile transmitter and antenna mounted in a truck, receivers for cuing and pickup of pack transmitters, and power supplies
for the equipment used.
Fig. 10-1 shows the fundamental layout of equipment used to broadcast any event as mentioned in the beginning of this chapter. Pack
transmitters are low -output transmitters (usually about 2 watts) such
as illustrated in Fig. 10-2. These transmitters are usually good for
line -of-sight transmission only and therefore are picked up on a re-
EYE -WITNESS PICKUPS AND MOBILE TRANSMITTERS
87
ceiver in the mobile truck and fed to the main mobile transmitter.
Mobile transmitters with their associated antenna systems are mounted
in trucks or cars, such as that illustrated in Fig. 10-3.
Frequency Assignments
A license issued to a broadcasting station for mobile relay purposes
covers a group of four frequencies as follows:
Group A (Kilocycles)
1622
2058
2150
2790
Group B (Kilocycles)
1606
2074
2102
2758
Group C (Kilocycles)
Group F (Kilocycles)
31,620
35,260
37,340
39,620
Group G (Kilocycles)
33,380
35,020
37,620
39,820
Group H (Kilocycles)
1646
2090
2190
2830
156,075
157, 575
Group D (Kilocycles)
Group I (Kilocycles)
30,820
33,740
35,820
39,980
156,750
158,400
159,300
161,100
Group E (Kilocycles)
Group J
Any 4 frequencies above
300,000 kc excluding band
400,000 to 401,000 kc.
31,220
35,620
37,020
39,260
159,975
161,925
Only one of any of these groups is assigned to each station. In
order to avoid interference problems insofar as is practically possible,
the FCC (Federal Communications Commission) has ordered that
the first application from any particular metropolitan area in groups
A, B, or C shall specify group A, the second shall specify group B,
the third group C, the fourth group A again, etc. The same is true of
groups D, E, F, or G.
88
BROADCAST OPERATORS HANDBOOK
Group H is assigned only when need for these frequencies may be
shown. Group I is for frequency modulation only. Group J is issued
only to stations capable of carrying out research and experimental
work for advancement of relay broadcast services.
Operation
Relay stations in groups A, B, C, and J are licensed to operate with
a power output no more than is necessary to receive the signal satisfactorily. Those in groups D, E, F, and G are not licensed for an out-
WOR Photo
Fig. 10-3. The second link in an on -the -spot broadcast
is often a mobile short-wave transmitter installed in a
truck.
put power in excess of 100 watts. The FCC also stipulates that before
any power in excess of 25 watts is used, tests shall be run to insure
that no interference will occur to the service of any government station.
A station with only one license may use only one of the four authorized frequencies at any one time. When it is desired to transmit the
program on one of these frequencies and maintain contact with the
studio on one or more of the other authorized frequencies at the same
time (such as for cuing purposes and instructions), two or more licenses must be obtained by the station.
The operator of a relay broadcast station must maintain the frequency of the transmitter within the following limits:
EYE-WITNESS PICKUPS AND MOBILE TRANSMITTERS
89
(a) 1622 to 2830 kc: within 0.04%
(b) 30,000 to 40,000 kc and above: 10 watts or less within 0.1%, over
10 watts within 0.05%
The operator must also be certain that the call letters of the relay
station are announced at the beginning and end of each period of operation (whether rebroadcast on the main station transmitter or not)
and at least once every hour during the operating period.
Chapter
11
THE LIVE SYMPHONY PICKUP
BY BERT H. KOSBLITZ
M
will probably never be called upon to handle a
live symphony program. This is because the proportion of
symphony programs to all the programs broadcasted is very
small, and when a technician has handled such an event well he is
likely to be used over and over again for this work. In other words,
such a job is not "passed around" to give everyone a chance at it as is
the case with many other things. No one knows, however, when he
may be given a chance to handle such a program, in which case a
little inside knowledge will be of great value. The information is not
lost in any case, because almost every fundamental point in symphony
handling is applicable to other types of programs. A great deal of
symphony technique can be used to advantage in recorded symphony
OST OPERATORS
programs.
Making a symphony pickup involves numerous problems, some of
which are technical and some which are not. Some of these problems
are psychological, some social, others political. Hence, not only the
technician, but representatives from all departments of the station
staff may be called upon at times to effect a solution. You are probably wondering why this should be mentioned in an operators' handbook. At WHK it is standard practice to have the technician attend
all rehearsals to get a reading on various orchestral numbers. Usually he is the only station representative present and so may be called
upon to handle details outside his own department; therefore it is
well for him to know the activities of all departments.
The symphony management perhaps has to be convinced that the
broadcasts will be beneficial to it and that they will be properly
handled by the radio station and its staff. The attitude of the conductor and the assistant conductor to the broadcast will make the
situation easier or more difficult, as the case may be. The acoustical
characteristics of the hall in which the orchestra plays will govern the
limits of what the technician can do to make a good pickup. The
type of microphone, the number of them used, the associated equip 90
THE LIVE SYMPHONY PICKUP
91
ment, especially the monitoring facilities, will all affect the pickup.
Finally, the technician who handles the faders can make or break
the program. Perhaps the best method of getting detail on all these
things would be to describe how these problems were handled by WHK
in its broadcasts of the Cleveland Symphony Orchestra to the Mutual
Network.
Pre-Broadcast Problems
Early in 1943, Mutual decided to furnish its listeners with a complete season of Cleveland Symphony broadcasts, if suitable arrangements could be made with the orchestra management. These arrangements, for the most part, were made by WHK personnel with the
cooperation and guidance of Mutual's president. The first and probably the greatest obstacle which had to be overcome was the symphony
management's fear of hurting box office receipts, which fear seems to
have been quite common in the past. A symphony orchestra has a
great many musicians in it. If the orchestra is to be really good, there
must be a fair proportion of the country's better musicians in it. This
costs money. It was feared that a weekly radiobroadcast would tend
to keep people from coming to the regular concerts, which would result in a smaller income and eventually would reduce the caliber of
men in the orchestra.
WHK was firmly convinced that such an impression was erroneous
and was finally able to get the symphony management to agree to let
Mutual hire the orchestra for a one -hour program each week. It was
agreed that the major work presented on the broadcast would never be
the same as the one performed at the Thursday and Saturday evening
regular concerts. Thus no one could hear a major work played over
the radio which someone else had to pay to hear. Before the season
was half over, the box office had exceeded its record for any previous
year since the orchestra had started. WHK feels, therefore, that the
broadcasts not only did not hurt the box office receipts, but actually
increased them to these unheard of proportions.
Once the business arrangements with the symphony management
had been completed there remained about a month's work to co-ordinate all the other factors before the first program was broadcasted.
Those factors included orchestra conductor, associate conductor,
radio script, orchestra seating, auditorium acoustics, announcer, technicians, microphone types and placement, and monitoring facilities.
The conductor during the first season of broadcasts was Erich
92
BROADCAST OPERATORS HANDBOOK
Leinsdorf who had been conducting Wagner for the Metropolitan
Opera Company. Despite his comparative youth, Mr. Leinsdorf had
a wealth of conducting experience and was a most thorough all-around
musician. He was extremely conscientious about respecting the composer's wishes rather than giving his own interpretation of the composer's ideas. He was enthusiastic about the broadcasts and helped
greatly with accurate timing and correcting minor unbalances in the
orchestra. The associate conductor was Dr. Rudolph Ringwall, who
also is a first-rate musician and conductor. Dr. Ringwall was not only
enthusiastic about the broadcasts, but was experienced in these matters
and therefore understood most of the problems. His experience in
both music and radio proved to be of inestimable value in making the
original setup and in properly presenting the orchestral works later.
On every program which he did not conduct he was in the monitoring
room with a score, telling the technicians in advance what they might
expect at various places.
The orchestra management was somewhat concerned over the program notes to be used on the broadcasts. It was certain that the notes
should be written by someone with a good knowledge of orchestras and
classic works, and it was equally certain that the broadcast had to be
timed out properly. This was worked out by two people. There was
no doubt that the person best qualified to write the program notes was
the program annotator of the Cleveland Orchestra. There was also no
doubt that the radio production man should control the timing. So,
early in the week, the orchestra would rehearse the radio numbers
so that they could be timed. Once the total music time was known,
the program annotator could be told how much script to write. This
would not give the desired effect, however, because the announcer
might have read at a different speed than the annotator had expected
and musicians and conductors vary their tempos with weather, auditorium acoustics, audience reaction, and their personal feelings.
To overcome this difficulty, articulated copy was used. The annotator wrote solid copy which would last two minutes less than the time
at his disposal. Then he would add to the middle and closing announcements several paragraphs of 15 or 20 seconds duration which
could be used or not. The closing announcement was written in four
parts in such a way that any part or any combination of parts made
a complete sign -off. These four parts were 11/2 minutes, 1 minute, 30
seconds, and 15 seconds long so that the announcer could adjust the
THE EYE SYMPHONY PICKUP
93
closing to take anywhere from 15 seconds to 31/4 minutes. This system
was highly successful because no deletion or padding was ever apparent to the listening audience, and hurrying or slowing down the
talking speed was never necessary.
Physical Arrangement of Orchestra
The physical arrangement of the orchestra is a matter over which
the radio státion has little control. Each conductor has his own preferred way of placing the men, and if there are to be any guest conductors, the radio people are faced with the problem of constantly
changing setups. At least so it would seem. As it worked out in practice with the Cleveland Orchestra broadcasts, no change of microphone position was necessary with rearrangement of orchestra personnel. The seating arrangement used by the regular conductor of
the Cleveland Orchestra was highly recommended from both practical
and theoretical points of view.
The strings were placed in rows which radiated like spokes from
the conductor's podium back to the last riser. As the conductor faced
the orchestra, the first few rows to his left were first violins and the
next few rows were second violins. The principal sound from a stringed
instrument radiates on a perpendicular to the belly. With the microphone placed above and directly behind the conductor, the violins were
in perfect position for optimum results. To the conductor's right were
violas and cellos in rows like the violins. Here it might be argued that
in theory the violas and cellos were in a poor position, since their
sound holes would point away from the microphone. In practice this
arrangement proved to be satisfactory because these instruments have
a slightly more robust tone than the violins and normally are a supporting rather than a lead voice. The cellos, which are often a weak
section, had a direct line to the microphone and picked up beautifully.
The strings mentioned so far roughly form a shallow letter "V" with
the conductor at the vertex. The front part of the remaining empty
space seats the woodwinds, not in spoke -like rows but as arcs of circles
with the conductor at the center. Behind them were trumpets and
trombones. Still farther back and constituting the last row were the
bass viols. To the left of the basses were the French horns and tuba
and to the right were tympani and percussion. The harps were on the
top riser back of the violas. When the guest conductors changed everything around, it was discovered that, within reasonable limits, there
94
BROADCAST OPERATORS HANDBOOK
was no difference in the pickup no matter how the orchestra was placed.
This possibly was because of the excellently designed shell around
the stage at Severance Hall.
The acoustics of the hall in which the orchestra plays will have
much to do with the microphone setup. A "live" hall is preferred by
a good many symphony listeners. Such a place need not be of undue
concern to the technician unless there is a bad reflective path coming
back to the stage. This can be tested initially by clapping the hands
while standing on the stage. If the noise reverberates but dies off, you
have nothing to worry about. If a second hard slap comes back, then
you have troubles. There is one hall in the United States that is so
poor acoustically that a curtain has to be hung between the stage and
the auditorium when the orchestra rehearses in order to keep reflected
notes from interfering. Severance Hall in Cleveland has excellent
acoustics. A person speaking with ordinary volume on the stage can
be heard in every seat in the house without the use of a public address
system. Another striking fact about this auditorium is that the
acoustics are the same whether it is empty or full. This is because the
seats are upholstered and covered with plush, thereby absorbing
sound just the same as clothing does.
The selection of a suitable announcer does not concern the technical
department except that the technician should exert whatever influence
he can to see that this man has a moderately deep and pleasing voice
and has a little knowledge of what he is talking about. The selection
of technicians for a symphony broadcast should be made carefully.
At WHK, there are several different groups in the technical department. Men are not specifically assigned to any one group, but each
more or less gravitates toward his major ability and preference. There
are studio control men, master control men, remote pickup men (usually studio men with extra ingenuity) , maintenance men (who also
build new equipment) , transmitter operators, and development engineers. It was decided by the executives to send two technicians out,
since all the equipment was in duplicate. It so happened that the best
studio control man, who was also the best remote man, liked symphony music, so he was selected to make the setup and push faders
on the program. One of the maintenance men, who was an excellent
mechanic and trouble shooter, also liked symphony music, so he was
sent along to provide whatever facilities the other man might require.
Selection of microphones is a matter of station facilities, individual
auditorium characteristics, and personal preference. Monitoring equip-
THE LIVE SYMPHONY PICKUP
95
ment should be the best obtainable and in no case inferior to the line
you are feeding.
Microphone Placement
It is perhaps just as important to know what not to do as to know
what to do in certain instalces. Therefore the whole process of arriving
at a microphone placement will be described. In some auditorium
other than Severance Hal_, the things discarded might have been retained. An all-around picture will give a clue to procedures possible
in any hall. To begin w=th, the two technicians agreed beforehand
that the pickup should be made with a single microphone. To use
more than one would take the problem of orchestral balance from the
conductor, where it prope-ly belongs, and make it the responsibility
of the technician, who nine times out of ten would garble it. The
conductor and the associate conductor were persuaded on this basis
that one microphone woulc be best and that it should be placed somewhere on the direct-center stage line. Three 1 -inch brass angle
brackets were made up to suspend three microphones each. Armed
with these brackets, nine microphones, and a bushel of clothes line, in
addition to the regular remote equipment, the two technicians arrived
at Severance Hall three hours before rehearsal time.
Before anything else was done, a height of 15 feet above stage
level was agreed on for the position of the microphone. The first
bracket was hung 15 feet high and about six feet into the orchestra from the conductor's position. It supported a Western Electric
618-A dynamic microphone, an RCA ribbon strapped for voice, and a
Western Electric cardioid set on cardioid. The second bracket was
directly over the conductor and supported an unbaf led eight -ball
microphone, a ribbon strapped for music, and a cardioid. The third
bracket was about six fee, behind the conductor and contained an
unbaffled salt -shaker microphone, a ribbon strapped for voice, and a
cardioid. Extension cords were run into a monitoring room and arrangements made to listen to each microphone separately.
By this time the stage began to look as though we were preparing
for a circus performance. The conductor went through his rehearsal
just as if nothing were amiss, while the associate conductor and technicians selected a microphone. It is useless to recount the endless discussions and ladder climbing; therefore only the results will be given.
First it was determined that the first and second bracket arrangements were too far forward to give sectional balance to the orchestra.
96
BROADCAST OPERATORS HANDBOOK
In either of these positions some group of musicians dominated beyond
all proportion over the volume of the rest. The third bracket arrangement was shifted back and forth until all were satisfied that the orchestra sections were balanced. This satisfactory position was 12
feet from a line drawn across the stage just touching the chairs of
the musicians closest to the audience. During intermission, all three
bracket arrangements were clustered together so that all the microphones could be tried.
The results of this experiment were as follows. The 618-A dynamic microphone had sufficient "highs" but not enough bass. Also,
the "highs" were spotty, certain high frequencies being accentuated
more than others. Both the unbaffied eight -ball and the unbaffied saltshaker microphones gave excellent reproduction and were thought by
the technicians to be satisfactory. However, the "highs" were reproduced so well that a considerable amount of extraneous noise such as
bowing rasp and reed sizzle were noticed. While this was faithful
reproduction, it was not pleasant reproduction. The ribbon strapped
either way did not even approach satisfactory fidelity. Since the cardioid gave splendid reproduction without accentuating the extraneous
noises, it was selected and it also had the virtue of wide-angle frontal
pickup and was electrically "dead" toward the audience. In practice,
a stand was used instead of the trapeze, two units being mounted side
by side with one for regular use and one for emergency use. This may
be summarized as follows: the pickup should be made with a single
microphone. That microphone should be somewhere on a line at the
direct center of the stage. In Severance Hall a Western Electric cardioid set on cardioid was used, 12 feet toward the audience from the
nearest musician, 15 feet above stage level, and tilted to point approximately at the center of the orchestra.
Other Problems
The amplifier following the microphone was flat to plus or minus 0.75
db from 30 to 15,000 cycles. One of its 500 -ohm outputs was fed to a
111-C coil strapped 1 -to -1, which in turn fed the phonograph input of
a speaker amplifier. The speaker amplifier was a high-fidelity type
with separate bass and treble tone controls arranged so that in the
middle position for each one the amplifier was flat. This in turn fed a
high-fidelity speaker. The room containing this equipment was about
20 by 30 feet and was furnished much like a living room. Those are
important considerations-the size of the room and the furnishings.
THE LIVE SYMPHONY PICKUP
97
The best speaker in the world is ineffectual in a small room, and a
room that is too live will tend to cause the technician to reduce the
"highs." The speaker was placed at one end of the room and the technician at the other so that the tones had a chance to develop and blend
before he heard them.
The next step was to set the speaker volume properly. It is well
known that the efficiency of the ear varies with volume intensity;
therefore some standard had to be set up which could always be usedin this case something in the nature of a hike. The two technicians
and the associate conductor tried seats in every section of the auditorium and finally agreed that the orchestra sounded best in the middle
seats of the 8th, 9th, and 10th rows of the middle section on the main
floor. These seats are directly in line with the microphone. After a
multitude of trips from the seats to the monitoring room, the volume
on the speaker was fixed so that the same level came to the control
position as was noticed in the referenced seats. Fortunately, the
speaker amplifier had a volume indicator on it so that this volume
could always be maintained regardless of tube wear.
Once the mechanical equipment is properly arranged, there remains
the problem of properly broadcasting the program. A psychological
reaction is strongly involved in this procedure. The most common
complaint from musicians and conductors is that the technician raises
the soft passages and reduces the loud passages, thereby defeating the
function of the conductor and destroying the symphonic intent of
the music. It is therefore mandatory that some procedure be used
which will insure at least the approximate dynamic range of the orchestra in the hall. The upper limit is, of course, the maximum operating level of the particular station involved. The lower limit is the
signal-to-noise ratio at the receiver location. Inside the primary service area of a station there is normally no difficulty with signal-to-noise
ratio. If the soft passages are raised to help the listeners outside the
primary service area, the loud passages, of necessity, will have to be
reduced. In that case no listeners in either area are able to enjoy the
full dynamic range. If the soft passages are not raised, the listeners
inside the primary service area can be given the full dynamic range of
the orchestra.
At WHK it was decided that it was better to serve some listeners
well, even at the expense of others, than to serve no listeners well. One
of the technicians assigned to the symphony was sent to all rehearsals.
He set up the equipment just as he would for the actual broadcast.
98
BROADCAST OPERATORS HANDBOOK
Then he would arrive at a fader setting for each number or movement
which would cause the vu meter to peak no more than the maximum
allowed. These settings were carefully written down so that on the
evening of the broadcast the orchestra fader was always set at the
correct place before each number started and was never moved during
the number. Thus listeners were furnished with the full dynamic range
of the symphony orchestra.
This proved to be only part of the total problem. Using the method
just described will mean that the listener has to increase the setting of
the volume control on his set if he desires to hear the softest passages.
If the listener does this (and he will if he is a symphony enthusiast),
the level normally permitted announcers will drive him out of the
room. Therefore it is necessary to keep the announcer's level somewhat
below standard.
The easiest way to state the comparative readings is in per cent.
If the maximum peak allowed the orchestra is 100%, then the maximum peak allowed the announcer should be 40%. Later in the season
it was discovered that this procedure resulted in a sort of automatic
set tuning action. The symphony programs from WHK always were
introduced by the announcer. Normally, the listener already had his
set turned on listening to some other program. When the symphony
announcer came on peaking only 40%, his voice would sound much
too soft so that the listener would increase the volume until the announcer's voice sounded normal. This usually proved to be approximately the correct volume for symphony listening.
The Soloist Microphone
The last important consideration in symphonic pickups is the presentation of soloists. In a way, the term "soloist" is erroneously
interpreted, especially where it pertains to instruments. Most of the
compositions written for this type of presentation are either concertos
or in concerto form. In a concerto, the solo instrument is no more important than any other voice in the orchestra. One has only to listen
to air presentations of such performances to realize that this fact is
generally ignored. About half of the time in an ordinary concerto
the orchestra is supposed to take precedence over the so-called soloist.
It is not only a matter of relative volume but also includes the delicate
distinction of relative auditory presence.
For example, a trumpeter three feet from the microphone can blow
softly enough so that he will produce a tone of the same electrical
THE LIVE SYMPHONY PICKUP
99
volume as a trumpeter ten feet from the microphone blowing a little
louder. Yet the two tones will not sound the same. Why? Actually
there are two reasons; the first of which is that a trumpet does not
sound the same when it is blown softly as when it is blown loudly.
That variable can be eliminated. Let the two trumpeters keep the
same distances mentioned and both blow at exactly the same volume.
Then the technician can adjust his fader so that they will both register
the same electrical volume; however, they still will not sound alike.
That is because their auditory presences are different. Therefore, to
present a soloist properly with an orchestra in a concerto, it is necessary to place the solo microphone far enough away so that the auditory
presence of the soloist regardless of volume is the same as that of the
orchestra.
There is no rule of thumb on how to accomplish this since the relative distances will vary with auditoriums. It has to be done by trial
and error during rehearsal; also, the distance will rarely be the same
for two different performers. Once the distance is established for a
given performer, the microphone fader must be carried only high
enough to give a small amount of definition to the instrument. If the
solo volume is allowed to go to 100%, it has the same effect as allowing
the announcer to peak 100%.
Transporting Equipment
There is one other consideration peculiar to the Cleveland Orchestra
that may not obtain in other cities. The experience gained, however,
has sufficient application in ordinary remote work to bear relating.
The Cleveland Orchestra makes three concert tours each year, which
means that five broadcasts will be in some city other than Cleveland.
Since so much care had been taken to insure a good pickup locally,
and since so much depended on the particular technicians assigned
and on the particular equipment used, WHK decided to take precautionary measures and send those men and that equipment along.
Transportation for the men was no problem, but there were 800
pounds of equipment that could not be condensed into a small shipping
case. Like Noah, it was decided to take two of everything.
There were no standard trunks, sample cases, piano boxes, etc.,
which would satisfactorily hold the equipment. An old trunkmaker
was found who agreed to build trunks especially for the equipment.
Accordingly, he was provided with a complete duplicate set of equipment. Two months later it was returned to WHK enclosed in two
100
BROADCAST OPERATORS HANDBOOK
THE LIVE SYMPHONY PICKUP
101
trunks, as shown in Fig. 11-1-trunks an expressman would consider
ideal to handle. The trunkmaker had done an ideal piece of work on
them because not a single piece of equipment has been damaged in two
years of travel, and on more than one occasion the trunks were delivered in a distant city by one man, which meant they were dropped
off the truck and rolled end over end into the auditorium.
The larger trunk is for microphones and stands. The microphone
heads are removed and placed in drawers which have compartments
lined with two inches of sponge rubber and fitted with tops, so that
when the drawers are closed nothing can move. The other half of the
trunk is devoted to an arrangement for solidly holding microphone
stand bases and shanks. There are two extra drawers for extension
cords and tools. The smaller is arranged to accommodate two remote
amplifiers and two battery boxes. One set fits into each side in sponge rubber -lined compartments. There are also two extra drawers for miscellaneous use.
To assure its delivery for the orchestra broadcasts on Sunday, the equipment is sent to the distant city on the previous Monday. The technicians arrive there either Thursday evening or Friday
morning apparently early for a Sunday broadcast, but for a good reason. The telephone companies usually terminate the lines somewhere
on the stage unless a specific place is requested; however, the technicians prefer to work in a separate room beyond the stage. Because
most auditoriums are devoid of help from Friday night until concert
time on Sunday, the technicians, by arriving at that earlier date, are
assured of having their individual room.
Problems of Strange Auditoriums
Another interesting problem arises in working in a strange auditorium. All auditoriums are different and there is no possibility of rehearsal because the orchestra does not usually arrive in the broadcast
city until two or three hours before concert time. First, the technician
should stand on the stage and clap his hands in a hopeful effort to ascertain the acoustics of the hall. From what he hears, he tries to determine how much that will change with an audience; however, he
does not have to be too particular. If the original clap echoes but dies
away, the pickup will be live but not distorted. If the sound of the
original clap is returned as though the hands were clapped twice, then
something has to be done. If a cardioid microphone is used, it can be
placed with no tilt and lowered about three feet from its normal posi-
BROADCAST OPERATORS HANDBOOK
102
tion. This places the dead side directly toward the clap and the reduced height partially restores any loss of balance resulting from no
tilt. Sectional balance would be difficult in such a live hall anyway.
The main problem is to get whatever sound is reproduced as clear as
possible.
Another problem is presented by the variety of stage sizes and shapes
in different auditoriums. In some the stage will be very wide but very
shallow, making it necessary for the orchestra to be in a long narrow
rectangular arrangement instead of a semicircular arrangement. In
such a case the microphone can be tilted almost to a horizontal position in order to diminish the pickup of wind instruments. The strings
will be physically farther from the microphone in this instance so it will
be necessary to keep the wind instruments down. Another type of stage
which gives trouble is one without any shell where a great deal of
the sound is not projected forward. The solution is to leave the microphone at normal tilt but lowered a couple of feet and moved in closer
to the conductor.
The final consideration on road trips is difference in level from the
home auditorium. A fader setting noted at rehearsal in the regular hall
will not necessarily pertain in some other hall. A live hall with a shell
is likely to give more deflection than expected, and a hall with no
shell is likely to give less. Unfortunately no indication can be had
from the announcer's voice since he is working so close to the microphone that acoustics have little if any bearing on his level. The
safest way is for the orchestra fader to be set where it would be in the
home auditorium. If the level is too high, the fader should be reduced
one notch after each group of excessive peaks. By the time that particular number or movement is completed, the normal level should be
determined for that auditorium. The amount reduced can then be
subtracted from all fader settings marked down for the other numbers,
eliminating any further guesswork. If the level is too low, as compared
to the local hall, the fader should be increased one point each time
a climax, remembered from rehearsal, fails to peak 100%. The difference thus arrived at can then be added to the other settings.
To sum up the symphony broadcast,
single microphone should be used behind the conductor on a
line with center stage and uplifted in the air (usually about half
1. A
the height of the proscenium arch) .
THE LIVE SYMPHONY PICKUP
103
Auditory presence should be adjusted for soloists without giving
them too much volume.
3. Fader settings should be determined at rehearsal and not changed
on the broadcast. Where this is impossible, faders should be
moved very gradually to obtain proper setting.
4. The best possible equipment should be used. The setup depends
upon what is heard through that equipment.
5. The symphony broadcast technician should be prepared to argue
with his fellow workers and A. T. & T. about low level. But be
firm, because they will give up in five or six weeks.
2.
Part
4
OPERATING THE TRANSMITTER
Chapter
12
OPERATOR'S DUTIES
and students familiar with the technical characteristics of transmitting equipment in general, and broadcast equipment in particular, are cognizant of the greatly advanced state of technical design and transmission fidelity. It will not
be the purpose of this section to duplicate the already published data
on broadcast transmitter circuit theory and relationships. A workable knowledge of this field is assumed in this text.
The discussion to follow will pertain to the all-important operation
of the broadcast transmitting installation in order to achieve the best
results possible from the finely engineered equipment available and
in use today. Operating practice at the transmitter is just as important in the final result of over-all performance as it is at the broadcast studio. The science of operating the transmitter and associated
speech input equipment may be shown to be a highly specialized art,
and we have chosen the term "operational engineering" to define the
content of the special study undertaken in this part of the handbook.
ALLENGINEERS
Outline of Responsibilities
It is true that the primary purpose of the transmitter operator
is to keep the station on the air. But with the rapidly progressing
demands for higher -fidelity program transmission, the day when the
typical "ship operator" of thorough technical understanding could step
into a broadcast installation, has passed forever. The operator of a
broadcast transmitting plant has a specialized range of duties requiring a technical education, plus a thorough understanding and appreciation of the more intangible values of program material.
A number of his fundamental duties are, of course, strictly technical
in nature and, since this is meant to be an analysis of an operator's
duties, the technical functions will be described from an operational
point of view. In brief, his technical duties consist in turning the
transmitter on ahead of the beginning of the daily program schedule,
checking all meter readings to make proper adjustments, checking
104
OPERATOR'S DUTIES
105
level with the studio, shutting down the transmitter after sign -off,
repairing and maintaining equipment, and testing for noise and distortion levels. During the daily operating schedule he consistently
monitors the program from a monitoring amplifier and loudspeaker,
adjusts line amplifier gain _n accordance with good engineering practice pertaining to percentage modulation (the transmitter operator
does not normally "ride gain" as does the studio operator), maintains
correct tuning of transmitter, logs all meter readings every 30 minutes
required by the FCC, and corrects any trouble that develops in the
shortest possible time. Useful hints for meeting technical emergencies
will be given later.
Typical Pre -Sign-on Prccedures
The transmitter operator in all but the lowest power local stations
is usually scheduled to be on duty at least 30 minutes prior to air
time for the purpose of getting the equipment ready for the broadcast
day. The start of an operatpr's day may be outlined as follows:
Audio rack power applied (including such measuring equipment as the frequency monitor and modulation monitor)
Audio line used as program loop opened by inserting patch cord
into the line jacks. This removes the line from the input to the
line amplifier and prevents any test program that might be on
the line from the studio from being applied to the transmitter
when turned on.
2. Visual inspection of all relays in antenna -phasing cabinets
(where used) and in coupling houses at the antennas. Relay
armatures manually operated to ascertain freedom of movement. Observation of pointers on all r -f meters for bent hands
or zero set.
3. Inspection of all safety gaps including antenna and transmission -line lightning gaps for approximate correct spacings.
4. Water pumps started (where used) and rate -of -flow meters
observed for correct rate of water flow. Water flow must be
normal before filament voltage is applied. Air-cooling systems
usually start the blower motors when "filament-on" switches
are operated. Transmitter filaments now turned on and filament voltages checked. In large power tubes using tungsten
type filaments, minimum voltage should first be applied, then
run up to normal filament voltage after about 3 or 5 minutes.
1.
.
106
BROADCAST OPERATORS HANDBOOK
This is a means of lengthening the usable life of such power
tubes but it is not observed in some stations. Tubes of the
thoriated-tungsten or oxide -coated filaments such as used in
the low -power stages, are always operated at normal filament
voltage for maximum tube life.
5. Plate voltage then applied to low -power units or exciter unit
(in power installations of 1 kw or more) to check for proper
excitation to final stage.
6. Low power then applied to final stage. All meter readings
checked for normal low -power operation. If everything is
normal, high power applied and meter readings checked.
7. Filament and line voltages checked and adjusted for high power operation. Final adjustment made on final stage for
optimum meter readings regarding resonance condition and
power input.
S. Since the control -room operator sometimes has circuits "hot"
with his own testing procedure, the transmitter operator plugs
patch cord from program line to monitor amplifier to ascertain
continuity of program line. Then notifies control operator to
stand by for over-all circuit test. When this has been done,
transmitter operator removes patch cord from jacks which
automatically restores line connection to input of line amplifier. A test tone may then be fed from studio to check over-all
continuity of circuits from studio to transmitter modulators.
Pre -Program Level Checks
Level checks with the studio are not required as a daily procedure
after an initial installation has been made, tested, and operated for
some time, since with properly operating equipment the level remains
very nearly the same over a period of time. At regular intervals, however, it is desirable to use a signal generator to check the frequency
characteristics of the line and transmitting equipment. In this connection it is well for the transmitter operator to understand the difference in modulator power requirements for sine wave and speech or
music program content.
It will be remembered from circuit theory that for a class C modulated amplifier, the power requirement for complete sinusoidal modulation is 50% of the d -c power input to the modulated tube or tubes.
Fig. 12-1, however, shows how the "peak -factor" of speech or music
waves varies greatly from that of a pure sine wave. This peak factor
OPERATOR'S DUTIES
107
of program waves is 10 to 15 db more than that of a sine wave. That
is, the ratio of peak to rms voltage is far greater for complex waveforms than that of a sine-wave form. In other words, the average
power for complete modulation of a transmitter over a period of time
is far less than the average power required for complete modulation by
means of a signal generator. It is a well-known fact that for program
Fig. 12-1. The "peak factor" of a
speech or music wave is 10 or 15 db
greater than that of a sine wave; i.e.
the ratio of peak to rms value is
greater for complex waves than for
sine waves.
signal waves the modulator power required may be 25% or less of the
d -c power input to a class C stage. Therefore, if a signal generator is
used at the studio for frequency runs or level checks, the transmitter
operator must realize that if he '-has adjusted the gain on the line
amplifier to give 100% modulation on sine wave, the same adjustment
will be 10 to 15 db high for program signals. Thus the gain adjustment must be lowered to the point that experience has dictated for
program modulation before -the actual program schedule starts. In the
past this has led to seme confusion among transmitter operators.
This difference in peak factor between program and sine waves is
also noticed when comparing the per cent of antenna -current increase
with 100% modulation. It is true that the antenna -current increase
should be approximately 22.5% over no modulation when a sine wave
is applied to the transmitter at 100% modulation value. Antenna current increases for 100% program modulation, however, will be much
less, due not only to the difference in peak factor, but also the sluggishness of the thermocouple r -f meter action. This slowness of action
is due to the heating effect of the two dissimilar metals upon which the
action of the meter depends.
Chapter
13
PROGRAMS ARE ENTERTAINMENT
broadcast day the transmitter operator
keeps the circuits properly tuned, maintains correct power input to the final stage, logs meter readings each 30 minutes
(which also aids in forestalling trouble), maintains frequency of operation within plus or minus 10 cycles, and maintains the program level
at a point consistent with good engineering practice and the type of
program in progress.
It is only natural that the program level being sent via wire line
from the studio be the most concern from a strictly operational point
of view to the transmitter operator. With competent studio personnel,
the line amplifier gain adjustment may be set for 100% modulation
on program peaks at the start of the day and left at that adjustment.
Many times, however, the transmitter operator who does not appreciate musical and dramatic values will become piqued with the control
operator when program level is very low. He should realize that broadcast stations are not strictly "communications," but intended to bring
entertainment into the home with as much of, the original intent as
possible consistent with the state of the art. Certain types of programs,
symphony concerts in particular, are meant for those listeners in the
primary service area and not intended to override the noise level at
some secondary service point. If the monitor speaker is turned up in
volume consistent with that of the interested listener at home for these
types of programs, the transmitter operator will be able to use
good judgment as to whether the signal is entirely too low to be usable.
In relation to the study of program levels, it is of prime importance
to understand the characteristics of indicating meters used at both ends
of the transmission system. These meters differ in characteristics because of the different function which they are intended to perform.
The standard vu meter used in most broadcast studios today is an
rms-indicating full -wave rectifier device intended to give a close
approximation visually of the sound waves emanating from the loud DURING THE REGULAR
108
PROGRAMS ARE ENTERTAINMENT
109
speaker. We are concerned, however, with modulating voltages at the
transmitter, and a semipeak indicating device is necessary and is required by the FCC. If peaks of the program signal content should be
excessive and occur in rapid succession, danger of circuit component
breakdowns would exist as well as severe adjacent channel interference. Theiefore, since the peak factor of program waves is high as
discussed earlier, the modulation meter is a "peak" indicating device.
It is also necessary that a phase reverse switch be incorporated in the
modulation meter circuit which switches the polarity of the input to
the vacuum-tube voltmeter so that either the positive or negative side
of the modulated envelope may be monitored separately. Thus it is
obvious that we are confronted with two distinct types of level meters;
namely, a full -wave rms meter at the studio and a half-wave peak
meter at the transmitter. In addition to these meters, we usually have
a limiting type amplifier (in most modern installations) which is used
at the transmitter as a line amplifier. This has a meter which measures the amount of compression (full -wave peak meter) and output
level in vu (full -wave rms meter) .
Correlation of Meter Readings
The number of different types of indicating meters used should not
confuse the operator as long as the proper interpretation is given to
the readings. Fig. 13-1 is a representation of the indication of a proTRANSMITTER
MODULATION
MONITOR
100
STUDIO
OUTPU'r
r...".100
STUDIO
VU
LINE
TRANSMITTER
LINE AMPLIFIER
3
+
5db+100
COMPRESSION
METER
VU
PEAK
100
OUTPUT
METER
\
PEAKS
/
MODULATION
PEAK
INDICATOR
Fig. 13-1. A representation of the indications on the various meters of a
program peak at any given instant.
gram peak at a given instant on the various meters involved. The
studio vu meter has registered 100, the compression meter on the trans-
BROADCAST OPERATORS HANDBOOK
110
amount of limiting, the line amplifier output
meter shows 100, and the modulation meter would show either 100%
modulation on positive peaks, or, if set to monitor negative peaks,
might show only 60% modulation. This, of course, could be just reversed with a change in polarity of the microphone output or any
connection in between.
It is a well-known fact that speech waves are not equal in positive
and negative peaks regardless of type of microphone used. This may
be observed from the graph of the speech wave shown in Fig. 12-1.
Two speakers working from opposite sides of a bidirectional microphone and "peaked" the same amount on the studio vu meter will not
give equal indication at the modulation meter when set to indicate a
certain peak (either positive or negative).
Assume, for example, that the modulation monitor switch is set
to monitor the negative peaks, and the indication of one voice is close
to 100%. The indication of the voice on the other side of the microphone (therefore oppositely poled at the microphone output transformer) may indicate only 40% or 50%, with the amplitude of the
studio vu meter remaining the same. For this' reason it is obvious why
misunderstandings sometimes arise between studio and transmitter
personnel regarding comparative level of two or more voices.
The question then arises as to what indication, if any, exists at the
transmitter plant to show a true indication of comparative levels from
the studio. It has been shown that the half -wave reading of the modulation meter, which depends upon the polarity of operation, is not a
mitter shows normal
5 db
POSITIVE
NEGATIVE
Figs. 13-2, left, 13-3. A drawing (left) of an oscillogram showing a sine -wave
carrier that is 100% modulated and one that is over -modulated is shown on
the right.
s
PROGRAMS ARE ENTERTAINMENT
111
true indication of comparative levels from the studios. The vu meter
on the output of a limiting amplifier would not be a true indication
since the output level is limited by the compression taking place in
the amplifier for signals over a predetermined level. The compression
meter, although a full -wave indicating device, is a peak reading instrument and, since the peak factor of program waves varies considerably, it is not an absolutely accurate indication of comparative levels.
It is, however, the most reliable indication (within limits) existing at
the transmitter, since it is full -wave rectified and is limited by only
wire line characteristics. If two voices, for example, show about the
same amount of compression, the comparative levels may be considered
very nearly the same.
100% Modulation
Fig. 13-2 is a drawing of an oscillographic pattern of a 100% modulated (sine tone) carrier, stowing what constitutes positive and negative modulation of the carrier. It may be seen that negative or
"trough" modulation cannon attain more than 100% of the available
range, whereas positive or "peak" modulation may go over 100%.
When a carrier is thus modLlated with a pure tone, the degree of modulation m is
m
average envelope amplitude-minimum envelope amplitude
average envelope amplitude
and the peaks' and troughs of the envelope will be equal. When the
minimum envelope amplitude (negative peak modulation) is zero in
the foregoing equation, the degree of modulation is 1.0 and the degree
of modulation is complete, or 100% expressed in percentage modulation.
When the envelope variation is not sinusoidal, such as is true for
program signals, the positive and negative peaks will not be equal as
explained earlier, and the degree of modulation differs for peaks and
troughs of modulation as folbws:
Positive peak modulation
Negative peak modulation
-
Emax
-Eat,
- Em:n X 100
Eat,
-
Em;n X
100
Eav
Thus it is possible to unde,stand the mathematical analysis of why
the trough modulation cannot exceed 100%, since the minimum
voltage cannot be less than zero. It may be seen, however, that the
positive peak voltage may be more than twice the average (or carrier)
BROADCAST OPERATORS HANDBOOK
voltage (Ea.,,) in which case positive peak modulation will exceed 100%
modulation. What important information does this hold for the
transmitter operator?
First, it should be clarified in the operator's mind that "overmodulation" can take place on the negative (trough) modulation as weil
as on the positive (peak) modulation. It is true that the degree of
modulation can never exceed unity on the negative peaks, but can
exceed unity on the positive peaks. Complete modulation (of a class
C stage) however, requires that the peak value of the modulating voltage equal the d-c plate voltage of the modulated stage. Fig. 13-3
shows a drawing of an oscillographic pattern of a carrier wave with
modulating voltage exceeding the d -c plate voltage causing overmodulation of the carrier. It is true that the positive modulation peaks exceed unity while the negative peaks are "cut off" by the excessive
negative modulating voltage and cannot exceed unity. This excess
energy, however, which allows the negative peak voltage to result in
a voltage applied to the r -f amplifier plate circuit to become negative
with respect to ground, causes a radiation of this excess energy in the
form of spurious frequencies, resulting in "splatter" and adjacent
channel interference.
This actually is "overmodulation" in its severest form, since positive peaks may extend beyond 100% modulation without amplitude
distortion, whereas negative peak "overmodulation" will cause severe
amplitude distortion. It will be remembered that the bandwidth occupied by the carrier and sidebands depends (for amplitude modulation) not upon the degree of modulation, but upon the highest frequency being transmitted. Amplitude distortion, however, resulting
from negative peak overmodulation, generates a number of distortion
frequencies at harmonics that may well extend high enough to spread
the sidebands into channels adjacent to the assigned frequency of the
transmitter in question.
This discussion has been presented in order to show the transmitter
operator that the negative side of the modulation is the most important peak to monitor on the modulation meter, and to hold under
100% at all times. It is well to remember that the modulation meter
of the vacuum-tube voltmeter type will not be able to indicate over
100% (negative) on the meter because the peaks cannot attain more
than this value as shown before. This is the reason why a cathode-ray
oscilloscope is invaluable at a broadcast transmitter to show negative
peak "overmodulation," since the negative peak "clipping" shows up
112
PROGRAMS ARE ENTERTAINMENT
113
as white lines across the center of the modulated pattern. When the
usual vacuum -tube voltmeter type of modulation indicator is used, the
flasher should be set to flash at 90% or 95% modulation so that when
observing negative peaks, the warning is given when the peaks go up
to 100% modulating value.
Operation of Limiter Amplifiers
The limiting amplifier, also known as a compression amplifier (see
panel view in Fig. 13-4) is a very important link in a broadcast installation. However, its effect may be small and detrimental, if the
RCA Plwto
Fig. 13-4. Panel view of a limiting or compression amplifier for preventing overloading transmitter components
and adjacent channel interference.
wrong operational interpretation is given to the main purpose for
which it is designed and intended. This type of amplifier, as designed
for use in a broadcast installation, is intended as a peak limiting device, the amount of gain reduction being a function of the program
peak amplitude. In order to prevent material reduction in the dynamic
range of the signal, the peak gain reduction is not intended to be more
than 3 to 5 db. A broadcast limiting amplifier, therefore, should
not be considered as a volume limiter, but as a peak limiter intended
to prevent overloading of transmitter components and adjacent channel interference.
114
BROADCAST OPERATORS HANDBOOK
The original advertising claims of manufacturers offering this type
of equipment proved misleading from an operational point of view. It is
true that doubling the output power of a transmitter raises the signal
intensity 3 db. It is also true that the limiter amplifier also raises the
signal level about 3 db on program peaks. To those familiar with
watching volume indicators on program circuits, however, this 3 -db
increase on speech or music is of small consequence. As far as the
transmitter operator is concerned, he should think of this amplifier as
a protective device to limit peaks caused by wire line transmission and
those program peaks that escape the action of the control -room
operator.1
That the primary purpose of a limiting amplifier may be defeated
by erroneous operation is a very important fact for the broadcast
operator to know. Seriously detrimental effects will result if this amplifier is operated as an actual "volume compression" device to attempt to prove a coverage area greater than a given power and transmitter location warrants. The "attack" time of peak limiting (about
0.001 second) is determined by a resistor -capacitor charging circuit
with the inherent characteristics of a low pass filter. At high frequencies, and where the duration of the peak is short compared to
this operating time, a portion of the peak energy will escape limiting
action. If the average signal level is so high that a great amount
of compress;( , takes place at all times, a larger amount of adj acentchannel interference will result, thus defeating one of the main purposes of the amplifier.
This has been quite noticeable in practice when the program content consists of music from dance orchestras of brass instruments
where high peak powers at high frequencies are very prevalent. A
limiting amplifier operated properly for broadcast service will show
about 3 to 5 db of intermittent gain reduction as indicated by the
peak reading meter used to show the amount of program peak compression. The operator must realize that for certain types of programs
such as symphonies, liturgical music, and operas, the average audio
signal may be very low over a period of time even with limiting amplifiers in use. Dynamic range is just as important to high-fidelity transmission of these types of programs as is the frequency range.
Another consideration is the recovery time value, or time required
to restore the gain to normal after a peak has momentarily reduced
the gain. Optimum recovery time may well be different for different
-1
'See Appendix for important adjustment of the
96 -AX limiting amplifier.
PROGRAMS ARE ENTERTAINMENT
115
types of program material. Piano music, for example, sounds unnatural when recovery time is too short, because the effect is similar
to inadequate damping of the strings after they are struck or to holding the sustaining pedal too long on the loud notes. The longer the
recovery time is made, however, reduced gain will be in effect a larger
proportion of the total time, and will result in unnatural transmission
of certain passages in specific musical compositions. When operated
properly in accordance with good operating practice, and not subjected
to more than the specified amount of peak load, very satisfactory results may be obtained?
When thinking of a compression amplifier as a means of increasing
the service area of a transmitter, it is well to keep in mind the known
facts concerning the psychological differences that exist in listening
habits for various types of programs. A lower relative signal level is
tolerable for dance music, news broadcasts, etc., where the average
audio level is high over a period of time. In this case where listeners
well outside the "primary service area" of the station may be numerous, the maximum amount of peak limiting may be used to help
raise the signal-to-noise ratio at the receiving point. It is realized,
however, that symphony broadcasts, choral music, certain liturgical
music, opera, etc., where the average audio signal may be very low
over a period of time, will appeal only to those listeners who are very
adequately served with strong carrier signals. In the interests of preserving the original dramatic effects of this type of program, it simply
is not technically feasible for a broadcaster to attempt to set a fixed
value of coverage area for all types of program material. Similarly,
the operator responsible for the transmission of programs should not
attempt to operate all equipment in the same manner regardless of
type of programs being transmitted.
2W. L. Black and N. C. Norman, "Program -Operated Level-Governing Amplifier," IRE Proc., Nov. 1941.
Chapter
14
MEASURING NOISE AND DISTORTION
any modern broadcast installation are adequate frequency range to convey as much of
the original sound as possible, low noise and distortion levels
necessary for required dynamic range, and dependability of performance. One of the most important pieces of auxiliary equipment about
a transmitting plant is the instrument for determining noise and/or
distortion over the usable frequency range to facilitate proper adjustment of the over-all installation. Several manufacturers are supplying such equipment for broadcast frequencies, and most stations are
equipped with means of checking noise and distortion. Definite instructions accompany all such equipment, but a typical description of
procedure for using one type of noise and distortion test equipment is
given here in outline form as a matter of general interest. This outline conveys the general principles of all noise and distortion measuring equipment.
Fig. 14-1 is an illustration of the RCA 69-C Distortion and Noise
meter, which may be used to measure distortion in transmitters or
audio equipment at any frequency from 50 to 7500 cycles, providing
THE IMPORTANT CHARACTERISTICS Of
RCA Photo
Fig. 14-1. Meter for measuring distortion in transmitters
or a-f amplifiers from 0.3% to 100% and noise levels
down to -85 db below 12.5 milliwatts.
116
MEASURING NOISE AND DISTORTION
117
measurements of rms total distortion from 0.3% to 100% and noise
levels down to minus 85 db below 12.5 milliwatts. This instrument
consists essentially of a diode detector which is used when taking
measurements on a transmitter to demodulate the modulated r -f signal,
047R.
PICKUP
COIL
DISTORTED
WAVE
F.
DIODE
DISTORTION
COMPONENT
Jr.,'"
ATTENUATOfÿ MIXER
AMPL.
ATTENUÁTOR METER
PURE
SINE -WAVE.,
V
-
TO
TRANSMITTER
INPUT
-WAVE
OSCILLATOR
S NE
Fig. 14-2. Functional block diagram
of the distortion and noise meter on
the opposite page.
TO
DISTORTION
METER
PHASE
SHIFTER
an attenuator to adjust the audio output of this detector, a phase -shifting network, a mixer stage to combine the output of the attenuator
with that of the phase shifter, an amplifier, a range attenuator to adjust amplifier gain, and the meter which measures the amplifier output.1 A functional diagram is shown in Fig. 14-2.
In operation, a sine wave from a stable oscillator is applied both to
the transmitter and the phase shifter of the RCA 69-C meter. The
phase -shifting network is adjusted until the signal is exactly in phase
with that derived from the output of the transmitter. The output
signal from the transmitter is adjusted in amplitude by the attenuator
so that its fundamental -frequency component is exactly equal to the
output of the phase shifter. In other words, the amplitude and phase
controls are adjusted until a minimum meter reading is obtained.
Each of these two signals is impressed on the grid of one of two mixer
tubes, whose plates are connected in push-pull by means of a transformer. The difference voltage of the two input signals appears
across the secondary of this transformer and is at minimum value
when the distorted and undistorted signals are adjusted in phase and
amplitude to have minimum difference. With this adjustment, the
3
For schematic and other data, see Appendix.
118
BROADCAST OPERATORS HANDBOOK
fundamental -frequency component of the distorted signal is canceled
out by the sine -wave signal, the difference voltage containing the distortion components. This difference voltage is amplified and the meter
reads the total rms distortion directly.
Noise and distortion measurements should be run on broadcast
transmitters at least every six months, as well as a complete frequency
run to determine frequency response of the equipment. For the guidance of the transmitter operator, the following excerpts from the "FCC
Standards of Good Engineering Practice" that directly affect his
duties, are presented.
Excerpts From Standards
Section 3.46 requires that the transmitter proper and associated
transmitting equipment of each broadcast station shall be designed,
constructed, and operated in accordance with the "Standards of Good
Engineering Practice" in addition to the specific requirements of the
"Rules and Regulations of the Commission."
The specifications deemed necessary to meet the requirements of
the "Rules and Regulations" and "Good Engineering Practice" with
respect to design, construction, and operation of standard broadcast
stations are set forth in the following text. These specifications will
be changed from time to time as the state of the art and the need
arises for modified or additional specifications.
A. Design. The general design of standard broadcast transmitting
equipment [main studio microphone (including telephone lines, if
used, as to performance only) to antenna output] shall be in accordance with the following specifications. For the points not specifically
covered, the principles set out shall be followed.
The equipment shall be so designed that:
(1) The maximum rated carrier power (determined by section 3.42)
is in accordance with the requirements of section 3.41.
(2) The equipment is capable of satisfactory operation at the
authorized operating power or the proposed operating power with
modulation of at least 85 to 95 per cent with no more distortion than
given in (3).
(3) The total audio -frequency distortion from microphone terminals, including microphone amplifier, to antenna output does not
exceed 5% harmonics (voltage measurements of arithmetical sum or
r.s.s.) when modulated from 0 to 84%, and not over 7.5% harmonics
(voltage measurements of arithmetical sum or r.s.s.) when modulating
MEASURING NOISE AND DISTORTION
119
85% to 95%. (Distorticn shall be measured with modulating frequencies of 50,100, 400, 1000, 5000, and 7500 cycles up to the tenth harmonic or 16,000 cycles, or any intermediate frequency that readings
on these frequencies indicate is desirable.)
(4) The audio -frequency transmitting characteristics of the equipment from the microphone terminals (including microphone amplifier
unless microphone frequency correction is included, in which event
proper allowance shall be made accordingly) to the antenna output
does not depart more than 2 db from that at 1000 cycles between 100
and 5000 cycles.
(5) The carrier shift (current) at any percentage of modulation
does not exceed 5%.
(6) The carrier hum and extraneous noise (exclusive of microphone
and studio noises) level (unweighted r.s.s.) is at least 50 db below
100% modulation for the frequency band of 150 to 5000 cycles and at
least 40 db down outside this range.
B. Operation. In addition to the specific requirements of the rules
governing standard broadcast stations, the following operating requirements shall be observed:
(1) The maximum percentage of modulation shall be maintained at
as high a level as practicable without causing undue audio -frequency
harmonics, which shall not be in excess of 10% when operating with
85% modulation.
(2) Spurious emissions, including radio -frequency harmonics and
audio -frequency harmonics, shall be maintained at as low a level as
practicable at all times in accordance with good engineering practice.
(3) In the event interference is caused to other stations by modulating frequencies in excess of 7500 cycles or spurious emissions, including radio -frequency harmonics and audio -frequency harmonics outside the band plus or minus 7500 cycles of the authorized carrier
frequency, the licensee shall install equipment or make adjustments
which limit the emissions to within this band or to such an extent
above 7500 cycles as to reduce the interference to where it is no longer
objectionable.
(4) The operating power shall be maintained within the limits of
5% above and 10% below the authorized operating power and shall
be maintained as near aE. practicable to the authorized operating
power.
(5) Licensees of broadcast stations employing directional antenna
systems shall maintain the ratio of the currents in the elements of the
BROADCAST OPERATORS HANDBOOK
array within 5% of that specified by the terms of the license or other
instrument of authorization.
(6) In case of excessive shift in operating frequency during warmup periods, the crystal oscillator shall be operated continuously.
The automatic -temperature -control circuits should be operated continuously under all circumstances.
120
Part
5
WE'RE OFF THE AIR
Chapter
15
EMERGENCY SHUTDOWNS
the situation that invariably causes a state of panic in
the newcomer to a transmitter operating job. In nearly all instances he is alone, with the responsibility of correcting the
trouble as quickly as possible to avoid loss of revenue by his employer.
The highest efficiency in correcting trouble will come with more experience at the particular installation. The operator, however, who
can visualize general circuit theory in relation to the particular circuits
with which he is concerned will find a logical and natural sequence of
looking for the fault. The main requirement quite naturally is to become thoroughly acquainted with the circuits used. He should be able
to draw from memory a good general functional picture of all circuits,
and be able to draw a block diagram of the sequence of operation of
starting relays and protective relays in the power -control circuits.
It is obvious that confidence and peace of mind can be achieved only
by a complete familiarity with all circuits and their relation to the
over-all performance of the transmitter.
It is, of course, impossible to set down a definite method of locating
and clearing specific troubles of any kind or description. We hope,
however, to be ableto set forth a clear concise approach to procedures
in general; that is, a logical and straightforward means of meeting
emergencies.
There is one piece of equipment at the transmitter installation that
should be the central focusing point for the operator's first attention
when trouble occurs. This is the modulation meter which has an r -f
input indication meter that reads a definite place on the scale 'for
normal operation, and, of course, the percentage modulation indicator.
The purpose of this will be evident in the following discussions.
At the first interruption of the program, or the occurrence of noise
or distortion in the monitoring loudspeaker, this modulation monitor
should be observed. Let us assume that the r -f input meter is at normal scale which assures us that the trouble is not in the r -f section
THIS Is
121
BROADCAST OPERATORS HANDBOOK
122
because any trouble there would cause some deviation in the r -f input
to the meter.
The following is a procedure to follow when the program suddenly
stops from the loudspeaker:
R -f input meter shows normal, modulation meter shows modulation taking place. Trouble obviously in monitoring line or amplifier and we are not off the air.
2. R -f input normal, no modulation as shown on meter.
Trouble either in audio section of transmitter, line amplifier,
program line from studio to transmitter, or at studio.
Call studio control to ascertain condition at that point. If everything there is normal, check line by patching line into monitor
amplifier or spare amplifier to see if program is coming into the
transmitter from line. If not, notify control to feed program on
spare line and call local test board of Bell Telephone Co. If
coming in satisfactorily from line, use spare line amplifier to feed
transmitter. If the regular line amplifier is working normally,
then the trouble obviously lies in the audio section of the transmitter itself. Usually any trouble here will be indicated by abnormal plate -current meter readings, and, of course, tube trouble
is the most common source of program interruption.
1.
The same procedure should be used where noise or distortion occurs,
first checking with studio, then line, line amplifier, and audio section
of transmitter. If all speech input tube currents are zero, then the
trouble is in the associated power supply. Most likely trouble again
is due to a tube, and it should be changed upon indication of abnormal plate current. Next in line comes bleeder resistors, resistor taps
from bleeder supply, and line -to -plate circuits of tubes. Power -supply
component parts usually show a visual indication of damage, such as
a smoking part, unless opened up.
If, at the first indication of trouble, a glance at the modulation
monitor position shows zero or low r -f input, then the trouble lies in the
r -f stages of the transmitter. The operator must accordingly proceed
to check for the trouble in the r -f section by observing all r -f circuit
meter indications. Observation of plate and grid current meters
aid in quickly determining the faulty stage.
When the transmitter is shut down by relay operation in the control
circuits, the cause of the failure is quickly traced if the operator is
EMERGENCY SHUTDOWNS
123
familiar with relay sequence and functions. Control circuits are divided into two functional purposes: (1) those which control circuits to
the primaries of power supplies, and (2) those of protective functions.
Pilot lights are often associated with the various relays to show when
open or closed. As stated before, the sequence of operation should
be committed to memory. The filament power supply, for example,
will not operate until the cooling motor contactors have functioned
to supply the cooling medium (water or air) to the tubes. After the
filament contactor has applied filament voltage, the plate -voltage contactor will not operate until the time delay relay has functioned, etc.
Rectifier tubes of the mercury-vapor type nearly always arc -back
several times before expiring. When arc -back indicators are used, the
faulty tube may be quickly observed and changed immediately.
Other troubles in high -voltage power supplies nearly always show
signs of physical deterioration as stated before.
Short circuits which cause a quick tripping of overload relays are
always the most difficult troubles to locate. In some difficult troubles
of this kind, overload relays have been strapped out of the circuits,
and limiting resistors put in the lower current fuse box to limit the
amount of current flowing. The circuits were then visually observed
for arc-overs with doors open and interlock switches short-circuited.
This is a dangerous procedure, however, and should be left to the more
experienced operators. More than one man should carry out any
unusual procedure of this kind.
This all may be summarized into the most important factor. Be
familiar with the transmitter, and know what indications would be
for the most common sources of trouble such as tubes and power supplies for the various circuits.
Chapter
16
WHY PREVENTIVE MAINTENANCE
any preventive maintenance schedule,
of course, is to reduce as much as possible the likelihood of
failure during the broadcast day of any component part of the
broadcasting installation. Regular maintenance schedules are in force
at most broadcast stations, and do much to increase their useful life
THE PRIMARY PURPOSE of
and anticipate and prevent many tube and parts failures that would
occur if neglected.
Preventive maintenance of any sort of equipment may be defined
as a systematic series of operations performed periodically on the
equipment in order to prevent breakdowns. This type of maintenance
may be divided into two phases: work performed while the equipment
is functioning and work performed during the normal shutdown periods. Here we are concerned only with the shutdown period preventive
maintenance.
The importance of preventive maintenance cannot be overestimated.
The owners of a broadcast station depend upon its being on the air
every second of its scheduled periods of transmission. It is of the
utmost importance that the personnel of radio stations properly maintain their equipment so that lapses in the transmission will be kept to
a minimum.
Cleanliness of equipment is of utmost importance since colleetion
of dust and dirt has been known to cause a number of troubles. This
is particularly true in the higher power stages of transmitters, since
accumulation of foreign matter over a period of time reduces the voltage insulation to a point where leakage currents and arc-overs are
common. High -voltage contacts have an extreme tendency to collect
dirt (this is the principle used in electronic smoke eliminators) , and
the higher relative humidity existing in summertime or southern locations tends to aggravate this characteristic. A dusting and clean-up
procedure, then, is a desirable nightly procedure at a transmitter plant.
A source of dry air under pressure is a common means of blowing out
dirt, dead insects, and the like from inaccessible corners and variable
124
WHY PREVENTIVE MAINTENANCE
125
tuning capacitors. Insulators, safety gaps, etc. should be polished
with a dry cloth or carbon tetrachloride used to loosen excessive dirt
and grime.
Proposed Transmitter Maintenance Schedule
In order that preventive maintenance be effective, it is essential that
it be performed at regular intervals; that is, certain portions of the
equipment must be inspected for certain things every day while other
parts of the equipment need only be inspected weekly or monthly in
addition, of course, to those things which are inspected daily. Below
will be found a comprehensive maintenance scheduler which may be
considered as a guide to anyone desiring to set up such a means of
preventing breakdowns. Naturally, items may be included in this
schedule which may be felt to be unnecessary at some particular transmitter, but it has been compiled with the thought that every precaution should be taken.
Later on in this chapter will be found the actual preventive
maintenance schedule which is followed at Station WIRE.
TRANSMITTER MAINTENANCE
A. DAILY
1. Hourly read all meters and check power tube filament voltages.
temperatures. Check water temperature of water-cooled tubes.
3. Check for correct cabinet temperature of air around high -voltage rectifiers.
4. After shutdown make a general inspection for overheated
components, such as capacitors, inductors, transformers, relays,
and blowers.
5. Investigate any peculiarities of meter readings.
6. In the event of overloads, examine safety gaps and transmitter
components for arc pits, etc. Clean and repolish surfaces
where arcs have occurred. Reset gaps if necessary. Investigate cause of outages.
7. In the event of lightning or heavy static discharges, inspect
the transmission line, terminating equipment, and antenna including gaps. Polish pitted surfaces.
8. If gas filled co -ax is used, check pressure.
2. Check air-cooled anode
1
By courtesy of RCA Mfg. Co.
BROADCAST OPERATORS HANDBOOK
126
B. WEEKLY (In addition to above)
1. Immediately after shutdown, check antenna terminating components for signs of overheating.
2. Clean antenna tuning apparatus. Check for arc pits, etc.
Clean and polish gaps and adjust if necessary.
3. Test antenna monitor rectifier tubes.
4. Calibrate remote antenna meters against meters in the antenna.
5. Clean transmitter with vacuum.
6. Clean component parts of transmitter.
a. Brush terminal boards,
b. Clean insulators with carbon tet,
c. Clean power tubes and high voltage rectifiers with tissue
and alcohol (or distilled water).
7. Check filament voltages and d-c voltages at the tube socket
of all tubes which are not completely metered by panel meters.
8. Check air flow interlocks for proper operation. Check all door
interlocks for proper operation.
9. Check operation of grounding switches. Examine mechanical
10.
operation and electrical contacts.
Inspect blowers for loose impellers, free rotation, and sufficient
oil.
11.
12.
13.
14.
15.
16.
17.
18.
Inspect relays for proper mechanical and electrical operation.
If necessary, clean and adjust components.
Inspect air filters; clean if excessive dirt has accumulated.
Check all sphere and needle gaps. Clean any pits or dirt.
Check gap spacings.
Check filter bank surge resistors with ohmmeter.
Check any power tube series resistors with ohmmeter.
Check power change switches if used; check for no serious
arcing during day -night antenna change -over if used.
Make general performance check-up. Distortion, noise, and
frequency response. Observe modulated wave form on CRO.
Check neutralization by cutting crystal oscillator and observing grid currents. Observe overmodulation waveform envelope on CRO.
proper operating voltage for pure tungsten filament
tubes. Operate at lowest voltage permissible as indicated by:
a. AM transmitters-distortion and carrier shift checks.
b. FM transmitters-decrease filament voltage until output
begins to drop.
19. Check
WHY PREVENTIVE MAINTENANCE
127
c. Operate filaments approximately 1% above filament voltage determined in a or b.
20. If water cooling is employed check entire system for any signs
of leakage and for electrical leakage.
21. Check pressure of any gas -filled capacitors.
C. MONTHLY (In addition to above)
1. Make detailed inspection of all transmitter components with
whatever tests of parts that may seem advisable.
2. Clean and inspect all vacuum and rectifier tube socket con-
tacts, and the tube pins.
3. Clean air filter or replace. Brush dust from blower impellers,
canvas boots, etc.
4. Clean and adjust all relay contacts. Clean pole faces on con-
tactors. Replace badly worn contacts.
5. Oil blower motors (carefully).
6. Operate all spare vacuum tubes for a minimum of two hours
under normal operating conditions. Clean up any gassy tubes.
7. Operate all spare mercury vapor rectifiers normally, after first
applying filament only for a minimum of 30 minutes. Store
S.
tubes upright.
Inspect all variable inductor contacts for tension, signs of
overheating, and dirt. Clean and adjust as required. Carbon
tet or crocus cloth may be used for cleaning. Do not use emery
cloth.
9. Check for proper operation of time delays, notching relays
and any automatic control systems.
attenuator and low
level switching contacts with cleaner; wipe off excess.
11. Check tubes in station monitor equipment, such as frequency
monitor, modulation monitor, etc.
12. Clean switches in monitoring equipment with cleaner.
10. Clean audio equipment (console, etc.)
D. QUARTERLY (In addition to above)
1. Lubricate tuning motors and inspect for ease of rotation.
2. Check all indicating meters (a -c, d-c, r -f) . Check a -c filament voltmeters with an accurate dynameter type of meter.
3. Check all connections and terminals for tightness.
4. Inspect any flexible cables to door connections.
5. Inspect and lubricate if necessary any flexible drive cables.
6. Inspect, clean, and service (if necessary), all switches. Volt-
BROADCAST OPERATORS HANDBOOK
128
meter selector switches, push button switches, control switches,
etc.
Clean transmission line insulators and take up slack if open
wire lines are used.
8. Check oil circuit breakers, if used, for sufficient oil and loose
or defective parts.
E. SEMIANNUALLY (In addition to above)
1. Test transformer oil for breakdown and filter it if necessary
(power company).
2. Check protective overload relays or circuit breakers for correct operation.
a. A -c overload relays may be checked by shorting the
high -voltage transformer secondary.
b. D -c overload relays may be checked by shorting the d.c.
through the relay in the circuit protected by the relay.
MAINTENANCE SUGGESTIONS
A. CONTACTORS GENERAL
1. Inspect all parts at regular intervals.
2. Parts should be kept free of dirt, grease, and gum.
3. Replace contact tips as needed (keep spares on hand).
4. Keep all contacts and interlocks clean and free from burrs
and pits.
5. Main copper contacts should not be lubricated. Darkened
tips due to overheating, or copper beads should be dressed with
a fine file. (Do not use emery cloth.)
7.
B. CONTACTORS-HUM
Clean off rust, dirt, or grease from pole piece and armature
and apply a small quantity of light machine oil to prevent
rusting.
2. Check pole shader and its circuit. Armature contact surfaces
above and below shader should be approximately equal.
3. Armature to pole piece contact should be made over a large
area; gaps should not be over 1/1000 to 2/1000 inch. If the
contact area is small or the gap too wide, the pole face may be
ground or filed down to a FLAT surface.
C. CONTACTS SILVER
1. If not burned or pitted they may be cleaned with a contact
burnishing tool.
2. If burned and pitted, dress with a small fine file and polish
with crocus cloth.
1.
WHY PREVENTIVE MAINTENANCE
129
Maintenance of Water -Cooling Systems
As has been stated before, it is not the purpose of this section to
duplicate otherwise available data on the engineering aspects of transmitting equipment. However, since cooling systems of transmitters
of more than 1 -kw rating are so highly important to the problem of
keeping the station on the air, some factors of operating and maintaining these cooling systems that have not been emphasized before will
be presented here for the operator's convenience.
Fundamentally, the power rating of a tube in free air is determined
by three characteristics, namely:
1. Plate voltage that may be safely applied (dependent on physical
parameters) .
2. Electron emission of filament.
3. Amount of heat that can be dissipated at anode without causing
overheating (dependent on physical and electrical parameters).
Thus it becomes apparent that insofar as the operator is concerned,
the third characteristic is the only variable in the problem of heat
dissipation, since electrical parameters such as operating angle in electrical degrees, bias voltage, etc. are more or less under the direct supervision of the operator.
In water-cooled systems, the temperature of the water at the outlet
of the tube jacket should never exceed 70° C. (158° F.) as indicated
by the water thermometer at that point. The rate of flow should be
approximately 15 gallons per minute; 20 gallons per minute is more
beneficial in retarding accumulation of foreign matter in the jacket
and the prevention of steam bubbles along the anode surface. The effect
of increasing the flow of water is to increase the turbulency of flow.
This increased turbulency breaks down the layer of steam present at
the anode wall and increases the heat exchange between the wall and
the water. The turbulency of the flow may be increased by mechanical
means, such as baffles.
Extraordinary precautions must be taken in the installation of the
tube in the water jacket. The movable metal parts of the jacket should
be coated with a light film of oil to help prevent corrosion. The tube
should then be placed gently in the jacket, and after it is correctly
seated the retaining studs or jacket clamping device is fastened firmly
into place to force the flange of the plate into solid contact with the
watertight gasket. The electrical connections may then be made. Care
should be taken that the wires are not near ôr do not touch the glass
130
BROADCAST OPERATORS HANDBOOK
bulb. Should this precaution be neglected, puncture of the glass from
corona discharge is likely to occur. Particular care should also be
observed in making the connection between hose and jacket tight and
clean. Because of electrolysis, trouble is likely to develop at this point,
and close inspection every two or three weeks is advisable.
A reasonably rigid maintenance schedule should be observed on the
entire system to forestall trouble from water leakage, scale formation,
or the formation of steam bubbles with resultant transmitter shutdown
and loss of time on the air. Leaks, of course, may be temporarily
sealed to a certain extent by using friction tape until permanent repairs can be made after sign -off. In some instances, it is possible to
cover the radiator used to cool the water with a blanket until the inlet
temperature of the water rises to around 104° F., resulting in a slight
expansion of the parts which will aid in sealing a minor leak.
Scale formation, if and when it occurs, will prevent adequate transfer of heat from anode to water. If it becomes necessary to remove
the tube for this or any other reason, the tube should be lifted carefully from the jacket after the clamping device has been released.
Sticking of the tube often occurs, and in this case a gentle twisting
back and forth while lifting will free the tube. Immersion of the plate
in a 10% solution of hydrochloric acid is usually recommended to dissolve scale formation. The anode should then be rinsed thoroughly
in distilled water.
The formation of steam bubbles may be checked periodically by
using a good insulating rod at least six feet long. This should be moved
along the jacket while aural observations are made. Precautions
should be taken to assure the operator's safety, including grounding
the testing tube between water jacket and the observer by a "hot
stick" or similar arrangement.
A convenient way for the operator to keep an approximate check on
the heat dissipation of the tube is by use of the formula:
P(KW)
- n (t04 ti)
where:
t; = known initial temperature of water in degrees C
to = temperature of water at jacket outlet in degrees C
n = rate of flow in gallons per minute.
It should be remembered here that the filament heat is also being
dissipated into the watet. It is recommended that the operator read
WHY PREVENTIVE MAINTENANCE
131
the manufacturer's instructions that come packed with transmitting
tubes. Some of the foregoing information is from RCA tube instruction sheets.
Forced -Air Systems
Although the problems of deteriorating hose, leaky hose connections,
electrolysis, and troublesome flow -interlocks have been largely overcome by porcelain reels, reliable flow -interlocks and completely nonferrous circulating systems (all -copper tank and pipes), the familiar
problems have remained of scale formation, gradual water evaporation,
and relatively large time consumption in changing tubes.
In recent years, the elimination of the water-cooling system has been
accomplished for transmitters up to and including 50 -kw rating by the
development of forced -air cooling systems. Control circuits for this
system are greatly simplified, consisting as they do of an air -interlock
damper on top of the blower motor, which prevents application of
filament and plate voltages until normal air -flow pressure is present,
and a blower motor "keep -alive" relay, which is a time -delay relay
keeping blower motors functioning 4 to 7 minutes after filament voltage is removed.
Maintenance of forced -air systems is simpler than that of water
systems but is just as important for trouble -free operation.
The canvas air ducts should be cleaned about once a month by removing them, turning them inside out, and using a vacuum cleaner
to remove accumulated dirt. While these ducts are removed, a cloth
may be used to slide between the fins of the tube, especially in against
the tube anode, to remove dust. Care should be taken not to damage
the mercury air -flow switches which are mounted on the blower housing. These switches prevent the application of filament and plate voltages until proper air flow is present. Both sides of the air -flow vanes
(half -circle disks used to operate the mercury switch) should be wiped
clean with a cloth or chamois and a small wire brush may be used
to clean the corners of the °an blades. A vacuum cleaner then should
be used to pick up any dust from inside the bottom of the blower
frames.
After this cleaning procedure has been carried out, the blowers
should be started to check ,he air-flow vanes for proper operation of
the mercury switches, canvas ducts replaced, and over-all operation
checked.
132
BROADCAST OPERATORS HANDBOOK
STATION WIRE PREVENTIVE MAINTENANCE SCHEDULE
The following preventive maintenance schedule has been in use at
Station WIRE and as may be seen from designations, it is planned to
have this work done on each Thursday night after the transmitter goes
off the air. This arrangement is different from the general schedule
presented earlier in this chapter inasmuch as some of the maintenance operations are performed weekly, others monthly, and the last
group is performed five or six times per year.
First Thursday Night of Month Maintenance Schedule
Before turning main transmitter off, after conclusion of program
from studio, read both North and South Tower Antenna Current
meters. Check and adjust Remote -Reading Antenna meters, on the
operating console, to read with their respective Tower meters. Turn
main transmitter off in accordance with the usual sign-off procedure.
Shift antenna change -over switch to the Auxiliary Transmitter side.
Turn on Auxiliary Transmitter for one-half hour check. Make regular
transmitter log on this half-hour operation. Also, enter the readings
of both the Antenna Current and Remote-Reading Antenna meters on
this log sheet.
In addition to the daily sign -off procedure, carefully remove the
two oscillator tubes and wipe them free of dust.
Clean both sides of plate glass partitions in front of the three large
tubes. Use damp cloth on this and dry with paper hand towel.
Open all glass meter partition doors at top of transmitter and clean
glass on both sides. Clean all glass meter faces including those on the
power panel and Audio racks.
After Auxiliary Transmitter has been tested, turned off and log completed, BE SURE TO RETURN ANTENNA CHANGE-OVER
SWITCH TO THE 5-D OPERATING SIDE.
Vacuum-clean the top of transmitter cabinets.
Wipe off all insulators on top of transmitter and insulators holding
copper bus bar to rear wall, and all insulators on top of phasing cabinet (to transmission line), and all insulators on modulation transformer and reactor.
Wipe off all insulators and all components on the filter rack (filter
condensers, reactors, resistors, relays, etc.) .
Remove all rectifier tubes (remember to keep them upright in case
of mercury-vapor rectifiers) from their sockets. Remove the shields
and clean the sockets and other components under shields.
WHY PREVENTIVE MAINTENANCE
]
23
Open all front interlock doors. Use vacuum to clean all reachable
space from the front, behind center panels, tube shelves, and floor
plates.
Wipe off the four high -voltage insulators between modulator blower
motors and the insulator above each of the high -voltage rectifiers.
Also the insulators above the first and second audio stage tubes. Wipe
off insulators on condenser above power-amplifier blower motor. Also
the rectifier and oscillator feed-thru insulators in bottom of Exciter
Unit.
Clean all components in modulator section ABOVE the final -tube
holders. Inspect and tighten all connections in this half section.
Open rear doors on modulation and final stage. Wipe off floor of
both from the rear. Wipe off all three blower frames. BE VERY
CAREFUL OF ALL INSULATORS, ESPECIALLY MICALEX.
Take and record reading of "Filament Elapsed Hours Clock."
REPORTS: Make Transmitter Operating Room Report, as shown
in Fig. 16-1, that this schedule was completed or any deviations from
it. Also any other observations made.
TRANSMITTER OPERATING ROOM REPORT
DATE
7-15-1947
PROGRAM
TIME
Melody Billboard
ANNOUNCER
5134 ym
o
(Musical ET)
Fisher
CONTROL OPERATOR
ORIGINATED
I3n5ort
TRANSMITTER OPERATOR
STU
C
(BT)
Ennes
REMARKS:
Carrier
off thirty seconds due electrical
Picteil lead on directional
burned open.
storm.
antenna relay in phasing'unit
Replaced with temporary clip jumper.
BY
(PILE IN
011.,112T
AT
MI TM
.jL,
OMI
I.OINE
)
transmitter operating-room report as used by
the author at Station WIRE.
Fig. 16-1. An example of a
FINAL CHECK: Turn on transmitter in usual manner, first on low
power of 1000 watts. If everything is normal then check the 5000 watt operation.
134
BROADCAST OPERATORS HANDBOOK
Second Thursday Night of Month Maintenance Schedule
Remove canvas air ducts beneath modulator and final tubes and
place paper or cloth cover over blower openings. Carefully clean between fins of all three large tubes by sliding cloth between fins especially in against tube anodes.
Clean all components in lower half of modulator section. Check all
components in this section including terminal blocks. .
Remove temporary cover over blower openings. Wipe off both sides
of air flow vanes. Check for free movement.
Brush corners of fan blades with small brush, then vacuum.
Some dust usually remains in bottom of blowers and should be removed by running each blower and using a deflector over blower opening on top to direct air away from tube bases. After all three are
cleaned, and with blowers running, check to see that the air -flow vanes
are operating mercury switches properly.
Replace canvas air ducts, and double-check for proper cond.
Run regular Auxiliary Transmitter test.
REPORTS: Make Transmitter Room Report that this schedule was
completed or any deviations from it. Also report if conditions of
air filters on back doors necessitates replacement.
FINAL CHECK: Check for low power and high power operation in
usual manner.
Third Thursday Night Maintenance Schedule
Regular Auxiliary Transmitter check.
Clean relay contacts in phasing unit.
Inspect and clean lightning gaps on transmission line above phasing
unit.
Tighten and clean all connection and chassis of tuning assemblies
in tower houses. Clean relay contacts.
Check relay operation for Directional and Non -Directional operation by turning transmitter on as outlined for previous maintenance
schedules.
Fourth Thursday Night Maintenance Schedule
Regular Auxiliary Transmitter check.
Clean input and output attenuators on 96-A line amplifier, also
monitor attenuator. (Use Lubriplate and clean cloth.)
Vacuum jack strips on speech input panel.
WHY PREVENTIVE MAINTENANCE
135
Inspect for tightness connections on relays in power -control panel.
Clean the above relay contacts.
Wipe off filament rheostats on power control panel.
Wipe off all accessible places on power control panel.
Clean "modulator bias" relay contacts.
Clean the contacts of the two overload relays and time -delay relay
in exciter unit.
Clean and inspect all components in exciter unit not covered in
previous schedules.
Vacuum inside of power -control console, tighten all connections.
Regular transmitter check for normal operation.
Fifth Thursday Night Maintenance Schedule
(where this occurs)
Regular Auxiliary Transmitter check.
Check all tubes (with tube checker) of 96-A line amplifier and associated power supply, modulation monitor, frequency monitor, program
monitor, and speech input tubes.
Check 6K7 balance in 96-A line amplifier.
Check spare line amplifier for proper operation.
Check lubrication of all motors including toilet and shower water
pumps and exhaust fans.
Take inventory of new transmitter log sheets, transmitter -room report sheets, spare tubes, spare fuses, indicator lamps, and illuminating
lamps for building and towers.
Chapter
17
PREVENTIVE MAINTENANCE INSTRUCTIONS
N THE PRECEDING chapter some general facts about preventive
maintenance were presented together with schedules showing when
the different operations should be performed. Inasmuch as some
of these operations deal with apparatus that can easily be damaged
unless proper care is exercised, certain procedures should be followed
so that no damage does result from the periodical inspections and so
that if repairs to the apparatus are necessary, they can be effected
properly. It should be borne in mind that the data in the following
pages are general for the most part and it may be that some manufacturers recommend specific procedures for their products, which, of
course, should be followed.
The reasons why preventive maintenance operations are followed
seem obvious with no further comment. It might be well, however, for
the men who are responsible for this maintenance work to keep in
mind that the procedures discussed in the following pages have been
designed to
Combat the detrimental effects of dirt, dust, moisture, water, and
the ravages of weather on the equipment.
2. Keep the equipment in condition to insure uninterrupted operation for the longest period of time possible.
3. Maintain the equipment so that it always operates at the maximum possible efficiency.
4. Prolong the useful life of the equipment.
1.
Preventive Maintenance Operations
The actual work performed during the application of the preventive
maintenance schedule items is divided into six types of operations.
Throughout this section, the lettering system for the six operations is
as follows:
136
PREVENTIVE MAINTENANCE INSTRUCTIONS
F-Feel
I-Inspect
T-Tighten
137
C-Clean
A-Adjust
L-Lubricate
The "Feel" operation is used most extensively to check
rotating machinery (such as blower motors, drive motors, and generators) for over -heated bearings. "Feeling" indicates the need for lubrication or the existence of some other type of defect requiring correction.
Normal operating temperature is that which will permit the bare hand
in contact with the motor -bearing cover for a period of 5 seconds
without feeling any discomfort. The "Feel" operation also is applied
to a few items other than rotating machinery; the "Feel" operation
for these items is explained in the discussion of each specific item.
Note: It is important that the feel operation be performed as soon
as possible after the shutdown, and always before any other maintenance is done.
b. Inspect (I). "Inspection" is probably the most important of all
the preventive maintenance operations. If more than one man is available to do this work, choose the most observant, for careful observation is required to detect defects in the functioning of moving parts
and any other abnormal conditions. To carry out the "Inspection"
operation most effectively, make every effort to become thoroughly
familiar with normal operating conditions and to learn to recognize
and identify abnormal conditions readily.
"Inspection" consists of carefully observing all parts in the equipment. Notice such characteristics as their color, placement, and state
of cleanliness. Inspect for the following conditions:
(a) Overheating, as indicated by discoloration, blistering or bulging
of the part or surface of the container; leakage of insulating compounds; and oxidation of metal contact surfaces.
(b) Placement, by observing that all leads and cabling are in their
original positions.
(c) Cleanliness, by carefully examining all recesses in the units for
accumulation of dust, especially between connecting terminals. Parts,
connections, and joints should be free of dust, corrosion, and other foreign matter. In tropical and high -humidity locations, look for fungus
growth and mildew.
(d) Tightness, by testing any connection or mounting which appears
to be loose, by slightly pulling on the wire or feeling the lug or terminal screw.
a.
Feel (F).
138
BROADCAST OPERATORS HANDBOOK
c. Tighten (T). Any movement of the equipment caused by transportation or by vibration from moving machinery may result in loose
connections which are likely to impair the operation of the set. The
importance of firm mountings and connections cannot be overemphasized; however, never tighten screws, bolts, and nuts unless it is definitely known that they are loose. Fittings that are tightened beyond
the pressure for which they were designed will be damaged or broken.
When tightening, always be certain to use the correct tool in the
proper size.
d. Clean (C). When the schedule calls for a "Cleaning" operation,
it does not mean that every item which bears that identifying letter
must be cleaned each time it is inspected. Clean parts only when inspection shows that it is necessary. The "Cleaning" operation to be
performed on each part is described later on.
e. Adjust (A). Adjustments are made only when necessary to restore
normal operating conditions. Specific types of adjustment are described later.
f. Lubricate (L).
Lubrication means the addition of oil or grease
to form a film between two surfaces that slide against each other, in
order to prevent mechanical wear from friction. Generally, lubrication
is performed only on motors and bearings.
Note: When a part is suspected of impending failure, even after
protective maintenance operations have been performed, immediately
notify the person in charge who will see that the condition is corrected
by repair or replacement before a breakdown occurs.
Suggested List of Tools Necessary for Relay and
Commutator Maintenance
A number of items on the preventive maintenance schedule require
work of a special and somewhat delicate nature. This work includes
cleaning and repairing relay contacts, cleaning plugs and receptacles,
polishing commutators, and adjusting motor and generator brushes.
To do the work properly, special supplies and specially constructed
tools are needed. A suggested list is given below:
Nonmagnifying dental mirror.
Cleaning brush, 2 -inch.
Canvas-cloth strip.
Sandpaper strip, fine.
Sandpaper strip, semifine.
PREVENTIVE MAINTENANCE INSTRUCTIONS
139
Crocus -cloth strip.
Small relay crocus -cloth stick.
Relay -contact burnishing tool.
Fine-cut file.
Brush seating stone.
Commutator polishing stone.
Canvas -cloth stick.
Crocus-cloth stick.
Sandpaper stick.
1 Brush, cleaning, 1 -inch.
1 Brush, cleaning, 2 -inch (2) .
1 Carbon tetrachloride, quart can.
2 Cement, household, tube.
1 Cloth, canvas, 2 x 4-feet.
1 Cloth or canvas, strip, 2 x 6 -inch, cut from sheet (3).
1 Cloth, lint -free, package.
6 Crocus -cloth, sheets.
1 Crocus -cloth, strip, 3/4 x 6 -inch, cut from sheet (6) .
1 File, small, fine cut.
1 Lubricant, Vaseline, container.
1 Mirror, nonmagnifying dental.
6 Sandpaper sheets, #0000.
6 Sandpaper sheets, #00.
1 Sandpaper, #0000, 3/4 x 6 -inch, cut from sheet.
1 Sandpaper strip, #00, 3/4 x 6 -inch, cut from sheet.
1 Stick, crocus -cloth, large.
1 Stick, special, canvas -covered.
1 Stick, special, crocus -cloth stick for relays, small.
1 Stick, special, sandpaper covered.
1 Stone, commutator polishing stone.
1 Stone, brush seating stone.
50 Tags, small marker.
1 Tool, relay contact burnishing.
Construction for Relay and Commutator Tools
Crocus -cloth, canvas -cloth, and sandpaper sticks are constructed in
the following manner:
1. First prepare a length of wood 33/4 inches long, % inch wide,
and 1/16 inch thick or less. Cut one piece of crocus cloth 21/2 inches
long and 1 inch wide.
140
BROADCAST OPERATORS HANDBOOK
2. Fold the crocus cloth as in Fig. 17-1 (A) and cement it to the
stick. Note that both sides of the stick are covered. Place the stick
in the vise, press it and wait until the cement hardens. Cut off the
piece of crocus cloth which extends over the edge of the stick.
CROCUS CLOTH
"
2'4"
OR LESS
11-12
-
GLUE HERE
END VIEW
CROCUS CLOTH
GLUE HERE
6
GLUE HERE
'
U
SUITABLE
WIDTH
SANDPAPER
OR
CROCUS CLOTH
GLUE HERE
Fig. 17-1. The crocus -cloth stick (A) is used for cleaning
relay contacts and the one in (B) is for cleaning motor
or generator commutators.
3. Obtain three pieces of wood which measure 8 inches long, 1 inch
wide, and approximately 1/4 inch thick. Cut one piece of crocus cloth,
one piece of #0000 sandpaper, and one piece of canvas cloth, each
51/4 inches long and 1 inch wide.
4. Fold the long, narrow pieces of crocus cloth, sandpaper, and canvas cloth as shown in Fig. 17-1 (B) and cement one of them to each
of the three sticks. Note that in this case the fold is over one end of
the stick rather than over the sides. Place the sticks in the vise, press,
and wait until the cement hardens.
PREVENTIVE MAINTENANCE INSTRUCTIONS
141
Use and Care of Tools
Proper care of tools is as necessary as proper care of radio equipment. Any effort or time spent in caring for tools is worth while. Clean
them when necessary and always replace them so that they are easily
accessible. The following information will be helpful in using and caring for the tools listed below.
a. Crocus -Cloth Stick. The crocus -cloth sticks are used to clean contacts of relays in the radio equipment.
b. Large Commutator Sticks. Commutator sticks with covering of
sandpaper or canvas are used for cleaning commutators of electric
motors and generator sets.
c. Commutator Dressing Stone. The dressing stone is used only in
case of emergency to dress a commutator or motor generator.
d. Brush Seating Stone. The seating stone is used when a set of new
brushes is installed in alternators or exciters. Only a very limited
application of the seating stone is required to seat the average set of
brushes.
e. Electric Soldering Iron. The use of the soldering iron is generally
known. Remember to keep the tip properly tinned and shaped.
the
f. Allen Wrenches. Allen wrenches are used to tighten or remove
small
are
These
Allen setscrews on fan pulleys, motor pulleys, etc.
wrenches and should be kept in the cloth bag provided for that purpose. After use, wipe them off with an oily rag, replace them in the
bag, and restore them to the tool box.
g. Diagonal -Cutting Pliers. Diagonal pliers are used to cut copper
wire (no larger than No. 14) when working in small places. Do not
cut iron wire with the diagonals.
h. Gas Pliers. Gas pliers are used to hold round tubing, round studs,
or any other round metal objects that do not have screw driver slots
or flat sides for wrenches.
i. Long -Nose Pliers. Long-nose pliers are used to hold and dent
small wires and to grip very small parts. They are generally used
around delicate apparatus.
j. Adjustable End -Wrenches. Adjustable end -wrenches are designed
to remove or hold bolts, studs, and nuts of various sizes. Keep the
adjusting -nut free from dirt and sand and oil them frequently.
k. Nut -Driver Wrenches. Nut -driver wrenches are used to remove
nuts of various sizes. Choose a wrench that fits the nut snugly.
1. Screw Drivers. Screw drivers of different sizes are important tools
and must be kept in good condition. Select the proper size for the job
142
BROADCAST OPERATORS HANDBOOK
to be done. Never force a screw; if undue resistance is felt, examine
the threads for damage and replace the screw if necessary.
m. Shorting Bar. The shorting bar must be constructed at the station. Obtain a piece of wood about 15 inches long and 1 inch thick.
Fasten a piece of copper or brass rod or tubing securely to one end of
the stick in such a manner that the rod extends 12 inches beyond the
end of the stick. Solder a piece of heavy flexible wire about 18 inches
long to the metal rod at the point where it is fastened to the stick
and attach a heavy clip to the free end of the wire. When using the
shorting bar, always attach the clip to a good ground connection BEFORE making contact with the terminal to be grounded.
Vacuum Tubes
The purpose of tube maintenance is to prevent tube failures caused
by loose or dirty connections and to maintain the tubes in a clean
operating condition at all times. Certain types of vacuum tubes, especially those used in high -voltage circuits, operate at high temperatures.
Careless contact with the bare hands or arms causes severe burns.
Sufficient time must be allowed for the tubes to cool before handling.
Maintenance of vacuum tubes involves making minor adjustments
and cleaning. Tubes requiring the most frequent maintenance are
those used in high -voltage circuits. Because of their high operating
potentials, these tubes require more frequent inspection and cleaning
than tubes used in low -voltage circuits. Loose coupling at the terminals of high -voltage tubes will result in the terminals becoming
pitted and corroded. Loose connections cause poor electrical contact
and lower the operational efficiency of the unit in which they are employed.
Maintenance of vacuum tubes should be applied onlÿ when necessary. Too frequent handling may result in damage to the tube terminals and connections. As a rule, vacuum tubes need little maintenance;
therefore, when the program calls for maintenance, but inspection
shows that the tubes do not require it, the operation should be omitted.
It is advisable, however, to clean the glass envelopes of the tubes and
remove dust or dirt accumulations surrounding their immediate areas.
The object of the maintenance program is to maintain the tubes free
from dirt, oil deposits, and corrosion.
Vacuum tubes for maintenance purposes are divided into two groups:
(1) Transmitting -type tubes.
(2) Receiving -type tubes.
PREVENTIVE MAINTENANCE INSTRUCTIONS
143
Maintenance procedures required for vacuum tubes differ according
to types. Certain maintenance operations that must be performed
on transmitting -type tubes may be omitted in the maintenance of receiving -type tubes. Transmitting -type tubes are those used in transmitters, modulators, and h:gh-voltage rectifier units. Because of their
physical construction they require careful inspection and cleaning during maintenance.
Five procedures are reqLired to the performance of maintenance of
vacuum tubes: feel, inspect, tighten, clean, and adjust. The procedures
involved depend on the type of tube being maintained. Transmitting
tubes may require the application of the above -mentioned procedures,
while the procedures requized for receiving tubes are limited by tube
types.
Maintenance Procedures
The following procedures should be employed for the maintenance of
vacuum tubes:
Caution: Discharge all high -voltage capacitors before performing
any maintenance operations. Avoid burns by allowing sufficient time
for tubes to cool before har_dling.
Feel (F). (1) This operation should be applied only to high -voltage
tubes, such as those used in transmitters, modulators, and high-voltage
rectifier units.
Note: The following operations should be performed 5 to 10 minutes
after power has been removed from the tubes.
(2) Feel the grid, plate, and filament terminals of the tubes for excessive heat. Practice will determine the temperature to be accepted
as normal. For example, when two grid terminals are felt, one should
not be warmer than the other. Excessive heat at terminals indicates
poor connections.
Inspect (I). This maintenance operation is applicable to all types
of vacuum tubes and should be performed after the tubes have had
sufficient time to cool.
'1) Inspect the glass or metal envelopes of tubes for accumulation3 of dust, dirt, and grease. Inspect the tube caps and connector
clips for dirt and corrosion. Inspect the complete tube assembly and
socket for dirt and corrosion. Check the tube caps to determine
whether any are loose. On glass tubes, check the glass envelope to
determine whether or not it has become loosened from the tube base.
Replace tubes which have loose grid caps or envelopes when these
144
BROADCAST OPERATORS HANDBOOK
faults are discovered. If replacement is impossible, do not attempt to
clean or handle the tube, operate the tube as it is, providing that its
operation is normal. Enter the tube condition in the log so that replacement can be made at the earliest possible time.
(2) Examine the spring clips that connect to the grid plate, and
filament caps for looseness. Also examine all leads connected to these
clips for poorly soldered or loose connections. These leads should be
free of frayed insulation and broken strands. When removing clips
from loosened grid caps, extreme care must be exercised, particularly
if corrosion exists. Never try to force or pry a grid clip from the grid
cap of a tube as damage to the tube or grid cap may result. If the
grid cap is loose and it is necessary to remove the grid clip, first loosen
the tension of the clip by spreading it open; then gently remove (do
not force) the clip from the tube cap.
(3) Inspect the tubes to be sure they are secure in their sockets.
Certain types of receiving tubes used are mechanically fastened with
tube spring locks; others have sockets in which the tube itself is locked
in place. Inspect by turning the tube in clockwise direction in its
socket until it is locked in place. This type of socket is generally used
for the transmitting-type tubes. However, the firmness with which the
tube is held in place depends upon the tension of the terminals in the
socket. These terminals are of the spring type (contact springs) and
must have sufficient tension to make good contact against the tube
prongs. The tension can be tested by grasping the tube and turning it
first counterclockwise and then clockwise to its original position. If
the tube seems to snap into place as it is turned, the spring tension
of the socket terminals is firm enough; however, if the tension seems
weak, they may be tightened or adjusted as explained in the tube
maintenance procedure under "Adjust."
(4) Inspect all metal tubes for signs of corrosion and looseness of
mounting. Many receiving -type tubes have keyways in the center
of the tube bases. These keyways sometimes become broken, and have
a tendency to loosen the tube in the socket. Do not attempt to replace
tubes that have broken keyways unless it is absolutely necessary tr do
so, and it is possible to replace the tube correctly in its proper position. Inspect the tube sockets of metal tubes for cracks or breaks. Do
not force metal tubes into their sockets. If they are hard to replace,
examine the tube pins for signs of corrosion or solder deposits.
Tighten (T). (1) In performing this operation, take care not to
overtighten tube sockets, tube clamps, and tube socket insulators.
PREVENTIVE MAINTENANCE INSTRUCTIONS
145
Porcelain sockets and stand-off insulators crack due to heat expansion
if they are excessively tightened. Do not overtighten them. Care
should be taken when tightening the tube caps of high -voltage tubes.
Use the proper screw driver or tool; if the tool should slip it may fall
against the glass envelope of the tube and ruin a perfect tube.
(2) Tighten all tube connections, terminals, sockets, and stand-off
insulators which were found loose during the inspection procedure.
When tightening tube sockets having stand-off insulators, determine
before tightening whether the fiber washers between the socket and
the stand-off insulators are intact. If these fiber spacers are cracked
or missing, replace them before tightening the tube socket. Tightening
the socket without these spacer washers breaks or cracks the porcelain -tube socket.
Clean (C). In the performance of this item, clean only where necessary. Do not remove tubes for cleaning purposes unless it is impossible
to clean them in their original positions. If the tube must be removed,
exercise care in doing so. Do not attempt to clean the envelopes if
they are located in an out-of-the-way place; in this case remove them
for cleaning. When tubes are removed for cleaning, replace them
immediately afterward. Do not leave them where they may be
broken.
(1) Clean the entire tube assemblies with a clean dry cloth if the
glass envelope is excessively dirty. Wipe the glass envelope with a
damp cloth moistened in water. Polish after cleaning with a clean
dry cloth. Do not wipe me _,al tubes with a cloth moistened in water,
as this causes the metal body of the tube to rust. Use a cleaning agent
if the tube is excessively dirty because of oil deposits. Generally, metal
tubes with oil deposits on their envelopes can be cleaned successfully
by polishing dry with a clean dry cloth. The oil film remaining on the
metal body of the tube prevents the tube from rusting. To remove oiliness, corrosion, or rust from tube envelopes, moisten a clean cloth with
cleaning agent and clean the area affected until it is clean. Wipe dry
with a clean dry cloth.
(2) Clean the grid and -plate caps, if necessary, with a piece of
#0000 sandpaper, or crocus cloth. The paper should be wrapped
around the cap and gently run along the surface. Excessive pressure
is not needed; neither is it necessary to grip the cap tightly. Clean
the caps completely before replacing them on the tube terminals if
corrosion is noted on the grid or plate caps.
(3) When the tube sockets are cleaned and the contacts are acces-
146
BROADCAST OPERATORS HANDBOOK
sible, fine sandpaper should be used if corrosion is present on the contacts. Clean the contacts thoroughly after sandpapering. Clean all
areas surrounding tube sockets with a brush and a clean dry cloth; this
prevents dust and dirt from being blown back on the tube envelopes
when the unit is put back into operation.
Adjust (A). When performing this operation, care must be taken
to arrange all leads and terminals to correspond as closely as possible
with their original positions.
(1) Adjust all leads and tube connections. Check to determine if
the leads are resting on the glass envelope of the high -voltage tubes;
if they are, redress the leads so that proper spacing is obtained.
Examine all leads connecting to the tube caps. These should not be
so tight that they barely reach the caps of the tubes. If this condition is found, redress these leads so that enough "play" is obtained.
Adjust all grid clamps so that the proper tension is obtained. To increase the tension of tube clamps, close the spring clamps slightly
with a pair of long -nose pliers until the proper tension is obtained. Do
not flatten the clamps.
(2) Tube sockets used for transmitting -type tubes should be adjusted if the tube is found loose in its mounting. The terminals of
these sockets are spring -tensioned so that they may be adjusted
to increase the pressure against the tube pins. To adjust these contacts, simply bend them toward the center on the socket until the correct tension is obtained. Do not apply too much pressure to the spring
contacts; they may be broken from their mountings in the porcelain
socket.
(3) Any difficulty in removing or inserting metal tubes can be remedied easily. Remove the metal tube and examine the tube pins to
determine if solder or corrosion has accumulated on the pins. Remove
solder deposits with a penknife; then polish the pins with fine sandpaper. Do not use a soldering iron to remove solder deposits; this
makes them worse, as the solder is built up on the pins rather than
removed. To remove corrosion, use fine sandpaper, but never use it
unless it is absolutely necessary. Saturate a small piece of cleaning
cloth with light lubricating oil or petroleum jelly, and wipe the tube
pins. Remove the excess oil from the pins by wiping them almost dry
with a clean dry cloth. If these procedures are followed, no difficulty
will be experienced in removing or reinserting the metal tube into its
socket.
Caution: Do not force metal tubes into their sockets. Do not pry or
PREVENTIVE MAINTENANCE INSTRUCTIONS
147
"wiggle" them loose, since this damages the prongs of the socket and
results in intermittent operation of the unit in which they are located.
Capacitors
High -Voltage Capacitors. High -voltage capacitors, because of their
high operating potentials, must be kept clean at all times to prevent
losses and arcing. Dirt, oil deposits, or any other foreign matter must
not be allowed to accumulate on the high -voltage terminals of these
capacitors. All leads and terminal connections must be inspected periodically for signs of looseness and corrosion, and the porcelain insulators inspected for cracks or breaks.
Low-Voltage Capacitors, Oil -Filled. Low -voltage oil -filled capacitors require the same care as those of the high -voltage type, although
the frequency of the maintenance operation is not so critical. The
terminals and connections of these capacitors should be given the
same careful inspection as those of the high -voltage types. The leads
of these capacitors are not as rugged as those used on the high -voltage
capacitors and should be inspected more closely for poorly soldered
connections.
Tubular Capacitors. These capacitors are of the low-voltage paper
type and are generally used in low -voltage circuits for coupling and
bypassing. They should be inspected and cleaned whenever the chassis
in which they are located is removed for maintenance. The only maintenance requirement for these capacitors is inspection of the tubular
body of the capacitor for bulging, excessive swelling of the capacitors,
and for signs of wax leakage. The terminal leads (pigtail type) of
the capacitors are inspected for firmness of contact at their respective points of connection. Never use a cloth to clean this type of capacitor, as damage to the surrounding circuits may result. These capacitors are easily cleaned with a small, soft brush. All dirt and dust are
brushed from the body of the capacitor and the surrounding area.
Mica Capacitors. Mica capacitors require very little maintenance
other than being kept free from dust and oil. Two types of mica capacitors are generally used the high -voltage and the low -voltage type.
The low-voltage types are inspected whenever the chassis of the unit
in which they are located is being maintained. The capacitors are inspected for cracked body conditions caused by excessive heat, while
their leads (pigtail type) are inspected for firmness of contact at their
respective points of connection. The high -voltage types, however, require terminals because of their high operating potentials. These ter-
148
BROADCAST OPERATORS HANDBOOK
minais must be inspected for tightness and corrosion, firmness of
mounting, and body conditions. The body of these capacitors is of a
ceramic material and care must be exercised when tightening the
mountings of these capacitors. The bodies of the capacitors are easily
kept clean with a dry clean cloth. For satisfactory operation the terminals must be free from dirt and corrosion at all times. Take care
when tightening the terminals of these capacitors, as excessive pressure
damages or cracks the ceramic case where the terminals are coupled
to the body of the capacitors.
Trimmer Capacitors. In very damp climates, trimmer capacitors
must be inspected often. Dampness, if allowed to accumulate on the
plates of the capacitors, results in erratic operation of the unit in which
the capacitors are used. In certain cases where high voltage is used,
serious damage to the capacitors results. A minute amount of moisture or a tiny bead of water is all that is necessary to short-circuit the
plates of the capacitor and cause abnormal operation. When such
conditions are encountered, the capacitor must be thoroughly dried by
the heat process which requires the use of a small portable heater.
A cleaning cloth used to dry the plates of the capacitors may throw the
plates out of alignment when the cloth is inserted between them. In
extreme cases where the plates of the capacitors are very closely
spaced, use a magnifying glass to locate the exact position of the moisture beads existing between the plates. Due to the sheen of the capacitor plates, very minute particles of moisture cannot always be detected by the naked eye.
Maintenance Procedures for Capacitors.
Caution: To avoid severe electrical shock in case of bleeder failures,
discharge all high -voltage capacitors before maintenance.
Feel (F). Feel the terminals of the high -voltage filter capacitors.
These should be fairly cool. Excessive heat probably indicates losses
due to loose, dirty, or corroded terminal connections. Feel the sides of
oil -filled and electrolytic capacitors. These should be cool or slightly
warm. If they are very warm or hot, the condition indicates excessive
internal leakage. Capacitors in this condition are subject to failure at
any time and should be reported for immediate replacement.
Inspect (I). Inspect the general condition of all capacitors regardless of type. Inspect for broken, frayed, or loose terminals, leads, and
connections. Inspect the condition of the terminals of the high -voltage
capacitors. Check these for dirt, corrosion, and looseness. Inspect the
body of the capacitors for excessive signs of bulging and oil leakage.
PREVENTIVE MAINTENANCE INSTRUCTIONS
149
Inspect the plates of the tuning capacitors for dirt and corrosion.
Check all capacitor shafts, bushings, bearings, and couplings for loose-
ness or binding.
Tighten (T). Tighten all loose terminals, connections, and terminal
leads on all types of capacitors. Tighten all capacitor mountings and
stand-off insulators. Tighten all loose shaft couplings and bushings.
Clean (C). Special at-ention should be given to all high -voltage
capacitors to insure that they are not only kept clean, but are free
from moisture. Thoroughly clean the insulators, terminals, and leads
of high -voltage capacitors. When extremely damp, due to high humidity, these capacitors frequently have to be wiped dry with a
clean, absorbent cloth to prevent arc-overs and breakdown of insulation. Remove terminals that appear to be either corroded or dirty; also
remove those causing power losses due to high -resistance connections.
Clean them with a crocus cloth which is either dry or moistened with
cleaning fluid. Polish the terminals dry after cleaning with a clean,
dry cloth. Replace all connections after cleaning, making certain that
good electrical contact is cbtained. The low-voltage capacitors require
little attention. However, all insulated bushings and supports should
be kept clean and free frcm foreign matter.
Adjust (A). Adjust all :eads if necessary. This requires the redressing of leads which may hive been dislocated during the maintenance
procedure. If capacitor leads are stretched too tightly, redress or replace them until the correct lead placement is obtained.
Resistors
Resistors may be divided for maintenance purposes into two groups:
the first group consists of those resistors easily detachable and known
as ferrule -type resistors; ;he second group includes those whose terminals are soldered and are known as pigtail-type resistors.
a. Ferrule-Type Resistors.
Caution: Do not touch power resistors immediately after the power
has been shut off. They are usually hot, and severe burns may result.
Feel (F). The springinss of ferrule clips may be ascertained when
removing the ferrule -type resistor. Insufficient pull at the clip may be
an indication of a loose connection and poor electrical contact.
Inspect (I). It is important to inspect all types of resistors for blistering or discoloration, fo: these are indications of overheating. Inspect the leads, clips, and :netalized ends of the resistors and adjacent
150
BROADCAST OPERATORS HANDBOOK
connections for corrosion, dirt, dust, looseness, and broken strands in
the connecting wires; also inspect the firmness of mounting.
Tighten (T). Tighten all resistor mountings and connections found
loose. If the tension at the end clips has decreased, it is common practice to press the clip ends together by hand or with a pair of pliers.
The hand method is preferred because the pliers may bend the clip or
damage the contact surface.
Clean (C). Dirty or corroded connections of ferrule -type resistors
can be cleaned by using a brush or cloth dipped in cleaning fluid. If
the condition persists, use crocus cloth moistened with cleaning fluid.
It may be necessary to sandpaper the resistors lightly with fine grade
sandpaper, such as #0000. Always wipe clean with a dry cloth before
replacing them. Vitreous resistors connected across high voltage should
be kept clean at all times to prevent leakage or flashovers between
terminals. They should be wiped clean with a dry cloth or a cloth
moistened with cleaning fluid. If cleaning fluid is used, the resistors
must be polished with a dry clean cloth.
Pigtail -Type Resistors. Maintenance of pigtail -type resistors is
limited to an inspection of soldered connections. Such connections
may break if the soldering is faulty or if the resistors are located in a
place subject to vibration. The recommended practice is to slide a
small insulated stick lightly over the connections and to inspect them
visually for solidity. If connections are noticeably weak or loose,
they should be re -soldered immediately. Discolored or chipped resistors indicate possible overloads. Although replacement is recommended, resistors in this condition have been known to last indefinitely. The pigtail -type connections should be dusted with a brush or
with an air blower if available.
Fuses
A fuse consists of a strip of fusible metal inserted in an electric circuit. When the current increases beyond a safe value, the metal melts,
thus interrupting the current. Fuses vary in size and rating depending
upon the circuits at which they are used. Some are designed to carry
currents in milliamperes. Being very rapid in action, they protect the
equipment from overloads and damage. Two types of fuses are used:
renewable and nonrenewable. The first type is designed so that the
fuse link, or element contained within the fuse cartridge, may be removed and replaced when blown. The second type, however, is constructed so that the fuse element is permanently sealed within the fuse
PREVENTIVE MAINTENANCE INSTRUCTIONS
151
housing. When a fuse blows, an attempt must be made to determine
the reason for its failure, and to make corrections, if possible, before a
new fuse is installed; then the complete fuse assembly must be replaced.
Renewable Type. The renewable type fuse assembly consists of a
housing or cartridge of insulating material with a threaded metal cap
(ferrule) at each end. The fuse element or link, as a precaution
against damage, is placed inside the cartridge or housing and it is held
in position by the two end caps, or ferrules. When a fuse is placed in
service, the two ends of the fuse cartridge are slid into spring contacts
mounted on the fuse block. This places the fuse in the circuit to be
protected.
Nonrenewable Type. When nonrenewable fuses are blown, they
must be discarded. Certain types of nonrenewable fuses are removed
by unscrewing and withdrawing the cap screws that hold them in place.
When removed, the fuse and cap screw are separated by pulling apart.
The glass fuses are easily removed for inspection. Care must be taken
to see that the fuse end and holding clips are kept clean and tight . If
they are not, overheating will result arid make replacement necessary.
Inspect (I). Inspect the fuse caps for evidence of overheating and
corrosion. Inspect the fuse clips for dirt, loose connections, and proper
tension.
Tighten (T). Tighten the end caps, the fuse clips, and connections
to the clips on replaceable fuses if they are found to be loose. The
tension of the fuse clips may be increased by pressing the sides closer
together. Fuse caps should be hand -tightened only. Excessive tightening results in difficulty in removing them when required.
Clean (C). Clean all fuse ends and fuse clips with fine sandpaper
when needed; wipe with a clean cloth after cleaning. If it becomes
necessary to use a file to remove deep pits in the clips, fuse ends, or
contacts, always finish up with fine sandpaper in order to leave a
smooth contact surface. As a final step, wipe the surface clean with a
clean dry cloth.
Bushings and Insulators
Bushings and insulators are extremely important elements in electric
circuits, especially when located in high -voltage circuits where insulation breakdown is most common. Most of the high -voltage insulators
are constructed of ceramic material with highly glazed surfaces.
BROADCAST OPERATORS HANDBOOK
Caution: Exercise extreme care when working near these insulators.
They are easily chipped or broken.
Inspect (I). Thoroughly inspect all high -voltage insulators and
bushings for moisture, dust, and other accumulated foreign matter.
Unless they are both clean and dry, leakage or arc-overs will occur
and damage them permanently. Check the chipped surfaces, hair line
cracks, carbonized arc -over paths, and other surface defects that may
make the insulator unserviceable. Insulators in this condition should
be reported to the person in charge for replacement.
Tighten (T). Feed -through bushings, stand-off and other insulators
should be tightened if found to have loose mountings or supports.
Tighten these insulators with care because gaskets absorb only a small
amount of pressure before breaking.
Clean (C). Cleaning operations are similar to those outlined for
tubes. Use a clean cloth (dampened with cleaning fluid if necessary)
to remove dust, dirt, or other foreign matter. Always polish with a
dry, absorbent cloth after cleaning.
152
Relays
The various types of relays may be classified as follows: overload
relays, time delay relays, and magnetic contactors. Relays require a
certain amount of preventive maintenance, which must never be performed except when absolutely necessary. Certain types will be
found to be completely encased in dustproof and moistureproof cases.
These require little maintenance other than a periodic inspection.
Maintenance of relays requires that they be inspected periodically
and preventive maintenance measures performed if necessary. The
inspection procedure requires that the terminals be inspected for
looseness, dirt, and corrosion. Contacts may have become loosened because of the jarring of the equipment during shipment. The contacts
may become dirty or corroded due to climatic conditions where the
equipment is being operated. Relay contacts must never be sandpapered or filed unless the operation is absolutely necessary for the
normal operation of the relay unit. A relay is considered normal if:
(1) The relay assembly is free from dirt, dust, and other foreign
matter.
(2) The contacts are not burned, pitted, or corroded.
(3) The contacts are properly lined up and correctly spaced.
(4) The contact springs are in good condition.
PREVENTIVE MAINTENANCE INSTRUCTIONS
153
(5) The moving parts travel freely and function in a satisfactory
manner. The solenoids of plunger type relays must be free
(6)
(7)
(8)
(9)
from obstructions.
The connections tc the relay are tight.
The wire insulation is not frayed or torn.
The relay assembly is securely mounted.
The coil shows no sign of overheating.
A relay is considered abnormal if it fails to meet any of the above -
mentioned requirements. The following are the maintenance procedures used in the maintenance of relay units.
Inspect (I). Inspect the relays, to determine abnormal conditions
using the check list given above. If the contacts are not readily accessible, they may be examined with the aid of a flashlight and mirror.
Many of the relays can be inspected and cleaned without being removed from their mountings or without being taken apart. Mechanical action of the relays should be checked to make certain that the
moving and stationary contacts come together in a positive manner
and that they are directly in line with each other. The armature or
plunger mechanism should move freely without binding or dragging.
Care should be taken during inspection not to damage or misalign the
relay mechanism. Relays that require the removal of the cover for
complete inspection may be found enclosed in glass, Bakelite, or metal
cases. Relays must never be taken apart unless it is absolutely necessary. If they must be taken apart for maintenance purposes, care
should be exercised in doing so. When disassembling relays, tag all
leads as they are being removed. This insures that the proper leads
are returned to their proper terminals after the maintenance procedure
is completed.
Tighten (T). Tighten all loose connections and mounting screws
found loose, but do not apply enough force to damage the screw or to
break the part which it holds. Do not start screws with their threads
crossed. If a screw does not turn easily, remove it and start again.
Relay coils can be tightened by inserting, if possible, a small wooden
or paper wedge between the coil and the core of the relay. This prevents chatter of the relay. Tighten any and all loose connections.
Tighten also the mounting of the relay assembly, if it is found loose.
When replacing glass or Bakelite covers over relay cases, take care
not to overtighten the screw cap holding the glass or Bakelite cover
over the relay assembly.
154
BROADCAST OPERATORS HANDBOOK
Clean (C). Clean the exterior of the relay with a dry cloth, if it is
very dirty; clean with a cloth or brush dipped in cleaning fluid; then
wipe the surface with a dry cloth. If loose connections are found,
they should be inspected. If inspection reveals that the connections
are either dirty or corroded, they should be removed and cleaned before tightening.
The relay service aid is a narrow piece of folded cloth or canvas. It
serves a twofold purpose: it is suitable for polishing a clean surface,
and it is used as a follow-up to a crocus cloth. It is also intended to remove grains of pumice which came off the crocus cloth and adhere to
the contact surface. The cloth is used as shown in Fig. 17-2.
Fig. 17-2.
faces are
row strip
as shown
Relay contact surpolished by a narof cloth or canvas
in the sketch.
Cleaning Relay Contacts. The following information should be carefully studied. It instructs how relay contacts of various types should
be cleaned.
Hard contacts. Hard alloy contacts are cleaned by drawing a strip
of clean wrapping paper between them while holding them together.
It may be necessary in some cases to moisten the paper with cleaning
fluid. Corroded, burned, or pitted contacts must be cleaned with the
crocus cloth strip or the burnishing tool as shown in Fig. 17-3.
Solid silver contacts. Dirty contacts. Dirty solid silver contacts are
easily cleaned with a brush dipped in cleaning fluid. After being
cleaned, the contacts are polished with a clean dry cloth.
Note: The brown discoloration that is found on silver and silverplated relay contacts is silver oxide and is a good conductor. It should
PREVENTIVE MAINTENANCE INSTRUCTIONS
155
be left alone unless the contacts must be cleaned for some other reason.
may be removed at any time with a cloth moistened in cleaning
fluid.
Corroded contacts: Dress the contacts first with crocus cloth, using
either the stick or the strip of crocus material. When all of the corrosion has been removed, wipe with a clean cloth moistened in cleaning
fluid and polish with a piece of folded cloth. Make certain that the
shape of the contacts has not been altered from the original.
It
FINGERS PRESSING
CONTACTS TOGETHER
TOOL BETWEEN
CONTACTS
Fig. 17-3. Hard alloy contacts of
a relay are cleaned by pulling a
strip of clean wrapping paper between them while pressing the
contacts together.
Burned or pitted contacts: Resurface the contacts, if necessary, with
#0000 sandpaper, making certain that the original shape of the contacts is not changed. Next, smooth the surface of the contacts with
crocus cloth until a high polish has been obtained. Wipe thoroughly
with a clean cloth to remove the abrasive remaining on the contacts.
When contacts are very badly burned or pitted and replacement is
not available, the small fine-cut file and #0000 sandpaper should be
used in keeping with instructions given later.
Silver-plated contacts. Dirty contacts: Dirty silver-plated contacts
are cleaned with a cloth or brush dipped in cleaning fluid. After being
cleaned, the contacts are polished with a dry cloth.
Corroded contacts: Dress first with crocus cloth, using either the
stick or strip of crocus material. The work must be done very carefully
not to remove an excessive amount of silver plating. When all of the
corrosion has been removed, polish with a clean dry cloth. Make
certain that the shape of the contacts has not been altered.
Burned or pitted contacts: Dress the contacts with crocus cloth
until the burned or pitted spots are removed. This may require an
appreciable amount of time and energy, but it is preferable to using
156
BROADCAST OPERATORS HANDBOOK
a file or sandpaper. If it is found that the crocus cloth does not remove
the burns or the pits, use the sandpaper tool very carefully. When
sandpaper is used, it must be followed with crocus cloth to polish the
contacts, and then wiped thoroughly with a cloth moistened in cleaning fluid. The contacts are then polished with a clean dry cloth.
Warning: Never use highly abrasive materials, such as emery cloth,
coarse sandpaper, or carborundum paper for servicing relay contacts,
as damage to the contacts will result.
Adjust (A). Adjust relay contacts after cleaning if necessary. The
contacts should close properly when the plunger is hand operated. Adjust the relay springs if necessary. Do not tamper with the relay
springs unless it is absolutely necessary. These springs are factory
adjusted and maintain a certain given tension and rarely get out of
adjustment. If the spring tension must be changed, exercise care when
doing so. The adjustment of the current control relays is accomplished
by setting calibrated knobs to the desired setting, or by turning a
knurled adjustment sleeve which has a calibrated scale mounted adjacent to it. The adjustments should not be changed from their original
factory setting except in cases of emergency. Overload relays must
never be adjusted unless the person in charge has been notified, and
has sanctioned the adjustment.
Shapes of Relay Contacts. Relay contacts are of varied shapes, as
shown in Fig. 17-4 depending upon their size and application. In some
I
FLAT CONTACT
r
Fig. 17-4. The original shape of
the contacts must be retained.
This shape may be either flat or
convex, as shown at the left.
CONVEX CONTACT
instances, both contacts are flat; in others, one contact is convex while
its mate is flat. The original shape of a contact must be retained during cleaning. If burning or pitting has distorted the contact so that
it must be reshaped, the original shape must be restored. It is essential that the maintenance personnel familiarize themselves with all
details of the relays by examining them while the relays are in good
condition. In this way, they will be better prepared to do their work
well.
PREVENTIVE MAINTENANCE INSTRUCTIONS
157
Relay Servicing Tools and Their Use
To service the relay contacts, several types of tools are needed.
Each of these has a special function, as described below.
The Burnishing Tool. This tool is used on relays which have extremely hard contacts made of palladium or elkonium. This tool is
not a file. A contact should not be burnished unless it is found to be
pitted or oxidized, and then not more than is necessary to restore a
clean smooth surface. The original shape of the contact must be retained.
Small Fine -Cut File. This file is to be used only on the larger contacts when they have becDme very badly burned or pitted, and a replacement is not available. This tool is not to be used on silver-plated
contacts, or on the contacts of the telephone-type relays. The file
should not be used more than is necessary to remove the pit. The
original shape of the contact must be preserved. After filing, #0000
sandpaper should be applied to the contact, and followed with crocus
cloth to obtain a smooth finish on the contact surface. A clean dry
cloth serves for final polishing.
The #0000 Sandpaper stick. This tool is made in the same way as
the crocus -cloth stick, except that sandpaper is used instead of crocus
cloth. The use of sandpaper is limited, as is the use of the fine-cut file,
to the treatment of badly burned or pitted contacts on the larger relays.
Sandpaper is not used on silver-plated contacts, except under extreme
circumstances, and when used should be followed with crocus cloth.
All contacts should be po:ished after sanding, with a clean dry cloth.
Crocus Cloth. This maintenance aid is available in two forms-as
a tool and as a strip of material. It serves a twofold purpose: it may
be used to remove corrosion from all relay contacts, or it may be applied to the contacts following the use of the fine-cut file and #0000
sandpaper. Neither the file nor sandpaper leaves a finish smooth
enough for proper relay operations. Use crocus cloth to polish the
surface of the contact. The choice between the stick and the piece of
cloth depends upon accessibility. If the location of the relay and the
position of the contacts permit the use of the crocus -cloth stick, it
should be used; otherwise, the strip of crocus cloth must serve. The
crocus cloth and tool are used as illustrated in Figs. 17-2 and 17-3. In
both cases the maintenance aid is inserted between the contacts and is
drawn through them while the contacts are pressed together with the
fingers.
15S
BROADCAST OPERATORS HANDBOOK
Switches
For the purpose of maintenance, switches may be classified into two
general groups: those whose contacts are readily accessible, and those
whose contacts are completely encased. The basic maintenance operations of "Inspection," "Cleaning," "Adjusting," and "Lubrication" are
applicable only to the first group. Because of the enclosed construction
of the second group, no maintenance can be applied. The work is
limited to a mechanical test of their operations.
Accessible Contact Switches. This group consists of knifeblade
switches, start-stop push-button switches, and high -voltage shorting
bars. With the exception of the shorting bars, all of these switches consist of blades which are mechanically inserted into spring contacts.
Inspect (I). Inspect all the terminal connections of each individual
switch for tightness and cleanliness. The mounting of the switch
should be checked for firmness. Operate the mechanism of the switch
and see if the parts move freely. Observe the stationary spring contacts to determine whether they have lost tension and whether they
are making good electrical contact.
Tighten (T). All loose mountings and connections should be tightened properly. If inspection shows that the fixed contacts have lost
tension, tighten them with the fingers or pliers. Tighten every connection or terminal found loose.
Clean (C). If inspection shows that any terminal, connection, or
section of the switch is dry, dusty, corroded, or pitted, clean the part
by using a dry clean cloth. If the condition is more serious, moisten
the cloth with cleaning fluid and rub vigorously. Surfaces which have
been touched with the bare hands must be thoroughly cleaned with
a cloth moistened in cleaning fluid, and then polished with a clean
cloth. The points of contact with the moving blade are naturally
those which most often show signs of wear. Examine these points very
carefully to insure that both sides of each blade, as well as the contact
surfaces of the clips, are spotlessly clean at all times. Crocus cloth
moistened with cleaning fluid should correct this condition; however, if
it is not corrected, #0000 or #000 sandpaper may be used. Always
polish clean after the sandpapering operation.
Adjust (A). Some of the switches have a tendency to fall out of
alignment because of loosening of the pivot. In most cases, tightening
the screw on the axis of motion corrects this condition.
Lubricate (L). If binding is noted during inspection of the opera-
PREVENTIVE MAINTENANCE INSTRUCTIONS
159
tion of the switch, apply a drop of instrument oil with a toothpick to
the point of motion or rotation. Do not allow oil to run into the electrical contacts, as a film of oil may cause serious damage or a poor
contact. Lubrication of switches is not recommended unless serious
binding is noticed.
Nonaccessible Contact Switches. Under this heading are included
all the remaining switches not discussed in the previous paragraph.
Interlock switches, toggle switches, meter protective push buttons, and
selector switches have been designed so that it is impossible to get
at the contact without breaking the switch assemblies. The only maintenance possible is to check the operation of the switch assemblies
and, if something abnormal is detected, to notify the person in charge
immediately so that a spare may be obtained and a replacement made
as soon as possible. Do not lubricate any of these switches under any
circumstances.
Generators and Motors
Certain preventive maintenance procedures must be applied to these
components if proper functioning and dependable performance are to
be obtained. There are three principal cases that contribute to faulty
operation of this type of equipment: accumulation of dirt, dust, or
other foreign matter on the windings and moving parts of the equipment; lack of sufficient lubrication on bearings and other moving parts;
and improper adjustments or damaged parts. Given proper maintenance care, motors and generators give long and efficient service. In
addition to the techniques given in the following paragraphs, additional
maintenance instructions covering certain motors or generators will be
found in various items of the manufacturer's instruction books. Unless specifically mentioned, the maintenance techniques that follow
apply to the motors and generators used in the transmitter.
Feel (F). The bearing and the housings should be tested by feeling
them to determine overheated conditions. An accepted test, except in
very hot climates, is to hold the bare hand in contact with the bearing
or housing for a period of at least 5 seconds. If the temperature can be
tolerated this length of time, the bearing temperature may be considered normal. Overheating may indicate lack of sufficient lubrication, a damaged bearing surface, or, in rare situations, an excessive
accumulation of dirt within the field windings.
Inspect (I). Each motor and generator exterior, and any other visible parts, must be inspected for dirt and signs of mechanical loose-
160
BROADCAST OPERATORS HANDBOOK
ness or defects. Wherever wires are exposed, see that all connections
are tight and in good condition and that the insulation is not frayed.
Inspect the motor ends for excess oil and the mounting for loose bolts.
Wherever possible and practicable, feel the pulleys, belts, and mechanical couplings to insure that the proper tension or tightness is
present.
Tighten (T). Any mounting, connection, or part found loose must
be properly tightened. If any internal part such as a commutator segment or an armature coil appears loose, notify the person in charge
and repair the part immediately or replace it at the first opportunity.
Operation under these conditions will cause considerable damage in a
very short period of time.
Clean (C). Carefully wipe the exterior, base, and mountings of
each motor and generator with an oiled cloth in order to leave a thin,
protective film of oil on the surfaces. If available, use an air blower, or
hand bellows to blow the dust and dirt out when inspection shows that
the windings are dusty or dirty.
If inspection of the commutator and brushes shows that cleaning
is necessary, the accepted cleaning practice is as follows: lift or remove the most accessible brush assembly and press a piece of canvas
cloth folded to the exact width of the commutator against the commutator; then run the motor for about 1 minute, exerting the necessary
pressure. If the condition still persists because the commutator has
been burned or pitted, use a piece of fine sandpaper (#0000), preferably mounted on the commutator cleaning stick, and, exerting the
necessary pressure, rotate the motor for approximately 1 minute.
Stop the motor and wipe around the commutator bars with a clean
cloth. It may be necessary to polish the commutator with a piece of
canvas, as explained in the first procedure. Identical maintenance procedures apply to slip rings.
Transformers and Choke Coils
Some transformers are enclosed in metal housings, others are external, but in all cases they are impregnated with insulating compound.
As a result, similar maintenance techniques are applicable to all of
them.
Inspect (I). Carefully inspect each transformer and choke for
general cleanliness, for tightness in connections of mounting brackets
and rivets, for solid terminal connections, and for secure connecting
lugs. The presence of dust, dirt, and moisture between terminals of
PREVENTIVE MAINTENANCE INSTRUCTIONS
161
the high -voltage transformers and chokes may cause flashovers. In
general, overheating in wax- or tar -impregnated transformers or coils,
is indicated by the presence of insulating compound on the outside
or around the base of each transformer or coil. If this condition is encountered, immediately notify the person in charge.
Tighten (T). Properly tighten mounting lugs, terminals, and rivets
found loose.
Clean (C). All metal -encased transformers can be cleaned easily
by wiping the outer casings with a cloth moistened with cleaning fluid.
Clean the casing and the immediate area surrounding the transformer
base. Clean any connections that are dirty or corroded. This operation
is especially important 071 high -voltage transformers and coils. It is
very important that transformer terminals and bushings on all types
of transformers be examined and kept clean at all times.
Variacs
Variacs, as a rule, are built sturdily and are protected so that very
little maintenance other than regular inspection is required.
Inspect (I). Carefully inspect the exteriors of the variacs for
signs of dirt and rust. Inspect the mounting of each variac to determine whether it is securely mounted. Inspect all connections for looseness, corrosion, and dirt. Ycheck the slip rings for signs of corrosion or
dirt.
Clean (C). The perforated casing of each variac as well as the area
surrounding the base must be cleaned regularly. If the slip rings need
cleaning, dismount the variac and clean with a cloth moistened in
cleaning fluid and then po_ish with a clean dry cloth. If the dirty condition persists, use crocus cloth and rub vigorously. Again polish with
a clean cloth. Reassemble the variac; then reinstall it, reconnecting all
terminals carefully.
Lubricate (L). If the variac shaft shows signs of binding or if it
squeaks, apply a few drops of household oil to the front and rear bearings. Rotate the control shaft back and forth several times to insure
equal distribution of the lubricant in the front and rear bearings.
Rheostats and Potentiometers
Rheostats and potentiometers fall into two main groups for maintenance purposes; those which have the resistance winding and the
sliding contact open and accessible, and those which, by construction,
have their inner parts totally enclosed. In the latter group, very little
162
BROADCAST OPERATORS HANDBOOK
maintenance can be performed, since opening and removing the metal
case may damage the unit.
Inspect (I). The mechanical condition of each rheostat must be inspected regularly. The control knob should be tight on the shaft.
Inspect the contact arm and resistor winding for cleanliness and good
electrical contact. Check the rheostat assembly and mounting screws
for firmness; the sliding arm for proper spring tension; and the insulating body of the rheostat for cracks, chipped places, and dirt.
Tighten (T). Tighten carefully any part of the rheostat or potentiometer assembly found loose.
Clean (C). The rheostat or potentiometer assembly is easily cleaned
by using a soft brush and then polishing with a soft clean cloth. If
additional cleaning is needed, or if the windings show signs of corrosion or grease, the brush may be dipped in cleaning fluid and brushed
over the winding and contacts. With a clean cloth, remove the film
that remains after the cleaning fluid has evaporated. If the contact
point of the sliding arm is found burned or pitted, it is good practice to
place a piece of folded crocus cloth between the contact and the winding and then to slide the arm a number of times over the crocus cloth.
When cleaning the winding, do not exert excess pressure, or damage
will result.
Adjust (A). If the tension of the sliding contact is insufficient, an
adjustment can be made with the long -nose pliers. Slight bending of
the rotating piece in the proper direction restores the original tension.
Lubricate (L). Apply lubrication only when necessary; that is, when
binding or squeaking is noticed. One or two drops of instrument oil
applied to the bearings with a toothpick is sufficient. Since the slightest
flow of oil into the winding or the sliding-arm contact may cause
serious damage, lubrication should be applied very carefully and only
on the bearings. Wipe off all excess oil.
Terminal Boards and Connecting Panels
Little preventive maintenance is required on terminal boards and
connecting panels.
Inspect (I). Carefully inspect terminal boards for cracks, breaks,
dirt, loose connections, and loose mountings. Examine each connection
for mechanical defects, dirt, corrosion, or breakage.
Tighten (T). All clean terminals, screws, lugs, and mounting bolts
found loose should be tightened properly. Use the proper rods for the
PREVENTIVE MAINTENANCE INSTRUCTIONS
163
tightening procedure and do not overtighten or the assembly may become cracked or broken.
Clean (C). If a connection is corroded or rusty, it is necessary to
disconnect it completely. Clean each part individually and thoroughly
with cloth or crocus cloth moistened with cleaning fluid. All contact
surfaces should be immaculate for good electrical contact. Replace
and tighten the connection after it has been thoroughly cleaned.
Air Filters
Air filters are placed in blowers and ventilating ducts to remove
dust from the air drawn into and circulated through the ventilating
system. Some filters are impregnated with oil and some are filled
with cut strands of glass to facilitate the filtering action. The following procedures cover their maintenance:
Inspect (I). The filter should be inspected for any large accumulation of dirt and for lack of oil. Note whether the filter is mounted
correctly and whether the retaining clips are in place. Improperly
assembled filter elements or wall frames, allow unfiltered air to leak
around the edges and thus permit dust to enter the ventilating system.
Tighten (T). Tighten the retaining clips if they are found loose, and
readjust the filter in its mounting.
Clean (C). The filters are easily accessible and may be taken out
after removal of the cover plate. The general procedure is, as follows:
mark the outside of the filter before removing it from the air duct.
Before washing it, tap its edges against the wall or on the ground to
remove as much dirt as possible. Wash the filter in gasoline, using a
brush to remove dirt from the steel wool. After the filter has been
washed, place it face down on two supports. Allow it to drain and dry
thoroughly before lubricating.
Lubricate (L). Lubricate or recharge the filter element by dipping
it in a bath of oil. In temperatures about 20 F., use SAE -10 oil.
Allow the filter to drain thoroughly, intake side down, before it is put
into use. While the filter is draining, keep the filter away from places
where sand or dirt is being blown through the air. Always replace a
filter with its intake side facing the incoming air flow.
Cabinets
The cabinets which house the various components of the set are
generally constructed of sheet steel.
Inspect (I). The outside and inside of each cabinet must be in-
164
BROADCAST OPERATORS HANDBOOK
spected. Check the door hinges (if any), the ventilator mountings, the
panel screws, and the zero -setting of the meters. Examine the pilot
light covers for cracks and breaks. Occasionally remove the covers and
see whether the pilot light bulbs are secure in their sockets. Inspect
the control panels for loose knobs and switches.
Adjust (A). Adjust the zero -setting of meters if found to be incorrect. Follow the specific instructions given below.
Clean (C). Clean each cabinet including the control panel, outside
and in, with a clean dry cloth. Clean the meter glasses and control
knobs with a clean dry cloth.
Lubricate (L). Door hinges and latches need little lubrication, but
if inspection reveals that they are becoming dry, apply a small amount
of instrument oil. All excess oil should be removed with a clean dry
cloth.
Meters
Meters are extremely delicate instruments and must be handled very
carefully. They require very little maintenance, but, because they
are precision instruments, they cannot be repaired in the field. A
damaged meter should be replaced with a spare; a defective meter returned to the maker for repair.
Inspect (I). Inspect the leads and connections to the meter. Check
for loose, dirty, and corroded connections. Also check for cracked or
broken cases and meter glasses. Since the movement of a meter is extremely delicate, its accuracy is seriously affected if the case or glass
is broken, and dirt and water filter through. If the climate is damp,
it is only a matter of time until enough moisture seeps through a crack
to ruin the meter movement.
Tighten (T). Tighten all loose connections and screws. Any loose
meter wires should be inspected for dirt or corrosion before they are
tightened. The tightening of meter connections requires a special
technique because careless handling can easily crack the meter case.
To prevent breakage, firmly hold the hexagonal nuts beneath the connecting lugs while the outside nut is being tightened. This permits the
tightening of the connection without increasing the pressure of the
head of the stud against the inside of the meter case.
Clean (C). Meter cases are usually made of hard highly polished
Bakelite, and can be cleaned with a dry cloth. If cleaning is difficult,
the cloth should be dampened with cleaning fluid. Dirty connections
may be cleaned with a small stiff brush dipped in the cleaning fluid
PREVENTIVE MAINTENANCE INSTRUCTIONS
165
or with a small piece of cloth dipped in the solvent. It should be emphasized that solvents do not remove dirt entirely from hard surfaces.
Some of the dirt remains in a softened state and must be removed with
a damp cloth. Corroded connections are cleaned by sanding them
lightly with a very fine grate of sandpaper, such as #0000. After they
are cleaned, the connections should be wiped carefully with a clean
cloth.
Adjust (A). Normally, all meters should indicate zero when the
equipment is turned off. The procedure for setting a meter to zero
is not difficult. The tool required is a thin -blade screw driver. Before
deciding that a meter needs adjusting, tap the meter case lightly with
the tip of one finger. This helps the needle overcome the slight friction
that sometimes exists at the pointer bearings and prevents an otherwise normal unit from coming to rest at zero. If adjustment is needed,
insert the tip of the screw driver in the slotted screwhead located below
the meter glass and slowly turn the adjusting screw until the pointer
rests at zero. Observe following precautions: View the meter face
and pointer full on and not from either side. Avoid turning the zero adjust screw too far, as the meter pointer may be bent against the stop
peg or the spring may be damaged. Zero adjustments should not be
made for several minutes after shutdown.
Pilot Lights
Pilot lights are used to indicate that power has been applied to a
circuit or that a circuit is ready for power to be applied. They are
easily removed and replaced. The colored pilot light covers should
be removed carefully, lest they be dropped and broken. The maintenance of pilot lights presents no special difficulty, but the following
instructions are given for general guidance.
Inspect (I). Inspect the pilot light assembly for broken or cracked
pilot light shields; loose bulbs; bulbs with loose bases; loose mounting
screws; and loose, dirty, or corroded connections.
Tighten (T). Tighten al_ mounting screws, and resolder any loose
connections. If the connections are dirty or corroded, they should be
cleaned before they are soldered. Loose bulbs should be screwed
tightly into their bases. Broken or cracked pilot light shields may
sometimes be temporarily repaired by joining the broken or cracked
pieces with a narrow piece of friction tape. Replace them as soon as
possible; also replace broken or burned -out pilot light bulbs as soon as
possible. While the remova= of a bulb may sometimes be difficult, the
166
BROADCAST OPERATORS HANDBOOK
process is made simple by folding a small piece of friction tape over
the top of the bulb and pressing firmly from the two sides. After the
tape is attached, the bulb can be unscrewed and removed from the
socket. The socket connections are, of course, inspected while the bulb
is out. A new bulb can be replaced with the fingers, but if difficulty
is experienced, use friction tape to grip the glass envelope of the bulb.
Clean (C). The pilot light shield, the base assembly, and the glass
envelope of the light bulb should be cleaned with a clean dry cloth.
Clean accumulated dust or dirt from the interior of the socket base
with a small brush. Corroded socket contacts or connections can be
cleaned with a piece of cloth or a brush dipped in cleaning fluid. The
surfaces are then polished with a dry cloth. Clean contacts and connections are important.
Plugs and Receptacles
There are two main types of plugs and receptacles used to interconnect the various components. The first type of plug is used with a
coaxial line and consists of a metal shell with a single pin in the center
insulated from the shell. When the plug is inserted into the receptacle,
this pin is gripped firmly by a spring connector. There is a knurled
metal ring around the plug which is screwed onto the corresponding
threads on the receptacle; while the female part is in the plug. The
insulation in these plugs is much heavier in order to withstand the
voltage. The second type of plug is used for connecting multiconductor
cables. The plug usually consists of a number of pins insulated from
the shell which are inserted into a corresponding number of female
connectors in the receptacle, although in some cases the plug has the
female connectors in it and the male connectors are in the receptacle.
This type of plug usually has two small pins or buttons which are
mounted on a spring inside the shell and protrude through the shell.
When the shell is properly oriented and placed in the receptacle, one
of these pins springs up through a hole in the receptacle, firmly locking the plug and receptacle together. When it becomes necessary to
remove the plug, the other pin is simply depressed and the plug
removed. Connections between all plugs and their cables are made inside the plug shell. The cable conductor may either be soldered to the
pin or there may be a screw holding the wire to the pin. Remove the
shell if it is necessary to get at these connections for repair or inspection. Loosen the screws if there is a clamp holding the cable to the
shell. In some cases, it is found that the shell and plug body are both
PREVENTIVE MAINTENANCE INSTRUCTIONS
167
threaded; then the shell may simply be unscrewed. Usually there are
several screws holding the shell. These are removed and the shell is
pulled off.
Inspect (I). (1) The part of the cable that was inside the shell
for dirt and cracked or burned insulation.
(2) The conductor or conductors and their connection to the pins for
broken wires; bad insulation; and for dirty, corroded, broken, or loose
connections.
(3) The male or female connectors in the plug for looseness in the
insulation, damage, and for dirt or corrosion.
(4) The plug body for damage to the insulation and for dirt or corrosion.
(5) The shell for damage such as dents or cracks and for dirt or
corrosion.
(6) The receptacle for damaged or corroded connectors, cracked insulation, and proper electrical connection between the connectors and
the leads.
Tighten (T). (1) Any looseness of the connectors in the insulation,
if possible; if not, replace the plug.
(2) Any loose electrical connections. Resolder if necessary.
Clean (C). (1) The cable, using a cloth and cleaning fluid.
(2) The connectors and connections using a cloth and cleaning
fluid. Use crocus cloth to remove corrosion.
(3) The plug body and shell using a cloth and cleaning fluid, and
crocus cloth to remove corrosion.
(4) The receptacle with a cloth and cleaning fluid if necessary. Corrosion should be removed with crocus cloth.
Adjust (A). The connectors for proper contact if they are of the
spring type.
Lubricate (L). The plug and receptacle with a thin coat of Vaseline
if they are difficult to connect or remove. The type of plug with the
threaded ring may especially require this.
Part
6
TECHNICALLY SPEAKING
INTRODUCTION
As has been mentioned several times in this handbook, it is not
our purpose to duplicate or rewrite any of the already excellently
presented technical phases of radio in other books. The content of
this section is technical in nature, but is slanted primarily to allow
a clearer insight of the why and wherefore of operating procedures
as presented in the first four sections. In addition to this, there are
a number of technical matters of outstanding interest to broadcast
operators that have not previously been written in the language of the
average technician who need not necessarily be a mathematical wizard.
It is hoped that the following pages will prove helpful in presenting
an understandable picture of the field of broadcast engineering to the
operating personnel and to students of the broadcasting arts.
168
Chapter
18
CONTROL ROOM AND STUDIO EQUIPMENT
may become very complex in number
of circuits and control functions, but is designed and installed
to achieve a practical easily operated setup that allows foolproof switching and flexibility of functions. Briefly, the general requirements are as follows:
CONTEOL-ROOM EQUIPMENT
(a) Amplifiers for stepping up the minute electric energy produced in the microphone by the program sound waves.
(b) Switching and mixing arrangements to allow selection of proper
program source and blending of microphone outputs for desired
program "balance."
(c) Facilities for "auditioning" or rehearsing a program to follow.
(d) Terminations of inputs and outputs of all amplifiers on jack
panels to allow rapic "rerouting" of the signal in case of trouble
in any one amplifier or channel.
(e) Incoming and outgoing line terminations on jack panels to permit flexibility in receiving or transmitting the signal in any way
desired.
Fig. 18-1 illustrates one type of commercial control -room console which
contains all amplifiers and relays within the cabinet. The power supply comes in an external wall mounting unit. This console provides
amplifiers, control circuits, and monitoring equipment necessary to
handle two studios, announce booth microphone, two transcription
turntables, control-room announce microphone, and six remote lines.
In addition to this, means are provided for simultaneously auditioning
or broadcasting from any combination of studios, turntables, or remote
lines. The volume indicator is a standard vu meter which has an adjustable attenuator mounted on the panel to the right of the instrument allowing a 100% deflection of the pointer on the scale to be
calibrated for +4, +8, +12, and +16 vu.
The technical layout of this speech input equipment is as follows:
169
170
BROADCAST OPERATORS HANDBOOK
Four preamplifiers connected to four of the six mixers on the panel
in center position serve to amplify the outputs of the microphones.
A 3 -position key switch is in the input of the fourth preamplifier to
allow its operation from a microphone in the studio, announce booth,
Fig. 18-1. One type of commercial control -room console
containing all amplifiers and relays within the cabinet.
or control room. The outputs of the mixers connect to lever keys to
provide switching to the regular program amplifier for broadcasting
or to the monitor amplifier for auditioning. When these key switches
are operated they also serve to disconnect the studio loudspeaker to
prevent feedback, and operate "on -air" light relays. The fifth and
sixth mixers may be connected by means of push keys to any of six
remote lines or the two turntables. Other push keys on the panel provide circuits for feeding the cue to remote lines and for bringing in
monitoring circuits such as transmitter or master -control (where used)
outputs. The monitoring amplifier may be used for the program amplifier in emergencies by operating the proper key. Means are also
provided to supply power to the preamplifiers from the monitoring
amplifier in case of power supply failure to the preamplifiers.
This is an example of the extreme flexibility and emergency provisions designed into control -room equipment. Fig. 18-2 is a simplified
schematic diagram of a typical installation. The "Override -Record"
switch permits a remote operator to call in from any of the six remote
lines and override the program on the control -room speaker. The
CONTROL ROOM AND STUDIO EQUIPMENT
171
woad 9Y1WJ
¡
O,gÁe
L-
i
`
,..rN
m
FY
p.-
¢
P..
..
2
¢i..
rO O
O
RR
*Si
s,
Y00110
90.0015
111009
'NW
I
'
o
-L
1. -p.
P--Pn n
ra
<
'
t
172
BROADCAST OPERATORS HANDBOOK
"Record" position of this switch furnishes a signal source for an external recording amplifier or other destination.
Control -room equipment and layout vary over a considerable range
and variety from composite setups through regular commercial consoles and custom-built equipment. Fig. 18-3 illustrates the type of studio control consoles at WHK in Cleveland..
At WHK, each studio has its own control room. The consoles for
all the studios are identical and were built by the WHK engineering
staff. This was not done for economic reasons, but because none of the
commercially available consoles were suitable for the particular needs
at hand. Each console is set up to handle six microphones normally,
with provision to patch in as many more as needed. Each input has a
preamplifier and mixing is done at high level. All mixers in studio
control and master control at WHK are the vertical type, which may
be a surprise to some readers.
Fig. 18-3. The handles of the faders on the studio consoles at Station WHK
are vertical, making them easier to handle than rotary faders.
Vertical faders have several advantages wherever space is no consideration. More vertical faders can be handled competently with one
hand than rotary faders. The amount which a vertical fader is opened
is instantly and graphically apparent; that is, the eye can tell whether
it is 1/2, %, or 34. Regardless of how a rotary fader is marked, it takes
some concentration to determine how far open it is, provided the
knob has not turned on the shaft. Every man who ever worked at
WHK and then worked somewhere else, has agreed that the vertical
type is much easier to use, especially on large programs.
CONTROL ROOM AND STUDIO EQUIPMENT
173
In addition to the micrcphone inputs there is a high level input into
which master control can patch any desired program source. This allows smooth handling of multisource programs. As a matter of fact,
any fader may be used as a high level input by patching the program
in after the preamplifier. It is standard practice at WHK to have
every piece of equipment come out on jacks. All equipment which is
normally used together is connected through normal through jacks.
Then there is a master fader which controls the console output. The
fader system is a completa unit hooked up between the preamplifiers
and the line amplifier, and has some interesting possibilities in case
of trouble. Fig. 18-4 illus=rates the basic mixing circuit.
FROM
HIGH
PRE-AMPLS.
LEVEL
1
5
'S
'S
îi
FADER CIRCUIT
s
TO LINE
AMPLIFIER
5
Fig. 18-4. The basic mixing circuit of the fader system used in the console
shown on the opposite pagre.
K1 faders whether used for high level, microphone, or master, are
exactly alike, so that anyone can be used for any purpose. When the
top of the fader is used as an input, it deposits the program onto a bus,
minus the vu loss of the fader setting. By using the top of the fader
for an output, the program on the bus is fed to any desired place minus
the vu loss of the fader setting. The faders are all 600 ohms in and
600 ohms out. If the maser fader in the diagram of Fig. 18-4 went
out of order, any of the microphone faders not in use, or the high level
mixer, could be patched to the line amplifier and would become the
new master fader.
There are two line ampl_fiers in each console, one of which is wired
through normal jacks and one which may be patched to replace the
regular. There are two power supplies, either one of which can be
selected by a change -over switch. There is also a monitor amplifier, a
p -a amplifier with separate gain control, and a communications amplifier for talking to studio or master control. The microphone and
speaker of the communication system are mounted flush in the surface
of the console. All ampliLers are vertically mounted in the console
174
BROADCAST OPERATORS HANDBOOK
with doors which expose the tubes on one side or the bottom of the
amplifier on the other. This makes for easy servicing. Characteristics
of all equipment except the communications portion, is plus or minus
0.5 db from 30 to 15,000 cycles. For the convenience of the operator
there are six monitor buttons by means of which he can select his own
console output, master control output, final station monitor, network,
Western Electric Photo
Fig. 18-5. This type of control-room console is more
usual than that illustrated in Fig. 18-3.
and two spares into which anything else may be patched. None of
these buttons affect the on -the -air program. There is also a pilot light
system which indicates to the studio operator every place his program
is going, local station, network, audition room, executive's office, etc.
Fig. 18-5 illustrates another type of control -room console.
BROADCAST MICROPHONES
The microphone, first gateway through which all sounds are passed
on to the "mixing" network of the control console, is the most important instrument under the direct supervision of the control operator
or producer.
Much depends on the characteristics and operational interpretation
of this first link. First, it must have a wide frequency range. Highfidelity amplifiers would be useless without high-fidelity microphones.
Second, it must have very low internal noise level for the wide dynamic range necessary to please exacting listeners, and to meet engineering standards of broadcast quality transmitters and receivers.
CONTROL ROOM AND STUDIO EQUIPMENT
175
Next, it must possess a definite and dependable response pattern in
relation to angle of incidence of the sound waves so that pickup areas
may be properly defined. In broadcasting, we are concerned with
wanted and unwanted sounds, and all shades in between. Aurally
correct blending of musical and vocal sounds involves correct usage of
the microphone characteristics as much as the proper manipulation of
the mixing controls on the control panel.
Since, in nearly all installations of broadcast studios it is necessary
for the microphone to be placed a considerable distance from the preamplifier, a low output impedance is desirable. This is important since
the microphone cable possesses distributed capacitance which would seriously affect the higher frequencies if a high impedance were used. The
most common preamplifier input impedances for broadcast use are
30, 50, and 250 ohms. All microphones, regardless of type, are of the
same impedance at any given broadcast station. A ribbon microphone,
condenser, dynamic, or combination type may be plugged into the
microphone inlet without adjustment of impedance values. Output
level is very low in most high -quality microphones, ranging from about
minus 55 db to minus 90 db where the reference level is one milliwatt
for a sound pressure of 10 dynes per square centimeter. Frequency response is comparatively good over a range of 30 to 15,000 cycles. Internal noise level is well under 50 db below no signal conditions.
Microphone Fundamentals
Fig. 18-6 shows the primary function of a "pressure" type microphone such as the dynamic, condenser, or crystal type. Sound waves
SOUND FROM REAR
/
/
SOUND EFOM
FRONT
180°
CASE
Fig. 18-6. The diaphraim of the "pressure" type microphone always moves
in the same direction w,ether the sound comes from the front or rear.
BROADCAST OPERATORS HANDBOOK
176
of alternate condensations and rarefactions of air entering the microphone cause the pressure variations of the diaphragm to actuate the
moving element between the magnetic pole pieces, which in turn generates a small electric current in accordance with the sound waves.
The diaphragm always moves in the same direction regardless of the
initial direction of the sound.
Fig. 18-7 illustrates the function of the "ribbon" or "velocity" microphone. This instrument consists essentially of a thin metallic ribbon
tee
o°
DIRECTION OF
RIBBON MOVEMENT
DIRECTION OF
RIBBON MOVEMENT
Fig. 18-7. Sound coming from the front or rear (0° or 180°) of the "velocity" microphone actuates the diaphragm, but sound coming from the side
(90°) does not cause the diaphragm to vibrate.
suspended between two magnetic pole pieces without a diaphragm or
associated cavity. As the sound waves strike the ribbon from one direction, the element is caused to move since a pressure difference exists
in any sound field between any two given points. Since this differential pressure exists between the front and back of the ribbon, tie
ribbon will naturally move in the direction of diminishing prese .re.
This rate of change of pressure with distance is called "pessure
gradient" and is the principle upon which the ribbon microphone
operates. As observed from Fig. 18-7, sound approachi,'ig from the
opposite direction causes the element to move in the opposite direction
according to the pressure gradient principle. The ribbon can move only
along the axis perpendicular to its surface, and sound waves entering
from the side 90° from either "face" of the microphone cause an equal
pressure on both sides, hence zero response. ..'hus this microphone
gives the conventional "figure eight" response rattern, in comparison
CONTROL ROOM AND STUDIO EQUIPMENT
177
to the nondirectional response pattern of the strictly "pressure" type
microphone.
Fundamentally, then, we have two distinct primary principles of
microphone operation, the "pressure," or nondirectional type, and the
"pressure gradient," or bidirectional type. These two functions may
be combined to achieve a third kind of response pattern, the unidirectional microphone.
The unidirectional, or one -direction response microphone is a very
important instrument in broadcasting pickup technique. This microphone consists essentially of a dynamic and ribbon element in one
assembly. The coil and ribbon are connected in series with the wires
poled so that the outputs of the two elements cancel for sound coming
from one direction, and augment one another for sound from the other
direction. Remember that the ribbon moves in the opposite direction
from that of the coil when sound waves impinge from one direction
Fig. 18-9, below. The family of response
curves for the ribbon microphone showing how the response varies for three frequencies at different angles.
Courtesy RCA
50°
50°
60°
60°
70°
80°
90°
70°
80°
90°
RCA Photo
Fig. 18-8, above. The ribbon or velocity type of microphone.
-------
10,000
6,000
1,000
cps
cps
cps
BROADCAST OPERATORS HANDBOOK
178
which causes an equal and opposite voltage to be generated in the
output (hence zero voltage) , whereas the movements are in the same
direction for sound waves on the opposite side of the microphone.
The Ribbon Microphone
The ribbon or "velocity" microphone is one of the most popular
types of microphone used in broadcast studios. Fig. 18-8 shows a
ribbon microphone, the associated response curve is shown in Fig. 18-9.
This type of microphone is free from effects of cavity resonance, diaphragm resonance, or pressure -doubling effects since the moving element is a metallic ribbon suspended so as to vibrate freely between
the pole pieces of the magnet. This microphone, as are most modern
microphones, has a "voice" and "music" connection to achieve the
best possible frequency characteristic for either vocal or musical
pickups. The frequency -response curves for both connections are
shown in Fig. 18-10.
+15
+10
+5
V1
0
r
W'
u
5
CI
to
W
t
VOICE CONNECTION
15
\--MUSIC
20
CONNECTION
25
20
50
200
500 1000
2000
FREQUENCY-CYCLES PER SECOND
100
5000
tOK
20K
Courtesy RCA
Fig. 18-10. The ribbon microphone has a "voice" connection and one for
"music" to obtain the best response for either type. The frequency response
curves for either connection are reproduced above.
As was mentioned in the section on studio setup technique, the ribbon microphone tends to accentuate the low frequencies under close
talking conditions due to the pressure -gradient characteristic. This is
because, although the pressure is independent of frequency, the pressure gradient is not and it becomes comparatively large for points close
to the source in relation to the wavelength. For this reason, the speech
"strap" is used to equalize the low-frequency "boom" under close talk-
CONTROL ROOM AND STUDIO EQUIPMENT
179
ing conditions. When the same microphone is used for musical pickup
and announcer, the "music" connection should be used and the announcer should work two feet or more away from the face of the microphone.
Variable Pattern Microphones
Fig. 18-11 illustrates the structure of the Western Electric 639B
cardioid microphone which has provisions to provide a number of re -
Fig. 18-11. The internal structure of the
cardioid microphone which provides a
number of response patterns by means of
a six-position switch in the rear.
Courtesy Western Electric Co.
sponse patterns by a six -position switch. It consists of a spec'al ribbon
and magnet structure in combination with a dynamic unit. The housing of the dynamic structure encloses the ribbon transformer, electrical
equalizer, and selector switch. In the "cardioid" position, the ribbon
and dynamic element are used together to obtain the familiar "cardioid" or unidirectional pattern, as described in a previous paragraph. It
may also be used as a ribbon microphone only with bidirectional characteristics, and dynamic only with nondirectional response, as well as
three other combinations of response patterns.
The new RCA polydirectional microphone Type 77-D consists of a
single ribbon element and a variable acoustic network. One side of
180
BROADCAST OPERATORS HANDBOOK
the ribbon is completely closed by a connector tube coupled to what
is known as a damped pipe or labyrinth. In the connector tube directly behind the ribbon is a variable aperture which adjusts the directional characteristics of the microphone. When this opening is large,
the back of the ribbon is exposed, as is the ordinary velocity microphone, and a bidirectional response pattern is obtained. When the
aperture is completely closed, the acoustic impedance of the network
is infinite and a nondirectional pattern is achieved similar to a dynamic microphone. The opening is continuously variable thus enabling
the operator to achieve a large variety of response patterns. Fig. 18-12
is a rear view showing the slotted shaft -control adjustment, Fig. 18-13
is a front view of the ribbon assembly, and Fig. 18-14 is a rear view
of the same assembly.
RCA Photo
Figs. 18-12, 18-13, 18-14, left to right. Rear external view of the polydirectional microphone. The middle view is the front of the ribbon assembly
and the rear view is at the right.
The plate of the slotted adjustment is marked "U," "N," and "B"
for "unidirectional," "nondirectional" and "bidirectional" designations,
and three other markings are used to provide reference points for other
obtainable patterns. Fig. 18-15 gives the reader an idea of the number
of different patterns that may be obtained by the aperture adjustment
of this instrument. The bidirectional pattern is approximately that of
C, the unidirectional pattern that of G, and the nondirectional that
of J or K.
CONTROL ROOM AND STUDIO EQUIPMENT
181
The lower half of the case of the 77-D contains the associated acoustical labyrinth, the output transformer tapped at 50/250/600 ohms,
99cP
OCDCD
t
Courtesy RCA
Fig. 18-15. Various response patterns obtainable with the polydirectional
microphone.
and a selector switch for voice or music. The frequency response
curves for either connection and for "U," "N" and "B" patterns are
illustrated in Fig. 18-16 on the next page.
OUTPUT CIRCUITS AND LINE EQUALIZATION
The line amplifier at the studio is always "isolated" from the line by
a pad and a repeater coil. The necessity for this becomes apparent if
the reader visualizes what would occur if such a means of coupling was
not employed. An amplifier with an output of 600 ohms to match a
600 -ohm line, if connected directly to the line, would have its fre-
quency response materially affected by the length and characteristics
of the line itself. Due to the distributed inductance and capacitance
of the line, a different impedance would exist at every different frequency. For this reason, a pad of at least 10 -db attenuation is always
used to load the output of the amplifier, followed by what is known as
a "repeating" coil. The control -room equipment is nearly always "balanced to ground" to prevent hum pickup and cross talk, in which case
the repeat coil has a center tap to ground on both primary and secondary. When the equipment is single ended (one side grounded),
the repeat coil is single ended on the primary side and balanced on
the secondary or line side in order to provide a suitable connection of
unbalanced to balanced conditions.
BROADCAST OPERATORS HANDBOOK
182
+10
+5
i
M
V1
\v2
20
50
100
200
400 600
1000
2000
4000
FREQUENCY- CYCLES PER SECOND
6000
15K
10K
(A)
+10
+5
s
M
O
lo
15
V2
-20
50
100
200
400
600
FREQUENCY
000
- CYCLES
4000 8000
2000
PER
10K
15K
SECOND
(B1
+ so
+5
V1
15
V2
20
50
100
200
400
800
FREQUENCY
-
2000
1000
CYCLES
(
l
PER
4000 8000
10K
15K
SECOND
Courtesy RCA
Fig. 18-16. When the switch of the polydirectional microphone is set
at "U," the response curve of (A) is obtained. Response curves for
bidirectional "B" and nondirectional "N" switch settings are shown in
(B) and (C) respectively.
CONTROL ROOM AND STUDIO EQUIPMENT
183
Operators and technicians are frequently confused when looking at
the schematic diagram of the control -room installation to find a 600 ohm to 150 -ohm output pad which is intended to feed a 600 -ohm line.
This arrangement is often used, however, where the line to be fed is
comparatively short and unequalized. It should be remembered that
the capacitive effect along the line attenuates the higher frequencies.
Using a mismatch of this kind provides a beneficial equalizing effect
which tends to compensate for the characteristics of the line. This arrangement is also often used on lines that are equalized, the amount
of equalization necessary being less, with less insertion loss due to a
great amount of equalization.
Line Equalization
Although the telephone company usually equalizes the incoming network lines and regular broadcast lines from studio to transmitter, it is
many times beneficial to equalize lines from remote pickup points
where the cost of high-class line service is not practical to the station.
For this purpose most stations have an equalizer of adjustable characteristics in the control room which may be used for this purpose.
Fig. 18-17 illustrates a typical setup for equalizing a broadcast line.
The signal source is a steady tone from an audio oscillator which is
vu
V
METER
METuER
LINE
600 A
COIL
TEL. LINE
OSC.
I
LOAD
LINE
AMPL
ISOLATION
PAD
Fig. 18-17. Block diagram for a typical setup for equalizing a broadcast line.
terminated in an isolation pad. The same load at any frequency must
be presented to the volume indicator and this instrument should therefore be bridged on the oscillator side of the pad. The equalizer must
be on the line side of the coil at the receiving point, as shown in Fig.
18-17.
A 1000 -cycle tone is usually used as the reference frequency. The
BROADCAST OPERATORS HANDBOOK
184
oscillator is set at this frequency and fed to the line at 0 -vu level.
The gain of the receiving amplifier is adjusted to give 0 -vu reading
at that point. The oscillator is then adjusted to 100 cycles, 1000, 3000,
and 5000 cycles with constant level maintained at each frequency,
and the equalizer adjustment made at the receiving point to compensate as much as possible for the line characteristics at each frequency.
This will determine the approximate setting of the equalizer, after
which finer adjustments may be made over the entire frequency range.
FREQUENCY RUNS OF STUDIO EQUIPMENT
Fig. 18-18 is a simplified block diagram of a studio control-room
setup for purposes of illustrating a convenient method of running
V U
METER
LOAD
MIC
JACKS
JACKS
PR
E-AMPL
JACKS
LOW
LEVEL
AMPL.
JACKS
HIGH LEVEL
AMPL.
PROGRAM
AMPL.
VU
METER
PA
DD
/\/\./.\/
AUDIO
OSC
^^^_
Iv
.
TO
EQUIPMENT
V
Fig. 18-18. Block diagram of a studio control-room setup for running fre-
quency-response curves on the equipment.
frequency -response curves on such equipment. The over-all frequency
response is first dctermined by plugging the output pad of the audio
oscillator into the input of the preamplifier and noting the final vu
meter reading at 1000-cycles reference point. On this initial reading,
both meters are driven to 0 -vu deflection. The oscillator output level
is now held constant over the entire frequency run and the number of
vu deviation from 1000 -cycle reference jotted down on paper or plotted
on a graph. Should the frequency response not be up to par over the
entire run, the frequency run of the main program amplifier may be
made, then going back down the line until the faulty stage is made apparent by noting where the frequency response begins to deviate from
normal.
CONTROL ROOM AND STUDIO EQUIPMENT
185
NOISE AND DISTORTION MEASUREMENTS
A typical noise and distortion meter is described in Part 4 and the
appendix for use on broadcast transmitters. This equipment may be
also used on control -room equipment. The diode detector is removed
from the circuit by a switch providing a connection through a balanced
input transformer for measurements on balanced audio equipment, or
for connection to the input attenuator for use with unbalanced circuits.
The rest of the procedure is then the same as that described for transmitter measurement. The same method of isolating noise or distortionintroducing stages may be used here as described above on frequency
runs.
TELEPHONE COMPANY LINE SERVICES
Line services offered by Bell Telephone and American Telephone
and Telegraph (AT&T) are divided into two general categories:
Metropolitan Area Circuits (Bell Telephone) which provide service
for remote pickup points and studio -to -transmitter loops.
Toll Circuits (AT&T) composing the national network of circuits
and long lines outside the metropolitan area.
The metropolitan area circuits are divided into services of the following general limitations:
(a) Frequency range of 35 to 8000 cycles per second within plus
or minus 1 db of 1000 -cycle reference, and a volume range of
40 db. This service is sometimes used for studio -to-transmitter
program loops.
(b) Frequency range of 100 to 5000 cycles per second within plus
or minus 2 db and a volume range of 40 db. This is the more
common studio -to -transmitter service, and sometimes used for
remote pickup points.
(c) Nonloaded commercial telephone service and unequalized, for
use of remote pickup points.
Toll circuits are divided into general classifications such as high quality, medium -quality, and speech -only services as follows:
(a) Frequency range of 100 to 5000 cycles and volume range of
30 db. This is the normal service of national network hookups.
BROADCAST OPERATORS HANDBOOK
(b) 150 to 3700 cycles, sometimes used where not enough time was
available to install the higher quality service.
(c) Speech -only service of about 250 to 2750 cycles. Also often
used for intercommunication between long-distance points and
emergencies.
186
Chapter
19
THE BROADCAST STUDIO
high-fidelity transmission of broadcast
programs is definitely not new; it has been the goal of at least
some engineers since the earliest days of broadcasting. The
realization of over-all high-fidelity service, however, includes the receiving set in the home and it has not been until very recently that
the "average" set in the medium price market was worthy of the extraordinary efforts of some broadcasters to render high-fidelity service.
Conversely, it is apparer_t at the present time that with a good receiver,
noticeable differences in fidelity characteristics of different stations
within the range of the receiving position are observed by the critical
listener.
If the present state of development in broadcast amplifier equipment
is taken as the sole criterion, then high-fidelity transmission is truly
here. Frequency response is within 2 db of 1000-cycle reference from
30 to 15,000 cycles, and is limited only by wire -line connecting links
in amplitude -modulation (a -m) installations, or not at all in frequency -modulation (f -m) installations. Noise level at the antenna
of the transmitter is at least 60 db below 100% modulation, and dynamic range capability :s at least 40 db for a.m. and 70 db for f.m.
Unfortunately, however, the actual existence of high-fidelity depends
on many factors other than the a -f and r -f amplifiers associated with
the installation. These amplifiers, according to the ideas of some, form
the "heart" of the transmission system insofar as high fidelity is concerned. Actually, they are merely a link in the chain of necessary
functions of broadcasting a program, and are no more important to
fidelity than the other links, as Fig. 19-1 demonstrates.
In order to focus attention on the possible weak links, by eliminating the amplifiers, as such, there remain: program and talent, production technicians respons:ble for pickup technique, the studio itself,
program producers and announcers, microphones, mixing and switching
circuits, control -room, master -control and transmitter operators, wire lines, feeder systems and matching units, antennas, and the limitations
THE ENDEAVOR to realize
.
187
BROADCAST OPERATORS HANDBOOK
188
PROGRAM
&
TALENT
-0-
CONTROL
ROOM
PRODUCTION
TECHNICIAN & PICKUP TECHNIQUE
STUDIO PRODUCER
& ANNOUNCER
-0-
OPERATOR
MASTER
CONTROL
EQUIPMENT
MIXING
-0-
MICROPHONES
INPUT
MASTER
CONTROL
OPERATOR
TRANSMITTER
PHASING EQUIPMENT
MATCHING UNITS
&
ANTENNA
AND/
FEEDING
OR
SYSTEM
a.
STUDIO
SPEECH
TRANSMITTER
INPUT
SPEECH
-.-
CIRCUITS
OPERATOR
--0-
WIRE LINES
OR
R.F. LINK
RADIO
TRANSMITTER
LIMITS SET BY
CHANNEL
BANDWIDTHS
Fig. 19-1. Various links in the chain of putting a program on the air, all of
which are important in high-fidelity broadcasting.
set by channel bandwidths subject to government regulations. This
presents quite a formidable list, and each item is recognizably inferior
to the modern amplifier associated with the broadcast installation in
performance. To those familiar with broadcasting, however, it may
be shown that the weakest links and those which cause most concern
at the present time, are the studio itself, operating personnel, wirelines, and bandwidth limitations in a -m stations.
The limitations set by wire -line transmission are not serious if considered in relation to the allowable 10-kc channel of the standard
broadcast installation. Most lines are equalized to 5000 cycles which
is, theoretically, the highest frequency tolerable of any effective
strength to prevent adjacent -channel interference. On the other hand,
insofar as the relatively small primary coverage area is concerned,
the frequency range of modern a -m transmitters (10,000 cycles) if
utilized, would allow a marked improvement over present fidelity
THE BROADCAST STUDIO
189
realization, with class B and C service areas suffering from increased
cross talk and interference. Although this situation is a deplorable
one, it requires little discussion, in that the problem is primarily one
to be solved in the future actions of the FCC.
Thus, there remain two factors to be considered, studio design and
operating personnel. It is obvious that the broadcaster could possess
high-fidelity equipment from microphone to antenna and still not
provide high-fidelity service. In the final analysis, the outcome of
any program for a given equipment installation depends entirely on
thé ability of the technical staff responsible for the operating technique of the equipment. Realizable dynamic range, for instance, which
is a highly important factor in high-fidelity transmission, is rarely
utilized by station operators. It should be stated here, however, that
this is not entirely the fault of operators, but is due rather to a combination of factors including an incomplete correlation between the
philosophy of dynamic range and compression amplifiers, inadequate
visual monitoring indicators for wide dynamic range, and a confusion
of ideas existent among personnel as to the amount of dynamic range
tolerable in the home receiver for various types of program content.
With the advent of f -m transmission, this problem will become more
and more important.
Problems in Studio Design
It is often surprising to discover from
a detailed study of the sequence of steps in the development of a certain product, that an indication of a definite direction exists which might well be given the term
evolution, and which inevitably indicates a trend that reveals to the
searcher an insight into future design of that product. The history
of broadcast studio development is interesting not only from this point
of view, but also from the viewpoint of establishing the present state
of the art as it affects high-fidelity possibilities.
In general the broadcast studio must meet the following requirements:
1.
Freedom from noise, internal or external
2. Freedom from echoes
3. Diffusion of sound, providing a uniform distribution of sound
energy throughout the microphone pickup area
4. Freedom from resonance effects
5. Reverberation reduction such that excessive overlapping of suc-
190
BROADCAST OPERATORS HANDBOOK
cessive sound energy of speech articulation or music does not
occur
6. Sufficient reverberation such that emphasis of speech and musical
overtones is provided to establish a pleasing effect as judged by
the listener.
Early Studio Design
In the earliest days of broadcasting, the foremost problems encountered were quite naturally noise and echoes, since "studios" were
simply rooms of rectangular shape, with windows of conventional type
and walls of ordinary architectural construction. The first steps in
1"
J -M
SOUND
ISOLATION FELT
FURRING CHANNEL
PLASTER
J
-M
WALL ISOLATER
METAL LATHE
WOOD GROUND
WOOD SLEEPER
J
-M FLOOR CHAIR
CONCRETE FLOOR
Courtesy
Johns Manville Corp.
Fig. 19-2. The "floating studio" type of wall and floor construction.
design procedure were then taken to treat the walls acoustically to prevent echoes and "flutter," and to cover the windows with the same
acoustical material. This sufficed for a certain era in broadcasting,
provided the operator with control over echoes, and practically isolated the microphone from factory whistles, fire sirens, etc. At that
THE BROADCAST STUDIO
191
time, this type of studio was entirely adequate to satisfy the fidelity
requirements of the program transmission possible with associated
transmitting and receiving equipment; indeed the electronic amplification of broadcast programs was so much better than the acoustic model
phonograph that the general public thought of the radio as a realization of true high-fidelity reproduction.
With the advent of the dynamic loudspeaker, microphone improvements, higher power and wider band amplifiers, the scope of fidelity
possibilities began to broEden considerably. Signal-to-noise ratio was
improved, and higher volumes could be handled in the receiver without distortion, resulting in a greater dynamic-range capability, but at
the same time adding to the burden of studio design, since extraneous
noises picked up at the studio were now more noticeable in the home receiver. This fact led to the "floating studio" type of construction,
shown in Fig. 19-2.
The period following saw many phenomenal improvements in broadcast equipment in general, such as 100% modulation of the transmitter
with greatly reduced distortion, improvement in syllabic transmission
characterstics, reduction of spurious frequencies and ripple level,
greatly reduced noise levels in switching and mixing circuits, and
nonmicrophonic tubes. Yet, strangely enough, studio design remained
nearly stagnant over a period of six or seven years except in isolated
cases. Indeed, the rectargular shaped, acoustically deadened studio
may be recognized by those familiar with the state of the art today
as being the most common type of studio among independent stations,
even of very recent installation.
The broadcast engineer found himself faced with many apparent
difficulties in studios of this type of construction. The big factor, in a
room with parallel walls, is the excessive acoustical treatment necessary to overcome the effect of echoes as mentioned previously. This
has resulted, in the past, in extreme high -frequency attenuation and a
lack of "liveness" such that the brilliancy of musical programs was
completely lacking. The loudness intensity for a given meter reading
on the volume indicator is very low for a studio of this type in comparison with that obtained from a modern studio.
The effect on speech, while not satisfactory, is not so pronounced
as that on music since speech originates within a few feet of the microphone and requires less reverberation to assure naturalness, whereas
the space between the scurce of the music and the microphone is
greater, and many things happen to the musical waveforms that must
e
192
BROADCAST OPERATORS HANDBOOK
eventually be translated into perceptions of loudness. This effect obviously leads into complex operational difficulties, requiring a lower
"peaking" of voice in relation to music on the volume indicator to obtain a comparative loudness intensity in the receiver at home. Furthermore, microphone placement technique for this type studio is such
that a number of microphones must be used for a group of performers,
since, if a single microphone is employed, a lack of reinforcement
of harmonics and overtones of the instruments results in a thin sound,
lacking in body.
Another difficulty resulting from parallel -wall construction is shown
in Fig. 19-3, where it may be observed that the angle of incidence of
Fig. 19-3. The effect on a sound
wave train of parallel -wall construction resulting in undesired
resonance effects.
(M. Rettinger: Acoustics in Studios,
Proc. IRE, July, 1940. By permission of the Proc. IRE.)
the wave-fronts remains the same no matter how many such reflections
occur. Due to the acoustical treatment this reflection (to any great
extent) occurs only at the lower frequencies and it may be seen that
the nodes would have marked regions of coincident reinforcement, resulting in resonance effects at the lower frequencies, and conditions
that would result in diffuse sound distribution are reduced. Thus it
becomes obvious that items 3, 4, and 6, as given earlier in requirements for good acoustics, are lacking in studios of this design. In addition, high -frequency response so necessary to brilliancy is reduced,
effective dynamic range is inadequate, and operational difficulties are
numerous. Thus, it is apparent that the studio becomes the weakest
link in the high-fidelity chain in the great majority of broadcast installations today. Exceptions, of course, are the main network studios,
and a few independent stations more "production conscious" than the
main body of independent broadcasters. It is certainly obvious that
the contemplated large scale expansion of f -m service will bring
about the need for a revolutionary education in studio requirements
for the independent station operator.
e
THE BROADCAST STUDIO
193
Advances in Studio Design
From the foregoing discussion the difficulties to be overcome may
be listed as follows:
1. Lack of diffusion of sound
2. Resonance conditions at low frequencies
3. Insufficient reverberation for music
4. High -frequency absorption
5.
Critical and multiple microphone placement
6. Operational complexities.
The size and dimensions of the studio comprise a certain problem
in studio design since an optimum volume per musician in the studio
exists. Reduced to practice, however, this problem becomes one of
9
8
7
6
5
4
3
2
40
120
80 90 100 110
20
30 40
50 60 70
DISTANCE FROM SOUND SOURCE (FEET)
Courtesy Johns Manville Corp.
Fig. 19-4. The absorption by the air of high -frequency sound
waves varies with the frequency and the distance from the source.
simply proportioning the studio for a certain maximum number of
musicians expected. This is possible because no difficulty exists in obtaining a good pickup of a smaller group in a studio designed for a
greater number of musicians; whereas, due to the fact that a small
room cannot conveniently be "aurally" enlarged, a large band in a
small studio presents a difficult problem. Portable hard "flats" Tire
BROADCAST OPERATORS HANDBOOK
often used in large studios to enclose a small group of musicians, thus
providing the optimum dimensions required for good pickup of a given
number of performers.
High -frequency absorption, particularly frequencies of over 5000
cycles, is relatively great as indicated in Fig. 19-4. The absorption
of sound by air at these frequencies is actually greater than the surface absorptivity of the studio even under normal temperature and
relative humidity conditions. It is not possible to construct a studio
having a reverberation time of over 1.2 seconds at 10,000 cycles even
with theoretical zero absorptivity in acoustical treatment.1 This, then,
makes obvious the fact brought out before concerning optimum volume
per musician in studio design. By distributing the reflector surfaces
in proximity to the musical instruments, a maximum of diffused, poly phased high -frequency sound will exist at the microphone without
being attenuated injuriously by space in back of the instruments. A
minimum number of microphones for adequate pickup is necessary
under these conditions.
In general, modern studios are of two types. First is the live -end,
dead-end type in which the talent is placed in the live -end and microphones placed in the "microphone area" in the dead-end, thus achieving the correct reverberation of sound waves striking the microphone
without bothersome reflections from side and rear walls. This type
of studio, as shown in Fig. 19-5, has the advantage of retaining a defi194
NBC Photo
Fig. 19-5. An example of a live -end, dead-end studio.
M. Rettinger, "Acoustics in Studios," Proc. IRE, July, 1940.
THE BROADCAST STUDIO
195
nite reverberation time not influenced by the size of the studio audience in the dead-end of the studio. It has the disadvantage of limiting
the pickup to a definite area in the studio. Second is the generalpurpose type studio, consisting of uniformly distributed acoustic treatment, or panels of different type of acoustical elements to achieve a
desired condition.
Fig. 19-6 shows graphically the sound -absorbing characteristics of
three materials developed by the research department of Johns -Manville in their acoustical _aboratory. By proportioning the amount or
adjusting the orientation of these three materials in a studio, the time frequency curve will achieve any desired contour. This type of studio
90
Z 80
u
aW
70
z
z
60
\
..
1
r'
50
0
¢
§
40
g30
20
10
o
I
'
/¡
80
i
ELEMENT
ú
ó
/-****"........../a.
...,/».---.
J.M.TRIPLE TUNED
/ /Ì
/
¡
,,
. .'
J M.HIGH FREQUENCY
ELEMENT
//
./.41';"----J M.LOW FREQUENCY
E_EMENT
I
100
200
300
I
500
700 1000
200
FREQUENCY IN CYCLES PER SECOND
2.0
Fig. 19-6, above. The sound absorbing characteristics of three
acoustical materials.
After Knudsen
iiiiiï
RIMMIUMMt
S5 MMMIIIMMZ
o.--mamma
Courtesy Johns Manville Corp.
Fig. 19-7, right. Optimum reverberation time for studios cf
various sizes.
400
0.5
51 2
10000
imimmumman
...mm\I
mumumr.-e
=I¡
Tp 2048(.miGii
.BBiiCMMMMMM
m»MOM
OiiGiiiiiiiiiiiiiiiiiiiiiiiiii
INIMMIIMUMMIMMIMIUMIMME
MOIMMOMMBIRMIM
BBBBB ZWZMOM
iiiiiiiiiiiiiiiiiiiiiiiiiiiiï
MMMMMMMMMMMMMMMMMIRMIMMIMBUMMIN
N
N
t0
in
ni
.-,
N
N
oIn
O
O
O
,-I
N
e
o
o
VOLUME IN THOU SANDS
OF CUBIC
FEET
o
BROADCAST OPERATORS HANDBOOK
has the advantage of unlimited pickup area, but has the disadvantage
of being affected by size of the studio audience, since a great difference
exists in reverberation time when the studio is vacant and when it is
occupied by a large group of performers and a large studio audience.
Optimum studio reverberation time is shown in the graph of Fig. 19-7.
196
Chapter 20
SELECTING THE BROADCAST TRANSMITTER
LOCATION
CHOICE
of the broadcast transmitter site is a highly specialized
field
that usually comes under the supervision of a consulting
engineering firm. A brief outline of the factors affecting the
proper location, however, is of prime importance to thé serious broadcast employee who likes to have a comprehensive picture of operation
and engineering.
In the discussion to follow, it is necessary to keep in mind that
field -strength of a radio wave is expressed in "millivolts" or "microvolts per meter." This is a measurement of the stress produced in the
ether by the carrier wave that is equivalent to the voltage induced in
a conductor one meter in length due to the magnetic flux of the wave
sweeping across the conductor at the velocity of light. This field
strength is greatly affected by the conductivity of the soil over which
it travels. The soil conductivity is expressed in "electromagnetic units,"
abbreviated emu. This value of soil conductivity varies over a considerable range with the type of soil concerned. Values will be around
3 x 10-13 emu for most loam (good conductivity) and about 1 x 10-14
emu for dry, sandy, or rocky ground which has relatively poor conductivity.
Service Area
The "primary coverage area" of a broadcast transmitter is that area
around the towers which provides a distortionless and interference free signal. This is provided by the ground wave, which must have a
carrer -to -noise ratio of at least 18 db, and a field strength of at least
several times the strength of the sky wave at the point measured.
The so-called "secondary coverage area" is that area outside the
primary area which is supplied primarily by the sky wave. The sky
wave, of course, is subject to selective fading (due to changing heights
of the Heaviside layer) with resulting distortion effects. The sky wave
at broadcast frequencies is almost completely absorbed in the daytime,
thus a secondary service area of any appreciable extent appears only
197
BROADCAST OPERATORS HANDBOOK
198
at night. Fig. 20-1 shows how the attenuation of the sky wave varies
through the sunset period.
t
05
0.2
0.1
0.05
Fig. 20-1. The relative field intensity
increases sharply after sunset. Measurements taken at 800 kc over 560 miles
during spring.
0.02
0.01
After FCC
0.005
0.002
0.0014
3 2
BEFORE
1
0
2
3 4
AFTER
HOURS FROM SUNSET
Required Field Strength
Since the required field strength for satisfactory coverage depends
on the existing interference level, the value will vary with location. It
may be assumed in general that the interference level is greatest in
the industrial and business sections of metropolitan areas, less in the
residential areas, and still less in rural areas.
TABLE
1
PRIMARY SERVICE
Field Intensity
Ground-Wave
Area:
City business or factory areas
City residential areas
Rural-all areas during winter or northern areas during
summer
Rural-southern areas during summer
10 to 50 my/m
2 to 10 mv/rn
0.1 to 0.5 my/m
0.25 to 1.0 my/m
-From FCC Standards
Table 1 shows the approxmate field strengths necessary to render
adequate service (for primary area) under various conditions. In
SELECTING THE TRANSMITTER LOCATION
199
some locations where conditions are more favorable than average,
primary service may be obtained with somewhat weaker field strength
than those indicated, and, of course, coverage of an intermittent na MILES FROM ANTENNA
.5
.1
1,000
.7
2
1
3
5
7
10
500
300
100
50
30
5000
WATER
10
30
10
6
3
ce
w
r
w
î
¢
a
.5
.3
a
1-
J
O
>
-
I
1
.05
.03
.01
.005
.003
.001
.0005
.0003
.000110
20
30
50
70
100
MILES
FROM
200 300
ANTENNA
500 700 1000
After FCC
The conductivity of the soil has
tion of the broadcast signal.
I+ig. 20-2.
a
great effect on the attenua-
BROADCAST OPERATORS HANDBOOK
200
TABLE 2
PROTECTED SERVICE CONTOURS AND PERMISSIBLE INTERFERENCE
SIGNALS FOR BROADCAST STATIONS
Class of
class of Channel
Used
Station
Signal Intensity Contour of
Area Protected From ObPermissible
jectionable Interference'
Power
Day3
Ia
Clear
50 kw
lb
Clear
10 kw
II
Clear
0.25 kw to
50 kw
500
kw to
5 kw
500
to
50 kw
SC 100
AC 500
SC 100
AC 500
uv/m
Regional
III-B
Regional 0.5 to 1 kw 500 uv/m
night and
5 kw
day
500 uv/m
Locale
0.1 kw to
0.25 kw
IV
wave)
2500 uv/me
Day3
2500
uv/m
Night'
5
uv/m Not du -
5
uv/m
plicated
25
uv/m
25 uv/m 125 uv/me
(ground
wave)
III-A
1
Night
uv/m Not duplicated
uv/m
uv/m 500 uv/m
uv/m
(50% sky
uv/m
Permissible Interfering Signal on
Same Channels
25
uv/m
125
uv/m
25
uv/m
200
uv/m
25 uv/m 200
uv/m
(ground
wave)
4000 uv/m
(ground
wave)
400
uv/m
(ground
wave)
1 When it is shown that primary service is rendered by any of the above classes
of stations, beyond the normally protected contour, and when primary service to
approximately 90 per cent of the population (population served with adequate signal)
of the area between the normally protected contour and the contour to which such
station actually serves, is not supplied by any other station or stations, the contour
to which protection may be afforded in such cases will be determined from the individual merits of the case under consideration. When a station is already limited
by interference from other stations to a contour of higher value than that normally
protected for its class, this contour shall be the established standard for such station
with respect to interference from all other stations.
2 For
adjacent channels see Table 3.
' Ground wave.
' Sky wave field intensity for 10 percent or more of the time.
6 These
values are with respect to interference from all stations except Class Ib,
which stations may cause interference to a field intensity contour of higher value.
However, it is recommended that Class II stations be so located that the interference received from Class Ib stations will not exceed these values. If the Class II
stations are limited by Class Ib stations to higher values, then such values shall be
the established standard with respect to protection from all other stations.
e Class IV stations may also be assigned to regional channels according to section 3.29.
SC = Same channel.
AC = Adjacent channel.
SELECTING THE TRANSMITTER LOCATION
201
ture prevails at times in localities where an hour -to -hour variation of
interference intensity occurs.
Approval of a transmitter site by the FCC must entail an application which includes a map showing the 250-, 25-, and 5-mv/m contours and the population residing in the 250-mv/m contour (the socalled "blanket area") . This map also indicates by symbols the
character of each area (business, manufacturing, residential, etc.),
heights of tallest buildings or other obstructions, density and distribution of population, and location of airports and airways. The field strength contours which would be produced by a transmitter at any
particular location, the population within each contour, and the areas
where the signal might be subject to nighttime fading and interference,
are the determining factors in choosing the most favorable site. For
this reason, propagation data that permit prediction of signal attenuation in all directions from a proposed location are of prime importance
to the engineer.
TABLE 3
ADJACENT CHANNEL INTERFERENCE
Maximum Ground Wave
Field Intensity of
Undesired Station
Channel separation between desired and undesired
stations:
10 kc.
20 kc.
30 kc.
0.25 my/m
5.0 my/m
25.0 my/m
-From FCC
Standards
Ground Wave Propagation Data
The primary service area resulting from a transmitter of given
frequency and power depends upon earth conductivity and directivity
of the antenna system. The graph of Fig. 20-2 illustrates the effect of
soil conductivity on signal attenuation. This type of graph is published by the FCC in blocks of frequencies as shown, some 20 graphs
being required to cover the broadcast -band assignments. They show
the ground -wave field intensity curve plotted against distance for
various conductivity values.
Fig. 20-3 is a map of the approximate and average soil conductivity
values for the United States. The protected service contours and permis'ihle interference signals on the same channel for various classes
202
BROADCAST OPERATORS HANDBOOK
SELECTING THE. TRANSMITTER LOCATION
203
of broadcast stations are shown in Table 2. Permissible interference
levels for adjacent channels is shown in Table 3.
The above curves and tables form the nucleus for gaining necessary
information concerning the proposed transmitter site as follows:
Using the Propagation Data
Assume that it is desired to locate a 5 -kw class
2 station on 980 kc,
-kw power on 990 kc. It is necessary to determine the amount of interference caused by the proposed
station to the established 1 -kw 990-kc transmitter. Assume also that
both stations use nondirectional antennas of such height as to produce
an effective field (for 1 kw) of 175 my/m. Assume further that they
are located so that observation of the map of Fig. 20-3 shows an estimated ground conductivity of 6 x 10-14 emu. Looking up the required protection to class II during the daytime in Table 2, it may be
seen that the protection is to the 500 µv/m contour. The curves of
Fig. 20-2 are plotted for 100 my/m at a mile; therefore, to find the
175 miles from a class 2 station of
1
5
2
-
,,
INVERSE DISTANCE
100 MV/M AT ONE MILE
-
.05
02
F
ELD INTENSITY
EXCEEDED 5 % OF THE
TIME
.01
-
`,®
,e
A05
.002
001
005
\®
0002
%urn
0
200 400
600
800 1000
1200
1400 1600 1800 2000 2200 2400 2600 2800
MILES
After FCC
Fig. 20-4. Average sky -wave field intensity, corresponding to the second
hour after sunset at the recording station.
BROADCAST OPERATORS HANDBOOK
distance to the 500 p.v/m contour of the 1 -kw station we must determine the distance on the appropriate curve to the
204
100 X 500
175
285
285 µv/m contour. Now, by using the graph of Fig. 20-2 and the
curve marked 6 (for 6 x 10-14 emu) it is found that the service area
(estimated) of the 1 -kw station is about 40 miles. Since 175 40
135, we have 135 miles for the interfering signal of the 5 -kw station to
travel. Again using the appropriate curve of Fig. 20-2, it is found that
the signal from the 5 -kw station at 135 miles would be 62.5 p.v/m.
Since the stations are separated by 10 kc, the interfering signal may
have a value up to 250 µv/m allowable by the FCC, as shown in Table
-
=
3.
The principles as outlined above are not used when the sky wave of
the interfering station is in excess of 5 times the established signal for
10% ormore of the time (with frequency separation of 10 kc) When
this condition prevails, the interference must be estimated on the basis
of the sky wave also, and the propagation curve of Fig. 20-4 for sky
wave signals must be considered.
.
Other Factors
Other considerations than effective conductivity of the area surrounding the proposed site must be taken into account. Following
are excerpts from the FCC Standards of Good Engineering Practice
which outline these extra factors:
As a guide, the Engineering Department has established certain engineering principles based on the extensive experience of the Engineering Department and all data available along this line, including those
presented at the informal engineering hearings of October 5, 1936,
January 18, 1937, and June 6, 1938.
The four primary objectives to be obtained in the selection of a site
for a transmitter of a broadcast station are as follows:
To serve adequately the center of population in which the studio
is located and to give maximum coverage to adjacent areas.
2. To cause and experience minimum interference to and from other
stations.
1.
SELECTING THE TRANSMITTER LOCATION
205
present a minimum hazard to air navigation consistent with
objectives I. and 2.
4. To fulfill certain other requirements given below.
3. To
TABLE A
Power of
Station
100 watts
100 watts
250-500 watts
250-500 watts
1 kilowatt
1 kilowatt
5-10 kilowatts
25-50 kilowatts
Population of
City or
Metropolitan
Areal
5,000-50,000
50,000 or more
5,000-150,000
150,000 or more
5,000 to 200,000
200,000 or more
All
All
Approximate
Radius of
Blanket
Area 250
my/m'
Miles
0.15
0.15
0.3-0.5
0.3-0.5
0.6-0.9
0.6-0.9
1.5-2.5
3.0-4.5
SiteMaximum
Distance
Percentage
From Center
of Total
of City
Population
(Business or in Blanket
Areal
Geographical)
Miles
%2--1
(3)
Percent
1
...
1-3
1
(3)
..
2-5
.
1
...
(3)
5-10
10-15
1
1
' The total population is the population of the city sought to be served except in
those instances when the station is to be located in an area classified by the Department of Commerce, Bureau of Census, as a metropolitan area, in which case
the population of the metropolitan area shall apply: Provided, however, That when
the power of the station is such that all the metropolitan area cannot be served,
the population that will actually be served shall determine. The population figures
are those determined by the latest official census and where greater population is
claimed, the burden of proof is on the applicant.
2 These radii are only approximate and the actual blanket area (area within the
250 my/m contour) may be materially different depending on the antenna employed
and other factors.
3
these instances it is usually necessary to locate the station within the city in
order to render satisfactory service throughout the city. Such sites shall be in or
near the center of the business district and under no circumstances will a site in the
residential area be approved.
I
-From
FCC Standards
Table A is offered as a general guide to be used in determining the
approximate site of broadcast transmitters.
In case the power and the population of the city are such that it
should be located at some distance from the center of the city, the approximate distance is given as well as the population of the so-called
"blanket area." The "blanket area" of a broadcast station is defined
as that area adjacent to the transmitter in which the usual broadcast
receiver would be subject to some type of interference to the reception
BROADCAST OPERATORS HANDBOOK
of other stations due to the strong signal from the station. The normal
blanket area of a broadcast station is that area lying within the 250 millivolt -per-meter contour line. The average radii of the blanket
areas for broadcast stations of the various powers are given in Table A.
In those cases where it is impossible or impractical to locate a station in accordance with the above specifications, the Commission will
give consideration to approving locations where not more than 1% of
the population (as above specified) is included within the 500 -millivolt -per -meter contour, provided the applicant submits an affidavit
setting forth the reasons why the normal specifications cannot be complied with, and further that the applicant will assume full responsibility for adjustment of any reasonable complaints arising from the
excessively strong signals of the applicant's station. Particular attention must be given to avoiding cross modulation.
In this connection, attention is invited to the fact that it has been
found very unsatisfactory to locate broadcast stations so that high
signal intensities occur in areas with overhead electric power or telephone distribution systems and sections where the wiring and plumbing are old or improperly installed. These areas are usually found in
the older or poorer sections of a city. These conditions give rise to
cross -modulation interference due to the nonlinear conductivity characteristics of contacts between wiring, plumbing, or other conductors.
This type of interference is independent of the selectivity characteristics of the receiver and normally can be eliminated only by correction of the condition causing the interference. Cross modulation tends
to increase with frequency and in some areas it has been found impossible to eliminate all sources of cross modulation, resulting in an unsatisfactory condition for both licensee and listeners.
Broadcast station transmitters will not be permitted to be located in
these areas even though the population is within the requirements of
Table A, unless the licensee assumes full responsibility for, and it appears it can adjust all complaints satisfactorily.
If the city under consideration is of irregular shape, the station is
of high power, a directional antenna system is employed, or if other
unusual conditions obtain, the table may not apply and special consideration must be given. However, the general principles set out
will still apply.
In selecting a site in the center of. a city it is usually necessary to
place the radiating system on the top of a building. This building
should be large enough to permit the installation of a satisfactory
206
SELECTING THE TRANSMITTER LOCATION
207
ground and/or counterpoise system. Great care must be taken to
avoid selecting a building surrounded by taller buildings or where
any near -by building higher than the antenna is located in the direction which it is desired to serve. Such a building will tend to cast
"radio shadows," which may materially reduce the coverage of the
station in that direction. Irrespective of the height of surrounding
buildings, the building where the antenna is located should not have a
height of approximately one -quarter wavelength. A study of antenna
systems located on buildings tends to indicate that where the building
is approximately a quarter wavelength in height, the efficiency of radiation may be materially reduced.
TABLE B
Type of Terrain
Sea water, minimum attenuation
Pastoral, low hills, rich soil, typical of Dallas,
Tex., Lincoln, Nebr., and Wolf Point, Mont ,
areas
Pastoral, low hills, rich soil, typical of Ohio and
Illinois
Flat country, marshy, densely wooded, typical
of Louisiana near Mississippi River
Pastoral, medium hills, and forestation, typical
of Maryland, Pennsylvania, New York, exclusive of mountainous territory and sea
coasts
Pastoral, medium hills, and forestation, heavy
clay soil, typical of central Virginia
Rocky soil, steep hills, typical of New England
Sandy, dry, flat, typical of coastal country
City, industrial areas, average attenuation
City, industrial areas, maximum attenuation
Absorption
InducFactor at
tivity Conductivity 50 Miles
1000 kcl
81
4.64 X 10-11
1.0
20
3 X 10-13
0.50
14
10-13
0.17
12
7.5 X 10-14
0.13
13
6 X 10-14
0.09
13
14
10
5
4 X 10-14
2 X 10-14
2 X 10-14
10-14
10-16
0.05
0.025
0.024
0.011
0.003
3
1 This figure is stated for comparison purposes in order to indicate at a glance
which values of conductivity and inductivity represent the higher absorption. This
figure is the ratio between field intensity obtained with the soil constants given and
with no absorption.
-From FCC Standards
If from Table A it is determined that a site should be selected removed from the city, there are several general conditions to be followed
in determining the exact site. The table gives the approximate dis-
208
BROADCAST OPERATORS HANDBOOK
tance from the center of the city. Three maps should be given consideration if available:
Map of the density of population and number of people by sections in the area.
2. Geographical contour map with contour intervals of 20 to 50 feet.
3. Map showing the type, nature, and depth of the soil in the area
with special reference to the condition of the moisture throughout
the year. (See Table B.)
1.
From these maps a site should be selected that is approximately the
required distance from the city, with a minimum population in the
"blanket area," and .with a minimum number of intervening hills between it and the center of the city. In general, because of ground conditions, it is better to select a site in a low area rather than on top of
a hill, and the only condition under which a site on top of a hill should
be selected is that only by this means is it possible to avoid a substantial number of hills between the site and the center of a city with
the resulting radio shadows. If a site is to be selected to serve a city
which is on a general sloping area, it is generally better to select a
site below the city than above the city.
If a compromise must be made between probable radio shadows from
intervening hills and locating the transmitter on top of a hill, it is
generally better to compromise in favor of the low area, where an efficient radiating system may be installed which will more than compensate for losses due to shadows being caused by the hills if not too
numerous or too high. Several transmitters have been located on top
of hills, but as far as data have been supplied, not a single installation
has given superior efficiency of propagation and coverage.
The ideal location of a broadcast transmitter is in a low area of
marshy or "crawfishy" soil or area, which is damp the maximum percentage of time and from which a clear view over the entire center of
population may be had and the shadow of the tall buildings in the business section of the city would be cast across the minimum residential
area.
The type and condition of the soil or earth immediately around a
site is very important. Important, to an equal extent, is the soil or
earth between the site and the principal area to be served. Sandy soil
is considered the worst type, with glacial deposits and mineral -ore
areas next. Alluvial, marshy areas, and salt -water bogs have been
found to have the least absorption of the signal. One is fortunate to
SELECTING THE TRANSMITTER LOCATION
209
have available such an area and, if not available, the next best condition must be selected.
Table B indicates the values of inductivity and conductivity which
it is recommended be used for various types of country in the absence
of surveys over the particular area involved. Naturally, values obtained from the use of these figures will be only approximate and
should, if possible, be replaced by actual measurements in the area
under consideration.
Careful consideration must be given to selecting a site so that the
number of people in the blanket area is a minimum. The last column
of Table A gives the percentage of the total population of the city
or metropolitan area that may be permitted in the blanket area. In
general, broadcast transmitters operating with approximately the same
power can be grouped in the same approximate area and thereby reduce the interference between them.
If the city is of irregular shape, it is often possible to take advantage
of this in selecting a suitable location that will give a maximum
coverage and at the same time maintain a minimum of people within
the blanket area. The maps giving the density of population will be
a key to this. The map giving the elevation by contours will be a key
to the obstructing hills between the site and city. The map of the
soil conditions will assist in determining the efficiency of the radiating
system that may be erected and the absorption of the signal encountered in the surrounding area.
Another factor to be considered is the relation of the site to airports
and airways. There are no regulations or laws with respect to distance
from airports and airways, but a distance of 3 miles from each is used
as a guide. In case a suitable location is found at less distance than
this, it may be satisfactory if the towers are suitably painted and
lighted in conformity with the requirements of the Civil Aeronautics
Administration, or if the towers are not higher than the surrounding
objects. The latter is normally considered poor engineering practice;
however, in selecting a site the local aeronautical authorities should
always be consulted if there is any question concerning erecting a
hazard to aviation, and in case of towers over 200 feet high this should
always be done. In passing on a location and antenna installation, the
Engineering Department refers each case to the Civil Aeronautics Administration for its recommendation. The action of the Administration
will be materially expedited by the district airline inspector and local
representatives of the airports and airlines forwarding their approval
BROADCAST OPERATORS HANDBOOK
or comments to the Civil Aeronautics Administration, Washington,
210
D. C.
In finally selecting the site, consideration must be given to the required space for erecting an efficient radiating system, including the
ground or counterpoise. It is the general practice to use direct grounds
consisting of a radial buried -wire system. If the area is such that it
is not possible to get such a ground system in soil that remains moist
throughout the year, it probably will be found better to erect a counterpoise. (Such a site should be selected only as a last resort.) It, like
the antenna itself, must of course be designed properly for the operating frequency and other local conditions.
While an experienced engineer can sometimes select a satisfactory
site for a 100 -watt station by inspection, it is necessary for engineers
of a higher power station to make a field -intensity survey to determine
that the site selected will be entirely satisfactory. There are several
facts that cannot be determined by inspection that make a survey very
desirable for all locations removed from the city. Often two or more
sites may be selected that appear to be of equal promise. It is only by
means of field -intensity surveys taken with a transmitter at the different sites or from measurements on the signal of near -by stations traversing the terrain involved, that the most desirable site can be determined. There are many factors regarding site efficiency that cannot be
determined by any other method.
The site selected should meet the following conditions:
minimum field intensity of 25 to 50 millivolts per meter will be
obtained over the business or factory areas of the city.
2. A minimum field intensity of 5 to 10 millivolts per meter will be
obtained over the most distant residential section.
3. The absorption of the signal is the minimum for any obtainable
sites in the area. As a guide in this respect the absorption of the
signals from other stations in that area should be followed, as
well as the results of tests on other sites.
4. The population within the blanket radius (250 my/m) does not
exceed that specified by Table A.
When making the final selection of a site, the need for a field -intensity survey to establish the exact conditions cannot be stressed too
strongly. The selection of a proper site for a broadcast station is an
important engineering problem and can only be done properly by experienced radio engineers.
1. A
SELECTING THE TRANSMITTER LOCATION
211
BROADCAST ANTENNA SYSTEMS
As was pointed out in the previous discussion of transmitter location
problems, the efficiency of service depends principally upon four
ANTENNAS FOR STANDARD
BROADCAST STATIONS
MINIMUM VERTICAL HEIGHT OF ANTENNAS
PERMITTED TO BE INSTALLED (A, B. AC)
A
CLASS IY STATIONS. OR A MINIMUM EFFECTIVE
FIELD INTENSITY OF 150 my/m. FOR I KW.
(100 WATTS, 47.5 mem 4,250 WATTS, 15 my/m)
B. CLASS)!
FIELD
C. CLASS
6I[I
STATIONS, OR A MINIMUM EFFECTIVE
OF 175 min FOR IKW
INTENSITY
I
INTENSITY
STATIONS, OR A MINIMUM EFFECTIVE FIELD
OF 225mv/m FOR IKW
C! WHERE IT IS SHOWN THAT THE
CIVIL AERONAUTICS
AUTHORITY WILL NOT APPROVE
AN ANTENNA
EXCESS OF 500 FEET AT ANY
LOCATION WITHIN THE METROPOLITAN AREA
HAVING HEIGHT IN
CONCERNED, A HEIGHT OF 500 FEET WILL BE
ACCEPTED.
0.
0.25
E
0.50 WAVELENGTH
F
0.625 WAVELENGTH
WAVELENGTH
Courtesy FCC
Fig. 20-5. Curves A, B, and C show minimum antenna height needed to
deliver the required field intensity for different class stations. Curves D, E,
and F show antenna heights for fractions of wavelengths between 500 to
1600 kc.
i..
BROADCAST OPERATORS HANDBOOK
/`
I
III
IIIIIIi
iQO
IJ/II/
á%----.
iC
\,
..,,
II:-:
I/II
i....a
/iIII
............
.---;:213:322.-1
II
/III//////
_-O
/ !iíi.i:C
I/I/Ì/j/I/j
;,!
%¡
:ï
.
,II/I///j/I/
//I/j i!i iii :.....,:
II /I//II/II/I
GIIi1/i iói!`i!
.':.:
II
..I
OP'
;.i
-17.9,-,-..r2.:.::::2,
i!1C
er.,
SELECTING THE TRANSMITTER LOCATION
213
factors: frequency of operaton, operating power, ground conductivity,
and orientation of transmitter with respect to distribution of population. A fifth factor, namely the design of the radiating system, will
also affect the over-all efficiency, especially in areas at a distance from
the particular transmitter site.
When application is made to the FCC for new, additional, or modified broadcast facilities (such as changing transmitter location), the
applicant must specify the nature of the radiating system to be employed. This system muet comply with efficiency standards adopted
by the FCC to meet the requirements of good engineering practice for
the particular class of service concerned.
To this end, the FCC has set up standards which specify a minimum
effective field intensity for any particular class of station. Fig. 20-5,
curves A, B, and C show the minimum actual physical height of antennas deemed necessary to deliver the required field intensity for the
class station involved.
Observation of these curves show the following requirements:
Curve A. Class IV stations, a minimum height of 150 feet (for frequencies 1200 kc and higher) or a minimum effective field intensity
of 150 my/m for 1 kilowatt (100 watts 47.5 my/m and 250 watts,
75
my/m).
Curve B. Class II and III stations. Minimum effective field intensity
of 175 my/m for 1 kilowatt.
Curve C. Class I stations. Minimum effective field intensity of 225
mv/m for 1 kilowatt.
Curves D, E, and F show the physical heights of the antenna for
0.25, 0.5, and 0.625 wavelengths for any frequency from 500 to 1600 kc.
Considerations in Antenna System Design
Some interesting points are involved in the design applications of
radiating systems for broadcast frequencies. Fig. 20-6 illustrates the
comparative vertical radiation patterns for antennas of 0.25, 0.311, 0.5,
and 0.625 wavelengths. Observation of this figure reveals that although an antenna of 0.625 wavelength has a large low-angle lobe, a
secondary lobe exists at a higher angle which decreases the effective
fade -free area. Fading occurs when the sky wave caused by the reflected energy meets the ground wave and tends to cancel out the
signal due to phase reversal.
It has been found in practice, for example, that the strength of the
BROADCAST OPERATORS HANDBOOK
ground wave at a given distance is increased only a few decibels by
increasing the height of the antenna from 0.125 to 0.5 wavelength, but
the effective fade -free area is greatly increased due to the reduction in
strength of the high-angle radiation producing a sky wave that re214
turns to ground close to the transmitting location. Increased directivity in the horizontal plane is the main purpose of using higher
physical wavelengths over a quarter wavelength antenna. It has been
found that an antenna of 190° or 0.53 wavelength is the most efficient
height to use where cost of such installation is warranted by conditions
involved.
An adequate ground system must be employed with the broadcast
antenna in order to obtain maximum efficiency. The FCC specifies that
where the vertical radiator is used with the base on the ground, a
ground system must be employed consisting of buried radial wires at
least one -quarter wavelength long. They require at least 90 such
radials, and recommend 120 radials of 0.35 to 0.4 wavelength spaced
3°. In case of high base voltage (such as occurs in antennas approaching 0.5 wavelength) a base screen of adequate dimensions should be
employed to prevent high dielectric losses.
Outline of Transmitter Installations
Modern broadcast transmitters come in sections with nearly all
the parts already mounted in place. Terminal boards with numbered
connections are used to provide connection to the power lines and
inter -unit connections, with wires run in raceways behind the units
or in the wiring channel along the elevated back base. Manufacturers
always furnish detailed blueprints and pictures showing wire connections to each number on each unit and recommended wire size.
Audio-frequency wires should be installed with twisted pair, leaded
covered wire, and audio grounds should be separate from power line
and r -f grounds. These precautions help to prevent background noise
in audio circuits which would result from voltage drops along common
ground wires carrying power and r -f ground currents. Audio line terminations, pads, equalizers, line amplifiers, and measuring equipment,
such as frequency monitors, modulation monitors, etc., are placed in
a rack apart from the regular transmitter, with power supply and
audio circuit wiring run in conduits and terminated at the base of the
equipment.
Before final testing can take place in a completed broadcast installation, it is necessary that a dummy antenna of the required imped-
SELECTING THE TRANSMITTER LOCATION
215
ance and power dissipation rating be available, or that the transmission lines and antenna circuits be properly adjusted so that the
power amplifier will work into its intended load.
Antenna Tuning
It is well known that the impedance
of an antenna follows conventional transmission-line theory and does not vary with frequency as
does the impedance of an ordinary tuned circuit. The reactive component of the antenna impedance varies rapidly from capacitive to inductive at each quarter wavelength point and antennas of near these
values in electrical height of the operating frequency must have accurate impedance measurements made so that tuning and feeding
methods may be devised. The reactance of the antenna must be determined since the tuning reactance required to bring the system to
resonance at the operating frequency must be equal to that value in
magnitude, but opposite in sign. The resistive component must be
determined in order to devise the coupling circuit necessary to match
the transmission line to the antenna.
Fig. 20-7. Schematic of apparatus used in one procedure of measuring antenna reactance.
One method of determining antenna reactance is shown in Fig. 20-7.
An oscillator tuned to the desired frequency is used to excite the variable inductance L and the calibrated variable capacitor C in the arrangement as illustrated. Closing switch SW/ connects the antenna
termination with the measuring elements. With the oscillator tuned to
resonance at the operating frequency as determined by minimum
plate -current indication of the oscillator tube (unity power factor),
the calibrated capacitor C is varied to the point of maximum indication of the ammeter A, indicating that the reactance of the entire cir-
216
BROADCAST OPERATORS HANDBOOK
cuit has been canceled. The capacitance at this point is noted from
the calibration and the capacitive reactance of the capacitor determined for the operating frequency as:
X° =
27rfc
ohms
SW/ is then opened and SW2 closed. The capacitor is again varied
until the series circuit is in resonance as again indicated by the ammeter. The new capacitive value is used to determine the reactance as
before. The difference between these two reactance values will be the
effective antenna reactance. The sign of the reactance is determined
by noting in which direction the capacitor was varied for the latter
operation to bring about resonance. If the capacitance was increased,
Fig. 20-8. Conventional circuit for measuring effective
resistance of antenna. The formula and the procedure
for obtaining this will be found on the opposite page.A
DRIVER
WAVEMETER
OSC.
J
SELECTING THE TRANSMITTER LOCATION
217
the antenna reactance is negative (-j) and a coil must be used to tune
the antenna system to resonance.
The resistive component of antenna impedance includes dielectric
losses, eddy -current losses in near -by objects, and radiation resistance.
The conventional circuit for measuring effective antenna resistance is
shown in Fig. 20-8, and the formula is:
RA
where
-IItIIRi
= antenna resistance
I = antenna current with the known resistance
RA
R1
short cir-
cuited
I1
= antenna current with
R1
in the circuit.
The procedure is as follows: the antenna circuit is adjusted to resonance by means of the capacitor C or inductance L, depending on the
reactance of the antenna as outlined earlier. The short-circuiting
switch is closed to remove R1 (the known resistance), and the reading
noted on the r-f milliammeter. This is I in the above formula. The
switch is then opened and a small value of the calibrated resistor inserted. This will result in a new reading Il in the formula. The antenna resistance RA is then calculated as shown. It is usual practice
to take meter readings at 5 or 6 different values of inserted resistance
and average the results.
Circuit Tests
High power should not be applied to the transmission line until the
coupling and tuning units have been adjusted to the correct characteristics by means of the oscillator as just described. High power applied
to a transmission line that may be out of correct adjustment is apt to
cause high standing waves on the line causing arc-overs, especially in
closely spaced elements of a concentric line. When the proper impedance matching has been achieved, low power is applied to the line,
and a final check made on the antenna installation by inserting an
ammeter in series with each end of the transmission line. It is usually considered a satisfactory adjustment if the two meters show an
indication within 20% of the value of the following formula:
IL
=
Go
BROADCAST OPERATORS HANDBOOK
218
where
= transmission line current in amperes
W = power in the radiator (antenna current squared X antenna
resistance)
Zo = characteristic impedance of transmission line.
IL
Before applying the power to the modulation and final stages, the
associated overload relays should be checked to assure satisfactory
operation. This may be done by applying a low d -c voltage of approximately 10 volts between the center tap and ground of the filament
transformer secondaries of the circuit tested. This will cause sufficient
overload current to flow to operate the relays.
The final stage may then be tested by applying low power to the
stage with the modulator power opened so that no power is being ap-
RCA
Photo
Fig. 20-9. Panel view of a direct-reading phase monitor
for use in directional antenna arrays, providing a continuous indication of antenna current phasing.
plied to the modulators. The tank circuit is then adjusted to resonance by the usual procedure. If everything is still normal, the high
power may then be applied. Checking of correct neutralization to assure that no spurious oscillation exists may be made by removing one
of the crystals from the spare crystal circuit so that the oscillator
SELECTING THE TRANSMITTER LOCATION
219
selector switch may be thrown to this circuit to kill the oscillator circuit with low power applied to the final stage. This should cause all
grid currents to drop to zero.
The final stage plate supply should then be opened at a convenient
point and power applied to the modulator plates and the static plate
currents adjusted by the means provided. If trouble is experienced
in bringing the static plate current down, it may be that the inverse
feedback circuit is improperly phased. This is, of course, easily determined by reversing the connections of the feedback circuit and observing the effect on the modulator plate current.
Fig. 20-9 shows a direct reading phase monitor (Type WM -30A,
RCA) for use in directional antenna arrays, which provides a convenient visual indication of antenna current phasing to the operator at
all times. The proper phase relations must be held within the tolerable
limits continually. (The schematic diagram of this instrument and
technical information pertaining to its use will be found in the Appendix.)
Factors Affecting Hum and Noise
Noise and distortion measurements as outlined in Part 4 of this
Handbook are a very important part of the transmitter personnel's
duties. Hum and noise in transmitters is most commonly traced to the
following factors:
(a) Grid excitation to the modulated amplifier
(b) Filament balancing resistors
(c) Phase balancing resistors for tubes using split filament construction of 90° phase relation to reduce effect of a -c filament supplies.
When a noise measuring meter is used, these resistors should be
adjusted to achieve minimum balance of the 60- and 120 -cycle components.
In order to achieve the lowest noise and distortion factor in a transmitter, the following points should be observed:
Correct filament and plate voltages
Sufficient grid excitation to modulated stage
Accurate neutralization
Correct grid -leak bypass capacitance on modulated stage
BOOK BIBLIOGRAPHY
(The following books contain excellent reading for the
broadcast operator and technician)
Charles A. Culver, "Musical Acoustics," P. Blakiston's Son & Company, Philadelphia, second edition, 1947.
John Mills, "Fugue in Cycles and Bels," D. Van Nostrand Company,
New York, 1935.
Creamer and Hoffman, "Radio Sound Effects," Ziff -Davis Publishing
Company, New York, 1945.
"Handbook of Sound Effects," Educational Radio Script Exchange,
United States Department of the Interior, Office of Education,
Washington, D. C.
John S. Carlile, "Production and Direction of Radio Programs."
Prentice Hall, Inc., New York, 1939.
John J. Floherty, "On the Air," Doubleday and Company, New York,
1937.
D. C. Miller, "Science of Musical Sounds," Macmillan Company,
New York, 1916.
H. F. Olson, Frank Massa, "Applied Acoustics," P. Blakiston's Son &
Company, Philadelphia, 1939.
H. F. Olson, "Elements of Acoustical Engineering," D. Van Nostrand
Company, New York, 1940.
W. T. Bartholemew, "Acoustics of Music," Prentice Hall, Inc., New
York, 1942.
Pender and Mcllwain, Engineering Handbook Series, "Electric Communication and Electronics," 3rd edition, John Wiley & Sons, Inc.,
New York, 1936.
Hoyland Bettinger, "Television Techniques," Harper and Brothers,
New York, 1947.
220
APPENDIX
RCA 96-A LIMITER AMPLIFIER
The dynamic balance of the push-pull input tubes is an important
adjustment for the limiter type amplifier, since tubes that are not
dynamically balanced will cause an audible "thump" on sudden program peaks. The following applies to the RCA Type 96-A limiting
amplifier.
Check the dynamic balance of the 6K7 input tubes as follows: after
installing 6K7's, let them heat for about 10 minutes. Turn the meter
switch on the panel to the "VI" position, the "6K7 MATCH" switch
on the chassis to "CHECK," and the "OUTPUT CONTROL" attenuator to plus 18 (wide open) . If the meter reads above the "6K7
MATCH" range on the scale, another combination of tubes must be
tried until the proper match is obtained. If the reading is within the
range, turn the "6K7 MATCH" switch to "OPERATE." This switch
must, of course, never be turned to "CHECK" during the program,
and the modulator should be turned off or disconnected during this
check. The output of the 96-A amplifier, however, must be properly
terminated.
The HUM adjustment is also on the chassis of the 96-A, and should
be checked periodically, especially after installing new input tubes.
An auxiliary amplifier of at least 60 -db gain should be used for this
check. The output of the 96-A should be fed through this auxiliary
amplifier, and checked with headphones on the output of the extra
amplifier. It will be noticed that the HUM adjusting screw may be
swung through a fairly wide arc where minimum hum occurs, and
should be adjusted in the center of this arc.
RCA DISTORTION AND NOISE METER
Description
The Type 69-C Distortion and Noise Meter was developed to supply
an accurate and reliable instrument for measuring the harmonic distortion and noise level in the output of radio transmitters, audio ampli*
Illustrations and other material furnished through the courtesy of RCA Mfg.
Co.
221
222
BROADCAST OPERATORS HANDBOOK
fiers, or modulated radio -frequency equipment of any type. Distortion
or noise measurements are read directly from the meter scale, which is
calibrated for several ranges. When used with the Type 68-A or 68-B
Low Distortion Oscillator, distortion measurements may be made at
any frequency from 50 to 8,500 cycles per second or higher with
weighting of the harmonics as indicated in the TECHNICAL SUMMARY under Frequency Range. Reliable readings as low as 0.3 percent may be made on any equipment having less than 180 degrees
phase shift throughout its frequency range. Under these conditions,
the inherent distortion in the oscillator approximates 0.1 percent
rms, which will have a negligible effect upon the distortion meter
readings. Under the worst possible phase conditions, a residual reading of approximately 0.2 percent would be obtained.
Distortion measurements may be made at frequencies down to 20
cycles per second with reasonable accuracy if the amount of distortion
to be measured is not too small. Using 1 mw in a 600 -ohm line as a
zero reference level, distortion can be measured at volume levels as
low as -17 db and noise levels may be measured as low as -75 db.
The essential elements of the 69-C Distortion and Noise Meter are
as follows:
(1) An input circuit for the essentially sinusoidal signal from the
68-A or 68-B Beat Frequency Oscillator, including a level control,
marked "CALIBRATE," and a phase -shift network comprising three
controls-coarse, medium, and fine, as shown in Fig. A-1.
(2) An input circuit for the distorted signal from the equipment
COARSE
MEDIUM
Fig. A-1. Partial schematic of the distortion and noise meter showing the
level control and the phase -shift network.
APPENDIX
223
under test. This includes a rectifier for demodulating an r -f signal
when desired, a selector switch marked "INPUT," a source of voltage
for standardizing the gain of a voltage amplifier, and three level controls-coarse, medium, and fine, as shown in Fig. A-2.
Fig. A-2. Input circuit for the distorted signal from the equipment under
test, including a rectifier, selector switch, and level controls.
(3) A push-pull amplifier stage which is used as a normal amplifier
for noise level measurements, and as a cancellation stage for distortion
measurements.
(4) A "DISTORTION -NOISE LEVEL" switch, which is used for
circuit switching and for controlling the attenuation between the pushpull amplifier stage ((3) above) and the voltage amplifier.
(5) A three-tube voltage amplifier with negative feedback. The
"GAIN" control determines the gain of this amplifier by controlling
the amount of feedback.
(6) A detector and output meter, for measuring the rms value of
signal. A small amount of bucking current is fed through this meter to
buck out the no -signal plate current of the detector. The amount of
bucking current is controlled by the "ZERO" control. Fig. A-3 iIlustrates the distortion measurement circuit.
(7) A power supply furnishing heater, plate, and screen voltages,
and the standardizing voltage mentioned in (2) above.
In making distortion measurements, the meter indicates the distortion factor-i.e., the ratio of rms total distortion to the fundamental
amplitude. This is accomplished by suppressing the fundamental frequency component of the wave in question and measuring the rms
total of the remaining components. Elimination of the fundamental
BROADCAST OPERATORS HANDBOOK
224
frequency component is accomplished by adding to the distorted wave
a sine wave of the same frequency, equal in amplitude to the fundamental component, but 180 degrees displaced in phase. This voltage is
secured from the same oscillator which supplies the signal to the equipment under test and is adjusted in amplitude and phase by the use of
AMPLITUDE
wartac
º.w[aw
a.riwc
6F8G
sit WWI
Fig. A-3. Distortion measurement circuit consisting of a detector and output meter through which a small current is fed to buck -out the no -signal
plate current of the detector.
the controls on the panel of the Distortion and Noise Meter. Distortion readings directly in per cent of the fundamental amplitude are
obtained by first adjusting the meter to read full scale (100%) with
only the sine wave input connected.
Measurements of noise levels are made by adjusting the meter for
full-scale deflection at the desired equipment output level and then removing the input signal from the equipment under test. The remaining
noise and hum is amplified until a reliable meter deflection is obtained.
The noise level is then read directly in decibels from the meter and
attenuator scales.
Installation
The power cable should be connected between the a -c receptacle of
the meter and a power supply outlet furnishing 105-125 volts, 25-60
cycles and delivering 50 watts. The power line fuse on the chassis
should be in the proper position corresponding to the applied line
voltage. Terminals for connecting the Distortion and Noise Meter
with the associated equipment are located on the rear of the chassis
with parallel -connected jacks located on the front panel.
APPENDIX
225
The pickup circuit used for modulated r -f signals must provide a
low -resistance d -c path between the r -f and ground terminals of the
distortion meter as well as low audio -frequency impedance.
These conditions will be met by the use of a small pickup coil consisting of several turns. Capacitative coupling or an antenna may be
used if a radio -frequency choke or a parallel resonant circuit is connected across the r -f and ground terminals. A low resistance, untuned
coil is the most desirable for this purpose, as it is least likely to introduce hum into the circuit or to cause frequency discrimination.
The chassis of the Distortion and Noise Meter should be well
grounded to minimize stray r-f pickup. This can be accomplished by
the use of a heavy strap or braid, as short as possible.
Operation
Distortion and noise measurements are read from the same meter,
which is calibrated to the following full scale readings:
Distortion
1%
3%
10%
30%
100%
Noise Level
-50
-40
-30
-20
-10
0
The desired meter range is selected through the meter range switch,
which is controlled by means of the large knob and scale. The desired
distortion range may be selected by rotating the knobs over the left
half of the scale. The desired noise level range may be selected by
rotating the knob over the right half of the scale.
INPUT LEVELS-For accurate distortion or noise measurements,
the input levels to the instrument should be adjusted to within the
following limits:
Modulated r -f-10 volts to 80 volts.
To determine the proper r -f input level modulate the transmitter
approximately 100 percent and set the "DISTORTION -NOISE
LEVEL" switch at "0." Adjust the input level until full-scale meter
reading is obtained with the "AMPLITUDE" control set between "0"
and "+16."
BROADCAST OPERATORS HANDBOOK
226
-2
volts to 4 volts.
Audio frequency from 68-A or 68-B oscillator
Audio frequency from equipment under test
1. Bridging input terminals or jacks (balanced)
Minimum-0.14 volts or -15 db below 1 mw on 600 -ohm line.
Maximum -9.0 volts or ±22 db above 1 mw on 600 -ohm line.
2. Audio and ground input terminals
(a) "Audio Low"-0.12 volts to 8.0 volts.
(b) "Audio High" -1.2 volts to 80 volts.
-
COUPLING METHODS-Modulated radio -frequency voltages to
be measured are obtained through inductive coupling. The pickup
coil should be designed with a low audio -frequency impedance in order
to eliminate any a -c hum component that may be picked up.
When the Distortion and Noise Meter is to be used in conjunction
with a balanced audio line having an impedance of 600 ohms or less,
a bridging transformer having an impedance of 20,000 ohms is provided. This impedance is sufficiently high to have no appreciable effect
upon the low -impedance line. The three transformer input connections
terminate in three binding posts, marked "BRIDGING," located at
the rear of the chassis, and a pair of parallel connected jacks located
on the front panel. The center tap of the transformer winding is not
grounded.
CONNECTIONS-Following are tabulated the correct connections
to be made for distortion and noise measurements under various conditions:
For Modulated Radio -Frequency Input-Connect the pickup coil
between the "R-F" and "Ground" terminals at the rear of the instrument and remove all connections from the audio terminal. Set the
"INPUT" switch to "R-F" position.
For Audio -Frequency Input Balanced Lines, Up to 600 OhmsConnect the audio line either to the "BRIDGING" terminals at the
rear or to the "BRIDGING" jacks on the front panel. The center
tap connection may be connected, left open, or grounded as desired.
Set the "INPUT" switch to "BRIDGING" position.
For Unbalanced Audio -Frequency Input(a) Below 4 volts
Connect the audio line to "LOW AUDIO" and ground binding
posts.
Set the "INPUT" switch to "LOW AUDIO."
APPENDIX
227
(b) Above 4 volts
Connect the audio line to "HI. AUDIO" and ground binding
posts.
Set the "INPUT" switch to "HI. AUDIO."
For Distortion Measurements-Connect the 250- or 500 -ohm 68-A
or B oscillator terminals to the two terminals at the rear of the distortion meter marked "OSCILLATOR," or to the pair of jacks on the
front panel marked "OSCILLATOR."
For Oscillograph Indication-When desired, a cathode-ray oscilloscope may be connected to the "CRO" binding posts to observe wave
form of distortion or noise, or to assist in balancing out the fundamental. Any circuit connected across these binding posts should have
an impedance of at least 100,000 ohms, and when an r -f field exists,
such as around a transmitter, a shielded lead should be used.
CALIBRATION-Prior to making measurements, the instrument
should be calibrated in the following manner:
Turn the power on by rotating the "CALIBRATE" control in
a clockwise direction, and wait at least five minutes to allow
voltages to stabilize.
2. With no input signal to the "OSC." binding posts or jacks and
with the "DISTORTION -NOISE LEVEL" switch at the "CALIBRATE" position, adjust the "ZERO" control for a meter reading of zero per cent (not 0 db) .
3. Set the coarse and medium "AMPLITUDE" controls to "0" positions and the "FINE" control with the pointer approximately
vertical. Also set the "DISTORTION -NOISE LEVEL" switch
to the "0" position, and the "INPUT" switch to the "CHECK"
position. Adjust the "GAIN" control for full-scale meter reading
1.
(0 db) .
NOISE LEVEL MEASUREMENTSNoise levels may be measured in either of two ways. One method
gives a result in terms of the standard zero level of the 69-C, which is
1 milliwatt in a 600 -ohm line. The other method gives a result in
decibels below some arbitrary output level of the equipment under test.
The first method is accomplished as follows:
(a) When using "LOW AUDIO" input, it is only necessary to remove input from equipment under test and adjust the "AMPLI-
BROADCAST OPERATORS HANDBOOK
228
TUDE" controls and the "DISTORTION -NOISE LEVEL"
switch until the meter reads on scale. The noise level (based
on a 600 -ohm line) is then read from the control settings and
the meter readings.
(b) When using "HI. AUDIO" input, a close approximation can be
obtained by using the above procedure and adding -20 db to
the result.
(c) When using "BRIDGING" input, a close approximation can be
obtained by using the above procedure and adding -1.5 db to
the result.
The second method, which is the most accurate, is accomplished as
follows:
Adjust the input to the device under test to obtain the output
level bèlow which it is desired to measure the noise level.
2. Adjust the "AMPLITUDE" and "DISTORTION -NOISE
LEVEL" controls to obtain a meter reading of "0" db.
3. Remove the input signal from the device under test and move
the "AMPLITUDE" and "DISTORTION -NOISE LEVEL" controls until the meter reads on the db scale. The sum of the amount
that it was necessary to move the controls and the established
meter reading denotes the noise level with respect to the original
1.
level.
-
DISTORTION MEASUREMENTS:
Audio measurements
Apply input signal from the low -distortion oscillator to the
"OSCILLATOR" input of the Distortion and Noise Meter,
place the "DISTORTION -NOISE LEVEL" switch on "CAL."
and adjust the "CALIBRATE" control for a full-scale meter
reading. This setting should remain unchanged.
2. Adjust the input to the equipment under test to the desired
level, remembering that output must be within the limits
specified in input levels above.
3. Place the "DISTORTION -NOISE LEVEL" switch on "0,"
the "INPUT" switch on appropriate position, and adjust the
"AMPLITUDE" controls for full-scale deflection of the meter.
1.
APPENDIX
229
4. Place the "DISTORTION -NOISE LEVEL" switch on "100"
and adjust the "PHASE" controls until meter reading is below
the calibrated portion of its scale. Turn the "DISTORTION NOISE LEVEL" switch to "30" and by further adjustment of
the "PHASE" and "AMPLITUDE" controls, obtain a mini-
mum meter reading, turning the "DISTORTION -NOISE
LEVEL" switch for increased sensitivity as required.
With the selector switch placed on "CAL," during distortion
measurements, the meter reading may vary with the position of the
"PHASE" controls. This is a normal characteristic resulting in an
error of not more than 10 per cent on the "70 DISTORTION" scale
indication. In order to eliminate this error, place the selector switch
on "CAL," after adjusting the phase controls for a balanced condition
and readjust the "CALIBRATE" control for a full scale meter indication. A slight readjustment of the "FINE" amplitude control will
then be necessary for the final balance.
After obtaining an exact balance, the amount of total distortion is
obtained by reading both the "meter" and "switch" scales. After a
reading has been taken, the switch should be returned to the "CAL."
position before making any adjustments to the equipment, in order to
protect the meter.
.
CIRCUIT LOADING-The output of the Type 68-A Beat Frequency Oscillator should terminate in the correct impedance in order
to secure minimum distortion of the oscillator signal. The correct
terminating impedance is indicated at each pair of output terminals.
To illustrate, an impedance of 500 ohms should be connected between
the two terminals marked 500, or an impedance of 250 ohms between
each terminal marked 500 and the center tap terminal. The Type
89-A Attenuator Panel will provide proper impedance loading.
EFFECT OF NOISE ON DISTORTION MEASUREMENTSThe Type 69-C Distortion and Noise Meter indicates the rms total
of all components of the input signal which fall within the limits of
the frequency range. The exception is the fundamental frequency
component, which is canceled by the voltage taken directly from the
oscillator. The reading of the meter will therefore include the following components:
BROADCAST OPERATORS HANDBOOK
230
Frequencies for 1,000 cycle
modulation
Component
(60 -cycle power supply)
2,000, 3,000, 4,000. .20,000, etc.
Harmonics
Modulation cross products be- 1,000 + 60 = 1,060
1,000
60 = 940
tween hum and fundamental
1,000 -F 120 = 1,120
120 = 880
1,000
1,000 ± 180 = etc.
(3) Modulation cross products be- 2,000 ± 60 = 2,060 and 1,940
2,000 ± 120 = 2,120 and 1,880
tween hum and harmonics
2,000 ± etc.
3,000 ± 60 = 3,060 and 2,940
-
3,000
3,000
4,000
(4) Hum components
(5) Noise components
±
±
±
120
=
etc.
etc.
60, 120, 180, etc.
All frequencies
The Distortion and Noise Meter sums all these quantities and thus
indicates, as per cent distortion, the ratio of the sum of all undesired
components to the fundamental frequency component. If it is desired
to determine the distortion due to the harmonic and cross -product
components alone, either of two methods may be used.
One method is to operate the equipment under test at a high output
level, which results in making the hum and noise components negligible
compared to the other components. Another method is as follows:
1. Measure distortion in the normal manner at the desired output level.
2. Measure the noise level in decibels, using the same output level as a
reference level.
3. Convert the reading in decibels to percent; for example, -40 db =
1%,
-60 db =
0.1%.
4. These values may then be substituted in
the following equation:
H=VD2-N2
where H = total harmonic and cross section distortion in percent
D = distortion percent obtained as per (1).
N = noise (in percent) obtained as per (2) and (3),
APPENDIX
231
When making distortion measurements, it should be kept in mind
that the noise level in the output of the beat frequency oscillator ap-
proximates 50 db below 1 milliwatt and is substantially independent
of the actual oscillator output voltage. While the design of the distortion meter is such that the effects of noise and distortion present in
the oscillator output tend to be canceled out, in most cases the cancellation will be more complete for the distortion than for the noise components.
Therefore, it is desirable to operate the oscillator at as high an output as practicable, thus improving the signal to noise ratio to the point
where the noise output of the oscillator (expressed in percent of signal)
is small compared to the percent distortion being measured. High
oscillator output may not always be consistent with the input voltage
requirements of the meter, but this difficulty can readily be overcome
by the use of one or two attenuator pads or the 89-B attenuator panel.
When operating the Noise and Distortion Meter at a point remote
from the oscillator, the effects of noise and distortion in the line may be
great enough to affect seriously the accuracy of the measurements.
Hence this type of operation is not recommended.
Normally, when taking measurements near 0 or 180 degrees phase
shift, a balance cannot be obtained at frequencies which are transmitted through the equipment under test with phase shifts which fall
within these narrow limits. This, however, can be overcome by inserting a capacitor in series with one of the two outside terminal connections (not the center tap) between the distortion meter and oscillator.
The value of the capacitor and the choice of which connection to use is
best decided by trial.
Maintenance
Service generally consists of replacing tubes which have become defective through usage. All tubes should be tested at regular intervals
in a tube tester.
The Distortion and Noise Meter is protected by a 1.5 -ampere fuse.
Should the clips holding this fuse become unduly heated through improper contact, the fuse will blow. Hence the holding contacts should
be free from foreign matter and hold the fuse firmly in place.
Resistance elements through constant usage, sometimes become
altered in value. This change, if sufficiently great, will affect operation
in that portion of the circuit in which the resistance element is located.
Check tube socket voltages against the values in the table below. In
BROADCAST OPERATORS HANDBOOK
e 14
trOC
Le
war
irowar
4
^
:It
Ire
e,>
º
,_
"°`",e`
ri
04
elir
`
.,cria
,ïQ..o .
aoéoyc`oo°
->
R
1
S_
410
1
£
R
¡í
eee1.
,
:
(lei
'
i
'
S R
n
c
:
:A
R
.1..(.,
J
l
.,Ï.ºÌ..IÄ
_
"
re
It
WPC
avi. ...°..
SIC
J
4.
tÿ
88887ß
LLLi1l
CZ=_
APPENDIX
233
event that the check on the tubes does not remove the cause of fault,
disconnect the Distortion and Noise Meter from its source of power.
With an ohmmeter, check through the entire equipment for continuity.
If such procedure shows the circuit to be intact, then check each
element therein with the ohmmeter and compare the resistance readings of the resistors against the corresponding resistor given in the
schematic, Fig. A-3 (A) .
In testing capacitors for open, short, and leaky circuits, it is necessary to remove one side of the capacitor under test from the circuit in
which it is connected. The probes of the ohmmeter are then placed
across the terminals of the capacitor under inspection and from the
nature of the ohmmeter deflection, the condition of the capacitor can
readily be ascertained. In the event that R55A, C8, C8A or T2 require replacement, it will be necessary to readjust R55A so that the
Low Audio response is flat within ±0.5 db from 30 cycles to 40,000
cycles, and down not more than 1 db at 45,000 cycles. Potentiometer
R55A is located underneath the chassis, on the shield.
Tube Socket Voltages
(120 -volt line, fuse in 120 -volt position)
All voltages except filament are d -c to ground, measured with a
20,000-ohm -per -volt voltmeter.
Tube
Ef
a-c
6X5G R-F Diode
6C5
6C5
6SJ7
6SJ7
6F8 -G
6X5 -G
6.3
6.3
6.3
6.3
6.3
6.0
6.3
ED
--
120
120
112
152
112
152
105
d -c out = 357, a-c pl.
VR105/30
VR150/30
Amperite 6-8.
Eag
Ek
EP#n
---
3.7
3.5
3.8
3.8
250
3.6
to pl. 600 volts rms
Ek#s
-11.5
105
255
.
. .
12.0
RCA PHASE MONITOR
APPLICATIONS
Relative Indications of Antenna -Current Amplitude and Phase
1.
The WM -30A Phase Monitor is designed primarily for remote indication of the relative amplitude and phase of antenna currents in
234
BROADCAST OPERATORS HANDBOOK
arrays employing up to three elements. It is indispensable in maintaining the correct relationships between phase and magnitude of currents in the directive array.
Measuring Phase Shift in Television I -F Circuits
Another important application of the instrument is its use in measuring the phase characteristics of television i -f circuits. This requires
the use of an i -f signal generator, two mixer stages and a variable frequency oscillator interconnected as shown in Fig. A-4. Output
Fig. A-4. Block diagram of equipment
for measuring phase
shift in television i -f
circuits.
ONAL
GEN.
from the common oscillator is fed to both mixers to beat with the input and output voltages of the circuit under test. In operation, the
beating oscillator is tuned 1 megacycle higher than the signal generator, and thus provides 1 -megacycle output voltage from each mixer.
The phase difference between the two mixer output voltages can be
measured by the Phase Monitor, and corresponds to the phase difference existing between the input and output voltages of the i -f circuit.
Fig. A-4 shows the use of 1 -megacycle i -f transformers for coupling
energy to the Phase Monitor. These transformers should have medium
Q and must be carefully tuned to the 1 -megacycle frequency to permit accurate phase measurements. The 1 -megacycle beat frequency
has been chosen arbitrarily as convenient for feeding into the Phase
Monitor. Other beat frequencies can be used but it is advisable not to
use a lower beat frequency when the signal generator and r -f oscillator
are operating at high frequencies. Also, for operation above 20 megacycles, it might be advisable to use mixer tubes which are better
adapted to the higher frequencies.
2.
DESCRIPTION
The RCA WM -30A Phase Monitor consists of a current indicating
235
APPENDIX
.
.li
r
1H
r
'.--v.V._.g
à
1---
--e
"%WV
s
I
_
Fr
=w
T
h
á$ñ'
S
4
r
M ti
$ é
>0
11,
.li
[
C'^
3s
si{
.$
e
s`
M
áª
}
áraot'
HI
i
íkia
se
iR
*Nye
--
33,
i
a
ii
L
lf
eF
7II
V
"Mel
8'^$
pp
r
1
BROADCAST OPERATORS HANDBOOK
236
panel which can mount three thermogalvanometers, and associated
fixed series and shunt resistances to provide proper termination for
three input lines. It also includes vertical and horizontal amplifiers, a
calibrated phase shifter, a blanking system and the 3 -inch cathoderay tube. A built-in power supply furnishes high and low voltages for
operation of all stages.
A1, B1, and C1, shown in the schematic, Fig. A-5, provide for connection of three r -f input transmission lines. Internal connections are
such that an antenna meter shunted by a 20 -ohm fixed resistance is
connected in series with each sampling line; the resistance of the
shunted meter is about 4 ohms. A 79-ohm plug-in resistor is provided
to terminate each 79 -ohm transmission line, but different values of
plug-in resistors can be obtained to make the termination correct for
different line impedances. While numerically the sum of the plug-in
resistor and the series resistance of the meter (4 ohms) does not equal
the termination resistance, a correction has been made in the value of
the series resistor to compensate for the shunting effect of the phase
measuring input circuit, which is connected directly across the sampling line. From the sampling lines, the inputs to the phase measuring
circuits are connected to the two "SELECTOR" switches. When the
"SELECTORS" are switched from one sampling line to another, a load
substitution is made, thereby maintaining constant loading on the lines.
The Phase Measuring Circuit
A block diagram of the phase measuring circuit is given in Fig. A-6.
As shown by the diagram, the "X" input and "Y" input voltages as
9eLAG
PHASE
MAIN
PHASE CONTROL
SHIFT
AM PL.
STAGE
INPUT
IN PHASE
SCALE SHIFT
TOWER A
CATHODE-RAY
TUBE
"PHASE
CAL!`
-\
INPUT
TOWER S
INTENSITY
BLANKING
STAGE
CONTROL
GRID
I
OUT OF
1111
HASE
\
AM PL.
IN PHASE
Fig. A-8. Block diagram of the phase monitoring circuit.
APPENDIX
237
provided by sampling lines from towers A and B, are fed through the
"SCALE SHIFT" switch to the horizontal amplifier channel "X" and
the vertical amplifier channel "Y." It should be noted that one function of the "SCALE SHIFT" switch is to reverse the "X" and "Y"
channel inputs. Input to the "X" channel is fed through a phase shifter
stage which will provide in the "X" channel a 0 -90 -degree (maximum)
phase lag behind "Y" channel depending on the setting of the main
phase control ("X -LEADS -Y") on the front panel. The blanking stages
in the "Y" channel operate to blank part of the trace at the proper instant, thus indicating the proper quadrant and, hence, the correct scale
to be read. Operation of the phase shifting and blanking stages is
described later.
In preliminary adjustment, both "SELECTOR" switches are placed
in position to select voltage from the same sampling line, thus assuring
in -phase input to both the "X" and "Y" channels. The "X -LEADS -Y"
main phase control is set on "0," to produce no phase shift. The
"PHASE CAL." control, a small compensating trimmer (C18) connected between V2 and V3 in the "X" amplifier, is adjusted if necessary, to make the over-all phase shift in the "X" amplifier identical
to that in the "Y" amplifier. C18 is controlled by a knob behind the
small door in the front panel. Then, since in-phase voltage is applied
to the input of both amplifiers, the voltages applied to the horizontal and vertical -deflection plates of the cathode-ray tube will be in phase,
producing an oblique, straight-line trace on the screen. Conventional
controls are provided for horizontal and vertical amplitude control and
for centering of the trace. If there is a phase difference between the
sampling lines to be measured, changing the "SELECTOR" switches
to these lines will then cause out -of-phase voltages to be applied to the
deflection plates of the cathode-ray tube; the phase relationship of
these voltages being identical to that existing between the "X" and
"Y" inputs under observation. At this point, a phase correction is
made in the "X" channel by means of the main phase control ("X LEADS -Y") to produce again in -phase voltages at the deflection
plates, and the amount of phase correction required is indicated
directly in degrees as the phase differences existing between the input
lines.
Inasmuch as the phase shifter stage provides for a maximum phase
shift of 90 degrees, and since it is desirable to have indications as
given by the scale on the front panel always in terms of "X" leading
"Y," provision was made for reversing the "X" and "Y" inputs for
BROADCAST OPERATORS HANDBOOK
238
cases where the phase difference between the sampling lines is greater
than 90 degrees or when the phase of the voltage in the "Y" sampling
line leads that in the "X" line. This is one function of the "SCALE
SHIFT" switch.
Another function of the "SCALE SHIFT" switch is to shift the phase
of the blanking signal 180 degrees, providing positive determination
of the quadrant in which the measured phase angle lies. Operation of
the blanking stages take place when the front panel scale check button
is pressed. A detailed description of the blanking system follows.
The Blanking Stages
As can be seen in the block diagram, Fig. A-6, when the "SCALE
SHIFT" switch is in one of its two positions, tower A feeds the "X"
channel and tower B feeds the "Y" channel. Assuming that tower A
is leading tower B by 180 degrees, that no phase shift is introduced in
the phase shifting stage, and that identical phase shift is present in
each amplifier, then voltages 180 degrees out -of-phase will be applied
to the horizontal and vertical deflection plates, and an oblique straight
line will appear on the screen as shown in Fig. A-7 (A) The slope of
.
Fig. A-7. Voltage 180 degrees out of
phase are indicated on the scope screen
by a pattern as shown at (A). When the
scale -check button is pressed, part of the
trace is blanked out and part intensified
as in (B).
(A)
(B)
the line will vary with adjustment of the gain controls, but the direction of the slope will not shift. When the scale check button is pressed,
the blanking signal applied to the control grid of the cathode-ray tube
is in phase opposition to the output of channel "Y." Thus the luminous
trace will be blanked during its excursion toward the top vertical -deflection plate, and slightly intensified during the opposite half of the
voltage cycle, when the trace is in the lower right quadrant. The visible portion of the trace, therefore, will be in the lower right quadrant of
the cathode-ray tube, as shown in Fig. A-7 (B) , indicating use of the
90 to 180 degree scale. The phase difference as indicated by the scale
pointer is then "180" degrees. However, if the "SCALE SHIFT"
switch is now placed in the other position, the voltage from tower A
APPENDIX
239
(which is leading that of tower B) will be applied to the "Y" channel.
But the blanking signal at the cathode-ray tube, will still be in phase
opposition to the tower B signal from channel "X" because the
"SCALE SHIFT" switch, in addition to reversing the "X" and "Y"
inputs, now selects output from the cathode circuit of the first blanking
stage instead of its plate circuit, thereby eliminating a 180-degree phase
shift which took place in this stage when the switch was in the normal
position. Since the inputs are reversed, the blanking will now take
place when the trace is in the lower right quadrant of the cathode-ray
tube. The visible part of the trace is, in this case, in the upper left
quadrant of the tube indicating use of the 180 to 270 degree scale on
which the pointer again indicates "180" degrees.
The Phase Shifter Stage
In the examples just cited, no phase shift has been introduced in the
phase shifter stage, and since the voltages were assumed to be exactly
in phase opposition at the "X" and "Y" inputs and also at the deflection plates, a straight line was obtained on the cathode-ray tube
screen in each case. It is well known that when the phase of sinusoidal
voltages applied to the horizontal- and vertical -deflection plates differs
by angles other than 180 degrees, a variety of elliptical patterns will be
obtained depending on the phase angle. Assume now that, in the
block diagram, tower A is leading tower B by 90 degrees. The "SCALE
SHIFT" switch is in position so that tower A feeds the "X" channel
and tower B the "Y" channel; no phase lag is being introduced by the
phase shifter stage (main phase control at "0") and initial correction
has been made for phase difference in the amplifiers by adjustment of
the "PHASE CAL." control. The voltage applied to the horizontal deflection plates, therefore, will lead by 90 degrees the voltages applied to
the vertical deflection plates, and the pattern observed on the screen
will be nearly circular. In order to measure the phase difference in
this case, it is necessary to adjust the main phase control, which will
introduce a phase lag in the "X" amplifier, until the circular pattern
becomes a straight line. The amount of phase lag introduced represents
the phase difference between the two sampling lines and is indicated
directly in degrees on the scale. The proper scale to be read ("0-90"
degrees in this case) is indicated by the quadrant (lower right) in
which the pattern appears when the scale check button is pressed. For
cases where "X" leads "Y" by an angle greater than 90 degrees, or
240
BROADCAST OPERATORS HANDBOOK
when "Y" leads "X," measurements must be made with the "SCALE
SHIFT" switch in its other position.
In making measurements, no confusion can result as to the correct
position for the "SCALE SHIFT" switch for different phase angles of
lead and lag between "X" and "Y." Usually a straight-line pattern can
be obtained for only one position of the switch. If the straight line
occurs when the phase shift introduced by the phase shifter stage is
either 0 or 90 degrees, the straight-line pattern can be obtained in
either of the two positions of the scale switch. In any event the scale check feature determines which scale should be read.
3.
INSTALLATION
Connections
The input terminals A1, B1, C1 provide for connection of three
sampling lines. The three terminals on the other side (A2, B2, 02) provide for interconnection of the Phase Monitor and the Remote Antenna Current Indicator described later. Use of the Remote Antenna
Current Indicator together with the Phase Monitor is not necessary
unless more than three antenna elements are to be monitored. Technical and mechanical data regarding the construction of various types
of sampling lines and coils is given in Section III below.
In order to obtain the best accuracy in measurements, the sampling
lines should be of equal length. If the physical layout of the antenna
array is such that this is not practical, correction factors must be applied to all phase measurements to compensate for the differences in
phase delays in the sampling lines. The correction may be estimated
if both the velocity of propagation of the particular type of sampling
line and the differences in their physical lengths are known. However,
for precise work, measurements should be made on the lines with an r -f
bridge and the exact unbalance in electrical degrees determined. Even
when the lines are cut to identical physical lengths an impedance
check should be made to prove that the lines are electrically identical.
There may be sufficient variation between samples of a given type of
line to produce phase unbalances. If unbalance exists, the lines must
be trimmed to produce electrical identity. It is important that these
lines be terminated in their characteristic impedance. This value depends of course on the type line used. A commonly used type of line
has a characteristic impedance between 75 and 80 ohms. The Phase
Monitor is supplied with a 79-ohm plug-in resistor (R4, 5 and 6) for
APPENDIX
241
each of the three inputs, and this resistor provides a termination impedance of 79 ohms. If lines.are used having other values of impedance, plug-in resistors which will provide the correct terminating impedance should be substituted for the resistors supplied.
Preliminary Adjustments
Refer to the frequency curve of Fig. A-8 and set the tuning dial
located on the left rear corner of the chassis to the number indicated
100
90
80
70
w
-1
60
u
j
ó
50
40
30
20
10
900
450
225
1000
500
250
1200
1100
600
300
550
275
1300
650
325.
1400
700
350
1500
750
375
1600
800
400
1700
850
425
1800
900
450
FREQUENCY KILOCYCLES
Fig. A-8. Phase monitor frequency vs. dial readings.
on the curve for the frequency used. Then lock the dial. Set the
range switch (S9) on top the shield box for the correct frequency range.
Replace the dust cover and connect the power cord to a 105 -125 -volt
50/60-cycle supply.
4.
OPERATION
a. Turn on the "POWER" switch, set the "X-GAIN" and "Y-
242
BROADCAST OPERATORS HANDBOOK
GAIN" controls at minimum, and the "INTENSITY" control at approximately mid -position. Focus the spot that appears on the screen,
by means of the "FOCUS" control, to obtain a sharply defined spot.
Adjust the "INTENSITY" control to produce medium brilliance.
CAUTION :.If an intense spot is allowed to remain in a fixed position, for even a short time, burning of the screen may result. The horizontal and vertical centering controls, which are located behind the
small door on the front panel, will provide for centering the spot.
b. Set the "SELECTOR -X" and the "SELECTOR -Y" each to the
same line (preferably the line indicating highest current) . Turn the
main phase control on the front panel until the scale pointer is at the
extreme left side of the scale ("0 degree"). Increase the settings of
the horizontal and vertical gain controls until a pattern of convenient
size is obtained. The settings of these controls must not be changed
after the next step is completed. The pattern obtained should be a
slanting straight line. If an ellipse appears instead, adjust the Phase
Cal. control, located behind the small door on the front panel, until the
pattern is a straight line of minimum width.
c. Change the X and Y "SELECTOR" switches to the lines between
which the phase shift is to be measured. The straight-line pattern
will probably become an ellipse. Rotate the main phase control, and
if necessary shift the "SCALE SHIFT" switch to its other position, to
obtain a straight line of minimum width. Then press the scale check
button which will cause a portion of the trace to disappear. The visible
part of the trace will then appear in one of the four quadrants of the
screen indicating which of the four scales should be read. The phase
difference of the two sampling lines is thus indicated directly in degrees. Since phase differences are always indicated in terms of "X"
leading "Y," the setting of the "SELECTOR" indicates the leading
line, i.e.; A1, B1, or C1.
Unless the amplitudes of the voltages on the "X" and "Y" channels
differ very widely, there can be no doubt in which quadrant the trace
is located. In an antenna array, the currents do not usually vary to
the extent that the straight-line pattern is so nearly horizontal or vertical that it is difficult to determine the correct quadrant.
If measurements are to be made at more than one frequency, it
will be necessary to reset the tuning dial at the rear of the chassis to
the setting specified on the calibration chart. The amplifier balancing
adjustment should be checked after any change in frequency.
If it is necessary to readjust the amplifier gain controls to maintain
APPENDIX
243
adequate pattern size during a measurement, the phase calibrating
adjusting should be checked for the new settings of the gain controls.
5.
MAINTENANCE
A schematic diagram (Fig. A-5) and a table of tube socket voltages
are included as an aid in servicing the equipment. Voltages varying
considerably from those shown is an indication of trouble in the circuit.
In general, tubes can be replaced with others of the same type without the necessity for circuit readjustment. In the event that proper
phase calibration cannot be obtained by manipulation of the Phase
Cal. control, a slight readjustment of the plate inductances (L1, 2, 3
and 4) will enable the calibration adjustment to be made. These coils
are provided with screw driver adjustments which are all accessible
from the top of the chassis.
WM-30A PHASE MONITOR
TABLE OF SOCKET VOLTAGES
Tube or Place
Plate
RCA-6AG7 output
RCA-6AC7 X channel
RCA-6AC7 Y channel
RCA-6AC7 phase shift tube.
RCA-6AC7*
RCA-6AC7**
RCA-6AB7 blanking amp
Reactor drop
RCA-2X2A
RCA-3AP1A****
250
295
295
160
380
245
330
-33
Screen
Sup.
Cathode
Fil.
300
0
165
165
160
0
0
160
0
0
9.8
2.5
2.5
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
2.5
260
160
210
0
3
0
3.3
6.3
-1100
0
1st
Anode
-960
Grid
0
0
0
0
-32
0
0
-840***
-710
Push-button normal.
Push-button depressed.
Inaccurate because of series resistance.
**** Measured with 11-megohm meter (RCA VoltOhmyst).
*
**
***
REMOTE ANTENNA-CURRENT INDICATOR
1.
DESCRIPTION
The Remote Antenna -Current Indicator is designed to give relative
indications of the currents in antenna arrays employing up to three
elements. The unit provides a means for insuring the correct current
BROADCAST OPERATORS HANDBOOK
244
relationship between elements, and hence, proper field patterns.
is furnished with a standard rack -mounting panel.
It
ANTENNA
AMMETER
ANTENNA
LI
F
SAM PL
REMOTE AMCCURR(MT
INDICATOR
COIL
PHASE METER
INPUT CIRCUIT
{
NOT SUPPLIED)
Fig. A-9. Schematic diagram of
the remote antenna -current indicator.
Each of the three current measuring circuits are wired as shown in
the schematic diagram of Fig. A-9. Resistors R4, 5, and 6 are 79 -ohm
plug-in resistors to provide the correct termination for sampling lines
having surge impedances between approximately 72 and 82 ohms.
Plug-in terminating resistors suitable for use with sampling lines
having other surge impedances can be obtained on separate order if
desired. In general, an exact line match is not necessary, and except
for critical line lengths, such as multiples of one -quarter wave, variations of as muoh as ten percent from the exact value should introduce
no appreciable error in either current or phase indications. The plug-in
resistors are located on the rear of the unit.
2.
INSTALLATION
The equipment is designed for mounting in a standard 19-inch rack.
If it is to be used in conjunction with the Phase Monitor, the Remote
Antenna -Current Indicator should be mounted either directly above or
below the monitor in order that short, direct open bus connections
can be made between the two instruments. When this is not feasible,
and distances up to 3 or 4 feet are involved, interconnections should be
made with concentric line. The capacitance per foot of the interconnecting cables should not exceed 30 p.µf. Interconnecting lines of
equal length should be used in the sampling line circuits for best accuracy in making phase measurements. Leads should be dressed away
from each other to avoid cross -coupling.
APPENDIX
245
The three line terminals at the left rear of the unit provide for connection of three sampling lines. The output terminals at the right provide for connecting the unit to three respective terminals (A2, B2, and
C2) of the Phase Monitor. If the Phase Monitor is not used, the output
terminals can be left open. Three resistors are included to simulate the
load imposed by the input circuit of the WM -30A. When the Phase
Monitor is used, these resistors should be removed.
3.
SAMPLING ADJUSTMENT
The relative advantages and disadvantages of various methods of
sampling, and the construction of suitable sampling lines and coils are
described later. Reference should be made to this, particularly if the
sampling system to be installed is intended to feed a phase monitor.
0.2 2
0.2 0
0.18
0.16
0.14
0.12
0.10
0.0 8
.W.,.
.,,
0.0 6
0.04
...i,
..,
I.
UMW
. n
0.0 2
0.2
.:
0.4
0.6
0.8
1.0
1.2
rd
Fig. A-10. Curve for determining the constant K in the formula for calculating the output voltage.
No means is provided in the equipment for adjusting the panel meter indication. The desired deflection is obtained experimentally
by varying the coupling between the sampling coil and the antenna.
246
BROADCAST OPERATORS HANDBOOK
Between 5 and 10 volts output is normally required at the output of
the sampling coil to provide sufficient excitation for the Phase Monitor
and the Remote Antenna -Current Indicator. The coil output voltage
can be estimated with reasonable accuracy when the antenna current
is known:
Output volts, E =
where:
f=
N =
I=
r =
K=
f NIrK
frequency in megacycles
number of turns
antenna current in amperes
radius of coil in inches
constant derived for distance (d) and
radius (r) as given in Fig. A-10.
For example, at a frequency of 1000 kc and with an antenna current of
4
amperes,
if
then,
= 4 inches
r = 1.5 inches
N = 54 turns
E = (1) (54) (4) (1.5) (0.04)
= 13.0 volts (approx.)
d
Slight rotation of the coil from maximum coupling will, in this case,
give the desired output voltage.
METHODS OF SAMPLING
This section is a detailed treatment of various methods of sampling,
together with their relative advantages and disadvantages as applied
to different antenna installations.
1.
USE OF TUNED CIRCUITS
a. General
The tuned sampling coil can be coupled at virtually any point along
the radiator or feed line in many installations and still pick up enough
voltage to operate the current and phase indicators. Considerations involved in locating the coil are discussed in Paragraph 3. The coil can
be made small, and if a phase meter is not used, the pickup voltage
can be conveniently varied over a limited range by slightly detuning
APPENDIX
247
the circuit, rather than by varying the degree of coupling which in
some installations presents a mechanical problem. The tuned coil has
one disadvantage for use with a phase meter. Unless the coil is kept
precisely tuned to transmitter frequency, errors will result in phase
measurements due to the reactive component in the sampling unit.
b. Location
Since the tuned circuit is more sensitive than a nonresonant loop,
care must be exercised in its location. Otherwise, misleading indications may be produced by pickup from adjacent towers or voltages
induced by other inductors in the installation. Pickup from an extraneous field will cause error in phase indication, and it may also
produce nonlinearity in current indication; therefore current indications will be in error when a change of operating conditions occurs.
Use of the RCA Sampling Kit MI -8217
In general, electrostatic shielding is essential to assure stability and
accurate indications. In the RCA Sampling Kit (MI -8217), no provision need be made for electrostatic shielding since each sampling
coil is constructed with an internal double electrostatic shield. If the
sampling equipment is to be located within a tuning house, a shield
compartment as outlined in Fig. A-11 can be constructed of copper or
copper -lined steel. For outdoor locations, the enclosure can be weatherproofed by the use of Type 306 5-3/8" ceramic bowl insulators for
powers up to 5 kilowatts and for radiators whose operating impedances are less than approximately 200 ohms at the sampling point.
For higher power, larger insulators should be employed. For 50 -kilowatt installations, where the radiator is sampled at a point of high
impedance, the clearance of the sampling coil from the antenna bus
should be increased an additional inch to prevent voltage breakdown.
In operation, the sampling coil should be carefully tuned to the
transmitter frequency. For frequencies above approximately 1000 kc,
Ll and Cl will tune to resonance. Below 1000 kc, a fixed capacitor
(Faradon Model "NF") should be connected in paralled with Cl
(across terminals 2 and 3). The values for this capacitor for several
frequencies ranging downward from 1000 kc, are given below:
100 µµf to 800 kc
200 µµf to 650 kc
300 µµf to 600 kc
400 µµf to 550 kc
c.
248
BROADCAST OPERATORS HANDBOOK
A thermogalvanometer connected across terminals 1 and 2 makes
an excellent resonance indicator. The coil should be loosely coupled to
the antenna lead or to one of the low power stages of the transmitter,
and Cl adjusted for maximum current indication and then locked securely in place. Any appreciable deviation from true resonance will
introduce error in measurements (Paragraph la).
For satisfactory results, care must be taken in the placement of the
pickup coil. A position should be chosen to eliminate magnetic coupling to all sources except the one which is to be measured. If more
than one antenna element is to be monitored, all coils should be placed
in the same relative physical location with respect to the antenna leads
to which they are coupled, otherwise an 180 -degree error may be introduced. A suggestion for mounting the sampling coil is given in Fig.
A-11, which shows the position for maximum coupling. Pickup may be
reduced by slightly rotating the coil assembly in the horizontal plane.
,...,,.
Fig. A-11. Suggestion for housing the sampling coil, showing the position
for maximum coupling.
Ninety degrees of rotation reduces the induced voltage to essentially
zero. In cases where the current in the antenna lead is too low to give
sufficient output voltage from the coil, the spacing between the coil and
the antenna lead may be decreased to increase the output. But in no
case should the clearance be less than one inch, in order that danger
from voltage surges be minimized. In extreme cases the antenna lead
can be formed into a single turn loop parallel to the turns of the pickup
coil, and the spacing reduced to approximately one inch.
APPENDIX
2.
249
NONRESONANT SHIELDED LOOP
a. An untuned pickup loop is easy to build and usually can be
fabricated on the site. Since it requires no tuning, an initial adjustment usually proves satsfactory for longer periods of time than can be
expected with a tuned pickup loop. Also, there is little danger of phase
shift being introduced in the nonresonant pickup circuit. As previously stated, phase shift in the sampling circuit can cause erroneous
indications by the phase meter.
b. The nonresonant loop must be rigidly mounted, and in cases
where it must be coupled to points of low current, the loop might be
necessarily very large to provide sufficient pickup. Since the size of
the loop limits its rigidity, it is desirable to couple it to points of relatively high current if possible, particularly in high-powered installations where high r -f voltages may be present.
c. The shielded nonresonant loop in Fig. A-12 is of single -conductor
cable which can be made rigid and rather large to provide adequate
COAXIAL LINE
FORMED INTO
LOOP
Fig. A-12. Nonresonant single -turn
loop of coaxial line which provides sufficient pickup.
CUT BACK
OUTER SHIELD AND
%T»
INSULATE FROM
"T"SECTION
SECTION
RUBBER
HOSE COUPLING
INNER CONDUCTOR
SOLDERED TO SHIELD
pickup. The shielding must be cut back at the end and taped so that
it does not short-circuit the single turn loop formed by it and the
inner conductor. This part of the loop can be effectively weatherproofed for outdoor installation by using a 1/4" copper tubing "T"
section and insulating hose couplings, as suggested in the drawing.
250
BROADCAST OPERATORS HANDBOOK
This type of loop can be pressurized along with the transmission line,
if air -dielectric lines are employed.
3.
LOCATION
a. Determining Factors
The ideal location for the sampling coil will vary with different
installations depending upon such factors as the electrical design of
the elements of the array and the feed lines, the construction of the
towers or other supports, and the power used. In high -power installations, sufficient pickup is insured at many points along either the feed
line or the antenna elements, but the problem of securing adequate
high -voltage insulation between the sampling system and the antenna
system require consideration. In low -power installations, the desired
type of sampling coil may not provide sufficient pickup unless it is
coupled to a point near a current maximum, which in some installations might be near the center of the antenna element, thus presenting
a problem in mounting and subsequent adjustment.
b. Sampling the Feeder at the Tower Base
In installations where the tower is fed at its base, sufficient current
is usually present to induce ample voltage into the sampling system.
A sampling unit which is installed at this point is easily weather-
FEINER COILED
CO PROVIDE ENOUGH
SAMPLING FIELD
BASE
CURRENT
PLING LINE
SAMPLINO UNO
Fig. A-13. Possible current distribution in half-wavelength and quarter wavelength antenna systems.
proofed and is accessible for frequent readjustment. However, a variety of stray currents are usually encountered at this point. In some
installations these stray base currents may be appreciable as compared
to the absolute antenna current of the system. For example, in a ver-
251
APPENDIX
tical halfwave antenna the capacitance of .the tower to ground across
the base insulators may draw an r -f current comparable in magnitude
to that fed into the antenna (Fig. A-13). Moreover, the stray currents at the base of the tower do not always provide accurate antenna current indications under a change in operating conditions. A decrease
in base feeder current might be indicated, for example, with an increase in absolute antenna current. Before making a sampling installation at the base of a tower or mast, it would seem advisable to determine both the magnitude of base currents and their relationship to
the absolute antenna current under different operating conditions.
c. Sampling on
the Tower Structure
A sampling system installed on the tower structure will indicate the
effective value of the antenna current. It is often difficult to determine
the absolute current in the tower; therefore, direct correlation between
the remote meter reading and the true antenna current is difficult to
achieve. An installation on the tower structure is advantageous in
that ample current is usually available for sampling, and indications
MARLINS
COIL
MOUNTED ON
TOWER
COILPLING
SAMPLING LINE
OILED ANO
TUNED TO TRANSMITTER
FREQUENCY
FEEDER
AUXILIARY
MAST
FEEDER
SAMPLIN
LINE
SAMPLING LINE
(A)
B)
Fig. A-14. Sampling near the point of maximum current in the tower.
are not influenced by base currents if the loop is located several feet
above the base. But such a system is usually costly and difficult to
install. The sampling line, which can be clamped to the tower, must
be brought across the tower base insulators. This requires the introduction of a high -impedance circuit at the base of the tower, which is
obtained in practice by forming sufficient length of the sampling line
252
BROADCAST OPERATORS HANDBOOK
into a coil that can be tuned by a shunt capacitor to the transmitter
frequency, as shown in Fig. A-14 (A) . The tuned circuit must be kept
accurately tuned to the transmitter frequency, otherwise the sampling system will of course disturb the electrical characteristics of the
antenna and will produce inaccurate phase and current relationships.
In some cases, the sampling line can be spaced from the tower by
high -voltage insulators, and brought across the base without an isolating network.
d. Sampling From an Adjacent Mast
To overcome the difficulty of bringing the sampling line across the
base of the tower the sampling coil can be mounted at the top of a
special mast erected adjacent to the antenna tower, as shown in Fig.
A-14 (B) . If the antenna tower is one -quarter wavelength at the frequency used, the sampling unit at the top of a short mast erected close
to the tower will provide ample voltage for antenna current and phase
indications. Moreover, these indications will not be influenced by stray
currents existing at the base of the tower. The sampling line can be
attached to the mast and its outer shield grounded at the base. Care
must be exercised in the location of the mast so that stray fields from
other adjacent towers do not induce appreciable current in the sampling system. The principal disadvantages in this system are mechanical.
The auxiliary mast must remain rigid under the most adverse
weather conditions to prevent variation in the spacing between the
pickup coil and the antenna tower. If the mast is laterally supported
by the tower structure the supports must be adequately insulated
from the mast, which might prove too costly in some installations. In
order to obtain the desired current in the sampling system, some provision must be made at the top of the mast for adjusting the position of
the sampling coil and perhaps its distance from the antenna tower. In
either case, where the sampling line is mounted near the antenna structure, the effect of the line on the electrical characteristics of the antenna system must be carefully considered.
4.
SAMPLING LINES
Current induced in the sampling coil by the field surrounding the
antenna or its feeder is fed by concentric transmission line to the
remote antenna -current and phase indicators. In practice, the degree
of coupling between the coil and antenna or feeder is usually adjusted
APPENDIX
253
that the pointer deflection on the scale of the antenna -current indicator is identical to that for the respective antenna ammeter. This
is described in section 3.
The sampling line can be any one of a number of types of concentric lines with surge impedances from approximately 50 to 100 ohms.
In general, open -wire lines prove unsatisfactory; if used in the vicinity of the antenna, objectionable currents will be induced in the
lines. The beaded coaxial line is an entirely satisfactory type for
sampling. This type line can be obtained with surge impedances ranging from 72 to 150 ohms. Its construction provides an efficient, low loss transfer of energy and makes it suitable for long periods of outdoor use. An ideal sampling line installation would be the use of
beaded coaxial line installed within gas -filled copper tubing. Such a
line could be depended upon to give reliable service over long periods
of time. Solid-dielectric coaxial lines have been developed which
should give long trouble -free service. They require no pressurizing.
In order that no phase shift is introduced in the sampling system,
particularly if a phase meter is used, each sampling line must be terminated in its characteristic impedance, which is nominally 79 ohms
for 1/4 inch concentric line. The terminating networks for each line
on the RCA WM -30A Phase Monitor and in the Remote Antenna Current Indicator are identical, except that when the two units are
used together the input impedance of the Phase Monitor, an effective
2000 ohms, is shunted across the output of the Remote Antenna -Current Indicator as shown in Fig. A-9. This should be considered when
calculating the correct value for the plug-in resistors (R4, R5, and R6)
of the Remote Antenna -Current Indicator. For example, assuming
that a transmission line of 70 ohms impedance is used, then the value
of plug-in resistor (R) can be determined as 68 ohms by using the
formula for d -c resistance:
so
Ziupue
=
Rm +-
R. R
R
R.
where: Ziurut = desired input resistance
Rm = resistance of the meter and its shunt (4 ohms)
= shunt resistance of Phase Monitor (2000 ohms)
Using these values and solving for R:
Rs
R
2000 Z
2004
- 8000
-Z
BROADCAST OPERATORS HANDBOOK
254%
!GI>.
e
o
0
N7
o-
ä 58
m V
m (p
Ñ
`l
2
Ñ}o .
cD
s
e
00000L*
00000!*
MM
C2.tl
JNN
Z2.tl
VOCI
UC01
06'251
V000ZZ
óortl
tl
osö
241
ó
_V000022
(34
Z1.
oopo_Q0º00
äádöObnmUrge
<
4
0206 6.N
g<
- ós
á
egg
8
8
Qm Y
.Q000400
o
2.
3
VOOOG2
O
1,0005
.--2.tl
70%T.:6%
am.
ZS
^7
vawl nr
}MNI
N
N-
Z
2
r
o
e
9
0
APPENDIX
255
As previously stated, an exact line match is unnecessary. Except
at critical line lengths, variations of as much as ten percent from the
correct load value will introduce no appreciable error in either current or phase indication. Whether any error is being introduced by
the Remote Antenna -Current Indicator can be determined by eliminating the unit from the circuit and calibrating the Phase Monitor. Any
existing error will then be indicated by the Phase Monitor when the
Remote Antenna -Current Indicator is again inserted into the circuit.
RCA LIMITING AMPLIFIER
Application
The Type 86 -Al Limiting Amplifier is intended for use in the
speech input channel of a radio transmitter to prevent overmodulation by limiting the high audio signal peaks which occasionally occur
in program material. This limitation permits a substantial increase
in the average level of modulation, and hence an increase in the effective range of the transmitter without any increase in carrier power.
The amplifier may also be used advantageously in recording.
Action of Limiter
The action of the limiter is similar to that of delayed automatic
volume control in a radio receiver. For signal levels below a specified
value, the gain in the amplifier is not affected. Above this level, however, the gain is sharply reduced, and the amount of reduction increases
with th,e strength of the signal. As a result, above the predetermined
level the output of the amplifier changes relatively little for large
changes in the input level. The electrical action of the limiter is shown
in the circuit diagram of the amplifier (Fig. A-15) . A portion of the
signal voltage across the secondary of T-2 is impressed on the grid of
the triode section of 6R7, and the resulting output of this triode is then
rectified by the two diodes of the same tube. The diode plates are
polarized negatively by a fixed amount so that the diodes do not conduct until the signal voltage exceeds the polarizing voltage.
Adjustment Controls
Several minor controls are provided in the amplifier for facilitating
restoration of balance in the circuit after tubes and other parts have
been replaced. These controls are taken up below.
a- Limited Level. The control marked LIMITED LEVEL on the
256
BROADCAST OPERATORS HANDBOOK
chassis and R-16 in the circuit diagram permits variation of the input
voltage to the control tube 6R7 when the limiting switch S-3 is in the
ON position, and in this manner allows variation in the degree of limiting. The range of variation is from about 73% to 90% of the total
signal voltage across the secondary of transformer T-2. The adjustment is effected with a screw driver through the door in the panel. The
use of this control is discussed under Maintenance.
b. Zero Adjustment. The control marked ZERO ADJ. is a 100 -ohm
potentiometer R-32 in the low potential side of the voltage divider of
the power supply. This is also adjusted with a screw driver and is
reached through the door in the panel. It serves to adjust the reading
of the gain reduction meter to 0 db when the amplifier is not limiting.
Its adjustment is discussed under Maintenance.
c. ,Hum Adjustment. This control is a 100 -ohm potentiometer R-6
in the cathode -heater circuit of the 6K7 tubes which serves to reduce
the hum to a minimum. It is reached through the door in the panel and
is adjusted with a screw driver. For further details refer to Hum Reduction in Maintenance.
d. Power Switch and Fuse. The power switch S-2 and the fuse F-1
are located at the right end of the chassis just inside the door in the
panel. When the signal is strong enough to make the diodes conduct,
capacitor C-8 charges up to a voltage which depends on the amount by
which the signal voltage exceeds the polarization voltage. The voltage
across the capacitor is then applied as bias on the control grids of the
two 6K7 tubes. The higher this bias, the less these tubes amplify.
Thus an automatic check on the gain in the amplifier is established as
soon as the signal voltage exceeds a predetermined value. The effectiveness of the limiting, for one particular setting of the controls, is
shown in Fig. A-16.
Time Constants
If overmodulation of the transmitter is to be prevented when sudden intense peaks of signal occur, the limiter circuit must respond almost instantaneously. This requires that capacitor C-8 be charged
through a low resistance and that its capacity be not excessively large.
The specified capacity of 0-8 is 0.25 µf and the resistance of the
charge circuit is virtually only that of the diodes. This combination is
such that the circuit responds in about 0.001 second, which is generally
considered fast enough.
After the gain has been depressed by a sudden strong peak, the cir-
APPENDIX
257
cuit must recover its normal amplification if signals of weak and
moderate levels are to reach the modulator with desired amplitudes.
This limiter recovers by the discharge of C-8 through resistor R-41.
For the specified values of C-8 and R-41 it requires about 2 seconds
for the circuit to recover 90% of its normal gain. A longer recovery
.-.
15
TYPE 86 -AI LIMITING AMPLIFIER
CHARACTERISTIC
LIMITING
u
/
u
u
POINT OF 3.0 DB
GAIN REDUCTION
I
M
SET
TED LEVEL' CONTR OL
FOR 0.1 DB G.R. W IT H
VU INPUT
+10
II
KX-288478
10
12
14
16
18
20
22
24
26
28
'
30
( WITH INPUT CONTROL AT +10 VU Ì
INPUT LEVEL
Fig. A-16. Effectiveness of limiting action performed by the limiting
amplifier.
time would cause noticeable loss of volume after each gain reduction,
and a much shorter recovery time might have an unfavorable effect on
the quality.
Amplifier Connections
Make all permanent connections of the amplifier to the terminal
board located at the rear of the amplifier.
a. Input Connections. The incoming signal line should be connected
to the terminals marked INPUT on the rear terminal board. These
terminals connect to terminals 1 and 13 on transformer T-1. With
this connection the input impedance is 500-600 ohms and therefore the
source impedance should have this value. If the source impedance
is 250 ohms, the input leads should be moved from terminals 1 and 13
258
BROADCAST OPERATORS HANDBOOK
to terminals 4 and 10, respectively, leaving the connection of R-1
undisturbed. The input leads should consist cf shielded and twisted
pair insulated for 200 volts. They should be kept away from all other
leads as much as practicable. In making connections to the source of
signal it should be remembered that the center of the input transformer T-1 is connected to chassis ground.
b. Output Connections. The load on the amplifier is connected to the
three terminals marked OUTPUT. When the load impedance is 500600 ohms, the two output leads (brown and black -brown) should be
left connected to the secondary of the output transformer T-3. But if
the load impedance is 250-300 ohms, the two outside leads should be
moved, respectively, from terminals 11 and 15 to terminals 12 and 14
on the output transformer. The middle of the three OUTPUT terminals is connected to the mid -point on the secondary of the transformer. When this impedance change is made, the two resistors R-45
and R-47 in the meter rectifier circuit should be short-circuited.
The output leads, like the input leads, should be shielded and twisted
pair insulated for 200 volts, and they need not be larger than No. 19
A.W.G. They should preferably go directly to the transmitter.
for the use of an exterc. External Meter. Provision has been made
the shunt on the
meter,
this
installing
In
nal gain reduction meter.
meter should be
and
the
removed
be
terminals marked METER should
The center
marking.
the
above
directly
connected to the terminals
terminal is negative.
Setting Up
After the input, output, and power connections have been made to
the amplifier, set the input and output controls to the approximate
levels to be used. Turn the meter switch to GR and impress a 200- to
2000 -cycle sine -wave signal of constant amplitude on the amplifier.
Use the LIMITED LEVEL control as a vernier on the OUTPUT
CONTROL to obtain the exact maximum modulator input level
when the meter shows a gain reduction of approximately 3 db. If the
LIMITED LEVEL control does not have sufficient range to bring
this about, readjust the input by the required amount. When this adjustment has been effected, the gain reduction in the amplifier is determined by the input signal level and by the setting of the INPUT control, as well as by the dynamic range and character of the signal
material. The INPUT control provides for changes in 2 db steps. If
the program limiting requires closer adjustment, it should be done with
APPENDIX
259
a continuous control in the channel preceding the Type 86 -Al am-
plifier.
The average reduction should not exceed about 3 db. This corresponds to a condition in which the meter needle normally stands at or
near 0 db gain reduction and only intermittently kicks to 3 db gain
reduction. In estimating the momentary gain reduction it should
be remembered that the meter needle tends to overshoot slightly.
When the system has been adjusted in this manner, momentary
overmodulation may occur on strong signal peaks. However, the
periods of overmodulation will be exceedingly short and will not give
rise to noticeable distortion or interference with other channels. They
will occur during the initial period of a gain reduction and during
periods of rapid change in the signal level.
Adjustment for Line Voltage
The Type 86-A1 amplifier has been' wired at the factory for a power
line voltage of 115 volts. If the line voltage regularly deviates from
this value by more than 5% in either direction, an appropriate wiring
change should be made in the primary of the power transformer T-5
(Fig. A-15). The lead containing the fuse should be moved to tap 4 if
the line voltage is high and to tap 2 if it is low.
MAINTENANCE
If the Type 86 -Al amplifier is to give top performance at all times,
it must be maintained in good operating condition. It should be tested
frequently and be subjected to such corrective measures as the tests indicate. In order to facilitate these tests, the meter switch has been
provided. With it the indicating meter can be connected into eleven
different points in the circuit. The quantity measured in each position and the result expected are shown in the table below.
Adjustments
If the indications are not as expected, adjustments must be made
to bring the circuit in balance. These adjustments may be required
because tubes have been replaced, because the old tubes have deteriorated unequally, or because of some other change in the circuit.
a. Plate Voltage. If the readings are consistently either above or
below the CHECK mark, it is likely that the plate voltage is at fault.
A check on step B+ will disclose whether the voltage is high or low.
If an adjustment must be made, turn the control marked B+ ADJ.,
BROADCAST OPERATORS HANDBOOK
260
Dial
GR
OFF
1
2
3A
3B
4
5
6
BAL
B+
Indication
Gain reduction
Meter disconnected
Ip of RCA-6K7 No. 1
Ip of RCA-6K7 No. 2
Ip of RCA-6N7 No. 3
Ip of RCA -6N7 No. 3
Ip of RCA -6R7 No. 4
Ip of RCA -1621 No. 5
Ip of RCA -1621 No. 6
RCA -6K7 balance
Rectified output voltage
Meter Range
DB Scale
Check
Check
Check*
Check*
Check
Check*
Check*
6K7 Match
Check
Readings on 3A and 3B should be in the check
* NOTE
range, but they may be between 1 and 4 on the meter scale
provided that the two readings do not differ from each other
by more than the width of the check range mark. The same
applies to the readings on steps 5 and 6 for the two RCA 1621 tubes.
which is the 750 -ohm rheostat R-30 in the lead from the center point
on the secondary of transformer T-5, until the voltage reading checks.
an
b. Zero Adjustment. Turn the meter to GR. Do not impress
input signal on the amplifier. Adjust the ZERO ADJ. control R-32
until the meter indicates 0 db gain reduction. Make the adjustment
slowly so that the meter will lave time to come to rest after a change
in the adjustment has been made. This precaution is necessary because of the long time constant of the reduction circuit on recovery.
the input
e. Hum Reduction. Connect a 600 -ohm resistor across
teroutput
the
connect
and
source
terminals in place of the signal
Noise
69-B
Type
a
of
terminals
input
minals of the amplifier to the
in
Level Meter. Set the input and output controls to the positions used
on
HUM
marked
R-6,
and adjust potentiometer
normal operation
the chassis, until the hum is minimum.
let them
d. Dynamic Balance of 6K7's. Turn the tubes on and
This
BAL.
on
switch
meter
warm up for about 10 minutes. Set the
the
with
6K7's,
of
the
grids
injects a 60 -cycle voltage into the control
amthe
of
output
-cycle
grids in parallel, and it also connects the 60
plifier, through the rectifier, to the indicator meter. Set the OUTPUT
outcontrol to +30 db, that is, to the point of greatest output. This
indication
meter
The
put will be due to unbalance in the amplifier.
should fall within the 6K7 MATCH range of the scale. If it falls outis close
side, other pairs of 6K7 tubes should be tried until the match
range.
enough to bring the needle within the match
APPENDIX
RCA-ORT
@.SAC
261
RCA41-10
RCA -6N?
RCA-OR7
RCA -1621
6JAC
O.SAC
OJAC
ILIAC
CHASSIS
REA -6T4
RAC
GROUND
ALL VOLTAGES D.C. UNLESS OTHERWISE
D.C. VOLTAGES
RCA-1021
OJAC
MEASURED
WITH
NOTED
20,000 OHM PER VOLT VOLTMETER
SOTTOM VIEW OR CHASSIS
Fig. A-17. Operating voltage chart for the limiting amplifier.
e. Limited Level. A change of tubes may result in a slight change
of gain in the amplifier, or a change in the level at which gain reduction starts, or a change in the level to which the output is limited.
Therefore the LIMITED LEVEL control should be readjusted whenever tubes have been changed. When this control is in mid -position,
the INPUT control calibration shows the approximate level at which
limiting action starts, and the OUTPUT control calibration shows the
approximate level at verge of limiting. The LIMITED LEVEL control changes both these calibrations over a range of about 1.5 db. In
setting this control, the limiting switch should be set to ON and the
meter switch to GR.
Operating Voltages
The normal operating voltages, a.c. as well as d.c., are shown in Fig.
A-17. These voltages should be obtained when the a -c line voltage is
115 volts and the d -c voltages are measured with a 20,000 ohms per
volt meter. Measured values should not differ by more than 5% from
the listed values. If the d-c voltages are measured with a voltmeter
having a lower resistance, all readings will be less than those listed
by an amount depending on the resistance through which the meter
current has to flow. The voltage across capacitor C-11 should be
about 280 volts.
BROADCAST OPERATORS HANDBOOK
21t2
Time Constant Changes
Occasionally after the amplifier has limited a strong peak in the
program or a sharp transient in the input line, a blank in the output
may be observed. That is, a note of music or a word of speech may be
missing. This lapse is due to the slow recovery rate of the gain in the
amplifier. While such lapses are normal, their observance is rare. If,
however, they should be observed so frequently as to become annoying,
it may be desirable to change the time constant of the recovery circuit.
This is done simply by changing the value of resistance R-41. The
table below gives the time constants for five different values of R-41
and the resulting time of gain recovery.
Time
50%
Time for
90%
Constar
Recovery
Recovery
1.4
.7
.35
.18
.07
5.2
2.6
1.3
.65
.26
Time for
R-41
meg.
meg.
2.5 meg.
1.25 meg.
.5 meg.
10
5
2.5
1.25
.625
.313
.125
sec.
sec.
sec.
sec.
sec.
sec.
sec.
sec.
sec.
sec.
As an aid in the selection of time constant for gain recovery the
following facts are presented:
a.
Fast Recovery Rate
(1) Smaller loss of low-amplitude passages which follow soon
after passages which are higher than the critical level. This is not
serious if high values of compression are avoided, as they should be.
(2) More readily obtainable in design.
b. Slow Recovery Rate
(1) More thorough filtering of the control voltage is obtained.
That is, the control voltage has less tendency to swing with individual
audio cycles and thus less distortion is introduced.
(2) Any background noise returns more slowly after removal of a
signal higher than the critical value, and thus is less noticeable.
(3) Other factors and adjustments being the same, on average
programs there is less loss of dynamic range.
INDEX
Absorption of sound, 21, 192, 194-196
Acoustics, effect on setups, 13, 18, 2122, 29-30, 77
Air filters, maintenance, 163
Amplifier, limiter, 113-115, 221, 255-262
meter, 116, 221-225
Drama, pickups, 31-33, 49
script, 32
Dynamic range, 13, 18, 31, 187
Equalization, of lines, 181-184
maintenance, 259-262
remote, 71-74
studio, 1, 169-174
transportation, 99-101
Announcer, difference in voices, 7, 9
microphone zone, 26-27
Antenna, current increase at 100%
modulation, 107
current sampling lines, 245-255
phase monitor, 234-242
remote meters, 243-244
requirements, 211-214
systems, 211-214
tuning, 215-217
Auditory presence, 34, 47, 54, 98
FCC standards, 118-120, 204-210
Field strength, 197-214
Filters, sound effect, 38
turntable, 41-42
Frequency, assignments (mobile relay),
87-88
runs, 184
Fuses, maintenance of, 150-151
Ground conductivity, 201-204
Ground systems, 214
Insulators, maintenance of, 151-152
Interference levels, 198-204
Balance, 2, 9, 24, 26, 30-31, 78
Band pickups, 81
Bibliography, 220
Blanket area, 201
Board fades, 32
Jacks, maintenance of, 40
Capacitors, maintenance, 147-149
Choir broadcasts, 34, 48-49, 83-84
Church broadcasts, 83-84
Cleveland Symphony Orchestra pickup,
90-103
Conductivity, of soil, 198-204
Consoles, control room, 1-3, 169-174
Contactors, maintenance, 128
Control, consoles, 1-3, 169-174
engineer (duties of), 2-4, 15-18
maintenance, 40
operating practice, 1-9, 15-21, 25-56
Cooling systems, maintenance, 129-131
Level, anticipation, 16
checking, 106-107
comparative, 7
meaning of, 4
reference, 4, 10-11
requirements for remote lines, 73
Limiter amplifiers, adjustments, 221,
255-257
characteristics, 15, 113-115, 221, 255262
installation, 257-259
maintenance, 259-262
operation, 113-115
Lines, equalization of, 181-184
kinds of service, 185-186
sampling for remote antenna meters,
Dance orchestra pickups, 33, 45-48, 80
Distortion, measurements, 116-118, 185,
243-255
Loudness, of speech and music, 19-22
sensation, 7-9, 13, 21-22, 35, 191
225-231
263
INDEX
264
setups, 33-35, 45-48, 50-51, 75-85, 90-
Maintenance, 124-167
air filters, 163
capacitors, 147-149
contactors, 128
cooling system, 129-131
103
Nemo (see Remote)
Noise, measurement, 116-118, 185, 225231
fuses, 150-151
insulators, 151-152
jacks, 40
limiter amplifier, 259-262
motor generators, 159-160
noise and distortion meter, 231-233
phase monitor, 243
pilot lights, 155-156
plugs, 166-167
relays, 152-156
resistors, 149-150
rheostats, 161-162
studio, 40
switches, 158-159
terminal boards, 162-163
transformer, 160-161
transmitter, 124-167
tube, 142-147
variacs, 161
Maps, ground conductivity, 202
Master control, 56-70
NBC switching system, 57-58
operating practice, 57-70
United Broadcasting Company, 58-59
WBBM rules and regulations, 59-70
Measurements, antenna, 215-217
distortion, 116-118, 185, 225-231
Meter, antenna, 107, 234-244
maintenance, 164-165
noise and distortion, 116-118, 185, 225231
volume, 3-7, 10-14, 108-112
Microphone, characteristics,
1, 6-7, 25-
28, 174-181
poling, 28
technique, 27, 31-32
use of, 1-2, 25-35, 45-56, 76-84, 95-96
Mobile relay, broadcasting, 85-89
equipment, 85-86
frequency assignments, 87-88
operation, 88
Modulation, characteristics of, 107, 109112
monitors, 4-7, 12, 109-112
Motor generators, maintenance of, 159160
Music, library, 43
microphone strap, 27, 178
meters, 116-118, 185, 225-231
Operator, control, 1-9, 15-21, 25-56
master control, 56-70
remote, 71-89
transmitter, 7, 104-120
Orchestra, dance, 33, 45-48, 80
pickups, 33, 45-48, 50-51, 80-84, 90-103
salon, 81-82
symphony, 17-18, 20-21, 82-83, 90-103
Organ pickups, 54-55, 84
Output circuits, 181
Pack transmitters, 86
Peak, distortion, 13
factor, 9, 19, 106-107, 110
Phase monitor, 234-242
Phase shift, in studios, 13, 27, 29-30
in television i-f circuits, 234
Piano pickups, 29, 33-34, 52-54
Pilot lights, maintenance of, 165-166
Plugs, maintenance of, 166-167
Poling of microphones, 28
Preventive maintenance, 124-167
Primary service area, 197
Production, directors, 2, 46-47, 92
technique, 25-39, 45-55
Propagation data, 198-204
Radials, 214
Recordings, care of, 43
instantaneous, 43
playing of, 16-17, 41-43
Reference file, 43
Reference level, 4
Rehearsals, 2, 30-31
Relay, maintenance, 152-156
mobile, 85-89
Remote, control, 71-89
equipment, 71-74
operating practice, 71-89
setups, 75-85
simplex of, 75
Repeat coil, 4
Resistors, maintenance of, 149-150
Reverberation, effect, 38-39
optimum, 22, 24, 196
INDEX
time, 21, 24, 101-102, 196
Rheostats, maintenance of, 161-162
Salon orchestra pickups, 81-82
Secondary service area, 197
Service area, 115, 197-210
Simplex of remote amplifiers, 75
Sky wave, 197-198
Solo pickups, 31, 98-99
Sound, absorbing materials, 195-196
absorption, 21, 192, 194-196
effects, 35-39
loudness, 7-9, 13, 21-22, 191
presence, 34, 47, 54, 98
reflection, 22-24, 38, 101-102, 193-196
Speech, microphone straps, 27, 178
waves, 9, 11, 19-21
Standards (FCC), 118-120, 204-210
Studio, characteristics, 9, 21-24, 29-30,
187-196
control equipment, 1-3, 169-174
operating practice, 1-9, 15-21, 25-56
Switches, maintenance of, 158-159
systems, 1, 3, 56-59, 169-174
Symphony, characteristics, 17-18, 20-21,
82
listener, 17, 20-21, 97-98
pickup, 33-34, 82-83, 90-103
Talk -back, 32
Telephone, effect, 39
lines, 181-186
265
Terminal boards, maintenance, of, 162163
Tools, for maintenance, 138-142, 157
Transcriptions, care of, 43
playing, 16-17, 41-43
Transformers, maintenance of, 160-161
Transmitter, coverage area, 115, 197210
emergencies, 121-123
installation, 214-215
location, 197-210
maintenance, 124-167
measurements, 116-118
operating practice, 7, 104-167
testing, 217-219
Transporting equipment, 99-101
Tubes, maintenance of, 142-147
prolonging life of, 106
Tuning, antenna, 215-217
Turntable, 37-38, 40
filters, 41-42
operation, 40-42
Variacs, maintenance of, 161
Vocal pickups, 31, 51-52
Volume, indicator, 1, 3-7, 10-14, 108-112
limiters, 15, 113-115, 221, 255-262
Waves, ground, 201-204
propagation, 198-204
sky, 197-198
Zero volume level, 4
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement