ENGINEERING ASPECTS OF FREQUENCY USAGE IN INTERNATIONAL BROADCASTING

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• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78-03424A001300010001-7
• Release Decision: RIPPUB
• Original Classification: S
• Document Page Count: 51
• Document Creation Date: December 23, 2016
• Document Release Date: August 21, 2013
• Sequence Number: 1
• Publication Date: December 1, 1954
• Content Type: MISC

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CONFIDENTIAL
(...ENGINEERING ASPECTS OF FREQUENCY USAGE
INTERNATIONAL BROADCASTING
December, 1954
Title Page
Table of Contents
40 Numbered Pages
9 Figures
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TABLE OF CONTENTS
Foreword
I - Purpose of the Report 10
II - General Conditions of Study 11
III - Present Usage by VOA, RFE and LIB 14
IV - Principles of Frequency Selection
and Usage Consistent with Engineering
Considerations 17
V - Relationship of Frequency Usage by VOA,
RFE and LIB to that of Other Countries
of the World
30
VI - Conclusions 36
VII - Recommendations 40
ONFIDENTIAL
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CONFIDENTIAL
F OREWORD
This report deals with the utilization of radio frequencies for
certain forms of international broadcasting. Of necessity consideration
must be given to the complex laws of nature governing the transmission
of radio signals from a radio transmitter to distant areas of reception
as well as to other factors which determine whether or not reception
conditions are adequate. The purpose of this foreword is to describe the
factors or to define the terms used in simple non-technical language.
It is common practice to divide the radio spectrum into parts
or sections with a name for each. For instance, frequencies lying be-
tween 30 and 300 kilocycles are called low frequencies, those between
300 and 3,000 kilocycles are called medium frequencies, those between
3,000 and 30,000 are called high frequencies, etc. This discussion will
be concerned only with the high frequency (h.f.) portion of the spectrum
lying between 3,000 and 30,000 kilocycles. .Since a megacycle is 1,000
kilocycles, the h.f. portion of the spectrum may be referred to as the
3 to 30 megacycle band.
Only specific parts of the h.f. range are assigned to interna-
tional broadcasting. Each portion is called an international broadcast
band. There are nine h.f. international broadcast bands. Of these, the
first six are of greatest interest in connection with the operations with
which this report is concerned:
The 4000 kc. or 4 mc. band between 3950 and 4000 kc.
The 6000 kc. or 6 mc. band between 5950 and 6200 kc.
The 7000 kc. or 7 mc. band between 7100 and 7300 kc.
The 9000 kc. or 9 mc. band between 9500 and 9775 kc.
The 11000 kc. or 11 mc.
The 15000 kc. or 15 mc.
The 17000 kc. or 17 mc,
band between 11700 and
11975 kc.
band between 15100 and
15450 kc.
band between 17700 and
17900 kc.
The 21000 kc. or 21 mc. band between 21450 and 21750 kc.
The 25000 kc. or 25 mc. band between 25600 and 26100 kc.
PNEIDENrIAL
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GUINFIDENTIAL
A single radio broadcast signal occupies not one but a number
of adjacent frequencies. The actual width of a radio channel is twice
the highest audio frequency transmitted. Therefore, it is common prac-
tice to divide each band into channels. In domestic broadcasting, 10
kilocycles is allocated to each channel, the center frequency being used
as the channel designator. Originally this was done on the theory that
if audio frequencies up to 5 kc. were transmitted there would be good
reproduction of both speech and music.
In international broadcasting, because of the over-crowded
condition of the radio spectrum, there has been a tendency to divide the
international broadcast bands into 5 kilocycle channels although it is
recognized that a single transmission may occupy a channel substantially
more than 5 kc. wide. This degradation is important because it means that
whenever two transmissions on adjacent 5 kc. channels are directed towards
the same geographic target area there is at least a reasonable probability
that receiving sets cannot differentiate between them. Obviously, if
two transmissions are directed at the same target on the same channel,
there is an even greater likelihood of interference.
Arbitrarily, dividing up the h.f. international bands into
5 kc. channels provides the following:
In the 4 mc. band 10 channels
In the 6 mc. band 50 channels
In the 7 mc. band 40 channels
In the 9 mc. band 55 channels
In the 11 mc. band 55 channels
In the 15 mc. band 70 channels
In the 17 mc. band 40 channels
In the 21 mc. band Go channels
In the 25 mc. band 100 channels
Total 5 kc. channels 480
Admittedly, the division of these bands into 5 kc. channels is
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partly empirical. However, it is necessary to an evaluation of the extent
to which duplicated use of the spectrum is possible. For reasons set
forth later, this study is concerned primarily with the utilization of
the 280 five kilocycle frequency broadcast channels which exist in the
six international broadcast bands lying between 3,950 and 15,450 kcs.
A large number of countries have broadcast operations in the
international broadcast bands. This report is concerned with interna-
tional broadcast operations such as those of the Voice of America (Vak),
Radio Free Europe (RFE), and the American Committee for Liberation from
Bolshevism, Inc. (LIB), which are intended to penetrate the Iron Curtain.
Each of these three organizations operates a plurality of broadcast
transmitters and two of them operate from a plurality of transmitter
locations. Each has as its objective the delivery of programs to a num-
ber of target areas.
Attention is first directed to one part of the systems problem,
namely, the delivery of one program from one transmitter over a particular
propagation path to one defined target area. With this limitation in
mind, the first step is to set forth the important factors which deter-
mine whether or not a program can be received by a willing listener,
that is, a listener who wants to receive it. Briefly, these factors are
six in number, as follows:
1, The power output of the transmitter
2. The radiation characteristics of the trans-
mitting antenna including its directivity
3. The radio frequency chosen for the trans-
mitter
4. The radio propagation characteristics of
the transmission medium between the
transmitter location and the desired
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ilU I-
4. (continued)
reception area at the time of broad-
casting
5. The intensity of various types of inter-
ference signals present at the receiving
location - In this discussion it will be
assumed that the principal interference
produced at receiving locations is from
jammers. There is much evidence to sup-
port this conclusion
6. The availability at receiving locations
in the target area of radio receiving sets
which can be tuned to the frequency of
transmission
The first two factors, namely, transmitter power and antenna
characteristics, are under the control of the broadcasting group. The
third factor, namely frequency used by the transmitter, is partly under
the control of the broadcasting group because presumably it has available
to it a number of frequencies scattered throughout the h.f. bands under
discussion. The fourth factor, namely, the propagation characteristics
of the transmission medium, is not under the control of the broadcaster.
The fifth factor, namely, interference assumed to be primarily signals
from jammer transmitters operated for the prevention of reception of the
broadcasts, is not under the control of the broadcasting group.
The sixth factor, namely, receiving set availability, is not
under the control of the broadcasting group. Yet, it influences the
choice of usable frequencies. Certain groups operate on the assumption
that listeners in the target areas of concern do not have receivers which
will tune above the 15 megacycle band. At least one group assumes that
listeners in its target areas do not have receivers tunable above the
11 megacycle band.
The fourth factor is all important. This is the propagation
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characteristics of the radio transmission medium path between the trans-
mitter and the desired reception area on the frequency in use at the
time of broadcasting. Any useful study and analysis of the effective-
ness of radio frequency utilization for International broadcasting must
turn the spotlight on the characteristics of the radio propagation
medium and particularly upon the variation of these characteristics
with time.
At any particular instant of time, for a particular propaga-
tion path between the transmitter and the receiver there is a radio fre-
quency which marks at least approximately the upper limit above which
transmission of signals is wholly unsatisfactory. This is called the
maximum usable frequency or MUF. A simple explanation of the meaning of
this term is as follows:
1. If the frequency of transmission from a radio trans-
mitter is moved upward from the MUF for a particular
path then the strength of the received signal will
fall off very rapidly to a point where no signal will
be received.
2. If the frequency of the transmitter is moved downward?
from the MUF then the strength of the received signal
will also decrease but not nearly so rapidly as when
the transmitting frequency is moved upward.
From the above the following conclusions may be drawn:
1. For a given power and antenna the strongest signals
will be produced in the target area if the frequency
chosen for the transmission is at or near the MUF for
the transmission path involved. Also, for this and
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1. (Continued)
other reasons, under these conditions reception in
the target area will be most difficult to jam.
2. The selection of the right radio frequency for a
particular broadcast is a matter of prime importance
having a far greater effect on the results obtained
than moderate changes in transmitter power or in
antenna efficiency and directivity.
To the propagation specialist, the treatment just given this
subject may appear to be both naive and superficial. Nevertheless, it
serves to emphasize the importance of the characteristics of the propa-
gation medium in determining the effectiveness of broadcasting. The
big question is how to determine what is the right frequency for a
particular broadcasting time, that is, how determine for some future
date and time just what will be the MUF?
Fortunately, propagation scientists while they cannot predict
with high accuracy the MUF for a future date and time can, from studies
of the ionosphere and historical data, make useful predictions. The
definition of this predicted MUF is such that it may be expected that
50% of the time the actual MUF will be above the predicted value and
50% of the time the actual MUF will be below the predicted MUF.
To recapitulate, to reach a given target area at a given time
from a particular transmitter location, the international broadcaster
has control of only three factors, namely:
1. The transmitter power
2. Transmitting antenna characteristics
including directivity
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tiiieerrr."`
3. A limited choice of frequency assignments in
the high frequency international broadcast
bands
The selection of frequency assignment is all important. This is par-
ticularly true if the effects of jamming are to be minimized. To guide
him in this selection the international broadcaster has available a pre-
dicted MUF for the time he proposes to broadcast, plus the knowledge that
the actual MUF, while it may be different from the predicted value, is
not likely to be too far removed from it.
To more clearly delineate the problems involved in attempting
to provide for the most efficient use of frequencies for international
broadcasting, it is desirable to resort to the case method of treatment.
Case 1 - Assume an international broadcasting group has
available to it one transmitter site for serving one
target area. Assume, however, a rather wide choice of
frequency assignments - Question - how should the fre-
quency to be used at a particular time be selected?
Obviously, the best results will be obtained if a fre-
quency close to or perhaps a little below the predicted
MUF is chosen. Also, to minimize the effects of jamming,
with only one transmitter the probability that tha
program will be received can be increased by repeating
it from time to time.
Case 2 - Assume an international broadcaster has avail-
able one transmitter site and for instance six trans-
mitters which may be used simultaneously to reach a
particular target area, Assume further that for the
time in question the predicted MUF falls in the middle
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of the 9 mc. broadcast band and also that there is
an unlimited choice of frequency assignments within
the 6 international broadcast bands of primary
interest. Question - would best results be obtained
by (a) broadcasting on one frequency in each of the
six bands? (b) broadcasting on a group of 6 frequencies
all in the 9 mc. band? or (c) utilizing some inter-
mediate form of frequency distribution between these
two extremes?
Case 3 - Assume one site, a number of transmitters, a
knowledge of the predicted MUF and the availability of
a number of frequency assignments grouped around this
predicted MUF. It is true that broadcasting the same
program on two channels will increase the probability of
good reception. The use of three channels may be
expected to still further increase the chance of hitting
the actual MUF. Question - when does the law of
diminishing returns make it unprofitable to add
channels and transmitters to the number directed to
the same area?
In this foreword attention has been directed to the parameters
involved in selecting high frequency assignments for delivering the
best possible service to a single target area from a single transmitter
site. Actually, the entities engaged in international broadcasting
operate considerably more complex systems than this. They all have a
number of target areas more or less accurately defined and most of them
have a plurality of transmitter locations. The logical approach to
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the broad problem of providing the most efficient utilization of
frequencies for this service is to break each system down into its
parts and then, after treating each part separately, integrate the
results for the whole.
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?OLleVEIT'
ENGINEERING ASPECTS OF FREQUENCY USAGE IN INTERNATIONAL BROADCASTING
PURPOSE OF THE REPORT
The purpose of this report is to review the manner in which
frequencies are used for international broadcasting and to recommend
improvements which might be made in frequency usage by the Voice of
America (VOA), Radio Free Europe (RFE) and American Committee for Libera-
tion from Bolshevism, Inc. (LIB). Accordingly, this report will be con-
cerned with the following subjects:
A. A review of the present selection, assignment
and frequency usage by VOA, RFE and LIB
B. An examination of frequency usage of other
countries and how this usage affects the
usage of VOA, RFE and LIB
C. An examination of methods in use to determine
technical effectiveness
D. A consideration of factors important to the
most efficient and effective use of frequencies
for international broadcasting
E. The determination of recommendations which in
the opinion of the authors are in accordance
with the following objective - "A determination
of the overall means for obtaining the most
efficient and successful utilization of all
frequencies presently used or usable for inter-
national broadcasting"
This report will emphasize the significance of engineering con-
siderations in the assignment of frequencies and will suggest an engineer-
ing approach to the selection of frequencies to be used for the transmission
of a particular program or programs or conversely for the designation of
programs which will be best received when a particular frequency or group
of frequencies is used.
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II - GENERAL CONDITIONS OF STUDY
This report is concerned with the international broadcast effort
directed towards penetrating the Iron Curtain. It will consider VOA, RFE
and LIB as representative of those groups which are interested in pene-
trating the Iron Curtain and will use the operations of these groups as
illustrative of this type of international broadcast effort. Emphasis
will be given to the frequencies used by these groups in and to the gen-
eral areas of Europe, Western Russia and the Near East wherein there is
overlap in the target areas which are the interest of all three. Generally
speaking, RFE is interested in the friendly satellite countries behind
the Iron Curtain; whereas both VOA and LIB are interested in reaching
all areas behind the Iron Curtain. VOA broadcasts to areas outside the
Iron Curtain as well. This report is not concerned with differences in
the nature of program; only with the areas to which programs are directed.
From a frequency utilization viewpoint, and thinking specifi-
cally of the transmissions which originate in or are directed to Europe,
Western Russia and the Near East, the engineering problems bearing upon
the effective use of frequencies are similar for all three organizations.
The same laws of propagation governing transmissions on various fre-
quencies prevail for all three and the same hazards to reception are
apparent. Generally speaking, the same frequency bands are available
to all three groups. Each is interested in using for each program that
combination of transmitting facilities and frequencies that will provide
the best signal in the target area of interest. While there are practi-
cal considerations which enter into a determination of what frequencies
to use for a particular program transmission, it is apparent that all
three groups are cognizant of the basic technical factors which bear
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upon effective frequency utilization and have the means for calculating
whether a frequency is appropriate for a particular program or not. Each
makes use of monitoring information to determine whether a signal is re-
ceived at designated locations and the nature of the signal.
The objective of this study is the determination of methods
for improving the effectiveness and the efficiency of frequencies used
for international broadcasting. International broadcasting takes place
at low, medium and high frequencies and all assigned bands in the spec-
trum are congested. The selection of low and medium frequencies is re-
latively simple when compared with the selection of high frequencies.
This report will therefore be concerned with the more complex problem of
high frequency broadcasting and with the application of engineering methods
to frequency assignments for the areas where the problem is most complex,
namely, the European, Western Russian and Near Eastern areas.
The very nature of high frequency broadcasting, depending as
it does on the vagaries of the ionosphere, makes the assignment and usage
of high frequencies difficult under the best of conditions. Under present
world conditions, wherein a cold war exists, this problem is complicated
still further. In international broadcasting at the present time, radio
transmission facilities are a weapon in a very real sense. Efforts to
transmit information across the Iron Curtain are countered by efforts
within the Iron Curtain to destroy reception of those signals. Whether
or not the effort to pierce the Iron Curtain is successful depends upon
whether the signals are strong enough at the point of desired reception to
overcome the counter efforts from within. It must be realized that under
jamming conditions, a signal which might otherwise be perfectly good and
usable may actually become of little or no use to the desired audience.
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4.
It is essential, therefore, that the broadcast effort be so planned that
It make full use of all available resources which provide an advantage
over those attempting to counter this effort.
Within the above general conditions of study, this report will
describe in the following sections the way in which frequencies are pre-
sently being used by VOA, RFE and LIB, the principles of frequency selec-
tion and usage which are consistent with engineering considerations, and
the relationship of frequency usage by the above-named groups to that of
other countries of the world.
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wwwv.111,,I
III - PRESENT USAGE BY VOA, RPE AND LIB
There is a wealth of material available with respect to the
use of frequencies by VOA, RFE and LIB. All of these groups have been
most helpful during the course of this study by making available such
material and by being available for discussion of various questions
which have arisen.
For purposes of orientation, Figure 1 has been prepared to
show for a typical day in May, 1954 the usage of frequencies by VOA,
RFE and LIB at certain arbitrary hours. It shows for various times
the number and types of frequencies being used to broadcast program
material in specified languages. Whereas Figure 1 is not complete, it is
illustrative of the nature of the broadcast effort of VOA, RFE and LIB.
It shows for example, the fact that RFE and LIB usage is fairly constant
throughout the day whereas VOA builds up to its heaviest schedule from
approximately 1600-2200 GMT. The same numbers of frequencies are used
by RFE and LIB at all times whereas the number of frequencies used by
VOA varies considerably for different periods of the day with the maxi-
mum number being used during the period from 1600 to 2200 GMT.
Attention is directed to two factors of significance in Figure
1. The number of frequencies used to broadcast a
particular program, that is, a particular
language, at a particular time, and
2. The wide spread in frequencies used to transmit a
program from a particular transmitting location
at a particular time.
A detailed study of 97 programs broadcast by VOA, RFE and LIB between
1, namely
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CThNI1ThNrTI A I
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TABLE OF FREQUENCY USAGE - MAY, 1954
IVOA
RFE
LIB
TIME
PROGRAM
STATIOI\
F"AUENCY
PROGWISTATICN
FREQUENCY ,PROGRAM
STATION
FREQUENCY
4
6
7
9
11
15
17
4
6
7
9_11
15
17,
4
6
7
9
11
15
17
1200
ALBAN-
IAN
TAN
2
2
4
1
POLISH
GER.
PORT.
1
1
1
1
2
2
RUSSIAN
AZERB
2
,
2
1
1
CZECH
GER.
PORT.
1
1
1
2
HURUAR-GER.
IAN
,
2
1
1
2
1
1600
,
LITH
URDUce,
TAMIL
SERV.
PROG.
TAN
NUN
BBC
SAL
E.COAST
1
2
1
1
1
1
1
3
1
2
1
3
1
4
1
3
POLISH
_PORT.
GER.
PORT.
1
1
1
1
2
2
iGEORG.
RUSSIAN
2
2
1
1
4
CZECH
GER.
PORT.
2
1
1
2
1
HUNGAR.
GER.
PORT.
2
1
1
2
1
COLON-
BO
I
IAN
4
E.COAST
2
4
:
2
2000
RUMAN-
IAN
GERMAN
CZECH
ARABIC
RUSSIAN
AFRS
MISC.*
TAN
NUN
BBC
SAL
E.COAST
1
1
2
1
2
1
1
1
2
2
2
CZECH
GER.
FORT.
1
1
1
1
1
RUSSIAN
1
1
2
1
1
POLISH
GER.
PORT.
1
1
1
2
2
Huma-
IAN
GER.
PORT.
1
1
2
1
TAN
NUN
BBC
SAL
E.COAST
1
1
1
2
1
2
1
2
BUYAR-
IAN
GER.
PORT.
1
1
1
TAN
NUN
BBC
SAL
E.COAST
1
1
1
1
1
1
2
COUR
NUN
E.COAST
MUN
1
1
2
1
2
1
2400
LITH.
ARMEN-
IAN
TAN
COUR
2
2
1
2
1
HUNGAR-
IAN
GER.
PORT.
1
4
1
5
4
3
RUSSIAN
1
2
2
1
CZECH
GER.
1
POLISH
1
1
--,
,
0400
'ATV=
MISC.*
TAN
TAN
E.COAST
2
1
2
1
2
1
1
1
HUNGAR
IAN
GEE.
PORT.
2
1
2
1
RUSSIAN
GEORG.
1
2
2
1
CZECH
GER.
PORT.
1
1
1
1
2
,
POLISH
GER.
PORT.
2
1
1
1
3
1
o800
--
--
15130
FJR
T
ne
-
INFORMATION
NO
CZECH
GER.
PORT.
1
1
2
1
RUSSIAN
,
2
2
2
Pomal
GER.
PORT.
2
1
2
2
HUNGAR-
IAN
GER.
PORT.
1
1
22
2
*Miscellaneous
which
program
frequencies
assignment
1
1
are
was
1
those
not
I
ascertained.
used
I
-
but
for
I
d??s? r rm rThI T I A 1
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the hours of 1600 and 2400 GMT shows the following distribution with res-
pect to the number of frequencies used per program:
20% of the programs used 2 or less frequencies,
50% of the programs used 5 or less frequencies,
80% of the programs used 10 or less frequencies,
95% of the programs used 15 or less frequencies,
Two programs out of the 97 studied used more than 20
frequencies; one using 26 frequencies to Lithuania,
the other using 36 frequencies to Russia.
In the above tabulation the number of frequencies indicated for a parti-
cular program includes all frequencies used for that program whether one
transmitter location or more than one location was used.
A study of the frequencies, transmitter characteristics and
antenna characteristics used for particular programs by the various
agencies shows that in each agency engineering principles of assignment
are evident. It is pertinent, however, to note that where a multiplicity
of facilities and frequencies is used for a single program, resort must
sometimes be made to the use of transmitter, antenna and frequency com-
binations which are not optimum. For example, at each transmitter
location there are only a limited number of antennas beamed in a parti-
cular direction and appropriate for use with a particular frequency band.
If more than that number of frequencies are used at a particular time from
that location or if some frequencies in other bands than the best bands
are used merely because facilities appropriate for such frequencies are
available, then less than the optimum use of facilities may result.
The principal limitations in the designation of frequencies for
programs in international broadcasting are the number of frequencies
- 15
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Declassified in Part- Sanitized Copy Approved forRelease2013/08/21 : CIA-RDP78-03424A001300010001-7
available and and the facilities appropriate for use with the available fre-
quencies to serve the desired target areas. A further limitation is a
feeling that there is a lack or sparcity of receivers in the target areas
Which will receive in the broadcast bands above the 15 megacycle band.
VOA uses no frequencies above 17 megacycles for transmission to the tar-
get area and only a few assignments in the 17 megacycle band. RFE uses
no frequencies above the 15 megacycle band. LIB uses no frequencies
above the 11 megacycle band. Propagation studies indicate that frequencies
In bands above the 15 megacycle band are most valuable at certain periods
of time and that these higher frequencies will become even more valuable
In the next few years as the sunspot number increases. It would appear
desirable, therefore, that a re-examination be made of the reasons behind
the decisions to limit the use of frequencies as indicated.
In this study specific attention has been given to the number
of frequencies used for broadcasting one program and to the spread in
frequencies used to broadcast the same program from a given transmitting
site. It is evident that the number of frequencies for many programs
Is quite large and that the spread of frequencies is quite wide. Ques-
tions may be raised as to what spread of frequencies is necessary and
how many frequencies should be used, and where they should fall in the
spectrum. Similarly, a question may be raised as to whether or not the
total frequency usage per program now in practice as well as the spread
used are greater than necessary. These are difficult questions to answer
but it appears that the answer to the latter question may be "Yes, at
times." The following sections will discuss these subjects in more detail.
-16-
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.001110
IV - PRINCIPLES OF FREQUENCY SELECTION AND USAGE
CONSISTENT WITH ENGINEERING CONSIDERATIONS
The present pattern of frequency usage by VOA, RFE and LIB re-
flects a significant amount of sound engineering consideration. The
basic question for consideration in this report therefore, is whether,
and to what extent the use of frequencies may be improved by giving in-
creased emphasis to engineering considerations in the programing of freq-
uency assignments. With the use of multiple frequencies having different
propagation characteristics and with the use of multiple transmission
locations each having different transmission paths to a particular target
area, one question must be continually in mind if efficiency in frequency
usage is to be realized and if the available frequencies are to be used
most effectively. That question is: Are some or any of the frequencies
which are assigned to a particular program of only marginal value and do
they have less than marginal potential for being effective? The corre-
lary question is: Are certain frequencies the ones which really count?
It is the purpose of this report to delineate those factors which have
an engineering significance in the planning of frequency usage so that
a particular frequency assignment may be evaluated in the light of
engineering considerations independently of other considerations.
If there were no jamming from behind the Iron Curtain it would
be possible and highly effective to use but one or two frequencies to
transmit one program to a particular area at a particular time. If
it were possible to monitor the program in the reception area and a
rapid means of communicating results of such monitoring were available,
it would be possible to adjust frequency assignments so that within the
limits of available frequencies the very best frequency would be used at
Declassified in Part - Sanitized Copy Approved for Release 2013/08/21 : CIA-RDP78-03424A001300010001-7
Declassified in Part- Sanitized Copy Approved forRelease2013/08/21 : CIA-RDP78-03424A001300010001-7
.401F1;61*rr.14
all times.
In international broadcasting at the present time the use of
multiple frequencies, that is more than two frequencies to a given target
area for a particular program is dictated by two factors; (1) propagation
vagaries of the transmission medium and (2) the presence of jamming.
The presence of jamming requires that the frequency used at a given time
provide the strongest signal possible if it is to be effective. It is
this factor which makes use of a frequency as close to the maximum usable
frequency (MUF) as possible at all times desirable even though some lower
frequency would be satisfactory in the absence of jamming. Since propa-
gation vagaries of the transmission medium make it difficult to know
exactly what frequency will be closest to the MUF at a given time, only
the relative magnitude of this frequency can be predicted with reasonable
accuracy. It is necessary for this reason to select from available fre-
quencies a group which is close to and if possible includes the predicted
MUF in order to insure that at any particular time a frequency as close
as possible to the MUF will be in use. The number of frequencies required
and the spread in frequencies for a particular group, and the best trans-
mitting facilities to be associated with these frequencies are important
engineering determinations which must be made if the most efficient and
most effective frequency usage is to result.
There is no place in this report for an exposition of the
theory of high frequency propagation via the ionosphere nor is it neces-
sary. All agencies of interest have competent personnel versed in the
art of making the necessary calculations provided they have available
the proper information. However, it is necessary to emphasize the effect
on frequency planning caused by the varying characteristics of the
- 18--
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propagation medium. It is this factor which is often neglected by those
not too familiar with the mechanics of ionospheric propagation. It is
important to realize that any prediction of future propagation conditions,
while indispensable in frequency planning, is at best but an estimate
which must be made on a probability basis and is subject to error. For
example, when a prediction is made as to the maximum usable frequency
(MUF) over a given path for a given time, the probability is equal that
the actual MUF at the time of the broadcast will be above or below the
predicted value. Thus, while the use of frequencies near the maximum
usable frequency generally results in the strongest signals at the point
of reception, the inability to predict such conditions with great accu-
racy requires the use of certain expedients.
One expedient is to select a frequency somewhat below the
predicted maximum usable frequency thus increasing the probability that
the ionosphere will support transmission over the path at the time of use.
For example, where available a frequency 3.5% below the predicted MUF is
often used in commercial practice. Another expedient is to use a number
of frequencies grouped about the maximum usable frequency. Such usage
may be from one location or more than one location, the latter being
preferable. A third is to repeat the program a number of times thereby
increasing the statistical probability of its being heard. Frequently a
combination of the latter two methods is used in international broadcast-
ing.
The MUF is important in international broadcasting because
the existence of jamming places a premium on getting the best possible
signal strength into the area to be covered. If frequency assignments
can be made which provide for use of a frequency as close to the actual
- 19 -
..Slialaiikao?"?'
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Declassified in Part - Sanitized Copy Approved for Release 2013/08/21 : CIA-RDP78-03424A001300010001-7
maximum usable frequency as possible at all times, two advantages will
accrue:
1. The strongest signal will be provided at the
desired point of reception.
2. The burden on the sky-wave jammer will be
increased by reducing its flexibility of
location. The jammer must be so located as
to have an equally good path if it is to
jam effectively with comparable power. At
some times of the day the problem of
locating a sky-wave jammer where it can
be effective is quite difficult.
Analyses made in this study tend to indicate that the value of
a frequency close to the maximum usable frequency is of such significance
that transmitter power and antenna directivity for a particular path,
at a particular time of day are of secondary importance if the wrong
choice of frequency is made. With the right choice of frequency both of
these factors become important in making the signal the best possible
signal, but they are not a substitute for the right frequency. The
importance of these considerations makes it desirable and worth-while
to exert considerable engineering effort to insure the use of that group
of frequencies which will be most effective in maintaining the use of a
frequency as close as possible to the maximum usable frequency without
at the same time spreading frequency usage to the point that relatively
ineffective frequencies are used.
The use of prediction information is essential in interna-
tional broadcasting sine,: programing and frequency assignments must be
- 20 -
.SWiCtww
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Declassified in Part - Sanitized Copy Approved for Release 2013/08/21 : CIA-RDP78-03424A001300010001-7
i? difii??????
planned in advance. An understanding of the nature and value of pre-
diction information is therefore necessary to effective programing and
frequency planning. In order to improve prediction information and
evaluate future potential broadcast effectiveness it is necessary to
determine as accurately as possible on a continuing basis the value of
the past broadcast effort and the effectiveness of past planning. VOA,
RFE and LIB engage in rather extensive monitoring operations to obtain
continuing information with respect to the effectiveness of their opera-
tions. Used properly, such information can be extremely valuable in
refining prediction information and in determining potential effective-
ness of the frequencies used. Until recently, the monitoring information
,of these groups had not been kept in a standard form nor was it readily
, available for analysis on a frequency by fr-iquency basis. Steps to
standardize monitoring reports and to use IBM methods for recording have
been activated which should greatly facilitate such analysis in the future.
The studies reported herein, while made without the benefit of the IBM
procedures, substantiate the value to be derived from improved methods
of gathering monitoring information and the need for a continuing study
of information so gathered. The need for tabulating this information in
a form specifically designed to facilitate a study of the effectiveness
of frequencies on a frequency by frequency basis is also indicated. Cau-
tion, of course, must be exercised in interpreting any monitoring reports
since they do not show local jamming conditions at other receiving loca-
tions in the target areas.
To evaluate the significance of frequency usage on a frequency
by frequency basis a detailed analysis was made in this study of VOA
monitoring conducted in Helsinki and in Belgrade during the first six
- 21
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Declassified in Part - Sanitized Copy Approved for Release 2013/08/21 : CIA-RDP78-03424A001300010001-7
SiiaalF?iP0'""'
months of 1954. Some study was also made of monitoring results obtained
by VOA at Teheran and Taipei. This monitoring information was studied
on a month by month basis for January, February, March, April, May and
June. Tabulations were made with respect to each program period and
for each transmitting location showing for each month the percentage
of times monitored that each frequency used for a program was received
satisfactorily or better at the monitoring location. Whereas for detailed
evaluation, account should be taken in such an analysis of all of the
characteristics of the transmission facilities used at a particular time
on a particular frequency, the most important consideration in determin-
ing whether a program is heard, appears to be whether or not the frequency
is a proper one - that is the best one - for the transmission path in-
volved. In the tabulation of data, plots were therefore made of all
transmissions received at a particular monitoring location even though
in some cases the antenna beaming was not optimum for reception at that
particular monitoring location and even though the power used may have
been low. It developed that if the frequency band used were not the best,
percentage reception of a program would be low irrespective of the antenna
bearing and the power used. For frequencies falling in what seemed to be
a best band some variation could be noticed with antenna beaming or with
power but the variation would generally be relatively less than the varia-
tion when a frequency band far removed from the best band was used except
in those cases where the beaming was completely off.
Figure 2 is representative of the results obtained from plot-
ting VOA monitoring data. It shows information gathered at Helsinki for
programs broadcast between 1730-1800 GMT. A, B, and C of Figure 2 show all
programs monitored during this period - this includes programs in Latvian
-22-
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MO
90
60
o 70
L' so
2 50
40
SI
30
20
10
0
100
SUMMARY OF PROGRAMS RECEIVED
SATISFACTORILY IN HELSINKI
ALL PROGRAMS (1730-1800)
TANGIER AT HELSINKI
OnninnO1MO
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4 6 7 9111517 4 6 7 91115 7 4 6 7 9 1115 7 4 6 7 9 II 1517
H.F BROADCAST BAND
MAR APR
JAN
FEB
MUNICH AT HELSINKI
4 6 7 9 111517 46 7 9 111517
MAY JUNE
100
90
80
70
60
50
40
30
20
10
0
90
80
o 70
60
40
11 30
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10
100
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4 6 7 9 111517 4 6 7 9 111517 4 6 7 9 I 15 7 4 6 7 9111517
HS. BROADCAST BAND
MAR APR
JAN FEB
BBC AT HELSINKI
.04
4 6 7 9111517
4 67 91115 7
MAY JUNE
AMMON MEMO EUMMIONOEMEO MEM MOM/EOM IMIOMMEOM
AMMO MOO MEM I MI OM OEM MAMMA' MEMO.?n n MOM
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4 6 7 9111517 4 6 7 9 1115 7 4 6 7 91 1517 4 6 7 9111517 4 6 7 9111517 4 6 7 9 111517 -
100
90
BO
70
60
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ao
20
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1W
90
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JAN
WF BROADCAST BAND
FEB MAR APR
MAY
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MO
90
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1, 50
0 40
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I0
0
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ELLY', 50
FIG. 2
, 40
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10
0
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0
4 6 7 91115 M 4 6 7 9 915M
ESTONIAN (1730-1745)
TANGIER AT HELSINKI
UMW MUMMA
MOW= =MEMO
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JAN
4 6 7 91 1517 4 6 7 111517 4 6 7 9 11 L517 4 6 7 9 111517
11.F. BROADCAST BAND
MAR APR
MAY
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?
En MOM OMOMO II ME MOO O WOO OOMOOOlin WOLOMM n
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HF. BROADCAST BAND
FEB MAR APR
JAN
BBC A
HELSINKI
00
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70
60
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HS. BROADCAST BAND
MAR APR MAY
JUNE
00
90
80
70
60
50
40
30
20
10
0
Declassified in Part - Sanitized Copy Approved for Release 2013/08/21 : CIA-RDP78-03424A001300010001-7
and Estonian; while D, E, and F show Estonian programs only. Each
symbol in Figure 2 represents a particular 15-minute program on a par-
ticular frequency monitored several times during a month. The frequency
band is indicated by the character of the symbol and by its location in
the table. The percentage of times that the program on a particular fre-
quency was received satisfactorily or better relative to the number of
times monitored during the particular month is shown in percentage value
as the ordinate.
It will be noted in Figure 2 that, for each month, programs in
one band tend to group higher in percentage of times received satisfac-
torily than programs broadcast in other bands. The band which is best
changes from month to month in a manner similar to the way in which the
MUF changes. For example, in January frequencies in the 9 megacycle band
417.14; seem to be best; in February the best band is still 9 megacycles; in
March the best band is 11 megacycles; in April the best band is 11 mega-
cycles; in May, 15 megacycles; and in June, 15 megacycles. None of the
bands used indicate very good results in June.
Figure 3 shows a similar picture with respect to information
gathered at Belgrade. In this case, the period shown is the period be-
tween 1845-1915 GMT. A, B, C, in this case show the results for
all programs during this period and include Hungarian and Serb; and
D, E, and F show the results for Hungarian only. The same type of
picture as obtained for Eelsinki is indicated in Figure 3 with respect
to Belgrade.
It will be noted in B and E of Figure 3 that there are several
broadcasts indicated on 4 and 6 megacycle frequencies which fall decidedly
below other broadcasts on frequencies in these bands. The broadcasts
- 23 -
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0
(D
0
(I)
0 0
CD
5'
-0
(I)
loo
90
80
CD
0_ o70
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(1. 7
SUMMARY OF PROGRAMS RECEIVED
SATISFACTORILY IN BELGRADE
ALL PROGRAMS (1845- 1915)
SERB a HUNGARIAN
TANGIER AT BELGRADE
48
8
04?0
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?
0
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4 6 7 911 6 17 4 6 7 9 11 15 7 4 6 7 9 1 15 7 4 6 7 9 II 1517 4 6 7 9 II 1517
H.Fmp BROADCAST BAND
APR MAY
JAN FEB
MUNICH
00
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100 100
90 90
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70 2 70
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4 6 7 9 II 15 17
JUNE
?
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4 6 79 II 1517 46 79 11 15 17 4 6 7 9 II 1517 4 6 7 9 II 15 17 4 6 7 9 II 1517
H.F. BROADCAST BAND
MAR APR
JAN
FEB
BBC AT BELGRADE
?
?
A
MAY
4 6 19 111517
JUNE
0
4 6 7 9 II 1517 4 6 7 9 .115 17 4 6 7 9 I 1517 4 6 7 9 II 1517 4 6 7 9 1 1517 46 7 9 II 1517
H.F. BROADCAST BAND
FE6 MAR APR
JAN
MAY
JUNE
100 100
90 90
80 BO
70 2 70
60 E 60
50 50
40 0 40
30 30
20 20
I 0 10
0 0
46 79 II 1517
HUNGARIAN (1845-1900)
MUNICH ORIGINATION
TANGIER AT BELGRADE
8
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?
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100
90
80
70
60
50
40
30
20
I0
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?
4 6 7 911 IS 17
JAN
46 7 9 II 15 7
4 6 7 9 I L517 4 6 7 9 1115 7
H.F BROADCAST BAND
FEB MAR APR
MUNICH AT BELGRADE
4 6 7 9 II 1517
MAY
4679 11 15 7
JUNE
?
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100 100
90 90
80 80
70 070
60 L' 60
SO 2 50
40 * 40
30 30
20 20
10 I 0
FIG. 3
JAN
46 79111517
FEB
BBC AT BELGRADE
a
4 6 7 9 II 1517 46 7 9 II 1517 4 6 79 II 5I7 46 79 II M 7
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H.F. BROADCAST BAND
MAR APR
MAY
JUNE
4 6 7 9 II 15 17 4 6 7 9 11 1517 46791115 7 46 7 9 II 15 17 46 79 111517 4 679 11 15 7
JAN
FEB
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MAR ' APR
MAY
JUNE
100
90
80
70
60
50
40
30
20
I0
100
90
80
70
60
50
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Declassified in Part - Sanitized Copy Approved for Release 2013/08/21 : CIA-RDP78-03424A001300010001-7
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falling low are those beamed 58/2380 from Munich and are intended for
reception in Tangier for relaying programs originating in Munich. This
beaming is decidedly poor for reception in Belgrade.
For purposes of comparison with the actual MUF trend, Figure
4 has been prepared to show the MUF curves for each month from January
to June for the path Tangier to Belgrade. An examination of these maxi-
mum usable frequencies and comparison with results obtained in Figure 3
show a close relationship between the best band as determined from
monitoring and the band closest to the MUF which may be predicted from
propagation curves.
Both Figures 2 and 3 show that there is a tendency for one band
to be the best at a particular time and that the seasonal trend is as
would be expected from prediction information. To analyze the relation-
ship between monitoring information and MUF more closely, more detailed
study of one set of data seemed warranted. Accordingly,, all programs in
Rumanian, Ukrainian, and Russian broadcast from Tangier and monitored in
Belgrade during the period 1645-2000 GMT were selected as a sample.
These broadcasts were chosen because these countries are generally in
line with Belgrade and the transmitting point and it is known that all
three broadcasts are jammed quite consistently. Figure 5 was then pre-
pared to show the per cent of times monitored each month that each of
these programs was graded "satisfactory" or better plotted against the
frequency used, normalized to the predicted MUF for the time and path.
In other words, a plot was made of the percentage of times a program was
received in Belgrade satisfactorily or better as a function of the ratio
Frequency used
MUF While the data shown in Figure 5 are admittedly meager
and the drawing of a curve is not justified, it should be noted that
214- -
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Declassified in Part - Sanitized Copy Approved for Release 2013/08/21 : CIA-RDP78-03424A001300010001-7
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there is a concentration of high percentage points in the vicinity of
0.9 to 1.0. This tends to support the conclusion discussed earlier that
frequencies close to the MUF have the best chance of getting through. To
illustrate the general effect of jamming a dotted line has been drawn in
Figure 5 to depict qualitatively the condition which might be expected if
there were no jamming. Without jamming, the poorer frequencies, that is,
those accounting for lower signal strengths because of the nature of the
transmission path, would drop off in effectiveness at a lower rate than
with jamming present. While this study has not developed this relation-
ship definitely or quantitatively there is sufficient evidence of such a
relationship to warrant further study to develop this in more definitive
fashion. This study does indicate that the use of frequencies close to
the MUF is highly important and that additional data gathered for the
express purpose of determining quantitative results would be helpful.
The results of this study confirm the fact that good monitoring data can
usefully supplement prediction procedures to refine engineering informa-
tion. It is clear that continued and increased effort in the use of
monitoring results and the evaluation of monitoring information is essen-
tial to effective frequency planning. The practices recently placed into
effect for improving the tabulation of monitoring information and for
preparing such information on IBM cards are warranted and should prove
highly valuable. Considerable time would have been saved in analyzing
data in this study had information been available in the form that it is
now being recorded.
While conclusions with respect to the quantitative determina-
tion of frequency grouping for multiple frequency broadcasts are not
warranted, it is pertinent to take note of the way in which the
25 -0iiipili4Lodr-
Declassified in Part - Sanitized Copy Approved for Release 2013/08/21 : CIA-RDP78-03424A001300010001-7
Declassified in Part - Sanitized Copy Approved for Release 2013/08/21 : CIA-RDP78-03424A001300010001-7
international broadcast bands are distributed throughout the,high fre-
quency spectrum and the spread of frequency which is necessary when two
or more bands are grouped for the same program. This is illustrated in
Figure 6 where the relative locations of the various bands are shown
along with a scale which may be used to determine the percentage spread
in frequencies about a given frequency, for example, the MUF, when fre-
quencies in various bands are used. For example, if the scale were cut
out and used as a sliding scale and 1.0 placed corresponding to the 15
megacycle band, it would be noted that the ratio of the 11 megacycle
band to the 15 megacycle band is .78 and the ratio of the 9 megacycle
band to the 15 megacycle band is .63. The ratio of the 17 megacycle
band to the 15 megacycle band is 1.2. The frequency spectrum shown in
Figure 6 and the scale have been drawn on a logarithmic basis and may
be used in slide rule form by copying or by cutting them out. Such a
slide rule would be a useful device in frequency planning if some simple
quantitative rules for grouping of frequencies could be developed.
Another example of monitoring analyses is shown in Figure 7.
This contains a condensation of the results of monitoring conducted by
RIPE in Berlin and Vienna for the two-week period around March 1, 1954.
The degree of shading is indicative of a rating given the particular
frequency at various times of the day during the two-week period. Figure
7 shows in effect the diurnal variation in program rating for each par-
ticular frequency usage. It may be observed that the higher frequencies
are the ones rated highest during the ?day and the lower frequencies rated
best during the night for broadcasting from Lisbon. For broadcasts from
Biblis the frequencies around 6 megacycles appear to be the best during
the day. As a general observation it may be noted that whereas most
- 26 -
...5aQiRshif
Declassified in Part - Sanitized Copy Approved for Release 2013/08/21 : CIA-RDP78-03424A001300010001-7
Declassified in Part - Sanitized Copy Approved for Release 2013/08/21 : CIA-RDP78-03424A001300010001-7
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