April 1959 Popular Electronics
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
Whoa! Take a look at the RF feedthrough and lightning arresting choke on the feed line on the original Voice of America transmitter in Munich, Germany. Now that is serious stuff. This story from an early Popular Electronics reports on the extreme lengths to which the Soviet bloc went in order to prevent its countrymen from hearing radio signals broadcast by the Voice of America and other non-state-approved beacons. Quarter megawatt transmitters sent messages of freedom that could be picked up by even the most remote crystal sets that didn't have the advantage of amplification. Ground-wave, sky-wave, and short-wave jamming techniques were employed to ensure the only signal that could be received was a buzz-saw type noise.
Not so long ago, and certainly in 1959, America was viewed as a beacon of freedom, both figuratively via word-of-mouth and underground newspapers, and literally via high powered radio broadcasts directed into cordoned off countries ruled by Communist rulers. Herculean efforts were made by the likes of Stalin, Khrushchev, Castro, Kim Il-sung, Pol Pot, and various other despots to prevent any form of communications with the outside world. I remember back when my grade school classmates and I were practicing hiding under our desks in the event of a nuclear bomb attack, how the teacher would tell of something as benign (to us) as a Sears, Roebuck catalog not being permitted beyond the Iron Curtain lest the people learn about what they are being denied by their dear leaders. Denim blue jeans and automatic washing machines were deemed to be the spawn of evil Capitalism. Such devices were according to the Communist propagandists prima facie evidence of how a free, industrious people thrived while the slothful (never identified as such) were mired in misery. Why should some people be happy and some not, when everyone can share in being miserable together? A 'worker's paradise' was the promise of every tyrannical regime. Multitudes of mass graves the world over show how well that always worked out. To this day we suffer the whims of powerful men and women who believe that the only reason Communism has failed is because the right people haven't tried it yet.
By Will Bohr
It is nearly 0400 hours, Moscow time. In a corner of the Soviet capital everyone sleeps except for one family which is huddled over an ancient short-wave receiver. The operator adjusts the tuning dial.
"Just one minute more," think the early morning listeners. The radio signal the Russians are listening to comes in loud and steady, with a slow rolling fade which indicates that there are thousands of miles separating these listeners from the transmitter about to speak. Everyone catches his breath as the voice from the loudspeaker comes to life:
"This program is coming to you from the United States of America. The following news program is brought to you in the Russian language ..." Suddenly the room is filled with a gathering roar that blots out the voice they are so eager to hear. The noise whipsaws across the signal and burns in their ears. Frantically the operator turns the dials of the receiver, trying to escape the unintelligible chaos of noise smothering the voice of the free world.
Sadly, the operator turns off the receiver, and the family disperses...
The Soviet Union started deliberate radio interference with the Russian language broadcasts of the United States and England shortly after the end of World War II. At the present time over 2500 separate jamming stations are scattered throughout the USSR and the satellites in an effort to blanket reception of the 85 transmitters of the Voice of America. They try to blot out all 16 frequencies used by the VOA.
When the Polish government ceased its radio jamming operations a few years ago, it informed the world of the cost of these operations. For every dollar spent by the Voice of America to produce the Polish language programs, the Polish government spent over one hundred dollars in a vain attempt to obliterate reception!
The total cost of the Communist jamming effort is estimated at over 100 million dollars. The evident fear of Voice of America operations is shown by the fact that the Soviets jammed the United Nations broadcasts over the VOA, even during the periods when the Soviet delegates were speaking!
Three separate jamming transmitters must be employed to "protect" three cities from one Voice of America transmitter, as shown above. A single high-power jammer at point "X" wastes power over unpopulated areas. Separate jammers provide maximum suppression in the cities, but leave countryside free from interference.
Jamming Techniques. Jamming a high-power radio station is a complicated as well as an expensive job. The general jamming technique takes the form of superimposing random noises and sounds upon the identical carrier frequency of the offending transmitter. Since it is usually impossible to locate the jamming equipment near the station to be jammed, the "jammer" is generally placed close to large population centers, where there are conceivably many receivers capable of tuning to the channel of the politically undesirable station.
The jamming signal usually consists of a buzz-saw-like noise, or random musical tones superimposed upon a steady buzz, much in the manner of a bagpipe. In rare instances, the jamming transmitter superimposes a program of its own atop the unwanted station. Jamming stations generally identify themselves by a two-character call sign, which may change frequently.
Ground-Wave Jamming. Radio communication during daylight hours in the broadcast band (500-1600 kc.) normally takes place by means of the ground wave, that portion of the radio wave which travels along or over the surface of the earth. Its usable range is a hundred miles or so.
Short-wave signals are reflected back to earth by the ionosphere so that cities "A" and "D" (in diagram above) must each have a jammer. A shift of frequency of the transmitter or a change in the ionosphere can project the signal to cities "B" and "C." so that all four cities must have separate jamming equipment to suppress a single transmitter completely.
The power of many European broadcast stations is about 150,000 to 250,000 watts (compared to a maximum limit of 50,000 watts in the United States). These stations are capable of producing a strong signal on even the most primitive radio receiver. To obliterate this signal over a small area such as a single city, a jamming transmitter of 10,000 to 15,000 watts may be employed. However, when it is desired to jam a large area of several thousand square miles, it is either necessary to use many jamming transmitters of this power spread over the area, or else one or two high-powered jammers equal to or greater in strength than the undesired station.
In general, the former technique seems to be in use, at the present time as twenty or thirty jammers are usually employed to block out the broadcast-band transmissions of the various VOA transmitters in Europe. The Soviets have found to their sorrow that a jammer signal weaker in strength than the undesired signal is worse than useless; it merely calls attention to the station that is condemned for obliteration!
Sky-Wave Jamming. During the evening hours, the characteristics of the broadcast band change, permitting excellent reception from stations many hundreds of miles away. This permits the VOA to reach deep within the Soviet Union with its programs of news and information.
Antenna tower base of the million-watt Voice of America transmitter in Munich, Germany, showing the feedthrough insulator and lightning surge loop. The high-power broadcast station can override most jamming signals.
Since the jamming equipment is not near the transmitting station, the jamming signal does not "overlap" the broadcast reception of the offensive station at points within Russia. This forces the Soviets to employ additional jamming equipment at various places. Dozens of jammers may be required to silence effectively a single radio station in a few populated areas, leaving relatively good reception of the unwanted station in sparsely settled areas.
Short-Wave Jamming. Due to the nature of short-wave propagation, a powerful short-wave transmitter is capable of blanketing tremendous areas of the Soviet Union, all of which must be covered by competing jammers in order to obliterate the signal. The action of short-wave "skip" is a result of the transmitted wave being radiated up into the ionosphere to be bent downward in a reflected ray returning to earth a considerable distance from the transmitter.
The amount of bending and distance covered depends upon many factors, most of which are uncontrollable. Separate jamming stations must be employed at each "skip point," since the "skip distance" of the jamming signal cannot be relied upon to be the same as that of the offending signal.
It can thus be seen that the problem of silencing literally hundreds of stations operating on various broadcast and shortwave frequencies is an extremely large operation.
Equipment Used. Special transmitting stations for jamming operations have been developed by Soviet engineers. These stations are designed for rapid frequency shifting and are capable of heavy noise modulation.
The usual modulation consists of a buzz-saw noise that completely fills a band of five or six kilocycles each side of the carrier frequency. Jamming equipment of this type is known to have power levels up to 1,000,000 watts!
As auxiliary jamming equipment, the Soviets sometimes press broadcasting stations into use, transmitting noise and chaos instead of the usual programs.
Anti-Jamming Techniques. Well aware of the jamming operations, the VOA and the British Broadcasting Corporation have several techniques at their disposal to combat jamming.
The most obvious and effective technique is to increase the power and range of the existing stations, and to add more stations, thus improving the coverage of the USSR. The VOA, for example, now broadcasts about 500 "transmitter-hours" (hours of broadcast multiplied by number of transmitters) daily to the Soviet Union, the satellites, and Red China.
A second technique is to change the wavelength (frequency) of the transmitting station, thus evading the jammer. This is usually impractical, as the Russians monitor the station being jammed and are quick to retune the jamming equipment when any frequency change is noted. Also, abrupt frequency changes make reception difficult for the listener.
Another evasive action is to choose a transmitter frequency immediately adjacent to the frequency used by a Soviet broadcast station, so that the program cannot be jammed without jamming the Russian broadcast.
Is Jamming Effective? Proof that the VOA programs are penetrating the barrage of jamming is evident from the amount of abuse heaped upon this activity by the Soviet Government.
Careful screening of refugees pouring into Berlin from the east confirms the value of every dollar spent in the electronic war. Clandestine listening posts behind. the Iron Curtain listen to the voices of freedom and report reception. Also letters smuggled out of the Soviet zones of influence attest to the impact these broadcasts have upon their audience.
It is therefore well known that the broadcasts do pierce the interference, and are successful in combating the efforts to prevent the flow of information and truth from reaching the citizens of the Soviet Union.
Posted October 29, 2013