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Jamming Radio Signals
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Jamming Radio Signals
by Anthony Uminn, Paige Chia, William Kangas (Winter 96)
Jamming is the intentional interference with the reception of
wanted signals from another station which renders the wanted
signals unlistenable. Jamming was first used by the Germans during
World War 1. In the early 1920s, competing broadcasters in the
United States jammed rival radio programs. During the 1930s,
jamming became a political weapon. World War II demonstrated
that a jamming network operating against military circuits, was a
potent wartime weapon.
The War's end saw jamming continued but on an even larger scale,
especially with the advent of the Cold War. Stalin decided in 1948
to launch massive jamming campaigns against the West. At first,
the commitment was made using a dozen jammers operating against
Russian-language broadcasts of the Voice of America. By 1956
about 3,000 Soviet bloc jammers were operating against Western
broadcasts in all languages. Their jamming system was
administered by a secret department in the Ministry of
Communications, privately known as the Krestyaninova Section. It
was named after Natalia Krestyanoniva who ran the department for
more than twenty-five years (Leinwoll, 1989, p.78).
How is jamming done and what does it sound like ? There are many
types of specially developed jamming signals. The most frequently
heard are :
Pulse-keyed CW which sounds like a power drill.
Random noise AM which sounds like a sudden increase in atmospheric noise.
Noise-burst (sounds like the above).
Carrier-sweep, which sounds like an automobile engine at high-speed.
Grunting; produced by modulating an AM transmitter with a very low audio
frequency varying at a random rate. Sounds exactly like it is named.
More advanced jamming techniques even involve the reception and
rebroadcasting of the transmission so that it comes out totally
distorted. This method is not normally used to jam shortwave
transmissions, but more commonly used to jam military voice or
data transmissions and radar (Schultz, 1972, p.141).
Jamming was effective because it prevented reception and made
listening so annoying that even repeated attempts to listen would be
discouraged. This way, authorities hoped to block the
dissemination of information to the general masses, particularly
where there were conflicting interests and idealogies.
Today the Cold War has ended and there has been a major shift
away from formal jamming operations. However, the core of the
jamming system- the transmitters, have been retained, ready to be
resumed in a matter of days should the political climate in the
former U.S.S.R. change drastically. Although the production of
noise for the sole purpose of blocking `objectional' broadcasts has
ended, it is not certain that jamming, in a broader context, has
disappeared entirely.
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