Duga radar
Duga (Russian: Дуга) was a Soviet over-the-horizon (OTH) radar system used as part of the Soviet ABM early-warning network. The system operated from July 1976 to December 1989. Two operational Duga radars were deployed, one near Chernobyl and Chernihiv in what was then called the Ukrainian SSR (present-day Ukraine), the other in eastern Siberia.
The Duga systems were extremely powerful, over 10 MW in some cases, and broadcast in the shortwave radio bands. They appeared without warning, sounding like a sharp, repetitive tapping noise at 10 Hz, which led to it being nicknamed by shortwave listeners the Russian Woodpecker. The random frequency hops disrupted legitimate broadcasts, amateur radio operations, oceanic commercial aviation communications, utility transmissions, and resulted in thousands of complaints by many countries worldwide. The signal became such a nuisance that some receivers such as amateur radios and televisions actually began including 'Woodpecker Blankers' in their circuit designs in an effort to filter out the interference.
The unclaimed signal was a source for much speculation, giving rise to theories such as Soviet mind control and weather control experiments. However, because of its distinctive transmission pattern, many experts and amateur radio hobbyists quickly realized it to be an over-the-horizon radar system. NATO military intelligence had already given it the NATO reporting name of either STEEL WORK or STEEL YARD. While the amateur radio community was well aware of the system, this theory was not publicly confirmed until after the fall of the Soviet Union.
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