Duga

Short answer: Duga, Russian for 'arc', was a Soviet over-the-horizon radar system that formed part of the USSR's early-warning network against ballistic missiles. Over-the-horizon radar bounces shortwave signals off the ionosphere to see far beyond the line of sight.

After an experimental Duga near Mykolaiv proved the idea, two operational systems were built: Duga-1 in what is now northern Ukraine, then the Ukrainian SSR, and Duga-2 in eastern Siberia near Komsomolsk-on-Amur. Duga-1 split its transmitter and receiver about 60 kilometers apart. The giant receiving array stands in the closed town of Chernobyl-2, a few kilometers from the Chernobyl nuclear plant, and the transmitters were near Liubech. From July 1976 to December 1989, its pulses, at up to about 10 megawatts, swept across the shortwave bands as a sharp tapping, usually 10 times a second. Listeners worldwide called it the 'Russian Woodpecker', and it disrupted broadcasts, amateur radio and aviation communications, drawing thousands of complaints. NATO reportedly gave it the reporting name STEEL WORK or STEEL YARD. The Chernobyl antenna is about 700 meters long and 150 meters high. The signals faded in the late 1980s and stopped in 1989; the reasons were never made public. The abandoned array, inside the Chernobyl Exclusion Zone, is now a listed monument in Ukraine. The footage shows its rusting steel towers and antenna elements.

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