The Duga was a Soviet “Over the horizon” radar system, and was a part of the Soviet missile defence early warning system that operated from July 1976 to December 1989. The first signals (probably from a predecessor) were detected in 1963.
There were only two operational Duga radars, one in Ukraine (near chernobyl) and one in Siberia.
The radar had a very high output signal, that could be heard all around the world, when it was activated. Amateur radio operators named it “The Russian Woodpecker”, after its “Tuk tuk tuk tuk” pulses, that interfered their shortwave radios.
It was estimated, that the output power on the radars were up to 10 MW.