Duga was a Soviet over-the-horizon (OTH) radar system used as part of the Soviet anti-ballistic missile early-warning network. The system operated from July 1976 to December 1989. Two operational Duga radars were deployed, one near Chernobyl and Chernihiv in the Ukraine SSR (present-day Ukraine), the other in eastern Sibera.
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.
Episode of Media Network on Radio Netherlands - 1986