This was followed by the first operational system Duga-1, known in the west as Steel Yard, which first broadcast in 1976. Built outside Gomel, near Chernobyl, it was aimed northward and covered the continental United States.[citation needed] Its loud and repetitive pulses in the middle of the shortwave radio bands led to its being known as the "Russian Woodpecker" by amateur radio (ham) operators. The Soviet Union eventually shifted the frequencies they used, without admitting they were even the source, largely due to its interference with certain long-range air-to-ground communications used by commercial airliners.[citation needed] A second system was set up near Komsomolsk-on-Amur in the Russian Far East, also covering the continental United States and Alaska.[citation needed]