TIL from 1976 to 1989 an unknown taping noise was audible worl | Today I Learned 🎓

TIL from 1976 to 1989 an unknown taping noise was audible worldwide on commercial and civilian communications (tv broadcast, commercial aviation, SW radio). The source was the Duga radar "The Russian Woodpecker" a huge over-the-horizon radar used by the Soviets as a missile detection system. [Source]