Duga

The Duga array was a massive over-the-horizon radar (OTHR) system designed to detect ICBM launches by transmitting high-power, shortwave radio pulses that bounced off the ionosphere’s F-layer, allowing coverage over ranges of 3,000 to 9,000 kilometers.

It operated on frequencies between 3 and 30 MHz, relying on ionospheric reflection to circumvent the Earth’s curvature.

The array’s effectiveness was highly sensitive to ionospheric density variations, impacted by solar activity, geomagnetic storms, and diurnal cycles, which could disrupt signal clarity.

Its distinctive, repetitive tapping interference earned it the nickname "Russian Woodpecker", but despite its ambitious scale, signal distortion and false returns limited its operational reliability as a Cold War early-warning detection system.