I want you to imagine for a second that it’s 1976, and you are an amateur short-wave radio enthusiast – strange request, I know, but just go with it. One night, whilst sitting in front of your equipment, you begin to receive a signal of unknown origin that drowns everything else out. Through your headphones, you hear a very distinct, repetitive tapping sound, and you are not the only one. The signal is so strong that radio hobbyists and legitimate broadcasters worldwide are hearing the same relentless tapping. You later find out that this mysterious signal is also interfering with public radio broadcasts and, more alarmingly, it also started to interfere with emergency frequencies for aircraft. The issue with interference becomes such a problem that, in later years, electronic manufacturers will begin to sell products that are capable of jamming it out.
Your speculation grows after you discover that fellow radio hobbyists managed to triangulate its origin and discovered it is coming from well behind the Iron Curtain in present day Ukraine. Now, back in 1976, the Cold War was in full swing and in the absence of information regarding the purpose of this signal, conspiracy theories flourished. Some thought it was a kind of weather manipulation experiment, whereas others believed the signal to be a form of mind control. However, there were short-wave listeners who right off the bat correctly identified it as signals from an over-the-horizon radar, which they nicknamed the Russian Woodpecker. NATO military intelligence called it STEEL WORK or STEEL RARD but its actual name was the Dugar Radar, although this was not publicly confirmed until after the fall of the Soviet Union.
I was recently able to visit the gargantuan receiving antennae located approximately 60 kilometres away from their transmitter which, together, were capable of detecting intercontinental ballistic missiles fired towards the Soviet Union from the States. There are actually two parts that make up the receiver, a low-frequency antenna with a height of 146 meters and length of almost half a kilometre, and a high-frequency antenna with a height of 100 metres and a length of 250 metres. As I said, the radar was operational from 1976, but towards the late 1980s the signals became less frequent, and in 1989 they disappeared altogether. It has since been left to decay, which is made eerier because of the fact that it is located in the Chernobyl exclusion zone.
The radar worked by reflecting the short-wave radio waves it generated off an ionised layer in the atmosphere called the ionosphere, back towards the ground over the horizon. A small amount of this signal was scattered back towards the antenna by the same path. This return signal is extremely small, which is one of the reasons why the Woodpecker is so large, in order to detect the signal. Then, to distinguish between a signal returned from hitting the ground from one hitting, let’s say an intercontinental ballistic missile, the operators would take advantage of the Doppler effect. By filtering out all the background noise from the signal reflected from the ground, they would detect frequency shifts created by moving objects.