Over-the-horizon radar

Powerful military radars that bounce signals off the ionosphere to see thousands of miles away. They often spill into shortwave bands, including ham bands.

My life list

ModeOver-the-horizon radar

FamilyRadar

Audio exampleComing

What does it sound like?

Plate 44Radar

A rapid, harsh tapping or 'woodpecker' sound, or a fast sweeping buzz.

Field marksHarsh tapping or buzzingSweeps many times a secondWide: often 10 kHz or more

Who uses it?

Defense organizations in several countries.

Where and when can I hear it?

Anywhere from about 5 to 28 MHz; they move frequency often and can be very wide.

Hear it live

University of Twente WebSDR (Enschede, the Netherlands)
No fixed time or frequency; these radars move often. Look along the 7, 14 and 21 MHz bands for a wide block of repeating stripes on the waterfall.

These are free public receivers run by other people; we only link to them. You'll hear the signal only if it's on the air right now and conditions carry it to that receiver, so if it's quiet, try another time. Links last reviewed 2026-09-28.

The science

Ordinary radar stops near the horizon because its microwave signals travel in straight lines. Over-the-horizon radar works in the shortwave range instead (Australia's Jindalee system uses 5 to 30 MHz) and bounces its signal off the ionosphere, the electrically charged upper atmosphere, down onto targets 1,000 to 3,000 kilometers away; faint echoes return the same way. It picks out ships and aircraft by the Doppler shift their motion adds to the echo, and its performance rises and falls with the ionosphere, which changes with time of day and solar activity. The signals are wide: amateur monitors list a necessary bandwidth of 12 kHz for one Russian system, and a radar at the British base in Cyprus usually uses 20 kHz, occasionally up to 80 kHz.

Why use it?

Australia's three-station network can detect aircraft and ships over about 13 million square kilometers, more than 1.7 times the country's land area, without satellites or forward outposts. For listeners, the International Amateur Radio Union's Region 1 monitoring service reported in 2021 that its reports of these radars dwarf those of every other interference source on the amateur bands.

Lore

The best-known was the Soviet Duga system. From 1976, shortwave listeners around the world heard its sharp, repetitive tapping, often about 10 pulses a second, and nicknamed it the Russian Woodpecker. The huge antenna near Chernobyl, closed after the 1986 nuclear disaster, still stands in the exclusion zone, where guided groups have been allowed to visit it since 2013.

Easily confused with

Time signal station: time stations tick once a second on fixed frequencies