Duga (Russian: Дуга, meaning "arc" or "curve") was a type of over-the-horizon radar (OTH) system used by the Soviet Union as part of its missile defense network. It operated from July 1976 to December 1989. Two Duga radars were built: one near Chernobyl and Liubech in the Ukrainian SSR, and the other in eastern Siberia.
The Duga system was very powerful, using up to 10 megawatts of energy, and sent signals through shortwave radio bands. People who listened to shortwave radio called it the "Russian Woodpecker" because its signals sounded like sharp, repeated tapping noises at a frequency of 10 Hz. These signals often interfered with radio broadcasts, amateur radio use, and communications used for ocean travel, airplanes, and utilities. This caused complaints from many countries around the world. To reduce the interference, some radio equipment was designed with special filters called "Woodpecker Blankers."
The mysterious signal led to many theories, such as ideas about Soviet brainwashing or weather experiments. However, experts and radio hobbyists recognized it as an over-the-horizon radar system because of its unique signal pattern. NATO military groups named it "STEEL WORK" or "STEEL YARD" due to the large size of its antenna, which was 700 meters long and 150 meters tall.
History
The Soviet Union worked on early-warning radar systems in the 1960s to help detect missile launches. Most of these systems could only see objects directly in view, which limited their ability to warn of attacks quickly. These systems could not detect launches within seconds or minutes, which would have given defenses time to prepare. At the time, the Soviet Union did not have a well-developed satellite system for early warning. An over-the-horizon radar located in the USSR could help solve this problem. Work on such a system began in the late 1960s.
The first experimental system, called Duga, was built near Mykolaiv, Ukraine. It successfully detected rocket launches from Baikonur Cosmodrome, which was 2,500 kilometers (1,600 miles) away. A later version of Duga, built on the same site, could track launches from the far east and submarines in the Pacific Ocean as missiles traveled toward Novaya Zemlya. These systems were aimed east and used low power, but they proved the concept. In 1972, a new version called Duga-1 was built, with a transmitter and receiver separated by about 60 kilometers (37 miles).
In 1976, a strong radio signal was detected worldwide and called "the Woodpecker" by radio hobbyists. Some Woodpecker transmitters had power levels as high as 10 million watts. Similar interference was reported earlier, with radio amateurs calling it "the Russian Woodpecker" as early as 1963. This signal was likely a test of the Duga radar system. Radio hobbyists and NATO traced the signal to an area in present-day Ukraine, then part of the Soviet Union. Reports placed the location near Kyiv, Minsk, Chernobyl, Gomel, or Chernihiv. The actual site had transmitters a few kilometers southwest of Chernobyl and receivers about 50 kilometers (31 miles) northeast of Chernobyl.
The Soviet Union called the system 5Н32-West and built it in two closed towns: Liubech-1, which held the transmitters, and Chernobyl-2, which held the receivers. NATO referred to the system as "STEEL WORK," though some sources used "STEEL YARD" or "STEEL WORKS." The earliest public mention of the NATO name used "STEEL WORK."
During the Cold War, experts suspected the Woodpecker signal was from an over-the-horizon radar. Other theories, like using it to block Western radio broadcasts or communicate with submarines, were later dismissed. Analysis of the signal showed it had a repeating pattern, similar to a code used in radar systems. This allowed the radar to detect objects with high accuracy. A second Woodpecker signal in eastern Russia helped cover areas not reached by the first system, confirming the radar’s purpose.
In 1988, the U.S. Federal Communications Commission studied the Woodpecker signal. It had a pulse repetition interval of about 90 milliseconds, a frequency range of 7 to 19 MHz, and a typical transmission time of 7 minutes. The signal had a wide bandwidth of 40 kHz, with repetition frequencies of 10, 16, and 20 Hz, most commonly 10 Hz.
To block the signal, radio hobbyists sent signals at the same rate as the Woodpecker. They formed a group called "The Russian Woodpecker Hunting Club." By the late 1980s, the Woodpecker signals became less frequent and stopped in 1989. The reasons for the shutdown are not public, but the end of the Cold War and the success of U.S. satellite systems, which provided faster and more secure warnings, may have contributed. Radar systems are vulnerable to interference and weather, while satellites are more reliable.
Locations
The original Duga was the first experimental system. It was built outside the Black Sea port of Mykolaiv in southern Ukraine. It successfully detected rocket launches from Baikonur Cosmodrome about 2,500 kilometers (1,600 miles) away. Duga could track launches from the Far East and from submarines in the Pacific Ocean as the missiles flew toward Novaya Zemlya in the Arctic Ocean. This large radar system was restored in 2002 after a fire seriously damaged it. The transmitter was located at 46°48′26″N 32°13′12″E and the receiver at 47°02′28.33″N 32°11′57.29″E.
The original Duga was replaced by two installations: Duga-1 in the west and Duga-2 in the east. Duga-1 was built in northern Ukraine, between Liubech and Chernobyl-2. Its receiver was located at 51°18′19.06″N 30°03′57.35″E, 12 kilometers west-northwest of Chernobyl. The transmitter was located at 51°38′15.98″N 30°42′10.41″E, about 50 kilometers (31 miles) northeast of Chernobyl, just west of Chernihiv and south of Gomel.
Duga-2, the eastern system, is near Komsomolsk-on-Amur in Khabarovsk Krai. Its receiver is located at 50°23′07.98″N 137°19′41.87″E, about 30 kilometers (19 miles) southeast of the city. The transmitter is located at 50°53′34.66″N 136°50′12.38″E, 45 kilometers (28 miles) north of the city.