The Russian Woodpecker was a notorious Soviet signal that could be heard on the shortwave radio bands worldwide between July 1976 and December 1989. It sounded like a sharp tapping noise, at 10 Hz, giving rise to the "Woodpecker" name. The random frequency hops disrupted legitimate broadcast, amateur radio, and utility transmissions and resulted in thousands of complaints by many countries worldwide. The interference dogged amateur radio operators worldwide and led to a thriving industry of "Woodpecker filters" and noise blankers. One idea amateur radio operators floated to combat this interference was to attempt to "jam" the signal by transmitting synchronized unmodulated continuous wave signals, at the same pulse rate as the offending signal. However, this technique would have had to employ a large number of amateur operators over a very wide area in order to attain enough power to overcome the offending signal.

In 1988, the Federal Communications Commission conducted a study on the Woodpecker signal. Data analysis showed a pulse repetition frequency of about 90 ms, a frequency range of 7 to 19 MHz, a bandwidth of 0.02 to 0.8 MHz, and typical transmission time of 7 minutes. A triangulated position of 51.4N 137.7E was also obtained.

The Woodpecker turned out to be an over-the-horizon radar system known to NATO as Steel Yard . The first operational site was located near Gomel in what is now Belarus, and the second site was at Komsomolsk-on-Amur in Siberia. The use of the shortwave spectrum, which was sensitive to ionospheric refraction, allowed the Soviets to detect alterations in ionosphere propogation caused by the depletion of ions by missile exhaust plumes.

References

• The Russian Woodpecker, Miami Herald, July 1982.
• Steel Yard OTH, globalsecurity.org.