A high-powered radio beam disrupting shortwave broadcasts all over northern Europe has been identified here as a new Soviet radar system that "bends" with the curvature of the earth.
According to Danish military intelligence, the system appears to have been designed to pick up and target incoming low-flying aircraft or missiles that elude conventional radar screens. Two such targets, according to the Danes, would be the U.S. cruise missile and B-1 bomber, both still under development.
Danish technicians have established that the troublesome beams emanate from a radar system and that the device is essentially defensive, according to military sources. They rule out speculation that the transmissions are part of an offensive aimed at giving the Soviets a strike capability after a nuclear attack.
The Danes, however, readily acknowledge that they are able to make only a limited examination of the Soviet beams. The United States, with its satellites and other technically advanced equipment, is relied upon by Denmark and other NATO allies to deliver a definitive analysis.
The Danish Postal and Telegraph Adminstration first picked up the signals in August, according to Borge Nielsen the chief engineer. Copenhagen sent routine complaints to the Soviet telecommunications authorities. These were ignored.
So Denmark, with Norway, protested formally to the Soviet Foreign Ministry in November. The Russians said they were carrying out experiments and would make an effort to reduce the interference.
Identical messages were given to other protesting nations, but the signals continue. Last fall, the victims tried to invoke the aid of the International Telecommunications Union in Geneva, the international governing body for radio traffic. This, too, has proved ineffective.
The signals continue to this day, appearing irregularly on different frequencies and at odd hours.
Nielson said that so far the interference has not caused any accidents involving planes or ships using radio for communication and navigation. He added, however, that he feared some disaster might occur if the experiments are not brought under control.
[King T. Hall, chief watch officer of the Federal Communication Commission's monitoring operation said in Washington at the end of last year that the Soviets apparently tried to avoid safety service frequencies following complaints from the United States in December.]
Other nations that have complained, Neilsen said, are U.S., Sweden, Britain, West Germany, Switzerland and Canada. Danish ship-to-shore and air-to-ground radio traffic in Greenland especially has been affected.
Nielsen observed that the Soviets may be trying to exploit the protests to gain useful information for their testing. Moscow has asked the complainers to report further incidents of interference. The danes have sent a few telegrams, citing new examples.
The beam is known as "the Russian woodpecker" in Britain because of the staccato drilling sound it makes. It appears to be coming from a site southeast of Minsk.
According to Flight International, a U.S. trade journal, the beams emanate from three or four transmitters. This suggests that the Soviets are trying to develop a system that will identify the shape or signature of incoming objects, enabling them to distinguish between a missile and an earth-hugging plane.
The beams are said to ber very highpowered, as much as 40 megawatts according to one report.
The Soviets are still testing the new system and apparently do not yet have it under control. This explains why the beams have been appearing all over the shortwave band.
The U.S. cruise missile which the radar is apparently designed to spot will be a low-flying weapon whose directions can be changed in flight.
Some beams have been picked up by British and U.S. ham operators. Some have blasted their way into overseas broadcasts. Others have interfered with point-to-point communications, from ship to shore and from airline pilots to control towers.
The United States has been working on over-the-horizon radar as its system is known, since the 1960s and has several already operating.
When the Soviet transmissions were first heard, some theorists suggested that the Soviets were trying to perfect a new radio system that would enable them to signal their nuclear submarines or missile bases even after a nuclear attack. Military intelligence here, however, rules this out and has concluded that the beams come from a radar system. That would be consistent with Soviet emphasis on defense, particularly air defense.