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Cold War Signals
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War on the Waves

An important part of the Cold War was fought over radio waves and this battle continues to this day. All kinds of radio signals, from communication signals in voice, Morse or data, to technical signals such as radar, navigation and radio jamming are transmitted and intercepted.

Especially during the Cold War, the arms race and the need for intelligence fueled a rapid development of sophisticated electronics. The interception and analysis of enemy signals became just as important as the performance and protection of one's own signals. Signals intelligence (SIGINT), the gathering of intelligence by interception of signals, comprises two main parts: communications intelligence (COMINT) and electronic intelligence (ELINT).

COMINT focuses on voice, Morse and data communications to retrieve the content of the messages, the identity and location of the person, organisation or unit that broadcast, and the broadcast frequencies and schedules. These communications are often encrypted to protect them from eavesdropping, requiring cryptanalysis to make them readable. Even when all cryptanalytic attacks fail, information can still be extracted by traffic analysis, the deduction of information from patterns in the communications (message size and volume, time, location).

ELINT comprises the interception and analysis of signals from weapons systems, navigation, guidance and radar systems, to find out which systems the opponent uses, how the equipment works and how it performs. Goal is to know the opponent's capabilities, his order of battle, and to develop electronic counter measures (ECM) against his equipment. The opponent, on the other hand, will develop electronic counter-counter measures (ECCM), for instance encryption or frequency hopping, to prevent exploitation or jamming of his systems.



SIGINT truck near Czechoslovakian border mid 1960's
Source: ASA Det J Schneeberg veterans


East versus West

In today’s world of global communications, the Internet and freedom of travel, we tend to forget that, only a few years ago, there were two separated worlds on this planet: the East and the West. Until the fall of the Berlin Wall in 1989, East and West weren’t merely geographically expressions. Almost every country on the globe had taken side, willingly or not. The Cold War raged over the world for almost 45 years and it was often far from cold in many Asian, African, Middle Eastern and South American countries.

The separation of these two worlds was nowhere more visible than on the border between Western Europe and the Soviet Union, the co-called Iron Curtain. It was a border that few were allowed to cross and on-the-spot intelligence gathering was a very risky business. Consequently, for decades, little was known about the opponent and huge efforts were made to retrieve even the smallest piece of military, political or economical information from 'the other side'. These were the heydays of espionage, intelligence agencies and SIGINT organisations.

Both the West and the Soviet Union had build up huge armies with an enormous arsenal. The skies were crowded with various signals and SIGINT was an ideal method to collect information from a – relatively – safe distance. Huge resources and a lot of money were spent to intercept each others signals. Both sides deployed many mobile and fixed intercept stations.


Eavesdropping on the Enemy

The content or technical information behind some signals could be read or analysed immediately, but much of the intercepted information could not be read because it was encrypted. The introduction of digital systems made possible the development of far more complex encryption schemes.

Nevertheless, both the Western countries and the Soviets still had their successes. A key factor in breaking encrypted signals was to collect enough data. More data means more statistical information for the mathematicians who attack the codes. Both the United States and the Soviet Union had plenty of the brightest mathematicians. Now they just needed plenty of data. No problem!

The global intercept capabilities of the American ECHELON system, in close cooperation with NSA’s codebreakers, are renowed. During the Cold War, ASA and later NSA operated important SIGINT stations in Germany, the United Kingdom and New Zealand, some of which are still operational. In Germany, the frontier of the Cold War, some well known examples were the American SIGINT Field Station Berlin on top of Teufelsberg and ASA Det J in Schneeberg, near Czechoslovakia.

The Soviets also had their share in the worldwide eavesdropping competition with, among others, SIGINT stations at Lourdes in Cuba, Cam Ranh Bay in Vietnam, near Tallinn in Estland and in South Yemen. They also had several stations in East Germany, such as the Yenisei and Urian listening posts in Brocken. The GRU (military intelligence), the KGB's 16th Directorat (interception of communications and Signal Intelligence) and 8th Main Directorat (communication and cryptography) did their part in processing the intercepted traffic. They also operate a large satellite network for interception and communications and have a large number of intercept stations around the world.

Teufelsberg Field Station Berlin


Nonetheless, even some smaller countries were more than capable. The HVA, the East German foreign intelligence service under control of the Ministerium für Staatssicherheit (Stasi), was well known and feared for its excellent espionage capabilities by human intelligence (HUMINT) with an enormous number of agents operating in the West. However, for decades, their technical capabilities were heavily underestimated.

After the dissolving of the German Democratic Republic, it became clear that the Stasi SIGINT directorat HA III had 25 departments, over 2000 staff officers and some 80 installations in East Germany. They monitored shortwave transmissions and more than 30,000 West German telephones from military, diplomatic and intelligence personnel from both West Germany and NATO. They eavesdropped on radio signal paths (telephone) used by the Federal Post Office, and on VHF radios of the BND (West German intelligence) surveillance teams. Virtually all West German satellite-based telephone, Telex, fax, and data transmissions were monitored.


Short range signals (VHF, radar, missile guidance) often required interception from closer distances. Airborne SIGINT and ELINT platforms constantly patrolled close to and often even beyond enemy borders to eavesdrop on their signals . These were most dangerous missions, even in peacetime. Many of the crews never returned home.

The shootdown of a C-130 above Armenia in 1958 and an EC-121 above the Sea of Japan in 1968 are only a few well known of over 40 U.S. aircraft that were lost. These reconnaissance programs were top secret and the public usually never knew about these losses. Other welll know U.S. SIGINT platforms were the RC-135, the EA-3B and EA-6B. The famous Soviet TU-95 and TU-142 were also known for their regular testing of the limits at the NATO borders.

SIGINT collection by ships was just as hazardous, with the capture of AGER-2 USS Pueblo by North Korea in 1968 being the most notorious and most damaging for U.S. communications security. The Soviet spy trailers were also regular visitors in Western coastal waters. Some naval SIGINT operations were most daring. In 1971, during operation Ivy Bells, the nuclear U.S. submarine USS Halibut placed a 6 ton weighing wiretap on an undersea communications cable in the Sea of Okhotsk.


AGER-2 USS Pueblo SIGINT vessel in 1967

The cable connected the Soviet naval submarine base in Kamchatsky, north-east of the Kuril Islands, with Vladivostok Fleet headquarters. The Sea of Okhotsk was Soviet territorial waters, forbidden for foreign ships, heavily protected and a playground for numerous Soviet surface and subsurface naval exercises. Not quite a friendly environment for U.S. submarines. Similar Soviet submarine SIGINT missions undoubtedly remain hidden in Russian archives.



Mysterious Cold War Signals

Often, the secrets behind unreachable signals were unveiled, either by ELINT, COMINT or espionage. However, despite huge efforts and risks, some signals remained unidentified and some of them even rose to the stardom of mysterious Cold War signals. These signals also caught the attention of both Intelligence organisations and civilian radio amateurs. There was much speculation about the purpose of these signals, some of which were in voice or Morse, others were strange analogue or digital transmissions that lasted for decades.

Once such station was nicknamed the Russian Woodpecker, because of its characteristic repetitive tapping noise. The Woodpecker's annoying high-power signal (an estimated 10 Megawatt) switched between different shortwave frequencies and disrupted legitimate utility and amateur broadcasts all over the world. The broadcast started in 1976 and continued for 10 years. For decades, its purpose remained unknown to the general public.

After the fall of the Soviet Union it was confirmed that the strange signal originated from an over-the-horizon (OTH) radar as part of the Soviet Anti Ballistic Missile early warning system. The enormous antenna of the Duga-3 OTH system is located in Chernobyl (now Ukraine). The transmitter site, called Chernobyl-2, was codenamed Steel Yard by Western military intelligence, who apparently managed to photograph the transmitter site during the Cold War. Noteworthy is that site now lays within the 18 miles Chernobyl exclusion zone, adding to its mystery status.

The United States also had their part in long-distance snooping by developing the MELODY system, a so-called bistatic interception that uses objects like the Soviet's own missiles, or even the moon, to reflect radar signals over very large distance, far beyond the horizon. This enabled tracking and analysis of remote radar locations inside Russia.

Another famous Soviet signal is known under its call-sign UVB-76. The station, nicknamed the Buzzer, started broadcast in 1982 with a two-second beep tone and switched, after a decade of operation, to a monotonous 25 buzz tones per minute. Continuously, every hour, every single day, year after year. The station is extensively observed by radio amateurs (without doubt an equally monotonous job) and only a handful of voice conversations were ever recorded in its 28 years of operation. Its call-sign UVB-76 was revealed during one of its rare voice conversations. The station, which apparently relocated in 2010, is currently known under its new callsign UVB-76 / MDZhB. The purpose of The Buzzer remains unknown until today.

"Woodpecker" Duga-3 antenna at the Chernobyl-2 site


Some believe that the Buzzer simply occupies certain frequencies to have them available in case of a crisis or war. Others believe that the uninterrupted signal is part of the notorious so-called Dead Hand, an autonomous launch system for clusters of nuclear missile sites that supposedly would be activated if the signal was interrupted, due to elimination of Soviet military command by an American first strike. As we now know, the dead hand systems did actually exist, but the relation between UVB-76 and the doomsday system is nothing more than pure speculation. Nevertheless, the few interrupts of the signal did raise some eyebrows at the time.

Another true Cold War icon is, of course, the notorious numbers station. These stations broadcast streams of numbers or letters in voice or Morse, and these unlicensed and officially non-existing stations are transmitting since many decades. During the Cold War, there was much speculation by radio amateurs who intercepted these mysterious messages. Some believed these were spy stations, but governments denied their existence or claimed them to be weather signals, buoys or beacons. Today, there’s plenty of evidence, from spy case court documents and archives, that they are indeed encrypted messages, send by intelligence agencies to their agents in the field. Mostly, these messages are encrypted with the unbreakable one-time pad system. Although the Cold War officially ended, there are still many active numbers stations and new keep popping up, sending messages in many different languages. Who is listening to them remains a mystery. More about numbers station is found on this webpage.


Sounds from the Cold War

How did the Cold War over radio waves actually sound like? Below some examples of intercepted signals, accompanied by a short description. Click the icons or the links to listen. You will notice that some sounds are very mysterious and, given the paranoid mind set during the Cold War, must have sounded pretty scary at the time. The most intriguing of all is that the end of the Cold War did not end this war of the waves. In the contrary, the Cold War is merely replaced by a Cold Peace, with a flourishing world of mysterious of signals. A shortwave receiver with a good antenna was, and still is, all you need to discover innumerable signals...

Woodpecker Soviet Duga-3 station at the Chernobyl-2 site. Its very powerful signal disrupted radio communications all over the world. According to the former commander of the Chernobyl-2 site, the installation was damaged during the 1986 Chernobyl disaster and never became operational again.
The Buzzer Soviet UVB-76 transmitter, sending its monotone buzz tones for several decades. The purpose of The Buzzer has never been disclosed. According to some sources, the transmitter site was located near Povarovo, 25 miles north-west of Moscow, but relocated in 2010.
ELBRUS Analogue T-217M voice encryption system from the former East German NVA (Nationale Volksarmee). Sound sample from Der SAS- und Chiffrierdienst. For more information about East German equipment, please visit Der SAS- und Chiffrierdienst website and select "Technik" pages.
Czech lady Numbers station from the former Czechoslovakian StB (State Security Service). A well recognizable introduction signals was followed by the actual message, mostly encrypted with the unbreakable one-time pad system
Stasi gong station This is one the most sinister numbers station ever, operated by the East German Stasi. The station with its very recognizable weird gong sounds transmitted nearly a decade and suddenly stopped in may 1990, in the last months of East Germany's existence.
Attencion Station Numbers station of the Cuban intelligence service DG. These stations remain very active to this day. Several Cuban agents, receiving orders through these stations, were arrested in the United States. The most recent spy case was in 2009.
Russian Male Unidentified Russian numbers station, believed to be KGB operated.

More on this website

  • Numbers Stations Explains what numbers station are and how they operate.
  • One-time pad The complete story of one-time pad encryption.
  • Cuban Agent Communications PDF Format paper on numbers stations and operational methods of the Cuban intelligence service.
  • SWL Shortwave Listening An introduction into how to receive shortwave stations and the equipment you need.
  • TEMPEST The origin of TEMPEST, the supression of spurious signals
  • Amanda Pinson The first female U.S. Army cryptologist killed during combat operations

Some of my blog posts related to Cold War SIGINT (off-site)

Additional information on Cold War signals (off-site - opens in new window)


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