Cold War Signals

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, telemetry and radio jamming are transmitted and intercepted, but it was also a war of words between many shortwave propaganda stations. There are many audio samples at the end of this page that show how the Cold War actually sounded.

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, organization 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. ELINT comprises the TechELINT collection of technical signals and OpELINT to gather operational intelligence.

SIGINT truck near Czechoslovakian border mid 1960's
ASA Det J Scheeberg veterans

East versus West Top

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 economic information from 'the other side'. These were the heydays of espionage, intelligence agencies and SIGINT organizations.

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 other's signals. Both sides deployed many mobile and fixed intercept stations.

Eavesdropping on the Enemy Top

The content or technical information behind some signals could be read or analyzed 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.

There were two major western alliances who shared SIGINT intelligence during the Cold War, and they are still active today. The first one started as UKUSA agreement, a cooperation between the United Kingdom and the United States to share SIGINT intelligence during WW2. Australia, Canada and New Zealand later joined the alliance to form the so-called Five Eyes (FVEY).

The second western SIGINT cooperation is a secret European alliance between Germany, the Netherlands, France, Denmark and Sweden, codenamed MAXIMATOR. An important source of their intelligence was the breaking of encrypted communications, secured by Crypto AG equipment. This seemingly independent Swiss firm was covertly owned by the Central Intelligence Agency (CIA) and the German Federal Intelligence (BND) and sold unnoticeable weakened crypto equipment worldwide, enabling the MAXIMATOR-countries to easily break these communications.

Teufelsberg Field Station Berlin

The global intercept capabilities of the American ECHELON system, in close cooperation with NSA’s codebreakers, are renowned. 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 Estonia 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.

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 well 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 Top

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 organizations 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 Soviet Duga-1 OTH system comprised two transmitter antennas at the Liubech-1 military site near Chernihiv and two receiver antennas at the Chernobyl-2 military site near Chernobyl, Ukraine.

The Chernobyl-2site was codenamed Steel Yard by Western military intelligence, who managed to photograph the site during the Cold War. The Chernobyl-2 installation was damaged during the 1986 Chernobyl disaster and never became operational again. The site now lays within the 18 miles Chernobyl exclusion zone, adding to its mystery status.

They also had the Duga-2, located in the far east of the USSR, with the transmitter in Lian and receiver in Bolshya Kartel . The first experimental OTH radar, simply called Duga without number, was located near Mykolaiv, close to the Black Sea.

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.

Receiver antennas at Chernobyl-2 site, part of Duga-1
with the "woodpecker" transmitters at
Liubech-1 site

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.

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. 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 information is found on our numbers stations page.

Cold War of Words Top

The Cold War was not limited to military communications, signals intelligence and spy radios but was also an open battle of words. Some countries with opposing ideologies imposed severe restrictions on free travel, media and freedom of expression. Radio signals however travelled freely across their borders.

The problem of information dissemination during the Cold War was resolved by using powerful shortwave transmitters that, according to one side, spread truthful political information to people who were denied free press and, according to the other side, harmful propaganda to turn the population against their government. This also included political and psychological warfare operations, known as Psy Ops. Both East and West used these methods and rhetoric. Some of these radio stations became true Cold War icons.

Radio Free Europe (RFE) and Radio Liberty (RL) are United States funded organizations, created in 1950 by the National Committee for a Free Europe, which was in fact a CIA front organization, created in 1949 to spread American and Western influence and counter the Soviet expansion. Over the years, RFE expanded its reach to most Eurasian countries. Radio Liberty started in 1951 and focused on the Soviet Union. RFE and RL had transmitter sites in Lampertheim, West Germany, later supplemented by transmitters in Portugal and Taiwan. Their mission was to provide an alternative to the targeted countries, with news and free press that was not available behind the Iron Curtain. Over the years, RFE and RL have broadcast in 54 different languages of the targeted countries and regions.

Radio Free Europe transmitter site West Germany

Voice Of America (VOA) is another major western radio station, established in 1942 during World War II to spread war news. VOA started broadcasting towards Russia in 1947 to counter Soviet propaganda against American leaders. VOA later extended its range to all Warsaw Pact countries. Another method to reach the public in the Eastern Bloc were more than 300.000 balloons with leaflets, books and posters, criticizing the communist regimes and supporting dissidents. A practice still used between South and North Korea to this day.

The Soviets, their satellite countries and other communist countries of course countered the Western aggression and expansion with their own means. Radio Moscow World Service was the official broadcast station of the Soviet Union. Their foreign service broadcasting started in 1929 with transmitters in Moscow and Leningrad, and later also relay stations in Vladivostok and Magadan, with regular programs in Europe, the Middle East, North and South America. By 1945 they reached whole Eurasia.

Over the years, their reach spread across the world with transmitters in the Soviet Union, Eastern Europe and Cuba, and they broadcasts in more than 70 languages. Radio Moscow changed its name in 1993 into Voice of Russia and renamed it again in 2014 into Radio Sputnik. More countries joined the battle of words. China started international broadcasts through Radio Peking in 1950, renamed it into Radio Beijing in 1983 and is now known as China Radio International.

The Cuban radio station Radio Rebelde, created in 1958 by the revolutionary army, was supervised by Che Guevara. Transmitting from Sierra Maestra, Radio Rebelde reached many south American countries, relayed messages to rebel states and eventually also targeted the United States and the Caribbean. The official Radio Havana Cuba (RHC) started in 1961. The shortwave station relayed and broadcast to countries in Europe, the Mediterranean, Africa and the Americas, and this in eight languages. As a communist ally of the Soviet Union, the Cubans were allowed to use transmitters from Radio Moscow to broadcast in Europe and the Mediterranean. RHC was also used by Cuban intelligence to support espionage operations in South America and the United States, and is known to broadcast numbers station messages.

Cold War propaganda and political warfare were not appreciated by the leaders of the targeted countries but no barbed wire, high fence or border guard could stop radio signals from travelling across their borders. A common practice to prevent these broadcasts from reaching their populations was radio jamming. To disrupt the powerful shortwave radio stations, they used even more powerful jamming transmitters, up to 500.000 Watt, with various interference signals such as noise, non-stop music or even recorded voices played backwards. More on this on the blog post Cold War Radio Jamming.

Radio Moscow (now Sputnik), Radio Havana Cuba, Voice of America and Radio Free Europe became true Cold War icons and are still in the air today. Propaganda remained important throughout the Cold War and continues to be relevant to this day, as it extended to television networks and Internet. Below are also some recording from Voice of America and Radio Moscow, but bear in mind that these stations had specific propaganda purposes and might not portrait the facts accurately. Also read the blog post Radio Moscow and the Cold War.

Sounds of the Cold War Top

How did the Cold War over radio waves actually sound like? Below some samples of intercepted signals, accompanied by a short description. 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-1 system with transmitter at Liubech-1 and receiver at Chernobyl-2. Its very powerful signal disrupted radio communications all over the world. 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, visit Der SAS- und Chiffrierdienstwebsite 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 of 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.
Atención 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 language numbers station, believed to be a transmitter operated by the Soviet secret service KGB.

Broadcast Station Recordings (all links to offsite archives - open in new tab) Top

Selection of audio recordings from well-known Cold War era broadcast stations.

More on this website Top

  • Numbers Stations What are numbers stations, who uses them and how are these spy transmitters operated.
  • One-time pad The complete story of one-time pad encryption and how it works.
  • 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 suppression of spurious signals
  • Hagelin Cryptos and Crypto AG History and ultimate compromise of a world leader in crypto equipment
  • Amanda Pinson The first female U.S. Army cryptologist killed during combat operations

SIGINT Chatter posts related to Cold War Signals (offsite - open in new tab)

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© Dirk Rijmenants 2004. Last changes: 15 August 2022