Tracking Cold War Signals

Adcock four element antenna array
WWII Naval direction finding station
(source: Frontline Ulster)

The Cold War was also a war of signals. This battle comprised chatter over radio, Morse, data and technical signals. Eavesdropping on enemy communications and analyzing their technical signals was a vital part of that battle. However, to know where those signals came from was just as important.

Directional antennas find the bearing of a signal. Early simple loop antennas had to be turned mechanically to find the signal bearing. With two or more such antennas on different locations, the target is located at the crossing of those bearings, but it was a cumbersome task. Later, double loop antennas and Adcock antenna arrays with four elements improved performance, but many more special  direction finding (DF) antennas were built to locate signals, and some were quite extraordinary.

German Wartime Research

The Wullenweber antenna array
(source: FGCRT)

Significant progress was made during the Second World War by Dr. Hans Rindfleisch, who invented the Circularly Disposed Antenna Array (CDAA). Rindfleisch also headed the Communications Research Command of the German Navy, and together with Telefunken they developed his antenna array under the codename Wullenweber.

The first Wullenweber, build in Skibsby in northern Denmark, was designed as high-frequency direction finding (HF/DF) antenna array and operated in the 6-20 MHz range. The above drawing shows, at the top, the view of the antenna array and the reflector screen wires behind them (click image to enlarge)

 

First Wullenweber at Skibsby site
(source unknown)

The antenna consisted of 40 vertical radiator elements, each supported by a wooden structure and placed in a large circle, 120 m (392 ft) in diameter. Inside that circle was a reflector screen of wires, supported by 40 poles and arranged in a smaller circle, 105 m (344 ft) in diameter.

The Foundation for German communication and related technologies (main page) has a description of the Wullenwever (original spelling), including German Naval research on Wullenwever (pdf p11-20) and the Landsberg-Lech conference (pdf) with technical details and several photos of  the Skibsby Wullenweber site.

German Technology in Soviet Hands

Many German scientists were rounded up by US and Soviet forces in the final days of the war. Both were interested in this new CDAA technology, but the Soviets were the first to start building them in 1951 with assistance of German scientists.

The Soviets eventually build 31 CDAA's of various types and called them KRUG. They were placed in Russia, Warsaw Pact countries, Mongolia, Cuba, Vietnam and Burma. These KRUG stations tracked radio communications of US and NATO reconnaissance aircraft and nuclear bombers. GlobalSecurity has info and photos on Soviet KRUG antenna arrays.

The Global U.S. Antenna Network

One of the German antenna researchers was moved to the United States to assists in the development of a CDAA. The US version of the Wullenweber was the AN/FLR-9 antenna, nicknamed "Elephant Cage". The first was built in 1962 at the RAF Chicksands base in the UK, leased by the US Air Force.

FLR-9 at USASA Field Station Augsburg, Germany (source: US Air Force ISR)

The huge FLR-9 antenna had an outer diameter of 440 m (1,443 ft) and height 37 m (121 ft). A network of eight FLR-9 was constructed in Alaska, England, Germany, Italy, Japan, Philippines, Turkey and Thailand. This network could accurately locate HF signals anywhere on Earth, to track enemy airplanes, ships or ground based transmitters, but also to follow own or friendly targets.

The US Naval Security Group operated the AN/FRD-10, also a Wullenweber antenna but smaller than the FLR-9. Its outer diameter was 263 m (863 ft). A network of sixteen FRD-10's was located at coastal lines of the Pacific and Atlantic on US mainland and Alaska, Hawai, Puerto Rico, Canada,  Panama, Japan, Spain and Scotland.

More about the Wullenweber

FLR stands for Fixed Countermeasures Receiving. FRD stands for Fixed Radio Direction-finder (see JETDS designations). More about the FLR-9 on FAS and Freedom Through Vigilance Association (USAFSS). Navy Radio has details of the AN/FRD-10. There's a report on the dismantling of the AN/FLR-9 at Misawa air base in Japan and the decommissioning of Joint Base Elmendorf-Richardson in Alaska (video). See also locations of AN/FLR-9 antenna system at the Station Hypo website.

More on WWII direction finding at the RSS Secret Listeners website and on Frontline Ulster's WWII Aircraft Direction Finding in the UK.

The NSA video below explains the history and purpose of the FLR-9.

The Last Elephant Cage

 
The American Forces Network Pacific gave a look inside Misawa’s FLR-9, build in 1962. The antenna was demolished in 2014.

FLR-9 AFN Misawa

More on Signals

Many different signals were sent, received and analyzed during the Cold War. Below some posts on this blog about Signals Intelligence (SIGINT), but there's much more to discover...

• Mysterious Cold War signals Fascinating signals revealed
• Field Station Berlin ASA/NSA listening post
• Russia’s Modern Early Warning Systems
  
• Electronic Intelligence at NSA History of  ELINT
• More posts about signals intelligence...

Visit also the Cold War Signals page about the battle over radio waves on our website

Field Station Berlin - Teufelsberg

Field Station Berlin 1980s

Teufelsberg (Devil's mountain), located in west Berlin, Germany, has a most unique history. With its 375 ft (114 m) it is the highest hill in the Berlin area, and it's man-made! It is made of 12 million cubic meter rubble, from about 400,000 destroyed buildings, during the rebuilt of Berlin after the Second World War.

In the late 1950's, Allied mobile listening post, eavesdropping on East German and Soviet communications, discovered that Teufelsberg was an ideal location, with its unobstructed reception of signals from all directions. In 1961, the US Amry Security Agency (ASA) started their first Signals Intelligence (SIGINT) operations out of trucks on top of the hill. Soon after, the first buildings were constructed of what became known as Field Station Berlin (FSB).

Eavesdropping on the East

Although Teufelsberg was located in the British sector of Berlin, there was a close cooperation between  US and British intelligence. Initially operated by the ASA, the American part of the station came under control of the Army Intelligence and Security Command (INSCOM) in 1977 and the National Security Agency (NSA) provided most of the personnel and equipment.

Field Station Berlin gradually grew over the next years to become one of the largest  SIGINT stations ever, with some 1500 personnel working in shifts. They lived in military barracks like Andrews Barracks or were housed in neighborhoods among the Berliners.

With its large antenna park and huge dishes in their radomes, FSB intercepted East German and Soviet radio communications, directional microwave links and satellite transmissions, and analysed different types of technical signals. If it was in the air, they got it. After the fall of the Berlin Wall and the collapse of the Soviet Union, the station became useless and American and British troops abandoned Teufelsberg in 1991.

More about the Teufelsberg SIGINT station on  CCC's Field Station Teufelsberg - A Late Post Mortem (archived). The Field Station Berlin Veterans Group (FSBVG) (archived) wants to save the Teufelsberg site. The story of veteran Lew McDaniel is found in Abandoned Berlin's Teufelsberg Tale. The Berlin Brigade website lists all U.S. Barracks in Berlin (archived) and has an installation map of Teufelsberg.

There's also an interesting website of the 13th British Signal Regiment Birgelen Vets, running several intercept stations in Germany during the Cold War and US border operations in Germany with a complete description of the Iron Curtain and related operations.

From 1982 to 1985, US Army SIGINT analyst James Hall worked at Field Station Berlin. He copied a huge amount of top-secret documents and sold them to the Russians and East Germans. This is explained in the post James Hall – The Spy Within Field Station Berlin. More about the battle over radio waves, including many audio samples, is available at Cold War Signals on my website.

The Dark History Beneath Teufelsberg

Welthauptstadt Germania model
Source: German Architecture

As if the hill wasn't mysterious enough, the secret that lies beneath is just as curious: the Nazi military-technical college, designed by Albert Speer. When the Allies captured Berlin, they tried to demolish it with explosives, which turned out to be impossible. They decided to bury the massive building under a pile of rubble from destroyed Berlin.

The story of the military-technical college starts in the 1930's, when Adolf Hitler ordered architect Albert Speer to develop a new Berlinn called 'Welthauptstadt Germania' (World Capital Germania). The project included a huge Olympic stadion, a new Chancellary, an avenue of victory, a triumphal arc and other monumental architecture. Here's a video of how it would look like.

In 1937, they started with the first part of the project, the Wehrtechnische Fakultät or military-technical college. Changing priorities during the Second World War halted the project and it was never resumed. Today, there's even an association, called Berlin Unterwelten (underground), that wants to explore the remains of the elite military academy underneath the Teufelsberg.

Teufelsberg Then and Now

To have a birds-eye look on Teufelsberg, start up your Google Earth and type "Berlin Teufelsberg" in the search box. Type "Bischofsgruen Schneeberg" to fly to another one. With "Brocken Schierke", you'll jump right to the most famous former Soviet station in East Germany.

On YouTube there are several videos about Teufelsberg and how it looks today. Below three good videos to start with. The fourth video by Andy Mcloone is the story of the Brocken mountain Soviet SIGINT station, a counterpart of Teufelsberg.

Top Secret - Teufelsberg Spy Station

Inside the Ruins of Berlin's NSA Spy Station


NSA Field Station Berlin "Teufelsberg" Part 2

The Brocken - The Soviet Spy Mountain (Teufelsberg's counterpart)

Related Posts

• The Spy Within Field Station Berlin James Hall
  
• Tracking Cold War Signals FLR-9 HF-DF Elephant Cage 
• Mysterious Cold War Signals reveal their secrets
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Silent Warriors

September 2, 1958. A four-engined C-130 Hercules from the US 7406th Support Squadron with tail number 60528 is flying along the Turkish-Soviet border. Six crew members and eleven US Air Force Security Service (USAFSS) personnel are on board.

The aircraft is flying in Turkish airspace, from Incirlik to Trabzon, and its mission is to gather intelligence by orbiting near the Soviet border. They are instructed to stay 100 miles from Soviet airspace. The crew reports passing over Trabson at an altitude of 25,500 feet and acknowledges a weather report.

Soviet air defense radars are tracking the C-130. At 1440 hours, four MiG-17 interceptors from the 25th Fighter Regiment's Yerevan base are scrambled and are heading toward the C-130. Suddenly, the C-130 mysteriously deviates from his route, turns east and crosses the border into Soviet Armenia. According to the Soviets, they entered their airspace at 1507 hours.

C-130 at NSA, refurbished to resemble C-130A-II #60528 (source NSA)

The first two Soviet interceptors arrive at 1508 hours and Senior Lieutenant Lopatkov fires several warning shots at 1509. The pilots of the C-130 start to maneuver and climb to an higher altitude. Meanwhile, the other two MiG arrive and the pilots request permission to engage the C-130. At 1511 hours, their Command gives permission to attack the C-130. All four MiGs attack the airplane in turn, using their cannon and rockets.

The camera of the third MiG captures the C-130 with its left outboard engine on fire and the fourth MiG pilot reports the C-130 breaking up before his attack. Seven minutes after the first attack, the C-130 crashes and explodes on impact, killing all seventeen crew members. It takes four days for the United States to confront the Soviets with the disappearing of their spy flight.

MiG 17 gun camera photo of C-130 #60528 (source: Soviet Air Defense archives)

On September 12, Soviet authorities acknowledged that they found an aircraft that 'apparently crashed' on their territory. Five months later, the US goes public on a United Nations meeting and present tape recordings of intercepted conversations between the Soviet fighter pilots during the attack on the C-130. The Soviets continue to deny any involvement in the shootdown. The remains of the six crew members were returned. There was no word on the eleven USAFSS members that were aboard the C-130.

This wasn't the first nor the last. During the Cold War period, more than 40 reconnaissance aircraft were shot down. Flying these spy missions was a risky business and the reconnaissance programs were kept secret. The public never knew about these losses and their families and fellow soldiers were left to mourn alone.

The end of the Cold War allowed the US to release some information and pay tribute to these Cold War warriors. In 1991, Russian President Yeltsin began releasing information on the shoot down. In 1993, a US Army graves excavation team recovered an ID tag that belonged to a USAFSS technician aboard 60528.

The National Security Agency (NSA) has a special page with the story on the C-130 aircraft 60528 and declassified documents with additional information. You can also listen to the actual recordings and read the transcripts of the intercepted radio traffic between the MiG pilots as they engage the C-130. A good moment to remember the soldiers, fallen in the silent war. Read NSA's C-130 Shootdown pages with many documents and audio recordings of the MiG pilots.

The Aerial Reconnaissance memorial at the National Vigilance Park, near the NSA building, honors these silent warriors. NSA also published A Dangerous Business about the U.S. Navy and National Reconnaissance during the Cold War and also released a quarterly titled The SIGINT on Thirteen Soviet Shootdowns.

There are several websites, dedicated to lost U.S Air Force, Navy and Army crews. 6994th Security Squadron and Silent Warriors are two of them. A history of the USAFSS is found in  Freedom Through Vigilance. The EC-47 History Site is dedicated to the Douglas EC-47 electronic warfare platforms, sometimes referred to as "Electric Gooneys". The Armed Forces Super Store blog has America's Cold War Missing in Action about the 1969 downing of U.S. Navy EC-121M Warning Star. More details at NSA's EC-121 Shootdown (pdf).

More on Signals

• Tracking Cold War Signals Wullenweber FLR-9 antenna 
  
• Electronic Intelligence at NSA History of  ELINT
• More posts about signals intelligence  

See also Cold War Signals on our website.

Mysterious Cold War Signals

ASA SIGINT truck at Czech border
Source: ASA Det J Schneeberg Vets

An important part of the Cold War was fought over radio waves and all sorts of radio signals filled the aether. A shortwave or VHF receiver with a good antenna was, and still is, all you need to discover innumerable signals. Of course, these signals also caught the attention of both radio amateurs and intelligence organisations.

 

Signals intelligence (SIGINT) comprises communications intelligence (COMINT) and electronic intelligence (ELINT). The latter is the interception and analysis of various technical signals such as weapons systems, navigation and radar. ELINT was an important part of the Cold War and is today still an indispensable part of modern intelligence gathering and warfare.

The secrets behind the signals were often revealed, either by ELINT or HUMINT (Human Intelligence i.e. espionage). However, some signals remained unidentified for decades and even rose to the stardom of mysterious Cold War signals. Speculation about their purpose fueled the paranoia of that era. Occupying certain frequencies for use in case of war, or the notorious Dead Hand autonomous launch system for nuclear missiles that would initiate a launch when the mysterious signal interrupted. Eerie, but only speculations.

Tracking Nukes

One of those mysterious signals was nicknamed Russian Woodpecker, with its characteristic repetitive tapping noise. The Woodpecker's annoying high-power signal - an estimated 10 Megawatt - switched between different frequencies and disrupted legitimate HF signals (3-30 MHz) from utility and amateur communications across the world. The signal first appeared in 1976 and continued until 1986. Only after the fall of the Soviet Union it was confirmed that the signal came from an over-the-horizon (OTH) radar, part of Soviet early warning system for  ICBMs (intercontinental ballistic missiles, i.e.nukes).

Receiver antennas Chernobyl-2 site from the Duga-1 (source: Ingmar Runge)

The Soviet Duga-1 OTH (Rus. Дуга-1 ЗГРЛС) comprised two military sites in the Ukrainian Soviet Socialist Republic (SSR). The Liubech-1 transmitter site near Kloniv, and 50 km southwest the Chernobyl-2 receiver site near Chernobyl. Both transmitter site and receiver site each had two giant antennas. The huge antenna for the lower HF frequencies (right on photo) was 450 m (1476 ft) wide and 150 m (492 ft) high. The "small" antenna for the higher HF frequencies (left) was 250 m (820 ft) wide and 90 m (295 ft) high.

Duga-1 became operational in 1976 and was directed over Greenland towards North America. The Chernobyl-2 site was codenamed STEEL YARD by Western military intelligence, who apparently managed to photograph the site during the Cold War.

Coverage Duga-1, 2 and N radars
(Earth's northerly top view)

The first experimental OTH radar, called Duga-N or Duga (no number) was located in Ukraine near Mykolaiv at the Black Sea and directed towards China. Duga-N became operational in 1972.

The Duga-2 radar was located in the far east of the USSR, in the region Komsomolsk-on-Amur, with the transmitter in Lian and receiver in Bol'shaya Kartel, 50 km southeast of Lian. Duga-2 was directed over the North Pole towards Canada and North America. Note that the map shows the approximate coverage of the radars, not necessarily the actual reach, which depended on various conditions.

The Duga was designed to track ICBMs at 6-10.000 km (3400-6200 mi) and aircraft up to 3000 km (1865 mi). The actual range depended on the ionospheric conditions. They operated between 5 and 28 MHz, right on HF band (3-30 MHz), causing the strong interference. The huge antennas were phased array antennas where the beam could be directed electronically without any moving parts. The received signals were processed digitally.

 

Peeking Beyond the Horizon 

 

Most radar waves (30 MHz up to 300 GHz) go straight ahead. Radar therefore works line-of-sight (LOS) and the curvature of the Earth limits its range. You can't look beyond the horizon, only above it. If the Duga with its 150 m (492 ft) high antenna was a normal LOS radar, it's horizon was a mere 44 Km (27 mi) away, since the distance to its horizon in kilometer = √ 13 x 150 m (for miles use 1.5 x ft).

Therefore, the further an ICBM or nuclear bomber is, the higher it must fly or the closer it must get to become visible above the radar's horizon, and that's way too long after its launch. LOS radar was therefore insufficient to provide early warning in case of an attack against the Soviet Union.

The solution to this problem was the over-the-horizon radar station. In Russian, Загоризо́нтная радиолокационная станция (ЗГРЛС) i.e. Zagorizóntnaya radiolokatsionnaya stantsiya (ZGRLS).

Over-the-horizon radar principle

Over-the-horizon (OTH) radar transmits a powerful HF signal towards the ionosphere. Depending on the angle of the signal, the ionosphere reflects the signal back to Earth over a long distance, a so-called skip (hence the name Duga, Russian for arc) and can also reflect the signal from Earth back to the ionosphere multiple skips in a zigzag pattern, traveling huge distances around Earth.

When the OTH signal hits a moving ICBM, the reflected signal creates a small frequency shift (Doppler effect) as any radar does. However, only a very small portion, called backscatter, is reflected back by the ionosphere and effectively received by the OTH station. Complex digital processing is required to extract and analyse the very weak signal and the effect of the ionosphere and skips on the backscatter. Its accuracy and resolution are low, but the system works good enough for a raw early warning.

Disaster and Downfall of Duga- 1 

 

Noteworthy is that the Duga-1 receiver site Chernobyl-2 is located only 10 km (6 mi) from the Chernobyl nuclear power plant. According to Vladimir Musiyets, former Commander Chernobyl-2, the installation was damaged during the 1986 Chernobyl disaster and never became operational again. The site now lays within the 30 km (18 mi) Chernobyl exclusion zone. Some sources state that the Woodpecker continued broadcasting until 1989. These reportings possibly refer to other OTH sites.

On the history of over-the-horizon radar (translation) by Yuri Davydov, chief designer OTH radar, details the history and technical aspects of the Duga radars. The Ukrainian Chernobyl -2: the secret twin of the city Chernobyl (translation) from the exclusion zone website has a short history and photos. Global Security also has details on the Duga stations. Radartutorial explains phased array antennas for radar, but if you're not that technical, watch Duga Radar - How it Works.

 

Chernobyl 35 Years Later has excellent photos of the Duga-1 antenna, the control station and its consoles. To get a good sense of the sheer size of the Duga-1 antennas, visit English Russia and check the 14th photo with people underneath the antenna. Many more photos at Lost Places and Egorka's gallery.

Note: The following video mistakenly states "Duga-3 alias Chernobyl 2". The Chernobyl-2 receiver in this video was, together with the Liubech-1 transmitter, part of Duga-1. There was never a Duga-3.

Chernobyl: The Duga radar (Russian Woodpecker)

 

Note: The BBC video mistakenly translated site "Chernobyl-2" into system "Duga-2", although Sergei Babakov in the interview correctly said "Чернобыль-2", which is part of Duga-1. Duga-2 was in the Far East, 9000 Km from Chernobyl. The video title should be Duga-1.

 

The secret Soviet radar hidden in Chernobyl’s shadow - BBC REEL

The mistakes about the different Duga radars are understandable, as each Duga had two separate sites, one transmitter and one receiver site, and the site numbers didn't match the unrelated Duga number.

 
Substitutes for the Duga System

By the mid-1980s it became clear that the computer technology, used for the Duga phased array radars, was insufficient. However, the 1972 Око program for early warning satellites resulted in the first-generation US-K and US-KS satellites, operational in 1982 and the Око-1 program with second generation УС-КMO satellites in 1991. From 2015 on, these satellites were replaced by satellites of the Unified Space Detection System and Combat Control system.

 

In 2005 the Russian Federation also started to build a new generation of phased array radars for early warning, called Voronezh. Seven of these radars are already operational across Russia. More detailed info at Russia's Modern Early Warning Systems.

Buzzing Air and Messages for Spies

Another famous mysterious Soviet signal is known under its call-sign UVB-76. The station, nicknamed The Buzzer, started in 1982 with a two-seconds beep tone and switched after a decade of operation to a monotonous 25 buzz tones per minute, every single day. The station was extensively observed by radio amateurs (without doubt an equally monotonous job) and only a handful of voice conversations were recorded in its 28 years of operation.

Its call-sign UVB-76 was revealed during one of its rare voice conversations. The purpose of The Buzzer remains unknown until today. UVB-76 stopped broadcasting in August 2010 and remains silent since then. The transmitter site is located near Povarovo, 40 km (25 mi) north-west of Moscow, and now appears abandoned.

The UVB-76 "Buzzer" at Numbers Stations Research and Information Center, including some rare voice recordings. Photos of the abandoned alleged Buzzer site are published on English Russia.

Another true Cold War icon are the notorious Numbers stations. The stations broadcast streams of numbers or letters in voice or Morse and are used by intelligence agencies to communicate with their agents, operating abroad. Although the Cold War officially ended, there are still many active numbers stations and new keep popping up.

 

Further Information about SIGINT on the Blog

• Tracking Cold War Signals Wullenweber FLR-9 antenna
• 3 Second from World War 3 Early warning going wrong 
• Russia's Modern Early Warning Systems
  
• OXCART and ELINT Research Stealth for A-12 and SR-71
• Silent Warriors, USAF C-130 downing in Soviet airspace
• USS Pueblo Incident Capture SIGINT ship by North Korea
• Numbers Stations and many related spy cases on the blog
  
• More posts about signals intelligence
  
  

More About SIGINT on the Website

Cold War Signals details the SIGINT battle during the Cold War. You can listen to many audio samples of signals from spy transmitter and international shortwave broadcast stations.

Numbers Stations explains the origins of these broadcasts, their purpose, who uses them and their encrypted messages. Also many documents of the spies cases that involved numbers stations.