Spy radio
Burst encoders
• • • Donate • • •
   Logo (click for homepage)
US satellite spy radio set - wanted item

The RS-804 was a spy radio set with built-in data encryption, developed in the US in the early 1980s. It was used in international espionage during the Cold War, for sending high-speed messages (bursts) from a hostile country via a UHF satellite link. The device was captured in the USSR in 1983 by the KGB, and is also believed to have been used in Cuba during the 1980s [1].
The RS-804 is believed to be one of the first spy radio sets that used satellite communications instead of short-wave transmissions (SW). Unlike with SW signals, a radio signal to a satellite is very difficult to intercept and trace, as the waves are 'beamed' straight up rather than all around.

The set is extremely small, especially when considering its age, and has a modular design, allowing it to be used in many configurations and concealments. The thickest part of the radio measures just 19 mm, making it very easy to hide it inside a piece of furniture or behind the false bottom of a briefcase as illustrated below.

The image on the right shows the complete self-contained RS-804 radio set that was confiscated by the Russian secret service KGB on 7 March 1983, when they compromised the US Embassy's First Secretary Richard Osborn whilst making an illicit transmission from a park in Moscow. The radio set consists of three larger modules plus some kind of connector that is fitted at the right.
Complete RS-804 set as photographed by the KGB [2]. Photograph kindly supplied by the Polish Institute of National Remembrance, via Jan Bury [1].

The transmitter operates in the UHF band around 300 MHz with an RF output power of 10 Watts, and is suitable for communication via the US MARISAT and FLTSATCOM satellites. A text based message with a maximum length of 1579 characters can be encrypted and stored with the CK-42 crypto unit at the bottom left. When transmitting, the message is sent as a high-speed burst that lasts 4 to 21 seconds, making it even more difficult for the authorities to trace the signal.

The diagram above shows how the messages are sent. The agent sends his messages directly via a satellite link to headquarters (HQ) in the US. New instructions for the agent are send by HQ via the short-wave one-way voice link as OTP-encrypted messages, for which separate OTP keys were provided. A variant for short-range agent communications (SRAC) is known as CDS-501.
Complete RS-804 set as photographed by the KGB [3]. Photograph kindly supplied by the Polish Institute of National Rememberance [2]. Complete RS-804 set as photographed by the KGB [3]. Photograph kindly supplied by Detlev Vreisleben [2]. Complete RS-804 set with antenna, as photographed by the KGB [3]. Photograph kindly supplied by Detlev Vreisleben [2].

The diagram below shows a complete RS-804 setup as it was usually built inside the hidden bottom of a common briefcase. The entire assembly is no larger than 31 x 31 cm, which is the size of the circular polarized antenna on which the other parts are mounted. It is just 2 cm thick.

Schematic overview of the various components of the RS-804. Copyright Crypto Museum 2015.

At the bottom right are the three basic modules: the RT-804 transceiver, the CK-42 encryption unit and the BS-804A battery pack with built-in PSU/charger. The latter also hold the controls (SEND/OFF/INPUT) and a socket for a remote control unit that is inserted at the right top.
The complete RS-804 set (with the exception of the antenna) measures just 198 x 168 x 19 mm and weights 2.3 kg. It consists of the following parts:

Operation of the RS-804 set was extremely simple, as indicated by the small instruction label that is fitted on top of the PSU. It shows how to enter a message and how to send it. It is likely that it could be operated by an unskilled user after just a short instruction or training. Transcribed:
  1. Switch to INPUT 1
  2. With stylus depress INPUT key 2
  3. Enter 19 character variable 3
  4. Enter twelve ↓
  5. Enter message number and an X
  6. Enter text
  7. Enter one ≡
  8. Enter four ↓
Switch to send,1 position antenna,
depress ACTIVATE.4 After 30 seconds
depress INTERROGATE.4 Observe MSG and
ACT lamps 5 for positive indication.
  1. 3-position rotary selector on the PSU.
  2. On the keypad of the CK-42 crypto unit.
  3. This is the message key that was supplied on a separate sheet.
  4. On the transceiver (aside the antenna socket), or on the remote control unit.
  5. We assume that these indicator lamps were on the wired remote control, along with the ACTIVATE button.

Captured by the KGB
During the Cold War, the RS-804 was used by US operatives in many countries that were regarded by the US as 'hostile', such as Cuba, East-Germany (DDR), Poland and the Soviet Union (USSR). The problem with the USSR however, was that Moscow was at the very outer limit of the MARISAT satellite's footprint. In June 1981, tests had shown that the RS-804 could not be used reliably from Moscow as the antenna was probably too small. The sets were then returned to the US [5].
The RS-804 set was improved by CIA technicians and about two years later it was returned to the Moscow station for testing. Towards the end of 1982, the Russian secret service KGB began to notice and intercept burst transmissions to US MARISAT satellites, which were believed to originate from parks and forests in the USSR [1].

Meanwhile, Richard Osborne, a diplomat in his mid-40s, had been placed at the US Embassy in August 1982 and was now living in Moscow with his wife and two daughters aged 6 an 8. He was assigned as Economics Section's First Secretary.
Poklonnaya Park, just outside the city centre of Moscow. Photograph copyright altertravel.ru

On 7 March 1983, Osborne was going to test the improved device, using a family walk as cover [5]. He went to an open spot in Moscow's Poklonnaya Gora Park and setup the device, concealed inside his briefcase, in such a way that it could 'see' the satellite. He then initiated a transmission.
Unknown to him however, was that he and his family were constantly being observed by a KGB surveillance party who had reason to believe that Osborne might be behind some of the illicit transmissions. As soon as the surveillance party received confirmation that a transmission was indeed taking place from his briefcase, they arrested him. He was caught 'red handed'.

In his briefcase the KGB found the sophisticated RS-804 satellite burst transmitter hidden behind a false bottom. It was set to 311.15 MHz in the UHF band: the uplink to the MARISAT satellite.

The KGB also found notes in his briefcase that were written on special water soluble paper. For the Russians this was the final proof that Osborne was indeed a spy and not a diplomat. After his arrest, Osborne (who had diplomatic immunity) was released and declared persona non grata for 'actions incompatible with diplomatic status'. He was then expelled from the Soviet Union [6].

The sophisticated minature RS-804 radio set was thoroughly investigated and photographed by the KGB, who codenamed the device PHOBOS, or FOBOS (ФОБОС), and the information was shared with friendly services in countries like Cuba, Poland and the DDR. They would later catch another few of these devices in Afghanistan in 1988, during the Russian War Against Afghanistan.
Modular design
The RS-804 has a modular construction, which allows the radio, or parts of it, to be used in a variety of configurations and concealments. As the thickest part measures only 19 mm, it is ideal for concealment inside a briefcase or a piece of furniture. Note that some parts are also used with the similar line-of-sight CDS-501 radio set. The modules are described in more detail below.

The basic modules of the RS-804. Copyright Crypto Museum 2015.

1. Transceiver   RT-804
The transceiver is L-shaped and measures approx. 100 x 188 mm. It has two sockets for connection to the other modules: one in the cut-out section at the bottom left that accepts the CK-42 crypto unit, and one at the top right that connects it to the battery pack/PSU/charger. Furthermore it has an antenna socket at the top. The device is controlled from the PSU.

The transmitter operates in the 300 MHz UHF band and delivers an RF output of 10W. It is suitable for use with the American MARISAT and FLTSATCOM satellites. The device that was captured by the KGB was preset to 311.15 MHz; the earth station uplink of the MARISAT satellite. The following FLTSATCOM frequencies (fleet satellite communication) are known to have been used by the CIA for data communication, all in narrowband FM/data [7]:
  • 243.000 - 244.000 MHz
  • 251.000 - 269.000 MHz
  • 292.000 - 317.000 MHz
2. Encryption device   CK-42
Apart from the remote interface, the crypto unit is the smallest part of the set. It measures 100 x 68 x 18 mm and weights just 160 grams. It is fitted inside the L-shaped cutout of the transceiver and connects to it via a large socket at the top. It can be detached easily, allowing it to be loaded with data externally. The CK-42 is labelled as a Confidential COMSEC Controlled Item.
The CK-42 allows messages with a length of up to 1579 characters to be stored in its internal memory, encrypted with a 19 character encryption key that was supplied on a separate sheet. It is likely that a new key was used for each message. The crypto unit also controls the transmission of the messages, which are as sent as high-speed bursts that last 4 to 21 seconds.

Messages are entered on the small keypad on top of the unit. It consists of 32 buttons, arranged as 4 rows by 8 columns, plus a separate INPUT button at the top. Because of the small size of the device, the buttons can only be operated with a sharp object like a stylus.

The encryption algorithm that is used by the CK-42 is currently unknown. The same crypto unit was also used with the CDS-501 line-of-sight (LoS) radio set, that was used by the CIA for short-range agent communications (SRAC).

 More information
The small CK-42 encryption unit

3. PSU   BS-804A
The PSU is the longest part of the set and measures approx. 69 x 180 mm. It holds a set of rechargable NiCd batteries plus a mains AC power supply unit (PSU) that is also used as a battery charger. This means that the set could be operated either from the batteries or the AC mains.

The bare PSU

The PSU is connected to the transceiver via the socket at the top left. The PSU also holds the main MODE selector: a 3-position rotary switch that can be set to SEND, OFF or INPUT. At the top right is a socket for a remote control unit, allowing the set to be operated whilst it is concealed. The PSU shown here is configured for the 220V AC mains, as indicated by a small tag at the top edge.

The PSU also holds a small CHARGE lamp at the top, that is lit when the unit is connected to the AC mains. It indicates that the NiCd batteries are being charged. At the lower part of the PSU is a label with the operating instructions, suggesting that the set was extremely easy to operate.
4. Remote control   CPK-804/A
A small remote control interface is connected to the socket at the top right of the PSU. It allows an external (wired) activation switch to be connected to the set. The switch could be mounted elsewhere in the or on briefcase, e.g. in the handle, so that it could be activated covertly.

The small remote control interface

The antenna is the largest part, but also the thinnest. It measures 310 x 310 mm and has rounded corners. Furthermore it acts as the base on which the other modules are mounted. The antenna is circular polarized and is fed via the large filter at the top. The antenna consists of laminated copper and was probably made of double sided PCB material that was painted black.
  1. Jan Bury, Project Kalina: The Lotos Operation Conundrum
    Cryptologia 36:2, April 2012, pp. 119-128.

  2. Archives of the Polish Institute of National Remembrance (IPN)
    Information on the PHOBOS agent radio communications device from the First
    Secretary of the US Embassy in Moscow R. Osborne on 7 March 1983. Warsaw 1983. 2
    Available at the Archives of the Polish Insitute of National Remembrance. File # IPN BU 01304/953.

  3. Detlev Vreisleben, Personal correspondence
    August 2015.

  4. KGB, Photographs of RT-804 spy radio set
    March 1983. Photographs from BStU, kindly supplied by [3]. 1

  5. David E. Hoffman, The Billion Dollar Spy: A True Story of Cold War Espionage
    Moscow station to headquarters, June 26 1981, 261440Z. Page 311, pt. 20.

  6. John F. Burns, Moscow ousts a US Diplomat, Calling Him a Spy
    The New York Times, 11 March 1983.

  7. New FFR, Communauté Underground, Old School → Ecoute (espionnage) radio
    Website: Les Forums Sécurité (French). Retrieved November 2015.

  1. In March 1983, the set was photographed by the KGB following the arrest of Richard Osborne. The information was shared with friendly services in Cuba, Poland and the DDR. The photographs that were formerly part of the Stasi archives in the DDR, are now maintained by the BStU in Germany (BRD) and are freely accessible. Many thanks to Detlev Vreisleben [1] for supplying these photographs.
  2. Original text: Informacja dotyczaca agenturalnej aparatury lacznosci radiowej 'FOBOS' zatrzymanej u pierwszego sekretarza ambasady USA w Moskwie R. Osborne'a w dniu 07.03.1983 r. Warszawa 1983.

Further information

Any links shown in red are currently unavailable. If you like the information on this website, why not make a donation?
Crypto Museum. Created: Saturday 05 September 2015. Last changed: Monday, 23 November 2015 - 20:02 CET.
Click for homepage