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SP-20
Spy radio set

The SP-20 was developed in the late-1970s in Germany by Pfitzner and AEG Telefunken as a replacement for the SP-15. It was used as a true spy set (stay-behind) as well as by the Army (Special Forces). The two versions can be determined by their colour, but are otherwise identical.
 
It consisted of a transmitter, antenna tuner, receiver, synthesizer and accessories. Messages were transmitted in morse by means of a manual key or a burst encoder. Various burst encoders have been used with the SP-20.

The image on the right shows the military version of the SP-20 that was used by German Special Forces. All units are painted in the standard NATO olive green colour. It is shown here with the RT-3 burst encoder. The version used by the stay-behind organisations (Gladio) was grey.
  

Most SP-20 units have been found without a matching receiver. Although the manufacturer (Pfitzner) developed a digital receiver for the SP-20, it was never put into production and the older FE-8 receiver (that was supplied with the SP-15 spy set) was used instead. All units are housed in a similar case of approx. 155 x 105 x 32 mm, except for the (older) FE-8 receiver (see below). A similar case was later used for the Speicher burst encoder.
 

 
Transmitter S-6800
The S-6800 transmitter was developed by AEG Telefunken and is fully transistorised. It is both crystal and synthesizer operated and is suitable for CW (morse) and FSK (frequency shift keying). The maximum ouput power is 25W.

Note the two rigs on top of the unit, allowing it to be attached to the ASG-6800 antenna tuner (see below).
  

 
The The Front The Cable Cable Cable Cable

 
Antenna Tuner ASG-6800
The ASG-6800 antenna tuner was designed for use in combination with the S-6800 transmitter. Like the transmitter, it was manufactured by AEG Telefunken in the mid 1970s (1975-1977).

The tuner was connected to the transmitter by means of a short coaxial cable with an SMB-connector at both ends. At the bottom it has two rigs that allows it to be slotted onto the S-6800 transmitter (see above).
  

 
ASG-8600 ASG-8600 front The Connection Connection Connection Coaxial

 
Synthesizer KS-30
Initially, the S-6800 transmitter was crystal operated. Later, an external synthesizer unit (KS-30) was developed by Pfitzner. This was probably early in 1983.

It was added to all existing SP-20 stations and connected to the transmitter via a multi-pin connector on the left. A rather long cable was supplied to connect the KS-30 to the S-6800.

The sythesizer allows a frequency coverage of 2-24MHz in steps of 1kHz.
  

 

 
Receiver
The SP-20 radio set in the above image is shown without a receiver. Although a suitable digital receiver, in a similar case, was developed by Pfitzner, it was never put into production. Instead, the FE-8 receiver of the older SP-15 (1958) spy set was used.

 More information
  

 
Toolkit
Each SP-20 unit came with a set of spare parts, tools and accessories. In most cases, these were packed in a sturdy 'lunch box' with a canvas strap to prevent the contents from falling out.

The image on the right shows an example of such a toolbox. It contains a screwdriver, pliers, insulation tape, ceramic antenna insulators, etc.
  

 
Toolkit Close-up

 
Antenna
The antenna tuner makes it possible to use virtually any type of antenna with the S-8600 transmitter. In practice, a long antenna wire was used on most occasions. The antenna, and a suitable ground, are connected to the left side of the tuner, via 2 banana-type sockets.

The images below show some of the typical wire antennas that were supplied with the SP-20. Please note that transmitter and receiver each needed a separate antenna.
  

 
Wooden Simple Military Antenna

 
Burst Encoder
In order to minimise the risk of detection during a transmission, a burst encoder was often used in combination with the SP-20. The burst encoder allowed a pre-recorded message to be played back at very hight speed, so that the transmission was kept as short as possible.
 
The first burst encoder to be issued with the SP-20 was this electro-mechanical RT-3 unit. A small military-grade metal box that allowed a message of 25 characters to be stored mechanically. Once on-air, the message was played back by operating a hand crank.

Later, more advanced burst encoders were issued, such as the GRA-71, MMP and Speicher.

 More information
  
The RT-3 burst encoder. Click for additional information.

 
Webbing kit
The SP-20 was also used by German Special Forces. The military version of the spy set was housed in olive-green cases and could be worn on the body by using a special canvas webbing kit with two plastic cases, as shown in the image on the right.

Each plastic case had two pockets, allowing all units of the spy set to be transported easily. The plastic cases could be attached to a canvas waist belt, which was held in place by suitable shoulder straps.
  

 
The The The

 
References

Further information

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