Spy radio
Burst encoders
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SP-15   FSS-7
German spy radio set

The SP-15 is a complete self-contained modular spy radio station, developed in Germany in the early 1960s by Wandel & Goltermann and H. Pfitzner for the German Intelligence Agency Bundes­achrichten­dienst (BND). It was intended for espionage, diplomatic radio traffic, Special Forces (SF), clandestine (covert) operations and Stay Behind-Organisations (SBO). Certain components of the SP-15 radio station were also used by the organizations and agencies of other countries. In The Netherlands and some other countries, the SP-15 was also known as FSS-7 and as FS-7.
A complete SP-15 radio station consisted of a receiver (FE-8), a transmitter (FS-7), a burst encoder, such as the RT-3 or the GRA-71, an AC mains power supply unit a 12V battery power supply unit, various battery chargers and a box with various accessories, spare parts and tools.

The image on the right shows the transmitter (right), the DC PSU (centre), the receiver (left), a morse key (front right) and various accessories. The set was often supplied with a burst encoder for high-speed transmissions in morse code, in order to minimize the chance of getting caught.
Typical SP-15 spy radio outfit

For use by agents, the radio set was usually packed in a leather suitcase. For the Special Forces a special webbing unit was available, allowing the units to be carried on the chest. When used by stay-behind organizations (SBO) the various units were commonly stored in a metal container.

The SP-15 was succeeded by the SP-20 in the 1970s, but remained in use in some countries well into the 1980s. In The Netherlands, for example, the SP-15 was used until it was replaced by the fully digital RACAL PRM-4150 in the mid-1980s. Finally, all SP-15 units, and in fact all other spy sets in Europe, were replaced by the pan-European FS-5000 (Harpoon) built by AEG Telefunken.
SP-15 spy radio set Typical SP-15 spy radio station Typical SP-15 spy radio outfit Crystal operated transmitter

Available parts
Pfitzner valve-based BN-22 (FS-7) transmitter
Wandel & Goltermann BN-58 (FE-8) receiver
BN-48 (UHU) backup receiver
Mains AC power supply unit
DC Power Supply Unit (12-24V)
Various types of burst encoders Accessories and spare parts Dutch stay-behind (Gladio) outfit
Special Forces outfit
FSK Modulator for very high speed burst transmissions
Calibrator for the receiver

Transmitter   FS-7 · BN-22
The transmitter of the SP-15 was developed by Pfitzner in Germany and was known as FS-7 or BN-22. It has two valves (EL95 for the oscillator and EL81 for the HF power amplifier) and one transistor (OC450) and is suitable for CW only.

Power output was 10W or 20W, switchable from the PSU (see below). The transmitter is crystal operated, but the Dutch version (FSS-7) was modified for use with a synthesizer.

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Receiver   FE-8 · BN-58
The FE-8 receiver was developed by Wandel & Golterman (W&G) in Germany in 1958 and can be used stand-alone. It can be powered by an internal battery or by an external DC source.

The receiver has two ranges (2-5.1 MHz and 5.1-9 MHz) with permeability tuning, resulting in a linear scale for both ranges. This receiver was also used with the later SP-20 radio sets.

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FE-8 (BN-58) receiver

Receiver UHU   BN-48
The SP-15 was sometimes equipped with an extra receiver for the broadcast frequencies. It was suitable for the reception of AM and CW signals. Like the FE-8 receiver (above) it was fully transistorized and was built by the same manufacturer.

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BN-48 (UHU)

AC Power supply
The SP-15 was supplied with a highly compact mains power supply unit (PSU) that was suitable for all common AC mains voltages in the world, between 95 and 235 V. It produces the LT and HT voltages for the transmitter.

It is slotted into the left side of the transmitter or, in the case of the modified Dutch FSS-7, into the left side of the junction box.
Mains AC power supply unit

DC Power Supply
When no mains AC network was available, it was also possible to power the SP-15 from a 12V DC source, such as the battery of a car. This was done by swapping the AC PSU for a DC one.

It contains a power inverter that converts the 12V DC input into 6.3V for the filaments and a HT AC voltage for the transmitter's valves. Like the AC PSU, it is slotted into the left side of the transmitter. It contains a relay to prevent the DC power source from being connected the wrong way around.
DC battery inverter

The SP-15 came with a large number of accessories, some of which are shown here. The most remarkable one is the surprisingly cheap looking morse key, made of a rather poor quality plastic. In use, the key is not as bad as it looks as it's rather heavy. Furthermore, the plastic is shielded on the inside.

Other accessories include antennas and cables.

The rather cheap-ish morse key Morse check light Side-tone cable Roll-up antenna Crystal tuner Crystal storage box Contents of the crystal box

Burst encoders
In order to minimise the risk of detection during a transmission, a burst encoder was often used in combination with the SP-15. The burst encoder allowed a pre-recorded message to be played back in morse code at very high speed, so that the transmission was kept as short as possible.
NATO-issue RT-3 burst encoder American GRA-71 burst encoder German Speicher (memory) burst encoder German MMP burst encoder

KSG Burst Encoder
In the early days of the SP-15, the burst encoder of the predecessor, the KSG-Sender, was used to send short messages of 20 to 25 digits in morse code. The KSG consisted of a metal disc in which a number of mechanically coded inserts had to be installed. A crank was then used to rotate it.

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KSG with the crank in place

RT-3 Burst Encoder
The second burst encoder to be issued with the SP-15 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.

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

GRA-71 Burst Encoder
For a long time, the SP-15 was used in combination with the American military GRA-71 burst encoder that allowed the dots and dashes of the morse characters to be recorded on a piece of ferro-magnetic (audio) tape.

Especially for use with the SP-15, they were supplied in grey hammerite, rather than the usual black as used by the US Army.

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CO-3A burst encoder as used with the GRA-71, in grey hammerite, especially for the SP15.

Speicher Burst Encoder
The Speicher (Eng: memory) was a fully electronic burst encoder for sending numbers at high speed in morse code. It was powered directly from the mains and was housed in a similar case as the SP-20 spy radio set.

The Speicher was probably issued in the 1970s to replace the rather limited RT-3. Eventually it was replaced itself by the more advanced MMP.

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Speicher (memory) burst encoder

MMP Burst Encoder
The MMP was a fully electronic high-speed (1200 baud) burst encoder that was used with both the SP-15 and the SP-20 spy sets.

The MMP replaced older devices, such as the mechanical RT-3, the American AN/GRA-71 and the early electronic Speicher. It could hold more than 1000 letters and numbers in its battery-backed CMOS memory and send them at various speeds between 15 and 1200 baud.

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High-speed morse burst encoder MMP-B

FSK Modulator
For burst transmissions at very high speed, such as the 1200 baud mode of the MMP burst encoder shown above, the existing keying methods were not adequate and this primitive FSK Modulator was developed as an alternative.

It was inserted between the crystal and the crystal socket of the FS-7 transmitter.

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FSK modulator and crystal

The analogue scale of the FE-8 (BN-58) receiver can be calibrated with this external calibrator, that is connected to the receiver's antenna and ground sockets.

It is powered by an internal 6V battery, which is identical to the one used in the FE-8 itself. It was supplied with the SP-15 sets that were used in Germany.

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FE-8 calibration device

RT-3 burst encoder connected to the FE-7 transmitter MMP connected to the FS-7 transmitter (SP-15)

Synthesizer   FSS-7
Modified FSS-7 used by Dutch Stay-Behind

In The Netherlands, the SP-15 was used for the national Stay-Behind organisation O&I (Dutch: Operatiën en Inlichtingen) during the 1960s and 1970s. O&I agents were given two green water-tight containers that could be burried underground, e.g. in the garden of their house. One of these contained a hand gun, ammunition, cash money and gold (the latter for bribing people).
The other one contained the SP-15 radio set, together with a wide range of accessories such as antennas, crystals, spare parts and a burst encoder. The image on the right shows a typical modified Dutch FSS-7 (SP-15) with synthesizer.

Around 1975, the set was given a mid-life upgrade by the addition of a synthesizer for the transmitter and a purpose-built junction box.

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Complete setup with standard morse key

Speicher Burst Encoder
The Dutch Stay-Behind version of the SP-15 is known to have been used in combination with various burst encoders. Some of these have been on display at the Dutch Signals Museum [4].

The only known surviving FSS-7 container, which is now in the collection Museum Jan Corver, was found with the Speicher burst encoder shown in the image on the right.

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Dutch FFS-7 (SP-15) set with Speicher burst encoder

Special Forces
For use by special forces and reconnaissance units, a special webbing pack was developed that allowed the various units to be worn on the chest. The webbing pack had a pocket for the transmitter and power convertor and another one for the receiver and the accessories.

Power for the set was delivered by a separate (heavy) battery belt that would be worn around the waist. The belt contained 10 rechargeable NiCd batteries of 1.2V/10Ah each.
The FS-7 transmitter inside one of the pockets

The complete webbing pack The complete webbing pack The complete webbing pack The complete webbing pack The complete webbing pack The FS-7 transmitter inside one of the pockets The FS-7 transmitter inside one of the pockets

  1. Helmut 'Jim' Meyer, HS0ZHK, My way to Ham - Radio and beyond
    Website QRZ.COM. Personal correspondence. Retrieved April 2013.

  2. Museum Jan Corver, Exhibition Secret Messages
    The Dutch version of the SP-15 was on display during this exhibition.

  3. Louis Meulstee, Wireless for the Warrior, volume 4
    ISBN: 0952063-36-0, September 2004.

  4. Museum Verbindingsdienst, Burst Encoders for Stay-Behind use
    Dutch Signals Museum. Photographed by Crypto Museum. 25 February 2009.

  5. Geschiedenis van de Sectie Algemene Zaken, Hoofdstuk VI, Consolidatie
    History of the Section General Affairs, Chapter 6, Consolidation. pp. 79 - 80 (Dutch)
    Describing the period May 1970 - December 1981. Dutch National Archives. Top Secret. Partly declassified and released in 2007 under the FOI Act.

Further information

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Crypto Museum. Created: Monday 03 August 2009. Last changed: Tuesday, 04 October 2016 - 12:49 CET.
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