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BND SW Converter
Short-wave converter

The BND SW Converter was a minature crystal-operated short-wave (SW) converter, introduced in the late 1950s by the West German intelligence service BND, for use by agents operating in the DDR (East Germany). The converter was a replacement for the OG/BND SW Receiver, and turned an ordinary domestic medium-wave (MW) broadcast radio into a clandestine SW receiver [1][2].

The BND Converter was generally used as one end of a One-Way Voice Link (OWVL), for the reception of instructions from a so-called Numbers Station operating from West-Germany, but they were also used in combination with the KSG Sender; a transmitter with burst encoder.

It was supplied with a short coaxial cable that could be connected to the antenna and ground sockets of the MW receiver, four quarz crystals, a small earphone for the MW receiver (the internal speaker had to be turned off), a frequency time table, and instructions for its use in German [A].
BND SW Converter with crystal installed

A major shortcoming of the BND SW Converter was the rather strong signal that was produced by its crystal-operated local oscillator (LO), that could easily be detected with appropriate direction finding (DF) equipment, and made the unit liable to detection and discovery by the DDR agencies.

BND SW Converter BND SW Converter with crystal installed Crystal placed in socket Adjustment knob Crustal socket Crystals Antenna socket (with built-in power switch) Output cable

The photographs below were kindly supplied by collector Detlev Vreisleben from Germany [2], and shows that some BND Converters were supplied with a dummy battery with two wires, that allowed an external DC supply (3 to 4.5V) to be used as an alternative to the internal 3V battery.

The BND Converter is an extremely simple device that does not have many connections and controls, as illustrated in the diagram below. The unit is powered by an internal 3V battery that can (optionally) be replaced by a dummy, in order to power it by an external source, such as a 4.5V dry battery. It is switched ON by inserting a plug in the antenna socket at the other side.

The output of the converter is available at the 3.5 mm jack socket at the front, that should be connected to the antenna and ground terminals of the MW receiver, using the supplied cable. The crystal for the desired channel should be installed in the grey socket at the top, whilst the circular grey dial should be set to a particular number, as listed in the frequency/time table (see below).

BND SW Converter Antenna socket (with built-in power switch) Output (to MW receiver) Output cable Output cable connected to Converter BND Converter with output cable
The BND SW Converter was introduced at a time when the Cold War tension between East and West had reached the point where East Berlin was about to be separated from West Berlin and/or the borders were about to be closed hermetically. In the past, the BND had supplied a miniature SW receiver to its agents in the DDR, but these were only suitable for the reception of messages in morse code (CW) and, hence, required the operator to be an experienced radio telegraphist or a radio HAM. Furthermore, the posession of a SW receiver was considered illegal in the DDR.

In order to overcome these problems, the BND started distributing the miniature SW Converter, which allowed an ordinary MW broadcast receiver to be used for the reception of verbal messages in the SW band. Initially it was used in combination with valve-based receivers like the Weimar 4680 and the WWII leftovers like the Volksempfänger (people's radio), but later it was also used with the first transistorized portable radios like Sternchen when these became widely available.

The agent was supplied with a frequency/time table such as the one shown above. He or she was required to listen to the specified channel at specific times of a particular day, each week. To ensure that the agent had found the correct frequency, each broadcast started with a particular melody that acted as the station's identification. Only messages that started with the agent's call­sign (RUF-NR) had to be taken down. All messages were coded one-on-one, which means that they were coded differently for each agent, using the unbreakable One-Time Pad (OTP) code [C].

Messages were sent in groups of 5 digits, separated by a space, eg. 35436. The first group was the message indicator (Kenngruppe) and identified which one-time pad had to be used. The agent wrote the OTP series above the received digits and then subtracted the two (modulo 10). The resulting digits were translated into plain text by means of the table above. This particular translation table is known as DEIN STAR. Full decoding instructions can be found here [C].

Circuit diagram
The converter was crystal-operated, and two channels in the Short Wave (SW) radio band are known to have been used for this purpose by the BND: DCF37 (3370 kHz) and DFD21 (4010 kHz). The block diagram below shows the basic operation of the converter, which is known as a down converter. This means that the crystal has to be 1500 kHz higher than the reception frequency.

Block diagram of the BND Converter

The circuit diagram below shows the rather simple construction of the BND converter. At the bottom is a crystal oscillator built around an OC170 transistor. The output of this Local Oscillator (LO) is mixed with the received signal in another OC170, and presented at the top right (Output).

Circuit diagram of the BND Converter

At the top left is the 3V battery which is connected with its (+) terminal to ground. The device is turned ON by inserting a banana plug in the antenna socket of the device. Note that in some versions, the battery could be replaced by a wired dummy for connection to an external source.

The BND Converter was suitable for common crystals with a pin distance of 12.5 mm. The socket on top of the device accepts crystals with thick and thin pins.

As the device is a down converter, the crystal frequency has to be chosen 1500 kHz higher than the desired frequency. For further details, please refer to the frequency table below.

Crystals Crustal socket Fitting crystals with thin pins Fitting crystals with thick pins Crystal placed in socket
As the Converter was used by agents operating in the hostile environment of the suppressive DDR regime, it was of the utmost importance to hide it properly, so that it would not be found by the authorities during an unexpected search.

The image on the right shows one of the most beautiful concealments that were used for the BND Converter, which is constructed from an operational 'Liliput' kitchen boiler (German: Durch­lauferhitzer) of the era. The Converter itself is stored at the centre, whilst the crystals and the other accessories are stored at the top.

It was discovered by the East-German MfS 1 (Stasi) and was documented in one of the reports of the Stasi's HA-IX department [D].

 Liliput promo
 Liliput concealment
 Liliput close-up
In-line kitchen water heater used as concealment for the BND Converter

The best possible concealments are often the most common objects that are used every day, and that can be hidden in plain sight, such as the thermos shown at the right. It consists of a glass bubble that is mounted inside a cylindrical metal enclosure. By making the glass bubble shorter than normal, an empty space becomes available at the bottom of the enclosure, which makes it a perfect concealment container.

The image on the right shows that the Converter and all of its accessories and paperwork, could be hidden inside the unobtrusive thermos.
A common thermos bottle used as a concealment for the BND Converter

The image on the right shows how the West-German intelligence service BND and the American CIA brought the Converter into the DDR. In this case it was concealed in a children's toy, a wooden train, but other concealments, such as DDR vegetable cans, were used as well.

The image on the right was shown in the East German newspaper Neues Deutschland on 6 September 1959, in a report about four Western agents that had been traced and convicted in the DDR: Erich Keimling (38), Gisela Gebhardt (26), Franz Brehmer (37) and Walter Huth (54) [4].
A wooden locomotive used as a concealment to bring the BND Converter into the country

Another beautiful concealment which was used by Western agents inside the DDR, is described in Stasi documents now held by the BStU [G]. In the event, the agent had a pair of hollowed-out wooden book supports that contained the BND Converter, its accessories and the paperwork.

The two concealments were found on his book­shelf, acting as inconspicuous book supports. Nevertheless they were discovered by the Stasi and became part of their internal 'museum', as proof of capitalistic subversive activities [G].
Wooden book support as a concealment for the BND Converter

  1. MfS = Ministerium fur Staatssicherheit (Ministry for State Security), also known as Staatssicherheit, or Stasi.

The BND converter featured on this page is not particularly well-built, and is certainly not of the famous German manufacturing quality. Instead, it seems to have been designed and built in a rush, probably due to the situation in the DDR.

In the image on the right, an alternative design is shown, that was probably introduced later, and that is more in line with the general German manufacturing standards. As the knob on the device was also used on the later FSK-modulator of the SP-15 spy radio set, we think it was made by either H. Pfitzner or Wandel & Goltermann.

An alternative SW converter, that was distributed by the British intelligence agencies, is shown in the image on the right. It is similar in operation to the BND Converter but is somewhat larger. It is shown here with two crystals at its top left.

Like the other converters, quite of few of these were discovered by the DDR's secret service, the Stasi, and are described in various reports.

In-line kitchen water heater used as concealment for the BND Converter In-line kitchen water heater used as concealment for the BND Converter A wooden locomotive used as a concealment to bring the BND Converter into the country A wooden locomotive used as a concealment to bring the BND Converter into the country A common thermos bottle used as a concealment for the BND Converter A common thermos bottle used as a concealment for the BND Converter Wooden book support as a concealment for the BND Converter Wooden book support as a concealment for the BND Converter
Liliput miniature in-line kitchen boiler promo. Bundesarchiv [5]. Later version of the converter Alternative converter produced in the UK
The BND Converter is housed in a black metal enclosure that measures 65 x 63 x 28 mm. The case consists of two shells of which the lower one is held in place by a large bolt at the bottom. After removing this bolt with a suitable screwdriver or a coin, the interior can be accessed.

Inside the case is a brow pertinax board with rounded corners. It has components fitted at both sides, but only the bottom side is visible after opening the case. At the centre is a large adjustable capacitor, which is made in Japan.

At the front left is a socket for connection of the antenna. When plugging a banana plug into this socket, a switch at the other side of the board is engaged and switches on the battery. The device is powered by a 3V dry battery cell, that fits the battery holder at the top right. Note that the holder might be damaged by leaking batteries.
PCB - top view

The brown pertinax board is held in place by three screws, two of which are located at either end of the crystal socket and can be removed easily. The third screw is located under the grey knob at the top panel, and requires the knob to be removed first. The board should then be loosened.

After removing the washer from the 3.5 mm jack socket, the pertinax board can be removed from the case. Be careful not to damage any of the extremely thin wires to the coils at either side.

The image on the right shows the top side of the board, which is usually hidden from view. At the right is the grey crystal socket, whilst the jack socket (the output) is visible at the left. At the bottom right is the rather long power switch, which is controlled by the banana socket at the other side. Power is automatically turned ON as soon as the antenna's banana plug is plugged in.
PCB - bottom view

Although the BND Converter featured here is in very good condition, especially considering its age, it should be obvious that it was designed and built in a rush, probably under pressure of the political situation in the DDR at the time. It is by no means built to the high quality standards that the Germans are famous for. This was improved in a later design, of which the name is unknown.

PCB - top view PCB - bottom view Bottom view Top view Power switch activated by the antenna socket Power switch at the bottom side Battery holder Output socket
  • Type
    Crystal operated
  • Input
    3 - 6 MHz
  • Output
    1500 kHz ± 50 kHz (200 metres)
  • Circuit
    oscillator, mixer (2 x OC170 transistor)
  • Power
    3V dry battery
Known channels
The BND Converter is a so-called down converter with an output frequency of 1500 kHz, which means that the crystal frequency has to be chosen 1500 kHz above the desired reception frequency. Two channels were commonly used, known as 1 and 2. If interference was expected from breakthrough of broadcast stations on 1500 kHz (i.e. the output frequency), alternative crystals (1A and 2A) could be used, which resulted in a slightly different output frequency.

# Name Frequency Crystal Output Remark
1 DCF 37 3370 kHz 4870.00 kHz 1500.00 kHz  
1A DCF 37 3370 kHz 4830.01 kHz 1460.01 kHz Backup
2 DFD 21 4410 kHz 5510.00 kHz 1500.00 kHz  
2A DFD 21 4410 kHz 5537.96 kHz 1527.96 kHz Backup
  1. Kurzwellen-Konverter (mit losem Kabel) - Gebrauchsanleitung
    Short Wave Converter with separate cable (German) - Instructions.
    MfS HA-IX Fo0959. BStU-Kopie. 1

  2. Frequency time table
    MfS HA-IX Fo0959. BStU-Kopie. 1

  3. Anleitung für die Entschlüsselung
    MfS HA-IX Fo0959. BStU-Kopie. 1

  4. Using a miniature kitchen heater as concealment
    MfS HA-IX Fo0959. BStU 0160. 1

  5. Using a children's toy as concealment
    MfS HA-IX Fo0959. BStU 0165. 1

  6. Using a thermos bottle as a concealment
    MfS HA-IX Fo0959. BStU 0167. 1

  7. Using a book stand as concealment
    MfS HA-IX Fo0959. BStU 0163. 1
  1. Document kindly provided by Detlev Vreisleben [2].

  1. Louis Meulstee, BND SW Converter
    Wireless for the Warrior - Volume 4, Supplement, Chapter 34-1.
    Retrieved March 2017.

  2. Detlev Vreisleben, BND Converter documentation
    Retrieved December 2014, March 2017.

  3. Len Scott, R Gerald Hughes, Intelligence, Crises and Security
    Prospects and Retrospects. The Secret Service and the Berlin Wall.
    2008, Routledge. pp. 186-187.

  4. ...und dann bekam ich den Decknamen 'König'
    ...and then I was given the covername 'King' (German).
    Neues Deutschland (Newspaper). 6 September 1959. 1

  5. Bundesarchiv, Photograph of woman with Liliput kitchen boiler
    Image 183-28773-0004. Retrieved March 2017 via Wikipedia.
  1. Document kindly provided by Detlev Vreisleben [2].

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Crypto Museum. Last changed: Wednesday, 15 March 2017 - 21:07 CET.
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