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Bosch SVZ-8/9
Speech protection unit

The Bosch SVZ-8/9 is a speech protection unit (German: Sprach Verschleierungs-Zusatz) for the FuG-8 and FuG-9 public services mobile radios, manufactured around 1985 by Robert Bosch GmbH in Gerlingen (near Stuttgart, Germany). It was developed especially for the German Police. 1

The SVZ 8/9 measures 17 x 11 x 5 cm and weights approx. 700 grams. It was connected externally between an existing FuG-8 or FuG-9 two-way radio and the handset. The device is actually a frequency domain voice scrambler, rather than a real encryptor, and has two modes of operation, marked KRYPTO A and KRYPTO B.

Furthermore it has 8 DIP-switches 2 that are located behind a removable screw at the front panel. The circuit is built around a single-chip FX-204 Variable Split Band (VSB) Frequency Inverter, made by the British company CML [3].
Bosch SVZ-8/9

The FX-204 was developed as a single-chip solution for cordless telephones and mobile radios, and can be configured as a frequency domain scrambler, a fixed code scrambler, or a rolling code scrambler. The A and B settings of the MODE selector at the front panel, probably refer to two of these operating modes. The same chip was used in the contemporary Teltron SP-612 scrambler.

Despite the fact that the FX-204 chip was very sophisticated for its time, voice scramblers in general, and frequency domain scramblers in particular, are inherently unsafe. Their 'code' can be broken by a professional interceptor within seconds. Nevertheless, it provided reasonable security against occasional or accidental eavesdroppers, such as the scanner listeners of the 1980s.

  1. It is believed that they were also used by the German Fire Brigade.
  2. Only five DIP-switches are actually used.

Bosch SVZ-8/9 Front panel Front panel PCB removed from the case shell Interior Top view Selector switch and DIP-switches CML FX-204 single-chip frequency inverter with 1 MHz crystal
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Bosch SVZ-8/9
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Front panel
3 / 8
Front panel
4 / 8
PCB removed from the case shell
5 / 8
6 / 8
Top view
7 / 8
Selector switch and DIP-switches
8 / 8
CML FX-204 single-chip frequency inverter with 1 MHz crystal

The device is housed a a dark green extruded aluminium enclosure, that consists of a strong rectangular case shell with flat end panels at both sides One panel holds the front panel controls, whilst the other one is used to feed in the cables. Each panel is held in place by four screws.

The circuit is built on a single printed circuit board (PCB) that measures 10 x 16 cm (Euro­card). After removing both end panels, the PCB can be removed from the aluminium case shell, as shown in the image on the right, The actual FX-204 scrambler chip is located at the centre.

Neither the PCB, nor the circuit itself, are very sophisticated. The device is little more than a simple fixed code scrambler developed from an example given in the datasheet of the FX-204. Judging from date codes on the components, the device shown here was made in or after 1986.

It is hard to believe that a renowned company like Bosch, offered its customers the SVZ-8/9 as a serious solution for secure voice communications, as late as 1986, whilst there were plenty of superior solutions available, such as the BBC Vericrypt 1100 that, although not perfect, provided a much better protection by using time domain scrambling. In fact, Bosch had been offering the Vericript 1100 as an integrated solution with its FuG-8b-1 since the early 1980s. It is possible though, that the SVZ-8/9 was offered as a low-cost alternative to the expensive Vericrypt 1100.
Rear connection
  1. LS (GND)
  2. LS (signal)
  3. Handset Ground
  4. Handset Microphone
  5. Handset Ground
  6. Handset LS
  7. Handset +12V
  8. Handset PTT
  9. Transceiver LS
  10. Transceiver PTT
  11. Transceiver Ground
  12. Transceiver Microphone
  13. Handset Ground
  14. Transceiver Ground
  15. Transceiver Ground
  16. Transceiver +12V
The handset is normally connected to the voice protection unit by means of a standard NATO 7-pin U-77 plug with the following pinout. Note that this connector is not part of the SVZ-8/9 but of the radio to which the SVZ-8/9 is connected.

  1. n.c.
  2. +12V
  3. PTT
  4. Speaker (ground)
  5. Speaker
  6. Microphone (ground)
  7. Microphone
  8. Ground
  1. Klaus Paffenholz, Verschlüsselte Sprach-/Datenübertragung
    Website: Geschichliche Entwicklung des BOS-Funks (German).
    Retrieved April 2017.

  2. Klaus Paffenholz, Telefunken FuG 8a/8b/8b-1
    Website: Geschichliche Entwicklung des BOS-Funks (German).
    Retrieved April 2017.

  3. Consumer Microcircuits Ltd (CML), FX204 VSB 1 Frequency Inverter
    Publication D/204/6, November 1986, Provisional Issue.
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Crypto Museum. Created: Wednesday 28 June 2017. Last changed: Friday, 23 February 2018 - 21:50 CET.
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