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Plug-in frequency domain speech scrambler

SVZ was a simple frequency domain speech scrambler, developed by Robert Bosch GmbH in the early 1990s. It was supplied as a retrofit solution for existing Bosch FuG-8 (KF-802) two-way VHF FM mobile radios, as a backup alternative to the existing Vericrypt 1100 time domain scrambler.

The circuit is built around a COM9046 single-chip single side band speech scrambler, made by Standard Microsystems Corporation (SMC) 1 in New York (USA) [2]. The chip runs on a 3.57 MHz crystal 2 and has a centre frequency of 3.5 kHz.

The mirroring frequency is not adjustable, which makes the device the most simple implemen­ta­tion of a fixed frequency speech inverter, which offers extremely low security. The effect of the scrambler can easily be undone by mirroring the audio frequency spectrum once more. During the 1980s, scanner conversion kits were available.
Top side

The name SVZ is the abbreviation of Sprach Verschleierungs-Zusatz (speech concealment add-on). It was offered as an upgrade kit for existing FuG-8 radios that were already fitted with a BBC Vericrypt 1100 time domain speech scrambler. Although the Vericrypt unit offered a far better 3 protection than the SVZ, there were situations in which the Vericrypt could not be used. This was the case, for example, when the receiving party did not have the appropriate cryptographic key.

In such situations, all parties in the network had to turn off their voice scramblers, making their conversation prone to eavesdropping. By using the SVZ as a (weak) fall-back, the use of a clear transmission was avoided. Many existing FuG-8 radios were retrofitted with an SVZ upgrade in 1991 and 1992. The SVZ can be seen as a smaller alternative for the earlier Bosch SVZ-8/9.

  1. SMC was acquired by Microchip Technology Inc. in August 2012.
  2. The chip was originally designed to work with a 3.58 MHz crystal, which was used for the colour burst in NTSC television sets in the US, and was therefore widely and cheaply available at the time [2].
  3. Relatively speaking. Although the BBC Vericrypt 1100 offered a much better protection against eaves­dropping than the SVZ module, all speech scramblers, no matter how complex, are inherently unsafe.

As a service part After unpacking Top side Bottom side Top Bottom Scrambler chip Operational amplifier
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As a service part
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After unpacking
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Top side
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Bottom side
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Scrambler chip
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Operational amplifier

  1. Klaus Paffenholz, Bosch FuG 8a / 8b / 8a-1 / 8b-1 (KF-802)
    Website: Geschichliche Entwicklung des BOS-Funks (German).
    Retrieved June 2017.

  2. SMC, COM9046 datasheet
    Preliminary datasheet. Date unknown.
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Crypto Museum. Created: Thursday 29 June 2017. Last changed: Friday, 23 February 2018 - 21:51 CET.
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