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← Teltron Voice
Secure voice frequency inverter
- this page is a stub
The SP-601 was a secure voice encryption unit,
based on the principle of
frequency inversion, also known as a
frequency domain speech scrambler,
developed by Teltron
in München (German) in 1972. The device was intended for use by the police
and other law enforcement agencies and was suitable for existing analogue
VHF/UHF 2-way radios. It had 6 different scrambling codes.
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The image on the right shows a typical SP-601. It is housed in an aluminium
enclosure with two rigs at the top, allowing it to be mounted in a vehicle
bracket. Radio and power are wired at the rear. The handset is connected
at the front.
Unlike later voice scramblers, which used a single-chip solution, the SP-601
is built with discrete components, spread over two PCBs.
Generally speaking, voice scrambling is not (and never was) very secure.
An eavesdropper could simply reverse the audio spectrum once more,
to make the secret conversation audible again.
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With just 6 available codes (i.e. frequency mirroring points), the interceptor
has little trouble finding the correct one. In fact, in the days when police
scanners were popular, some listeners got so experienced that after a while
their brain would 'translate' the scrambled speech 'on the fly' without any
technical means. The SP-601 was succeeded by the SP-612 which was based on a
single-chip solution and offered 16 scrambling codes, but even this was not
secure enough.
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Documentation kindly supplied by Jim Meyer [1].
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© Crypto Museum. Created: Thursday 02 July 2015. Last changed: Saturday, 24 February 2018 - 21:21 CET.
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