Voice scrambler for HF radio
The TST-7595 was a small military-grade voice encryption unit,
developed by Tele Security Timmann (TST)
in Pöcking (Germany) around 1985.
It was intended for use in combination with military HF transceivers
and was so small that it could be fitted to the side of
such a radio set.
The image on the right shows a typical 7595, which is housed
in an extruded aluminium casing, similar to the ones used for
other TST devices, such as the TST-3010 message unit.
The device is shown here with a modern German handset that is
connected to the NF10 socket at the right of the front panel.
The socket at the left is used for connecting the TST-7595 to
the transceiver, which should also provide the necessary power.
The cryptographic key is entered into the device by using the
rotary dial (0-9) in combination with the push-button.
The TST-7595 was sold world-wide and was rather popular with
foreign armies. In the UK, the device was sold by Marconi,
who used it in combination with their
Clansman radio sets.
Although the nearby German Army Signals School in Feldafing
helped testing the usability of the TST-7595 in the field,
Timmann, to his dismay, was not allowed to supply the devices
to the German Army.
Please note that the TST-7595 is not a digital encryption
device, but rather an analogue one, that was built with the latest
digital techniques of the era. It was intended for use in
situations where digital encryption was not possible or practible,
such as in combination with analogue narrow-band HF radio sets.
It offered good voice quality and did not reduce the operational
range of the radio. As long as clear voice was possible,
the TST-7595 would scramble it, using three different techniques:
Frequency Domain, Time Domain and Inverted Time Domain scrambling .
From the outside, the TST-7595 is a rather simple device,
with only a few controls and connections. The larger socket is
used for connection to a transceiver, such as the British
whilst the smaller one is used for connection of a handset
The rotary dial at the center is used in combination with the
LED indicator and the Push-To-Talk switch on the handset (PTT),
for entering the cryptographic key into the device. In normal use,
i.e. when operating the device, the rotary is used to select one
of the previously stored keys.
The TST-7595 is housed in a strong aluminium enlosure that
consists of an extruded aluminium shell with die-cast aluminium
panels at both ends. These side panels are inserted into the
case and are each held in place by four
tiny hex bolts in
the corners of the outer shell.
Removing the hex bolts in the corners is easy, but removing
the side panels is more difficult as the bolts have caused the
aluminium to deform somewhat. With proportional force and the
right tools however, it should be possible to remove them
without causing damage to the front panel.
After removing the control panel, the interior of the TST-7595
becomes visible. Inside the case are
two PCBs that are held in
place by rigs in the sides of the outer shell. After carefully
removing the front panel connectors from the PCBs, the two
PCBs can be extracted from the case.
The two PCBs are slightly longer than standard Eurocard
format (10 x 16 cm). One board is the
analogue processing card,
marked TST 7595 APC, whilst the other one does holds the
It is marked TST 7595 DPC and has a cut-out
that accomodates the front panel.
The internal power supply
is located in the side panel opposite
to the side of the front panel.
- Size: 4 x 10 x 25 cm
- Weight: 1 kg
- Power: +9 to +15V DC (+8 to +33V by special order)
- Consumption: < 1W
- Power supply: via transceiver
- Storage temperature: -20°C to +70°C
- Operating temperature: -10°C to +60°C
- Shock and vibration: C/514.2-3 B
- TST-0606 Random Generator (for creating random keys)
- TST-0810 Key management System
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