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Voice
  
MSC-2001 →
  
PSQ-188
Voice encryption unit

AN/PSQ-188/VRC, commonly abbreviated to PSQ-188, is a voice encryption unit for half-duplex military VHF and UHF radios, made in the early 1980s by Telemit Electronic GmbH in München (Germany). The device is actually a rebadged and repackaged Siemens MSC-2001 voice encryptor.

The device measures 270 x 99 x 54 mm and weights 990 grams. All controls and connections are at the device's front panel, as shown in the image on the right. Two rather obsure 16-pin sockets are present at the left (I) and right (II), for connection to the radio (I) and peripheral equipment like a handset and a key loader (II).

When connecting the Siemens Key Gun to socket II, a suitable adapter cable should be used. In between socket I and II is a more common NF7 socket for connection of a handset or headset, with a separate volume control at the top left.
  
AN/PSQ-188 front panel

The device was intended for use in combination with the RT-880/PRC-88/GY military manpack radio, and could easily be fitted alongside, with sort cables connecting the PSQ-188 with the radio. At present we do not have any further information about this device or the RT-880 radio. Furthermore, we are looking for the appropriate cables to connect the PSQ-188 to a radio set. For a detailed description of the key loading procedure, please refer to the Siemens MSC-2001.

AN/PSQ-188/VRC unit Rear view AN/PSQ-188 front panel Front panel Rear side with model and serial number tag
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AN/PSQ-188/VRC unit
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Rear view
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AN/PSQ-188 front panel
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Front panel
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Rear side with model and serial number tag

Features
All controls and connections of the PSQ-188 are at the front panel, which is shown in the diagram below. Two 16-pin sockets (I and II) are available for connection of the transceiver and peripheral equipment like a remote control unit or the key loader. For the latter, the Siemens Key Gun must be used with a suitable converter cable. At the centre is a separate audio output that has its own volume control. It can be used for connecting a local handset, headset or an external speaker.

PSQ-188 control panel

At the top right is a rotary switch that is used for selecting the required MODE of operation. For clear (unencrypted) speech, it should be set to CLEAR. For encrypted speech it should be set to any of the eight KEY compartments (1-8). Emergency erase (zeroize) is possible by rotating the MODE selector counter clockwise to before the '1' (code erase). This is destructive and requires breaking the blocking pin aside the number '1'. The broken pin has to be repaired afterwards.


Interior of the PSQ-188 seen from the top rear

Interior
The interior of the PSQ-188 can be accessed by removing two crosshead bolts from the rear side, and sliding-off the green metal case shell (do not damage the rubber gasket). This exposes three PCBs that are held in place by a metal frame that is fitted to the die-cast aluminium front panel.

The image on the right shows the interior of the PSQ-188 after the case shell has been removed. At the left is the front panel. At the right are two metal stubs by which the case shell is bolted to the frame. The frame holds three circuit boards.

The lower two boards are made by Siemens – also based in München – and are marked MSC-2001 EINSATZ (MSC-2001 insert). These two boards are in fact a complete MSC-2001 voice encryption unit. The upper board is basically an audio interface made by Telemit, to adapt the MSC-2001 to the RT-880/PRC-88 military radio.
  
Interior

A lot of wiring is present between the three printed circuit boards (PCBs) and the front panel. The thicker wires are all shielded audio cables. The rather obscure 16-pin sockets at the front panel are wired in such a way that they can be connected directly to the RT-880, using short 1:1 cables. For a detailed description of the MSC-2001 part of the interior, please check the MSC-2001 page.

Case shell removed Interior Interior Bottom side Bottom side, showing the MSC-2001 module Side view Wiring detail Circuit detail
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Case shell removed
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Interior
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Interior
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Bottom side
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Bottom side, showing the MSC-2001 module
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Side view
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Wiring detail
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Circuit detail

Help wanted
Crypto museum are still looking for cables with the special 16-pin plugs (are bare 16-pin plugs), to connect the PSQ-188 to a radio set. We are also looking for further documentation about this device – including operating instructions – and about the manufacturer Telemit.

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Further information
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Crypto Museum. Created: Sunday 11 March 2018. Last changed: Monday, 12 March 2018 - 09:47 CET.
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