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Bob042

Cossor gct1052

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Anyone know about this bit of kit for a 320?

http://www.ebay.co.uk/itm/RARE-CLANSMAN-RADIO-MILITARY-PRC320-CODE-MESSAGE-UNIT-CGT1052-/201889052390?hash=item2f018676e6:g:xt0AAOSw~CFY7j~6

It's obviously a sim as the l/h keyboard doesn't exist. BID?

Never seen before, pre 319 add on for the 320?, cannot find anything about it on the net.

Iain one for you?

 

Regards

Bob

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Bob

 

It is the first time I have ever seen one properly - there is a line drawing of the "Digital Message Handling Device" in the UK/PRC-319 AESP which looks the same size and shape with only the RH keyboard installed - the 1984 date on the label of this item is about 5 years before the 319 so a very interesting item to fill the gap between UK/PRC-316 with the clockwork AN/GRA-71 burst sender and the 319.

 

I suppose the 2nd keyboard was a factory option - because of tooling costs it would make sense for a low volume product to use a common casting for the case in all variants but not cut the keyboard aperture(s) on variants that don't need it. The keyboard shown is sufficient to match the early versions of the 319 EMU and I suppose the 2nd keyboard was either alphabetic or application specific (e.g. for artillery use) if fitted

 

Cossor were already a Raytheon subsidiary by 1984 so I suppose it is one of the last things branded as such.

 

Iain

Edited by g0ozs
Add DMHD identification

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Iain,

 

Fascinating, I knew you would know something of it.

So do you think it was in UK service? or just trialed?

As I'm sure you know, a 320 can be run through the DMU/BID250 for encryption so why this? It can obviously can be fixed to the standard 320 mountings a la 12W surf, so I guess it's a stand alone encryption unit?

Apologies for all the questions.

 

Regards

Bob

Edited by Bob042

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Bob

 

Different application - the BID-250 (and the less well documented BID300 for the UK/PRC-351M) was used for secure speech on VHF nets using 16KBits/s CVSD digital encoding followed by non-trivial encryption (and requires 8KHz bandwidth in a UK/VRC-353 using "wide data" mode or a UK/PRC-351M using audio socket 2) - the HF UK/PRC-320 and 319 are always limited to 3 KHz or so could not support encrypted digital speech using 1970s technology so they use data terminals for encrypted "text message" communications - initially the RACAL TDED or the Cossor DMHD - later the 319 EMU. I only have practical experience of the EMU which is not itself encrypted - the message needs to be encrypted and then encoded into numeric form by "pencil and paper" methods before it is keyed in.

 

The main reason for using them - especially if deployed in hazardous locations - is to reduce time on air compared with sending the same hand-encrypted message using morse - the EMU sends at 75, 150 and 300 Baud - up to 45 Baudot (5 bit) characters per second or 9 5 digit groups per second, whereas a good CW operator will send 30 5-character groups per minute by hand. This was sufficient to defeat swept-tuned scanning receivers and manually coordinated direction finding in the 1960s and 1970s - by the late 1980s I doubt it would have been safe in the presence of near-instantaneous FFT spectrum analysers with automatic handoff to a DF system, so modern (RACAL Panther, Marconi Scimitar and more modern sets like Bowman) frequency hop many times per second to avoid detection.

 

See:

http://www.cryptomuseum.com/crypto/uk/bid250/index.htm

http://www.cryptomuseum.com/crypto/racal/ma4450/index.htm

 

Regards

 

Iain

Edited by g0ozs

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Hi Iain,

Thanks for all the excellent info, much appreciated. It has certainly filled a gap in my knowledge.

I was aware of the crypto museum site.

Another thing, I have tried to find out info on the BID300 in the past but failed, don't even know what it looks like.

Anything on that?

Regards

Bob

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Bob

 

I have never seen the BID 300 - two of my 351M sets came with the holder for it which is a metal clamp that would have held an object about the size of a VHS cassette on the back of the radio.

 

The audio bandwidth through the radio on socket 2 is expanded from 300Hz-3KHz to about 150Hz - 8500Hz (I have measured it on the bench) so would be enough for 16Kbits/s CVSD.

 

Regards

 

Iain

73 de G0OZS

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