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MEL EMU
Electronic Message Unit
BA-1304 was an Electronic Message Unit for the
PRC-319
manpack radio, introduced in the mid 1980s
by MEL in Crawley (UK) for use by Special Forces (SF)
such as the British Special Air Service (SAS).
The device transmits and receives nessages at high speed, which reduces the
risk of being intercepted and discovered (ECCM).
It can be installed in a dedicated slot of the
PRC-319 radio,
but can also be used detached or stand-alone.
The device does not feature message encryption.
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The image on the right shows a typical BA-1304 EMU with numerical keypad
and an LCD display. The LCD has a protective lid, which is open here.
Below the keyboard, at the bottom left, is the ON/OFF/MODE-selector that is
used to turn the unit on.
To the right of the mode-switch is a button that illuminates
the display momentarily.
When powered by its own 9V battery, the BA-1304 can be used completely
stand-alone for the preparation, entering and reading messages.
The on-board static RAM memory allows stored messages to be retained
for over 500 hours.
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The BA-1304 uses the RWOP 1 data communication protocol,
which uses standard frequency shift keying (FSK) with 850 Hz shift
and Forward Error Correction (FEC) for protection against reception
errors [1].
The bandwidth varies with the keying speed from 1055 Hz at 75 baud to
1320 Hz at 300 baud data rate. It also has an intermediate speed of
150 baud with a bandwidth of 1170 Hz.
Three different versions are known, designated EMU Mk I thru EMU Mk III.
In the late 1980s it was complemented
by the alphanumeric EMU Alpha, that had a larger message buffer
and encryption.
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- EMU (later designated EMU Mk I)
- EMU Mk II
- EMU Mk III
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The EMU measures approx. 16 x 9 x 4 and is easily accessible.
Removing 7 bolts from the bottom of the unit provides access to the interior.
After opening, the solder side of the main printed circuit board (PCB)
is exposed. The main PCB is stacked and is held in place by 6 further bolts.
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After removing these bolts, the PCB assembly can be separated from the case.
The PCBs are connected to the controls and connectors of the case by means of
two multi-coloured cable assemblies, each plugged to one of the PCBs.
The PCB assembly consists of two multi-layer boards stacked on top of each other.
They are connected together by means of a simple inter-board connector and are
easily separated. The upper board contains the display and the display drivers,
whilst the lower board contains the microcontroller, memory and crypto engine.
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At present we have no further information about the operating principle
of this device. It you have additional information, such as the circuit
diagram or the service manual, please contact us.
The standard operator's manual
is available for download below [A].
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For many years, the PRC-319 and the BA-1304 (EMU) were standard issue
for the S.A.S., the British Special Forces.
It was used for behind-enemy-lines missions in Iraq during
the First Gulf War in 1991.
A good example of the use of the EMU and the PRC-319 radio is given in the book
Bravo Two Zero by SAS Sergeant Andy McNab. 1
This book is based on a real mission in Iraq, designated Bravo Two Zero [2],
lead by McNab in January 1991.
The 8-member team had one PRC-319 radio with EMU for emergency use.
It had to be used in burst mode (i.e. no voice calls) in order to avoid
interception
and Direction Finding (DF) by the enemy .
The team also carried four TACBE
(Tactical Beacon) units for emergency distress calls in case the PRC-319 got
lost or damaged.
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Any McNab is the pseudonym of sergeant Steven Billy Mitchell, the patrol commander.
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© Crypto Museum. Created: Wednesday 07 April 2010. Last changed: Tuesday, 15 February 2022 - 16:12 CET.
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