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Electronic Message Unit
The BA-1304 was an Electronic Message Unit for the
PRC-319
manpack radio. It was built by MEL in the late 1980s
as part of the Clansman radio system.
It allowed secure messages to be sent between Special Operations units.
The EMU was usually contained in a special 'slot' on the body of the
PRC-319, but could also be used stand-alone, powered by a simple 9V battery.
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The image on the right shows a typical BA-1304 EMU with numerical keypad
and an LCD display. In this case, the flap over the display is opened.
Below the keyboard, at the bottom left, is the power/mode-switch that is
used to turn the unit on.
To the right of the mode-switch is the display illumination button.
When powered by its own 9V battery, the BA-1304 can be used completely
stand-alone for the preparation or read-out of a message. Messages can be
retained in the on-board memory for over 500 hours.
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The BA-1304 uses the RWOP
[1]
system.
It uses standard frequency shift keying (FSK) with 850 Hz shift
and Forward Error Correction (FEC) for protection against reception errors.
The bandwidth varies with the keying speed from 1055 Hz at 75 baud to
1320 Hz at 300 baud. It also has an intermediate speed of 150 baud with a
bandwidth of 1170 Hz.
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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 PCB is uncovered. It 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 cable assemblies, each plugged to one of the PCBs.
The PCB assembly consists of two multi-layer PCBs stacked on top of each other.
The 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.
The lower board contains the microcontroller, memory and crypto unit.
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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 (pseudonym).
The book is based on a real mission in Iraq 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 by the enemy and Direction Finding (DF).
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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© Copyright 2009-2013, Paul Reuvers & Marc Simons. Last changed: Thursday, 20 December 2012 - 10:04 CET
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