Homepage
Crypto
Index
Glossary
Enigma
Hagelin
Fialka
Nema
AT&T
Datotek
Gretag
HELL
ITT
Motorola
Mils
OMI
Philips
Racal
Siemens
STK
Tadiran
Telsy
Teltron
Transvertex
TST
USA
USSR
UK
Yugoslavia
Voice
Hand
OTP
EMU
Mixers
Phones
FILL
Codebooks
Algorithms
Spy radio
Burst encoders
Intercept
Covert
Radio
PC
Telex
People
Agencies
Manufacturers
• • • Donate • • •
Kits
Shop
News
Events
Wanted
Contact
About
Links
   Logo (click for homepage)
MEL BA-1304   EMU
Electronic Message Unit

The BA-1304 was an Electronic Message Unit for the PRC-319 manpack radio. It was built by MEL in the UK 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 single 9V block battery.
 
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.
  
EMU with display open

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.
 
EMU with display open The EMU with the display open, showing the battery compartment at the left The EMU slotted into the PRC-319 rig (left) The EMU (left) aside the control unit of the PRC-319 rig

 
Interior
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.
 
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.
  
The interior of the EMU after the electronics assembly (left) has been removed

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].
 
Interior of the EMU Contents of the EMU Cables inside the EMU The interior of the EMU after the electronics assembly (left) has been removed Interior of the EMU Rear of the display board

 
Bravo Two Zero
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.
 
  1. Any McNab is the pseudonym of sergeant Steven Billy Mitchell, the patrol commander.

Documentation
  1. MEL, Operator Handbook for the Electronic Message Unit (EMU) BA 1304
    Publication number 1673. June 1988. 26 pages.

References
  1. Paul Signorelli, RWOP (RW Open Protocol)
    ARRL website. Retrieved April 2010.

  2. Wikipedia, Bravo Two Zero
    Retrieved April 2010.

Further information

Any links shown in red are currently unavailable. If you like the information on this website, why not make a donation?
Crypto Museum. Created: Wednesday 07 April 2010. Last changed: Friday, 20 May 2016 - 07:51 CET.
Click for homepage