Click for homepage
Racal
Voice
  
Racal MA-4470
F/T voice scrambler

The MA-4470 was a high-grade privacy unit, also known as a frequency and time domain speech scrambler, developed around 1996 by Racal COMSEC Ltd in Salisbury (Wiltshire, UK), just before the company was sold to Thomson CSF (now Thales) in 2000. The device was intended for use on military narrow-band radio voice circuits. A civil telephone-variant is known as the MA-4471.

The unit is smaller than any of its predecessors and measures just 16 x 6 x 21 cm. It is inserted between the handset and the transceiver and allows voice signals to be encrypted using a combination of Time Element scrambling and Frequency Processing, in half-duplex [1].

The MA-4470 employs a novel continuous synchronisation system that allows late-entry and that is virtually transparent to the user when switching the transmission direction of the half-duplex link. The unit can be powered by the host radio set, or by an external power supply unit.
  
MA-4470 front panel

All controls and connection are at the front panel. At the left are the sockets for the handset (or headset) and the transceiver. To the right of the sockets is a 4-character LED display and some LED indicators that are used for user feedback. The right half of the front panel is taken by the 25-button rubber keypad, which is used for switching between clear and secure, entering the base key, using the fill-gun, selection of the current key and ereasure of the key(s).

MA-4470 voice crypto unit
MA-4470 front panel
MA-4470 front panel
Another view of the print panel
A
×
A
1 / 4
MA-4470 voice crypto unit
A
2 / 4
MA-4470 front panel
A
3 / 4
MA-4470 front panel
A
4 / 4
Another view of the print panel

Entering keys
The cryptographic keys are 80-bits long and can be entered by typing 20 hexadecimal digits on the keypad. Alternatively, the keys can be entered using a suitable key-fill device (fill-gun), such as the MA-4255 Master Programmer or the MA-4459 Slave keygun [1].

The image on the right shows the Racal MA-4083 fill-gun that looks similar to the MA-4459 slave keygun that is used with the MA-4470. The MA-4255 Master Programmer is housed in the same case as the MA-4225 portable encryptor.
  
MA-4083 fill gun, which is similar to the MA-4459 slave keygun.

Interior
The MA-4470 unit can be opened from the rear. The device consists of 4 PCBs plus a font panel. After removing the rear panel, the four PCBs are revealed. From top to bottom there are the interface board, the key processor board, the speech store board, and finally the audio board.

The front panel of the unit acts as a backplane for the four PCBs. Each board uses a 64-way DIN connector for connection to the backplane. A small metal bracked, that is usually stored in between the PCBs, can be used to pull-out the individual boards.

The image on the right shows the processor board, which is the 2nd board from the top, half-way out of the case. The metal bracket is shown here in front of the PCB. Detailed pictures of each board can be found below.
  
Key Processor Board being removed

Interior of the MA-4470
Key Processor Board being removed
Key Processor board
Speech store board
Interface board
Audio board
Close-up of the audio board
Another detail of the audio board
B
×
B
1 / 8
Interior of the MA-4470
B
2 / 8
Key Processor Board being removed
B
3 / 8
Key Processor board
B
4 / 8
Speech store board
B
5 / 8
Interface board
B
6 / 8
Audio board
B
7 / 8
Close-up of the audio board
B
8 / 8
Another detail of the audio board

Specifications
  • Principle
    Time Element scrambling and Frequency processing
  • Keystream
    Non-linear keystream generator
  • External key
    8·1031
  • Internal key
    26 bits
  • Base key
    80 bits per key (from fill-gun) or 20 hex digits (via keyboard)
  • Stored keys
    16 base keys + 1 guard key (selectable via keyboard)
  • Key period
    1024 bits
  • Message key
    24 bits
  • Modulation
    FSK in frequency processed channel at 48 baud
  • Cycle time
    > 90 days
  • Battery life
    5 years
  • Response
    400Hz - 2400Hz
  • Bandwidth
    400Hz - 2700Hz
  • Audio delay
    495 ms
  • Input level
    TX: 0dB, 1mV - 50mV, RX: 70mV - 3.5V
  • Output level
    Adjustable to match input level (max. 1.5W into 8 Ω)
  • Power supply
    12V - 32V DC, 120 - 300mA
  • Temperature
    -20°C to +65°C (operation), -40°C to +70°C (storage)
Accessories
  • MA-4255
    Master Programmer
  • MA-4459
    Slave Keygun
  • MA-4220
    NiCd Battery for Master Programmer
  • MA-4234
    Battery Charger (230V AC) for Master Programmer
  • MA-4454
    Battery Charger (115V AC) for Master Programmer
Documentation
  1. MA-4470 Sales Leaflet
    Racal-Comsec Limited, February 1991. 1

  2. MA-4470 Maintenance Manual
    TH 8466. Racal-Comsec Limited, Issue 1, July 1990.
References
  1. Racal-Comsec Limited, MA-4470 Sales Leaflet
    February 1991. 1
  1. Leaflet kindly supplied by Paul Ratcliffe, January 2013.

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: Thursday 26 August 2010. Last changed: Tuesday, 10 August 2021 - 16:29 CET.
Click for homepage