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Racal MA-4014B
Time-division voice scrambler

The MA-4014B is a medium-grade voice encryption unit developed by Racal Datacom Ltd. in the UK around 1977. The device uses a time-division scrambling technique which shuffles small time segments in a pseudo-random sequence that changes every half second. It is suitable for narrow-band voice transmission on HF and VHF bands, in tactical (military) situations.

The MA-4014B offers a higher level of security than the nearly identical MA-4204, but less than its successor, the MA-4224. It was often used with the Racal PRM-4031 manpack radio.

The scrambling order of the time segments changes each half second and is controlled by a pseudo-random number generator (PRNG). The PRNG itself can be controlled by five rotary switches at the top half of the front panel. The first two switches have 8 positions each, whilst the remaining three each have 10 positions, producing a total of 64,000 combinations.
  
MA-4014B front panel

The MA-4014B can be used for voice signals in any mode (AM, FM, SSB) but also for keyed signals (morse, CW). It can be powered directly from the transceiver (TCVR) or from an optional battery that can be attached to the bottom of the device. The MA-4014B belongs to the same family of devices as the slightly simpler MA-4204, that has just 3 code-selectors. Speech is first digitized using Delta-Sigma modulation, than scrambled in the time domain, and then converted to analogue again, so that it can be transmitted over a conventional audio channel.

Although 64,000 combinations might seem a lot, it hardly provides any serious protection. Nevertheless it was considered sufficient for tactical use at the time. With modern techniques it should be relatively easy to break the code, simply by observing the discontinuities in the signal.

Racal MA-4014B Racal MA-4014B front panel Adjusting the code Font panel Rear panel of the MA-4204 (bottom) MA-4014B front panel

Controls
The MA-4014B is extremely easy to operate and has very few controls and indicators. It is connected to a radio set and suitable accessories through the 3 connectors at the front panel. Once connected, the mode of operation can be selected with the 3-position rotary switch at the bottom center (MODE). The required scrambling code is selected with the 5 switches at the top.


Two red indicators are present to the right of the TCVR connector, marked AUX and PTE. The AUX indicator lights up when the unit gets power from the connected transceiver (see below). The PTE indicator lights up in PRIVATE or ENCRYPTED mode. It flashes when the voltage drops too low.

MODE of operation
  • OFF
    This mode bypasses the encryption and decryption circuits of the MA-4014B. It forces communication in CLEAR.

  • ON
    In this mode, automatic encryption is enabled. It can be used for the reception of CLEAR signals, whilst it switches automatically to decryption when a suitable synchronising signal is detected.

  • SEND
    This mode forces continuous transmission in encrypted mode.
Connections
The MA-4014B has three connectors at the front, through which all signals and power lines are connected. The leftmost connector (TCVR) is intended for connection to a transceiver. It is also used to supply power to the unit. The unit can be fed by any DC power source between 12 and 30V and draws just 120mA. Socket AUDIO 1 is used for the connection of a handset, a morse KEY or a battery charger (when the external battery MA-968A is used). AUDIO 2 can be used for connecting an extra handset or ancillary equipment.

TCVR (Transceiver)

  1. MIC out (to transceiver)
  2. Power (+12 to 30V)
  3. PTT out (to transceiver)
  4. GND (common rail)
  5. KEY out (when MODE-switch is OFF)
  6. Audio in (from transceiver)
AUDIO 1

  1. MIC in
  2. Battery supply
  3. PTT in
  4. GND (common rail)
  5. Key
  6. AUDIO out
AUDIO 2

  1. MIC in
  2. AUX supply output
  3. PTT in
  4. GND (common rail)
  5. PRIVATE indicator (remote)
  6. AUDIO out
Operation
Inside the MA-4014B, speech is first digitized using a Delta-Sigma modulator, which produces a data stream with a bit-rate of 32 kbps (kilo-bits per second). The data is temporarily stored in memory, where it is divided into eight segments of 2048 bits each (2 kb). This way, each segment represents 62.5 ms, with 500 ms for all 8 segments. The eight segments are then scrambled.


Scrambling of the eight segment is controlled by a pseudo random generator, assisted by pre-recorded scrambling orders that were stored in ROM. These pre-recorded orders were carefully selected to guarantee minimum intelligibility. After scrambling, the data was coverted back to an analogue signal again, so that it could be transmitted over a standard voice channel.

Interior
Considering the fact that the MA-4014B was used in the mid-1970s, it is a rather sophisticated device with modern circuitry. The electronics are nearly identical to that of the MA-4204. After removing the cover, the PCBs are immediately revealed. The solder sides of the two large PCBs are facing outwards, and the PCB can be folded away after removing a series of screws.

The unit consists of four PCBs: the Power Board, the Speech Processing Board, the Logic Board and the Audio Board.

Most of the ICs inside the unit are made by RCA, with an occasional one by Harris. The rather strange unidentified IC in the image on the right is probably an custom-made OEM chip made by an unknown manufacturer.
  
Unknown custom chip?

Top view of the PCB Bottom view of the PCB Power board and speech processing board Interior, mode switch Interior, power board Speech processing board Logic board with modification Audio board

At present, we have no access to a free copy of the user manual or the service manual of the MA-4014B. Some information on this page was taken from a protected copy of the manual. If you have access to any of these manuals, or if you have further information about these devices, please contact us.

References
  1. Racal Datacom Ltd., Technical Manual, MA. 4014B, Audio Encryption Unit
    Ref. WOH 5062. Issue 1.1.75-150.

  2. Signetics, 2524 and 2525 datasheet
    512 and 1024 bit Recirculating Dynamic Shift Registers.
    Publication date unknown. Retrieved April 2012.
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