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Morse burst encoder

The MA-4230 was a morse burst encoder, built by Racal Datacom Ltd (UK) in the late 1970s. It allowed messages, stored in its internal (1024 character) memory, to be sent as a high speed burst, in order to minimize the chance of interception and detection. It was part of the MA-4235 family of devices, that included a complementary decoder, a printer a various power sources.

The encoder is powered by an internal VARTA rechargeable battery that lasts about 16 hours before recharging. The two connectors at the right side of the unit are identical male-type Fischer sockets.

The keyboard consists of 40 keys that represent the Latin alphabet, the digits 0-9, space, question mark, slash and a dot. Just above the keyboard are another 8 keys that are used to control the unit's operation. At the top left are three indicator lights (FULL, POWER and SEND).

In manual-mode, characters can be sent one at a time by entering them slowly on the keyboard. When typing too fast, the unit has a 16 character buffer. In store-mode, up to 1024 characters can be stored in the unit's battery-backed non-volatile memory.
MA-4230 morse encoder

The unit can send the stored data at two different speeds: at 15 wpm (normal speed) or 'squirted' (SQT) at 120 wpm (burst). The latter is used to reduce the chance of Direction Finding (DF), interception and detection. A message that is stored in memory, is retained for up to 30 days after power is turned off, provided that the battery is good shape and fully charged.

A transmitter can be keyed in two ways: by means of a 1 kHz tone (20 mV ±3 dB into 300 ohms) or my means of a contact closure (0.5 A max). Please note that the latter is only possible when transmitting at normal speed (i.e. 15 wpm). The following controls are available:

MA-4230 morse encoder A look at the connectors Close-up of the connectors Interior of the MA-4230 Interior of the MA-4230 The MA-4230 morse encoder (top) and the MS-4231 morse decoder (bottom)
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MA-4230 morse encoder
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A look at the connectors
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Close-up of the connectors
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Interior of the MA-4230
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Interior of the MA-4230
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The MA-4230 morse encoder (top) and the MS-4231 morse decoder (bottom)

The MA-4230 has two identical Fischer 5-pin male sockets at its right side. These two connectors are wired in parallel, so either can be used for the connection of a radio set, a battery charger, or an MA-4231 morse decoder.

Looking into the Fischer sockets
The pins of these sockets are numbered from 1 thru 5, but note that this numbering is different from the numbering inside the matching plug! The pins are wired according to the wiring diagram below. The colours specified in the table are the ones used in the original Racal cables.

Pin Name Colour Description
1 RX Blue Straight through (audio from receiver to MA-4231)
2 TX Red Keyed Tone Output (audio from MA-4230 to transmitter)
3 PTT White PTT or KEY output (relay) depending on jumper *)
4 Power Yellow Power supply or battery charger (+ 11 to 30V)
5 GND Green Common connection (ground)
Shield GND Braid Common connection (ground)

A suitable female connector for this socket is Fischer S103 Z054-130+.

*) The operation of the PTT signal at pin 3, is determined by a link on the Keyer board inside the MA-4230. When the link is open, pin 3 is configured as a PTT output. During a tranmission, pin 3 is held low (GND) for the duration of the message plus 1.5 sec. When the link is closed, pin 3 acts as a KEY output (active low), synchronised with the tones at pin 2.

Power supply
Power is supplied to the same pins of the sockets on all devices of the MA-4230 family. These pins (4 and 5) are all interconnected, allowing a battery charger or external power supply to be connected anywhere in the chain. Generally though, a battery charger would be connected to the printer (if present). When connected to a suitable radio, power would generally be supplied by the radio (connected to the MA-4230 unit).

As each unit has a built-in rechargeable battery that lasts approx. 16 hours, it can also be used stand-alone (i.e. without an external power source). This would typically be the case for any field application, such as the use of these unit by Special Forces (SF). As each unit has a 5-pin male Fischer socket, the optional battery charger can be connected directly to any of the individual units.

Please note that, when using an external power source (or power from a transceiver), the battery charger should be disconnected.

Operating procedure
The MA-4230 can be operated in the following modes:

Key Mode (KEY)
In this mode, the MA-4230 can be used to send morse codes directly, just as if it was a morse key. As the KEY button is rather small, it will not be convenient for long messages. KEY-mode works as follows:

  • Press MAN
  • Operate KEY is if it was a morse key
  • Press OFF at the end of the message
Manual Mode (MAN)
In manual mode, a message, typed on the keyboard, can be transmitted simultanously. The MA-4230 has a buffer for 1024 characters, allowing the message to be entered at a higher speed that the system can transmit. Operation in manual mode is as follows:

  • Press MAN
  • Type the message on the keypad
  • Press OFF at the end of the message
When entering text into the 1024 character buffer, the FULL LED will be illuminated when 896 characters are in the buffer. After that, a further 127 characters may be entered.

Store mode (STO)
In this mode, a message can be entered into the buffer whithout sending it immediately. Once entered, the message can either be sent at normal speed (TX) or as a high speed burst (SQT)

  • Press STO and CL simultaneously (when entering a new message)
  • Type the message on the keypad
  • Press OFF
  • Transmit the message in TX or SQT
Pressing STO and CL simultaneously, clear the message buffer. Text can be added to the message in the buffer, by just pressing STO to turn the unit on. Please note that this is only possible when the message has not been transmitted yet. If the original message has already been transmitted, only the new message will be stored and the original will be lost. Text can be added as follows:

  • Press STO to swith the unit on
  • Enter the additional text
  • Press OFF
  • Transmit the message as usual
Transmit mode (TX)
In transmit mode, messages stored in the internal buffer can be sent at normal speed. During transmission, the SEND LED will blink in the rithm of the morse signal. Transmit mode is operated as follows:

  • Press STO to switch the unit on
  • Press TX to start transmission
  • The MA-4230 will switch off automatically at the end of the message
Repeat mode (RPT)
This mode allows a message to be repeated at normal speed over and over again, until stopped manually. Repeat mode works as follows:

  • Press STO to switch the unit on
  • Press TX to start transmission. Message will be repeated continuously.
  • To terminate transmission: press and hold OFF until SEND LED stays off.
Squirt mode (SQT)
The MA-4230 is actually intended for transmission of morse characters at very high speed in order to minimize the chance of interception and detection. Such hight speed transmissions are generally called burst transmissions. Burst mode is operated as follows:

  • Press STO to switch the unit on
  • Press SQT to start transmission
  • The MA-4230 will switch off automatically at the end of the message
After pressing the SQR-button, the MA-4230 first transmits a so-called pretone, which is used to synchronise the MA-4231 morse decoder. This way, there is no need to send synchronisation characters to the MA-4231 in the preamble of the message.


  1. Technical Manual MA.4230 MA.4230S Morse Encoder (with Battery Charger MA.4232)
    Racal-Datacom Limited. 1 October 1980, issue 1.10.80-100.

  2. Technical Manual MA.4231 Automatic Morse Receiver
    Racal-Datacom Limited. 2 February 1980, issue 2.2.80-100.

  3. Conversion notes for the Racal MA4230/4231
    John's Radio, Conversion from Arabic to English. Date unknown.
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Crypto Museum. Created: Thursday 26 August 2010. Last changed: Saturday, 01 July 2017 - 11:13 CET.
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