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Racal MA-4235 MA-4231 → Arabic →
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.
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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.
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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:
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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.
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Looking into the Fischer sockets
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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.
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| Pin | Name | Colour | Description |
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| 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) |
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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.
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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.
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The MA-4230 can be operated in the following modes:
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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:
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- Press MAN
- Operate KEY is if it was a morse key
- Press OFF at the end of the message
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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:
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- Press MAN
- Type the message on the keypad
- Press OFF at the end of the message
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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.
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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)
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- 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
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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:
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- Press STO to swith the unit on
- Enter the additional text
- Press OFF
- Transmit the message as usual
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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:
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- 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
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This mode allows a message to be repeated at normal speed over and over
again, until stopped manually. Repeat mode works as follows:
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- 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.
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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:
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- 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
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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.
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© Crypto Museum. Created: Thursday 26 August 2010. Last changed: Tuesday, 12 December 2023 - 08:52 CET.
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