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← UK Cold War SF SBO
Automatic clandestine transceiver
- wanted item
The PRM-4150 was a spy radio station developed by
HMGCC at Hanslope Park (UK)
and built by Racal Tacticom
in Reading (UK) from 1979 onwards [7].
It was a complete self-contained radio station
with a fully digital messaging system, supplied in a standard
attaché case. It was intended for use by
Stay-Behind Organisations (SBO),
the Diplomatic Wireless Service (DWS)
and Special Forces (SF).
The PRM-4150 is also known as TITHE and (in The Netherlands)
as DZO-81.
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The image on the right shows a typical PRM-4150 radio station packed
in a standard executive style briefcase.
It consists of three main units:
- RA-4151 Receiver (right)
- TA-4152 Transmitter (left)
- MA-4153 Message store (centre)
Each of the units is self-contained and is powered by its own built-in
rechargeable batteries. A brief description of each unit is given below.
The Operator's Instruction Manual is available for download at the
bottom of this page.
The radio station could be extended with secure communication features
by adding the optional external
MA-4245 data encryption unit.
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This is a message compilation and storage unit capable of storing a coded
message of up to 1020 numeric characters, for periods in excess of 7 days when switched OFF. The message is displayed 2 groups at a time, and each group
consists of 5 digits.
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The transmitter accepts data messages from the Message Store (MA-4153)
or from an external Data Unit, such as the Racal
MA-4245 portable cipher unit.
It transmits messages as a two-tone Frequency Shift Keying (FSK) signal
on the selected frequency channel at a rate of 50 characters per second.
This is equivalent to 600 groups per minute.
Furthermore, facilities are provided for transmissions in
morse code (CW).
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When set to DATA, this self-contained unit is capable of receiving data
messages on a selected frequency channel and storing this message until
reset by the user. The stored message can be recalled at any time up to at least 7 days after reception. It is displayed on the receiver's display.
Facilities are available to process the data message externally, e.g. on
a Racal MA-4245 portable cipher unit,
whilst it is being received. When in VOICE or CW mode, the receiver acts as a standard radio
with frequency pre-selection, capable of receiving voice (LSB or AM LSB)
or morse (CW).
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Data encryption unit
MA-4245
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The PRM-4150 could optionally be expanded with an
MA-4245 Cipher Unit
that is compatible with the data format of the MA-4153 Message Store
and can be connected directly to the set.
It allows the entry and encryption of alpha-numeric messages
directly from a full Latin keyboard.
➤ More information
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Stay-behind organisation O&I
The PRM-4150 was also used by the Dutch
Stay-behind Operation (SBO)
O&I, where it was known as
DZO-81, short for Digitale ZendOntvanger
(Digital Transceiver), 1981.
It was introduced in 1981 as a gap-fil solution between the ageing
SP-15
and the pan-European FS-5000 Harpoon.
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Not many PRM-4150 units of the Dutch Stay-Behind Organisation have survived.
In fact, the only one known to have survived is now in the collection of
the Dutch Signals Museum
[5].
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State Security Service (SSS)
Following WWII, Yugoslavia was a communist state that was more or less
trapped between two military powers: the Soviet Union (USSR), led by Russia,
and the free West, led by the UK and the US. Initially, only the UK
and the US were seen its most serious threat, but after the 1948 Informbiro
Crisis, the Soviet union and its allies were added to the list of enemies.
An efficient weapon against these enemies, turned out to be a wll-organised
network of agents, for which modern communication equipment was needed.
Around 1980, the State Security Service (SSS) of the (then) communist
republic of Slovenia purchased an unknown number of MA-4150 spy radio
field stations, plus one base station [8][9]. 1
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It is known that Slovenia had plans for ordering 13 field stations, but
it is unknown how many units were actually ordered [8].
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Device Spy radio set Purpose Covert clandestine and diplomatic communication Manufacturer Racal Model PRM-4150 (MA-4150) Country UK Year 1979 Frequency 2-29.999 MHz Channels 28,000 (1 kHz steps) Speed 200 baud (synchronous) Data 600 five-figure groups/minute Message 204 groups (1020 digits) Duration 21 sec. max. Modulation 2-tone FSK (1563 and 2083 Hz) Shift 520 Hz Error det. 1 parity bit per character pair
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Model TA-4152 Modulation LSB FSK (F2J), LSB CW (A2J) Output 5W minimum from ATU into 50 ohm load Harmonics < -40 dB (ralative to PEP in 50 ohms load) Spurious < -45 dB Carier sup. Better than -40 dB IMD3 Better than -25 dB Tuning Automatic ATU to tune long wire antenna (< 10 s) Storage 1 message with up to 1020 digits (204 groups) Memory Volatile (erased when transmitter is switched OFF)
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Model RA-4151 Modulation LSB FSK (F2J), LSB CW (A2J), LSB Voice (A3J) Display 2 x 5 digit LED (2 groups) Sensitivity > mW into 300 ohms for 2µV EMF RF input (into 50 ohms) S/N ratio CW 22dB @ 2µV EMF, Voice 15dB @ at 2µV EMF Selectivity CW 3dB bandwidth 100Hz ±30Hz, Voice 6dB/2kHz, 40dB/5kHz Image rej. Better than 70dB IF rej. Better than 70dB AF output 20mW into 300 ohms Storage 1 message of up to 120 digits (204 groups) Memory Non volatile
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Model MA-4153 Input Numeric keyboard Display 2 x 5 digit LED Output Serial data multiplexed over power line to transmitter Storage 1020 digits (204 groups) Memory Non volatile
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- Diplomatic Wireless Service (UK)
- Stay-behind organisation O7I (Netherlands)
- Ministry of Defense (Netherlands)
- Bundeswehr (Germany)
- State Security Service (Slovenia, Yugoslavia)
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- Racal Tacticom Ltd., PRM-4150 Portable High Speed Data Station
TH1344/T. Operator's Instruction sheet (8-pages fold-out).
2 September 1980.
- Racal Tacticom Ltd., PRM-4150 Technical Manual Vol. 1 (Parts 1 to 5)
Technical Service Manual with updates. 1 May 1981.
- Racal Tacticom Ltd., PRM-4150 Technical Manual Vol. 2 (Parts 6 to 10)
Technical Service Manual and updates. 1 May 1981.
- Racal Mobical Ltd. Racal PRM-4150 Technical Assembly Manual
Original PCB assembly instructions, with hand-written notes (2 binders).
Various dates - June 1978 to June 1981.
- Museum Verbindingsdienst, PRM-4150 in display case
PRM-4150 (without suitcase) formerly used by Dutch Stay Behind organization.
Photograph Copyright Crypto Museum, 25 February 2009.
- Louis Meulstee, Wireless for the Warrior, volume 4
ISBN 0952063-36-0, September 2004.
- Electronics & Power, Five more comms. products announced by Racal
September 1979. Page 599.
- Technology of the Yugoslav State Security Service's James Bond
Republic of Slovenia (website: gov.si). 1 June 2019.
- Lojze Golob (Chief Department VI of USDV) to Danilo Kovačevič (Security Institute)
VI-Z-18/92-83. 30 June 1983.
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© Crypto Museum. Created: Wednesday 03 February 2010. Last changed: Tuesday, 19 December 2023 - 12:20 CET.
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