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 .
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)
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:
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.
- RA-4151 Receiver (right)
- TA-4152 Transmitter (left)
- MA-4153 Message store (centre)
The radio station could be extended with secure communication features
by adding the optional external
MA-4245 data encryption unit.
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.
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).
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).
The Dutch Stay-Behind Organisation
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
and the pan-European FS-5000 Harpoon.
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
- Frequency range: 2-29.999 MHz
- Channels: 28,000 (1 kHz steps)
- Telegraphy speed: 200 baud (synchronous)
- Data rate: 600 five-figure groups/minute
- Message length: 204 groups (1020 digits)
- Message duration: 21 sec. max.
- Modulation: 2-tone FSK (1563 and 2083 Hz)
- Frequency shift: 520 Hz
- Error detection: 1 parity bit per character pair
- Modulation: LSB FSK (F2J), LSB CW (A2J)
- Output power: 5W minimum from ATU into 50 ohm load
- Harmonic emissions: < -40 dB (ralative to PEP in 50 ohms load)
- Spurious emissions: < -45 dB
- Carier suppression: Better than -40 dB
- 3rd order intermodulation distortion: Better than -25 dB
- Antenna Tuning: Automatic ATU to tune long wire antenna
- Tuning time: < 10 sec.
- Storage capacity: 1 message with up to 1020 digits (204 groups)
- memory type: Volatile (erased when transmitter is switched OFF)
- 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 rejection: Better than 70dB
- IF rejection: Better than 70dB
- Maximum AF output: 20mW into 300 ohms
- Storage capacity: 1 message of up to 120 digits (204 groups)
- Memory type: Non volatile
- Data input: Numeric keyboard
- Display: 2 x 5 digit LED
- Data output: Serial data multiplexed over power line to transmitter
- Storage capacity: 1020 digits (204 groups)
- Memory type: Non volatile
- 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.
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