Homepage
Crypto
Spy radio
Index
Glossary
USA
USSR
UK
Germany
Poland
Czechoslovakia
Hungary
Yugoslavia
OWVL
Stay-Behind
Special forces
Receivers
Other
Burst encoders
Intercept
Covert
Radio
PC
Telex
Telephones
People
Agencies
Manufacturers
• • • Donate • • •
Kits
Shop
News
Events
Wanted
Contact
About
Links
   Click for homepage
FRM-4750 (Kaynard)
Mobile Data Radio Station - under construction

The FRM-4750 was a automatic transceiver developed by HMGCC at Hanslope Park (UK) and built by Racal in the late 1970s. It was a self-contained radio station with a digital messaging system, that was intended as a mobile emergency system for the UK's Diplomatic Wireless Service (DWS). As such, it replaced earlier Piccolo systems and, to a lesser extent, manually operated morse-code-based systems such as the Mk.123. The system is also known by its codename Kaynard.

Kaynard consisted of three units: a transceiver, a power amplifier and a coder/decoder. The radio station was available in three versions: (1) as a single device, with all three units mounted in a 19" rack, or (2) as three separate units that were each packed inside a large Samsonite briefcase. The latter version was intended for British embassies abroad, as it was easier to bring three briefcase into a country via diplomatic mail.

The image on the right shows the all-in-one C-version of the radio station. It was is use at a site of the British Foreign Office for many years.
  
Close-up of the controls of the FRM-4750 (Kaynard)

The FRM-4750 (Kaynard) was suitable for several purposes. It could be used as an alternative to the portable PRM-4150 suitcase radios, for example when used in an embassy abroad. In that case the radio station would act as a field station, typically with an FRM-4780 Base Station at the other end. It could also be used as an extended-range field station, in which case it was equipped with a 400W power amplifier. When used with a 100W power amplifier, the FRM-4750 could be used as a medium-power base station, suitable for communication with other FRM-4750 units.

Font view of the FRM-4750 Model C Close-up of the controls of the FRM-4750 (Kaynard)

Piccolo
Messages are passed to the FRM-4750 in digital form on 5-level punched paper tape via a serial communications interface. Transmission of CCITT characters (ITA2) at medium speed (20 cps) is achieved using narrow-band 6-tone Multiple Frequency-Shift Keying (MFSK) modulation [4]. This system is a variant of Piccolo II, which has been in use by the DWS since 1962. In most cases, the FRM-4780 is used as the base station. Although Piccolo has been largely phased out now, the latest Piccolo Mark IV standard is still occasionally being used for military point-to-point links.

In addition, direct communication between two stations is possible by using the numerical key­pad for input and the 7-digit LED display for showing the output. The FRM-4750 has a 3000-character memory for the transmission or reception of messages consisting of several A4 pages.

Units
  • MA-4751 (RT) receiver/transmitter
  • MA-4752 (PA) power amplifier
  • MA-4753 (CD) coder/decoder
  • MA-4754 Suitcase with AAMTU, BCC 540B and system cables
Versions
  1. FRM-4750A - All three units housed in an anti-vibration cabinet
  2. FRM-4750B - As three separate units, each stored in a suitcase
  3. FRM-4750C - All three units housed in a desktop cabinet
Power options
The standard FRM-4750 radio stations delivers an RF output power of 20W, which is sufficient for world-wide communication under good (antenna) conditions. Two enhanced power options were available, enabling the radio station to be used in a medium power base station role, or as an extended range field station.

  • 400W - For use as an extended range field station
  • 100W - For use as medium power base station
FRM-4750A version
In this version, the RT unit, the PA unit and the CD unit are housed in an anti-vibration cabinet, making it suitable for transportation and operation in mobile environments. The AAMTU, the cables and the other accessories are caried in a separate MA-4754 executive-style suitcase.

The image on the right shows an example of the A-version, taken from the Technical Manual [1].
  

FRM-4750B version
In the B-version, the three units (RT, PA and CD) are housed in individual desktop cabinets and are carried around separately in executive-style suitcases. They are stacked for operation after unpacking. The AAMTU, the cables and the other accessories are caried in a (fourth suitcase).

The image on the right shows an example of the B-version, as it is present in the collection of the IWM in London [3]. The transceiver (RT-unit) is missing from this photograph, but is shown in the image below, together with the 4th suitcase that carries the accessories.
  
FRM-4750B in suitcases. Copyright IWM London. Reproduced here by kind permission [3].

The image on the right shows the MA-4754 executive-style suitcase with the Automatic Antenna Matching and Tuning Unit (AAMTU), the various cable for connecting the three units together, and various other accessories.

The suitcase on the right contains the RT-unit. The entire radio station could be carried around in four high-profile Samsonite briefcases. After unpacking, the three units were stacked and connected. If the antenna was already present, the station could be operational within minutes.
  
FRM-4750B in suitcases. Copyright IWM London. Reproduced here by kind permission [3].

FRM-4750C version
In the C-version, the three units (RT, PA and CD) are housed in a single desktop cabinet, ready for operation. The AAMTU, the cables and the other accessories are caried in a separate MA-4754 executive-style suitcase.

The image on the right shows an example of the C-version, which is part of the Crypto Museum collection. It was used for many years by the British Foreign Office on Diplomatic Wireless Service links with their embassies abroad. It was donated to Crypto Museum in 2011.
  

MA-4751 RT-unit
...   

MA-4752 PA-unit
...   

MA-4753 CD-unit
...   

MA-4754 Accessories
The MA-4754 suitcase was common to all three versions. It contained the cable for connecting the three units together, the antenna wires, the BCC-540B Automatic Antenna Matching and Tuning Unit (AAMTU), ground spike, etc.   

Technical specifications
  • Frequency coverage: 3 - 30 MHz
  • Channels: 27000 (in 1kHZ steps)
  • Operating mode: SSB, Upper Sideband (USB)
  • Modulation: 6-tone multi-frequency shift keying (MFSK)
  • MFSK: 6 tones with 40Hz spacing centered around 2kHz
  • Data rate: 200 words per minute (WPM) at 6 characters per word
  • Frequency stability: Better than 2Hz at 30 MHz
  • Power output: 20 Watts (nominal)
  • Receiver S/N ratio: 15dB minimum in a 400Hz bandwidth for 1µV emf.
  • Receiver bandwidth: 400Hz or 2kHz minimum (selectable)
  • Power supply: 110V or 230V AC (50-60Hz), or 18-32V DC
  • Power consumption: 45W (RX) and 125W (TX) at 24V DC supply
References
  1. Racal Tacticom Ltd., FRM-4750 Technical Manual - Vol. 1 (Parts 1 & 2)
    HF Data Radio Station. February 1985.

  2. Racal Tacticom Ltd., FRM-4750 Technical Manual - Vol. 2 (Parts 3 & 4)
    HF Data Radio Station. February 1985.

  3. Imperial War Museum (IWM), Wireless Equipment 'Kaynard'
    Images of FRM-4750B in suitcases. Reproduced here under licence of IWM London.
    Retrieved December 2012.

  4. Wikipedia, Multiple frequency-shift keying
    Retrieved April 2015.
Further information
Any links shown in red are currently unavailable. If you like the information on this website, why not make a donation?
Crypto Museum. Last changed: Wednesday, 05 August 2015 - 11:08 CET.
Click for homepage