|
|
|
|
|
|
|
← UK Cold War
Clandestine transceiver
Mk.122 was a compact valve-based transceiver,
developed in the early 1950s by HMGCC
(now CGHQ) at Hanslope Park (UK).
The device was the successor to the Mk.121,
and was used
by Special Forces (SF), agents, stay-behind organisations
and the Diplomatic Wireless Service (DWS).
|
The device is housed in a metal wrinkle-finished enclosure
that measures 33 x 23 x 8.5 cm and weighs 5.6 kg. It has a removable
protective lid at the top, and can be powered directly from the AC
mains (100-250V in 10V steps), or by an external 6V vehicle battery
with a vibrator pack.
The device has several improvements over its predecessor, the
Mk.121,
including an improved internal morse key – mounted at the front right.
Furthermore, it
combines the full 2.5 to 20 MHz frequency range in a single device,
whereas five
Mk.121 variants were needed to do the same.
|
|
|
|
In addition, the Mk.122 as a a variable antenna tap
on the tank coil of the RF output stage.
The transmitter is crystal-operated, whereas the receiver can be tuned
freely by means of its Variable Frequency Oscillator (VFO).
For reception of CW signals (morse),
the built-in Beat Frequency Oscillator (BFO) can be enabled
separately.
The device was succeeded in 1956 by the Mk.123.
|
|
The Mk.122 was a very compact transceiver; slightly larger than an A4 sheet
of paper. The radio can be divided into three sections: a power supply,
with a convential transformer at the center of the unit, a freely
adjustable receiver on the left,
and a crystal-operated transmitter on the right.
|
|
The Mk.122 can be powered directly from any mains AC voltage between
100 and 250V in 10 steps.
It consumes 20W in standby and 34W when the receiver is used.
When transmitting (with the key down) it consumes 65W.
The radio was often supplied with a external Vibrator Pack (No.14),
to allow it to be powered by a 6V battery. In that case, the maximum
current would be 3A (standby), 5A (receive) or 10A (transmit).
The battery was recharged with the Mk.812A Charging Unit.
Alternatively, the radio could be powered by the Mk.810A hand/pedal
genarator that supplied 110V (45-80W).
|
|
The receiver is freely adjustable between 2.5 and 20MHz, divided over
3 ranges as shown above. The sensitivity is depending on the frequency
and lies between 1 and 5 µV (at 20dB S/N).
The Audio output stage produces approx. 20µV, which is enough to feed
a high-impedant (50K) crystal earphone.
The receiver consists of three valve-based circuits:
|
- Mixer/oscillator (CV3888 or ECH42)
- IF/detector (CV3883 or EAF42)
- Audio/BFO (CV3888 or ECH42, CV1833 or OB2)
|
|
The transmitter, that covers the same three frequency ranges as the receiver,
is crystal operated and is only suitable for CW (Morse).
The crystal should be placed in a socket along
the front of the transceiver, to the left of the morse key.
It produces an output power of 10-13W and consists of only two circuits:
|
- Crystal Oscillator/Doubler (CV3990 or 2E26)
- RF Power Amplifier (CV3889 or EL41, NE48)
|
|
Crystals can be used in three modes:
|
- Fundamental frequency
- Double frequency (using the doubler)
- Third harmonic
|
- Main lead
- Battery lead
- Mains voltage tester (with neon light)
- Crystal earphones
- Reel antenna
- Wire antenna (36m, with insulators)
- Crystal adapter
- Tools (screwdriver, soldering iron, knife, paper, pencil, etc.)
- Spares (vibrator, fuses, lamp and valves)
- Mk.810A Hand/pedal generator (optional)
- Mk.812A Charging Unit (optional)
|
Device Spy radio transceiver Organisation HMGCC (now: GCHQ) Users Special forces (SAS, SBS), agents, stay-behind, DWS Year 1952 (est.) Power Mains 100 - 250V in 10V steps, 40 - 400 Hz AC Battery 6V accumulator and external vibrator pack No. 14, 6V Consumption Mains: 20W (standby), 34W (RX), 65W (TX)
Battery: 3A (standby), 5A (RX), 10A (TX) Dimensions 330 × 230 × 85 mm Weight 5.6 kg
|
Circuits Mixer/oscillator, IF/Detector, AF/BFO Modulation AM R/T, CW Bands 3 (see below) Sensitivity 1 - 5 µV (at 20dB S/N) Selectivity 5.5 kHz at -6dB, 13 kHz at -20dB IF 470 kHz Output 20 µW into 50 kΩ earphones Valves 2 × CV3888 (ECH42), CV3883 (EAF42), CV1833 (OB2)
|
Circuits Crystal oscillator/doubler, RF power amplifier Modulation CW Bands 3 (see below) Output 10 - 13 W Valves CV3889 (EL41), CV3990 (2E26), NE48
|
- 2.5 - 5 MHz
- 5 - 10 MHz
- 10 - 20 MHz
|
- Louis Meulstee, Wireless for the Warrior, volume 4
ISBN 0952063-36-0, September 2004.
|
|
|
|
Any links shown in red are currently unavailable.
If you like the information on this website, why not make a donation?
© Crypto Museum. Created: Wednesday 05 August 2015. Last changed: Wednesday, 05 November 2025 - 12:07 CET.
|
 |
|
|
|
