The DFG 12 (Mk1) was a HF, Adcock type, direction finding set manufactured by the Marconi Company (UK) and primarily used by Special Wireless sections.  Mk 1 was a transportable set  used in conjunction with Adcock Aerial No. 2 which comprised of 20 foot masts. The version used by the British Army was designated as Reception Set R104. Frequency range was 1.5 to 20 MHz.

This DF set consisted of two physical units - a coupling unit/receiver containing the search coils and a separate unit for the two radiogoinometers. One goinometer covered the upper radio band while the the other covered the lower band. Power for the receiver was derived from a 6 volt battery and a vibrator power supply

The Mk.2 model was similar, but was intended for use in fixed station applications. As it result, it used 30 foot masts. Following that set, was the Mk.3 model which was also intended for use as a fixed station. It was provisioned with new features such as spinning goniometers and a cathode ray tube as an indicator of bearing.

Supplied with the unit was an Adcock aerial system which consisted of four vertical aerials which were installed on the corners of a square with diagonals of  20 feet (for Mk.l) or 30 feet (for Mks.2 and 3). A fifth aerial, used to derive the 'sense' of the bearings was centrally positioned and the lead-in connected to the goniometer which was in the centre of the aerial system. It was normal practice to place the aerials on N-S and E-W diagonals. In the product literature, it was found that the sets were declared obsolete in 1945 and replaced by other portable and mobile DF systems.

1940: The original DFG12 DF set, Mk 1. It was a conventional superheterodyne receiver using an RF stage, mixer, separate local oscillator, two IF stages, detector, AVC amplifier, AF output amplifier and a BFO. 
(Photo provided by Louis Meultsee, Wireless for the Warrior Vol 3) 

Model DFG12-2. The Mk 2 variant used the original DFG12 design but only one goniometer wa provided instead of two. Frequency coverage was 250 kHz to 545 kHz. The actual device did not have those huge letters marking the panel and knobs.
Model 579.  It covered 260 to 545 kHz and was designed for use with a crossed loop aerial system. It shared the same goniometer as the DFG 12 Mk 2.
(Both photos provided by Louis Meultsee, Wireless for the Warrior Vol 3) 

Type: MF-HF Adcock type direction finding set
Modes: AM/ RT and CW
Frequency Range:  1.5 to 20 MHz
Intermediate Frequency: 400kHz
Performance: Sensitivity: 5uV for 20dB signal to noise ratio
                     Selectivity: 6.5 kHz at 6dB down
Aerial: Adcock consisting of four 20 ft or 30 ft masts
Power Supply: 6V LT and 160V HT (Units HT No. 1)
Current consumption: HT 35 ma and LT 3.1 A
Dimensions (inches):  Receiver and coupling unit - 15H x  15L x 26W
                                 Radiogoniometer  - 18H x  12L x 18W
Weight: Complete set - 1cwt,1 qr (63.5 kg? or 136 lbs?)
Stores reference No.:  DFG12 Mk.1   ZA 5955
                                   DFG12 Mk.2   ZA12201
                                   DFG12 Mk.3   ZA 12209
Tube Lineup:

RF amplifier                  ARP15
Local oscillator              ARP16
Mixer                            X63  (ARTH1)
IF amplifier (2x)            ARP15
Detector/AF amplifier    ARP16
Output                          ARP17
AVC amplifier               ARP16
BFO                             ARP16


This DFG 12 is one of the exhibits in HMS Collingwood collection. (Photo by John Wise) 

A surviving 579 outfit  receiver but without a goniometer. (Photo by Jacques Hamel) 
579 nameplate detail. (Photo by Jacques Hamel) 
A surviving 579 outfit goniometer but without a receiver. This goniometer is one of the exhibits in HMS Collingwood collection. (Photo by John Wise) 

Contributors and References:

1) Louis Meulstee <l.meulstee(at)wxs.nl>
2) Wireless for the Warrior Web page   http://www.wftw.nl
3) Jacques Hamel <hamja(at)videotron.ca>

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Dec 20/20