Reception Set R. 107

Developed by SEE (SDRE) and Radio Transmission Equipment Ltd.

For use with the medium and high power Wireless Set No.12 and No.33 transmitters and as a communications receiver, the British armed Forces had an urgent need for a powerful receiver in 1940.
It was decided early on during the development to use tubes with indirect heaters instead of battery tubes, and the receiver was developed in 1940 by the SEE (Signals Experimental Establishment, later SDRE) together with Radio Transmission Equipment Ltd.

Technical data

Principle: single conversion superhet, IF 465 kHz
Operation modes: A1 with BFO, AM (A3)
Frequency range: SW (1.2 - 17.5 MHz)
Frequency display: Analogue dial
Frequency memory: none
Signal strength indicator: none
Signal processing:
Features:
Sensitivity: < 2 μV / Selectivity: 2.5-3.25 / 6.8 kHz (-6 dB)

Power supply

Mains operation: 100 - 250 V
Batteries: 12 V DC

Dimensions

610 x 330 x 439 mm, weight 48.5 kg

Accessories

Operation

The R107 receiver comes in a heavy sheet steel cabinet and its dimensions are 61 x 33 x 44 cm and it weighs a considerable 43.2 kg; the set can be operated from the 220 V mains or with 12 V DC. It has separate sockets to connect to a long-wire and a dipole antenna.

On the right-hand side of the front panel is the semi-circular dial calibrated in frequencies, the wave band switch is located directly below and selects the three band ranges 1.2 - 3 MHz / 2.9-7.25 MHz and 7.0-17.5 MHz. The connectors for the long-wire and dipole antennas and the earth are located at the top right, the antenna trimmer at the bottom right of the front panel.

In the centre of the front panel, below the holder for the station clock and the pilot light, you will find the BFO pitch control, the BFO / OFF (manual control) / AVC switch, further right the volume control(AUDIO GAIN) and in the bottom row of controls the switch for the audio filter, the RF gain control (R.F.Gain) and the NARROW/WIDE bandwidth switch.

The switchable monitor loudspeaker is located at the top left of the front panel, below it the socket for the connection cable to the W.S. No.12 (muting / monitoring), the switch for sidetone monitoring, the mains switch and at the bottom right the 12 V DC and 220 V AC connections and the sidetone volume control. Right next to it on the black contact board are two headphone sockets (bottom) and the LINE output (top).

For operation, the receiver is supplied with 220 V mains voltage (because the original English plug coupling is often unavailable, improvisation may be necessary, take appropriate precautions; the supply voltage switch at the rear of the chassis must be in the A.C. position), a long-wire antenna is connected to the OPEN AERIAL connector and the receiver is connected to earth.

The internal loudspeaker is switched on at the top left with L.S. ON, the main switch with the red POWER mark is located on the right under the loudspeaker, after the tubes have warmed up, a hiss should be audible.

The R.F. GAIN should be set to maximum and the RF gain switch to AGC for automatic gain control, LIMITER and AUDIO FILTER to OFF, IF to WIDE, with the band range switch RANGE set to „2“ you can hunt for radio stations in the 49m band above the 6 MHz mark, to receive SSB or CW signals in the 40m amateur radio band, the IF filter NARROW is selected and the BFO is activated, the RF gain must then be set manually with the R. F.GAIN control.

The various currents of the tubes can be tapped at the TEST PANEL next to the mains indicator light and resistance measurements can be taken at various control points on all tube sockets.

The R107 is a relatively archaic-looking shortwave receiver in a huge, heavy package. Conveniently, the mains power supply is built in (which is not always the case with military sets), as is a monitor loudspeaker, so that the set can be used for reception without any further accessories. The receiver diagram, operating instructions and tube voltage measurements are located on the cover.

The sensitivity and mirror frequency stability of the single conversion is moderate, the frequency reading accuracy on the rudimentary calibrated analogue dial is poor, especially in the higher frequency ranges.

However, it should be kept in mind that the then state-of-the-art National general coverage receiver HRO, which was used in parallel, was still equipped with plug-in coils and a calibration chart; for known frequencies, the corresponding numerical values had to be written down in a logbook. The Autophon [E44]], the first general coverage receiver of the Swiss Army from the same era, used a calibrated dial with a turret tuner, Zellweger used an intermediate solution in their E41 which used plug-in coil sets with a frequency dial calibrated with frequencies - a receiver with a high accuracy dial was still wishful thinking in the early 1940s… if one did not want to go the way of the German E52 „Köln“ with the individually manufactured calibrated projection dials.

The tropicalised version is marked with a „T“.

Technical principle

The receiver acts as a single conversion, after an RF amplifier stage (V1A: ARP34/EF39) the signal is mixed with the oscillator signal (V2A: AR21/EBC33) in the mixer stage (V1B: ARP34) to create the intermediate frequency of 465 kHz. This was demodulated (V2B:AR21) after two IF amplifier stages (V1C/V1D; two ARP34), and after AF preamplification in the same tube (V2B), the audio signal is fed to the output stage (V2C:AR21) and then to the loudspeaker or headphone output. A second AR21 (V2A') is used in the BFO for CW reception. The mains rectifier is a 6X5G (V3A).