R1147A Homing Receiver

 This rather rare radio was used in various aircraft including the Spitfire and was developed from a navy equipment loaned to the RAF for letting the pilot or navigator steer correctly for his base. It replaced the earlier R1110.

Ordinarily I'd have expected the aerial for a set such as this could be rotated and thus determine the direction of a beacon. Usually a null in signal is easier to detect than a peak although I'm unsure in this application which method was used. I understand however that this set used a retractible quarter-wave whip. A clue to its operation might be inferred by the choice of words "rotating beacon transmitters" in the technical manual. The beacon station would transmit an AM signal carrying a supersonic tone. The R1147A can be tuned to the signal and an audible AF tone peaked by the control on the upper left which is an adjustable audio frequency coil used much like a BFO. The R1147 tuneable band extends from 180 to 220Mc/s and is marked on the dial by letters A, B, C and so on.

The other day, Paul Smith down under contacted me with information on how the R1147 was used and now everything falls into place. The brief description is here and an interesting paper from 1947 can be seen here. The system must have saved countless aircraft from running out of fuel.

In a single seat aircraft such as a Spitfire the set could be positioned such that the pilot could tune the set directly using the toothed ebonite knob. The set could also be tuned remotely using a duplicate of the geared mechanism connected by Bowden cable. See the remote tuner.

I'll need to carry out some experiments on this set in order to determine exactly how it works; basically the beacon transmits a tone above the normal audio range and this is heterodyned or mixed down to an audible note by turning on a BFO signal via the socket adjacent to the headphone socket. There is also a remote control connector. See below.

A standard installation used a power supply box, driven from the aircraft's batteries, carrying a rotary transformer supplying HT to the receiver.


 Here's the circuit diagram for the R1147.. click it to see a larger picture


 Below you can see pictures looking inside the box. There are a couple of pentode valves (VR56) and a double diode triode (VR55) visible.

VHF tuning which appears to cater for RF amplifier and oscillator is on the right.

Another view shows the IF transformers which were set to 25Mc/s and had a broad tuning to compensate for oscillator frequency drift. Preset tuning controls for the IF transformers are located in a line along the top of the picture below.


 Below you can see the other side of the chassis where you can see its unusual complement of valves.

Bottom left is a triode (VR59) oscillator, in fact an HA2 which is the version of the US 955 acorn triode made in the UK. Above the 955 is a VR95 pentode. This is a ZA2, the British version of the US 954 acorn pentode. The first IF transformer (10K12173) is top right. Next are two IF amplifiers using two more VR95s with their IF transformers (10K12175)

More detailed pictures follow below.
 Close-up picture of the 955 and 954 oscillator and mixer with their unusual valve holders. Presumably the two differing materials were chosen to optimise the RF performance but keeping wartime economy in mind. the first IF stage has a Tungsram version of the 954.


 The later version of this receiver, the R1147B was redesigned to incorporate some EF50 valves.




  Below you can see the side view of the receiver including its shockmount. The input connector provides HT and LT from the power supply box.

The Remote control socket provides audio output plus volume control connections and on/off control.

The picture below shows the headphone output socket plus a socket labelled "BEAT OSC" which carries a link supplying HT to the BFO (the triode section of the EBC33). The knob shown behind these sockets allows the BFO to be adjusted.


 View showing the connection for the remote control cable. The operator would use letters A, B, H etc to select the appropriate beacon signal.

The blanked off connector (designated "P1") was possibly used for testing the set in a workshop? It connects to the LT+ and LT- circuits and the internal VHF oscillator output coupling coil.

 Remote tuning control

 This was designed for connection to the R1147 plus a second remote control if required. Depending on exactly where the set was mounted, the pilot could operate the set directly or by remote control or, via an extension to a further remote controller, the R1147 could be operated by a navigator/observer.

To facilitate remote operation a remote control box was fitted for the pilot or for the observer, or both. These were slightly different in design, that for the observer had a 6-way input connector wired to an on/off switch and a volume control plus a 6-way output connector which was coupled to the pilot's remote controller. The latter had only a single 6-way connector and had an additional feature which could switch operation between the pilot and observer.

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