RF Unit 31B any ideas?

[mike g3zii]

I have just got hold of some gear from a deceased Hams shed, the relatives wanted it cleared, other wise it would be skipped.
among the stuff is an RF unit 31B, it's the same size as the well known ones, the RF24,5,6 etc but not seen one of these before.
Instead of the switched tuning or slow mo dial it has three separate tuning caps
with reduction drives from the front panel marked Aerial,Osc and Mixer.
it's got three sp61 inside. the Ae and mixer coils tune up on about 45-65 megs on a GDO.I think it could be a plug in 'front end' for the GEE system but I wonder if anyone else knows anything about this item.
By the way I have found this forum very interesting, can spend hours browsing it.

[trh01uk]

A photo would be interesting. According to my data your RF unit is part of ATGRI.5690, and also part of R.1441.

ATGRI (which stands for "Air Transportable Ground Radio Installation") 5690 is part of the ground system for GEE-H Tropical. Its also known as "AMES Type 100 Mk.1C". In other words, this is a transportable GEE-H ground station transmitter system which produces the RF pulses. It looks like receiver R1441 is also a sub-system of this system - probably with the RF unit as a plug-in, though I have no definite data on this.

Richard

[trh01uk]

And its probably worth adding that AMES 100 was designed for a chain of ground stations between UK and India, which were fully planned for rollout just before the end of WWII, but the end of the war meant the plan was abandoned. Your RF Unit 31B was part of that - and is probably a very rare unit, since there can't have been many of these ground stations made I would think.

Richard

[M0FYA Andy]

I have what is obviously a closely-related unit, RF Unit Type 31 (no 'B' suffix), 10D/1337.

Andy

[trh01uk]

Andy,

yes if you read AP2557V, you will see that it explains all this detail. ATGRI5690 includes RF units 26B, 27B, 31B and 32B. There is another system - TGRI5615 - which includes RF units 26, 27, 31 and 32. The former is tropical, while the latter is not.

Richard

[mike g3zii]

Thanks for the replies on this one, sorry for slow response. DIY jobs got in the way.
I have powered this up from a bench power unit into an RX at 7.5 Mhz.
quarter inch spade connectors fit neatly to the pins on the Jones plug and I found the LO was very dodgy, it would cut out as I tuned up the band.
I found that a 300 pf mica cap on the oscillator cathode to earth was broken off at one end, replaced this and it now tunes from about 40-55 megs and peaks up on noise with a bit of wire to the aerial socket.
it has an RAF 'for repair' ticket with it so that was probably the original fault.
the circuit looks pretty similar to the RF25 except for the different tuning set up.not tried it on a vhf aerial yet, there is probably not much activity on those frequencies these days.
I would probaly have scrapped it for parts in my younger days but I think old stuff like this is now worth preserving even though I can't think of an immediate use for it. What a wealth of knowledge there seems to be on this site.

[trh01uk]

Mike,

that fact that it has separate tuning knobs for mixer, oscillator and aerial tells you this is not a unit for any ordinary purposes. At each change of RF frequency, it would need alignment. Its clearly a specialist unit used as part of the receiver sub-system used in the GEE ground transmitters. Without checking the detail, I vaguely recall the slave stations have to receive the master signals off-air - so this is part of the receiver that does that job.

Richard