Is this a Rebecca unit ?

[Gi4CZW Cliff]

My friend says this is a Rebecca, so I do the usual internet search but I'm not getting close to radio equipment. Anybody know of a link to follow. thanks, Cliff.

[Station X]

A picture of the whole unit would be useful.

[M0FYA Andy]

I believe it is a Test Set associated with Rebecca, probably Rebecca Mk4.
If you ever decide to sell it I would be an willing customer, I am interested in any aircraft equipment including test sets!
Andy

[tis your junk]

This could start you off

http://www.duxfordradiosociety.org/e...reka-hist.html

BTW Duxford is always on the look out for interesting pieces.

TYJ

[Gi4CZW Cliff]

Thank you for the replies. More photo's here. Not sure it will be of much interest. Also I have asked the owner to measure and weigh it, so as to get a courier quote. Thanks, Cliff.

[Station X]

The mechanical enclosure looks similar to the Rebecca MKIV transponder on the IWM Duxford website linked to in post #4.

It is obviously an item of test equipment though and the name plate seems to confirm this.

[Radio1950]

Here is the complementary Eureka equipment at Duxford 2017

[VT FUSE]

Given the near identical case and use of US derived miniature valves this is spot on for REBECCA 2, also used aboard D day troop landing gliders, the PTFE valve holders of the McMurdo type fitted are just about the earliest implementation that I have seen, in more widespread use from 1947 on.

Of course, I stand ready to be corrected...

Quick edit-had this not been test set equipment but instead the airborne TX,then it would have carried the HE demolition charges to be blown by crew/operator
in the case of aircraft being downed to ensure that an enemy would be denied a working complete example in case they should use it to devise jamming countermeasures or copying as a whole.

[M0FYA Andy]

I don't agree that this Test Set is for Rebecca Mk2, it is referenced in A.P.2914Y, A.R.I.5610, Rebecca Mk4.

Rebecca Mk2 uses the typical construction methods of WW2-era equipment, prior to the introduction of cylindrical sealed housings as used in the Rebecca Mk4 Transmitter/Receiver airborne unit.

Why this Test Set also used a cylindrical housing I don't know, perhaps for commonality, but this was then housed in a rectangular framework/case, presumably to stop it rolling about on the test-bench!

The A.P. for Rebecca Mk2 lists the applicable Test Equipment, I could extract the details if anyone is interested.

The A.P. for Mk4 makes no mention of demolition charges, wartime experience showed that they were more trouble than they were worth in IFF, Gee and H2S units - to be big enough to successfully destroy the equipment would be big enough to bring the aircraft down, and inadvertent operation occurred far too frequently, so they were deleted before the end of the war.

Andy

[ms660]

Who was the manufacturer?

Lawrence.

[turretslug]

Picture 3 in post 5 has answered a long-term puzzle- as a kid, I acquired a compact British-made IF strip, passed onto me by a military tech, and the upper left hand corner of that shot is exactly it- if so, it'll be 6x CV138 (EF91) VHF (45MHz?) amp stages folowed by CV140 (EB91) detector and CV136 (EL91) cathode follower "video" output to the adjacent coax cable. The round items between them with a small oval detail being the trimmer cores and the alternating triangular thingies each containing 3x 1nF "Metalmites"! Unfortunately, I dismantled it long, long ago. I suppose the post-war replacement/equivalent for the likes of the famous EF50-laden Pye strip.

One thing that I've always found slightly amusing/puzzling about quite a lot of older avionics kit in particular is that some aspects of it will be almost ludicrously overbuilt, with almost trifling weight savings made elsewhere and this is a good example- that hefty great enclosure casting (?) like a particularly beefy beer keg, and then a few grams of weight shaved with the internal chassis punchings. I suppose it convinces those appraising it that some effort has been made.

[ms660]

Nothing to do with the unit I suppose but Marconi went for cylindrical casing with the Silvita lifeboat Tx/Rx.

Lawrence.

[turretslug]

Originally Posted by M0FYA Andy

The A.P. for Mk4 makes no mention of demolition charges, wartime experience showed that they were more trouble than they were worth in IFF, Gee and H2S units - to be big enough to successfully destroy the equipment would be big enough to bring the aircraft down, and inadvertent operation occurred far too frequently, so they were deleted before the end of the war.

This is something I'd wondered about myself- even before the advent of the copper magnetron resonator block, it must have been difficult to ensure that an item of equipment would be sufficiently disrupted to prevent determined, knowledgable and insightful enemy personell from piecing together its principles, function and even details without making it a serious munitions hazard in itself. Also, getting out of many aircraft was difficult on a good day, never mind if it was seriously out of control with high-g tumbling and/or being ablaze. It's quite common to read of aircrew who were otherwise brave, skilled and responsible having little recollection of how they had actually escaped from a stricken aircraft, so it's easy to imagine that arming demolition charges would often get overlooked in the general melee and traumatic excitement of survival.

[M0FYA Andy]

Cylindrical casings came into use in aircraft equipment post-war as a result of wartime experience. Equipment returning from a bombing mission at high altitude (for the time) would be soaked through with condensation in the unpressurised fuselage of a Lancaster or Halifax. You can read reports of it all being removed after a flight, dried out, and refitted for the next. Apart from the effort involved, it must have caused major reliability problems with connectors being repeatedly broken and remade.
So casings were introduced where the insides were installed dry and warm, and then the casing pressurised, often with nitrogen rather than air, through a valve akin to that on a bicycle tyre. A desiccator absorbed any residual water.

[G3VKM_Roger]

Originally Posted by ms660

Nothing to do with the unit I suppose but Marconi went for cylindrical casing with the Silvita lifeboat Tx/Rx.

Cylindrical cases being tougher than box-shaped, the round case made the radio more able to withstand being dropped into the sea from its stowage on upper decks like the radio room or bridge.

Regards

Roger

[GMB]

I would say that this is not a set to test Rebecca, it IS a Rebecca unit but with lots of diagnostic features and knobs, for checking out a whole Rebecca-Eureka system.

Clearly it is an airborne unit with a pressurised housing that helps with corona discharge of compact transmitters.

[M0FYA Andy]

George, sorry but I don't agree!

The AP for Rebecca Mk4 can be downloaded from the VMARS archive. Look at page 127 of 137 in the pdf, this test set is mentioned briefly, albeit with no details.
It is not an airborne unit, but I surmise that the designers used a lot of existing parts from the airborne equipment.

Andy

[GMB]

Oh yes, Andy is right. I had missed that particular AP for some reason.

I guess they just built it in a handy airborne unit.

[Gi4CZW Cliff]

Thank you for the information. More interesting than I thought. The owner does not do internet, seldom uses the phone with most comms via ham radio, thus the delay in my updates.
Andy, PM sent. Cliff.