[Premium-Rx] Racal 1782, 178x series

[machine.age]

This discussion has been the biggest gathering of all the old elephants in many a moon. Enjoying immensely.

John England

Sent from my iPhone

On Aug 16, 2010, at 1:19 PM, "Michael O'Beirne" <michaelob666 at ntlworld.com> wrote:

> 
> Gents
> 
> All this talk of RA1781s and 1782s (which I too had never heard of anywhere) 
> tempts me to ask the obvious question as to what else was in the RA177/8 
> series.
> 
> The 1770 was the start with a VFO film scale neary identical to that on the 
> RA117.  All I have of it is a brief pic and mention in SWM volume XXIX page 
> 757 showing a model.
> 
> The 1771 and 72 we know all about and ditto 1778/79.
> 
> What about the 1773/74/75/76 and 77 and the 1780 and 83?
> 
> When did manufacture finally cease?
> 
> Were these perhaps developments or specials?
> 
> The fact that the IF filter sets run to nearly 130 variants shows what a 
> wide range of applications the sets must have been put to.
> 
> The 100kHz IF output was a requirement for all receivers for use by GCHQ, 
> and the sideband at the IF output had to correspond to the sideband at the 
> areial input, which is pretty indicative of the use.  I have a copy of 
> Plessey's engineering submission to GCHQ for the PR2280 series containing 
> the GCHQ technical requirement.  I don't recall any requirement for a vastly 
> wide bandwidth.  Surely anything more than 13kHz would be pointless in view 
> of the early filtering.
> 
> Pat has suggested that all manner of FFT gear was probably hung onto the IF 
> output (and probably digital recording as well).
> 
> 73s
> Michael
> G8MOB
> 
> ----- Original Message ----- 
> From: "John Graham" <john.graham02 at btinternet.com>
> To: <premium-rx at mailman.qth.net>
> Sent: Monday, August 16, 2010 11:09 AM
> Subject: [Premium-Rx] Racal 1782, 178x series
> 
> 
> I've been following the discussions about the RA1772 and the RA178x series 
> with great interest.
> 
> One receiver that nobody seems to have mentioned is the RA1782. I am the 
> proud possessor of two RA1782 receivers, and a couple of RA1781s that I 
> bought for spares [they were very cheap, bought from a dealer who was moving 
> to new premises and disposing of old stock!]
> 
> The RA1782 is the locally-controlled variant of the RA178x series [think 
> RA1781 with an MA1072 front panel].
> Most of the RA178x series were remotely controlled, and the RA1782 reflects 
> that pedigree:
>  a.. Instead of mechanically-switched MHz bands, tuning is continuous 
> throughout the entire range, with "bandchanging" using the fastest of the 4 
> tuning rates [625Hz, 2.5kHz, 20kHz or 5MHz per revolution]
>  b.. Instead of the manually-tuned preselector, there is either a wideband 
> front end or automatically-switched half-octave filters
>  c.. Instead of rotary switches, there are illuminated push-buttons that 
> latch logic circuits
>  d.. consequently, the mode and bandwidth are independently selectable
> All the filters are symmetrical; the RA1782s have 13kHz, 6kHz, 3kHz, 1.2kHz, 
> 750Hz and 100Hz filters; the two RA1781s have a 300Hz filter instead of the 
> 13kHz one. [i.e. all 4 receivers have the "incredibly rare" 6kHz filter!].
> There is no SSB mode as such, but the "xtal" mode uses a 1.4MHz CIO, so all 
> one would need to do is install asymmetrical filters.
> I looked at obtaining crystals for BFO frequencies for +/-1.8kHz or 
> whatever, but was put off by the cost [cheapest quote £37.50 each].
> 
> All the receivers have a converter to give a 100kHz IF output. This seems to 
> be standard in those applications. [does anyone know why they all - RA1782, 
> RA1792, Eddystone 1650/6, etc - have a 100kHz output that has a 185kHz 
> bandwidth when the roofing filters are all around 16kHz?!]
> 
> I was able to get one receiver working without too much difficulty by 
> referring to the RA1772 manuals, which cover most of the signal path, but 
> the second receiver has faults in the control logic, for which I have no 
> information, so that is on the back burner for the moment.
> 
> I'd be interested to hear from anyone else who has experience of these 
> receivers, and if anyone can provide a circuit diagram for the front-panel 
> logic and/or either/both of the RF input boards, that would be wonderful!
> 
> I also have RA6790 and RA1792 receivers, and I agree with the comments about 
> their relative merits.
> 
> regards,
> 
> John G.
> RS 86946
> 
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