[Premium-Rx] 100kHz converter outputs - more

Tue Aug 17 05:28:40 EDT 2010

Hello John,
you just mentioned the 1650/6 that reminds me that I have one for  
about 10 years, which I was never able to operate.
My last search for a manual a couple years ago turned up empty.
I see that you have the manual. Would it be possible to get a copy  
either paper or pdf.
I will of course cover all expenses.
vy 73 Heinz DH2FA, KM5VT

Von meinem iPhone gesendet

Am 17.08.2010 um 11:01 schrieb "John Graham" <john.graham02 at btinternet.com 
 >:

> The Plessey PR2280 does indeed have an output that is peaked at  
> 100kHz.
>
> The RA1792 and 1650/6 just have lowpass filters, though looking more  
> closely at the 1650/6 circuit, the 185kHz LPF is followed by an amp  
> with a single tuned circuit that limits the bandwidth to approx.  
> 50kHz [still 3x the bandwidth of the roofing filter].
>
> I could understand a bit of headroom to avoid phase shifts at the  
> edge of the passband, but this seems like serious overkill - the  
> RA1792 LPF really is flat to 200kHz!
>
>
> From: John Graham
> Sent: Monday, August 16, 2010 9:53 PM
> To: Michael O'Beirne
> Cc: PREMIUM-RX
> Subject: Re: [Premium-Rx] Racal 1782, 178x series
>
>
> Michael,
>
> I agree that the wide bandwidth is on the face of it pointless;  
> that's why I found it puzzling.
>
> The fact remains that the 100kHz converter for the RA1792 is  
> specified as flat to 200kHz at -0.5dB [p.9 of the manual Addendum]  
> -- or at -1dB if you prefer to believe the Functional Block Diagram,  
> and the converter for the Eddystone 1650/6 is stated to be 185kHz at  
> -3dB [Manual section 4, p.4]. Yet both receivers have 16kHz roofing  
> filters.
>
> The 1773 and 1774 were just the 1771 and 1772 fitted with the MA1070  
> connector panel and mounted in a Creeth Field Transit Case (see  
> Appendix 2 of the 1771/1772 Operator's Manual).
>
> 73s,
>
> John G.
>
>
> From: Michael O'Beirne
> Sent: Monday, August 16, 2010 9:19 PM
> To: John Graham
> Cc: PREMIUM-RX
> Subject: Re: [Premium-Rx] Racal 1782, 178x series
>
>
>
> 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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