[Premium-Rx] Racal 1782, 178x series

[John Graham]

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

  Message: 6
  Date: Sun, 8 Aug 2010 19:30:58 EDT
  From: Pat1McA at aol.com
  Subject: Re: [Premium-Rx] Racal RA1772
  To: dibene at usa.net
  Cc: premium-rx at mailman.qth.net
  Message-ID: <552a2.330103e5.39909832 at aol.com>
  Content-Type: text/plain; charset="ISO-8859-1"

  Hello Alberto,
   
  After repairing over 20 RA1772s and over 45 RA1792s I think that I can  
  comment on this subject.
   
  The RA1772 appears to have been designed, at the time, with little  regard 
  for cost saving.
  There is a reason for this. After the valve/tubed RA17 receiver, Racal  was 
  struggling to produce a comparable solid state successor, in the event they 
   produced the transistorised RA1217 - which turned out to be  a disaster in 
  terms of performance.
  I remember visiting Portishead Radio, in those days GRL (1612kHz), but  
  later as GKA/B etc, around 1969, when they had replaced the RA17s with RA1217s  
  and the Operators were NOT happy at all !
  The general performance was so dreadful that Racal just had to come up with 
   a satisfactory replacement.
  Enter the RA1772 which was designed from the floor up with no short cuts.  
  The result was a truly superb receiver.
  Consider at the same time competition was fierce from Marconi, Redifon,  
  Plessey, Rohde & Schwarz, Telefunken etc etc,  remember this was in the  era 
  of "Real" HF CW and voice SSB Communications. WJ did not get a look in, not  
  at least on this side of the "Pond!"
   
  The thing that sets the RA177X series apart from the others is the very low 
   noise synthesiser with discreet crystal filters, this is basically  superb 
  and the excellent rotary Tuning shaft encoder  is copied right up to the 
  later RA3701 model. Unfortunately the  RA1772 "hang" type agc lets it down - 
  for Amateur use.
   
  The RA177X series had a useable Preamplifier that would show signals down  
  to -139dBm with a 3Ip of around +35dBm. This was seriously good in 1974, it  
  still is now! Most other receivers of the time, the EK070, E1700, and later 
   E1800 did not have a preamp and consequently had impressive 3Ip figures. 
  But,  under most common circumstances this does not matter at all for us  
  Amateurs.
   
  The RA1772 was unbelieveably and expensively labour intensive, rather  like 
  the E1500/1700. Even worse for wiring intensity was the RA1784 and  
  RA1778/9 series. So the RA1792 was born, a beancounters dream!
   
  I think that there is no comparison between a properly aligned (few were)  
  RA1772 and an RA1792. The RA1772 wins hands down BUT from the operational 
  point  of view the RA1792 is absolutely unbeatable!!!
  The later RA1778/9 series is nicer to use than the RA1772 but much  harder 
  to find now.
   
  For my choice the finest Racal HF Receiver is the Remote Controlled RA1784. 
   These were hugely expensive but had the option of a switchable  600Hz  
  Roofing Filter in them, rather like the RA1772 prototype I was offered many  
  years ago, and, like an idiot, did not purchase! That had a switch, in place of 
   the normal AFC one that switched in an Optional CW Roofing Filter - an 
  Option  that got dropped by Racal as being too expensive at the time, around 
  ?600 in  19772.
   
  If you compare an RA1772 against an RA1792 on the bench the RA1772 wins  
  easily on readability but then, as usual, everything is " Horses for Courses"  
  with the 1792 being much more intuitive to use, but (I believe) it was an  
  American design based on the RA6790GM. For intuitiveness and ease of  
  operation nothing beats American Radios eg. WJ8711A ,  WJ8718, etc etc
   
  Regards & 73 
   
  Pat G3YFK