[Premium-Rx] Racal 1772/78

[Dan Rae]

I have owned the same 1772 for nigh on 30 years now, for better or for 
worse, but have so far refrained from adding to the exchanges, but I do 
have some acquaintance with them, perhaps not to the extent of Pat McA 
however :^) 

I suppose that getting this one was the start of the downward path that 
led to my current excessive collection of Racals...

Before you all rush out and spend silly money on one, there are a couple 
of negative points that nobody has so far referred to.  First the 
variable BFO has a woeful lack of stability, of no import if you are 
mainly using the radio for AM or SSB listening, but a real disadvantage 
if you use CW or RTTY.  The crystal BFO option provided for on the board 
will of course help and I have implemented this on both my 1772 and my 
1778, but the crystals are now very hard to source, my local 
manufacturer has gone out of business.  

Secondly the system of IF filter switching used with diode switches is 
less than perfect; possibly this was a design decision to give some 
"context" around the wanted signal, but for some it is a disadvantage 
since the best available filters like the 8 pole McCoys will have their 
skirt selectivity degraded.

Also if buying, be aware that the majority of ex-RAF 1772s were fitted 
with an odd arrangement of filters and filter switching with ISB and two 
offset data filters. These can be modified back to the "standard" 
arrangement if you can find the filters but is a real disadvantage in my 
opinion.  The ex-RAF 1778s seem to have not been fitted with a wider 
symmetrical  filter than 3 kHz which is a bit less than useful for AM 
listening, but at least they have no offset filters.  I did have a large 
number of the McCoy 6.8 kHz filters, but they have all gone now. 

Thanks to a generous list member my 1772 is now fitted with a first 
mixer board with switchable roofing filters, the usual 12 kHz one and a 
narrow 1.5 kHz one which switches in automatically with narrow IF 
bandwidths.  This was built in 1978, several decades before Yaesu and Co 
were doing it.

I suspect that the PCB manufacturing process was the best available at 
the time.  There are no VIAs, small rivets were used to link top and 
bottom, and the adhesion of the copper to the substrate is not that 
good, but in all those I have seen it is fibreglass, not SRBP.  I think 
it is a little unkind to blame the designers for any failings here, as 
with the PVC wiring, how were they to know what forty years or more 
would do? 

I still have a very yellowed clipping of the 1974 "Wireless World" 
article by R.F.E.Winn, the head designer of the RA1772 describing the 
concepts behind the design which still makes interesting reading.  I 
have an electronic copy of this, if anyone would like it, it can be 
emailed; requests direct please.

Dan

ac6ao / g3ncr