Fig. 1: The RA1792 audio performance using short a.g.c. decay.
Fig. 2: RA1792 'spike' at the onset of the input burst.
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I wrote at the end of my review of the RA17 that I would probably ruffle a few feathers and this has proved to be the case. The most vocal supporter of the RA17 is undoubtedly Michael O'Beirne and he has advocated its cause very effectively.
The major point which Michael makes, and with which I totally agree, is that a good RA17 can be very good, but after such a long production run there are receivers around which are showing signs of incipient electronic arthritis and which need to be viewed with some caution - much the same as the very shiny 40 year old car which may hide dreadful secrets under its bonnet or back axle. Should you succumb to the desire to have an RA17 or any other elderly receiver, please keep in mind that skilled assistance will almost certainly be needed, supported by a battery of quite expensive test equipment and the knowledge of how to use it.
Michael and I (and many others like us such as Bob Ellis who bought a trade-in from me at Lowe's) take delight in restoration of these elderly beauties just for the feeling of achievement when it all comes together at the end, but it would be impossible to place a commercial value on such restoration, particularly considering Michael's normal rates of pay at the top end of the legal profession, or my position running a UKAS accredited EMC test house. We do it for the love of the hobby alone. If you are the same, by all means start collecting and restoring.
I have been fortunate to have a second loan of an RA1792 and am even more convinced that this was an outstanding piece of technology in its time, and a receiver that will show you what real h.f. performance and ergonomic design can mean. However, the stricture regarding support service applies with even more force should you acquire an RA1792 with hidden problems, and you had better be equipped with some digital data analysis capability should there be something amiss in the processor controlled functions. Bearing in mind the poor results shown by the RA17 a.g.c. system, I took the time to carry out the same tests on the RA1792, and there is a world of difference to report. There are three a.g.c. speeds selectable from the keypad, labelled 'short', 'med.' and 'long', but at first use they are very different. The short and medium decay characteristics are very similar, with a fast(ish) attack time and well controlled restoration of full gain, but when Racal use the term 'long', they mean very long indeed.
I was surprised to find when I went to locate my original review of the RA1792 that it was way back in the previous century (actually September 1998), prior to my using the a.g.c. tests I now carry out as a matter of course, so I thought I should check and see exactly how it compared to other receivers tested more recently.
Look at Fig. 1 and see the RA1792 audio performance using short a.g.c. decay, with near perfect gain control and smooth recovery after about 100ms of delay. However, note the 'spike' at the onset of the input burst which turned out to be the now familiar overload as shown in Fig. 2, the surprise being that the RA1792 behaves just like a classic valve receiver such as the 51S-1, rather than producing the usual semiconductor 'click'. Fig. 3 shows the recovery time in the 'med.' a.g.c. setting, with about 200ms delay before the smooth gain restoration. In the 'long' a.g.c. setting Racal sneakily introduce a proper 'hang' system which keeps gain down for about 1.5s after the incoming signal ends before restoration at the same rate as seen in the 'med' setting. In real on-the-air action this long setting is just perfect for s.s.b. listening and is probably nicer than the Collins 51S-1 in this regard, hard though that is for me to confess. Racal certainly redeemed themselves after the disastrous a.g.c. in the RA17.
Fig. 1: The RA1792 audio
performance using short a.g.c. decay.
Fig. 2: RA1792 'spike' at the
onset of the input burst.
Fig. 3: RA1792 recovery time
in the 'med.' a.g.c. setting, with about 200ms
delay.
Happy listening
John Wilson's article featured in the April 2001 Airband Special edition of Short Wave Magazine, and is reproduced here by kind permission of Short Wave Magazine and PW Publishing Ltd