[Racal] RA 1792 infos & problems

[Dan Rae]

Carlo Adamo wrote:

>Hello,
>about one  months ago I bought my second Racal, a RA1792, the first one
>being a R17L. The receiver is in good condition and, indeed, it works
>fine. Its serial number is 10052 and the accompanying manual is dated
>"Feb. 1987".
>The option installed are labeled GB/S2/S/D/1/A.  Looking at the details
>(inside and outside) of the receiver, there is something which is not
>clear to me. First of all, the display has three digits after the dot (8
>digits in total), corresponding  to a  tuning step of 1 Hz and not of 10
>Hz as reported in the manual or in the Oesterman.
>
First of all, Carlo, do not believe all that you read in Osterman!
The 1 Hz tuning step is an alternative that was available. It is changed 
by firmware in the EPROMs and in your version combined with the 100 KHz 
IF convertor, was usually referred to as the frequency measuring 
version.    You can change the ROMs for the 10 Hz step version, if you 
can find them.  There are many versions of this radio.

>  Next, my Racal does not have inside the standard IF card at 455
>kHz, but rather
>a metallic box with a writing "IF 100 kHz output. 
>
This is in addition to the regular IF A4 card, it is a synthesized 
convertor from 455 to 100 KHz to enable accurate frequency comparisons. 
 Also Racal made a bunch of add on devices for signal analysis that 
worked at 100 KHz.   The IF convertor goes where the ISB IF card would 
be, between the IF and the RF amp.

> Finally, the BFO
>works also in USB and LSB but only between +0 and +8 kHz. 
>
This I don't understand.  Of course the BFO should work in sideband mode 
but with the GB set of filters, it should always be at 455 KHz dead. 
 The GA set (one 3 KHz symmetrical filter) will need an offset for 
sideband switching.  In ssb mode the bfo display is normally absent.   
It may be for some data mode that I don't know about.  Some of the 
versions of the RA1772s (in fact most of the UK surplus ones around) 
were fitted out for ISB use, voice on one sideband, and data on the other.

>So, do you
>have any comments on these  apparently non-standard  features?  Also, I
>have to change the battery (it is not leaking, but it is old). Do you
>have any suggestion or advice on this point?
>
If the battery is old, it is probably worth changing, even if there is 
no visible liquid leaking, there may be corrosive gas given off.  The 
later models had the battery mounted on a little sub-board away from the 
main A6A2 board, for this reason.  This is quite easy to do.  If you 
have ever worked on a board that had a bad battery, you'll change it 
right away!

>
>This about the general features of the receiver and the good news.  Now
>the bad news. Yesterday evening the receiver suddenly stopped to work
>correctly. The display just flashed "8888888888" and no signals came out
>from the speakers (or some noise). After a while, and several switching
>on and off,  it comes back to normal activity. It seems to me that it
>was an software problem and so I wanted to run the BITE test.
>
This sounds like the cpu resetting itself.  This could be from a number 
of causes.  A very common fault is the bead Tantalum capacitors going 
short circuit, anywhere in the set, this can short out one of the supply 
lines.  This tends to be a permanent fault, rather than an intermittent 
one though.

As a general point, both the 6790 and the very similar 1792, don't like 
getting too hot.  If they are mounted in a confined space, extra 
ventilation is helpful.  In some of the UK government installations fans 
were fitted.

>
>Unfortunately  in my operator manual the corresponding page is missing.
>
Keith's racal site has a lot of information on the BITE codes:

http://www.recelectronics.demon.co.uk/main-page.htm

should get you to the site.

Bonne chance,
Dan ac6ao g3ncr