[Premium-Rx] Racal RA6790/R-2174B

[Dan Rae]

On 11/23/2013 3:55 PM, Charles Steinmetz wrote:
> There is currently an auction listing for a Racal RA6790GM that has been converted to receive LF signals.  The homemade model plate says "Receiver, VLF       Radio R2174B (P) URR      S/N 2".
>
> The seller is upfront that it is a conversion.  However, while it may receive LF, it does NOT appear to have been changed to the actual R-2174B(P)/URR configuration.
Charles,

Despite the claims by the seller that it has been converted by Gary 
Wingerd etc., etc., it does appear to be a bit of an odd one...  The 
filter complement is wrong, in that there is only the one offset ISB 
filter, the second slot is a nominal 3 KHz wide symmetrical filter of 
the type fitted to HF/DF receivers that is nearer 6 kHz wide and no good 
for SSB, while the third slot has the normal 3.24 kHz symmetrical 
sideband filter.  Anyone trying to use it for ISB is going to be a bit 
puzzled.

It has the antenna switching board and so two antenna inputs with what 
appears to be an ISB board hidden underneath.

Since there are no pictures of the mixer boards it is impossible to say 
what they are.  The true VLF first mixer has a much larger mixer can ( I 
uploaded a picture of such a board to the group a while back) a lot of 
additional LO filtering and would also have a 16 KHz roofer.  The second 
mixer would then have an 8 kHz wide roofer. The LF versions can have the 
bigger mixer but the usual 20 kHz roofing filter.   As you say these 
boards were also fitted to some 6793s, but were not exclusive to those.

But it has attracted 22 bids so far and a lot more money than I'd pay 
for it :^)

73 - Dan

ac6ao / g3ncr