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

[Charles Steinmetz]

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.  The seller says that it has "optional A2, A3, and A7 boards for VLF reception," which sounds as if it may have the optional LF A2, A3, and A7 modules for an RA6793 installed.  See RA6793 manual (1985) at pp. 1.7 and 1.8.  (Note that all RA6790s and RA6793s have modules A2, A3, and A7 installed, and some RA6793s have optional versions of these cards that allow reception down to 20kHz or 10kHz.)

A real R-2174B(P)/URR has additional modules A14, A15, A23, A24, and A25, which other RA6790s do not have.  The A14 and A15 boards are stacked behind the IF board, where the A5 ISB option goes in radios so equipped (thus making the R-2174B(P)/URR incompatible with the ISB option).  The A24 module stacks on top of the main IF board on a clever hinged carrier.  A real R-2174B(P)/URR has a standard black anodized aluminum model plate that, in addition to identifying the radio as an R-2174B(P)/URR, gives its Part No., Mfr. No., Contract No., and its 4-digit, "B" suffix US Serial No.

I'm not trying to put anybody off bidding on the radio in the auction -- it may well be a fine radio, and it may do a good job of receiving LF signals.  It just does not appear to be an R-2174B(P)/URR conversion, contrary to what its homemade model plate says.  

Best regards,

Charles