[Premium-Rx] VLF version of the RA6790/GM

[Dan Rae]

DAVEINBHAM at aol.com wrote:

>  
> Does anyone know what it takes to get a Racal RA6790/GM to actually 
> tune down to VLF.
>  
>  I found and copied a set of the VLF EPROM's so the radio now tunes 
> down to 0Hz but, unfortunately, it is deaf below about 400 kHz. 
> Obviously, the VLF version of this excellent radio had a different 
> mixer, but is there anything else different in the VLF version ?

1:  The A2 (first mixer card) is different.  A different mixer box, much 
larger,  special filtering in the LO injection chain to remove noise 
near the first IF, and a narrower first roofing filter, 16 kHz.
2:  The second mixer card has an even narrower 8 kHz roofing filter.
3:  There are some slight changes to the A7 1st LO synth output stage, 
to give a slightly higher level of output.
4:  The firmware, which you have.
That's about it...  AFAIK
73
Dan
ac6ao / g3ncr