If you have log before ADC I think you need a superhet conversion rather
than direct conversion to baseband, for the reasons I mentioned earlier. If
you just ADC'ed the lot there'd be some chance of sorting the confusion out
in software, though it'd take a brave heart to try it.

So use 2 18-bit ADC's (sound card maybe 16-bit but you won't get 90dB range from
it, you'll find a fair bit of noise from your average sound card - well the
first 3 bits will be noisy), one with the I and the other with the Q (from the
DC output) and do it that way ?

Clive