"gareth" wrote in message
...
Presumably those SDR rigs which do not work on the IF but
directly from antennae must have, separately from the DSP processor,
some semblance of a DDS generator (but without the final DAC) to
act as the equivalent of the VFO, for I cannot perceive that a
fractional-Hz
tuning rate could be achieved with machine code running in the DSP
processor?

Thanks to all who responded, even he whose post was riddled throughout
with gratuitous rudeness, and it seems that I was almost correct, but with
the
exception of Brian Morrison's URL where the heterodyning was done
with a PLL and fractional-N synthesizer.

I wonder if Mr.Gratuitously Rude actually read through his URL reference
for therein is a clear reference to the phase accumulator, a necessary
part of the DDS process?