An SDR or DDS question?
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?
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