> I don't think your proposal would work well, though I find myself
> lacking a deep enough understanding to explain why clearly. Perhaps
> someone else could contribute here also. But I'll try. ... Weaver
> demodulation is used in some SDRs. A disadvantage is that there is a
> hole in the response at the sub-carrier frequency (the CW sidetone
> frequency, in your nomenclature). In the analog world it is hard to
> make the hole small but in DSP it could be made a lot smaller, such
> that it is unobtrusive on an SSB receiver. However for CW, I wonder
> how that would work... the "hole" would be exactly at the center of
> the passband, and the CW transmission could well have energy either
> side of it, and given that the actual bandwidth of a CW transmission
> could be only 10 or 20 Hz, even a small "hole" would have a marked
> effect.
There is no "hole" in the Weaver modulation if we make it digital. All
the information of the received signal is present in the I and Q
channels.
OK...??
?
Suppose we want to listen to a CW signal transmitted at 7020 kHz. We set
the VFO to 7020-12 = 7008 kHz. The mixed signals contain the sum and
difference of these frequencies: 14028 and 12 kHz. Only the 12 kHz
components pass through the lowpass filters in front of the ADC, and
appear digitally as cosine and sine of a 12 kHz signal.
What about a signal occurring at 6996 kHx? This is the "superhet image", it also mixes with the 7008 VFO to produce a 12 kHz IF signal. In your scheme I don't think you are handling this image signal?
