It would be (as you point out) a bad idea to have the the ADC sampling rate to be exactly the same as the downconversion oscillator.
In many cases they would both be derived from the same master oscillator. But the ratios would be consciously chosen to not be simple integer multiple relations so beating between the ADC and the downconversion oscillator would get washed out. This issue of avoiding simple harmonic relationships between receiver oscillators (and samplers) long predates digital radios, it is a goal in any superhet to avoid "birdies". Tim N3QE On Sat, Dec 23, 2017 at 9:46 AM, Stephan Sandenbergh <ssandenbe...@gmail.com > wrote: > Hi All, > > Consider the following very common scenario: A perfect RF signal is > heterodyne down-converted to baseband using an offset oscillator. Let's > assume this oscillator has x(t) = xo + yot. This produces a time and > frequency offset baseband signal. Then, this baseband signal is coherently > ADC sampled using that same offset oscillator. > > What would the effect of this coherent ADC sampling be? > > See attached diagram. Here I assumed the ADC timebase is a time-dependent > function of the oscillator offset. However, it feels like I'm making a > logic error? I can't remember ever seeing anyone accounting for the ADC > time-base errors in coherent heterodyne down-converter stages. I have > limited experience though. > > Regards, > > Stephan. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.