Hi, The goal would be to be able to tell what the phase and frequency of the down-converted and sampled signal is. So no modulation on the carrier (for now).
So given the RF signal is perfect sinusoid, and given that you know the parameters x(t) = xo + yot (time and fractional frequency offset) of the reference oscillator, one should be able to determine the phase and frequency of the ADC output at any given time (in a perfect world). In general, the ADC sampling frequency (and the LO frequency for that matter) could be at non-integer multiples of the reference oscilator. However, both the LO and sampling frequency will be a derivative of the reference and will have the x(t) = xo + yot time and frequency offset. Hence, that should be accounted for in both down-conversion and ADC sampling. However, I have not seen examples where time and frequency offsets have been included in the ADC sampling. But, it seems logical that reference oscillator's imperfections modulate both the down-conversion and the ADC timebase. I guess I'm just worried that I might be missing something obvious here? And I know there is no better place to ask such a question other than on time-nuts :) Regards, Stephan On Sat, 23 Dec 2017 at 18:11 Bob kb8tq <[email protected]> wrote: > Hi > > What is the Time Nut goal here? Are we after the carrier frequency or > after the > modulation on the signal? > > Bob > > > On Dec 23, 2017, at 10:46 AM, Stephan Sandenbergh < > [email protected]> wrote: > > > > Oops, I noted a sign error in the previous diagram. The attached seems > > better... > > > > On Sat, Dec 23, 2017 at 4:46 PM Stephan Sandenbergh < > [email protected]> > > 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. > >> > >> > >> > > <img1.png>_______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
