"Turns out that professional gear for this does not do time-stamping in this regard. Rather, they I-Q demodulate the signal with a reference signal at the nominal rate, low-pass filter it and pay attention to details of filtering like group-delay and compensation thereof."
It makes sense to me. That way, you use the entire signal instead of just the zero crossing. You know that the signal is generated as a sine wave. Therefore, essentially you synthesize a local sine wave that is a best fit to the input signal and you measure the zero crossings of the synthesized signal. Didier KO4BB Magnus Danielson <mag...@rubidium.dyndns.org> wrote: >Tom, > >On 11/17/2013 03:02 AM, Tom Van Baak wrote: >> Charles, et al. >> >> I think we agree. Just to clarify... >> >> I rely on no hardware and no software filters when I use a >time-stamping counter such as a sub-nanosecond Pendulum CNT-9x or >sub-microsecond picPET. An electrical zero-crossing happens when it >happens. If you "filter" you're just trying to change history: spikes >are spikes; noise is noise; history is history. Deal with it. Record >it, don't filter it away. >> >> The beauty of the time-stamping method is that you capture any and >all positive zero-crossings. If there is "noise" all it does is create >unexpected and obvious artificial too-early or too-late samples -- >which are trivial to analyze or eliminate in software. >> >> Some call them "outliers" and ignore them. This is correct. However, >if one "filters" or "averages" them, you give validity they may not >deserve. Bogus data should be eliminated by *logic*, not attenuated >with pseudo-analog *filtering*. >> >> You can either focus on the signal, or the noise. That's two separate >plots. An extraneous time-stamp happens to me a couple times a month; >they are easy to spot and ignore. Similarly, a couple times a year I >might miss a 60 Hz sample; these are also easy to spot and repair. For >best time & frequency results, never "divide by =60"; instead "decimate >by ~1 second". >Standard wide-bandwidth counters isn't really ideal for signals like >this. > >When you measure the mains signal, nominally 60 Hz in this case, spikes >etc. is noise which is local and not of interest when comparing over a >large area. Inter-area oscillations have much slower properties. >If you go the time-stamping way, you *should* remove such noise. > >Removing or padding over it by logic will mean dropping data, which is >not helpful. > >Turns out that professional gear for this does not do time-stamping in >this regard. Rather, they I-Q demodulate the signal with a reference >signal at the nominal rate, low-pass filter it and pay attention to >details of filtering like group-delay and compensation thereof. It's a >rather wise approach for the type of conditions you have. > >Cheers, >Magnus >_______________________________________________ >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. -- Sent from my Motorola Droid Razr 4G LTE wireless tracker while I do other things. _______________________________________________ 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.