[time-nuts] Testing frequency using NTP
Tom Van Baak
tvb at LeapSecond.com
Thu Oct 2 23:29:25 EDT 2008
> The time constant should have been 22ms and the phase shift 1.16us with
> a tempco of 580ps/C.
> Since both channels have the same nominal low frequency cutoff the
> differential phase shift tempco will be somewhat smaller.
Thanks for the calculations. So it's probably safe to say the
differential phase shift stability is many orders of magnitude
less than NTP jitter. Good.
Anyway, I think it would make a fun project to see how well a
typical PC sound card actually does as a 1PPS or LF phase
comparator and frequency counter. I wouldn't expect better
results than a $50 surplus eBay time interval counter, but it
would be interesting to see just how bad or even how good it
might be. There are, after all, many timing applications where
nanosecond and picosecond resolution isn't required.
More information about the time-nuts