On 15/06/2020 15:38, David Taylor wrote:
https://www.eecis.udel.edu/~mills/ntp/html/cluster.html
What is the clock resolution? If you try and measure jitters that aren't several times the resolution, they are not going to be particularly valid.
If the hardware clock is almost dead on, and the peak to peak dither is just less than the resolution, there will be long periods in which it will read as as zero, even though it is actually close to one resolution unit. You could also get cases where dither was very low but read as one resolution unit for long periods. In fact, if it was possible to find tune the actual clock oscillator, during an ideal lock you would have peak to peak dither, as measured, of one or two resolution units, even though the actual phase noise was much less.
(Arguably, a jitter that is less than the clock resolution will result in worse time accuracy than one that a few times it, as the clock resolution will not be dithered out.
That makes the, normally unrealistic, assumption that the systematic error is less than the clock resolution.)
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