Darryl Otzen said the following on 04/06/2006 08:08 PM: > For comparing Cs oscillators I use an old fashioned analogue phase meter > coupled with a chart recorder. > The meter is centre zero with +/- 5 degree FSD. > Once I'm happy with the performance of the analogue outputs of the > oscillator I'd start looking at the PPS. > How accurate is your TIC? > Feed the same signal to both inputs, check if there is any unstable > measurement error.
Hi Darryl -- I have also used an HP 8505 (I think that's the number) vector voltmeter which has a phase meter, feeding the chart recorder output into an ADC and then logging the data. That does work well -- as long as you don't slip a cycle! The main issues with the TIC are resolution and jitter; when you're measuring intervals of ~10us (which is what I use) the stability of the timebase aren't really important because any drift over such small intervals is way below the resolution of the counter. Be that as it may, I normally use an external timebase, typically an Rb standard which has better short term stability than the Cs. Theinexpensive HP 5334A counter I dedicate to long-term logging has a 2ns resolution, but I'm using it in 100 sample average mode, which yields effectively 200ps. Against a tau of 100 seconds, that's about 2x10e-12. There is probably still some counter jitter in that, so the actual usable resolution is maybe 5x10e-12 in 100 seconds. For long term measurements, with averaging times of an hour to several days, the resolution becomes even less of an issue -- 10ns/day is about 1.15x10e-13. I haven't measured the single-shot jitter of this particular counter, but based on other HP counters I have looked at, the jitter is typically a couple of times the resolution (e.g., for 2ns single shot, jitter might be in the 5ns range). John _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
