[time-nuts] Second FTS4060 shows Drift, is it me?

Tom Van Baak tvb at leapsecond.com
Tue Feb 7 14:11:02 EST 2006


> For most of the test the SR620 was using it's internal oscillator and 
> just recently I changed it to the PRS10 external standard but that does 
> not seem to have made any difference.

Correct. Since your time interval values are on the
order of 1 microsecond or less the accuracy of the
SR620 timebase makes little or no difference.

In some cases the stability of the timebase could
make a difference but since the jitter of your GPS
source is on the order of 10 ns the stability of the
SR620 timebase is also not an issue.

In general, you should be able to convince yourself
that making any TI measurement at 1 ns resolution
and 1 us range requires a timebase accuracy of only
0.1%. Thus the decision of using Qz or Rb or Cs as
the internal or external timebase is totally irrelavant
for this kind of short-term TI measurement.


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