[time-nuts] GPS 1PPS ultimate accuracy

Andrea Baldoni erm1eaae7 at ermione.com
Mon Jan 12 05:59:26 EST 2015

Hello all.

I am planning to do some experiments to evaluate the aging of oscillators
(this one of the reasons I'm willing to buy the Milleren without EFC).
What I would like to do exactly is to sample the total of a counter (of
suitable number of bits, taking in account the fact that it will overflow)
whose clock is the DUT.

The sampling interval could come from a (long time based on a) sawtooth
uncorrected PPS from a cheap GPS, a sawtooth corrected from a good one (perhaps
the Lucent GPSDO), or a computer using NTP.

Each of these sources should reach a goal stability (say, 1 part in 10^13)
after averaging them on a different (and very high I suppose) number of
seconds (averaging them for an infinity number of seconds should give the
stability of the underlying reference clock, but I'm willing to stop sooner...).
I know there's no reason to go 1E-13 when the Milliren couldn't go that far,
but the DUT may be also something else like a FE-5680A).

The sawtooth uncorrected GPS receiver may never yeld a good stability in the
short term, but in the long one it should as well because the internal clock
jitter would average results.

If I'm using the correct teminology, after what tau the ADEV graph of the
different references intersect the 1E-13?

By the way, the stability of the TAI is known or, because it's
the reference one, it has zero deviation for definition (so you can reach
its ultimate stability through GPS really only at the infinity...)?

Best regards,
Andrea Baldoni

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