[time-nuts] PRS-10 findings
magnus at rubidium.dyndns.org
Wed May 30 11:00:14 EDT 2007
From: "Poul-Henning Kamp" <phk at phk.freebsd.dk>
Subject: Re: [time-nuts] PRS-10 findings
Date: Wed, 30 May 2007 14:35:37 +0000
Message-ID: <92477.1180535737 at critter.freebsd.dk>
> In message <465D89BD.8000106 at xtra.co.nz>, Dr Bruce Griffiths writes:
> >> The HP5370 has a rather heavyhanded piece of electronics that
> >> eliminate this effect with a jitter based approach and as far as I
> >> have been able to measure, it works.
> >Not quite true the HP5370 has a whole host of anomalies like
> >differential linearity errors of 100psec or more for certain time
> >interval ranges, at least according to its designers.
> I did say "as far as I have been able to measure", didn't I ? :-)
You did, you did... :-)
If you lock a low-noise oscillator to the reference of your counter, such that
you have a fixed but slight frequency deviation and then start on one clock
and stop on the other, you will very slowly pass through all phase-states over
and over again. If the clocks are stable enougth the locking is mearly means to
ensure the frequency offset over the measurement period. Using this you can
predict the expected time difference for each measurement point with fair
precission and can then compare that with the measured one and as a result you
should be able to make a fairly decent measured vs. actual TI plot or if you
so wish, a TIE plot for the instrument.
The center point between stop->start worst injection and start->stop worst
injection is not nessecarilly around 0 s in time interval.
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