[time-nuts] ADEV test setup [was GPSDO TC & Damping]

Bruce Griffiths bruce.griffiths at xtra.co.nz
Fri Jan 9 20:56:16 EST 2009

Tom Van Baak wrote:
>> Tom
>> Doesnt that introduce some correlations for larger tau as both the
>> Thunderbolt and the 58503B are both locked to GPS?
>> Bruce
> Correct, the choice of reference often has some impact on the plots.
> Since I used a GPSDO (a nice one), if the plot extended well
> past 10^4 or 10^5 the GPS correlation effects would show up in
> the long-term, I think. In that case the plots would start to appear
> slightly optimistic.
> On the other hand, because I used a GPSDO instead of a maser
> reference, the plot I posted appears slightly pessimistic in the
> short- and mid-term.
> So the main thing about the plot was just how well the difference
> between tc=10, 100, 1000 showed up, regardless if the reference
> was a maser or a GPSDO. A nice Rb might work too.
> That the TC setting was so visible using (only) a GPSDO as a
> reference is promising. It means normal time-nuts (oxymoron?)
> who don't have cesium or masers lying around have a good
> chance to investigate the optimal TC for their GPSDO. Looks
> like a 5370 or SR620 would also work for the TI counter.
> /tvb

What does the MDEV plot for the particular Thunderbolt look like when
the Thunderbolt itself measures the phase error of the its unlocked OCXO
against GPS?

In other words how reliable a guide is setting the loop TC to coincide
with the value of Tau at the minimum of such an MDEV plot?


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