[time-nuts] Z3801A performance plots

Tom Van Baak tvb at LeapSecond.com
Fri Jan 25 17:34:10 EST 2008

> Tom's plots at http://www.leapsecond.com/pages/z3801a-osc/ show 13
> Z3801As running in unlocked mode, measured against one of his most
> excellent references.  So I think that plot shows what you're looking
> for.  I was just trying to show what you get when you are running in the
> normal locked condition (my units almost never go into holdover, so I
> was more interested in what the normal behavior was).
> One thing that's not clear from Tom's page, though, is whether the units
> were in "smart" holdover mode (ie, no GPS signal but the CPU still
> steering based on its learned aging curve) or truly freestanding with no
> EFC being applied.


I'm pretty sure those Z3801A were in factory reset mode when
I made the stability measurements. For that experiment I was
only interested in short-term stability; a range of tau where the
smart ageing correction has little or no effect.

You also asked about z3801a free-run vs. GPS locked plots. I
found old data for GPSDO #4 (of the 13 I tested in 2002).

Free-run stability for #4.

GPS locked stability for #4:

Here I put the two runs in color on the same plot:

Between the three plots you get a good feel for the function
of a GPSDO.


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