[time-nuts] Z3801 lockin behaviour

[Tom Van Baak]

> Hi!
>
> I have powered up my Z3801A and monitored the 10 MHz on a counter (with
fancy
> histogram and statistics) with the Cs as reference. The Z3801 is moving
around
> quite a bit and the SatStat shows that it hasn't really converged towards
> precission (the 24h time error prediction). Infact, it drops out of lock
into
> holdover every now and then. When it jumps in or out of hold over, a
"large"
> (50 mHz) frequency jump is clearly vissible. I have about 1 mHz of Allan
> Deviation and about 4 in Standard Deviation.
>
> I have made comperative measurements of my counter setup by hooking it up
to my
> Rb, and that is noticeably lower in noise.
>
> Is this to be expected or not?
>
> Any thoughts & recommendations?
>
> Cheers,
> Magnus

While watching the syst:stat screen did your Z3801A
already complete its multi-hour site survey and the
coarse/fine frequency adjustments? If it's still in a
start-up acquisition mode ignore the 10 MHz output.

If it doesn't lock after a few hours, I'd suggest a full
reset. Also check your signal levels, and elevation
mask. Did it get your lat/lon/alt correct?

The predicted time error won't settle down for a few
days (it's a long time constant), so don't worry about
that quite yet.

Not sure what you mean by "The Z3801 is moving
around quite a bit". You should get 10 solid digits
of accuracy out of a Z3801A at short sample times.
That grows to 11 or 12 over several hours; 12 to 13
over several days (at which point you won't quite be
sure if the errors are your counter, your Z3801A, or
your cesium).

/tvb