[time-nuts] Timelab Query (likely noob error)

Jason Ball jason at ball.net
Sat Oct 24 01:38:21 EDT 2015

Hi all,

I'm afraid this may be a noob question as I've undoubtedly done something
wrong, either that or I have some phenominal time sources... more likely
I've made an error in an assumption or two.   This should to my mind be
within the capabilities of the counter I have, but right now I'm starting
to wonder.

The problem is I'm seeing a 10s tau of 9.29E-18 which to my limited
understanding is highly doubtful.

So what have I done wrong ?

The setup:

Time Source: Thunderbolt Trimble, 24 hour survey from a full reset and 7
days running with full visibility.
Lady Heather: Running, although just restarted so it will take a while to
gather the adev stats.
GPIB: Agilent 82357B GPIB->USB.  Probably a chinese clone, but it seems to
work well.
IO LIB: keysight IO Libraries version 17.1.20011.4
Timelab: v1.28 Beta
Counter: HP 5335A
DUT: Efracom Rubidium Frequency Standard Model LPRO-101

The counter is using  the GPSDO for the external reference, although I
should probably retest using the internal OXCO time base for comparison.

The counter is set to period mode, the gate time is currently set to
maximum (5.92 seconds), I do suspect the integrator is enabled (should it
be?) but this seems to be being reset by Timelab when it initialises the
counter.   The following is from a recently started run to show what, to my
mind can't be right.

[image: Inline image 1]
[image: Inline image 2]
I've checked the data being received and it matches what is shown on the

Is this simply an issue of counter resolution ?

The counter does perform correctly when I use a variable frequency source,
its right on when fed a signal from my Stanford Research DS345 syncronised
to the same time source.

Any ideas where this newb has stuffed it ?


Teach your kids Science, or somebody else will :/

jason at ball.net
vk2vjb at google.com <vk2flnx at google.com>
callsign: vk2vjb
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