[time-nuts] 53230A TIC and TimeLab

Ole Petter Ronningen opronningen at gmail.com
Thu Oct 4 09:42:49 EDT 2018


On Thu, Oct 4, 2018 at 1:40 PM Magnus Danielson <magnus at rubidium.dyndns.org>
wrote:

> Who-oh! OK. This means that one should intentionally let a number of
> samples pass before trusting it.
>

Precisely. But, crucially, discard 1-2 samples *since the last INIT* -
which may not be obvious without some investigation. It is a bit
convoluted, but the behaviour is easily observed using TimeLab: Feed the
counter the same 10  MHz signal both on the EXTernal REFerence, and channel
1. Set up a frequency measurement, and collect data using timelab. Observe
the phaseplot (taking care to NOT have the phase plot in "residual mode").

After a few minutes, a slope will be observed on the phase plot that should
not be there - it is measuring its own reference, so the plot should be
pretty much dead flat over a sufficiently long interval. It is because
timelab calls READ every time it wants a sample, and the instrument returns
a biased frequency estimate. Shorter gate-times, steeper slope.

It would be interesting to get some better qualifications of this.


I have attempted to make a thorough writeup on the previously mentioned
http://www.efos3.com/53230A/HPAK53230A-1.html Also parts 2 and 3 - in
short, the behaviour has been observed on three separate instruments. The
data is available for download on my website. Oh, and Keysight has
acknowledged the issue, but not offered anything towards a solution.

Ole


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