[time-nuts] 53230A TIC and TimeLab
kb8tq at n1k.org
Thu Oct 4 10:02:52 EDT 2018
Probably also worth mentioning:
For short tau, you are probably measuring the ADEV of the counter noise floor rather than the
ADEV of the GPSDO. Yes, there are noisy GPSDO’s out there but most of what you run into
is not in that category.
> On Oct 4, 2018, at 8:42 AM, Ole Petter Ronningen <opronningen at gmail.com> wrote:
> On Thu, Oct 4, 2018 at 1:40 PM Magnus Danielson <magnus at rubidium.dyndns.org>
>> 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.
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