On Thu, Oct 4, 2018 at 1:40 PM Magnus Danielson <[email protected]> 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 _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
