So what’s going on is that the TIA is “Mr. Magoo” and isn’t seeing sufficiently well to evaluate these oscillators?
I can believe that. I might just have to stop there, then. I can’t justify an upgrade today. > On Jun 2, 2016, at 7:24 PM, Bob Camp <[email protected]> wrote: > > Hi > > If the counter is the limiting factor, it should scale by 10 as the timebase > scales by 10. Your data goes from > 90 ppt at 1 second to 9 ppt at 10 seconds. That is the expected outcome. > > Bob > > >> On Jun 2, 2016, at 8:57 PM, Nick Sayer via time-nuts <[email protected]> >> wrote: >> >> Oh, the limitation is on the TimeLab side? I was blaming the TIA. :) >> >> Since then, I have found an advanced gate setting that appears to add 500 ms >> after start. The time intervals seem to be without that delay, so it works. >> The resulting ADEV is unchanged (other than obviously truncated at low tau >> and having a longer duration). >> >> Looking at the phase and frequency data, I don't see anything wrong. The >> ADEV plot is linear, and it arrives to the spec at around tau 10s or so... >> It's just way steeper than I expect. An order of magnitude north of spec at >> tau 1s. >> >> The only thing I can think of is that it's compounding the error because I'm >> comparing two (of the same) oscillators to each other, but my understanding >> is that I can only attempt to compensate for that by scaling by sqrt(2). >> >> Sent from my iPhone >> >>> On Jun 2, 2016, at 11:12 AM, John Miles <[email protected]> wrote: >>> >>> One workaround for the 1-million point limitation on imported data is to >>> use "Acquire->Acquire from live ASCII file" instead of "File->Import ASCII >>> phase/frequency data." Most of the same code is used for both cases, but >>> unlike the static file-import version of the dialog, the live data importer >>> will let you specify the expected duration yourself. So you can give it a >>> duration value that you know will be long enough to cover the whole data >>> set. >>> >>> I'm not too familiar with the 532x0A counters myself, but 8.9E-11 at t=1s >>> doesn't sound too unrealistic. When in doubt, look at the 'f'requency >>> and/or 'p'hase trends and residuals to sanity-check your data, rather than >>> trying to puzzle out what's going wrong with the ADEV plot as many users >>> seem to do. First you should satisfy yourself that the data makes sense, >>> is unwrapped and scaled properly, and doesn't contain glitches, large >>> crystal jumps, obvious beatnotes or other interference, or unexpected >>> amounts of drift. >>> >>> -- john, KE5FX >>> Miles Design LLC >>> >>>> I’ve gotten a little further with this. If I capture 60 seconds worth of >>>> time >>>> interval measurements (between two FE-5680As that are GPS disciplined, but >>>> with a long enough time constant that they’re basically free-running), I >>>> get >>>> 60,000 of them. So I imported at a sample interval of 1e-3 and got the >>>> right >>>> duration. There are a couple of problems, however. 1 is that even if I >>>> attempt to >>>> log to a USB stick, it appears I can only log 1e6 samples before it stops. >>>> That’s >>>> 16:40 or so, which isn’t very long. I haven’t figured out how to change the >>>> sample gate for time intervals (I’m assuming that a million samples is a >>>> hard >>>> limit). Also, importing the interval samples into TimeLab still shows me a >>>> graph >>>> that’s still much steeper than I would expect. The graph is linear, with >>>> points at >>>> tau 1s = 8.9E-11, 10s = 9.47E-12, 100s = 1.5E-12 (by then, the ADEV graph >>>> is >>>> starting to flatten out a bit, which probably indicates the noise floor of >>>> the >>>> 53220A near 1E-12), but the FEI datasheet shows a spec with points more >>>> like >>>> tau 1s = 1.5E-11, 10s = 4.5E-12 and 100s = 1.5E-12. >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
