Hi One “cute” thing to do when looking at GPSDO’s or GPS modules is to use the “cable delay” setting. It will allow you to move the pps of one unit relative to the pps of the other one. You then can be sure of which pps happens first. That makes the A to B measurement much easier to analyze.
Short intervals also can lessen the impact of the time base accuracy in the counter ( you always are measuring a microsecond or so to a nanosecond resolution). Indeed there are other issues (like jitter) that still are an issue. Bob > On Nov 16, 2017, at 4:10 AM, Azelio Boriani <azelio.bori...@gmail.com> wrote: > > As already stated here, the best measurement mode is the time-interval > mode. The 5335A is a 2ns single-shot resolution counter. Use the PPS > output from the GPSDO, route it to the A (start) input and to a > coaxial cable used as a delay line (10m, 50ns, should be enough). The > other end of the cable into the B input (stop), select the time > interval mode TIME A -> B. Let the internal reference clock the > counter. Set trigger levels and the various parameter to get stable > readings and collect your data. > > On Thu, Nov 16, 2017 at 3:59 AM, Mike Garvey <r3m...@verizon.net> wrote: >> Could you post some phase plots? The data you show is not 1/tau and very >> likely not white phase noise. >> Mike >> >> -----Original Message----- >> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of CubeCentral >> Sent: Wednesday, November 15, 2017 11:12 >> To: time-nuts@febo.com >> Subject: [time-nuts] Interpreting and Understanding Allen Deviation Results >> >> Greetings, time-nuts! >> >> After reading [ http://www.leapsecond.com/pages/adev/adev-why.htm ] I felt >> that I better understood how an Allan Deviation is calculated and endeavored >> to try an experiment. It should be noted that I have a hobbyist-level >> understanding of the concepts described and tools used below. If my >> thinking or test methodology is incorrect, please let me know so that I >> might learn something. >> >> A GPSDO with a 10MHz output was run into the EXT TIME BASE input on the back >> of an HP5335A. >> Then, the TIME BASE OUT on the back was run to the A input on the front of >> the HP5335A. >> My intention was to characterize the performance of the HP5335A counter >> itself so that I might understand better future plots involving other GPSDO >> and the counter's internal clock (which was bypassed for this test). >> >> The settings of the HP5335A were as follows: >> Gate Mode: Normal >> Cycle: Normal >> >> A Input ------------------------------ >> Trigger Adjust: Full left to 'Preset' detent >> Z select = in = 50ohm >> x10 ATTN = in = x10 ATTN (should have been out/off?) >> Slope = out = up >> AC = in = AC coupled >> COMA = out = Not ComA >> AutoTrig = out = Not Auto Tiggered (should have been in/on?) >> >> (Tangentially, if someone has a good 'primer' or how-to resource detailing >> Universal Counter operation, showing when/why/how to set the knobs in >> certain situations it would be welcome!) >> >> I then set the Time Lab V1.29 software to repeatedly acquire data for 12 >> hours, starting the next test as soon as I could. This means that, >> normally, a test was run during the day for 12 hours, and then overnight for >> 12 hours. >> >> The results are shown here: [ https://i.imgur.com/0sMVMfk.png ] The >> associated .TIM files are available upon request. >> >> So, now we get to the heart of the matter and the questions this test and >> results have raised. >> I am trying to understand what the data is telling me about the test, and >> therefore the character of the counter. >> >> 1) Why are the plots a straight line from ~0.25s until ~100s? >> 2) Why, after falling at the start, do the plots all seem to go back up >> from ~100s to ~1000s? >> 3) What do the "peaks" mean, after the plot has fallen and begin to rise >> again? >> 4) Why is the period from ~1000s to ~10000s so chaotic? >> 5) The pattern "Fall to a minimum point, then rise to a peak, then fall >> again" seems to be prevalent. What does that indicate? >> 6) Why does that pattern in question (5) seem to repeat sometimes? What is >> that showing me? >> >> And finally, some general questions about looking at these plots. >> a) Would a "perfect" plot be a straight line falling from left to right? >> (Meaning a hypothetical "ideal" source with perfect timing?) >> b) Is there some example showing plots from two different sources that then >> describes why one source is better than the other (based upon the ADEV plot)? >> c) I believe that if I understood the math better, these types of plots >> would be more telling. Without having to dive back into my college Calculus >> or Statistics books, is there a good resource for me to be able to >> understand this better? >> >> Lastly, thank you for your patience and for keeping this brain-trust alive. >> I am quite grateful for all the time and energy members pour into this list. >> The archives have been a good source of learning material. >> >> -Randal (at CubeCentral Labs...) >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
