If you have only one GPSDO, a coaxial cable is your best friend to test the performance of the counter in time-interval mode. If you have two GPSDOs, the Segal's law apply: <https://en.wikipedia.org/wiki/Segal%27s_law>, better go directly for three.
On Thu, Nov 16, 2017 at 7:18 PM, Bob kb8tq <kb...@n1k.org> wrote: > Hi > > The exact software command used depends on the GPSDO you have. How you send > the command to > the GPSDO depends a bit on the driver software you are running. Not all > GPSDO’s or modules have > cable delay. All the ones I run do have the feature. Normally it comes set to > some random default setting > like 60 ns. I typically take one GPSDO and deliberately make it the odd one > out of the group. By making > the offset large (say a microsecond or two) it’s easy to spot the “false > ticker” in the group if things get > mixed up. > > Assuming you set the odd GPSDO to be early (which could be cable delay + or > cable delay -) it would > go to input A on the counter. That would be the start channel. Input B would > come from any normal > pps signal and it would be the stop channel. You can of course do this other > ways that work just as > well. > > Again - this is for looking at a pps relative to a GPSDO using a 5335 or > similar counter. > > Bob > >> On Nov 16, 2017, at 12:05 PM, Jerry <jster...@att.net> wrote: >> >> Bob, >> >> I am also a time newbie... how do you adjust this in software? For time >> interval as discussed below, the unaltered GPSDO output goes to A and how do >> you create the GPSDO delay for B without a physical coax delay? Any change >> in GPSDO cable delay setting will affect A and B the same. Sorry if this is >> a stupid question >> >> Jerry, NY2KW >> >> -----Original Message----- >> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob kb8tq >> Sent: Thursday, November 16, 2017 11:15 AM >> To: Discussion of precise time and frequency measurement <time-nuts@febo.com> >> Subject: Re: [time-nuts] Interpreting and Understanding Allen Deviation >> Results >> >> Hi >> >> Yes, that’s exactly what I’m saying. You just use the software rather than >> dragging around a big hunk of coax. It makes it easy to get one pps into the >> “that’s way more than I need” range. >> With the coax approach, is 50NS enough? Might 100NS be needed? Is there a >> 231NS case?. >> I’ve spent a *lot* of time finding those cases in the middle of long data >> runs …. >> >> Bob >> >>> On Nov 16, 2017, at 10:37 AM, Jerry <jster...@att.net> wrote: >>> >>> Bob, >>> >>> Do you mean then you do not need to put a physical long length of cable for >>> the delay, just do it in software or do you do both? >>> >>> Jerry, NY2KW >>> >>> -----Original Message----- >>> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob >>> kb8tq >>> Sent: Thursday, November 16, 2017 9:58 AM >>> To: Discussion of precise time and frequency measurement >>> <time-nuts@febo.com> >>> Subject: Re: [time-nuts] Interpreting and Understanding Allen >>> Deviation Results >>> >>> 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. >>> >>> _______________________________________________ >>> 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. _______________________________________________ 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.
