-Randal (at CubeCentral Labs...)

Jerry: > 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? You are correct. In Randal's hp 5335A frequency counter experiment he was splitting a single GPSDO 10 MHz output to both the REF input and the chA input. As such, as you thought, no amount of GPS h/w or s/w delay would affect the phase difference between those two ports. Bob: > 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. Note the plural. What Bob is saying here applies to the case where you have two or more GPS timing receivers, or one GPS timing receiver and a local atomic clock. In these cases adjusting the s/w antenna delay is an easy way to adjust the phase of one of the signals. I use this method when I want to introduce large delays, many us or ms. Most timing receivers offer a way to shift the phase of the 1PPS. For small delays it may not work like you expect. If it's a plain GPS/1PPS board there will be plenty of 1PPS jitter so changing the antenna delay by a few ns or few tens of ns may not be immediately visible. For a GPSDO it depends on how the firmware handles the antenna delay parameter. If it's a FLL-based GPSDO the antenna delay has no effect. If it's a PLL-based GPSDO the unit may go into holdover, or jam sync the 1PPS, and/or begin the slow process of slewing the output frequency to get the oscillator output to match the now-shifted GPS/1PPS output. Does anyone have experience with binary programmable video delay boxes like http://www.allenavionics.com/V_Delay/var.htm which are found on eBay all the time? /tvb ----- Original Message ----- From: "Jerry" <jsternmd@att.net> To: "'Discussion of precise time and frequency measurement'" <time-nuts@febo.com> Sent: Thursday, November 16, 2017 9:05 AM Subject: Re: [time-nuts] Interpreting and Understanding Allen DeviationResults 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-bounces@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 <jsternmd@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-bounces@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.boriani@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 <r3m1g4@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-bounces@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.

Hi Randal, On 11/15/2017 05:12 PM, CubeCentral wrote: > The results are shown here: [ https://i.imgur.com/0sMVMfk.png ] The > associated .TIM files are available upon request. As mentioned before, the preferred way of doing this is to do a time interval measurement between a start and a stop signal. Typically you trigger on the GPSDO PPS output as a start signal and then stop with another signal. That way the time-base for re-trigger does not care as long as it is shorter than a PPS period. > 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? The straight line slope, we call it 1/tau slope, is typically due to white phase noise and the counter time-quantization. Without going into details about how they mix, you often find that slew-rate limiting and non-ideal trigger-point can push this limit upwards. One reason for slew-rate limiting is low amplitude while the trigger point should be somewhere with a high slew-rate, that is quick change of voltage per time unit. The starting-point of ~0.25 s is due to time-base setting in your setup, and it would not surprise me if the different levels is due to slight different time-base settings. Avoid using the time-base like that using the trick above. Also, one should make sure that one get all the samples, they can play havoc with you. The slope ends when other noise-formms become strong enough to reach over the slope. We try to use better counters to push this slope downwards, such that we can see the other noises for shorter time-intervals. If you don't really care about ADEV until 100 s or so, you are fine. > 2) Why, after falling at the start, do the plots all seem to go back up > from ~100s to ~1000s? That's where thermmal of A/Cs, house heating etc. starts to come in. Also, the top part of the plot should not be too much trusted, it needs to run for a time to average out other noiseforms that obstruct the reading of a particular tau. Another way of saying this is that the confidence interval is very high for the top taus, and decreases. > 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? These probably is a combination of thermal and lack of convergence effects. I would try to redo the measurement as described above, you should get more consistent results. > 5) The pattern "Fall to a minimum point, then rise to a peak, then fall > again" seems to be prevalent. What does that indicate? Cyclic disturbances such as a house heater or A/C can create such patterns. > 6) Why does that pattern in question (5) seem to repeat sometimes? What is > that showing me? You should be looking at the phase-plot, I expect you to see a few cycles of some pattern there. As you look at different distances they self-correlate or not at different multiples of time, as cyclic or semi-cyclic patterns tend to do. ADEV was never made to handle such systematic noises, so you need to cancel them out as they form an disturbance to your measurement. > 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)? You can expect a 1/tau slpoe from the source, to can expect it to flatten out and you can expect an sqrt tau slope up before hitting the tau slope, which often is obstructed by the tau slope from linear drift of oscillator. The later usually settles down. The amplitude of these slopes represents the noise level of different noise types, but can only be seen once systematics have been reduced to negligable. > 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? The math behind these is kind of difficult if you are somewhat out of tune, but look at the Allan deviation wikipedia article, I tried to give some clues there. > 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. As it should be. Be patient, try to learn from mistakes and you will pick up and learn tricks of trade. What you have in toys suffice to learn a lot useful stuff and get hands on practice. Cheers, Magnus