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" <jster...@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-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.
