Hi, If you have a GPSDO, then PPS as re-generated from the locked oscillator is naturally less noisy than straight from the GPS. Using a PICDIV helps you to use another reference instead, and the TADD-2 is a useful option to consider.
I have my TADD-2:s modified such that one of the outputs is the input clock buffered, which is a simple wire from the clock input of the PIC over to one of the output drivers. This gives better jitter performance than feeding a 5 MHz or 10 MHz sine straight into a TIC channel. However, the important is that you start measure. Even somewhat imperfect measures is better than nothing, and taking several measures as you do, I think you will see a pattern re-emerge in them as being the tell-tail of your measurement limits. Consider that single-shot resolution and white noise has a 1/tau slope on them, so eventually you go down to the combination of the actual DUT and GPS noise, rather than that of the PPS placement. Cheers, Magnus On 2020-03-01 01:25, Taka Kamiya via time-nuts wrote: > YES, please. [email protected]. > So far, I've taken HP105B and did adev frequency reading based, T.I. based > adev, and while at it, I am doing PRS-10 T.I. based. > I have a question. My 1 second reference for channel A is coming from GPS > based 1 second. I understand it's only 10E-8 precision on second to second > basis? Is this sufficient for OCXO and Rb based oscillators? > > --------------------------------------- > (Mr.) Taka Kamiya > KB4EMF / ex JF2DKG > > > On Saturday, February 29, 2020, 7:21:28 PM EST, Magnus Danielson > <[email protected]> wrote: > > Hi, > > On 2020-02-29 23:10, Taka Kamiya via time-nuts wrote: >> One question for Magnus. >> >> Ch A start - pps (standard)Ch B stop - DUT >> On item 4, you said "frequency of the signal on time B". That much is >> obvious. But then you said: "give it the time-base of the period on the >> A-channel". Will you explain this? >> Say I give 1 Hz, period is 1s. Say I give 10Hz, period is 0.1s. Is this >> what you mean? > Yes. Exactly. >> I'm using HP5370A. This instruction is valid on this TI counter, correct?? > Yes. It will work. >> A request for everyone: >> I am conducting an one hour measurement on HP105B. Does anyone have 1 hour >> plot of this signal generator handy? If so, will you DM me a copy? For >> some reason, I cannot find one on the great Internet. > I have one of the 00105 oscillator ,as mounted and free-running in a > HP5065A, against hydrogen maser at hand. I can locate that and send you > if you wish. It's longer than 1 hour, but you get additional precision > from this. > > Cheers, > Magnus > >> ------------------- clip from Magnus's previous email------------------ >> A setup I use a lot is this: >> 1) Connect a reference oscillator to produce a 1 Hz or 10 Hz signal and >> feed into a counter Channel A/TI-start channel. For PPS signals, I make >> sure to trigger a but up on the rising edge not to false-trigger. For >> some counters this means turning of automatic trigger and set it to 1 V >> manually. It is important that no false triggers occurs. >> >> 2) Connect a signal under test to Channel B/TI-stop. Adjust trigger to >> through-zero or up on the edge as suitable. >> >> 3) TI-mode, continuous trigger >> >> 4) Collect data in TimeLab, give TimeLab the frequency of the signal on >> B-channel, give it the time-base of the period on the A-channel. >> >> 5) Look at data as it comes in. Look at phase view, frequency view, >> wrapped phase. Look at the ADEV, how the upper end flaps with data, but >> how the same tau becomes more and more stable as it comes >> in.--------------------- >> --------------------------------------- >> (Mr.) Taka Kamiya >> KB4EMF / ex JF2DKG >> >> >> On Friday, February 21, 2020, 9:26:47 PM EST, Magnus Danielson via >> time-nuts <[email protected]> wrote: >> >> Hi Taka, >> >> On 2020-02-21 23:26, Taka Kamiya via time-nuts wrote: >>> I'm sorry, I messed up. I jumped on more advance topic than I intended. >>> I'm sure there were answers in the replies but they must have gone way over >>> my head because some of original questions still remain. I bulletized (is >>> that a word?) the original question with my NEW understanding. Would >>> someone please respond for me, point-to-point? >> No problem. No worries. I hope you end up reading these and the other >> replies again and acquire good knowledge. I know it's like drinking from >> a fire-hoze, but you did ask some very relevant and fair questions. >>> 1) A frequency counter that measures DUT basically puts out a reading >>> every second during the measurement. When TimeLab is well into 1000s or >>> so, it is still reading every second; it does not change the gate time to >>> say, 1000s. I understand now, Adev is about phase, not the frequency. But >>> assuming DUT is sine wave, if there is enough phase change, frequency do >>> change. I think of phase change as frequency change that is less than full >>> cycle. So how does counters that outputs every 1 second end up in tau of >>> 1000s? It will entirely miss phase change that spans more than 1 cycle. >> ADEV is about the frequency stability. ADEV can be calculated using >> phase or frequency measures. We tend to prefer using phase measures from >> Time-Interval Counters for these things. >> >> OK, so let's say that we want to output a counter which provides output >> of frequency estimates but for a time-base which is longer than 1 s, >> even if we output results every 1 s? >> >> Classically counters could not do that. You acquired a start-value, >> waited the time-base, acquired a stop-value, calculated a result to >> display and then arm to get a new start-value for the next result. Such >> counters will have a limit that the rate of readings will be limited by >> the time-base, so if it is set to 10 s, only every 10 s and output is >> produced. >> >> To tackle this, one needs a counter that can interleave frequency >> measurements, so that it generates new start-points at the update rate >> even if the stop-point has not occurred. So, for a time-base of 10 s and >> an update rate of 1 s, then every 1 s a new start-trigger is produced, >> and then remembered until a stop trigger can be produced, at which time >> the start-trigger 10 s back is used to estimate the frequency. In fact, >> for this to work, the stop trigger time-stamp is also the start trigger >> time-stamp for a new measurement. You can do this with any time-base >> really, and the degree of interleaving only depends on the number of >> start-points one can keep in memory. >> >>> 2) I recall reading on TICC manual, in time interval mode, anything that's >>> reasonably good is good enough, because it has time stamp and the count >>> reading. Clock is used to chunk the data. Is this still true? Through >>> this discussion, I ended up with conclusion that there is no inherent >>> advantage over TI measurement when compared to frequency measurement. Am I >>> understanding this correctly? >> There is benefits in time-measures over frequency measures when one >> monitors long-term properties. Also, as one tries to create a >> phase-curve from frequency estimates, any rounding off errors show in an >> slope, as there is a tiny average frequency offset from round-offs. Only >> really good such setups does not have significant slope. >> >>> 3) I understand even the BEST counter is only good for Adev nE-12 >>> measurement. Then, with my collection of counters, HP53132A (which averages >>> tons of short period measurement), 5335A (not enough resolution), HP5370A >>> (interval reading is no better than frequency), TICC by TAPR, Do I even >>> have a chance of doing any meaningful work? (say work with GPSDO and Rb >>> which some of it does reach E-13) Yes, I know now, it is NOT possible to >>> do 1 sec Adev but say over 100 seconds? Right now, I don't have any >>> standard that has adev that good at 1 sec anyway. >> The resolution of your counter tells you about where your 1/tau curve >> will cut tau = 1 s, and it goes from there. There is a slight scaling >> factor, but if we assume it is 1 for now, it is pretty simple. Your >> 5335A has 1 ns single-shot resolution, this gives 1E-9 at 1 s, but 1E-10 >> at 10 s, 1E-11 at 100 s and 1E-12 at 1000 s. You see very clearly when >> the linear slope ends and "lands" in the noise, at which time the noise >> becomes dominant and is giving you the interesting reading. The 5370A is >> 20 ps single-shot resolution, giving you a whopping 2E-11 at 1 s, 2E-12 >> at 10 s, 2E-13 at 100 s and 2E-14 at 1000 s. It's some serious >> improvement. You are more likely to be limited by your oscillators as >> ref and under test at 1000 s with that one, than the instrument itself. >> >>> 4) Would one person who has infinite patience and experience guide me >>> through getting one reading done correctly with what I already have? That >>> may include email and phone call. (I speak English and Japanese) I don't >>> want to lower S/N of this mailing list by doing this here. >> I think you have contributed by asking some really good questions. >> >> A setup I use a lot is this: >> >> 1) Connect a reference oscillator to produce a 1 Hz or 10 Hz signal and >> feed into a counter Channel A/TI-start channel. For PPS signals, I make >> sure to trigger a but up on the rising edge not to false-trigger. For >> some counters this means turning of automatic trigger and set it to 1 V >> manually. It is important that no false triggers occurs. >> >> 2) Connect a signal under test to Channel B/TI-stop. Adjust trigger to >> through-zero or up on the edge as suitable. >> >> 3) TI-mode, continuous trigger >> >> 4) Collect data in TimeLab, give TimeLab the frequency of the signal on >> B-channel, give it the time-base of the period on the A-channel. >> >> 5) Look at data as it comes in. Look at phase view, frequency view, >> wrapped phase. Look at the ADEV, how the upper end flaps with data, but >> how the same tau becomes more and more stable as it comes in. >> >> Using even old counters this setup have helped a lot for many measures. >> It is simple and sturdy for many measures. Remember to save traces, to >> annotate it carefully so one can understand afterwards what one did. >> >> Using this setup, I swapped a HP53132A (150 ps) for a HP5335A (1 ns) and >> then PM6853A (2 ns) to show that a particular problem did not needed the >> best counter in the house to be well characterized. >> >>> 5) One time, it was mentioned many of Adev graphs posted are basically a >>> graph of instruments noise graph. How do I tell when a given reading/graph >>> is exceeding the limit of a setup? I did do base line where same signal >>> goes to counter's reference input and signal input. I always have that on >>> my chart so traces does not go below. Is that enough? >> Almost. It's a good start. The first slope for lower taus is due to the >> instrument for sure. If you look carefully you will notice that the >> actual performance shifts around, because it is more complex than just >> being instrument limit, but it is the right ball-park for that part of >> the plots. For the upper end, you can be limited by your device under >> test drift. This can be handled by simply letting them be turned on >> longer. Sub-sequent measurement will have that rising slope move more >> and more towards higher taus and thus becomming less like a limit-issue >> for a certain tau. >>> I appreciate everyone's input. I am learning a lot but just not digesting >>> well enough. I'd like to do DMTD after I understand the basics. >> Good spirit. DMTD takes some care, but once you learned it, it can be a >> magnificent tool. >> >> Cheers, >> Magnus >> >>> --------------------------------------- >>> (Mr.) Taka Kamiya >>> KB4EMF / ex JF2DKG >>> >>> >>> On Thursday, February 20, 2020, 1:41:06 PM EST, Taka Kamiya via >>> time-nuts <[email protected]> wrote: >>> >>> I have a question concerning frequency standard and their Allen >>> deviation. (to measure Allen Dev in frequency mode using TimeLab) >>> >>> It is commonly said that for shorter tau measurement, I'd need OCXO because >>> it's short tau jitter is superior to just about anything else. Also, it is >>> said that for longer tau measurement, I'd need something like Rb or Cs >>> which has superior stability over longer term. >>> Here's the question part. A frequency counter that measures DUT basically >>> puts out a reading every second during the measurement. When TimeLab is >>> well into 1000s or so, it is still reading every second; it does not change >>> the gate time to say, 1000s. >>> That being the case, why this consensus of what time source to use for what >>> tau? >>> I recall reading on TICC, in time interval mode, anything that's reasonably >>> good is good enough. I'm aware TI mode and Freq mode is entirely >>> different, but it is the same in fact that measurement is made for very >>> short time span AT A TIME. >>> I'm still trying to wrap my small head around this. >>> >>> --------------------------------------- >>> (Mr.) Taka Kamiya >>> KB4EMF / ex JF2DKG >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>> and follow the instructions there. >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>> and follow the instructions there. >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
