Thanks to all who replied, and sorry for the delay. I was away and unfortunately unable to follow the discussion until today. >From Tom's comments and others I extract that the PM6681 can only be used for measuring the ADEV when employing the picket fence technique. A direct measurement is prevented by the counter's dead-time. Apart from a suitable divider, I'd probably need to write my own piece of software for massaging the data so that it can be used for an ADEV plot. Unless of course there is some software readily available that includes handling of the picket fence technique. My other idea of using two counters in lockstep, so that they measure alternate periods of the signal, hasn't been commented on. Is it a silly idea, apart from the fact that it needs two counters? Has anyone tried anything like it? Thanks and Cheers Stefan -----Ursprüngliche Nachricht----- Von: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] Im Auftrag von Tom Duckworth Gesendet: Samstag, 25. Oktober 2008 03:11 An: 'Discussion of precise time and frequency measurement' Betreff: Re: [time-nuts] Measuring ADEV with a PM6681 or CNT-81 Stefan, Well, I have been sort of staying out of the recent discussions regarding oscillator stability measurements, ADEV, etc., but here goes my two cents worth. I hope it doesn't muddy the waters too much and is somewhat helpful. There is a fundamental problem with trying to do ADEV (Allan Deviation) with a counter that has a gated measurement engine (all standard counters). The problem is that when the count engine gate closes (so the counter can compute the number of events, report the result as a frequency, and clear its registers), the counter is blind (dead time) to any signal at the input. Allan deviation REQUIRES than a minimum number of measurements be made back-to-back (no dead time between measurements) in order to capture nondeterministic fluctuations of the signal you're trying to measure. This requires a measuring device (counter) that continuously records ALL events. It does this by time-stamping a fixed period in a separate register in the counter along with the input register (the signal being measured), and a time-base register that records the frequency the signal is to be compared with. There is no 'gate' as such in a time-stamping counter. Most stability measurements, longer than say 100 seconds, are made in the frequency domain because energy changes, as a result of heat, are by far the predominate cause of stability (aging) issues (see below). Stability issues within shorter time periods, say <100 sec., are often nondeterministic, and cannot be accurately quantified in the frequency domain, but must be measured in the time domain, using statistical weighting. In other words, unpredictable, and often little understood, events (Shot and thermal noise in the active devices, random variations in the frequency-determining elements, cosmic rays, etc.) often predominate short term stability measurements and must be described statistically, as their occurrence and duration are random. Allan deviation is a widely accepted time-domain statistical measurement whose calculated results compare well with the more common frequency domain measurement of longer time periods. Allan deviation measurements are based on the sample variance of the fractional-frequency fluctuations. Without specifying the number of samples N, and the repetition interval T, for measurements of duration t, the measure of frequency stability is dimensionless and would converge to a meaningless limit. Secondly, some actual noise processes contain substantial fractions of the total noise power in the instantaneous fractional-frequency range below one cycle per year. In order to improve compatibility of data, it is important to specify a particular N and T. The Allan variance chooses N=2 and T=t (i.e. no dead time between measurements). A good estimate can be obtained by a limited number, m, of measurements (m=*100). Root Allen variance is expressed as a quantity divided by the square of the measurements of duration t, (i.e., 3 x 10-11/*t). . Classical variance diverges for commonly observed noise processes, such as random walk (i.e., the variance increases with an increasing number of data points). The advantage with the Allan variance is that it: * converges for all noise processes observed in precision oscillators; * has straightforward relationship to power law spectral density (spectral density of the frequency fluctuations); * is easy to compute, and; * is faster and more accurate in estimating noise processes than the Fast Fourier Transform. Aging in quartz crystal oscillators is caused by changes in either the quartz crystal itself or the associated components found in the oscillator assembly. Aging is the result of a combination of several factors having complex, and only partially understood, components that effect the aging specification. Effects can include the cut (orientation) of the crystal; vibration modes; frequency of cut size; temperature of operation and variations of temperature; drive energy; gravity; physical orientation; shock; electromagnetic interference; diffusion of impurities and the outgassing of the quartz crystal; the glass or ceramic base; the adhesive used to mount the quartz; metal migration from the electrodes into the quartz surface; stress relief of the crystal mounts; changes of electric component values over time; and, voltage regulation. This is probably more information than you really wanted, but oh well, enjoy. Tom Tom Duckworth 510-886-1396 -----Original Message----- From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On Behalf Of Heinzmann, Stefan (ALC NetworX GmbH) Sent: Friday, October 24, 2008 2:03 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Measuring ADEV with a PM6681 or CNT-81 Thanks, Tom! Apart from the specifics with TimeView, how does one go about measuring ADEV with a counter that does have a dead-time? Are there tricks that can be played, either with a special measurement setup or with some data postprocessing? Or with two counters that are somehow made to cooperate? Sorry if I'm asking the obvious, you can see that I'm a greenhorn. ;-) Cheers Stefan -----Ursprüngliche Nachricht----- Von: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] Im Auftrag von Tom Duckworth Gesendet: Donnerstag, 23. Oktober 2008 22:19 An: 'Discussion of precise time and frequency measurement' Betreff: Re: [time-nuts] Measuring ADEV with a PM6681 or CNT-81 Stefan, I am retired from Pendulum Instruments and could answer your question but I have instead refered your question to a current engineer with the company and you should receive an answer from them shortly. They are the experts for this question. Tom Tom Duckworth 510-886-1396 -----Original Message----- From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On Behalf Of Heinzmann, Stefan (ALC NetworX GmbH) Sent: Thursday, October 23, 2008 10:12 AM To: time-nuts@febo.com Subject: [time-nuts] Measuring ADEV with a PM6681 or CNT-81 Hi all, I hope you can clear up some confusion that I have regarding ADEV measurement. I was under the impression that you need a counter that is able to timestamp each rising edge of the clock under test, or equivalently measure period time continuously with no dead time. Now, while the CNT-90 can do this, the CNT-81 ( = PM6681 ) can't. Still, a message last December to the list here (http://www.mail-archive.com/time-nuts@febo.com/msg10963.html) seems to indicate that using TimeView you can have ADEV plotted with the "lesser" model, too. I have a PM6681 and TimeView, but I couldn't find out how to do it. Maybe it can't be done. So what's the deal on this? Can it be done, with or without TimeView, and if yes, how? If this has been answered earlier, a link would be just fine. Thanks and cheers Stefan _______________________________________________ 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.

Stefan, > Apart from a suitable divider, I'd.... If you a dedicated follower of PIC microcontrollers you find something suitable here on Tom's pages http://www.leapsecond.com/pages/ppsdiv/ Otherwise if you like AVRs then you can find something on my pages http://www.ulrich-bangert.de/html/downloads.html Suitable sine to ttl circuits designed by Bruce Griffiths are to be found at http://www.ko4bb.com/~bruce/CLKSHPR.html Best regards Ulrich > -----Ursprüngliche Nachricht----- > Von: time-nuts-bounces@febo.com > [mailto:time-nuts-bounces@febo.com] Im Auftrag von Heinzmann, > Stefan (ALC NetworX GmbH) > Gesendet: Donnerstag, 30. Oktober 2008 12:42 > An: Discussion of precise time and frequency measurement > Betreff: [!! SPAM] Re: [time-nuts] Measuring ADEV with a > PM6681 or CNT-81 > > > Thanks to all who replied, and sorry for the delay. I was > away and unfortunately unable to follow the discussion until today. > > From Tom's comments and others I extract that the PM6681 can > only be used for measuring the ADEV when employing the picket > fence technique. A direct measurement is prevented by the > counter's dead-time. Apart from a suitable divider, I'd > probably need to write my own piece of software for massaging > the data so that it can be used for an ADEV plot. Unless of > course there is some software readily available that includes > handling of the picket fence technique. > > My other idea of using two counters in lockstep, so that they > measure alternate periods of the signal, hasn't been > commented on. Is it a silly idea, apart from the fact that it > needs two counters? Has anyone tried anything like it? > > Thanks and Cheers > Stefan > > > -----Ursprüngliche Nachricht----- > Von: time-nuts-bounces@febo.com > [mailto:time-nuts-bounces@febo.com] Im Auftrag von Tom Duckworth > Gesendet: Samstag, 25. Oktober 2008 03:11 > An: 'Discussion of precise time and frequency measurement' > Betreff: Re: [time-nuts] Measuring ADEV with a PM6681 or CNT-81 > > Stefan, > > > > Well, I have been sort of staying out of the recent > discussions regarding oscillator stability measurements, > ADEV, etc., but here goes my two cents worth. I hope it > doesn't muddy the waters too much and is somewhat helpful. > > > > There is a fundamental problem with trying to do ADEV (Allan > Deviation) with a counter that has a gated measurement engine > (all standard counters). The problem is that when the count > engine gate closes (so the counter can compute the number of > events, report the result as a frequency, and clear its > registers), the counter is blind (dead time) to any signal at > the input. Allan deviation REQUIRES than a minimum number of > measurements be made back-to-back (no dead time between > measurements) in order to capture nondeterministic > fluctuations of the signal you're trying to measure. This > requires a measuring device (counter) that continuously > records ALL events. It does this by time-stamping a fixed > period in a separate register in the counter along with the > input register (the signal being measured), and a time-base > register that records the frequency the signal is to be > compared with. There is no 'gate' as such in a time-stamping counter. > > > > Most stability measurements, longer than say 100 seconds, are > made in the frequency domain because energy changes, as a > result of heat, are by far the predominate cause of stability > (aging) issues (see below). Stability issues within shorter > time periods, say <100 sec., are often nondeterministic, and > cannot be accurately quantified in the frequency domain, but > must be measured in the time domain, using statistical > weighting. In other words, unpredictable, and often little > understood, events (Shot and thermal noise in the active > devices, random variations in the frequency-determining > elements, cosmic rays, etc.) often predominate short term > stability measurements and must be described statistically, > as their occurrence and duration are random. Allan deviation > is a widely accepted time-domain statistical measurement > whose calculated results compare well with the more common > frequency domain measurement of longer time periods. > > > > Allan deviation measurements are based on the sample variance > of the fractional-frequency fluctuations. Without specifying > the number of samples N, and the repetition interval T, for > measurements of duration t, the measure of frequency > stability is dimensionless and would converge to a > meaningless limit. Secondly, some actual noise processes > contain substantial fractions of the total noise power in the > instantaneous fractional-frequency range below one cycle per > year. In order to improve compatibility of data, it is > important to specify a particular N and T. The Allan variance > chooses N=2 and T=t (i.e. no dead time between measurements). > A good estimate can be obtained by a limited number, m, of > measurements (m=*100). Root Allen variance is expressed as a > quantity divided by the square of the measurements of > duration t, (i.e., 3 x 10-11/*t). > > . > > Classical variance diverges for commonly observed noise > processes, such as random walk (i.e., the variance increases > with an increasing number of data points). The advantage with > the Allan variance is that it: > > * converges for all noise processes observed in precision > oscillators; > > * has straightforward relationship to power law > spectral density > (spectral density of the frequency fluctuations); > > * is easy to compute, and; > > * is faster and more accurate in estimating noise > processes than > the Fast Fourier Transform. > > > > Aging in quartz crystal oscillators is caused by changes in > either the quartz crystal itself or the associated components > found in the oscillator assembly. Aging is the result of a > combination of several factors having complex, and only > partially understood, components that effect the aging > specification. Effects can include the cut (orientation) of > the crystal; vibration modes; frequency of cut size; > temperature of operation and variations of temperature; drive > energy; gravity; physical orientation; > shock; electromagnetic interference; diffusion of impurities > and the outgassing of the quartz crystal; the glass or > ceramic base; the adhesive used to mount the quartz; metal > migration from the electrodes into the quartz surface; stress > relief of the crystal mounts; changes of electric component > values over time; and, voltage regulation. > > > > This is probably more information than you really wanted, but > oh well, enjoy. > > > > Tom > > Tom Duckworth > > 510-886-1396 > > > > > > -----Original Message----- > From: time-nuts-bounces@febo.com > [mailto:time-nuts-bounces@febo.com] On Behalf Of Heinzmann, > Stefan (ALC NetworX GmbH) > Sent: Friday, October 24, 2008 2:03 AM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Measuring ADEV with a PM6681 or CNT-81 > > > > Thanks, Tom! > > > > Apart from the specifics with TimeView, how does one go about > measuring ADEV with a counter that does have a dead-time? Are > there tricks that can be played, either with a special > measurement setup or with some data postprocessing? Or with > two counters that are somehow made to cooperate? > > > > Sorry if I'm asking the obvious, you can see that I'm a greenhorn. ;-) > > > > Cheers > > Stefan > > > > -----Ursprüngliche Nachricht----- > > Von: time-nuts-bounces@febo.com > [mailto:time-nuts-bounces@febo.com] Im Auftrag von Tom Duckworth > > Gesendet: Donnerstag, 23. Oktober 2008 22:19 > > An: 'Discussion of precise time and frequency measurement' > > Betreff: Re: [time-nuts] Measuring ADEV with a PM6681 or CNT-81 > > > > Stefan, > > > > I am retired from Pendulum Instruments and could answer your > question but I > > have instead refered your question to a current engineer with > the company > > and you should receive an answer from them shortly. They are > the experts for > > this question. > > > > Tom > > Tom Duckworth > > 510-886-1396 > > > > > > -----Original Message----- > > From: time-nuts-bounces@febo.com > [mailto:time-nuts-bounces@febo.com] On > > Behalf Of Heinzmann, Stefan (ALC NetworX GmbH) > > Sent: Thursday, October 23, 2008 10:12 AM > > To: time-nuts@febo.com > > Subject: [time-nuts] Measuring ADEV with a PM6681 or CNT-81 > > > > Hi all, > > > > I hope you can clear up some confusion that I have regarding ADEV > > measurement. I was under the impression that you need a > counter that is able > > to timestamp each rising edge of the clock under test, or equivalently > > measure period time continuously with no dead time. Now, > while the CNT-90 > > can do this, the CNT-81 ( = PM6681 ) can't. Still, a message > last December > > to the list here > > (http://www.mail-archive.com/time-nuts@febo.com/msg10963.html) > seems to > > indicate that using TimeView you can have ADEV plotted with > the "lesser" > > model, too. I have a PM6681 and TimeView, but I couldn't find > out how to do > > it. Maybe it can't be done. > > > > So what's the deal on this? Can it be done, with or without > TimeView, and if > > yes, how? If this has been answered earlier, a link would be > just fine. > > > > Thanks and cheers > > Stefan > > > > _______________________________________________ > > 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.

> Apart from a suitable divider And I have one PCB left for my divider if that's of interest ... Price as before GBP20 plus shipping (GBP12 outside UK) plus 5% Paypal tax! PS has anyone had a chance to measure the phase noise from my divider yet - I just don't have the tools to do it, and I know that a few of you suggested you'd look at that after building it. Cheers Dave -----Original Message----- From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On Behalf Of Heinzmann, Stefan (ALC NetworX GmbH) Sent: 30 October 2008 11:42 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Measuring ADEV with a PM6681 or CNT-81