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: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] 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: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] 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: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] 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: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] 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: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On > > Behalf Of Heinzmann, Stefan (ALC NetworX GmbH) > > Sent: Thursday, October 23, 2008 10:12 AM > > To: [email protected] > > 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/[email protected]/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 -- [email protected] > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
