John If you have the raw phase data, can you post a plot of what the well filtered freq offset looks like over that 10 day period? I've have found a properly filtered high resolution freq vs. time plot provides a lot more useful information than the couple of data numbers of a ADEV plot for evaluating long term performance of an Osc and helps separate all the many different possible causes of poor ADEV numbers. This is because then one can see the shape and magnitude of the Freq drift, therefore being able to see if the freq drift has a short term cycle due to temperature or if it is linear due to ageing or 2nd order due to still stabilizing or if it contains freq jumps due to 1/f flicker, or a single large jump due ...etc, etc. To be of any long term use, the freq data must be filtered over a long enough time period, such as a 1 hr running averaged, so the plot is more than just the 1 sec noise shown on most freq plots. The big avantage of using long term freq plot instead of a ADEV plot is the freq error is not noise but sytimatic errors which I have found to generally be the casse over longer time periods, then 10days worth of data can be use to prdict the what the future performance will be, compart that to what 10days of ADEV give, a lot of uncetaiy to even prdict what the one day drift will ber.if the Noise is not noise but due to Using a 10 day ws **************** John Ackermann N8UR jra at febo.com This isn't the real long-term stability test I'm planning to do, but I did let the measurement continue on the last unit I was testing (an Efratrom FRS-type) out to 10+ days, which should give fairly reasonable data out to 100K seconds. An ADEV plot is attached. I would ignore the last two plot points as there isn't enough data for them to be very meaningful. Bottom line is that Efratom specs the FRS units at <1e-10/day, and this one seems to do more than an order of magnitude better. But also looks like you need a lot more than 10 days data to draw any real conclusions; you can look at this plot and think that the ADEV is maybe heading back down after a peak near 1e-11. John

Hi Warren -- for these tests, I wasn't capturing raw data, jut using the tables and graphs that come out of the TSC box. John On Feb 18, 2012, at 11:57 PM, "ws at Yahoo" <warrensjmail-one@yahoo.com> wrote: > John > > If you have the raw phase data, can you post a plot of what the well filtered freq offset looks like over that 10 day period? > I've have found a properly filtered high resolution freq vs. time plot provides a lot more useful information than the couple of data numbers of a ADEV plot for evaluating long term performance of an Osc and helps separate all the many different possible causes of poor ADEV numbers. > This is because then one can see the shape and magnitude of the Freq drift, therefore being able to see if the freq drift has a short term cycle due to temperature or if it is linear due to ageing or 2nd order due to still stabilizing or if it contains freq jumps due to 1/f flicker, or a single large jump due ...etc, etc. > To be of any long term use, the freq data must be filtered over a long enough time period, such as a 1 hr running averaged, so the plot is more than just the 1 sec noise shown on most freq plots. > The big avantage of using long term freq plot instead of a ADEV plot is the freq error is not noise but sytimatic errors which I have found to generally be the casse over longer time periods, then 10days worth of data can be use to prdict the what the future performance will be, compart that to what 10days of ADEV give, a lot of uncetaiy to even prdict what the one day drift will ber.if the Noise is not noise but due to Using a 10 day > ws > **************** > > John Ackermann N8UR jra at febo.com > > This isn't the real long-term stability test I'm planning to do, but I > did let the measurement continue on the last unit I was testing (an > Efratrom FRS-type) out to 10+ days, which should give fairly reasonable > data out to 100K seconds. An ADEV plot is attached. I would ignore the > last two plot points as there isn't enough data for them to be very > meaningful. > > Bottom line is that Efratom specs the FRS units at <1e-10/day, and this > one seems to do more than an order of magnitude better. But also looks > like you need a lot more than 10 days data to draw any real conclusions; > you can look at this plot and think that the ADEV is maybe heading back > down after a peak near 1e-11. > > John > > _______________________________________________ > 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.

John said in part; > ignore the last two (ADEV) plot points as there isn't enough data for > them to be very meaningful. > you need a lot more than 10 days data to draw any real conclusions; IMHO, ADEV is not the right tool or even a very useful tool for evaluation the long term performance of these Rb Osc. Whenever possible, best to record the Raw data so other tools, such as available in TimeLab can be used to better compare the different Rbs. I have to wonder how many others notice ADEV's severe limitation in its able to reliable predict even 1 day in the future from 10 days worth of past data. Where as, ADEV is a great tool for measuring 1 sec noise, It is a poor tool to use for predicting future 1 day errors. This is especially true when the majority of the errors are due to measurable systematic things such as ageing and tempCo, as is the case with these Rb oscillators. This seems like a case of using the wrong tool for the job. ADEV's usefulness and power is its ability to predict future errors from past "random" Noise. For this, it helps to have at least a 10 to one and preferable a 100 to one ratio of raw data to tau. Because of the randomness of "Noise", in order to get good consistent ADEV results, The larger the ratio of recorded data to tau the better the answers. So to get a good consistent 1 sec ADEV answer, best to have 100 seconds or more of raw data. To get good 1 day ADEV answers from "noisy" data, would need to have 100 or so days worth of raw data. One of the ironic things of trying to use ADEV plots to predict long term future errors, is that during the 100 days of recording raw data, the systematic things that are causing the errors will have likely changed enough that the raw long data run may still be near useless to predict future errors over even the next day or two using ADEV. The ratio of time that raw data needs to be collected compared to future predicable time, can be greatly improved by using any number of more appropriate tools. By using something rather than ADEV, taking 10 days worth of the right data, one can then better predict the next 10 or even 100 days in the future when the major error sources are systematic rather than Random. from <http://en.wikipedia.org/wiki/Allan_variance> "The Allan variance is intended to estimate stability due to noise processes and not that of systematic errors or imperfections such as frequency drift or temperature effects" ws ******************** ----- Original Message ----- From: "John Ackermann N8UR" Subject: Re: [time-nuts] Update on Rb Performance Hi Warren -- for these tests, I wasn't capturing raw data, just using the tables and graphs that come out of the TSC box. John ************* On Feb 18, 2012, at 11:57 PM, "ws at Yahoo" > John > > If you have the raw phase data, can you post a plot of what the well > filtered freq offset looks like over that 10 day period? > > I've have found a properly filtered high resolution freq vs. time plot > provides a lot more useful information than the couple of data numbers of > a ADEV plot for evaluating long term performance of an Osc and helps > separate all the many different possible causes of poor ADEV numbers. > > This is because then one can see the shape and magnitude of the Freq > drift, therefore being able to see if the freq drift has a short term > cycle due to temperature or if it is linear due to ageing or 2nd order due > to still stabilizing or if it contains freq jumps due to 1/f flicker, or a > single large jump due ...etc, etc. > > To be of any long term use, the freq data must be filtered over a long > enough time period, such as a 1 hr running averaged, so the plot is more > than just the 1 sec noise shown on most freq plots. ... > ws > **************** > > John Ackermann N8UR jra at febo.com > > This isn't the real long-term stability test I'm planning to do, but I > did let the measurement continue on the last unit I was testing (an > Efratrom FRS-type) out to 10+ days, which should give fairly reasonable > data out to 100K seconds. An ADEV plot is attached. I would ignore the > last two plot points as there isn't enough data for them to be very > meaningful. > > Bottom line is that Efratom specs the FRS units at <1e-10/day, and this > one seems to do more than an order of magnitude better. But also looks > like you need a lot more than 10 days data to draw any real conclusions; > you can look at this plot and think that the ADEV is maybe heading back > down after a peak near 1e-11. > > John

There seems to be some confusion about stability and drift; about ADEV and other tools. The tone of this thread is not heading in a positive direction. So instead I will offer to put together a short tutorial or series of tutorials that focus on factual education and gracious explanation. Give me a few days. If any of you have a week or two of Rb raw data, however good or bad it looks, send it to me off-line and I'll add it to the mix of phase data that I already have for the worked examples. Thanks, /tvb

On 2/19/12 2:47 PM, Tom Van Baak wrote: > There seems to be some confusion about stability and drift; about > ADEV and other tools. The tone of this thread is not heading in a > positive direction. > > So instead I will offer to put together a short tutorial or series of > tutorials that focus on factual education and gracious explanation. > Most excellent.. I'm always looking for this kind of thing for new engineers at work..

Thank you, Tom. I REALLY look forward to your tutorials. How interesting and thought provoking for you to take your time(sic) for such. Thanks a million. -Don ------------------------------------------------------------- -----Original Message----- From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On Behalf Of Tom Van Baak Sent: Sunday, February 19, 2012 4:48 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Update on Rb Performance There seems to be some confusion about stability and drift; about ADEV and other tools. The tone of this thread is not heading in a positive direction. So instead I will offer to put together a short tutorial or series of tutorials that focus on factual education and gracious explanation. Give me a few days. If any of you have a week or two of Rb raw data, however good or bad it looks, send it to me off-line and I'll add it to the mix of phase data that I already have for the worked examples. Thanks, /tvb _______________________________________________ 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.