Re: [time-nuts] Measuring short term stability minus linear drift
On 08/10/11 06:32, Rick Karlquist wrote: I want to measure the short term stability of a source with substantial linear drift. I would like some measure of stability along the lines of Allan deviation, but I only want to measure the noise and ignore the drift. AFAIK, ADEV treats linear drift like a form of noise. Has this problem been solved before? Yes. Any ideas? Oh yes. Record your time-stamps (say using TimeLab). Use HDEV plot as a first approximation, as it will remove first degree linear drift. If this drift does not meet your needs (for high taus higher degrees of drift leaks through even HDEV), then on a copy of the raw data use a high degree curve-matching (again TimeLab can do this for you) and remove the matched trend. Use ADEV on the resulting value. Use ADEV and MADEV to separate between WPM and FPM levels. Look at the Allan Variance article on Wikipedia, and you will find more about it there, but also references to online manuals such as NIST Special Publication 1067 for instance. Cheers, Magnus ___ 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.
Re: [time-nuts] Measuring short term stability minus linear drift
On 10/7/11 9:32 PM, Rick Karlquist wrote: I want to measure the short term stability of a source with substantial linear drift. I would like some measure of stability along the lines of Allan deviation, but I only want to measure the noise and ignore the drift. AFAIK, ADEV treats linear drift like a form of noise. Has this problem been solved before? Any ideas? what if you (least squares?) fit a straight line to the frequency measurement data, remove that, then look at ADEV? We do something similar with testing deep space transponders which will be handling a signal with varying Doppler so our test signal is varying in frequency. ___ 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.
Re: [time-nuts] Measuring short term stability minus linear drift
On 08/10/11 16:45, Jim Lux wrote: On 10/7/11 9:32 PM, Rick Karlquist wrote: I want to measure the short term stability of a source with substantial linear drift. I would like some measure of stability along the lines of Allan deviation, but I only want to measure the noise and ignore the drift. AFAIK, ADEV treats linear drift like a form of noise. Has this problem been solved before? Any ideas? what if you (least squares?) fit a straight line to the frequency measurement data, remove that, then look at ADEV? We do something similar with testing deep space transponders which will be handling a signal with varying Doppler so our test signal is varying in frequency. This is what a simple fit does or HDEV does. The benefit of higher degrees fit is that it would cause better fits and high tau ADEV values will be less poluted by the weaker terms. For first degree effect, swap between ADEV and HDEV. For second degree effect, use quadratic fit and ADEV that. You still want to know the systematic behaviour and how those systematic effects behave, but it would be fairly ridicolous to teach you Rick on the merits of that. Cheers, Magnus ___ 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.
Re: [time-nuts] Measuring short term stability minus linear drift
what if you (least squares?) fit a straight line to the frequency measurement data, remove that, then look at ADEV? We do something similar with testing deep space transponders which will be handling a signal with varying Doppler so our test signal is varying in frequency... ...and with frequency being the first derivative of phase use a least squares quadratic fit for phase data! Easily done with the tools that John has mentioned. Best regards Ulrich -Ursprungliche Nachricht- Von: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] Im Auftrag von Jim Lux Gesendet: Samstag, 8. Oktober 2011 16:45 An: time-nuts@febo.com Betreff: [?? Probable Spam] Re: [time-nuts] Measuring short term stability minus linear drift On 10/7/11 9:32 PM, Rick Karlquist wrote: I want to measure the short term stability of a source with substantial linear drift. I would like some measure of stability along the lines of Allan deviation, but I only want to measure the noise and ignore the drift. AFAIK, ADEV treats linear drift like a form of noise. Has this problem been solved before? Any ideas? what if you (least squares?) fit a straight line to the frequency measurement data, remove that, then look at ADEV? We do something similar with testing deep space transponders which will be handling a signal with varying Doppler so our test signal is varying in frequency. ___ 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.
Re: [time-nuts] Measuring short term stability minus linear drift
On 10/8/11 7:56 AM, Magnus Danielson wrote: On 08/10/11 16:45, Jim Lux wrote: On 10/7/11 9:32 PM, Rick Karlquist wrote: I want to measure the short term stability of a source with substantial linear drift. I would like some measure of stability along the lines of Allan deviation, but I only want to measure the noise and ignore the drift. AFAIK, ADEV treats linear drift like a form of noise. Has this problem been solved before? Any ideas? what if you (least squares?) fit a straight line to the frequency measurement data, remove that, then look at ADEV? We do something similar with testing deep space transponders which will be handling a signal with varying Doppler so our test signal is varying in frequency. This is what a simple fit does or HDEV does. The benefit of higher degrees fit is that it would cause better fits and high tau ADEV values will be less poluted by the weaker terms. For first degree effect, swap between ADEV and HDEV. For second degree effect, use quadratic fit and ADEV that. You still want to know the systematic behaviour and how those systematic effects behave, but it would be fairly ridicolous to teach you Rick on the merits of that. Yeah, but it's always nice to know how other people do it and if someone has published something somewhere with more analysis. I find that at JPL (and I assume others have found this too) that we'll go off and reinvent the wheel (maybe because we're working in parallel ignorance) for something. And a lot of times, especially if it's in service of a get the hardware tested and delivered the analytical backup for whatever we did may not be as rigorous as one might like. There's also the classic gap between the groups doing theoretical work in one building and groups building and testing hardware in another building 1000 meters away, and the two groups never have time to meet, and in some cases, may not even be aware of the other's existence. This is especially true when you're talking about early career hires (aka fresh-outs). These days, with tight budgets, you may not be able to put two people on a job (one senior, one junior) which would provides some of that knowledge transfer.(to be honest, I don't know that it's much worse than it ever was.. tight budgets are a perennial complaint since they were building pyramids in Egypt) ___ 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.
Re: [time-nuts] Measuring short term stability minus linear drift
On 08/10/11 17:16, Jim Lux wrote: On 10/8/11 7:56 AM, Magnus Danielson wrote: On 08/10/11 16:45, Jim Lux wrote: On 10/7/11 9:32 PM, Rick Karlquist wrote: I want to measure the short term stability of a source with substantial linear drift. I would like some measure of stability along the lines of Allan deviation, but I only want to measure the noise and ignore the drift. AFAIK, ADEV treats linear drift like a form of noise. Has this problem been solved before? Any ideas? what if you (least squares?) fit a straight line to the frequency measurement data, remove that, then look at ADEV? We do something similar with testing deep space transponders which will be handling a signal with varying Doppler so our test signal is varying in frequency. This is what a simple fit does or HDEV does. The benefit of higher degrees fit is that it would cause better fits and high tau ADEV values will be less poluted by the weaker terms. For first degree effect, swap between ADEV and HDEV. For second degree effect, use quadratic fit and ADEV that. You still want to know the systematic behaviour and how those systematic effects behave, but it would be fairly ridicolous to teach you Rick on the merits of that. Yeah, but it's always nice to know how other people do it and if someone has published something somewhere with more analysis. I do it when I care about it. HDEV gives me the quick view I need as the first degree effect dominates typically. However, I often find that environmental aspects kick in and I still lack a good tool to combat them. I find that at JPL (and I assume others have found this too) that we'll go off and reinvent the wheel (maybe because we're working in parallel ignorance) for something. And a lot of times, especially if it's in service of a get the hardware tested and delivered the analytical backup for whatever we did may not be as rigorous as one might like. That would not put you in a very unique position. There's also the classic gap between the groups doing theoretical work in one building and groups building and testing hardware in another building 1000 meters away, and the two groups never have time to meet, and in some cases, may not even be aware of the other's existence. This is especially true when you're talking about early career hires (aka fresh-outs). These days, with tight budgets, you may not be able to put two people on a job (one senior, one junior) which would provides some of that knowledge transfer. (to be honest, I don't know that it's much worse than it ever was.. tight budgets are a perennial complaint since they were building pyramids in Egypt) You do not need to have the senior sitting with each junior engineer, but available at need, down the hall, meet over coffie-breaks. Creating the environment that asking stupid questions is better than asking no questions, and once the stupid questions are out the more initiated come along... that how we do it and by raising the level of others, they stop pestering me with stupid stuff, we get much higher level questions and fewer trouble reports but of higher quality. Cheers, Magnus ___ 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.
Re: [time-nuts] Measuring short term stability minus linear drift
-Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts- boun...@febo.com] On Behalf Of Rick Karlquist Sent: Friday, October 07, 2011 9:32 PM To: Discussion of precise time and frequency measurement Subject: [time-nuts] Measuring short term stability minus linear drift I want to measure the short term stability of a source with substantial linear drift. I would like some measure of stability along the lines of Allan deviation, but I only want to measure the noise and ignore the drift. AFAIK, ADEV treats linear drift like a form of noise. Has this problem been solved before? Any ideas? Use TimeLab, Plotter, Stable32, or any other graphing application that supports Hadamard deviation. Any of these apps will also let you subtract the linear or quadratic trend from the data itself... but if all you want to do is view ADEV without the effects of drift, HDEV will do that. -- 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.
Re: [time-nuts] Measuring short term stability minus linear drift
I want to measure the short term stability of a source with substantial linear drift. I would like some measure of stability along the lines of Allan deviation, but I only want to measure the noise and ignore the drift. AFAIK, ADEV treats linear drift like a form of noise. Has this problem been solved before? Any ideas? Rick Karlquist Right, ADEV will suffer with linear drift. Plot the frequency first to see how linear the drift is. If it looks like you expect (that is, mostly a straight line) then it's safe to remove it from the raw data with a quadratic least squares fit. Then compute ADEV on the residuals. Another way it to use HDEV on the raw data. Let me know if you want the command line tools I use for all this. The other suggestion is to use John Miles' TimeLab. /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.
