Re: [time-nuts] Allan variance Vs Plain Old Accuracy
On Thu, 14 Feb 2008 11:00:32 -, you wrote: Hi All, This comment is bound to get you all going. Maybe I'm being stupid, but why does everyone use Allan Variance and not plan old accuracy? I am very familiar with David Allan's full article on Allan Variance. However Allan Variance isn't the same as accuracy. Accuracy is what is important to most people. And that's not RMS but peak to peak, e.g worse case. And not averaged over 24 hours but averaged over 1 second or less. Something I rather miss is some good old phase or frequency plots - especially if done at different timescales - which seem to be becoming rather less common now. As well as having a plot of ADEV or its relations, seeing what the reference is doing and when is useful, and most ADEV plots using so few values of tau does not help. Angus. ___ 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] Allan variance Vs Plain Old Accuracy
Something I rather miss is some good old phase or frequency plots - especially if done at different timescales - which seem to be becoming rather less common now. As well as having a plot of ADEV or its relations, seeing what the reference is doing and when is useful, and most ADEV plots using so few values of tau does not help. Angus. Angus, I agree with you. Each representation has its merits and a combination of several is often necessary to tell the whole story. One feature (problem?) of ADEV is that it's a statistic and so some anomalies, clearly revealed in the phase or frequency domain, are hidden in the statistics. On the other hand, the ability of ADEV to resolve noise types, gives it a greater power than linear strip charts. A recent example of using all three graph types is here: http://www.leapsecond.com/pages/8607-drift/ On your comment about too few values of tau -- since adev is calculated by software tools these days, there is less reason to use only a few tau per decade. What I and others sometimes use is all tau or many tau where the tools calculate as many tau as necessary so that the plot is as close to a continuous, non-interpolated line as possible. For a well-behaved oscillator this is overkill (see above example) since all the points land on the line anyway, but for oscillators with any sort of periodic frequency modulation (e.g., an OCXO with bad tempco), the many tau method turns an adev plot into a sort of spectral plot. A cute example of the power of a many tau adev plot is here: http://www.leapsecond.com/museum/earth/ This is a free adev tool that calculates as many tau as you like: http://www.leapsecond.com/tools/adev1.htm /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.
Re: [time-nuts] Allan variance Vs Plain Old Accuracy
Steady boys and girls... This discussion would be fun however, I get the feeling it would only supply a marketing department with more copy. ___ 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] Allan variance Vs Plain Old Accuracy
Martyn, The stability of timing systems depends on both the type of fundamental noise processes in a timing distribution system and how the various processes spectrally combined through processes that shape noise such as clock servo loops and measurements system. Consider the noise processes of an oscillator which is a fundamental building block. Oscillator noise can be modeled effectively as a sum of power-law noise processes. Power law noise has a fixed slope when observed on a log-log spectral plot. When the slope is zero, the nose is simply white noise. White noise is well behaved statistically and we can describe stability using strait-forward concepts like standard-deviation or variance. Unfortunately oscillators exhibit other power-law noise that is not well behaved. For example, flicker noise (1/f) is a non-stationary divergent process. One cannot associate a simple standard-deviation or variance metric to a flicker noise process. Allan variance metrics address this issue by providing a theoretically sound means of extracting and estimate of the type of power-law noise processes present as well as the intensity. On a log-log Allan Variance plot, the type of noise is identified by the slope in the region the noise dominates. The intensity of the noise is identified by the position of the line. Allan variance is not a single metric but rather a family of metrics. New members of the family have been adopted over the years to address new modeling needs. Including TVAR, TDEV, MTIE and minTDEV. minTDEV might be interesting for many people on this list since it is used to measure stability of sync in a packet network !! Let me know if that helps, -Jeremy B. PS. What products did your friend test :-) -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Thursday, February 14, 2008 4:05 AM To: time-nuts@febo.com Subject: time-nuts Digest, Vol 43, Issue 33 Send time-nuts mailing list submissions to time-nuts@febo.com To subscribe or unsubscribe via the World Wide Web, visit https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts or, via email, send a message with subject or body 'help' to [EMAIL PROTECTED] You can reach the person managing the list at [EMAIL PROTECTED] When replying, please edit your Subject line so it is more specific than Re: Contents of time-nuts digest... Today's Topics: 1. Re: gps timing antennas (WB6BNQ) 2. Z3801A schematics? ([EMAIL PROTECTED]) 3. Re: gps timing antennas (Brian Kirby) 4. Re: Trimble Thunderbolt Rs-232 Levels (Didier Juges) 5. Re: gps timing antennas (Didier Juges) 6. Re: GPS Locked and Unlocked Performance Comparison (Didier Juges) 7. Allan variance Vs Plain Old Accuracy (Martyn Smith) 8. Re: GPS Locked and Unlocked Performance Comparison (Luis Cupido) -- Message: 1 Date: Wed, 13 Feb 2008 18:57:46 -0800 From: WB6BNQ [EMAIL PROTECTED] Subject: Re: [time-nuts] gps timing antennas To: Discussion of precise time and frequency measurement time-nuts@febo.com Message-ID: [EMAIL PROTECTED] Content-Type: text/plain; charset=us-ascii Hi Brian, Have you ever published your efforts with making the choke ring out of pie plates ? If so do you have that available with, hopefully, pictures, deminsions and so forth ? I have one of the Timing 2000 antennas. Did you use the choke ring pie plate with it ? thanks, 73BillWB6BNQ Brian Kirby wrote: The Motorola Timing 2000 and 3000 antennas are patch antennas. They have a pointed radome. The have very little ground plane, which reduces reception near the ground, which is desirable because of multipath effects.They also have quite a bit of filtering, so transmitting antennas near the units, will not affect them. If you are not having a problem with multipath, a regular patch type antenna probally from anybody should work well. If you are having multipath problems a timing antenna should help or a choke ring assembly should help. I have built choke rings out of pie plates, and Dr. Tom Clark made a basic choke assembly using a common electric junction box. I had problems with multipath because of mountains about 3/5 around my location. I changed the look angles so my receivers only receive above 20 degrees above the horizon and I use timing antennas now. Brian KD4FM Matt Ettus wrote: Is there really anything in particular which is different about the antenna requirements of timing receivers as compared to ordinary high-quality receivers? The timing antennas seem to be in pointy radomes, so that tells me they are probably quad-helixes rather than patch antennas. How is that advantageous for timing in particular? Thanks, Matt ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to
Re: [time-nuts] Allan variance Vs Plain Old Accuracy
At 06:00 AM 2/14/2008, Martyn Smith wrote... I have an article on my web site You might want to proof read that again. very gone Allan variance, and there's more. where I compare a OXCO based unit versus my rubidium's unit. Please explain how a counter resolves to .0003 cycles in a one second gate. A counter, well, counts. Counting involves natural numbers. Also, please tell us what time base was used on this unspecified counter for these measurements. ___ 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] Allan variance Vs Plain Old Accuracy
Modern counters have interpolators (now called time to digital converters) that can measure fractions of a cycle. Even the old Agilent 53132, designed 15 years ago, measures any frequency to 12 significant figures in one second. For example, it will display 10 MHz to .1 Hz using a 1 second gate time. Rick Karlquist N6RK Mike S wrote: At 06:00 AM 2/14/2008, Martyn Smith wrote... I have an article on my web site You might want to proof read that again. very gone Allan variance, and there's more. where I compare a OXCO based unit versus my rubidium's unit. Please explain how a counter resolves to .0003 cycles in a one second gate. A counter, well, counts. Counting involves natural numbers. Also, please tell us what time base was used on this unspecified counter for these measurements. ___ 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] Allan variance Vs Plain Old Accuracy
Martyn, I think you're comparing apples to oranges by mixing short term stability of a 10MHz source with long term stability of a time reference, since different processes are responsible for the observed variances. Your data suggests that the OXCO device you've characterized is orders of magnitude worse than the most recent devices Tom Van Baak posted data for. Am I missing something here? Pete Rawson ___ 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] Allan variance Vs Plain Old Accuracy
At 10:56 AM 2/14/2008, Richard (Rick) Karlquist wrote... Modern counters have interpolators (now called time to digital converters) that can measure fractions of a cycle. It appears he used an SRS620, which despite being called a counter, really measures a time interval, and then computes the frequency. Counter is a misnomer. I was just tweaking him a bit for giving conclusions based on measurements from an unstated instrument with an unstated timebase. ___ 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.
