[time-nuts] How can one measure ADEV of a good oscillator?
Just because it's a maser does not mean it has good ADEV. Masers use the hydrogen physics package to discipline an external oscillator just like a GPSDO uses GPS. So a maser can be considered to be a HDXO... hydrogen disciplined crystal oscillator. Your maser ADEV is only as good as its output oscillator/pll. Granted, if somebody is going to design a zillion dollar maser, they are probably going to use a decent output oscillator/pll. ___ 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] How can one measure ADEV of a good oscillator?
Hi The simple answer: 1) There are setups that increase the resolution of a counter 2) There are devices that are far more accurate at measuring frequency than a SR620 3) If you have three reasonably identical samples of a device you can indeed inter compare them once the resolution is there. Bob On Dec 1, 2014, at 2:09 AM, Dr. David Kirkby (Kirkby Microwave Ltd) drkir...@kirkbymicrowave.co.uk wrote: I think I have a flaw in my understanding of this. How can something like an SR620 measure the ADEV of an oscillator, if the oscillator is of a similar or better than the reference fed into the SR620? I see plots of ADEV for hydrogen masers, but I can't understand how this can be measured from the phase data unless the reference is better than the DUT, which is not going to be possible with a good hydrogen maser. I was thinking it might be possible if one has 3 oscillators and 3 time interval counters to perhaps solve 3 simultaneous equations. I can't prove that, but it seems intuitively correct. I must be missing something! Also I have seen graphs of both Allan variance and Allen deviation. Both are typically 10^-12 for a decent oscillator, but given the variance and standard deviation are related by a square root, they can't both be around 10^-12. I would expect to see values of 10^-6 or 10^-24, but I don't see such dramatic differences from 10^-12. If I see numbers around 10^-12 on an OCXO, is that the Allen variance or Allen Deviation? Dave ___ 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] How can one measure ADEV of a good oscillator?
Your maser ADEV is only as good as its output oscillator/pll. Upto the disciplining algorithm time constant, then it will be better. On Mon, Dec 1, 2014 at 9:07 AM, Mark Sims hol...@hotmail.com wrote: Just because it's a maser does not mean it has good ADEV. Masers use the hydrogen physics package to discipline an external oscillator just like a GPSDO uses GPS. So a maser can be considered to be a HDXO... hydrogen disciplined crystal oscillator. Your maser ADEV is only as good as its output oscillator/pll. Granted, if somebody is going to design a zillion dollar maser, they are probably going to use a decent output oscillator/pll. ___ 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] How can one measure ADEV of a good oscillator?
and then, for the second part of the question, the 10^-12 is an Allan deviation but usually the terms variance and deviation are unfortunately used one in place of the other. On Mon, Dec 1, 2014 at 1:41 PM, Bob Camp kb...@n1k.org wrote: Hi The simple answer: 1) There are setups that increase the resolution of a counter 2) There are devices that are far more accurate at measuring frequency than a SR620 3) If you have three reasonably identical samples of a device you can indeed inter compare them once the resolution is there. Bob On Dec 1, 2014, at 2:09 AM, Dr. David Kirkby (Kirkby Microwave Ltd) drkir...@kirkbymicrowave.co.uk wrote: I think I have a flaw in my understanding of this. How can something like an SR620 measure the ADEV of an oscillator, if the oscillator is of a similar or better than the reference fed into the SR620? I see plots of ADEV for hydrogen masers, but I can't understand how this can be measured from the phase data unless the reference is better than the DUT, which is not going to be possible with a good hydrogen maser. I was thinking it might be possible if one has 3 oscillators and 3 time interval counters to perhaps solve 3 simultaneous equations. I can't prove that, but it seems intuitively correct. I must be missing something! Also I have seen graphs of both Allan variance and Allen deviation. Both are typically 10^-12 for a decent oscillator, but given the variance and standard deviation are related by a square root, they can't both be around 10^-12. I would expect to see values of 10^-6 or 10^-24, but I don't see such dramatic differences from 10^-12. If I see numbers around 10^-12 on an OCXO, is that the Allen variance or Allen Deviation? Dave ___ 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.
Re: [time-nuts] How can one measure ADEV of a good oscillator?
On 11/30/2014 11:09 PM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote: I think I have a flaw in my understanding of this. How can something like an SR620 measure the ADEV of an oscillator, if the oscillator is of a similar or better than the reference fed into the SR620? What HP did with the 10811 was to make a few special crystals that were 500 Hz off frequency and build them into oscillators. These oscillators were mixed with the DUT and the 500 Hz beat note was then squared up and its ADEV measured with a frequency counter. After measuring a bunch of production line oscillators, they could establish a minimum ADEV that would be attributed to the offset oscillator. If this level of performance wasn't good enough, other offset crystals could be tried until a golden crystal was found. I was thinking it might be possible if one has 3 oscillators and 3 time interval counters to perhaps solve 3 simultaneous equations. I can't prove that, but it seems intuitively correct. In theory this makes sense, however, it would require a high offset crystal and a low offset crystal to do a 3 way round robin. There wasn't enough need to go to the trouble of having 2 crystal designs. There is an NBS paper written maybe 40 years ago explaining the magic of the beat note method. Rick Karlquist N6RK I must be missing something! Also I have seen graphs of both Allan variance and Allen deviation. Both are typically 10^-12 for a decent oscillator, but given the variance and standard deviation are related by a square root, they can't both be around 10^-12. I would expect to see values of 10^-6 or 10^-24, but I don't see such dramatic differences from 10^-12. If I see numbers around 10^-12 on an OCXO, is that the Allen variance or Allen Deviation? Dave ___ 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] How can one measure ADEV of a good oscillator?
Back in the day, you built two devices measured the noise and then assumed that they where so near each other that you just split the noise in two and assigned the same noise to them both. Doing the three-cornered hat allows you to make thee observations from three sources, so breaking the sums up you can extract the noise of each individual. Another trick is to use cross-correlation of two independent channels. The common source (DUT) is (idealy) the only signal correlating between the channels, so when accumulating measures, the noise of the two channels correlate out while common noise stays. Cross-correlation is a very strong method, as you can measure noise at or below your references noise, but you need to pay in measurement time. Cheers, Magnus On 12/01/2014 01:41 PM, Bob Camp wrote: Hi The simple answer: 1) There are setups that increase the resolution of a counter 2) There are devices that are far more accurate at measuring frequency than a SR620 3) If you have three reasonably identical samples of a device you can indeed inter compare them once the resolution is there. Bob On Dec 1, 2014, at 2:09 AM, Dr. David Kirkby (Kirkby Microwave Ltd) drkir...@kirkbymicrowave.co.uk wrote: I think I have a flaw in my understanding of this. How can something like an SR620 measure the ADEV of an oscillator, if the oscillator is of a similar or better than the reference fed into the SR620? I see plots of ADEV for hydrogen masers, but I can't understand how this can be measured from the phase data unless the reference is better than the DUT, which is not going to be possible with a good hydrogen maser. I was thinking it might be possible if one has 3 oscillators and 3 time interval counters to perhaps solve 3 simultaneous equations. I can't prove that, but it seems intuitively correct. I must be missing something! Also I have seen graphs of both Allan variance and Allen deviation. Both are typically 10^-12 for a decent oscillator, but given the variance and standard deviation are related by a square root, they can't both be around 10^-12. I would expect to see values of 10^-6 or 10^-24, but I don't see such dramatic differences from 10^-12. If I see numbers around 10^-12 on an OCXO, is that the Allen variance or Allen Deviation? Dave ___ 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.
Re: [time-nuts] How can one measure ADEV of a good oscillator?
Rick, On 12/01/2014 07:11 PM, Richard (Rick) Karlquist wrote: On 11/30/2014 11:09 PM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote: I think I have a flaw in my understanding of this. How can something like an SR620 measure the ADEV of an oscillator, if the oscillator is of a similar or better than the reference fed into the SR620? What HP did with the 10811 was to make a few special crystals that were 500 Hz off frequency and build them into oscillators. These oscillators were mixed with the DUT and the 500 Hz beat note was then squared up and its ADEV measured with a frequency counter. After measuring a bunch of production line oscillators, they could establish a minimum ADEV that would be attributed to the offset oscillator. If this level of performance wasn't good enough, other offset crystals could be tried until a golden crystal was found. I remember that HP had some simpler mixer-squarer box that could be used. Essentially the same as the NBS receiver chain. I was thinking it might be possible if one has 3 oscillators and 3 time interval counters to perhaps solve 3 simultaneous equations. I can't prove that, but it seems intuitively correct. In theory this makes sense, however, it would require a high offset crystal and a low offset crystal to do a 3 way round robin. There wasn't enough need to go to the trouble of having 2 crystal designs. There is an NBS paper written maybe 40 years ago explaining the magic of the beat note method. Thinking of the NBS phase-noise set or Dave Allans DTMF paper? 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] How can one measure ADEV of a good oscillator?
I think I have a flaw in my understanding of this. How can something like an SR620 measure the ADEV of an oscillator, if the oscillator is of a similar or better than the reference fed into the SR620? The key is to realize that all measurements are actually just comparisons: the instrument itself has no knowledge if the REF or your DUT is the better frequency source. If you use a SR620 to measure a TCXO then you are [mostly] measuring the DUT. If you use a SR620 to measure a cesium then you are [mostly] measuring the REF. I say mostly because no frequency standard is perfect, and the instrument itself contributes noise to the measurement. So strictly speaking, any measurement is always the sum of REF noise, instrument noise, and DUT noise. Never assume any of these are zero. I see plots of ADEV for hydrogen masers, but I can't understand how this can be measured from the phase data unless the reference is better than the DUT, which is not going to be possible with a good hydrogen maser. You measure a good hydrogen maser with a better hydrogen maser, or with another good hydrogen maser. The same is true if all you have a couple of OCXO. I was thinking it might be possible if one has 3 oscillators and 3 time interval counters to perhaps solve 3 simultaneous equations. I can't prove that, but it seems intuitively correct. Correct. That's what we do. And you can use more than 3 if you want. Also I have seen graphs of both Allan variance and Allen deviation. Both are typically 10^-12 for a decent oscillator, but given the variance and standard deviation are related by a square root, they can't both be around 10^-12. I would expect to see values of 10^-6 or 10^-24, but I don't see such dramatic differences from 10^-12. In the 70's it was common to [incorrectly] call it Allan variance. These days it is [correctly] called Allan deviation, or root Allan variance. Note that it's also called the two-sample variance/deviation, especially by mathematicians. If I see numbers around 10^-12 on an OCXO, is that the Allen variance or Allen Deviation? It's Allan deviation. Not Allen. Not variance. /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] How can one measure ADEV of a good oscillator?
Tom, On 12/01/2014 11:05 PM, Tom Van Baak wrote: I think I have a flaw in my understanding of this. How can something like an SR620 measure the ADEV of an oscillator, if the oscillator is of a similar or better than the reference fed into the SR620? The key is to realize that all measurements are actually just comparisons: the instrument itself has no knowledge if the REF or your DUT is the better frequency source. If you use a SR620 to measure a TCXO then you are [mostly] measuring the DUT. If you use a SR620 to measure a cesium then you are [mostly] measuring the REF. I say mostly because no frequency standard is perfect, and the instrument itself contributes noise to the measurement. So strictly speaking, any measurement is always the sum of REF noise, instrument noise, and DUT noise. Never assume any of these are zero. Indeed. You will need to learn the instruments limits, and assess when you are sufficiently away from the instrument or reference limits so that you to some degree can trust that your DUT is dominating the plot. Beyond the tools limits, the way you set things up can significantly impact your measurement. Also, some limitations such as drift may require you to compensate it to see the random noise behind the systematic signature. One trick to overcome the white-noise limit of the counter, is to plot the modified Allan deviation rather than the Allan deviation. This causes the white noise limit to have a 1/f^3 slope rather than a 1/f^2 slope which will have the effect of the measurement hitting the oscillator behavior at a lower tau than otherwise. You can gain more by making measure more often, as the modified Allan deviation is then given the oppertunity to even further surpress that noise. This also serve as a tool to verify that your measurement is indeed white-noise measurment limited. I see plots of ADEV for hydrogen masers, but I can't understand how this can be measured from the phase data unless the reference is better than the DUT, which is not going to be possible with a good hydrogen maser. You measure a good hydrogen maser with a better hydrogen maser, or with another good hydrogen maser. The same is true if all you have a couple of OCXO. I was thinking it might be possible if one has 3 oscillators and 3 time interval counters to perhaps solve 3 simultaneous equations. I can't prove that, but it seems intuitively correct. Correct. That's what we do. And you can use more than 3 if you want. Also I have seen graphs of both Allan variance and Allen deviation. Both are typically 10^-12 for a decent oscillator, but given the variance and standard deviation are related by a square root, they can't both be around 10^-12. I would expect to see values of 10^-6 or 10^-24, but I don't see such dramatic differences from 10^-12. In the 70's it was common to [incorrectly] call it Allan variance. These days it is [correctly] called Allan deviation, or root Allan variance. Note that it's also called the two-sample variance/deviation, especially by mathematicians. Allan deviation is the root square of the Allan variance. Any number you usually see listed is most likely the Allan deviation. There is uses for the Allan variance, but for most graphing purposes, we want the Allan deviation. Dave actually jokes himself about his Allan deviation. :) If I see numbers around 10^-12 on an OCXO, is that the Allen variance or Allen Deviation? It's Allan deviation. Not Allen. Not variance. Indeed. 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] How can one measure ADEV of a good oscillator?
HI On Dec 1, 2014, at 1:11 PM, Richard (Rick) Karlquist rich...@karlquist.com wrote: On 11/30/2014 11:09 PM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote: I think I have a flaw in my understanding of this. How can something like an SR620 measure the ADEV of an oscillator, if the oscillator is of a similar or better than the reference fed into the SR620? What HP did with the 10811 was to make a few special crystals that were 500 Hz off frequency and build them into oscillators. These oscillators were mixed with the DUT and the 500 Hz beat note was then squared up and its ADEV measured with a frequency counter. After measuring a bunch of production line oscillators, they could establish a minimum ADEV that would be attributed to the offset oscillator. If this level of performance wasn't good enough, other offset crystals could be tried until a golden crystal was found. Others did a similar thing by simply taking production OCXO’s to the limit of their EFC range. That let you do a coarse sort to find some number of “likely” units. Next step was to pop a few of them open and short this or that out to get a reasonable beat note. Numbers in the 10 to 20 Hz range were pretty common. After that a single mixer setup followed by a simple limiter got things good enough to screen the production lots. Bob I was thinking it might be possible if one has 3 oscillators and 3 time interval counters to perhaps solve 3 simultaneous equations. I can't prove that, but it seems intuitively correct. In theory this makes sense, however, it would require a high offset crystal and a low offset crystal to do a 3 way round robin. There wasn't enough need to go to the trouble of having 2 crystal designs. There is an NBS paper written maybe 40 years ago explaining the magic of the beat note method. Rick Karlquist N6RK I must be missing something! Also I have seen graphs of both Allan variance and Allen deviation. Both are typically 10^-12 for a decent oscillator, but given the variance and standard deviation are related by a square root, they can't both be around 10^-12. I would expect to see values of 10^-6 or 10^-24, but I don't see such dramatic differences from 10^-12. If I see numbers around 10^-12 on an OCXO, is that the Allen variance or Allen Deviation? Dave ___ 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.
Re: [time-nuts] How can one measure ADEV of a good oscillator?
On 12/1/2014 4:08 PM, Bob Camp wrote: Others did a similar thing by simply taking production OCXO’s to the limit of their EFC range. That let you do a coarse sort to find some number of “likely” units. Next step was to pop a few of them open and short this or that out to get a reasonable beat note. Numbers in the 10 to 20 Hz range were pretty common. After that a single mixer setup followed by a simple limiter got things good enough to screen the production lots. Bob I am fairly sure they would have done that if it was workable, to avoid special crystals. One rather huge problem with a 10 Hz beat note is that you are never going to measure ADEV at short (1 second) sample times that way. Rick N6RK ___ 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] How can one measure ADEV of a good oscillator?
Hi On Dec 1, 2014, at 7:23 PM, Richard (Rick) Karlquist rich...@karlquist.com wrote: On 12/1/2014 4:08 PM, Bob Camp wrote: Others did a similar thing by simply taking production OCXO’s to the limit of their EFC range. That let you do a coarse sort to find some number of “likely” units. Next step was to pop a few of them open and short this or that out to get a reasonable beat note. Numbers in the 10 to 20 Hz range were pretty common. After that a single mixer setup followed by a simple limiter got things good enough to screen the production lots. Bob I am fairly sure they would have done that if it was workable, to avoid special crystals. One rather huge problem with a 10 Hz beat note is that you are never going to measure ADEV at short (1 second) sample times that way. Correct. The technique was used for 1 second and longer ADEV screening. That’s what most of the specs were based on. Tight numbers at 1 second were rarely seen. For what ever reason, phase noise stopped at 1 or 10 Hz and ADEV went from 1 second out to longer tau. Bob Rick N6RK ___ 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] How can one measure ADEV of a good oscillator?
I think I have a flaw in my understanding of this. How can something like an SR620 measure the ADEV of an oscillator, if the oscillator is of a similar or better than the reference fed into the SR620? I see plots of ADEV for hydrogen masers, but I can't understand how this can be measured from the phase data unless the reference is better than the DUT, which is not going to be possible with a good hydrogen maser. I was thinking it might be possible if one has 3 oscillators and 3 time interval counters to perhaps solve 3 simultaneous equations. I can't prove that, but it seems intuitively correct. I must be missing something! Also I have seen graphs of both Allan variance and Allen deviation. Both are typically 10^-12 for a decent oscillator, but given the variance and standard deviation are related by a square root, they can't both be around 10^-12. I would expect to see values of 10^-6 or 10^-24, but I don't see such dramatic differences from 10^-12. If I see numbers around 10^-12 on an OCXO, is that the Allen variance or Allen Deviation? Dave ___ 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.
