Re: [time-nuts] Oscilloscope-based measurements of frequency stability
Hello Dana, thank you for your detailied description. I will try this out in the next days. Scopes became a right normal permanent instrument in the electronics lab of time-nuts like a multimeter for the electrician. Before I connect a counter onto a signalsource which I want to characterize I am first looking with the scope on it. A few month ago I built an dual card for a quarz ofen oscillator from Eb... After measuring the output frequency on both channels I was wondering why this one gave absolute nonsense instead of the expected 10 MHz count. After some experiments I hooked on the scope and looked on the signaltrace. Instead of a pure sinusoidal signal which I assumed the scope showed a totally distorted multisinusoidal signal which had no definitive wavelength but a overlapped form with several peaks like a modulated sinusoidal carrier wave mixed with with another sinusoidal signal with a frequency relation of 10 : 1. After rerouting some circuit tracks and optimizing the shielding the effect was gone. So this was the reason why my scope became an every time instrument in my lab. -- mit freundlichen Gruessen - with best Regards Christoph Kopetzky Am 07.10.2018 um 23:03 schrieb Dana Whitlow: Hello, Here is the promised discussion (from about a week ago) of my scheme for using a DSO to capture the information needed to produce detailed plots of phase and frequency modulations of a noisy source under test. Alas, the method is apparently inadequate for characterizing a source as quiet as I feel I need for some future experiments, but I felt that the method itself (if implemented with better equipment) could be of interest as an alternative to TIC-based methods. The text file also includes some discussion of a different method that I feel will probably be better suited to my future needs. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Oscilloscope-based measurements of frequency stability
yes and 1 ppt is 1 E-12 In a message dated 10/2/2018 3:30:31 PM Eastern Standard Time, k8yumdoo...@gmail.com writes: Hello Bert, What is the cyan-colored trace seen in these screen shots? And is "1 ppt" the same as 1E-12 (just to be sure)? Are these from LH? Thanks, Dana On Tue, Oct 2, 2018 at 1:46 PM ew via time-nuts wrote: > We see the glitches all the time, they exist and with proper equipment are > very visible. These are telecom timing devices and the way they correct the > 1 pps is by changing the frequency. Even LH shows it and it is very visible > when you eliminate the other traces.What we call the Tbolt 2, the nicely > packaged Trimle that also was part of the fraud listing does the correction > once an hour. It is exact an hour function of when you powered it up.In my > case night time spikes where mostly negative Air conditioner. Recovery is a > function of the accumulated error. Standing next to it in front of my 19 > year old M300 it did effect the recovery since my legs where within a > foot. One picture shows the analog trace to.Original Tbolt does it > constantly. We have spend a couple of years on this, hoping to optimize a > clean up loop.so far no good results.Bert Kehren > In a message dated 10/2/2018 1:04:50 PM Eastern Standard Time, > tsho...@gmail.com writes: > > Dana, the short term few-ns jitter of the two phases, I think in a digital > instrument is most likely data acquisition glitches. > > Even on a good old analog scope, jitter in the trigger circuit or jitter in > amplitudes (with resulting changes in harmonic content and thus the shape > of the curves) can cause the apparent zoomed in zero crossing to shift very > similarly. > > In days of old the telco standards for frequency stability also included > requirements for amplitude stability noise, directly related to making > repeatable measurements using scopes. I'm gonna see if I can find some of > those. I remember some crazy looking telco standard that required measuring > amplitude noise on time scales measured in weeks. > > Tim N3QE > > On Mon, Oct 1, 2018 at 8:47 AM Dana Whitlow wrote: > > > I cheered when I saw Dave B's "silly question", for > > then I realized that I'm not the only one who likes > > to measure things with an o'scope. > > > > I had purchased a GPSDO a few weeks before and > > had been observing its behavior relative to a free- > > running Rb by watching 10 MHz sinewaves drift with > > respect to each other as an aid in setting the Rb's > > frequency. However, I was seeing enough fairly > > rapid random drift to limit the usefulness of this kind > > of observation. It dawned on me that I was sometimes > > seeing drifts of several ns over the course of just > > several seconds, thus implying that sometimes the > > relative frequency error between the two sources was > > reaching as high as roughly 1E-9. I wanted to be able > > to capture and plot a somewhat extended run of data > > so I could try to understand this behavior better. > > > > Being TIC-less, I decided to see what I could do with > > my o'scope, which is a Chinese-made 2-channel DSO > > with synchronous sampling by the two channels and > > with a respectable trace memory depth (28 MSA per > > channel). > > > > I began this effort in earnest a couple of days before I > > saw Dave's question, and have only now brought it to > > a sufficient state of completion to feel justified in reporting > > some results. > > > > I am presently able to record about 45 minute's worth of > > data as limited by the 'scope's trace memory, but my XP > > computer's RAM space limits me to processing only about > > 35 minutes of that in a seamless run. Over that time > > span I've seen a peak relative frequency discrepancy of > > about 1.4E-9, with a handful reaching or exceeding 1E-9. > > I've also measured average frequency differences between > > the source's a a few parts in 10E11. > > > > Most of the effort went into developing a C program to do > > the processing and then correctly scaling and displaying > > the results in a form which I considered useful to me. This > > processing of course had to deal with an off-frequency and > > drifting 'scope timebase, which is *horrible* compared to the > > quantities under measurement (as expected from the outset). > > > > Present indications are that at this level of GPSDO mis- > > behavior, the results I'm viewing are about 20 dB higher > > than the basic floor, which I am still characterizing. I > > believe that the floor is limited primarily by uncorrelated > > sampling jitter between the two 'scope channels. > > > > If there is an expression of interest in this technique, I'll > > publish a detailed description of the technique and some > > plots showing results, probably in the form of an attachment > > in pdf format. > > > > Dana > > ___ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe, go to > >
Re: [time-nuts] Oscilloscope-based measurements of frequency stability
Yes they are LH and the blue? is satelite In a message dated 10/2/2018 3:30:31 PM Eastern Standard Time, k8yumdoo...@gmail.com writes: Hello Bert, What is the cyan-colored trace seen in these screen shots? And is "1 ppt" the same as 1E-12 (just to be sure)? Are these from LH? Thanks, Dana On Tue, Oct 2, 2018 at 1:46 PM ew via time-nuts wrote: > We see the glitches all the time, they exist and with proper equipment are > very visible. These are telecom timing devices and the way they correct the > 1 pps is by changing the frequency. Even LH shows it and it is very visible > when you eliminate the other traces.What we call the Tbolt 2, the nicely > packaged Trimle that also was part of the fraud listing does the correction > once an hour. It is exact an hour function of when you powered it up.In my > case night time spikes where mostly negative Air conditioner. Recovery is a > function of the accumulated error. Standing next to it in front of my 19 > year old M300 it did effect the recovery since my legs where within a > foot. One picture shows the analog trace to.Original Tbolt does it > constantly. We have spend a couple of years on this, hoping to optimize a > clean up loop.so far no good results.Bert Kehren > In a message dated 10/2/2018 1:04:50 PM Eastern Standard Time, > tsho...@gmail.com writes: > > Dana, the short term few-ns jitter of the two phases, I think in a digital > instrument is most likely data acquisition glitches. > > Even on a good old analog scope, jitter in the trigger circuit or jitter in > amplitudes (with resulting changes in harmonic content and thus the shape > of the curves) can cause the apparent zoomed in zero crossing to shift very > similarly. > > In days of old the telco standards for frequency stability also included > requirements for amplitude stability noise, directly related to making > repeatable measurements using scopes. I'm gonna see if I can find some of > those. I remember some crazy looking telco standard that required measuring > amplitude noise on time scales measured in weeks. > > Tim N3QE > > On Mon, Oct 1, 2018 at 8:47 AM Dana Whitlow wrote: > > > I cheered when I saw Dave B's "silly question", for > > then I realized that I'm not the only one who likes > > to measure things with an o'scope. > > > > I had purchased a GPSDO a few weeks before and > > had been observing its behavior relative to a free- > > running Rb by watching 10 MHz sinewaves drift with > > respect to each other as an aid in setting the Rb's > > frequency. However, I was seeing enough fairly > > rapid random drift to limit the usefulness of this kind > > of observation. It dawned on me that I was sometimes > > seeing drifts of several ns over the course of just > > several seconds, thus implying that sometimes the > > relative frequency error between the two sources was > > reaching as high as roughly 1E-9. I wanted to be able > > to capture and plot a somewhat extended run of data > > so I could try to understand this behavior better. > > > > Being TIC-less, I decided to see what I could do with > > my o'scope, which is a Chinese-made 2-channel DSO > > with synchronous sampling by the two channels and > > with a respectable trace memory depth (28 MSA per > > channel). > > > > I began this effort in earnest a couple of days before I > > saw Dave's question, and have only now brought it to > > a sufficient state of completion to feel justified in reporting > > some results. > > > > I am presently able to record about 45 minute's worth of > > data as limited by the 'scope's trace memory, but my XP > > computer's RAM space limits me to processing only about > > 35 minutes of that in a seamless run. Over that time > > span I've seen a peak relative frequency discrepancy of > > about 1.4E-9, with a handful reaching or exceeding 1E-9. > > I've also measured average frequency differences between > > the source's a a few parts in 10E11. > > > > Most of the effort went into developing a C program to do > > the processing and then correctly scaling and displaying > > the results in a form which I considered useful to me. This > > processing of course had to deal with an off-frequency and > > drifting 'scope timebase, which is *horrible* compared to the > > quantities under measurement (as expected from the outset). > > > > Present indications are that at this level of GPSDO mis- > > behavior, the results I'm viewing are about 20 dB higher > > than the basic floor, which I am still characterizing. I > > believe that the floor is limited primarily by uncorrelated > > sampling jitter between the two 'scope channels. > > > > If there is an expression of interest in this technique, I'll > > publish a detailed description of the technique and some > > plots showing results, probably in the form of an attachment > > in pdf format. > > > > Dana > > ___ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe, go to > >
Re: [time-nuts] Oscilloscope-based measurements of frequency stability
Hello Bert, What is the cyan-colored trace seen in these screen shots? And is "1 ppt" the same as 1E-12 (just to be sure)? Are these from LH? Thanks, Dana On Tue, Oct 2, 2018 at 1:46 PM ew via time-nuts wrote: > We see the glitches all the time, they exist and with proper equipment are > very visible. These are telecom timing devices and the way they correct the > 1 pps is by changing the frequency. Even LH shows it and it is very visible > when you eliminate the other traces.What we call the Tbolt 2, the nicely > packaged Trimle that also was part of the fraud listing does the correction > once an hour. It is exact an hour function of when you powered it up.In my > case night time spikes where mostly negative Air conditioner. Recovery is a > function of the accumulated error. Standing next to it in front of my 19 > year old M300 it did effect the recovery since my legs where within a > foot. One picture shows the analog trace to.Original Tbolt does it > constantly. We have spend a couple of years on this, hoping to optimize a > clean up loop.so far no good results.Bert Kehren > In a message dated 10/2/2018 1:04:50 PM Eastern Standard Time, > tsho...@gmail.com writes: > > Dana, the short term few-ns jitter of the two phases, I think in a digital > instrument is most likely data acquisition glitches. > > Even on a good old analog scope, jitter in the trigger circuit or jitter in > amplitudes (with resulting changes in harmonic content and thus the shape > of the curves) can cause the apparent zoomed in zero crossing to shift very > similarly. > > In days of old the telco standards for frequency stability also included > requirements for amplitude stability noise, directly related to making > repeatable measurements using scopes. I'm gonna see if I can find some of > those. I remember some crazy looking telco standard that required measuring > amplitude noise on time scales measured in weeks. > > Tim N3QE > > On Mon, Oct 1, 2018 at 8:47 AM Dana Whitlow wrote: > > > I cheered when I saw Dave B's "silly question", for > > then I realized that I'm not the only one who likes > > to measure things with an o'scope. > > > > I had purchased a GPSDO a few weeks before and > > had been observing its behavior relative to a free- > > running Rb by watching 10 MHz sinewaves drift with > > respect to each other as an aid in setting the Rb's > > frequency. However, I was seeing enough fairly > > rapid random drift to limit the usefulness of this kind > > of observation. It dawned on me that I was sometimes > > seeing drifts of several ns over the course of just > > several seconds, thus implying that sometimes the > > relative frequency error between the two sources was > > reaching as high as roughly 1E-9. I wanted to be able > > to capture and plot a somewhat extended run of data > > so I could try to understand this behavior better. > > > > Being TIC-less, I decided to see what I could do with > > my o'scope, which is a Chinese-made 2-channel DSO > > with synchronous sampling by the two channels and > > with a respectable trace memory depth (28 MSA per > > channel). > > > > I began this effort in earnest a couple of days before I > > saw Dave's question, and have only now brought it to > > a sufficient state of completion to feel justified in reporting > > some results. > > > > I am presently able to record about 45 minute's worth of > > data as limited by the 'scope's trace memory, but my XP > > computer's RAM space limits me to processing only about > > 35 minutes of that in a seamless run. Over that time > > span I've seen a peak relative frequency discrepancy of > > about 1.4E-9, with a handful reaching or exceeding 1E-9. > > I've also measured average frequency differences between > > the source's a a few parts in 10E11. > > > > Most of the effort went into developing a C program to do > > the processing and then correctly scaling and displaying > > the results in a form which I considered useful to me. This > > processing of course had to deal with an off-frequency and > > drifting 'scope timebase, which is *horrible* compared to the > > quantities under measurement (as expected from the outset). > > > > Present indications are that at this level of GPSDO mis- > > behavior, the results I'm viewing are about 20 dB higher > > than the basic floor, which I am still characterizing. I > > believe that the floor is limited primarily by uncorrelated > > sampling jitter between the two 'scope channels. > > > > If there is an expression of interest in this technique, I'll > > publish a detailed description of the technique and some > > plots showing results, probably in the form of an attachment > > in pdf format. > > > > Dana > > ___ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > >
Re: [time-nuts] Oscilloscope-based measurements of frequency stability
The correct cite is arXiv:1711.07917. On 10/1/2018 4:05 PM, Ralph Devoe wrote: This is just what I was trying to do with my paper on "sine-wave fitting", which can be found at arXiv:1711.07911 . Look at the relative phase of two frequency sources using a scope and then plot it versus time. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Oscilloscope-based measurements of frequency stability
I've done the Lissajous thing, but it takes an extra bit of effort to work out the phase angle. I've always gone back to the sliding waveforms display for simplicity. But I'll admit the Lissajous pattern is a lot prettier, and looks great in Sci Fi movies. Dana On Mon, Oct 1, 2018 at 4:06 PM Richard (Rick) Karlquist < rich...@karlquist.com> wrote: > No one mentioned using Lissajous patterns for comparing > frequencies if the scope has an XY mode. Google Lissajous > if interested. > > Rick N6RK > > On 10/1/2018 11:40 AM, Bryan _ wrote: > > Interested as well > > > > -=Bryan=- > > > > > > From: time-nuts on behalf of Chris > Burford > > Sent: October 1, 2018 6:20 AM > > To: Discussion of precise time and frequency measurement > > Subject: Re: [time-nuts] Oscilloscope-based measurements of frequency > stability > > > > This sounds interesting enough and I would appreciate any notes or > insight on doing this. I have a PRS10 and several GPSDOs that I would like > to evaluate for performance on my scope. > > > > Many thanks. > > > > > > Dana Whitlow wrote: > >> I cheered when I saw Dave B's "silly question", for > >> then I realized that I'm not the only one who likes > >> to measure things with an o'scope. > >> > >> I had purchased a GPSDO a few weeks before and > >> had been observing its behavior relative to a free- > >> running Rb by watching 10 MHz sinewaves drift with > >> respect to each other as an aid in setting the Rb's > >> frequency. However, I was seeing enough fairly > >> rapid random drift to limit the usefulness of this kind > >> of observation. It dawned on me that I was sometimes > >> seeing drifts of several ns over the course of just > >> several seconds, thus implying that sometimes the > >> relative frequency error between the two sources was > >> reaching as high as roughly 1E-9. I wanted to be able > >> to capture and plot a somewhat extended run of data > >> so I could try to understand this behavior better. > >> > >> Being TIC-less, I decided to see what I could do with > >> my o'scope, which is a Chinese-made 2-channel DSO > >> with synchronous sampling by the two channels and > >> with a respectable trace memory depth (28 MSA per > >> channel). > >> > >> I began this effort in earnest a couple of days before I > >> saw Dave's question, and have only now brought it to > >> a sufficient state of completion to feel justified in reporting > >> some results. > >> > >> I am presently able to record about 45 minute's worth of > >> data as limited by the 'scope's trace memory, but my XP > >> computer's RAM space limits me to processing only about > >> 35 minutes of that in a seamless run. Over that time > >> span I've seen a peak relative frequency discrepancy of > >> about 1.4E-9, with a handful reaching or exceeding 1E-9. > >> I've also measured average frequency differences between > >> the source's a a few parts in 10E11. > >> > >> Most of the effort went into developing a C program to do > >> the processing and then correctly scaling and displaying > >> the results in a form which I considered useful to me. This > >> processing of course had to deal with an off-frequency and > >> drifting 'scope timebase, which is *horrible* compared to the > >> quantities under measurement (as expected from the outset). > >> > >> Present indications are that at this level of GPSDO mis- > >> behavior, the results I'm viewing are about 20 dB higher > >> than the basic floor, which I am still characterizing. I > >> believe that the floor is limited primarily by uncorrelated > >> sampling jitter between the two 'scope channels. > >> > >> If there is an expression of interest in this technique, I'll > >> publish a detailed description of the technique and some > >> plots showing results, probably in the form of an attachment > >> in pdf format. > >> > >> Dana > >> ___ > >> time-nuts mailing list -- time-nuts@lists.febo.com > >> To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > >> and follow the instructions there. > > > > ___ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe, go to > ht
[time-nuts] Oscilloscope-based measurements of frequency stability
This is just what I was trying to do with my paper on "sine-wave fitting", which can be found at arXiv:1711.07911 . Look at the relative phase of two frequency sources using a scope and then plot it versus time. With a digital scope (Digilent Analog Discovery) , there's no reason to take a screen shot, all you have to do is write the ADC outputs to files. The paper was written for a peer-reviewed journal, so I had to write it in a tedious style, but it's basically the same as what is suggested here. I used a least-square fitting routine to calculate the phase difference in the paper, but eyeballing the phases also works. I've been measuring the drift and aging of a pair of HP 5065a's versus a 5071a for the last ten months and have over 200 GB of data on disk. I'm a lousy programmer but the Python analysis routine is short ( about 100 lines) and works fine. Ralph ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Oscilloscope-based measurements of frequency stability
No one mentioned using Lissajous patterns for comparing frequencies if the scope has an XY mode. Google Lissajous if interested. Rick N6RK On 10/1/2018 11:40 AM, Bryan _ wrote: Interested as well -=Bryan=- From: time-nuts on behalf of Chris Burford Sent: October 1, 2018 6:20 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Oscilloscope-based measurements of frequency stability This sounds interesting enough and I would appreciate any notes or insight on doing this. I have a PRS10 and several GPSDOs that I would like to evaluate for performance on my scope. Many thanks. Dana Whitlow wrote: I cheered when I saw Dave B's "silly question", for then I realized that I'm not the only one who likes to measure things with an o'scope. I had purchased a GPSDO a few weeks before and had been observing its behavior relative to a free- running Rb by watching 10 MHz sinewaves drift with respect to each other as an aid in setting the Rb's frequency. However, I was seeing enough fairly rapid random drift to limit the usefulness of this kind of observation. It dawned on me that I was sometimes seeing drifts of several ns over the course of just several seconds, thus implying that sometimes the relative frequency error between the two sources was reaching as high as roughly 1E-9. I wanted to be able to capture and plot a somewhat extended run of data so I could try to understand this behavior better. Being TIC-less, I decided to see what I could do with my o'scope, which is a Chinese-made 2-channel DSO with synchronous sampling by the two channels and with a respectable trace memory depth (28 MSA per channel). I began this effort in earnest a couple of days before I saw Dave's question, and have only now brought it to a sufficient state of completion to feel justified in reporting some results. I am presently able to record about 45 minute's worth of data as limited by the 'scope's trace memory, but my XP computer's RAM space limits me to processing only about 35 minutes of that in a seamless run. Over that time span I've seen a peak relative frequency discrepancy of about 1.4E-9, with a handful reaching or exceeding 1E-9. I've also measured average frequency differences between the source's a a few parts in 10E11. Most of the effort went into developing a C program to do the processing and then correctly scaling and displaying the results in a form which I considered useful to me. This processing of course had to deal with an off-frequency and drifting 'scope timebase, which is *horrible* compared to the quantities under measurement (as expected from the outset). Present indications are that at this level of GPSDO mis- behavior, the results I'm viewing are about 20 dB higher than the basic floor, which I am still characterizing. I believe that the floor is limited primarily by uncorrelated sampling jitter between the two 'scope channels. If there is an expression of interest in this technique, I'll publish a detailed description of the technique and some plots showing results, probably in the form of an attachment in pdf format. Dana ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Oscilloscope-based measurements of frequency stability
Interested as well -=Bryan=- From: time-nuts on behalf of Chris Burford Sent: October 1, 2018 6:20 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Oscilloscope-based measurements of frequency stability This sounds interesting enough and I would appreciate any notes or insight on doing this. I have a PRS10 and several GPSDOs that I would like to evaluate for performance on my scope. Many thanks. Dana Whitlow wrote: > I cheered when I saw Dave B's "silly question", for > then I realized that I'm not the only one who likes > to measure things with an o'scope. > > I had purchased a GPSDO a few weeks before and > had been observing its behavior relative to a free- > running Rb by watching 10 MHz sinewaves drift with > respect to each other as an aid in setting the Rb's > frequency. However, I was seeing enough fairly > rapid random drift to limit the usefulness of this kind > of observation. It dawned on me that I was sometimes > seeing drifts of several ns over the course of just > several seconds, thus implying that sometimes the > relative frequency error between the two sources was > reaching as high as roughly 1E-9. I wanted to be able > to capture and plot a somewhat extended run of data > so I could try to understand this behavior better. > > Being TIC-less, I decided to see what I could do with > my o'scope, which is a Chinese-made 2-channel DSO > with synchronous sampling by the two channels and > with a respectable trace memory depth (28 MSA per > channel). > > I began this effort in earnest a couple of days before I > saw Dave's question, and have only now brought it to > a sufficient state of completion to feel justified in reporting > some results. > > I am presently able to record about 45 minute's worth of > data as limited by the 'scope's trace memory, but my XP > computer's RAM space limits me to processing only about > 35 minutes of that in a seamless run. Over that time > span I've seen a peak relative frequency discrepancy of > about 1.4E-9, with a handful reaching or exceeding 1E-9. > I've also measured average frequency differences between > the source's a a few parts in 10E11. > > Most of the effort went into developing a C program to do > the processing and then correctly scaling and displaying > the results in a form which I considered useful to me. This > processing of course had to deal with an off-frequency and > drifting 'scope timebase, which is *horrible* compared to the > quantities under measurement (as expected from the outset). > > Present indications are that at this level of GPSDO mis- > behavior, the results I'm viewing are about 20 dB higher > than the basic floor, which I am still characterizing. I > believe that the floor is limited primarily by uncorrelated > sampling jitter between the two 'scope channels. > > If there is an expression of interest in this technique, I'll > publish a detailed description of the technique and some > plots showing results, probably in the form of an attachment > in pdf format. > > Dana > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Oscilloscope-based measurements of frequency stability
This sounds interesting enough and I would appreciate any notes or insight on doing this. I have a PRS10 and several GPSDOs that I would like to evaluate for performance on my scope. Many thanks. Dana Whitlow wrote: > I cheered when I saw Dave B's "silly question", for > then I realized that I'm not the only one who likes > to measure things with an o'scope. > > I had purchased a GPSDO a few weeks before and > had been observing its behavior relative to a free- > running Rb by watching 10 MHz sinewaves drift with > respect to each other as an aid in setting the Rb's > frequency. However, I was seeing enough fairly > rapid random drift to limit the usefulness of this kind > of observation. It dawned on me that I was sometimes > seeing drifts of several ns over the course of just > several seconds, thus implying that sometimes the > relative frequency error between the two sources was > reaching as high as roughly 1E-9. I wanted to be able > to capture and plot a somewhat extended run of data > so I could try to understand this behavior better. > > Being TIC-less, I decided to see what I could do with > my o'scope, which is a Chinese-made 2-channel DSO > with synchronous sampling by the two channels and > with a respectable trace memory depth (28 MSA per > channel). > > I began this effort in earnest a couple of days before I > saw Dave's question, and have only now brought it to > a sufficient state of completion to feel justified in reporting > some results. > > I am presently able to record about 45 minute's worth of > data as limited by the 'scope's trace memory, but my XP > computer's RAM space limits me to processing only about > 35 minutes of that in a seamless run. Over that time > span I've seen a peak relative frequency discrepancy of > about 1.4E-9, with a handful reaching or exceeding 1E-9. > I've also measured average frequency differences between > the source's a a few parts in 10E11. > > Most of the effort went into developing a C program to do > the processing and then correctly scaling and displaying > the results in a form which I considered useful to me. This > processing of course had to deal with an off-frequency and > drifting 'scope timebase, which is *horrible* compared to the > quantities under measurement (as expected from the outset). > > Present indications are that at this level of GPSDO mis- > behavior, the results I'm viewing are about 20 dB higher > than the basic floor, which I am still characterizing. I > believe that the floor is limited primarily by uncorrelated > sampling jitter between the two 'scope channels. > > If there is an expression of interest in this technique, I'll > publish a detailed description of the technique and some > plots showing results, probably in the form of an attachment > in pdf format. > > Dana > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Oscilloscope-based measurements of frequency stability
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[time-nuts] Oscilloscope-based measurements of frequency stability
I cheered when I saw Dave B's "silly question", for then I realized that I'm not the only one who likes to measure things with an o'scope. I had purchased a GPSDO a few weeks before and had been observing its behavior relative to a free- running Rb by watching 10 MHz sinewaves drift with respect to each other as an aid in setting the Rb's frequency. However, I was seeing enough fairly rapid random drift to limit the usefulness of this kind of observation. It dawned on me that I was sometimes seeing drifts of several ns over the course of just several seconds, thus implying that sometimes the relative frequency error between the two sources was reaching as high as roughly 1E-9. I wanted to be able to capture and plot a somewhat extended run of data so I could try to understand this behavior better. Being TIC-less, I decided to see what I could do with my o'scope, which is a Chinese-made 2-channel DSO with synchronous sampling by the two channels and with a respectable trace memory depth (28 MSA per channel). I began this effort in earnest a couple of days before I saw Dave's question, and have only now brought it to a sufficient state of completion to feel justified in reporting some results. I am presently able to record about 45 minute's worth of data as limited by the 'scope's trace memory, but my XP computer's RAM space limits me to processing only about 35 minutes of that in a seamless run. Over that time span I've seen a peak relative frequency discrepancy of about 1.4E-9, with a handful reaching or exceeding 1E-9. I've also measured average frequency differences between the source's a a few parts in 10E11. Most of the effort went into developing a C program to do the processing and then correctly scaling and displaying the results in a form which I considered useful to me. This processing of course had to deal with an off-frequency and drifting 'scope timebase, which is *horrible* compared to the quantities under measurement (as expected from the outset). Present indications are that at this level of GPSDO mis- behavior, the results I'm viewing are about 20 dB higher than the basic floor, which I am still characterizing. I believe that the floor is limited primarily by uncorrelated sampling jitter between the two 'scope channels. If there is an expression of interest in this technique, I'll publish a detailed description of the technique and some plots showing results, probably in the form of an attachment in pdf format. Dana ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
