Re: [time-nuts] Question about SoundCard stability?
Gents, I have already pointed to this paper http://ipnpr.jpl.nasa.gov/progress_report/42-121/121G.pdf for a number of times but appearantly it is still too less known or too less understood. Its appendix explains completely the necessary signal processing for frequency and phase extraction from a sampled sine using ALL samples. While the paper itself addresses this algo to radio frequencies it naturally works as well at audio frequencies. Those who are thinking of using a soundcard for serious time nuts applications, say as a phase detector in a double mixer system, may be warned: Not the math is the problem, even the soundcard's clock is easily locked to a stable reference and this even if the soundcard is not prepared for that. The real enemies are there where you won't expect them. If you have never seen the worse impact that even a 100 dB damped channel to channel crosstalk (a very good value for semi-prof soundcards, bad ones may give you 60 dB or less) has on a tau sigma diagram then you won't believe. Been there, done that. A tau sigma diagram merciless reveals everything that is periodic in time and has a period Tau0. The combined phase/amplitude modulation that results from sitting of a damped version of one channel's signal on top of the other channel's signal due to crosstalk may be small but the tau sigma diagram will reveal it with umpteen dBs up and down bumps in the graph where you otherwise would have expected a straight line. The position of the first bump is directly related to the beat frequency's period length. When I noticed these artefacts in my real-world measurements it took me quite a time to understand that it was due to crosstalk. In order to find out if crosstalk in such a small amounts could give this big impact I wrote me a piece of software where instead of sampling real world sines two sines were computed and where I could add noise and crosstalk to the signals just as I liked to do. When I set the noise level according to the value that the manufacturer of the soundcard would claim for his product and did the same for the crosstalk then I received EXACTLY the bad artefacts that I had seen in my real world measurements. I have even tried to improve the crosstalk by mathematics. In principle that is easy: If Crosstalk is merely ADDING one signal to another then remove the crosstalk by SUBTRACTING a damped copy of the other channel's signal. But as it is in life: Things that are easy in principle may be a problem in reality. As it turned out the level of the subtracted signal was very difficult to adjust to give a satisfying cancellation of added and subtracted signal. In addition it turned out that the signal due to the crosstalk had a phase delay against the signal in the producing channel. So I needed to construct me not only a damped version but also a phase delayed version of the sampled signal with damping AND phase delay freely setable. And it seemed as if these parameters were slightly changing in time, making necessary a permanent variation of the cancellation parameters. That increased the necessary processing power to a point where the software would not more run stable. Note that Greenhall's paper applies the algo offline to signals which you have been sampled into files while I was going to compute everything online to chunks of data worth one second of samples signals. Best regards Ulrich Bangert -Ursprungliche Nachricht- Von: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] Im Auftrag von shali...@gmail.com Gesendet: Donnerstag, 14. Oktober 2010 22:36 An: Time-Nuts Betreff: Re: [time-nuts] Question about SoundCard stability? I think that's what Jim is saying. If you try to fit to the signal using only the zero crossing, it will be hard unless you have a lot of zero crossing, because you will have only one point per period to fit to. If you fit 10 or 100 points per period, you improve your fitting considerably. That assumes the signal waveform is stable of course. Didier Sent from my Verizon Wireless BlackBerry -Original Message- From: David McClain d...@refined-audiometrics.com Sender: time-nuts-boun...@febo.com Date: Thu, 14 Oct 2010 00:08:58 To: Discussion of precise time and frequency measurementtime-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Question about SoundCard stability? Or, now that I think about it, it's similar to what we do when measuring ADEV.. you can do a crude how many zero crossings in the time window or you can do a fit a sinusoid to a series of ADC samples. One has an uncertainty of one count/epoch, the other can be substantially better. How could it be substantially better for the same analysis period? Unless the frequency under test is an integral number of periods during the analysis period, you will have a variation in the sine
Re: [time-nuts] Question about SoundCard stability?
Ulrich Bangert wrote: Gents, I have already pointed to this paper http://ipnpr.jpl.nasa.gov/progress_report/42-121/121G.pdf for a number of times but appearantly it is still too less known or too less understood. Its appendix explains completely the necessary signal processing for frequency and phase extraction from a sampled sine using ALL samples. While the paper itself addresses this algo to radio frequencies it naturally works as well at audio frequencies. And, in any case, the RSA described in the paper is sampling an audio frequency beat note, so it's exactly applicable to what is contemplated here. As Ulrich comments in the rest of his post, the math is straightforward, the performance is all in the hardware execution. When measuring a gnat's eyelash, you need to worry about the bumps on the eyelash. Sound cards in PCs have all sorts of idiosyncracies. Consider them as a 10 bit/ 60dB sort of device: For instance, the sampling clock may be fairly stable, but it has interference from the processor clock on it, so you'll see spurs from that. There's leakage between channels. The low frequency response isn't very wonderful. etc. The folks doing ham software defined radios (in particular with the Flex-Radio boxes of the SDR1000 vintage a few years ago) spent a lot of time trying out different external sound interfaces: the performance of the interface directly affects the RF performance in the Flex direct conversion scheme. Unfortunately, a lot of the mail reflector archives aren't on-line, but there was a lot of empirical data that some dedicated people collected. ___ 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] Question about SoundCard stability?
Hi I do not follow al the techniques in detail but a lot of work has been done on soundcard sampling rates in the low frequency amateur radio groups where GPS locking is used to extract very weak signals from the noise in very narrow band widths. It has been found that some of the supposed standard samping rates are not exact divisors of the clock crystal and are achieved by a bodge in teh software but are regarded as close enough for some audio work The 11kHz rate is a particularly odd one but many of the 8kHz rates are quite a way off. There are several ways of locking the spectrogram software to a harmonic of the 1pps. If there is interest I may be able to dig out some URLs a quick check didnt yield what I wanted to show. Alan G3NYK - Original Message - From: jimlux jim...@earthlink.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, October 15, 2010 2:26 PM Subject: Re: [time-nuts] Question about SoundCard stability? Ulrich Bangert wrote: Gents, I have already pointed to this paper http://ipnpr.jpl.nasa.gov/progress_report/42-121/121G.pdf for a number of times but appearantly it is still too less known or too less understood. Its appendix explains completely the necessary signal processing for frequency and phase extraction from a sampled sine using ALL samples. While the paper itself addresses this algo to radio frequencies it naturally works as well at audio frequencies. And, in any case, the RSA described in the paper is sampling an audio frequency beat note, so it's exactly applicable to what is contemplated here. As Ulrich comments in the rest of his post, the math is straightforward, the performance is all in the hardware execution. When measuring a gnat's eyelash, you need to worry about the bumps on the eyelash. Sound cards in PCs have all sorts of idiosyncracies. Consider them as a 10 bit/ 60dB sort of device: For instance, the sampling clock may be fairly stable, but it has interference from the processor clock on it, so you'll see spurs from that. There's leakage between channels. The low frequency response isn't very wonderful. etc. The folks doing ham software defined radios (in particular with the Flex-Radio boxes of the SDR1000 vintage a few years ago) spent a lot of time trying out different external sound interfaces: the performance of the interface directly affects the RF performance in the Flex direct conversion scheme. Unfortunately, a lot of the mail reflector archives aren't on-line, but there was a lot of empirical data that some dedicated people collected. ___ 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] Question about SoundCard stability?
On 10/13/2010 12:58 PM, Bob Camp wrote: Hi Controller cycling is often a result of one of two things: 1) Resistance in the power lead I think I can write this off. 2) Extra insulation / dead air I can write this one off too. 3) Internal controller issues Most likely the issue. It was a very linear behaviour and was there from power-on to power-off... days later. On all samples. There are a few other possibilities, but they are remote enough that you are unlikely to ever come across them. There's no advantage to building a controller that's cycling. It was more likely a bug than a feature. I consider it a bug. 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] Question about SoundCard stability?
Or, now that I think about it, it's similar to what we do when measuring ADEV.. you can do a crude how many zero crossings in the time window or you can do a fit a sinusoid to a series of ADC samples. One has an uncertainty of one count/epoch, the other can be substantially better. How could it be substantially better for the same analysis period? Unless the frequency under test is an integral number of periods during the analysis period, you will have a variation in the sine fitting due to starting phase. OTOH, as admonished in Horowitz Hill, if the frequency to be counted is substantially below your counter timebase, then you should count zero crossings of the higher timebase frequency in the period of the lower frequency under test. Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 13, 2010, at 22:30, jimlux wrote: Jim Lux wrote: That's not precisely true. You can get a frequency estimate that is substantially more precise than 1/T if the snr is high. Consider super-resolution in an interferometer which is mathematically similar. What you give up is ambiguity. Probably one of the oldest techniques is that of Prony, but there are lots of others Or, now that I think about it, it's similar to what we do when measuring ADEV.. you can do a crude how many zero crossings in the time window or you can do a fit a sinusoid to a series of ADC samples. One has an uncertainty of one count/epoch, the other can be substantially better. ___ 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] Question about SoundCard stability?
I think that's what Jim is saying. If you try to fit to the signal using only the zero crossing, it will be hard unless you have a lot of zero crossing, because you will have only one point per period to fit to. If you fit 10 or 100 points per period, you improve your fitting considerably. That assumes the signal waveform is stable of course. Didier Sent from my Verizon Wireless BlackBerry -Original Message- From: David McClain d...@refined-audiometrics.com Sender: time-nuts-boun...@febo.com Date: Thu, 14 Oct 2010 00:08:58 To: Discussion of precise time and frequency measurementtime-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Question about SoundCard stability? Or, now that I think about it, it's similar to what we do when measuring ADEV.. you can do a crude how many zero crossings in the time window or you can do a fit a sinusoid to a series of ADC samples. One has an uncertainty of one count/epoch, the other can be substantially better. How could it be substantially better for the same analysis period? Unless the frequency under test is an integral number of periods during the analysis period, you will have a variation in the sine fitting due to starting phase. OTOH, as admonished in Horowitz Hill, if the frequency to be counted is substantially below your counter timebase, then you should count zero crossings of the higher timebase frequency in the period of the lower frequency under test. Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 13, 2010, at 22:30, jimlux wrote: Jim Lux wrote: That's not precisely true. You can get a frequency estimate that is substantially more precise than 1/T if the snr is high. Consider super-resolution in an interferometer which is mathematically similar. What you give up is ambiguity. Probably one of the oldest techniques is that of Prony, but there are lots of others Or, now that I think about it, it's similar to what we do when measuring ADEV.. you can do a crude how many zero crossings in the time window or you can do a fit a sinusoid to a series of ADC samples. One has an uncertainty of one count/epoch, the other can be substantially better. ___ 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] Question about SoundCard stability?
Indeed... when I make the FFT bins substantially narrower than the expected drift cycle amplitude, I do in fact see the drift cycles in the reported interpolated peak frequency. However, now that the bins are so narrow, the window duration is significant in relation to the cycle periods of interest (20 minutes per window, cool down time is 15 minutes). And so the amplitude of the drift is very small -- much smaller than might have been expected. Again, I think this is due to convolving with the window period -- taking the average deviation over the period of the window, and that would be much smaller than the peak deviation experienced from TCXO effects. What seems amazing here is that one can derive a valid soundcard frequency correction by using the shorter period windows and using reported interpolated peak frequencies. I guess that is still reasonable since, when you do make the deviation visible with long window periods, you want those deviations to be equal-ripple about the zero deviation line. And using an averaged deviation works just as well for all averaging periods. There is a trade-off between accuracy and one's human patience... Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 12, 2010, at 22:52, David McClain wrote: Yes, indeed. I demodulate in AM mode, specifically to remove any sensitivity to the LO wandering with ambient temperature. And no I wasn't seeing any variation bigger than 4 ppb with a 0.1 ppm TCXO wander. That's what the quandary was all about. I think I have answered the question... You cannot get around the uncertainty principle, which states that your precision in resolving frequencies is limited by the inverse of your resolution in time. Attempting some hair-brained interpolation across a peak in the FFT is just a mathematical game without any meaning. A *proper* interpolation in frequency space is performed by zero- padding the time record. When you do that, you introduce many inter- bin sidelobes. But more to the point, when the FFT bin-size is the same width as the expected drift amplitude, you get a broad, convolved bin content from the duration of the window, and attempting to say, on the basis of adjacent bin amplitudes, that you know where the frequency of *the peak* is to any better than the bin-width is just nonsense. So SpectrumLab, while offering a fancy interpolated peak frequency, must be interpreted with caution. What it reports can be wildly off- base. Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 12, 2010, at 19:47, Mark Spencer wrote: Just curious, if you have set your radio to AM mode to remove any variations due to wonder in the radio LO, how would any minor deviations in the TCXO of the radio affect the measurement ? If you are looking at the difference between a 10.00 mhz carrier and a 10.000100 mhz sub carrier wouldn't the difference always appear to be 100 hz in AM mode even if your TCXO drifted slightly ? You might be seeing the affects of varrying doppler shift between WWV and WWVH (although I'd expect the variation to be larger.) Sorry it's been a long day for me and I may be missing something obvious (: All the best Mark Spencer - Original Message From: David McClain d...@refined-audiometrics.com To: time-nuts@febo.com Sent: Tue, October 12, 2010 4:48:56 PM Subject: [time-nuts] Question about SoundCard stability? Hi, I have a Flex-3000 receiver, running freely on its internal TCXO (0.1 ppm). I have been recording the reported deviations in the measurements of the 100 Hz sizeband of 10 MHz WWV all day long. I do this in AM detection mode, to remove any variations due to the wander in the radio LO. Recording from the 48 kHz audio stream and into SpectrumLab for analysis. After taking out the measured frequency error in the soundcard (which I believe is the Flex Radio internal CODEC), of 17.5 mHz, I'm seeing frequency deviations of 0.2 mHz RMS, and +/- 1 mHz p-p, with no measurable long term drift. The FFT uses a bin size of 11.44 mHz. SpectrumLab interpolates to the peak assuming high SNR and a Hann window, with no nearby interference. This implies that my soundcard is giving me a stability of 0.004 ppm, or around 10^-9. How can this be? I already know that the TCXO wanders about by as much as +/- 1 Hz at 10 MHz due to temperature variations in the room. (10^-7). If that TCXO were used to derive the soundcard (CODEC) clock then I should be seeing variations of 25x larger. And I can assure you the CODEC is *not* being driven by an OCXO or GPSDO of any kind
Re: [time-nuts] Question about SoundCard stability?
Le 13/10/2010 03:41, David McClain a écrit : Hi, No you aren't missing anything... except that I *DON'T* see the 5 mHz drift that one should expect. Hence my contention that relying on interpolated frequencies from FFT peaks and their adjacent bins is bogus when the FFT bin size is as large or larger than the expected drift. Am I being naive? I thought the point that Bob made in the original reply, though unstated explicitly, was that if you are measuring the signal against the same reference being used to generate it, then you are only measuring the noise. The drift will be masked. Somehow that seems like it violated the uncertainty principle in the first place. And now I'm seeing that the principle rules supreme. I'm going to do another run, with a bin size about 1/4 the expected drift, to see if the reported interpolated peak frequencies really do show the drift one should expect. I therefor don't expect that you will see any significant difference and will not detect drift. Cheers, Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 12, 2010, at 18:25, Randall Prentice wrote: 1 Hz in 10Mhz is about the same ratio as 5mHz in 64Khz. This would make sense if the Clock for the A/D is divided off the same TXCO. Or am I missing something. The reason I jumped in, in a recent frequency measuring contest the winner was using that interpolation for his results. Regards Randall ZL2RJP -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of David McClain Sent: Wednesday, 13 October 2010 2:18 p.m. To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Question about SoundCard stability? Ahh.. so... Now since my TCXO is drifting to and fro by 1-2 Hz over the period of 45 minutes, why don't I see similar drift in the 100 Hz audio signal, down around 5 mHz amplitude? This happens to be about the same size at the FFT bins. So I am led to conclude that interpolated peak frequencies are a bogus technique, and you can only truly count on variations on the order of the FFT cell size as being measurable... Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 12, 2010, at 17:57, Bob Camp wrote: Hi Yes it is a reasonable expectation as long as you don't have a lot of drafts. A good TCXO can get down to sub 0.1 ppb over that period. Bob On Oct 12, 2010, at 8:21 PM, David McClain wrote: Okay, perhaps I should rephrase the question... Is is reasonable to expect a TCXO to perform at 4e-9 over the FFT window period of about 87 sec? I can only imagine that the enormous (87 s) averaging period is making my measurements look so good. Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com ___ 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. ___ 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] Question about SoundCard stability?
I think I have answered the question... You cannot get around the uncertainty principle, which states that your precision in resolving frequencies is limited by the inverse of your resolution in time. Attempting some hair-brained interpolation across a peak in the FFT is just a mathematical game without any meaning. Well, not entirely -- it's common enough to see FFT applications that compute frequency readings at sub-bin precision by tracking atan(Q,I) across multiple time records. That is a well-defined thing to do, since the relationship between the time-record length and the period of the dominant signal in a given bin is what's ultimately being measured. But this sounds like a case where the readings reported by the software are based on assumptions that aren't valid. What is the connection between the Flex 3000 and the PC like? Where does the 48 kHz rate you mentioned come from, exactly? If, for instance, the 48 kHz is some fraction of the same TCXO that's driving the baseband conversion in the receiver, then it could make sense if the frequency readings appear mysteriously constant. The drift would be in the wall-clock duration of the time record in this case, influencing the true frequency of the FFT bin in ways the software doesn't know about. In other words, as far as SpectrumLab is concerned, the frequency associated with bin 123 of a 1024-bin record at 48 kHz is exactly 2882.8125000... Hz, because it's assuming that the 48 kHz sample rate is also exact. If the latter isn't true, and it won't be, then the former won't be true either. A *proper* interpolation in frequency space is performed by zero- padding the time record. When you do that, you introduce many inter- bin sidelobes. But more to the point, when the FFT bin-size is the same width as the expected drift amplitude, you get a broad, convolved bin content from the duration of the window, and attempting to say, on the basis of adjacent bin amplitudes, that you know where the frequency of *the peak* is to any better than the bin-width is just nonsense. It doesn't work that way (or shouldn't, at least, if they are claiming to report true peak-frequency readings). -- john, KE5FX ___ 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] Question about SoundCard stability?
Sorry, we must be talking past one another... I'm measuring the 100 Hz sideband from 10 MHz WWV in AM demodulation. I should see about 5 mHz cyclic drift, and I wasn't seeing it. I now know that is because the FFT bin size was about 11 mHz wide and the interpolated peak frequency assumes zero drift, infinite SNR, and no nearby interference. Hence the reported values are totally bogus in this case. Once I resized the FFT bins to around 1 mHz, I could see the 5 mHz cyclic drift, reduced in amplitude by averaging effects. Quandary solved... point of note regarding interpretation of SpectrumLab reported frequencies taken... Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 12, 2010, at 23:08, mike cook wrote: Le 13/10/2010 03:41, David McClain a écrit : Hi, No you aren't missing anything... except that I *DON'T* see the 5 mHz drift that one should expect. Hence my contention that relying on interpolated frequencies from FFT peaks and their adjacent bins is bogus when the FFT bin size is as large or larger than the expected drift. Am I being naive? I thought the point that Bob made in the original reply, though unstated explicitly, was that if you are measuring the signal against the same reference being used to generate it, then you are only measuring the noise. The drift will be masked. Somehow that seems like it violated the uncertainty principle in the first place. And now I'm seeing that the principle rules supreme. I'm going to do another run, with a bin size about 1/4 the expected drift, to see if the reported interpolated peak frequencies really do show the drift one should expect. I therefor don't expect that you will see any significant difference and will not detect drift. Cheers, Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 12, 2010, at 18:25, Randall Prentice wrote: 1 Hz in 10Mhz is about the same ratio as 5mHz in 64Khz. This would make sense if the Clock for the A/D is divided off the same TXCO. Or am I missing something. The reason I jumped in, in a recent frequency measuring contest the winner was using that interpolation for his results. Regards Randall ZL2RJP -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts- boun...@febo.com] On Behalf Of David McClain Sent: Wednesday, 13 October 2010 2:18 p.m. To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Question about SoundCard stability? Ahh.. so... Now since my TCXO is drifting to and fro by 1-2 Hz over the period of 45 minutes, why don't I see similar drift in the 100 Hz audio signal, down around 5 mHz amplitude? This happens to be about the same size at the FFT bins. So I am led to conclude that interpolated peak frequencies are a bogus technique, and you can only truly count on variations on the order of the FFT cell size as being measurable... Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 12, 2010, at 17:57, Bob Camp wrote: Hi Yes it is a reasonable expectation as long as you don't have a lot of drafts. A good TCXO can get down to sub 0.1 ppb over that period. Bob On Oct 12, 2010, at 8:21 PM, David McClain wrote: Okay, perhaps I should rephrase the question... Is is reasonable to expect a TCXO to perform at 4e-9 over the FFT window period of about 87 sec? I can only imagine that the enormous (87 s) averaging period is making my measurements look so good. Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com ___ 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. ___ 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
Re: [time-nuts] Question about SoundCard stability?
Hello John, Well, not entirely -- it's common enough to see FFT applications that compute frequency readings at sub-bin precision by tracking atan (Q,I) across multiple time records. That is a well-defined thing to do, since the Yes, indeed, I am familiar with that technique from my SIGINT days... however, what you are really doing is extending the sampling period by looking at multiple scans. And so that isn't really any different at its base than just taking a longer period FFT. The only way I have ever seen super-resolution is when you do AR deconvolution, bearing in mind that wherever there are instrumental induced zeros in the spectrum, you will get nonsense values in the result. AR, aka maximum-entropy, attempts to produce a minimum norm estimate, akin to that from SVD analysis. And yes, SpectrumLab appears to be assuming infinte SNR, no nearby interference, absolutely drift free, monochromatic lines. And there (maddeningly) seems no way to disable this *feature*. The soundcard interface of SpectrumLab was manually adjusted by me to ensure that the 100 Hz sideband actually reads as 100 Hz. My Flex3K codec was about 17.5 ppm slow. Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 12, 2010, at 23:25, John Miles wrote: I think I have answered the question... You cannot get around the uncertainty principle, which states that your precision in resolving frequencies is limited by the inverse of your resolution in time. Attempting some hair-brained interpolation across a peak in the FFT is just a mathematical game without any meaning. Well, not entirely -- it's common enough to see FFT applications that compute frequency readings at sub-bin precision by tracking atan (Q,I) across multiple time records. That is a well-defined thing to do, since the relationship between the time-record length and the period of the dominant signal in a given bin is what's ultimately being measured. But this sounds like a case where the readings reported by the software are based on assumptions that aren't valid. What is the connection between the Flex 3000 and the PC like? Where does the 48 kHz rate you mentioned come from, exactly? If, for instance, the 48 kHz is some fraction of the same TCXO that's driving the baseband conversion in the receiver, then it could make sense if the frequency readings appear mysteriously constant. The drift would be in the wall-clock duration of the time record in this case, influencing the true frequency of the FFT bin in ways the software doesn't know about. In other words, as far as SpectrumLab is concerned, the frequency associated with bin 123 of a 1024-bin record at 48 kHz is exactly 2882.8125000... Hz, because it's assuming that the 48 kHz sample rate is also exact. If the latter isn't true, and it won't be, then the former won't be true either. A *proper* interpolation in frequency space is performed by zero- padding the time record. When you do that, you introduce many inter- bin sidelobes. But more to the point, when the FFT bin-size is the same width as the expected drift amplitude, you get a broad, convolved bin content from the duration of the window, and attempting to say, on the basis of adjacent bin amplitudes, that you know where the frequency of *the peak* is to any better than the bin-width is just nonsense. It doesn't work that way (or shouldn't, at least, if they are claiming to report true peak-frequency readings). -- john, KE5FX ___ 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] Question about SoundCard stability?
OTOH, I do see the virtue in the phase examination approach... A longer FFT would average over any short-term variations in a cyclostationary process. If you take shorter FFT's you can catch the signal in the act of drifting, and perhaps use the phase examination to augment your frequency estimate. However, if the signal is drifting, you'd have to account for that in the phase advancement too... Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 12, 2010, at 23:25, John Miles wrote: I think I have answered the question... You cannot get around the uncertainty principle, which states that your precision in resolving frequencies is limited by the inverse of your resolution in time. Attempting some hair-brained interpolation across a peak in the FFT is just a mathematical game without any meaning. Well, not entirely -- it's common enough to see FFT applications that compute frequency readings at sub-bin precision by tracking atan (Q,I) across multiple time records. That is a well-defined thing to do, since the relationship between the time-record length and the period of the dominant signal in a given bin is what's ultimately being measured. But this sounds like a case where the readings reported by the software are based on assumptions that aren't valid. What is the connection between the Flex 3000 and the PC like? Where does the 48 kHz rate you mentioned come from, exactly? If, for instance, the 48 kHz is some fraction of the same TCXO that's driving the baseband conversion in the receiver, then it could make sense if the frequency readings appear mysteriously constant. The drift would be in the wall-clock duration of the time record in this case, influencing the true frequency of the FFT bin in ways the software doesn't know about. In other words, as far as SpectrumLab is concerned, the frequency associated with bin 123 of a 1024-bin record at 48 kHz is exactly 2882.8125000... Hz, because it's assuming that the 48 kHz sample rate is also exact. If the latter isn't true, and it won't be, then the former won't be true either. A *proper* interpolation in frequency space is performed by zero- padding the time record. When you do that, you introduce many inter- bin sidelobes. But more to the point, when the FFT bin-size is the same width as the expected drift amplitude, you get a broad, convolved bin content from the duration of the window, and attempting to say, on the basis of adjacent bin amplitudes, that you know where the frequency of *the peak* is to any better than the bin-width is just nonsense. It doesn't work that way (or shouldn't, at least, if they are claiming to report true peak-frequency readings). -- john, KE5FX ___ 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] Question about SoundCard stability?
On 10/13/2010 05:32 AM, Jim Lux wrote: On Oct 12, 2010, at 6:09 PM, Magnus Danielsonmag...@rubidium.dyndns.org wrote: Hi Bob and Dave, On 10/13/2010 02:57 AM, Bob Camp wrote: Hi Yes it is a reasonable expectation as long as you don't have a lot of drafts. A good TCXO can get down to sub 0.1 ppb over that period. This is why I like ADEV plots in datasheets. I rarely get to see them. TDEV plots is a nice complement naturally. Cheers, Magnus Bob And I wish there were adev plots for cheap tcxo's on the mgr data sheets Me too. I have to make the measurement myself. In one case I found that the oven control in one OCXO was unstable and had a resonance at about 7 second period. It was possible to measure it on the current supply too. The oven-control was having a relatively high-Q resonance and self-oscillation around the stability point. It increased the ADEV at that point to almost about 10 times more than expected. I learned that it was a good thing I measured it and yes, that spec didn't exist in the datasheet. It is unclear if they knew it or not. Even my half-crap setup proved valueable as I got aware of an issue on sample level rather than out in production phase. 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] Question about SoundCard stability?
Hi Controller cycling is often a result of one of two things: 1) Resistance in the power lead 2) Extra insulation / dead air 3) Internal controller issues There are a few other possibilities, but they are remote enough that you are unlikely to ever come across them. There's no advantage to building a controller that's cycling. It was more likely a bug than a feature. Bob On Oct 13, 2010, at 4:00 AM, Magnus Danielson wrote: On 10/13/2010 05:32 AM, Jim Lux wrote: On Oct 12, 2010, at 6:09 PM, Magnus Danielsonmag...@rubidium.dyndns.org wrote: Hi Bob and Dave, On 10/13/2010 02:57 AM, Bob Camp wrote: Hi Yes it is a reasonable expectation as long as you don't have a lot of drafts. A good TCXO can get down to sub 0.1 ppb over that period. This is why I like ADEV plots in datasheets. I rarely get to see them. TDEV plots is a nice complement naturally. Cheers, Magnus Bob And I wish there were adev plots for cheap tcxo's on the mgr data sheets Me too. I have to make the measurement myself. In one case I found that the oven control in one OCXO was unstable and had a resonance at about 7 second period. It was possible to measure it on the current supply too. The oven-control was having a relatively high-Q resonance and self-oscillation around the stability point. It increased the ADEV at that point to almost about 10 times more than expected. I learned that it was a good thing I measured it and yes, that spec didn't exist in the datasheet. It is unclear if they knew it or not. Even my half-crap setup proved valueable as I got aware of an issue on sample level rather than out in production phase. 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. ___ 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] Question about SoundCard stability?
Hi Should have been two out of three things ... Bob On Oct 13, 2010, at 6:58 AM, Bob Camp wrote: Hi Controller cycling is often a result of one of two things: 1) Resistance in the power lead 2) Extra insulation / dead air 3) Internal controller issues There are a few other possibilities, but they are remote enough that you are unlikely to ever come across them. There's no advantage to building a controller that's cycling. It was more likely a bug than a feature. Bob On Oct 13, 2010, at 4:00 AM, Magnus Danielson wrote: On 10/13/2010 05:32 AM, Jim Lux wrote: On Oct 12, 2010, at 6:09 PM, Magnus Danielsonmag...@rubidium.dyndns.org wrote: Hi Bob and Dave, On 10/13/2010 02:57 AM, Bob Camp wrote: Hi Yes it is a reasonable expectation as long as you don't have a lot of drafts. A good TCXO can get down to sub 0.1 ppb over that period. This is why I like ADEV plots in datasheets. I rarely get to see them. TDEV plots is a nice complement naturally. Cheers, Magnus Bob And I wish there were adev plots for cheap tcxo's on the mgr data sheets Me too. I have to make the measurement myself. In one case I found that the oven control in one OCXO was unstable and had a resonance at about 7 second period. It was possible to measure it on the current supply too. The oven-control was having a relatively high-Q resonance and self-oscillation around the stability point. It increased the ADEV at that point to almost about 10 times more than expected. I learned that it was a good thing I measured it and yes, that spec didn't exist in the datasheet. It is unclear if they knew it or not. Even my half-crap setup proved valueable as I got aware of an issue on sample level rather than out in production phase. 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. ___ 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] Question about SoundCard stability?
Greetings, I may be missing something here but when you receive a signal in the AM mode the audio is derived from the transmitted carrier. Even if your local osc moves around the audio is generated from the difference between the transmitted carrier and the audio sidebands. I have found it quite convenient to calibrate a soundcard/SpecLab system using AM and the signals sent out by WWV at 500 and 600 Hz I think. Now if I could just get comfortable with SpecLab. Hi HI 73 Gordon WA4FJC -- Message: 1 Date: Tue, 12 Oct 2010 17:03:26 -0700 From: David McClain d...@refined-audiometrics.com Subject: Re: [time-nuts] Question about SoundCard stability? To: Discussion of precise time and frequency measurement time-nuts@febo.com Message-ID: 2ff30bd1-78dc-4283-9470-b1ce29305...@refined-audiometrics.com Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed Best guess is that the codec in the Flex runs on the same TCXO as the rest of the radio. That's my best guess too... so how is it that I'm seeing 25x less variation in the audio signal than the TCXO is capable of yielding? I have the central air conditioner cycling on and off all day (Tucson desert), and I can see the radio wander by as much as +/-2-4 Hz at times, at 10 MHz. It shows an irregular sawtooth deviation in sync with the cycling of the air conditioner, with a period of about 45 minutes, 15 of which are cool down times. This is mid-day, so the ionosphere is not producing much in the way of Doppler shifting. And even if it were, that shouldn't be measurable to me at the audio frequencies. Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com ___ 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] Question about SoundCard stability?
That's not precisely true. You can get a frequency estimate that is substantially more precise than 1/T if the snr is high. Consider super-resolution in an interferometer which is mathematically similar. What you give up is ambiguity. Probably one of the oldest techniques is that of Prony, but there are lots of others On Oct 12, 2010, at 10:52 PM, David McClain d...@refined-audiometrics.com wrote: Yes, indeed. I demodulate in AM mode, specifically to remove any sensitivity to the LO wandering with ambient temperature. And no I wasn't seeing any variation bigger than 4 ppb with a 0.1 ppm TCXO wander. That's what the quandary was all about. I think I have answered the question... You cannot get around the uncertainty principle, which states that your precision in resolving frequencies is limited by the inverse of your resolution in time. Attempting some hair-brained interpolation across a peak in the FFT is just a mathematical game without any meaning. A *proper* interpolation in frequency space is performed by zero-padding the time record. When you do that, you introduce many inter-binq sidelobes. But more to the point, when the FFT bin-size is the same width as the expected drift amplitude, you get a broad, convolved bin content from the duration of the window, and attempting to say, on the basis of adjacent bin amplitudes, that you know where the frequency of *the peak* is to any better than the bin-width is just nonsense. So SpectrumLab, while offering a fancy interpolated peak frequency, must be interpreted with caution. What it reports can be wildly off-base. Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 12, 2010, at 19:47, Mark Spencer wrote: Just curious, if you have set your radio to AM mode to remove any variations due to wonder in the radio LO, how would any minor deviations in the TCXO of the radio affect the measurement ? If you are looking at the difference between a 10.00 mhz carrier and a 10.000100 mhz sub carrier wouldn't the difference always appear to be 100 hz in AM mode even if your TCXO drifted slightly ? You might be seeing the affects of varrying doppler shift between WWV and WWVH (although I'd expect the variation to be larger.) Sorry it's been a long day for me and I may be missing something obvious (: All the best Mark Spencer - Original Message From: David McClain d...@refined-audiometrics.com To: time-nuts@febo.com Sent: Tue, October 12, 2010 4:48:56 PM Subject: [time-nuts] Question about SoundCard stability? Hi, I have a Flex-3000 receiver, running freely on its internal TCXO (0.1 ppm). I have been recording the reported deviations in the measurements of the 100 Hz sizeband of 10 MHz WWV all day long. I do this in AM detection mode, to remove any variations due to the wander in the radio LO. Recording from the 48 kHz audio stream and into SpectrumLab for analysis. After taking out the measured frequency error in the soundcard (which I believe is the Flex Radio internal CODEC), of 17.5 mHz, I'm seeing frequency deviations of 0.2 mHz RMS, and +/- 1 mHz p-p, with no measurable long term drift. The FFT uses a bin size of 11.44 mHz. SpectrumLab interpolates to the peak assuming high SNR and a Hann window, with no nearby interference. This implies that my soundcard is giving me a stability of 0.004 ppm, or around 10^-9. How can this be? I already know that the TCXO wanders about by as much as +/- 1 Hz at 10 MHz due to temperature variations in the room. (10^-7). If that TCXO were used to derive the soundcard (CODEC) clock then I should be seeing variations of 25x larger. And I can assure you the CODEC is *not* being driven by an OCXO or GPSDO of any kind. Anyone? Dr. David McClain, N7AIG Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com ___ 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. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi
Re: [time-nuts] Question about SoundCard stability?
On Oct 13, 2010, at 12:32 AM, David McClain d...@refined-audiometrics.com wrote: Hello John, Well, not entirely -- it's common enough to see FFT applications that compute frequency readings at sub-bin precision by tracking atan(Q,I) across multiple time records. That is a well-defined thing to do, since the Yes, indeed, I am familiar with that technique from my SIGINT days... however, what you are really doing is extending the sampling period by looking at multiple scans. And so that isn't really any different at its base than just taking a longer period FFT. The only way I have ever seen super-resolution is when you do AR deconvolution, bearing in mind that wherever there are instrumental induced zeros in the spectrum, you will get nonsense values in the result. AR, aka maximum-entropy, attempts to produce a minimum norm estimate, akin to that from SVD analysis. That's but one way. There's also music and esprit as well of a host of other similar methods. ___ 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] Question about SoundCard stability?
Hi Jim, Can you give any more precise hints, e.g., links to articles? You mentioned Prony, Music, and Espirit. You caught my attention with your analogy to interferometry... Cheers, Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 13, 2010, at 05:27, Jim Lux wrote: That's not precisely true. You can get a frequency estimate that is substantially more precise than 1/T if the snr is high. Consider super-resolution in an interferometer which is mathematically similar. What you give up is ambiguity. Probably one of the oldest techniques is that of Prony, but there are lots of others On Oct 12, 2010, at 10:52 PM, David McClain d...@refined- audiometrics.com wrote: Yes, indeed. I demodulate in AM mode, specifically to remove any sensitivity to the LO wandering with ambient temperature. And no I wasn't seeing any variation bigger than 4 ppb with a 0.1 ppm TCXO wander. That's what the quandary was all about. I think I have answered the question... You cannot get around the uncertainty principle, which states that your precision in resolving frequencies is limited by the inverse of your resolution in time. Attempting some hair-brained interpolation across a peak in the FFT is just a mathematical game without any meaning. A *proper* interpolation in frequency space is performed by zero- padding the time record. When you do that, you introduce many inter-binq sidelobes. But more to the point, when the FFT bin-size is the same width as the expected drift amplitude, you get a broad, convolved bin content from the duration of the window, and attempting to say, on the basis of adjacent bin amplitudes, that you know where the frequency of *the peak* is to any better than the bin-width is just nonsense. So SpectrumLab, while offering a fancy interpolated peak frequency, must be interpreted with caution. What it reports can be wildly off-base. Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 12, 2010, at 19:47, Mark Spencer wrote: Just curious, if you have set your radio to AM mode to remove any variations due to wonder in the radio LO, how would any minor deviations in the TCXO of the radio affect the measurement ? If you are looking at the difference between a 10.00 mhz carrier and a 10.000100 mhz sub carrier wouldn't the difference always appear to be 100 hz in AM mode even if your TCXO drifted slightly ? You might be seeing the affects of varrying doppler shift between WWV and WWVH (although I'd expect the variation to be larger.) Sorry it's been a long day for me and I may be missing something obvious (: All the best Mark Spencer - Original Message From: David McClain d...@refined-audiometrics.com To: time-nuts@febo.com Sent: Tue, October 12, 2010 4:48:56 PM Subject: [time-nuts] Question about SoundCard stability? Hi, I have a Flex-3000 receiver, running freely on its internal TCXO (0.1 ppm). I have been recording the reported deviations in the measurements of the 100 Hz sizeband of 10 MHz WWV all day long. I do this in AM detection mode, to remove any variations due to the wander in the radio LO. Recording from the 48 kHz audio stream and into SpectrumLab for analysis. After taking out the measured frequency error in the soundcard (which I believe is the Flex Radio internal CODEC), of 17.5 mHz, I'm seeing frequency deviations of 0.2 mHz RMS, and +/- 1 mHz p-p, with no measurable long term drift. The FFT uses a bin size of 11.44 mHz. SpectrumLab interpolates to the peak assuming high SNR and a Hann window, with no nearby interference. This implies that my soundcard is giving me a stability of 0.004 ppm, or around 10^-9. How can this be? I already know that the TCXO wanders about by as much as +/- 1 Hz at 10 MHz due to temperature variations in the room. (10^-7). If that TCXO were used to derive the soundcard (CODEC) clock then I should be seeing variations of 25x larger. And I can assure you the CODEC is *not* being driven by an OCXO or GPSDO of any kind. Anyone? Dr. David McClain, N7AIG Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com ___ 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
Re: [time-nuts] Question about SoundCard stability?
David McClain wrote: Hi Jim, Can you give any more precise hints, e.g., links to articles? You mentioned Prony, Music, and Espirit. You caught my attention with your analogy to interferometry... Prony has been around for centuries (first used to predict tides in the 18th century, as I recall) MUSIC - Multiple Signal Classification - look for the papers by Schmidt.. IEEE Trans on Ant and Prop March 1986 ESPRIT - Estimation of signal parameters using Rotational Invariant Technique... I think Roy and Kailath are the authors of most of the early papers. Perhaps MILCOM conference papers? ___ 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] Question about SoundCard stability?
David McClain wrote: Hi Jim, Can you give any more precise hints, e.g., links to articles? You mentioned Prony, Music, and Espirit. You caught my attention with your analogy to interferometry... Yes.. many of the spectral estimation techniques share a common mathematical basis with direction finding using multiple antennas/receivers. ___ 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] Question about SoundCard stability?
Thanks for that Jim, ... I see that Prony's method bears some relationship to AR deconvolution. Interesting... http://www.dsprelated.com/dspbooks/filters/Prony_s_Method.html Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 13, 2010, at 07:32, jimlux wrote: David McClain wrote: Hi Jim, Can you give any more precise hints, e.g., links to articles? You mentioned Prony, Music, and Espirit. You caught my attention with your analogy to interferometry... Prony has been around for centuries (first used to predict tides in the 18th century, as I recall) MUSIC - Multiple Signal Classification - look for the papers by Schmidt.. IEEE Trans on Ant and Prop March 1986 ESPRIT - Estimation of signal parameters using Rotational Invariant Technique... I think Roy and Kailath are the authors of most of the early papers. Perhaps MILCOM conference papers? ___ 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] Question about SoundCard stability?
Group, The primary controller issue is too little reset because the integrating capacitor is too small or bad. After that comes too much gain. Power lead resistance would reduce the gain. Conversely, high voltage would increase gain. Don't think extra insulation is a stability issue, unless it's between the heater and the sensor. One other thing - dead time will destabilize the control loop, when there's too much delay between the heater's heat being sensed by the thermistor. This is usually a location problem. Bill Hawkins (50 years in industrial process control) -Original Message- From: Bob Camp Sent: Wednesday, October 13, 2010 5:58 AM Hi Controller cycling is often a result of one of two things: 1) Resistance in the power lead 2) Extra insulation / dead air 3) Internal controller issues There are a few other possibilities, but they are remote enough that you are unlikely to ever come across them. There's no advantage to building a controller that's cycling. It was more likely a bug than a feature. Bob ___ 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] Question about SoundCard stability?
Hi Here's pretty much how it works: Integrating capacitor: You rarely if ever see one in an oven controller that's actually acting as an integrator in the control sense. What you do see are caps to roll off the AC gain of the loop to drop noise. In other words the time constant is way to short to be useful in a control sense. Since you would need 100's or 1000's of seconds in the integrator that's not real surprising. Resistance: A normal oven controller acts as a current sink. Low temperature = pull more current. The gotcha comes when the voltage drops as the current increases. You pull more current, but don't get (much) more power. It takes longer to get back to equilibrium than normal. Once you get there you have the opposite problem on the hot side. Drop current and the power does not go down (much). The controller hunts with a period measured in seconds or 10's of seconds. Insulation: Insulation adds to the thermal gain. Pull an amp and the oven should heat up by 50 C. With X extra insulation it heats up by 100 C when you pull an amp. Twice as much gain = way more gain than the controller was designed to accommodate. Thermistor: As long as the gain is correct for the thermistor location, the controller will be stable. Too much gain / to far away is a problem. There is indeed a correct gain that pairs up with any rational thermistor location. Been around a while myself Bob On Oct 13, 2010, at 11:36 AM, Bill Hawkins wrote: Group, The primary controller issue is too little reset because the integrating capacitor is too small or bad. After that comes too much gain. Power lead resistance would reduce the gain. Conversely, high voltage would increase gain. Don't think extra insulation is a stability issue, unless it's between the heater and the sensor. One other thing - dead time will destabilize the control loop, when there's too much delay between the heater's heat being sensed by the thermistor. This is usually a location problem. Bill Hawkins (50 years in industrial process control) -Original Message- From: Bob Camp Sent: Wednesday, October 13, 2010 5:58 AM Hi Controller cycling is often a result of one of two things: 1) Resistance in the power lead 2) Extra insulation / dead air 3) Internal controller issues There are a few other possibilities, but they are remote enough that you are unlikely to ever come across them. There's no advantage to building a controller that's cycling. It was more likely a bug than a feature. Bob ___ 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] Question about SoundCard stability?
Jim Lux wrote: That's not precisely true. You can get a frequency estimate that is substantially more precise than 1/T if the snr is high. Consider super-resolution in an interferometer which is mathematically similar. What you give up is ambiguity. Probably one of the oldest techniques is that of Prony, but there are lots of others Or, now that I think about it, it's similar to what we do when measuring ADEV.. you can do a crude how many zero crossings in the time window or you can do a fit a sinusoid to a series of ADC samples. One has an uncertainty of one count/epoch, the other can be substantially better. ___ 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] Question about SoundCard stability?
Hi, I have a Flex-3000 receiver, running freely on its internal TCXO (0.1 ppm). I have been recording the reported deviations in the measurements of the 100 Hz sizeband of 10 MHz WWV all day long. I do this in AM detection mode, to remove any variations due to the wander in the radio LO. Recording from the 48 kHz audio stream and into SpectrumLab for analysis. After taking out the measured frequency error in the soundcard (which I believe is the Flex Radio internal CODEC), of 17.5 mHz, I'm seeing frequency deviations of 0.2 mHz RMS, and +/- 1 mHz p-p, with no measurable long term drift. The FFT uses a bin size of 11.44 mHz. SpectrumLab interpolates to the peak assuming high SNR and a Hann window, with no nearby interference. This implies that my soundcard is giving me a stability of 0.004 ppm, or around 10^-9. How can this be? I already know that the TCXO wanders about by as much as +/- 1 Hz at 10 MHz due to temperature variations in the room. (10^-7). If that TCXO were used to derive the soundcard (CODEC) clock then I should be seeing variations of 25x larger. And I can assure you the CODEC is *not* being driven by an OCXO or GPSDO of any kind. Anyone? Dr. David McClain, N7AIG Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com ___ 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] Question about SoundCard stability?
Hi Best guess is that the codec in the Flex runs on the same TCXO as the rest of the radio. Bob On Oct 12, 2010, at 7:48 PM, David McClain wrote: Hi, I have a Flex-3000 receiver, running freely on its internal TCXO (0.1 ppm). I have been recording the reported deviations in the measurements of the 100 Hz sizeband of 10 MHz WWV all day long. I do this in AM detection mode, to remove any variations due to the wander in the radio LO. Recording from the 48 kHz audio stream and into SpectrumLab for analysis. After taking out the measured frequency error in the soundcard (which I believe is the Flex Radio internal CODEC), of 17.5 mHz, I'm seeing frequency deviations of 0.2 mHz RMS, and +/- 1 mHz p-p, with no measurable long term drift. The FFT uses a bin size of 11.44 mHz. SpectrumLab interpolates to the peak assuming high SNR and a Hann window, with no nearby interference. This implies that my soundcard is giving me a stability of 0.004 ppm, or around 10^-9. How can this be? I already know that the TCXO wanders about by as much as +/- 1 Hz at 10 MHz due to temperature variations in the room. (10^-7). If that TCXO were used to derive the soundcard (CODEC) clock then I should be seeing variations of 25x larger. And I can assure you the CODEC is *not* being driven by an OCXO or GPSDO of any kind. Anyone? Dr. David McClain, N7AIG Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com ___ 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] Question about SoundCard stability?
Best guess is that the codec in the Flex runs on the same TCXO as the rest of the radio. That's my best guess too... so how is it that I'm seeing 25x less variation in the audio signal than the TCXO is capable of yielding? I have the central air conditioner cycling on and off all day (Tucson desert), and I can see the radio wander by as much as +/-2-4 Hz at times, at 10 MHz. It shows an irregular sawtooth deviation in sync with the cycling of the air conditioner, with a period of about 45 minutes, 15 of which are cool down times. This is mid-day, so the ionosphere is not producing much in the way of Doppler shifting. And even if it were, that shouldn't be measurable to me at the audio frequencies. Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 12, 2010, at 16:58, Bob Camp wrote: Hi Best guess is that the codec in the Flex runs on the same TCXO as the rest of the radio. Bob On Oct 12, 2010, at 7:48 PM, David McClain wrote: Hi, I have a Flex-3000 receiver, running freely on its internal TCXO (0.1 ppm). I have been recording the reported deviations in the measurements of the 100 Hz sizeband of 10 MHz WWV all day long. I do this in AM detection mode, to remove any variations due to the wander in the radio LO. Recording from the 48 kHz audio stream and into SpectrumLab for analysis. After taking out the measured frequency error in the soundcard (which I believe is the Flex Radio internal CODEC), of 17.5 mHz, I'm seeing frequency deviations of 0.2 mHz RMS, and +/- 1 mHz p-p, with no measurable long term drift. The FFT uses a bin size of 11.44 mHz. SpectrumLab interpolates to the peak assuming high SNR and a Hann window, with no nearby interference. This implies that my soundcard is giving me a stability of 0.004 ppm, or around 10^-9. How can this be? I already know that the TCXO wanders about by as much as +/- 1 Hz at 10 MHz due to temperature variations in the room. (10^-7). If that TCXO were used to derive the soundcard (CODEC) clock then I should be seeing variations of 25x larger. And I can assure you the CODEC is *not* being driven by an OCXO or GPSDO of any kind. Anyone? Dr. David McClain, N7AIG Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com ___ 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] Question about SoundCard stability?
Okay, perhaps I should rephrase the question... Is is reasonable to expect a TCXO to perform at 4e-9 over the FFT window period of about 87 sec? I can only imagine that the enormous (87 s) averaging period is making my measurements look so good. Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com ___ 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] Question about SoundCard stability?
Hi Yes it is a reasonable expectation as long as you don't have a lot of drafts. A good TCXO can get down to sub 0.1 ppb over that period. Bob On Oct 12, 2010, at 8:21 PM, David McClain wrote: Okay, perhaps I should rephrase the question... Is is reasonable to expect a TCXO to perform at 4e-9 over the FFT window period of about 87 sec? I can only imagine that the enormous (87 s) averaging period is making my measurements look so good. Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com ___ 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] Question about SoundCard stability?
Hi Bob and Dave, On 10/13/2010 02:57 AM, Bob Camp wrote: Hi Yes it is a reasonable expectation as long as you don't have a lot of drafts. A good TCXO can get down to sub 0.1 ppb over that period. This is why I like ADEV plots in datasheets. I rarely get to see them. TDEV plots is a nice complement naturally. Cheers, Magnus Bob On Oct 12, 2010, at 8:21 PM, David McClain wrote: Okay, perhaps I should rephrase the question... Is is reasonable to expect a TCXO to perform at 4e-9 over the FFT window period of about 87 sec? I can only imagine that the enormous (87 s) averaging period is making my measurements look so good. Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com ___ 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] Question about SoundCard stability?
Ahh.. so... Now since my TCXO is drifting to and fro by 1-2 Hz over the period of 45 minutes, why don't I see similar drift in the 100 Hz audio signal, down around 5 mHz amplitude? This happens to be about the same size at the FFT bins. So I am led to conclude that interpolated peak frequencies are a bogus technique, and you can only truly count on variations on the order of the FFT cell size as being measurable... Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 12, 2010, at 17:57, Bob Camp wrote: Hi Yes it is a reasonable expectation as long as you don't have a lot of drafts. A good TCXO can get down to sub 0.1 ppb over that period. Bob On Oct 12, 2010, at 8:21 PM, David McClain wrote: Okay, perhaps I should rephrase the question... Is is reasonable to expect a TCXO to perform at 4e-9 over the FFT window period of about 87 sec? I can only imagine that the enormous (87 s) averaging period is making my measurements look so good. Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com ___ 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] Question about SoundCard stability?
1 Hz in 10Mhz is about the same ratio as 5mHz in 64Khz. This would make sense if the Clock for the A/D is divided off the same TXCO. Or am I missing something. The reason I jumped in, in a recent frequency measuring contest the winner was using that interpolation for his results. Regards Randall ZL2RJP -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of David McClain Sent: Wednesday, 13 October 2010 2:18 p.m. To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Question about SoundCard stability? Ahh.. so... Now since my TCXO is drifting to and fro by 1-2 Hz over the period of 45 minutes, why don't I see similar drift in the 100 Hz audio signal, down around 5 mHz amplitude? This happens to be about the same size at the FFT bins. So I am led to conclude that interpolated peak frequencies are a bogus technique, and you can only truly count on variations on the order of the FFT cell size as being measurable... Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 12, 2010, at 17:57, Bob Camp wrote: Hi Yes it is a reasonable expectation as long as you don't have a lot of drafts. A good TCXO can get down to sub 0.1 ppb over that period. Bob On Oct 12, 2010, at 8:21 PM, David McClain wrote: Okay, perhaps I should rephrase the question... Is is reasonable to expect a TCXO to perform at 4e-9 over the FFT window period of about 87 sec? I can only imagine that the enormous (87 s) averaging period is making my measurements look so good. Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com ___ 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. ___ 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] Question about SoundCard stability?
Hi, No you aren't missing anything... except that I *DON'T* see the 5 mHz drift that one should expect. Hence my contention that relying on interpolated frequencies from FFT peaks and their adjacent bins is bogus when the FFT bin size is as large or larger than the expected drift. Somehow that seems like it violated the uncertainty principle in the first place. And now I'm seeing that the principle rules supreme. I'm going to do another run, with a bin size about 1/4 the expected drift, to see if the reported interpolated peak frequencies really do show the drift one should expect. Cheers, Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 12, 2010, at 18:25, Randall Prentice wrote: 1 Hz in 10Mhz is about the same ratio as 5mHz in 64Khz. This would make sense if the Clock for the A/D is divided off the same TXCO. Or am I missing something. The reason I jumped in, in a recent frequency measuring contest the winner was using that interpolation for his results. Regards Randall ZL2RJP -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts- boun...@febo.com] On Behalf Of David McClain Sent: Wednesday, 13 October 2010 2:18 p.m. To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Question about SoundCard stability? Ahh.. so... Now since my TCXO is drifting to and fro by 1-2 Hz over the period of 45 minutes, why don't I see similar drift in the 100 Hz audio signal, down around 5 mHz amplitude? This happens to be about the same size at the FFT bins. So I am led to conclude that interpolated peak frequencies are a bogus technique, and you can only truly count on variations on the order of the FFT cell size as being measurable... Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 12, 2010, at 17:57, Bob Camp wrote: Hi Yes it is a reasonable expectation as long as you don't have a lot of drafts. A good TCXO can get down to sub 0.1 ppb over that period. Bob On Oct 12, 2010, at 8:21 PM, David McClain wrote: Okay, perhaps I should rephrase the question... Is is reasonable to expect a TCXO to perform at 4e-9 over the FFT window period of about 87 sec? I can only imagine that the enormous (87 s) averaging period is making my measurements look so good. Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com ___ 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. ___ 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] Question about SoundCard stability?
Just curious, if you have set your radio to AM mode to remove any variations due to wonder in the radio LO, how would any minor deviations in the TCXO of the radio affect the measurement ? If you are looking at the difference between a 10.00 mhz carrier and a 10.000100 mhz sub carrier wouldn't the difference always appear to be 100 hz in AM mode even if your TCXO drifted slightly ? You might be seeing the affects of varrying doppler shift between WWV and WWVH (although I'd expect the variation to be larger.) Sorry it's been a long day for me and I may be missing something obvious (: All the best Mark Spencer - Original Message From: David McClain d...@refined-audiometrics.com To: time-nuts@febo.com Sent: Tue, October 12, 2010 4:48:56 PM Subject: [time-nuts] Question about SoundCard stability? Hi, I have a Flex-3000 receiver, running freely on its internal TCXO (0.1 ppm). I have been recording the reported deviations in the measurements of the 100 Hz sizeband of 10 MHz WWV all day long. I do this in AM detection mode, to remove any variations due to the wander in the radio LO. Recording from the 48 kHz audio stream and into SpectrumLab for analysis. After taking out the measured frequency error in the soundcard (which I believe is the Flex Radio internal CODEC), of 17.5 mHz, I'm seeing frequency deviations of 0.2 mHz RMS, and +/- 1 mHz p-p, with no measurable long term drift. The FFT uses a bin size of 11.44 mHz. SpectrumLab interpolates to the peak assuming high SNR and a Hann window, with no nearby interference. This implies that my soundcard is giving me a stability of 0.004 ppm, or around 10^-9. How can this be? I already know that the TCXO wanders about by as much as +/- 1 Hz at 10 MHz due to temperature variations in the room. (10^-7). If that TCXO were used to derive the soundcard (CODEC) clock then I should be seeing variations of 25x larger. And I can assure you the CODEC is *not* being driven by an OCXO or GPSDO of any kind. Anyone? Dr. David McClain, N7AIG Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com ___ 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] Question about SoundCard stability?
On Oct 12, 2010, at 6:09 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Hi Bob and Dave, On 10/13/2010 02:57 AM, Bob Camp wrote: Hi Yes it is a reasonable expectation as long as you don't have a lot of drafts. A good TCXO can get down to sub 0.1 ppb over that period. This is why I like ADEV plots in datasheets. I rarely get to see them. TDEV plots is a nice complement naturally. Cheers, Magnus Bob And I wish there were adev plots for cheap tcxo's on the mgr data sheets ___ 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] Question about SoundCard stability?
Yes, indeed. I demodulate in AM mode, specifically to remove any sensitivity to the LO wandering with ambient temperature. And no I wasn't seeing any variation bigger than 4 ppb with a 0.1 ppm TCXO wander. That's what the quandary was all about. I think I have answered the question... You cannot get around the uncertainty principle, which states that your precision in resolving frequencies is limited by the inverse of your resolution in time. Attempting some hair-brained interpolation across a peak in the FFT is just a mathematical game without any meaning. A *proper* interpolation in frequency space is performed by zero- padding the time record. When you do that, you introduce many inter- bin sidelobes. But more to the point, when the FFT bin-size is the same width as the expected drift amplitude, you get a broad, convolved bin content from the duration of the window, and attempting to say, on the basis of adjacent bin amplitudes, that you know where the frequency of *the peak* is to any better than the bin-width is just nonsense. So SpectrumLab, while offering a fancy interpolated peak frequency, must be interpreted with caution. What it reports can be wildly off- base. Dr. David McClain Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com On Oct 12, 2010, at 19:47, Mark Spencer wrote: Just curious, if you have set your radio to AM mode to remove any variations due to wonder in the radio LO, how would any minor deviations in the TCXO of the radio affect the measurement ? If you are looking at the difference between a 10.00 mhz carrier and a 10.000100 mhz sub carrier wouldn't the difference always appear to be 100 hz in AM mode even if your TCXO drifted slightly ? You might be seeing the affects of varrying doppler shift between WWV and WWVH (although I'd expect the variation to be larger.) Sorry it's been a long day for me and I may be missing something obvious (: All the best Mark Spencer - Original Message From: David McClain d...@refined-audiometrics.com To: time-nuts@febo.com Sent: Tue, October 12, 2010 4:48:56 PM Subject: [time-nuts] Question about SoundCard stability? Hi, I have a Flex-3000 receiver, running freely on its internal TCXO (0.1 ppm). I have been recording the reported deviations in the measurements of the 100 Hz sizeband of 10 MHz WWV all day long. I do this in AM detection mode, to remove any variations due to the wander in the radio LO. Recording from the 48 kHz audio stream and into SpectrumLab for analysis. After taking out the measured frequency error in the soundcard (which I believe is the Flex Radio internal CODEC), of 17.5 mHz, I'm seeing frequency deviations of 0.2 mHz RMS, and +/- 1 mHz p-p, with no measurable long term drift. The FFT uses a bin size of 11.44 mHz. SpectrumLab interpolates to the peak assuming high SNR and a Hann window, with no nearby interference. This implies that my soundcard is giving me a stability of 0.004 ppm, or around 10^-9. How can this be? I already know that the TCXO wanders about by as much as +/- 1 Hz at 10 MHz due to temperature variations in the room. (10^-7). If that TCXO were used to derive the soundcard (CODEC) clock then I should be seeing variations of 25x larger. And I can assure you the CODEC is *not* being driven by an OCXO or GPSDO of any kind. Anyone? Dr. David McClain, N7AIG Chief Technical Officer Refined Audiometrics Laboratory 4391 N. Camino Ferreo Tucson, AZ 85750 email: d...@refined-audiometrics.com phone: 1.520.390.3995 web: http://refined-audiometrics.com ___ 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.
