Re: [time-nuts] GPSDO uncertainties
Nobody in this group could answer my question. Thankyou, nevertheless, to all those who replied. Kind regards...Don Collie jnr ZL4GX On Wed, Oct 10, 2018 at 7:33 AM Mark Sims wrote: > I did some measurements on the Trimble using a TAPR TICC. The "PPS" > adevs are the Trimble and the "OSC" adevs are an Oscilloquartz STAR-4. > > > http://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/msg1143960/#msg1143960 > > --- > > >Has anyone on the list used a GPSDO like Don's? > ___ > 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] Fwd: IFCS-EFTF 2019: Call for Papers
Hi Chris, On 10/10/18 4:36 PM, Attila Kinali wrote: > On Sat, 22 Sep 2018 06:42:59 -0500 > Chris Howard wrote: > >> I read these "calls for papers" things and try to think of >> something "meta" since I am not anywhere near the 'bleeding edge' >> of any such topic. Maybe a survey of the number of NTP-using >> devices in the world (people love charts and statistics), >> or something about the history of something. > > You don't need to be at near the bleeding edge for a successful > paper. There are still a lot of questions that nobody has asked, > much less answered. A lot of these questions arise only when > you work in the trenches and try to properly understand what > is going on. So, if you think you have something that nobody > has writen about before, please do so. I agree fully. As you come in and view things with a fresh pair of eyes, seeing problems, trying to make sense of things you bring up topics that others overlooked. Very often you get "We never spent much time on that" or similar comments from the folks you thought had checked *EVERYTHING*. I intentionally sent the Call for Papers here, since I think there might be more people out there that can contribute. Cheers, Magnus ___ 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] Noise of digital frequency circuits (was: Programmable clock for BFO use....noise)
In message , Azelio Boriani writes: >How many samples of the Loran input signal in that 1/6th of the period? Not many: At 5MHz sample rate it was 8 samples. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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] Noise of digital frequency circuits (was: Programmable clock for BFO use....noise)
How many samples of the Loran input signal in that 1/6th of the period? On Wed, Oct 10, 2018 at 5:22 PM Poul-Henning Kamp wrote: > > > In message <20181010165425.df6d24aa3825ca765f301...@kinali.ch>, Attila Kinali > w > rites: > > >> >"A Physical Sine-to-Square Converter Noise Model," > >> > by Kinali, 2018 > >> > >[...] > >Hence the first gain stage already aliases the noise from its whole > >bandwidth, which can be a lot of noise if the BW is large. > > Some years ago I spent a lot of time trying to find a way to > "oversample" single-shots of the 3rd zero-crossing of Loran-C > signals. > > My finding was that of all the technologies available, the simple > comparator was the worst, because it only "looks" at a very tiny > time-slice around the actual zero-crossing, and thus is needlessly > sensitive to noise. > > To make matters worse, the window is always late, it cannot be > symmetric, because at least some electrons have to move in the > opposite direction before the comparator changes state. HP has > interesting info about this in an old app-note on TI counters. > > If the incoming curve-shape is unknown, that is the only thing one > can do, but when the curve-shape is known to be a sine or a loran-C, > better results can be had with a wider time window. > > The final version of my code (This was SDR with an ADC directly on > the antenna) found the optimal least-square match between the sampled > signal and the theoretical signal for a configurable time-window, > produced the zero crossing from the theoretical signal. > > Best performance was around 1/6-th period, which I'm sure there was > a reason for, but I gave up looking for it. > > I have not found a way to implement it in the analog domain. > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > p...@freebsd.org | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > > ___ > 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] Noise of digital frequency circuits (was: Programmable clock for BFO use....noise)
In message <20181010165425.df6d24aa3825ca765f301...@kinali.ch>, Attila Kinali w rites: >> >"A Physical Sine-to-Square Converter Noise Model," >> > by Kinali, 2018 >> >[...] >Hence the first gain stage already aliases the noise from its whole >bandwidth, which can be a lot of noise if the BW is large. Some years ago I spent a lot of time trying to find a way to "oversample" single-shots of the 3rd zero-crossing of Loran-C signals. My finding was that of all the technologies available, the simple comparator was the worst, because it only "looks" at a very tiny time-slice around the actual zero-crossing, and thus is needlessly sensitive to noise. To make matters worse, the window is always late, it cannot be symmetric, because at least some electrons have to move in the opposite direction before the comparator changes state. HP has interesting info about this in an old app-note on TI counters. If the incoming curve-shape is unknown, that is the only thing one can do, but when the curve-shape is known to be a sine or a loran-C, better results can be had with a wider time window. The final version of my code (This was SDR with an ADC directly on the antenna) found the optimal least-square match between the sampled signal and the theoretical signal for a configurable time-window, produced the zero crossing from the theoretical signal. Best performance was around 1/6-th period, which I'm sure there was a reason for, but I gave up looking for it. I have not found a way to implement it in the analog domain. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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] Noise of digital frequency circuits (was: Programmable clock for BFO use....noise)
On Mon, 17 Sep 2018 00:37:43 -0500 Dana Whitlow wrote: > For example, take the case of 10 MHz starting frequency; the phase noise > several MHz out > is likely to be nil. But divide the 10 MHz down to, say, 1 Hz; then > there's likely to be quite a > lot of phase noise within "folding range" of many Nyquist bands about 1 Hz. For most low-noise systems, the white noise floor is dominated by the thermal (Johnson) noise due to the 50 Ohm source impedance. Although, one could say this noise is very low, it is wrong to assume it can be ignored. Jitter, for a low-noise 10MHz system, is dominated by the white noise and very little of the contribution is due to flicker noise (unless you go for very long integration times). > This, again, is why I wonder so much about our efforts in re-synthesizing > higher frequencies from > the 1PPS from GPS receivers. I don't know much the architecture of GPS > receivers, but it seems > to me it would sure be nice if there were some convenient way to extract a > clean signal at the > chipping rate, for use in generating standard reference frequencies. There are systems that do that, but one has to use signals from multiple satellites to get the noise down. But for proper combination of multiple signals one has to calculate a fix. Hence it is easier to just check the reference oscillators phase against the fix. And synthesizing from PPS is exactly this process of referencing the 10MHz oscillator to the calculated fixes. Attila Kinali -- Science is made up of so many things that appear obvious after they are explained. -- Pardot Kynes ___ 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] Noise of digital frequency circuits (was: Programmable clock for BFO use....noise)
Salut Mattia, On Thu, 20 Sep 2018 12:31:01 +0200 Mattia Rizzi wrote: > > People talk of aliasing and sampling, > > but do not describe where the sampling happens in the first place. > > After all, it's a time-continuous system and as such, there is no > > sampling. > > I would say that the sampling occurs when you're using only a slice of an > input signal. For instance, If you're using only the zero-crossing slice > of a sinewave to produce a divided version rather than the full envelope. > It's a matter of how you process information in your circuit. Yes. That's the basic way how the sampling/noise-aliasing happens. I just wonder why nobody (as far as I am aware of) has described this process in detail. It looks obvious and if you look at the general information theory/signal processing literature, it almost falls out of the basic text books. > >"A Physical Sine-to-Square Converter Noise Model," > > by Kinali, 2018 > > I read the paper, very interesting as well! > I have a minor remark, in the paper you relate the ISF (let's say > "sampling window") to the output slew rate of the comparator. I would say > that the sampling window should be related to the comparator input stage > bandwidth. If you have an high bandwidth input stage (e.g. 5 GHz) followed > by a slew rate limited output stage (e.g. 100 MHz) , high frequency noise > will trigger the output circuit and aliasing it. Viceversa, if you have a > low bandwidth input stage, even if the output stage is very fast, you don't > get input noise aliasing. Yes, exactly! Though, you have to look at a comparator IC as a multi-stage system, where each gain-stage represents one "comparator" in my paper. Hence the first gain stage already aliases the noise from its whole bandwidth, which can be a lot of noise if the BW is large. Hmm.. I probably should have made it more clear that the model I defined applies only to single gain stages and not to whole components. Attila Kinali -- Science is made up of so many things that appear obvious after they are explained. -- Pardot Kynes ___ 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] Noise of digital frequency circuits
On Thu, 20 Sep 2018 23:45:27 +0200 Achim Gratz wrote: > Attila Kinali writes: > > People talk of aliasing and sampling, but do not describe where the > > sampling happens in the first place. After all, it's a > > time-continuous system and as such, there is no sampling. > > That may be quibbling over terminology and definitions not actually > specified in those papers. Localization in the frequency domain > requires periodicity in the time domain (by definition) and moving > spectral features around can be done by convolution of the noise > spectrum with a localized signal (not necessarily of compact support, > but assume for the moment it is so you get a clearly defined pivot > frequency). That means you need to do multiplication in the time domain > with something periodic, so all you need to produce noise folding is for > instance a periodically varying NTF. I guess we can tick that box in > all instances you've mentioned. Exactly. But sofar nobody has properly specified what the other term of the multiplication is. > > One could look at it as a (sub-harmonic) mixing system, but > > even that analogy falls short, as there is no second input. > > Does it even matter if you call it a "second input"? Not really, but if you want to argue about the noise folding process as being a sub-harmonic mixing process, then you need to specify what the second signal is that does the mixing. Which in turn is again specifying the two terms of the multiplication process as above. > > It also fails at describing why there is not infinite energy being > > down-mixed, as the resulting harmonic sum does not converge. > > The actual integral or sum to compute would likely be governed by > something sinc-like, so convergence would eventually still happen with > any physically realizable input. That assumes you don't already need to > start with some generalization of the Fourier transform that has more > strictly defined convergence behaviour. This is exactly one of the things that made me stumble when I first went through the relevant literature. A sinc pulse-train in time domain becomes a rectangular pulse-train in the frequency domain, whose amplitude decays with 1/f. This means, the folded down noise is a sum of terms decaying with 1/f. But this sum does not converge, ie it goes to infinity. One has to add an addtional filter of some sort that increases the rate of decay to 1/f^2 for the sum to converge. > Funnily a paper I just read in TCAS-I (February 2017) by Pepe and > Andreani about phase noise in harmonic oscillators seems to mention this > (I think) as a known result w.r.t. flicker noise upconversion and Oh.. thanks! I somehow missed this paper. The results look indeed interesting. But I have to spend some time to work through the math in order to fully understand it. Attila Kinali -- Science is made up of so many things that appear obvious after they are explained. -- Pardot Kynes ___ 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
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] Fwd: IFCS-EFTF 2019: Call for Papers
On Sat, 22 Sep 2018 06:42:59 -0500 Chris Howard wrote: > I read these "calls for papers" things and try to think of > something "meta" since I am not anywhere near the 'bleeding edge' > of any such topic. Maybe a survey of the number of NTP-using > devices in the world (people love charts and statistics), > or something about the history of something. You don't need to be at near the bleeding edge for a successful paper. There are still a lot of questions that nobody has asked, much less answered. A lot of these questions arise only when you work in the trenches and try to properly understand what is going on. So, if you think you have something that nobody has writen about before, please do so. Attila Kinali -- Science is made up of so many things that appear obvious after they are explained. -- Pardot Kynes ___ 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.
