Re: [time-nuts] Modified Allan Deviation and counter averaging
Hi James, On 07/30/2015 06:34 PM, James Peroulas wrote: My understanding is that MVAR(m*tau0) is equivalent to filtering the phase samples x(n) by averaging m samples to produce x'(n) [x'(n)=1/m*(x(n)+x(n+1)..x(n+m-1))] and then calculating AVAR for tau=m*tau0 on the filtered sequence. Thus, MVAR already performs an averaging/ lowpass filtering operation. Adding another averaging filter prior to calculating MVAR would seem to be defining a new type of stability measurement. Yes, fhat's how MVAR works. Not familiar with the 5370... Is it possible to configure it to average measurements over the complete tau0 interval with no dead time between measurements? Assuming the 5370 can average 100 evenly spaced measurements within the measurement interval (1s?), calculating MVAR on the captured sequence would produce MVAR(m*.01)) for m being a multiple of 100. i.e., tau0 here is actually .01, not 1, but values for MVAR(tau) for tau's less than 1s are not available. The stock 5370 isn't a great tool for this. The accelerator board that replaces the CPU and allows for us to add algorithms, makes the counter hardware much more adapted for this setup. Shouldn't the quantization/ measurement noise power be easy to measure? Can't it just be subtracted from the MVAR plot? I've done this with AVAR in the past to produce 'seemingly' meaningful results (i.e. I'm not an expert). You can curve-fit an estimation of that noise and "remove" it from the plot. For lower taus the confidence intervals will suffer in practice. I calculated the PSD of x(n) and it was clear where the measurements were being limited by noise (flat section at higher frequencies). From this I was able to estimate the measurement noise power. It is. Notice that some of it is noise and some is noise-like systematics from the quantization. AVAR_MEASURED(tau)=AVAR_CUT(tau)+AVAR_REF(tau)+AVAR_MEAS(tau) i.e. The measured AVAR is equal to the sum of the AVAR of the clock under test (CUT), the AVAR of the reference clock, and the AVAR of the measurement noise. If the reference clock is much better than the CUT AVAR_REF(tau) can be ignored. AVAR_MEAS(tau) is known from the PSD of x(n) and can be subtracted from AVAR_MEASURED(tau) to produce a better estimate of AVAR_CUT(tau). Depending on the confidence intervals of AVAR_MEASURED(tau) and the noise power estimate, you can get varying degrees of cancellation. 10dB of improvement seemed quite easy to obtain. Using the Lambda counter approach, filtering with the average blocks of Modified Allan Variance, makes the white phase noise slope go 1/tau^3 rather than 1/tau^2 as it is for normal Allan Variance. This means that the limiting slope of the white noise will cut over to the actual noise for lower tau. so that is an important tool already there. Also, it achieves it with known properties in confidence intervals. Using the Omega counter approach, you can get further improvements by about 1.25 dB, which is then deemed optimal as the Omega counter method is a linear regression / least square method for estimating the frequency samples and then those is used for AVAR processing. The next trick to pull is to do cross correlation of two independent channels, so that their noise does not correlate. This can help for some of it, but systematics can become a limiting factor. Cheers, Magnus James Message: 7 Date: Tue, 28 Jul 2015 21:51:07 + From: Poul-Henning Kamp To: time-nuts@febo.com Subject: [time-nuts] Modified Allan Deviation and counter averaging Message-ID: <2884.1438120...@critter.freebsd.dk> Content-Type: text/plain; charset="us-ascii" Sorry this is a bit long-ish, but I figure I'm saving time putting in all the details up front. The canonical time-nut way to set up a MVAR measurement is to feed two sources to a HP5370 and measure the time interval between their zero crossings often enough to resolve any phase ambiguities caused by frequency differences. The computer unfolds the phase wrap-arounds, and calculates the MVAR using the measurement rate, typically 100, 10 or 1 Hz, as the minimum Tau. However, the HP5370 has noise-floor in the low picoseconds, which creates the well known diagonal left bound on what we can measure this way. So it is tempting to do this instead: Every measurement period, we let the HP5370 do a burst of 100 measurements[*] and feed the average to MVAR, and push the diagonal line an order of magnitude (sqrt(100)) further down. At its specified rate, the HP5370 will take 1/30th of a second to do a 100 sample average measurement. If we are measuring once each second, that's only 3% of the Tau. No measurement is ever instantaneous, simply because the two zero crossings are not happening right at the mesurement epoch. If I measure two 10MHz signals the canonical way, the first zero crossing could come as late as 100(+epsilon) nanoseconds after the epoch, and the second as much as 100(+epsilon) nanoseconds later. An actual point o
Re: [time-nuts] Source of Rubidium Lamp for Efratom FRK
Thanks Bob and Chuck for the comments. As Bob says, the lamp is easily replaceable (just unscrews) and the service manual gives the procedure. Maybe I'm too worried about how long the lamp is likely to last but the lamp voltage was below the range stated in both the Efratom and Racal manuals. The lamp itself certainly works but is a bit blackened. I had hoped that Corby's procedure for rejuvenating lamps might do more than it did for this particular lamp - maybe I chickened out too early in the heating process, but I was monitoring the local temperature with a thermocouple at over 150C consistently. Anyway, I have asked Sematron in the UK whether a replacement lamp can still be had. If it is available at $300-500, it is really not economic as the whole Racal 9475 cost a lot less. Mind you, I did put in a fair amount of work repairing both the Racal main unit and the FRK to get the system working. So, probably the best way of getting a spare lamp is to try and pick up another whole FRK and hope that its lamp still has some life in it. Anybody know whether the same lamp was fitted to other Efratom Rb sources? This would widen the search somewhat. Mike >On 30 July, 2015 11:40 Bob Camp" wrote: >Hi > >In the (unique) case of the Efratom “light bulb” cell, you can indeed pop them >out and replace them. Been there / done that with the (then) factory guys >involved. >The new bulbs were sold as replacements and did indeed fix the problem of >a dead bulb. About the only added work involved was to re-adjust the frequency >after it had burned in for a few weeks. Repeating that adjustment process as >it was >done then would be a bit tough with no Loran :) I still have the Austron, >apparently >it was well enough cared for as a demo in the UK that it’s survived all these >years. > >Bob > >> On Jul 29, 2015, at 11:49 PM, Chuck Harris wrote: >> >> Hi Mike, >> >> The Rb lamp voltage is just a guide. If your Rb isn't working, then it >> is important... If it is, it is just a guide. >> >> If your bulb is clear, and it is glowing, it is probably also working. >> >> I seem to recall from HP's descriptions of how their 5065 was made >> that the lamp, and filter cell are a specially matched set. Just any >> lamp is not necessarily going to work with any filter cell. >> >> -Chuck Harris >> >> Mike Niven wrote: >> Thanks for the comment Bob. Tracing Efratom through the ages, I see they >> are now >> Microsemi. I wonder whether they will still have a lamp for such a >> geriatric Rb >> source and at what price - probably more than the cost of the complete Racal >> 9475? I will follow it up anyway as I hardly ever see working or scrap FRKs >> for >> sale in the UK. >>> On Tue, 28/7/15, Bob Camp wrote: >>> >>> Hi >>> >>> The Efratom bulbs have a “magic mix” of gas in them. The only place I have >>> ever >>> bought them is direct from Efratom. They were fairly expensive back in the >>> early 90’s … >>> >>> Bob >>> On Jul 28, 2015, at 9:56 AM, Mike Niven wrote: Would anyone know of a source of the Rubidium bulb fitted in the Efratom FRK (and probably other FRx) standards? I have repaired and refurbished my Racal 9475, which is fitted with the older style FRK (not -H or -L) module. It is working properly at present but the lamp voltage is down to 5.5V, which is below the stated minimum of 6V. I have tried rejuvenating the bulb using a hot air gun, as described by Corby, but this has had no obvious impact. Hence, I have little feel for how much life the existing lamp has left and a spare would be good for my peace of mind. Many thanks. Mike ___ 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] Just When You Thought It Was Safe ....
Well if you look at his sales counts it isn't working very well, and now after the latest comments he might have to deal with a backlash effect. Right now I'm definitely in at $60-70, unlikely but possibly in at $100, although that is still hard to justify, $150 not a chance. I'd buy a James Miller GPSDO before I would buy a KS24361 at $150. It's not nearly the same bang for the buck adev wise as a KS24361, even at $150, but at least I get some serious space savings and I am far more confident that the money is going to an honest seller. -- Thomas Valerio > It is a common fishing technique, and the guy has done this > several times over the last year, or so. > > When his sales dry up, he drops the price to $100, and then > waits for a sale I'm pretty sure that he monitors this > group for news of the new low price to leak out... and then > quickly he bops the price back up to $150. > > I considered buying one about two such casts ago, and missed > the low price point... and then decided that I didn't really > need to play this game with the seller. > > -Chuck Harris > > > > paul swed wrote: >> Bob >> Just took a look and the pair seems to still be at $150. Maybe it was a >> special? >> The ovens are as you say $25 each and shipping for either 1 or 2 is >> $18.75. >> Regards >> Paul >> WB8TSL >> >> On Mon, Jul 27, 2015 at 8:44 PM, Bob Camp wrote: >> >>> Hi >>> >>> For all of you who dropped off the list back around Christmas and >>> decided >>> to re-join now that the KS box yack has died down â¦.. >>> >>> The usual auction site now has the pair selling for $100 and the âno >>> GPS >>> insideâ part of the pair selling for $25 or two for $50. >>> >>> Mighty fair prices considering that they are new old stock rather than >>> salvage units. >>> >>> (Yes I suppose that if we all hold off, they could go lower still. They >>> also could head over for scrap metal reclamation) >>> >>> 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] Source of Rubidium Lamp for Efratom FRK
Hi Mike, That bulb was sealed with an oxy-fuel torch at the melting point of the glass. It was then annealed, starting at a much higher temperature than 150C before cooled slowly to avoid breaking. Heat it uniformly with your hot air gun until it is no longer black. Reducethe heat slowly to allow it to cool... or, you can toss it into a can full of white ashes from your fireplace. Or, leave it be and wait until it really fails before fixing it. -Chuck Harris Mike Niven wrote: Thanks Bob and Chuck for the comments. As Bob says, the lamp is easily replaceable (just unscrews) and the service manual gives the procedure. Maybe I'm too worried about how long the lamp is likely to last but the lamp voltage was below the range stated in both the Efratom and Racal manuals. The lamp itself certainly works but is a bit blackened. I had hoped that Corby's procedure for rejuvenating lamps might do more than it did for this particular lamp - maybe I chickened out too early in the heating process, but I was monitoring the local temperature with a thermocouple at over 150C consistently. Anyway, I have asked Sematron in the UK whether a replacement lamp can still be had. If it is available at $300-500, it is really not economic as the whole Racal 9475 cost a lot less. Mind you, I did put in a fair amount of work repairing both the Racal main unit and the FRK to get the system working. So, probably the best way of getting a spare lamp is to try and pick up another whole FRK and hope that its lamp still has some life in it. Anybody know whether the same lamp was fitted to other Efratom Rb sources? This would widen the search somewhat. Mike ___ 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] Source of Rubidium Lamp for Efratom FRK
Hi At least the “common wisdom” always was that the replaceable lamps all came out of the same production process. There may have been enhancements as time went on, but the lamps all *looked* the same. There also is very little change in the circuits that use them. The observation made earlier by others still holds - there is no real guarantee that your gizmo has a bad lamp. They get pretty black and still work OK. There are a LOT of other things that can age out / wear out / go bad in one of these gizmos. That’s not to say don’t replace the bulb. It’s more to say that having a second working Rb might have some other benefits ….. Bob > On Jul 31, 2015, at 10:04 AM, Mike Niven wrote: > > Thanks Bob and Chuck for the comments. As Bob says, the lamp is easily > replaceable (just unscrews) and the service manual gives the procedure. > Maybe I'm too worried about how long the lamp is likely to last but the lamp > voltage was below the range stated in both the Efratom and Racal manuals. > The lamp itself certainly works but is a bit blackened. I had hoped that > Corby's procedure for rejuvenating lamps might do more than it did for this > particular lamp - maybe I chickened out too early in the heating process, but > I was monitoring the local temperature with a thermocouple at over 150C > consistently. Anyway, I have asked Sematron in the UK whether a replacement > lamp can still be had. If it is available at $300-500, it is really not > economic as the whole Racal 9475 cost a lot less. Mind you, I did put in a > fair amount of work repairing both the Racal main unit and the FRK to get the > system working. So, probably the best way of getting a spare lamp > is to try and pick up another whole FRK and hope that its lamp still has some > life in it. Anybody know whether the same lamp was fitted to other Efratom > Rb sources? This would widen the search somewhat. > > Mike > > >> On 30 July, 2015 11:40 Bob Camp" wrote: >> Hi >> >> In the (unique) case of the Efratom “light bulb” cell, you can indeed pop >> them >> out and replace them. Been there / done that with the (then) factory guys >> involved. >> The new bulbs were sold as replacements and did indeed fix the problem of >> a dead bulb. About the only added work involved was to re-adjust the >> frequency >> after it had burned in for a few weeks. Repeating that adjustment process as >> it was >> done then would be a bit tough with no Loran :) I still have the Austron, >> apparently >> it was well enough cared for as a demo in the UK that it’s survived all >> these years. >> >> Bob >> >>> On Jul 29, 2015, at 11:49 PM, Chuck Harris wrote: >>> >>> Hi Mike, >>> >>> The Rb lamp voltage is just a guide. If your Rb isn't working, then it >>> is important... If it is, it is just a guide. >>> >>> If your bulb is clear, and it is glowing, it is probably also working. >>> >>> I seem to recall from HP's descriptions of how their 5065 was made >>> that the lamp, and filter cell are a specially matched set. Just any >>> lamp is not necessarily going to work with any filter cell. >>> >>> -Chuck Harris >>> >>> Mike Niven wrote: >>> Thanks for the comment Bob. Tracing Efratom through the ages, I see they >>> are now >>> Microsemi. I wonder whether they will still have a lamp for such a >>> geriatric Rb >>> source and at what price - probably more than the cost of the complete Racal >>> 9475? I will follow it up anyway as I hardly ever see working or scrap FRKs >>> for >>> sale in the UK. On Tue, 28/7/15, Bob Camp wrote: Hi The Efratom bulbs have a “magic mix” of gas in them. The only place I have ever bought them is direct from Efratom. They were fairly expensive back in the early 90’s … Bob > On Jul 28, 2015, at 9:56 AM, Mike Niven wrote: > > Would anyone know of a source of the Rubidium bulb fitted in the Efratom > FRK > (and probably other FRx) standards? I have repaired and refurbished my > Racal > 9475, which is fitted with the older style FRK (not -H or -L) module. It > is > working properly at present but the lamp voltage is down to 5.5V, which is > below the stated minimum of 6V. I have tried rejuvenating the bulb using > a > hot air gun, as described by Corby, but this has had no obvious impact. > Hence, > I have little feel for how much life the existing lamp has left and a > spare > would be good for my peace of mind. > > Many thanks. > > Mike > ___ > 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/l
Re: [time-nuts] Modified Allan Deviation and counter averaging
>> Shouldn't the quantization/ measurement noise power be easy to measure? So I guess I havn't explained my idea well enough yet. If you look at the attached plot there are four datasets. "100Hz", "10Hz" and "1Hz" are the result of collecting TI measurements at these rates. As expected the X^(3/2) slope white PM noise is reduced by sqrt(10) every time we increase the measurement frequency by a factor 10. The "1Hz 10avg" dataset is where the HP5370 does 10 measurements as fast as possible, once per second, and returns the average. The key observation here is I get the same sqrt(10) improvement without having to capture, store and process 10 times as many datapoints. Obviously I learn nothing about the Tau [0.1 ... 1.0] range, but as you can see, that's not really a loss in this case. *If* this method is valid, possibly conditioned on paying attention to the counters STDDEV calculation... and *If* we can get the turbo-5370 to give us an average of 5000 measurements once every second. *Then* the PM noise curtain drops from 5e-11 to 7e-13 @ Tau=1s Poul-Henning PS: The above plot is made by processing a single 100 Hz raw data file which is ny "new" HP5065 against an GPSDO. -- 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@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Symmetricom / Truetime XL-AK
Jim, I have a Truetime XL-AK and have tried several 5 volt antennas with it including the little square magnetic ones. They all worked OK as long as they were outside. I did find a $30 imported bullet on ebay that I am using now. Since I installed the bullet last winter I have had no dropouts. But then it is mounted higher and in the clear. I think almost 5 volt antenna would work for you as long as it has a reasonable look at the sky. The XL-AK does measure current to the antenna but other than a short or an open I don't know what its limits are to be happy. Al, k9si I picked up one of these from the usual site, and it is supposed to be in working condition. I wonder if someone may have a suitable antenna for it I might acquire, or a pointer to one that will work. It is the type with a 5v amplifier in it from what I was told, and is working. I have the manual, but it doesn't mention anything but "bullet" antenna as far as the one to be used with the unit or the optional downconverter. Multiple discussions are in the list archive about that requiring switch settings, but I have only found a user manual for the RS232 interface online for this unit. thanks Jim ___ 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] Modified Allan Deviation and counter averaging
>If you look at the attached plot there are four datasets. And of course... Here it is: -- 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@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
