Re: [time-nuts] Any experienced HP 2804A thermometer users outthere?
In message b93bfa41a81249bf81041167a7891...@didierhp, Didier writes: I have some PIC18F code if you want it ? Sure, it's gotta help compared to starting from scratch, as long as it's C. http://phk.freebsd.dk/patch/onewire.c -- 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] Home made GPS disciplined atomic clock
I think that it should be a much better (in theory) than OCXO which comes short therm stability (what I'm actually seeking for). It should be much more accurate with long holdovers also. Right, it all depends on what stability you're after. The OCXO will have much better short-term stability than the LPRO -- the LPRO is close to ten times worse. So do not replace the TBolt OCXO with a LPRO if short-term stability is your goal. See: TBolt OCXO plots: http://www.leapsecond.com/pages/gpsdo/ http://www.leapsecond.com/pages/tbolt-tc/ LPRO plots: http://www.leapsecond.com/museum/lpro/ However, if long-term, GPS-unlocked, holdover performance is the goal, then using a Rb would make a good choice. This is very simple modification by the way. Infact my original plan was to use the 1PPS to synchronize the LPRO C-field with separate control ... See John Miles work to replace the Thunderbolt OCXO: http://www.thegleam.com/ke5fx/tbolt.htm /tvb Here's a link for the log: http://www.amigazone.fi/files/gpsdo/tbolt-lpro-test.log (Log format: TOW, PPS offset, DAC voltage, Disciplining mode activity) I'll have a look at this; but it's not accessible for some reason. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Home made GPS disciplined atomic clock
The challenge is to detect a failure of the GPS source (LOS) before the DPLL moves the OCXO. I used to design Stratum clocks for a large telecom company, and I used several trick do detect a phase ramp on the digital phase detector; this was used to declare a probable bad source. At that point, we halted the movement of the DPLL and observed the phase detector activity. We had two DPLLs, and if both detected a phase ramp, we declared the source bad. -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on Behalf Of Tom Van Baak Sent: Sunday, January 25, 2009 11:03 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Home made GPS disciplined atomic clock I think that it should be a much better (in theory) than OCXO which comes short therm stability (what I'm actually seeking for). It should be much more accurate with long holdovers also. Right, it all depends on what stability you're after. The OCXO will have much better short-term stability than the LPRO -- the LPRO is close to ten times worse. So do not replace the TBolt OCXO with a LPRO if short-term stability is your goal. See: TBolt OCXO plots: http://www.leapsecond.com/pages/gpsdo/ http://www.leapsecond.com/pages/tbolt-tc/ LPRO plots: http://www.leapsecond.com/museum/lpro/ However, if long-term, GPS-unlocked, holdover performance is the goal, then using a Rb would make a good choice. This is very simple modification by the way. Infact my original plan was to use the 1PPS to synchronize the LPRO C-field with separate control ... See John Miles work to replace the Thunderbolt OCXO: http://www.thegleam.com/ke5fx/tbolt.htm /tvb Here's a link for the log: http://www.amigazone.fi/files/gpsdo/tbolt-lpro-test.log (Log format: TOW, PPS offset, DAC voltage, Disciplining mode activity) I'll have a look at this; but it's not accessible for some reason. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ 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] Home made GPS disciplined atomic clock
I think it is a bad idea except if holdover due to loss of GPS is an issue. For all practical purposes disciplined oscillators make rubidium obsolete because the majority use lower performance cheaper oscillators in their systems. Looking at Corby Dawson's data on oscillators and HP 5065 shows that it does outperform even the best oscillators but there is no comparison between a HP 5065 and what is on the market today. Look at the specs of Rubidium standards and look at their 100 sec. data. If you want improvement take the output of a Thunderbolt and lock it to something like a FTS 1000, 1200 or 2000 adjusting the loop constant to the specification of the external oscillator. As an example the 100 sec.spec on the FE 5600 is 4 X -12 versus 1 X-12 on the FTS series oscillators. And I consider the FE 5600 one of the better Rubidium's! I have not personally characterized Thunderbolt and Rubidium oscillators but I doubt that there is very much difference in performance. Bert WB5MZJ **Know Your Numbers: Get tips and tools to help you improve your credit score. (http://www.walletpop.com/credit/credit-reports?ncid=emlcntuswall0002) ___ 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] Home made GPS disciplined atomic clock
Right, it all depends on what stability you're after. The OCXO will have much better short-term stability than the LPRO -- the LPRO is close to ten times worse. Basicly I'm seeking an accurate frequency standard for RF lab. It should be always as accurate as possible, regardless the state of GPS receiving etc. Before doing this modification I did some test runs Trimble versus LPRO with phase comparator circuit. I noticed that Trimble is accurate as long as it gets the GPS signal and phase change between LPRO and Trimble was changing evenly. It is even accurate after the GPS drops (holdover mode) but after the signal comes back the things start to go badly wrong. It starts to roll it's phase / 1 PPS back to alignment woth GPS time and this caused very badly looking phase activity when compared to LPRO. Another bad issue was that if there's a change in satellite receiving (satellite hopping or some) it causes rapid change the PPS offset and OCXO frequency starts to roll to get the 1 PPS back to alignment. So it seems that Trimble's main principle is 1000 pulses per PPS, with no exceptions and when the PPS goes off the 10 MHz must also go off to get the 1 PPS back to aligment. So there's no constant 10 MHz frequency either. That's not acceptable because in normal use I should be always aware of GPS receiving states - I'd just like to trust that I'm getting accurate 10 MHz - any time! So I become to think that may be very slow loop dynamics will solve that problem (if the DAC value isn't changed at every little change at satellite reception). And for that purpose the rubidium sound better than OCXO. I also got misunderstanding from this: http://www.ptsyst.com/GPS10RB-B.pdf It claims that rubidiums will have good short therm drift. My problem here is that there's no way to measure the different setups because my only rb is now part of the experiment. All I can do is the log them and look the change between PPS timing offset readings. When doing the GPS vs. LPRO phase comparison told before I noticed that the changes of PPS offsets are correlated the phase changes between LPRO and Tbolt output, when observed quite short time. So it seems that the PPS offset is somehow accurate measurement of oscillator stability as well. I also done some noise measurements with spectrum analyzer between LRPO and Trimble outputs. LPRO had lower noise floor around fundamental. See John Miles work to replace the Thunderbolt OCXO: http://www.thegleam.com/ke5fx/tbolt.htm Hmm. May be the OCXO on my tbolt is then somehow bad if the LPRO should be even worse? It has Trimble label on and the unit is manufactured on 2005, in China. Is there any logs available with that better OCXO? It would be nice to see the PPS offsets variance between readings with that oscillator. http://www.amigazone.fi/files/gpsdo/tbolt-lpro-test.log I'll have a look at this; but it's not accessible for some reason. Oops.. Now you should get it. -- 73s! Esa OH4KJU ___ 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] Home made GPS disciplined atomic clock
ewkeh...@aol.com wrote: Do not forget the Trimble was never intended to be a frequency standard. Bert Bert Why do you believe that? Bruce ___ 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] Home made GPS disciplined atomic clock
Its main purpose was time synchronization. Bert **Know Your Numbers: Get tips and tools to help you improve your credit score. (http://www.walletpop.com/credit/credit-reports?ncid=emlcntuswall0002) ___ 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] Home made GPS disciplined atomic clock
ewkeh...@aol.com wrote: Its main purpose was time synchronization. Bert Bert But time and frequency are dual aspects of the same phenomenon. The only real concern is the behaviour of the Thunderbolt when recovering from holdover. There will be transient time (phase ) and frequency excursions. One can either allow a jam sync for fast correction of any accumulated time error or disable it and accept the potentially larger frequency excursions as the disciplining loop locks the PPS output to GPS time. Performance during holdover depends on whether the Kalman filter has accumulated sufficient information to correct for drift tempco and other predictable errors during holdover. Bruce ___ 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] Home made GPS disciplined atomic clock
There are techniques to remove/eliminate the phase error when the GPS source comes back on line. If the holdover is entered appropriately, the frequency error should be small and dependent on the stability of the OCXO. -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on Behalf Of Bruce Griffiths Sent: Sunday, January 25, 2009 1:01 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Home made GPS disciplined atomic clock ewkeh...@aol.com wrote: Its main purpose was time synchronization. Bert Bert But time and frequency are dual aspects of the same phenomenon. The only real concern is the behaviour of the Thunderbolt when recovering from holdover. There will be transient time (phase ) and frequency excursions. One can either allow a jam sync for fast correction of any accumulated time error or disable it and accept the potentially larger frequency excursions as the disciplining loop locks the PPS output to GPS time. Performance during holdover depends on whether the Kalman filter has accumulated sufficient information to correct for drift tempco and other predictable errors during holdover. Bruce ___ 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] Home made GPS disciplined atomic clock
Do not forget the Trimble was never intended to be a frequency standard. Ok, then it might be a better idea to use only it's 1 PPS output to count the frequency of the some other oscillator and build own steering electronics for that. Infact my original plan was to do right that. If the count/steering period is set long enough there should be any problem caused the satellite hopping or such things anymore. Let's say that if I make 24 hours running average for 10 MHz using Trimble's 1 PPS as a reference to determine the oscillator control then I would get the better results, right? But if LPRO is useless, which oscillator should I seek for main output? With low short therm drift and good phase noise characteristics etc? Also the goal is to build the reference with surplus (etc) parts as a hobby project, no interest to invest thousands for that. -- 73s! Esa OH4KJU ___ 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] Home made GPS disciplined atomic clock
Esa You can change the Thunderbolt recovery mode from holdover. One test you can perform that should give an indication of the location of the Allan intercept is to: 1) connect the receiver to an antenna. 2) let it run for a few days so the Kalman filter learns the drift, tempco and other parameters. 3) manually disable the disciplining leaving the thunderbolt connected to the antenna. 4) Log the Thunderbolt PPS offset (plus time stamp) for a day or more. 5) Analyse the resultant data to determine the relative Allan deviation between the receiver and the 10MHz source. Ulrich's Plotter is good for this (use the overlapping ADEV algorithm - although TOTDEV and Theo1 are even better estimators of the Allan deviation) All going well, you will see a minimum in the Allan deviation versus tau plot. In most cases the value of tau at the minimum will be relatively close to the value of tau at the Allan intercept. However to do this successfully your antenna will need a good view of the sky. For short tau the GPS receiver noise will dominate. For long tau the 10MHz source noise and drift will dominate. Bruce Esa Heikkinen wrote: Right, it all depends on what stability you're after. The OCXO will have much better short-term stability than the LPRO -- the LPRO is close to ten times worse. Basicly I'm seeking an accurate frequency standard for RF lab. It should be always as accurate as possible, regardless the state of GPS receiving etc. Before doing this modification I did some test runs Trimble versus LPRO with phase comparator circuit. I noticed that Trimble is accurate as long as it gets the GPS signal and phase change between LPRO and Trimble was changing evenly. It is even accurate after the GPS drops (holdover mode) but after the signal comes back the things start to go badly wrong. It starts to roll it's phase / 1 PPS back to alignment woth GPS time and this caused very badly looking phase activity when compared to LPRO. Another bad issue was that if there's a change in satellite receiving (satellite hopping or some) it causes rapid change the PPS offset and OCXO frequency starts to roll to get the 1 PPS back to alignment. So it seems that Trimble's main principle is 1000 pulses per PPS, with no exceptions and when the PPS goes off the 10 MHz must also go off to get the 1 PPS back to aligment. So there's no constant 10 MHz frequency either. That's not acceptable because in normal use I should be always aware of GPS receiving states - I'd just like to trust that I'm getting accurate 10 MHz - any time! So I become to think that may be very slow loop dynamics will solve that problem (if the DAC value isn't changed at every little change at satellite reception). And for that purpose the rubidium sound better than OCXO. I also got misunderstanding from this: http://www.ptsyst.com/GPS10RB-B.pdf It claims that rubidiums will have good short therm drift. My problem here is that there's no way to measure the different setups because my only rb is now part of the experiment. All I can do is the log them and look the change between PPS timing offset readings. When doing the GPS vs. LPRO phase comparison told before I noticed that the changes of PPS offsets are correlated the phase changes between LPRO and Tbolt output, when observed quite short time. So it seems that the PPS offset is somehow accurate measurement of oscillator stability as well. I also done some noise measurements with spectrum analyzer between LRPO and Trimble outputs. LPRO had lower noise floor around fundamental. See John Miles work to replace the Thunderbolt OCXO: http://www.thegleam.com/ke5fx/tbolt.htm Hmm. May be the OCXO on my tbolt is then somehow bad if the LPRO should be even worse? It has Trimble label on and the unit is manufactured on 2005, in China. Is there any logs available with that better OCXO? It would be nice to see the PPS offsets variance between readings with that oscillator. http://www.amigazone.fi/files/gpsdo/tbolt-lpro-test.log I'll have a look at this; but it's not accessible for some reason. Oops.. Now you should get it. ___ 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] Home made GPS disciplined atomic clock
Esa Heikkinen wrote: Do not forget the Trimble was never intended to be a frequency standard. Ok, then it might be a better idea to use only it's 1 PPS output to count the frequency of the some other oscillator and build own steering electronics for that. Infact my original plan was to do right that. If the count/steering period is set long enough there should be any problem caused the satellite hopping or such things anymore. Let's say that if I make 24 hours running average for 10 MHz using Trimble's 1 PPS as a reference to determine the oscillator control then I would get the better results, right? But if LPRO is useless, which oscillator should I seek for main output? With low short therm drift and good phase noise characteristics etc? Also the goal is to build the reference with surplus (etc) parts as a hobby project, no interest to invest thousands for that. Esa Given the large PPS output jitter wrt to the OCXO output frequency, this is probably a bad idea. There's nothing wrong with the idea of using a rubidium standard, you just need to cleanup its output first by phase locking a low noise OCXO with a suitable loop time constant to the rubidium output first. Use the cleaned up output as the 10MHz signal for the Thunderbolt and lock the rubidium standard to GPS using the thunderbolt with a suitably long loop time constant. This should result in low phase noise and drift during holdover. Bruce ___ 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] Home made GPS disciplined atomic clock
Hi Bruce, since the LPRO has significantly worse STS (according to this thread) than the Tapr Tbolt itself, then using the LPRO would only make sense if GPS is not available, and the unit is in holdover. This is similar to what you mentioned with the long time-constant. One would not want the LPRO to make the Tbolt worse than it is when perfectly locked to GPS. Our Fury and FireFly-II units allow an external 1PPS input to be connected, and the switchover will automatically happen if the internal GPS goes into holdover. Using the LPRO on the external 1PPS, and selecting auto-switchover would give the best of both worlds: the excellent ADEV over all measurement intervals when GPS is available, and the Rubidium stability when GPS is out for longer time periods. Another advantage of this is that when the Fury/FireFly-II is using the LPRO 1PPS it will act as a cleanup-filter for the LPRO, and one would not lose the better STS of the Fury/FireFly OCXO. I am not sure if the Tbolt has an external 1PPS fail-safe backup input, I could not see one on the PCB. bye, Said In a message dated 1/25/2009 11:23:53 Pacific Standard Time, bruce.griffi...@xtra.co.nz writes: Given the large PPS output jitter wrt to the OCXO output frequency, this is probably a bad idea. There's nothing wrong with the idea of using a rubidium standard, you just need to cleanup its output first by phase locking a low noise OCXO with a suitable loop time constant to the rubidium output first. Use the cleaned up output as the 10MHz signal for the Thunderbolt and lock the rubidium standard to GPS using the thunderbolt with a suitably long loop time constant. This should result in low phase noise and drift during holdover. Bruce ___ 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] Home made GPS disciplined atomic clock
Sorry, I offended you Bruce. True time and frequency are definitely inter related, but as you and Esa pointed out the Trimble has an output that does change under certain circumstances. And the reason Esa is pursuing his approach is that for his need as a frequency standard the unit is not doing the job. Bert **Know Your Numbers: Get tips and tools to help you improve your credit score. (http://www.walletpop.com/credit/credit-reports?ncid=emlcntuswall0002) ___ 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] Home made GPS disciplined atomic clock
Google df6jb plotter. It's great! 73 de Norm n3ykf ___ 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] Upgrade for LPRO 10 MHz Oscillator?
Has anyone upgraded the LPRO oscillator by out-boarding a suitable OCXO unit? Bruce Hunter **Know Your Numbers: Get tips and tools to help you improve your credit score. (http://www.walletpop.com/credit/credit-reports?ncid=emlcntuswall0002) ___ 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] Upgrade for LPRO 10 MHz Oscillator?
HelloŃ Sunday, January 25, 2009, 23:05:01, Bruce Hunter wrote: B Has anyone upgraded the LPRO oscillator by out-boarding a suitable OCXO unit? Why not just lock external oscillator to LPRO output with long enough time constant? Is there any real difference? -- Best regards, Yuri mailto:y...@ostry.ru ___ 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] Home made GPS disciplined atomic clock
Esa Heikkinen wrote: One test you can perform that should give an indication of the location of the Allan intercept is to: Ok, thanks for your clear instructions! My test periods have been much too short, if the Kalman filter learning takes even days! But with these instructions I'lll get better data for OCXO vs. LPRO comparison and maybe also the OCXO health. Ulrich's Plotter is good for this Hmm. Is that software available somewhere? No luck with quick Google tour... However to do this successfully your antenna will need a good view of the sky. And that's also one of my problems here. Many trees in the yard. No problems with normal hand GPS reception but when it comes to these timing systems this could be one explanation of these strange timing changes at satellite hops already noted. However the antenna sees most of the sky clearly but not so close to horizon. Will the Northen position (Lat 62.33302) also cause inaccuracy to GPS? Esa You'll need a good view of the sky to the south where the GPS SVs will be located. You'll also need to set the elevation mask appropriately. Multipath will be more problematic with low elevation SVs. It would also be helpful if you plot the SV tracks across the sky (as seen by a GPS receiver) as this will show if and where obstructions are significant. There's a lot of software out there for doing this. Bruce ___ 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] Home made GPS disciplined atomic clock
Esa, I would do a clean up using an oscillator like a HP 10811 and use the rubidium to check if you do have an improvement. Right now you have no way of knowing what you are getting. It allows you to play with the time constant and there is enough data available to figure out what the optimum time constant is. Corby as we speak has some of my 1200's 2000, 1000 and others to gather data but also to select two units, using one with a Shera board and one with a FE 5602 replacing the internal oscillator also locked with a Shera board and than do a comparison. Ten years ago I did play with time and frequency and have had all the time an Austron Loran running and a HP 10811 with the Shera board and at one time six Cesium but did loose interest, now back in the game. It will take time to catch up and have capability that allows me to do some more meaningful tests. Still have five HP 5061A but am working on modifying a HP 5062 to a FTS tube. Bert in Miami **Know Your Numbers: Get tips and tools to help you improve your credit score. (http://www.walletpop.com/credit/credit-reports?ncid=emlcntuswall0002) ___ 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.
