Re: [time-nuts] Home made GPS disciplined atomic clock
Esa, the answer to your problem is, as I said before, to clean up the signal, use a high quality oscillator locked to your system with a PLL that has the appropriate time constant. The time constant will smooth out the jumps you see right now. The question is only which oscillator. A Wenzel was suggested but in my opinion it is not what you need. I have used a Wenzel because I wanted the low phase noise when multiplied to 10 Ghz. You would pay for something you do not need. I have not seen Allan variance data on them. There are plenty of oscillators out there at a reasonable price starting with the HP 10544. Yes, the 10544 will clean up your present setup and will be at least a 10X improvement over the LPRO solution. But the most widely available unit is the HP 10811 which will do a great job. Depending on how much you want to spend the FTS 1200, 1000 or 2000 are an option. Bert WB5MZJ **A Good Credit Score is 700 or Above. See yours in just 2 easy steps! (http://pr.atwola.com/promoclk/10075x1215855013x1201028747/aol?redir=http://www.freecreditreport.com/pm/default.aspx?sc=668072%26hmpgID=62%26bcd=De cemailfooterNO62) ___ 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, the answer to your problem is, as I said before, to clean up the signal, use a high quality oscillator locked to your system with a PLL that has the appropriate time constant. Yes. My problem is to find time constants, with measurements and that's currently under work with GPS, later with LPRO. I've done some HW and SW planning also. It could be like this: - Tbolt is used to synchronize LPRO with own designed steering system. - LPRO steering time constant will be long, let's say 24h or something, to cancel out any day/night variations (if any) on GPS reception. - The goal for LPRO synchronization is to have constant frequency, not exact time. This will ease the LPRO steering algorithm and there's no need to catch up the exact time by changing the output frequency (like tbolt always does). - Own steering electronics will constantly monitor the state of tbolt with serial port. If holdover is detected then the LRPO steering will also be stopped and averaging loop will be reset. DAC remains as it was. - When the holdover is over the running averaging will be started again but C-field DAC will remain as it was until there's enough data for last 24h to do some C-field corrections. - It might be a good idea to reset the steering also if the frequency error (ppt value) of Tbolt's 10 MHz output is detected to be too high. - Steering MCU uses LPRO as it's clock because it will count it. MCU's HW peripherals like counters and capture unit is used to handle the 10 MHz count, the software just reads out the counter values occassionally. - The counters are read only every n'th:s PPS so that mHz resolution can be achieved without using external frequency multipliers etc. Also the PPS drift will be averaged this way. The n could be at least 3600. - These counted values are used as input data to running avg having a long time constant such as 24h or even more. - So the period for DAC changes will depend how long counts (in seconds) is done at first stage. It's sure that the DAC won't be changed here in about every second like Tbolt does! - Then LPRO's output is cleaned with Wenzel or some other OCXO, with suitable time constant which has to be find out. Phase detector and good reference OCXO is needed for that. May be it's wise to buy only one OCXO and use it for measurements frist and then as output oscillator for final setup. - Finally there will be some kind of distribution amplifier for 10 MHz. So it will be slow to settle but should be good enough for stable 10 MHz source. I think it will have good long term stability due GPS, good holdover performance and if the final OCXO cleanup works as excepted there will it should also have good short term stability. Much work to do but for now this is only a hobby project. The time constant will smooth out the jumps you see right now. The question is only which oscillator. A Wenzel was suggested but in my opinion it is not what you need. The output phase noise may be not so bad issue as it sounds like. It seems that some RF instruments (like my spectrum analyzer) have their own clean up loops for external ref. Only problem is that their time constants are unknown. But it's in there - at least in spectrum analyzer; checked that from service manual yesterday. I have used a Wenzel because I wanted the low phase noise when multiplied to 10 Ghz. In these days my maximum needed frequency in about 5.2 GHz so any error on 10 MHz ref will be multiplied by 520. For that reason I also want CONSTANT frequency, it's not so bad if it's off ±1 mHz at some day but it's very bad if it has different frequency error between measurements done on same day. So I'd like to drive that DAC as rarely as possible and as little steps as possible. May be even only one correction per day, done at nighttime when there are no measurements on going.. There will be LCD screen for status so it could also told the actual frequency difference to averaged GPS reference but without any DAC changes if they are not desired that time. plenty of oscillators out there at a reasonable price starting with the HP 10544. Yes, the 10544 will clean up your present setup and will be at least a 10X improvement over the LPRO solution. But the most widely available unit is the HP 10811 which will do a great job. Haven't seen those available here in Finland. We have much too fanatic recycling on going on Finland and so even fully working electronics are doomed to be destroyed (shredded to get the metals out of them). One friend has seen his own eyes the destroying of only couple of years old servers etc. Madness! And any plastic material remained for this process is dumped as huge lumps for next generations. Saves nature indeed! All thanks to this goes to one company which just want to recycle metal and export it to china. So there's no such treasures
Re: [time-nuts] Home made GPS disciplined atomic clock
Except at very short tau (measurement interval), the Wenzel oscillator ADEV (at least the Ultra Low Noise versions) is nothing to write home about compared to something like a surplus 10811A. Designing for absolute phase noise isn't necessarily consistent with designing for longer term stability. John ewkeh...@aol.com said the following on 01/28/2009 06:30 AM: Esa, the answer to your problem is, as I said before, to clean up the signal, use a high quality oscillator locked to your system with a PLL that has the appropriate time constant. The time constant will smooth out the jumps you see right now. The question is only which oscillator. A Wenzel was suggested but in my opinion it is not what you need. I have used a Wenzel because I wanted the low phase noise when multiplied to 10 Ghz. You would pay for something you do not need. I have not seen Allan variance data on them. There are plenty of oscillators out there at a reasonable price starting with the HP 10544. Yes, the 10544 will clean up your present setup and will be at least a 10X improvement over the LPRO solution. But the most widely available unit is the HP 10811 which will do a great job. Depending on how much you want to spend the FTS 1200, 1000 or 2000 are an option. Bert WB5MZJ **A Good Credit Score is 700 or Above. See yours in just 2 easy steps! (http://pr.atwola.com/promoclk/10075x1215855013x1201028747/aol?redir=http://www.freecreditreport.com/pm/default.aspx?sc=668072%26hmpgID=62%26bcd=De cemailfooterNO62) ___ 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
Esa, once you have a finite plan I am sure we can get it to you. I have regular visitors coming from Germany and I could ask them to take it back and ship it from Germany. My cousins son is here till Febr. 18 and could take it. Miami is in the winter a very popular place. Today it will be 25 C. 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
I know what that is all about I did spend my young days in Halmstad Sweden. I will get a 10544 and we can communicate direct. My Email is _ewkeh...@aol.com_ (mailto:ewkeh...@aol.com) 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.
[time-nuts] Home made GPS disciplined atomic clock
I bought a couple of those UCT 108663 (aka Oscilloquartz 8663) double oven OCXO cans off of Ebay for $30 each shipped from China. Tiny little devils, easy to use. Short term ADEVs seem to be in the 1E-12 range (spec is 1E-12 and _ Windows Live™: E-mail. Chat. Share. Get more ways to connect. http://windowslive.com/howitworks?ocid=TXT_TAGLM_WL_t2_allup_howitworks_012009 ___ 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
Hello again... 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: I'm wondering what could be the cause of this. According to operating manual LPRO's output should be crystal oscillator (VCXO) generated signal, which is synchronized to rubidium. So why it is so much worse than any other crystal oscillator (or other Rd oscillators). Are there any schematics for LPRO available anywhere? I cannot see the any phase noise difference between Trimble's OCXO and LPRO with spectrum analyser. Measured with different spans from 500 kHz to 200 Hz, using resolution bandwiths 300 Hz to 6 Hz. So the noise which is causing bad short term drift must be very close to fundamental. It seems that only way to see this noise is to use phase detector circuit but my problem with that is that I haven't got any good reference for it and this kind of equipments are quite hard to find here in Finland. It would be nice to see what kind of noise there are, to design the filter bandwith for external OCXO lock circuit. Other idea to bring that noise visible could be multiplying it with some kind of comb generator circuit (might be hard to build one). Then it would be possible to measure it's harmonics. Not sure if there's enough level present anymore at GHz frequencies... What kind of test setup did you use when getting this result: LPRO plots: http://www.leapsecond.com/museum/lpro/ -- 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.
[time-nuts] Home made GPS disciplined atomic clock
One thing you may be able to do if you can find and old, klunky, bulky enough laptop is to install the Thunderbolt in the laptop CDROM bay. A friend of mine did this and it worked out great. Since he powers the tbolt off of the laptop internal power, the tbolt is automatically battery backed up. If you are a noise fiend, you may want to install some additional filtering to the tbolt power. If your laptop is too modern, there is probably not enough space to install the tbolt internally. You could then mount the tbolt to the laptop case and run the power out to it. Even more modern laptops may not have a strong enough 12V supply to warm up the tbolt oven. --- Thanks again. Just tested that (runs also with XP DOS mode) and it's great! Have to set some older laptop for this. It even shows me that the Kalman filter was still OFF, that information seems to be missing in tboltmon. _ Hotmail® goes where you go. On a PC, on the Web, on your phone. http://www.windowslive-hotmail.com/learnmore/versatility.aspx#mobile?ocid=TXT_TAGHM_WL_HM_versatility_121208 ___ 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] Home made GPS disciplined atomic clock
Hello Bruce, The Thunderbolt documents four filters that you can enable (PV, ALTITUDE, STATIC, and KALMAN). The KALMAN setting is not documented for the regular Thunderbolt. The Thunderbolt-E lists it as being available. Lady Heather gray's out the option unless you have a -E (but does let you try and set it if you have a normal Thunderbolt, no telling if it actually does anything). I think these filters are for receiver dynamics and not oscillator disciplining. Mark _ Hotmail® goes where you go. On a PC, on the Web, on your phone. http://www.windowslive-hotmail.com/learnmore/versatility.aspx#mobile?ocid=TXT_TAGHM_WL_HM_versatility_121208 ___ 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 Wenzel has a introduction to low cost phase noise measurement at: http://www.wenzel.com/documents/measuringphasenoise.htm Its relatively easy to assemble such a system. A PC sound card can be used as a spectrum analyser for measuring phase noise to within a few Hz of the carrier. There are low noise amplifiers with lower flicker noise than Wenzel's low noise FET input audio amplifier http://www.wenzel.com/pdffiles1/pdfs/lowamp.pdf. It is also possible to build a variant of Wenzel's amplifier that doesnt require selection of JFETs. If one wishes to measure the Allan variance of an oscillator, the 3 cornered hat technique can be used with 3 oscillators having similar performance. For longer tau (1000sec or more depending on the OCXO being characterised) the PPS output of a good gps timing receiver can be used as a reference. However a clear view of the southern sky is required, Bruce Esa Heikkinen wrote: Hello again... 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: I'm wondering what could be the cause of this. According to operating manual LPRO's output should be crystal oscillator (VCXO) generated signal, which is synchronized to rubidium. So why it is so much worse than any other crystal oscillator (or other Rd oscillators). Are there any schematics for LPRO available anywhere? I cannot see the any phase noise difference between Trimble's OCXO and LPRO with spectrum analyser. Measured with different spans from 500 kHz to 200 Hz, using resolution bandwiths 300 Hz to 6 Hz. So the noise which is causing bad short term drift must be very close to fundamental. It seems that only way to see this noise is to use phase detector circuit but my problem with that is that I haven't got any good reference for it and this kind of equipments are quite hard to find here in Finland. It would be nice to see what kind of noise there are, to design the filter bandwith for external OCXO lock circuit. Other idea to bring that noise visible could be multiplying it with some kind of comb generator circuit (might be hard to build one). Then it would be possible to measure it's harmonics. Not sure if there's enough level present anymore at GHz frequencies... What kind of test setup did you use when getting this result: LPRO plots: http://www.leapsecond.com/museum/lpro/ ___ 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
Mark Sims wrote: Hello Bruce, The Thunderbolt documents four filters that you can enable (PV, ALTITUDE, STATIC, and KALMAN). The KALMAN setting is not documented for the regular Thunderbolt. The Thunderbolt-E lists it as being available. Lady Heather gray's out the option unless you have a -E (but does let you try and set it if you have a normal Thunderbolt, no telling if it actually does anything). I think these filters are for receiver dynamics and not oscillator disciplining. Mark Mark A Kalman filter is built in to the Thunderbolt, you just cant directly turn it on or off or set its parameters. A Kalman filter is used to measure and store the frequency drift and temperature drift characteristics of the OCXO and use them to improve the holdover performance. The altitude filter allows the GPS receiver to ignore GPS SVs whose altitude is too low. The static mode is for fixed position operation where either a manually entered or an auto surveyed fixed position is used by the GPS receiver. This allows timing information to be derived from a single visible GPS SV. When more SVs are usable more accurate timing information can be derived. 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 relatively easy to assemble such a system. A PC sound card can be used as a spectrum analyser for measuring phase noise to within a few Hz of the carrier. I still need some high quality reference oscillator. Do you have any clue how much those Wenzel oscillators cost? There wasn't any prices on website, may be the only way is to ask? There seems to be interesting alternatives for the output oscillator too (to clean the LPRO signal). One of those was even named timekeeper. Maybe it could be wise to buy one and use it for phase noise measurement first and then put it in permament use as the output oscillator of the reference, when the desired loop bandwith is known. But of course if those units has price tag with four figures or so then this is only daydreaming... :-) -- 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
-Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Esa Heikkinen Sent: Tuesday, January 27, 2009 2:46 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Home made GPS disciplined atomic clock Its relatively easy to assemble such a system. A PC sound card can be used as a spectrum analyser for measuring phase noise to within a few Hz of the carrier. I still need some high quality reference oscillator. Do you have any clue how much those Wenzel oscillators cost? There wasn't any prices on website, may be the only way is to ask? The run of the mill Wenzel Streamline series runs about $250 each. http://www.wenzel.com/pdffiles1/Oscillators/STR_4_to_30.pdf There seems to be interesting alternatives for the output oscillator too (to clean the LPRO signal). One of those was even named timekeeper. Wenzel sells cleanup loops as a packaged device for a variety of frequencies. Maybe it could be wise to buy one and use it for phase noise measurement first and then put it in permament use as the output oscillator of the reference, when the desired loop bandwith is known. But of course if those units has price tag with four figures or so then this is only daydreaming... :-) I would imagine a packaged cleanup loop (oscillator and PLL) is right around $1K. I can't recall what we paid for our 10MHz widgets a few years back, but that seems about right. Clearly, one can build it yourself for less (e.g. you could use a $250 oscillator and use a PLL eval board of some sort to drive the EFC input, for instance) , but that's only if your time is free. Send Wenzel an email and ask.. ___ 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
If you have an older PC/laptop that can run DOS or WIN98 and has a VESA compatible video BIOS then you might want to try Lady Heather's Disciplined Oscillator Controller Program (downloadable from the archives). It has bulilt in support for calculating and graphing the ADEV/OADEV of the PPS and OSC parameters. Also graphs the PPS and OSC values along with the DAC and TEMP parameters and the satellite count. Constellation changes are also marked. Thanks again. Just tested that (runs also with XP DOS mode) and it's great! Have to set some older laptop for this. It even shows me that the Kalman filter was still OFF, that information seems to be missing in tboltmon. -- 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
Hi Mark, Where from could I download this program (Lady Heather) Thanks Predrag Dukic At 23:14 25.1.2009, you wrote: If you have an older PC/laptop that can run DOS or WIN98 and has a VESA compatible video BIOS then you might want to try Lady Heather's Disciplined Oscillator Controller Program (downloadable from the archives). It has bulilt in support for calculating and graphing the ADEV/OADEV of the PPS and OSC parameters. Also graphs the PPS and OSC values along with the DAC and TEMP parameters and the satellite count. Constellation changes are also marked. The source code is there if you want to modify it for a more modern system. The distributed version was compiled with Quick C and set up for a 1024x768 screen. - 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... _ Windows Live Hotmail®: more than just e-mail. http://windowslive.com/explore?ocid=TXT_TAGLM_WL_t2_hm_justgotbetter_explore_012009 ___ 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
Hallo Folkert, Ik zag C, gps en source dus misschien iets voor jou On Mon, Jan 26, 2009 at 12:26 PM, Esa Heikkinen scifisc...@sci.fi wrote: I found a link from message archives: http://www.febo.com/pipermail/time-nuts/attachments/20081224/4a474e8d/attachment-0001.zip -- 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. -- Je hoeft het niet met elkaar eens te zijn om naar elkaar te luisteren. Ook van Loesje ___ 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 hit the wrong button, Henk On Mon, Jan 26, 2009 at 1:46 PM, Esa Heikkinen scifisc...@sci.fi wrote: Hallo Folkert, Ik zag C, gps en source dus misschien iets voor jou Anteeksi mutta en ymmärrä kieltä... :-) In english: Sorry, I do not understand that language. -- 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. -- Je hoeft het niet met elkaar eens te zijn om naar elkaar te luisteren. Ook van Loesje ___ 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] Home made GPS disciplined atomic clock
I think that the KALMAN setting of the filter is not actually available in the Thunderbolt. It is only supported in the Thunderbolt-E. -- Thanks again. Just tested that (runs also with XP DOS mode) and it's great! Have to set some older laptop for this. It even shows me that the Kalman filter was still OFF, that information seems to be missing in tboltmon. _ Windows Live™ Hotmail®:…more than just e-mail. http://windowslive.com/explore?ocid=TXT_TAGLM_WL_t2_hm_justgotbetter_explore_012009 ___ 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
Mark So why does the Thunderbolt distinguish between a fixed DAC voltage (as when the disciplining is turned off) and a corrected value (as in manual holdover). How does it learn the drift correction parameters without using a Kalman filter or its equivalent. Are you perhaps suggesting that the Tunderblt doesnt allow the Kalman filter to be manually enabled or disabled? Bruce Mark Sims wrote: I think that the KALMAN setting of the filter is not actually available in the Thunderbolt. It is only supported in the Thunderbolt-E. -- Thanks again. Just tested that (runs also with XP DOS mode) and it's great! Have to set some older laptop for this. It even shows me that the Kalman filter was still OFF, that information seems to be missing in tboltmon. _ Windows Live™ Hotmail®:…more than just e-mail. http://windowslive.com/explore?ocid=TXT_TAGLM_WL_t2_hm_justgotbetter_explore_012009 ___ 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 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.
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.
