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.
