Re: [time-nuts] Best GPS 1PPS Accuracy
HI Tom, got it. I was wondering because there is a 10MHz OCXO in the block diagram as well. bye, Said ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] LPRO-101 with Brooks Shera's GPS locking circuit
Tom, i believe that Bruce as well as me is always referring to what the receiver CAN do i.e. not the raw but always the sawtooth corrected signal. That is indeed 2 ns (1 sigma). Don't mislead yourself. At 1 s you are limited by GPS 1PPS noise. Having a better TIC doesn't fix this. If your GPS noise is 2e-9 at 1 s you don't really need a TIC that is good to 5e-10 at 1 s. So the gain isn't as useful as you might think. Thank you for clarifying this again! While i have been referring to the measurement apparatus's noise floor for which my statements are correct, one might indeed get into believing that every increase in resolution leads to a increase in performance in a GPSDO. Clearly once that you are below a certain point the GPS's jitter is the limiting number. I second Bruces's opinion about what is an overshot or not. When ps reolution is ready available then why not use it? I attach a online output from my DIY GPSDO from a few minutes ago that shows the M12+'s signal properties when measured with abt. 110 ps resolution against a FTS1200. The yellow line reperesents a prefiltered version of the sawtooth corrected values (blue). The filter time constant is 1/3 of the loop time constant as in a PRS-10. The yellow values are the ones to feed the regulation loop. What I wanted to explain is the Shera concept noise floor is a factor 20 above what a modern receiver can deliver (again inc. the sawtoth correction). And yes, you are right: There were different numbers when this concept was thought out! And exactly because different number were there when this concept was thougt out I am going to ask why people still built it today. Best regards Ulrich Bangert, DF6JB -Ursprüngliche Nachricht- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Im Auftrag von Tom Van Baak Gesendet: Freitag, 15. Dezember 2006 08:23 An: Discussion of precise time and frequency measurement Betreff: Re: [time-nuts] LPRO-101 with Brooks Shera's GPS locking circuit Tom A TIC with 0.5ns jitter at 1 second isn't actually too much in the way of overkill when the PPS signal has 2ns of jitter. Bruce, Can you clarify about the jitter, though. The TIC jitter that was quoted (500 ps) is the single-shot resolution for the 53131A. The 2 ns M12+ jitter is an rms value, no? The short-term or single-shot M12+ jitter, if you could call it that, is more like +/- 20 ns. Averaging it, over many minutes, gets you below 10 ns. Also the sawtooth correction helps even further but that isn't being done with Shera's board. Maybe we're all agreeing even if with different words. /tvb ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi- bin/mailman/listinfo/time-nuts AOSChart.pdf Description: Adobe PDF document ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] PTS 250
I have pinouts of the BCD connector at http://www.febo.com/hardware/PTS/index.html. Note the big red warning sign -- the first 250 I had was in some way goofy and that led me down an erroneous path for the pinout. The pinout described for the 160 is correct for all the units (at least the ones below 500MHz). Dunno about the OCXO; I don't think any of the units I have came with an internal oscillator. Note that there's an interesting variant of the 250 -- option SX51 which provides very low phase noise from 0.1 to 25 MHz; basically, it adds a divide-by-ten on the output. You select the low noise mode by selecting (I think) the 0.8Hz line and dividing the rest of the frequency you entered by 10. So, entering 100.000 000 0 gives you 100MHz output; entering 100.000 000 8 gives you 10MHz output. The divided output is a square wave, so might require filtering depending on the application. Manuals are available from PTS, though they don't necessarily have a lot of useful information. PTS doesn't seem to be too interested in having anyone but them work on the units, so there's not a lot of circuit-level information. Hope this helps. John Rex wrote: Does anyone have information on the PTS 250 Synthesizer? I bought one on eBay. Seems to work pretty well, except the OCXO is not great. I have a hard time even setting it below about 5x10^-9, but output seems accurate and functional if I use external 10 MHz. Do cal and service manuals exist for these things? My searches haven't found any. Does anyone have the pin-out for the external BCD 50-pin connector? I found a document for a PTS 160 and the programming pins seem to match as far as the 10 MHz digit, but the PTS 250 must have more pins that are used for the 100 MHz digit. Anyone know how the high order is programmed through the 50-pin connector? Thanks for any information you can share. ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Happy 5th anniversary, Time Nuts
Tom Van Baak wrote: Speaking of timing, today is the 5th anniversary of our time-nuts mailing list. Thanks to all of you who have made this such a great list over the years. The quality of the postings has been rather amazing. For example, the long posting two days ago by Brian Kirby detailing his efforts with GPSDO and Rb is a time-nuts classic. A special thank you to John Ackermann for hosting the list on his server. John, how many people on the list by now? I'll add my thanks to Tom -- I think this is one of the highest SNR mailing lists around, thanks to all of you. We have 384 subscribers now. I wonder what percentage of the world's privately held Cs and Maser standards are represented here? John ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] PTS 250
John Ackermann N8UR wrote: I have pinouts of the BCD connector at http://www.febo.com/hardware/PTS/index.html. Screwed up the URL -- it's http://www.febo.com/time-freq/hardware/PTS/index.html Sorry about that. John ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
[time-nuts] News from NPL
Just put two recent releases from NPL on my web site - Autumn 2006 TF News http://www.timing-consultants.com/images/Web%20Site%20App%20Notes/NPL%20TF%2 0News%20Autumn%2006.pdf MSF Update (UK's 60 KHz Time Tx) http://www.timing-consultants.com/images/Web%20Site%20App%20Notes/MSF%20leaf let.pdf Rob K ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] News from NPL
I see that the links didn't get through the system correctly. If anyone has a problem, just go to http://www.timing-consultants.com and hit the Application Notes page. And yes, I know I need to take out the blank spaces in the file names which get translated to %20 :-) Rob K -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Rob Kimberley Sent: 15 December 2006 17:16 To: 'Discussion of precise time and frequency measurement' Subject: [time-nuts] News from NPL Just put two recent releases from NPL on my web site - Autumn 2006 TF News http://www.timing-consultants.com/images/Web%20Site%20App%20Notes/NPL%20TF%2 0News%20Autumn%2006.pdf MSF Update (UK's 60 KHz Time Tx) http://www.timing-consultants.com/images/Web%20Site%20App%20Notes/MSF%20leaf let.pdf Rob K ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] LPRO-101 with Brooks Shera's GPS locking circuit
Hi Ulrich: I think the answer is what other low cost options are available? I would like to have a more modern TIC capability to add to the clock I'm working on. But although there's been a lot of discussion about different ways of making TIC measurements, it's not clear to me how to do it on a budget. For example the TIC232 circuit by Richard H McCorkle is easy to implement, but how good is it's noise floor. See: http://www.piclist.com/techref/member/RHM-SSS-SC4/TIC232.htm Then there's the low cost frequency counting TIC that appeared in QEX that we know trades performance for low cost so it's not a candidate. Any ideas on what circuits have a noise floor that's compatible with the M12+T or it's newer equivalents and at the same time are in the low cost category? Have Fun, Brooke Clarke w/Java http://www.PRC68.com w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml http://www.precisionclock.com Ulrich Bangert wrote: Tom, . What I wanted to explain is the Shera concept noise floor is a factor 20 above what a modern receiver can deliver (again inc. the sawtoth correction). And yes, you are right: There were different numbers when this concept was thought out! And exactly because different number were there when this concept was thougt out I am going to ask why people still built it today. ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] News from NPL
Rob Kimberley wrote: I see that the links didn't get through the system correctly. http://tinyurl.com reliably tames unwieldy links. ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] LPRO-101 with Brooks Shera's GPS locking circuit
Brooke Clarke wrote: Hi Ulrich: I think the answer is what other low cost options are available? I would like to have a more modern TIC capability to add to the clock I'm working on. But although there's been a lot of discussion about different ways of making TIC measurements, it's not clear to me how to do it on a budget. For example the TIC232 circuit by Richard H McCorkle is easy to implement, but how good is it's noise floor. See: http://www.piclist.com/techref/member/RHM-SSS-SC4/TIC232.htm Then there's the low cost frequency counting TIC that appeared in QEX that we know trades performance for low cost so it's not a candidate. Any ideas on what circuits have a noise floor that's compatible with the M12+T or it's newer equivalents and at the same time are in the low cost category? Have Fun, Brooke Clarke w/Java http://www.PRC68.com w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml http://www.precisionclock.com Ulrich Bangert wrote: Tom, . What I wanted to explain is the Shera concept noise floor is a factor 20 above what a modern receiver can deliver (again inc. the sawtoth correction). And yes, you are right: There were different numbers when this concept was thought out! And exactly because different number were there when this concept was thougt out I am going to ask why people still built it today. ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts Brooke I agree that most will tend to use an available circuit particularly if they are not too experienced/adventurous. The noise/resolution of the TIC232 will be a little worse than that of the Brooks Shera circuit. It would appear to use the internal counter timer which is clocked at 16MHz. Also this timer has no hardware for latching its count on the leading edge of an external signal so there must be some software component used to do this. This will almost inevitably add extra noise/uncertainty due to variations in the delay in reading the timer. The quoted resolution of 1.04ns for a 1 minute average is probably derived from a 62.5ns resolution for each individual measurement. One can only achieve the subnanosecond resolution required to avoid degrading the performance of an M12+ by using a clock frequency of 1GHz or more. Thus this method is probably too expensive and difficult to implement. Perhaps there would be some demand for a higher resolution replacement for the Brooks Shera system for those who have M12+ or equivalent performance timing receivers and high performance OCXOs or Rubidium standards who wish to achieve the best performance they can without breaking the bank. If so then perhaps we can collectively design such a system. Breaking the task down into more manageable parts will help ensure that the design is more quickly implemented As I see it the following methods can achieve the desired phase measurement resolution 1) Use a commercial TDC chip as the phase detector. Range 4millisec ( can be extended almost indefinitely by using a synchroniser and counter implemented in a gate array or its functional equivalent) Noise 65ps rms Cost ~ 100 euro Advantages someone has already designed and debugged the chip as long as the circuit layout recommendations are adhered to there should be no unforeseen problems. 2) Use an ADC to sample a sinewave formed by dividing down the OCXO frequency and filtering the resultant square wave Range half period of the sinewave frequency Noise (rms) 0.0005 of the sinwave period (500ps with a 1MHz sinewave) Cost ~ $US20 ?? 3) Use dual simultaneous sampling ADCs to sample quadrature phased sinewaves derived by dividing down the OCXO frequency filtering the resulting square wave and using a quadrature hybrid to produce the quadrature phase sinwave pair. Extend range to as much as 1 second or more using dual synchroniser to sample a continuously running digital counter/timer. Range to several days or centuries if required, depending on counter lenght Noise (rms) 0.0005 of the sinewave period (500ps with a 1MHz sinewave) Cost ~ $US40 ?? Bruce ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
[time-nuts] [Fwd: Austron 2201 MANUAL (fwd)]
This got caught in the spam filter for some reason. Sorry for the delay in fishing it out. John - Forwarded message from SCOMM - From: SCOMM [EMAIL PROTECTED] To: time-nuts@febo.com cc: [EMAIL PROTECTED] Date: Sun, 10 Dec 2006 23:17:25 -0600 I AM LOOKING FOR A DATUM-AUSTRON 2201 MANUAL OR COPY! ! THANKS,JIM BRIERLY DISABLED VET - End of forwarded message from SCOMM - ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] LPRO-101 with Brooks Shera's GPS locking circuit
- Original Message - From: Ulrich Bangert [EMAIL PROTECTED] To: 'Discussion of precise time and frequency measurement' time-nuts@febo.com Sent: Friday, December 15, 2006 05:47 Subject: Re: [time-nuts] LPRO-101 with Brooks Shera's GPS locking circuit ... I second Bruces's opinion about what is an overshot or not. When ps reolution is ready available then why not use it? I attach a online output from my DIY GPSDO from a few minutes ago that shows the M12+'s signal properties when measured with abt. 110 ps resolution against a FTS1200. The yellow line reperesents a prefiltered version of the sawtooth corrected values (blue). The filter time constant is 1/3 of the loop time constant as in a PRS-10. The yellow values are the ones to feed the regulation loop. What I wanted to explain is the Shera concept noise floor is a factor 20 above what a modern receiver can deliver (again inc. the sawtoth correction). And yes, you are right: There were different numbers when this concept was thought out! And exactly because different number were there when this concept was thougt out I am going to ask why people still built it today. Best regards Ulrich Bangert, DF6JB I believe the sawtooth correction is of little or no value for a GPSDO, which typically requires a low pass filter between the GPS 1pps and the disciplined oscillator. This filter is quite effective in removing the sawtooth quantization introduced by the GPS rcvr clock, just as it removes the similiar quantization caused by my phase detector. For example, reading from your graph I averaged the raw data (as best I could by reading the blue line). The running average of the raw data over 40 sec (starting at 12:31:30) was -4.5 nsec, after 60 sec it was -4.2 nsec. These values appear to be indistinguishable from the values you get by averaging the sawtooth corrected data (the yellow line). It appears from your plot that the sawtooth correction has contributed very little or nothing that averaging does not already provide. Have I misunderstand something? I believe that your noise floor is a factor 20 above what a modern receiver can deliver statement is incorrect. With an HP 5720B (about 100 psec resolution), I have measured the phase difference between the GPS 1pps and the phase of a 5 MHz oscillator controlled by my controller. This data has been compared with simultaneous phase serial output from the controller as determined its maligned 24 MHz asynchronous internal phase measurement circuitry. ADEV Stable 32 plots of both data sets are essentially identical. From this I conclude that nothing would be gained, for the purpose of discipling an oscillator, by using a more elaborate and expensive phase detector (the phase detector in my controller costs $6.61, including $5.35 for the dual 24 MHz osc that is shared as the PIC clock). It was my goal when I designed the controller was to make the design transparent to the builder and to use as few parts as necessary consistant with performance limited only by available GPS receivers and VCXOs. When I wrote the QST article I was totally ignorant of the fact that I could buy the HP58503 with similiar performance for $5400. Your earlier comment about the capture range of the phase detector is well taken. For the past several years the PIC software I provide has included an option designed for use with inexpensive TCVCXOs. It requires only an external 128 divider chip and produces EFC voltages suitable for inexpensive oscillators. It works very well and provides sufficient performance for many applications. Regards, Brooks ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] LPRO-101 with Brooks Shera's GPS locking circuit
Brooks Shera wrote: - Original Message - From: Ulrich Bangert [EMAIL PROTECTED] To: 'Discussion of precise time and frequency measurement' time-nuts@febo.com Sent: Friday, December 15, 2006 05:47 Subject: Re: [time-nuts] LPRO-101 with Brooks Shera's GPS locking circuit ... I second Bruces's opinion about what is an overshot or not. When ps reolution is ready available then why not use it? I attach a online output from my DIY GPSDO from a few minutes ago that shows the M12+'s signal properties when measured with abt. 110 ps resolution against a FTS1200. The yellow line reperesents a prefiltered version of the sawtooth corrected values (blue). The filter time constant is 1/3 of the loop time constant as in a PRS-10. The yellow values are the ones to feed the regulation loop. What I wanted to explain is the Shera concept noise floor is a factor 20 above what a modern receiver can deliver (again inc. the sawtoth correction). And yes, you are right: There were different numbers when this concept was thought out! And exactly because different number were there when this concept was thougt out I am going to ask why people still built it today. Best regards Ulrich Bangert, DF6JB I believe the sawtooth correction is of little or no value for a GPSDO, which typically requires a low pass filter between the GPS 1pps and the disciplined oscillator. This filter is quite effective in removing the sawtooth quantization introduced by the GPS rcvr clock, just as it removes the similiar quantization caused by my phase detector. For example, reading from your graph I averaged the raw data (as best I could by reading the blue line). The running average of the raw data over 40 sec (starting at 12:31:30) was -4.5 nsec, after 60 sec it was -4.2 nsec. These values appear to be indistinguishable from the values you get by averaging the sawtooth corrected data (the yellow line). It appears from your plot that the sawtooth correction has contributed very little or nothing that averaging does not already provide. Have I misunderstand something? I believe that your noise floor is a factor 20 above what a modern receiver can deliver statement is incorrect. With an HP 5720B (about 100 psec resolution), I have measured the phase difference between the GPS 1pps and the phase of a 5 MHz oscillator controlled by my controller. This data has been compared with simultaneous phase serial output from the controller as determined its maligned 24 MHz asynchronous internal phase measurement circuitry. ADEV Stable 32 plots of both data sets are essentially identical. From this I conclude that nothing would be gained, for the purpose of discipling an oscillator, by using a more elaborate and expensive phase detector (the phase detector in my controller costs $6.61, including $5.35 for the dual 24 MHz osc that is shared as the PIC clock). It was my goal when I designed the controller was to make the design transparent to the builder and to use as few parts as necessary consistant with performance limited only by available GPS receivers and VCXOs. When I wrote the QST article I was totally ignorant of the fact that I could buy the HP58503 with similiar performance for $5400. Your earlier comment about the capture range of the phase detector is well taken. For the past several years the PIC software I provide has included an option designed for use with inexpensive TCVCXOs. It requires only an external 128 divider chip and produces EFC voltages suitable for inexpensive oscillators. It works very well and provides sufficient performance for many applications. Regards, Brooks ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts Brooks Your comparison of your circuit with measurements taken with the 5270 (is this a typo? did you mean 5370? which is known to have differential non linearities well in excess of 100 picoseconds, at least according to the designers - some later modifications to the circuitry reduced this effect somewhat) demonstrates very little unless the measurements were corrected for the sawtooth error. The only true test is to compare a sawtooth corrected GPSDOCXO alongside a sawtooth corrected GPSDOXO. Both should of course use equivalent performance oscillators and GPS timing receivers. The short plot that Ulrich furnished doesn't include any hanging bridges which occur when the GPS oscillator drifts through a harmonic of 1Hz. Most M12+ GPS timing receivers produce sawtooth correction errors in which such hanging
