Re: [time-nuts] Hanging bridge question
Some people say: HP = High Price Sorry, couldn't resist! :) On 3/26/2014 6:10 PM, time-nuts-requ...@febo.com wrote: Message: 3 Date: Wed, 26 Mar 2014 17:47:36 -0400 From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Hanging bridge question Message-ID: 2674b568-04b1-4ebc-ac6d-d7f4dd347...@rtty.us Content-Type: text/plain; charset=windows-1252 Hi HP = Hewlett Packard Bob On Mar 26, 2014, at 10:31 AM, Matthew Martin dr_g...@yahoo.com wrote: Hi, Just a quick question from a novice. Sometimes I see abbreviations here and don't know, but usually I can make a good guess. Your first paragraph, HP is perhaps high precision? Just want to make sure I am not missing some other meaning. Thanks, learning a lot from reading this group! Matt Martin ___ 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] Hanging bridge question
In message B92E1A45BB35480FA213DA5F32CEA2BA@pc52, Tom Van Baak writes: That's only true for time scales less than the cross-over point. Beyond that, the 1 PPS from the GPS receiver is actually better (more accurate). That's why the LO is disciplined by GPS, not the other way around. I would also like to add that the jitter on the 1PPS from the GPS (aka: The hanging bridge) actually helps measurement precision in exactly the same way systematic jitter makes life better a lot of other places, from tape recording (bias = jitter) to machine tools. The best way to use the sawtooth correction is to apply it in software after all the hardware measurements had their errors smoothed out by it. -- 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] Hanging bridge question
Hi Take a look at the PIC-TIC stuff. They have the HP circuit in the middle of it. Bob Stewart posted a circuit with a pair of tri-state gates in it within the last month or so. They all pretty much: 1) Measure the “coarse time” with a counter Today that’s just about always a counter in an MCU. 2) Based on the clock to the counter (say 25 ns), you have a roundoff / truncation error. (say 0 to 25 ns) 3) You use a gate or two and your capture flip flop to convert the truncation to a pulse. (normally 25 to 50 ns) 4) You pick an R/C time constant to be “useful” (say 50 ns, could be less). 5) You charge the RC with the pulse 6) After the pulse is done, you open circuit the R/C so charge / discharge stops. 7) When you get around to it, you measure the voltage on the cap with an ADC Starting from the 50 ns example, an 8 bit converter likely gives you 500 ps resolution. 10 bits gets you to 250 ps and 12 bits to 125 ps. More bits or a faster clock would do even better. Since the R/C charge voltage vs time is pretty well known, you can do the first part of the math fairly easily. You have a clock and flip flops are pretty cheap. If you want to shoot cal pulses at it, send it a 25 and 50 ns wide pules. The delta between the two should be pretty good. If you have the range, go to 75 ns and get 3 points to fit. The basic R/C is about 5 cents. The one tri-state gate you need is about 16 cents. A quad nand is about the same these days. You already need a pair of flip flops to capture the pps edge (two to a package …). If you want to do the whole calibration thing, one of Bert’s $2 CPLD’s has way more parts in it than you will ever need. The ADC can be what you get with your MCU. In that case 12 bits may be stretching it. There are very nice 12 bit parts from TI that run about $3 or so. 16 bits is still under $10. Bob On Mar 25, 2014, at 11:08 PM, Jim Miller j...@jtmiller.com wrote: Bob I'm not sure who you're responding to but I have a couple of questions: TDC = Time Delay Correlator? Could you point me to one of these 50 cent threads? I've read a ton of this list from 2007 forward but must have missed that. Thanks jim ab3cv (much to learn) Hi There have been multiple posts about analog TDC's of various designs that get you into the sub 100 ps range without costing very much money. I believe the cheapest posted so far adds 50 cents to a basic PIC based design. Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ 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] Hanging bridge question
Hi, Just a quick question from a novice. Sometimes I see abbreviations here and don't know, but usually I can make a good guess. Your first paragraph, HP is perhaps high precision? Just want to make sure I am not missing some other meaning. Thanks, learning a lot from reading this group! Matt Martin On Wed, 3/26/14, Bob Camp li...@rtty.us wrote: Subject: Re: [time-nuts] Hanging bridge question To: Discussion of precise time and frequency measurement time-nuts@febo.com Date: Wednesday, March 26, 2014, 4:45 AM Hi Take a look at the PIC-TIC stuff. They have the HP circuit in the middle of it. Bob Stewart posted a circuit with a pair of tri-state gates in it within the last month or so. They all pretty much: 1) Measure the “coarse time” with a counter Today that’s just about always a counter in an MCU. 2) Based on the clock to the counter (say 25 ns), you have a roundoff / truncation error. (say 0 to 25 ns) 3) You use a gate or two and your capture flip flop to convert the truncation to a pulse. (normally 25 to 50 ns) 4) You pick an R/C time constant to be “useful” (say 50 ns, could be less). 5) You charge the RC with the pulse 6) After the pulse is done, you open circuit the R/C so charge / discharge stops. 7) When you get around to it, you measure the voltage on the cap with an ADC Starting from the 50 ns example, an 8 bit converter likely gives you 500 ps resolution. 10 bits gets you to 250 ps and 12 bits to 125 ps. More bits or a faster clock would do even better. Since the R/C charge voltage vs time is pretty well known, you can do the first part of the math fairly easily. You have a clock and flip flops are pretty cheap. If you want to shoot cal pulses at it, send it a 25 and 50 ns wide pules. The delta between the two should be pretty good. If you have the range, go to 75 ns and get 3 points to fit. The basic R/C is about 5 cents. The one tri-state gate you need is about 16 cents. A quad nand is about the same these days. You already need a pair of flip flops to capture the pps edge (two to a package …). If you want to do the whole calibration thing, one of Bert’s $2 CPLD’s has way more parts in it than you will ever need. The ADC can be what you get with your MCU. In that case 12 bits may be stretching it. There are very nice 12 bit parts from TI that run about $3 or so. 16 bits is still under $10. Bob On Mar 25, 2014, at 11:08 PM, Jim Miller j...@jtmiller.com wrote: Bob I'm not sure who you're responding to but I have a couple of questions: TDC = Time Delay Correlator? Could you point me to one of these 50 cent threads? I've read a ton of this list from 2007 forward but must have missed that. Thanks jim ab3cv (much to learn) Hi There have been multiple posts about analog TDC's of various designs that get you into the sub 100 ps range without costing very much money. I believe the cheapest posted so far adds 50 cents to a basic PIC based design. Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ 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] Hanging bridge question
Hi HP = Hewlett Packard Bob On Mar 26, 2014, at 10:31 AM, Matthew Martin dr_g...@yahoo.com wrote: Hi, Just a quick question from a novice. Sometimes I see abbreviations here and don't know, but usually I can make a good guess. Your first paragraph, HP is perhaps high precision? Just want to make sure I am not missing some other meaning. Thanks, learning a lot from reading this group! Matt Martin On Wed, 3/26/14, Bob Camp li...@rtty.us wrote: Subject: Re: [time-nuts] Hanging bridge question To: Discussion of precise time and frequency measurement time-nuts@febo.com Date: Wednesday, March 26, 2014, 4:45 AM Hi Take a look at the PIC-TIC stuff. They have the HP circuit in the middle of it. Bob Stewart posted a circuit with a pair of tri-state gates in it within the last month or so. They all pretty much: 1) Measure the “coarse time” with a counter Today that’s just about always a counter in an MCU. 2) Based on the clock to the counter (say 25 ns), you have a roundoff / truncation error. (say 0 to 25 ns) 3) You use a gate or two and your capture flip flop to convert the truncation to a pulse. (normally 25 to 50 ns) 4) You pick an R/C time constant to be “useful” (say 50 ns, could be less). 5) You charge the RC with the pulse 6) After the pulse is done, you open circuit the R/C so charge / discharge stops. 7) When you get around to it, you measure the voltage on the cap with an ADC Starting from the 50 ns example, an 8 bit converter likely gives you 500 ps resolution. 10 bits gets you to 250 ps and 12 bits to 125 ps. More bits or a faster clock would do even better. Since the R/C charge voltage vs time is pretty well known, you can do the first part of the math fairly easily. You have a clock and flip flops are pretty cheap. If you want to shoot cal pulses at it, send it a 25 and 50 ns wide pules. The delta between the two should be pretty good. If you have the range, go to 75 ns and get 3 points to fit. The basic R/C is about 5 cents. The one tri-state gate you need is about 16 cents. A quad nand is about the same these days. You already need a pair of flip flops to capture the pps edge (two to a package …). If you want to do the whole calibration thing, one of Bert’s $2 CPLD’s has way more parts in it than you will ever need. The ADC can be what you get with your MCU. In that case 12 bits may be stretching it. There are very nice 12 bit parts from TI that run about $3 or so. 16 bits is still under $10. Bob On Mar 25, 2014, at 11:08 PM, Jim Miller j...@jtmiller.com wrote: Bob I'm not sure who you're responding to but I have a couple of questions: TDC = Time Delay Correlator? Could you point me to one of these 50 cent threads? I've read a ton of this list from 2007 forward but must have missed that. Thanks jim ab3cv (much to learn) Hi There have been multiple posts about analog TDC's of various designs that get you into the sub 100 ps range without costing very much money. I believe the cheapest posted so far adds 50 cents to a basic PIC based design. Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ 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. ___ 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] Hanging bridge question
Bob, Thanks. That was too obvious, but having not looked at HP's similar circuits I ruled it out. Many thanks. Still lots to learn here….. Matt On Wed, 3/26/14, Bob Camp li...@rtty.us wrote: Subject: Re: [time-nuts] Hanging bridge question To: Discussion of precise time and frequency measurement time-nuts@febo.com Date: Wednesday, March 26, 2014, 2:47 PM Hi HP = Hewlett Packard Bob On Mar 26, 2014, at 10:31 AM, Matthew Martin dr_g...@yahoo.com wrote: Hi, Just a quick question from a novice. Sometimes I see abbreviations here and don't know, but usually I can make a good guess. Your first paragraph, HP is perhaps high precision? Just want to make sure I am not missing some other meaning. Thanks, learning a lot from reading this group! Matt Martin On Wed, 3/26/14, Bob Camp li...@rtty.us wrote: Subject: Re: [time-nuts] Hanging bridge question To: Discussion of precise time and frequency measurement time-nuts@febo.com Date: Wednesday, March 26, 2014, 4:45 AM Hi Take a look at the PIC-TIC stuff. They have the HP circuit in the middle of it. Bob Stewart posted a circuit with a pair of tri-state gates in it within the last month or so. They all pretty much: 1) Measure the “coarse time” with a counter Today that’s just about always a counter in an MCU. 2) Based on the clock to the counter (say 25 ns), you have a roundoff / truncation error. (say 0 to 25 ns) 3) You use a gate or two and your capture flip flop to convert the truncation to a pulse. (normally 25 to 50 ns) 4) You pick an R/C time constant to be “useful” (say 50 ns, could be less). 5) You charge the RC with the pulse 6) After the pulse is done, you open circuit the R/C so charge / discharge stops. 7) When you get around to it, you measure the voltage on the cap with an ADC Starting from the 50 ns example, an 8 bit converter likely gives you 500 ps resolution. 10 bits gets you to 250 ps and 12 bits to 125 ps. More bits or a faster clock would do even better. Since the R/C charge voltage vs time is pretty well known, you can do the first part of the math fairly easily. You have a clock and flip flops are pretty cheap. If you want to shoot cal pulses at it, send it a 25 and 50 ns wide pules. The delta between the two should be pretty good. If you have the range, go to 75 ns and get 3 points to fit. The basic R/C is about 5 cents. The one tri-state gate you need is about 16 cents. A quad nand is about the same these days. You already need a pair of flip flops to capture the pps edge (two to a package …). If you want to do the whole calibration thing, one of Bert’s $2 CPLD’s has way more parts in it than you will ever need. The ADC can be what you get with your MCU. In that case 12 bits may be stretching it. There are very nice 12 bit parts from TI that run about $3 or so. 16 bits is still under $10. Bob On Mar 25, 2014, at 11:08 PM, Jim Miller j...@jtmiller.com wrote: Bob I'm not sure who you're responding to but I have a couple of questions: TDC = Time Delay Correlator? Could you point me to one of these 50 cent threads? I've read a ton of this list from 2007 forward but must have missed that. Thanks jim ab3cv (much to learn) Hi There have been multiple posts about analog TDC's of various designs that get you into the sub 100 ps range without costing very much money. I believe the cheapest posted so far adds 50 cents to a basic PIC based design. Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ 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. ___ 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] Hanging bridge question
In message CACYeN9zf-UO1sCTCRMHSDPN4u=ye0xb9+x71eLxBnbT=xgw...@mail.gmail.com , Jim Miller writes: I've spent a good part of the afternoon looking at all the plots, websites and the few papers I could find mentioning the hanging bridge. As far as I can tell as long as one is correcting for sawtooth there's nothing additional to do about hanging bridges. The sawtooth correction *is* the correction for the hanging bridge. -- 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] Hanging bridge question
Hi Exactly correct, the sawtooth corrects for the hanging bridges. Since that’s what it does, sawtooth correction error is not totally random. Hanging bridges are not totally random. One looks like the other. Sawtooth correction errors can / will have hanging bridges in them. If you are doing sawtooth correction, it’s best to do it with decent accuracy. Bob On Mar 25, 2014, at 3:27 AM, Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message CACYeN9zf-UO1sCTCRMHSDPN4u=ye0xb9+x71eLxBnbT=xgw...@mail.gmail.com , Jim Miller writes: I've spent a good part of the afternoon looking at all the plots, websites and the few papers I could find mentioning the hanging bridge. As far as I can tell as long as one is correcting for sawtooth there's nothing additional to do about hanging bridges. The sawtooth correction *is* the correction for the hanging bridge. -- 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. ___ 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] Hanging bridge question
In message 6b362a4d-834a-4733-bed8-fcfec0ccb...@rtty.us, Bob Camp writes: I should add here, that you _can_ do a little bit better than the sawtooth correction. We know, or at least assume, that the GPS's internal clock is step-less and slowly changing, so if you put a predictive filter on this stuff, it can actually do a reasonable job at estimating which way the rounding of the sawtooth correction went (since it is integral ns). This reduces the random rounding error on the sawtooth correction from +/- 0.5 ns to something like +/- 0.3 ns. Totally not worth it, but a cool and educational project :-) -- 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] Hanging bridge question
Hi Most of the more modern receivers don’t stop at one ns resolution on the correction. You can go well below the ns level with them. If you are doing it in software, it’s pretty much free. Bob On Mar 25, 2014, at 7:27 AM, Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message 6b362a4d-834a-4733-bed8-fcfec0ccb...@rtty.us, Bob Camp writes: I should add here, that you _can_ do a little bit better than the sawtooth correction. We know, or at least assume, that the GPS's internal clock is step-less and slowly changing, so if you put a predictive filter on this stuff, it can actually do a reasonable job at estimating which way the rounding of the sawtooth correction went (since it is integral ns). This reduces the random rounding error on the sawtooth correction from +/- 0.5 ns to something like +/- 0.3 ns. Totally not worth it, but a cool and educational project :-) -- 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] Hanging bridge question
The lowest cost solution is a DS chip in combination with a PIC. How ever has any one thought about a fix by going to the source of the problem. The TCXO. Use a DDS with internal multiplier like the AD9851 or AD 9913 and use the sawtooth message from the GRS receiver and change the frequency. An other alternative would be to use the sawtooth word to fine tune a TCXO or any VCXO for that matter. Bert Kehren In a message dated 3/25/2014 7:28:11 A.M. Eastern Daylight Time, p...@phk.freebsd.dk writes: In message 6b362a4d-834a-4733-bed8-fcfec0ccb...@rtty.us, Bob Camp writes: I should add here, that you _can_ do a little bit better than the sawtooth correction. We know, or at least assume, that the GPS's internal clock is step-less and slowly changing, so if you put a predictive filter on this stuff, it can actually do a reasonable job at estimating which way the rounding of the sawtooth correction went (since it is integral ns). This reduces the random rounding error on the sawtooth correction from +/- 0.5 ns to something like +/- 0.3 ns. Totally not worth it, but a cool and educational project :-) -- 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. ___ 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] Hanging bridge question
Thanks for all the helpful replies! Lots to learn. 73 jim ab3cv ___ 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] Hanging bridge question
On Tue, Mar 25, 2014 at 5:44 AM, ewkeh...@aol.com wrote: The lowest cost solution is a DS chip in combination with a PIC. How ever The lowest cost solution is to do the correct entirely in software. After the measure the phase, simply add the correction. All you need to know is the phase. There is not point in correcting the pulse, you don't need a corrected pulse. What you want is a measurement of the phase. Chris Albertson Redondo Beach, California ___ 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] Hanging bridge question
Yes if you want to use it only in a GPSDO and it is being done but if you are a time nut you may want the 1 PPS.. Bert Kehren In a message dated 3/25/2014 6:33:12 P.M. Eastern Daylight Time, albertson.ch...@gmail.com writes: On Tue, Mar 25, 2014 at 5:44 AM, ewkeh...@aol.com wrote: The lowest cost solution is a DS chip in combination with a PIC. How ever The lowest cost solution is to do the correct entirely in software. After the measure the phase, simply add the correction. All you need to know is the phase. There is not point in correcting the pulse, you don't need a corrected pulse. What you want is a measurement of the phase. Chris Albertson Redondo Beach, California ___ 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] Hanging bridge question
Hi If you are building a GPSDO, then the 1 pps out of the GPSDO should be much better than the pps out of the GPS. Making that happen is part of the control optimization. Bob On Mar 25, 2014, at 7:46 PM, ewkeh...@aol.com wrote: Yes if you want to use it only in a GPSDO and it is being done but if you are a time nut you may want the 1 PPS.. Bert Kehren In a message dated 3/25/2014 6:33:12 P.M. Eastern Daylight Time, albertson.ch...@gmail.com writes: On Tue, Mar 25, 2014 at 5:44 AM, ewkeh...@aol.com wrote: The lowest cost solution is a DS chip in combination with a PIC. How ever The lowest cost solution is to do the correct entirely in software. After the measure the phase, simply add the correction. All you need to know is the phase. There is not point in correcting the pulse, you don't need a corrected pulse. What you want is a measurement of the phase. Chris Albertson Redondo Beach, California ___ 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. ___ 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] Hanging bridge question
The lowest cost solution is to do the correct entirely in software. After the measure the phase, simply add the correction. All you need to know is the phase. There is not point in correcting the pulse, you don't need a corrected pulse. What you want is a measurement of the phase. Chris I'm baffled as to how one would do this in software without a ton of expensive hardware to give phase information. Could you provide in words a simple block diagram of where you would get phase information without a Ghz TIC to read? Thanks Jim ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Hanging bridge question
Hi There have been multiple posts about analog TDC’s of various designs that get you into the sub 100 ps range without costing very much money. I believe the cheapest posted so far adds 50 cents to a basic PIC based design. Bob On Mar 25, 2014, at 7:38 PM, Jim Miller j...@jtmiller.com wrote: The lowest cost solution is to do the correct entirely in software. After the measure the phase, simply add the correction. All you need to know is the phase. There is not point in correcting the pulse, you don't need a corrected pulse. What you want is a measurement of the phase. Chris I'm baffled as to how one would do this in software without a ton of expensive hardware to give phase information. Could you provide in words a simple block diagram of where you would get phase information without a Ghz TIC to read? Thanks Jim ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ 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] Hanging bridge question
Right now I'm planning to use a DS1123 driven by the PIC in my system to provide sawtooth correction. The phase measurement is strictly binary with a D FF. The PIC reads the value once a second and integrates with a bit of feedforward for stability. The numerical result will be fed to a DAC which controls the OCXO. The DS1123 is about $14, not unreasonable. The same PIC is used to setup the M12+T and read the status and sawtooth info, do the math for the PI filter, drive the D/A and communicate optionally with a PC to log D/A commands and relay any M12+T communication. It will also maintain a few simple indicator lights for status. Jim ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Hanging bridge question
Bob I'm not sure who you're responding to but I have a couple of questions: TDC = Time Delay Correlator? Could you point me to one of these 50 cent threads? I've read a ton of this list from 2007 forward but must have missed that. Thanks jim ab3cv (much to learn) Hi There have been multiple posts about analog TDC's of various designs that get you into the sub 100 ps range without costing very much money. I believe the cheapest posted so far adds 50 cents to a basic PIC based design. Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Hanging bridge question
If you are building a GPSDO, then the 1 pps out of the GPSDO should be much better than the pps out of the GPS. Bob, That's only true for time scales less than the cross-over point. Beyond that, the 1 PPS from the GPS receiver is actually better (more accurate). That's why the LO is disciplined by GPS, not the other way around. For example, when monitoring the performance of a cesium clock at 1 Hz, there is no need to use a GPSDO -- a sawtooth-corrected 1PPS from a GPS timing receiver is the more accurate way to measure. A GPSDO can only make the quality of the 1PPS worse for tau beyond the crossover point. /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] Hanging bridge question
The lowest cost solution is to do the correct entirely in software. After the measure the phase, simply add the correction. All you need to know is the phase. There is not point in correcting the pulse, you don't need a corrected pulse. What you want is a measurement of the phase. This depends on the goal. There are two types of GPS timing products. Those which output time frequency and those which output time only. For time and frequency you design a GPSDO, in which case you have a choice of h/w or s/w sawtooth correction. Most people choose s/w since, as you correctly assume, a GPSDO already includes some sort of phase or time interval measurement circuit along with a microprocessor to do the math. But for a timing only GPS product (e.g., the base models from www.cnssys.com) the goal is just a precise 1PPS output. This class of product tends to use h/w sawtooth correction, since by design there is no TIC or OCXO in the box. There's also a third way to do it -- sawtooth correction provided by PC software tools like Tac32Plus or DSPmon (similar to TBoltmon). In this case the PC reads correction messages from the receiver and measurements from an external TIC and applies the sawtooth correction before writing the composite result to a log file. DSPmon has support for the hp 5334 and 53132. I hope this helps more than it confuses. /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] Hanging bridge question
I've spent a good part of the afternoon looking at all the plots, websites and the few papers I could find mentioning the hanging bridge. As far as I can tell as long as one is correcting for sawtooth there's nothing additional to do about hanging bridges. They merely show up as funny waveforms in the data that has not been corrected for sawtooth. Am I correct? Thanks jim ab3cv (still learning...) ___ 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] Hanging bridge question
j...@jtmiller.com said: I've spent a good part of the afternoon looking at all the plots, websites and the few papers I could find mentioning the hanging bridge. As far as I can tell as long as one is correcting for sawtooth there's nothing additional to do about hanging bridges. They merely show up as funny waveforms in the data that has not been corrected for sawtooth. Am I correct? I think so. Another way to look at it is that the normal pattern is the beat between the local crystal and the target frequency. If the result is a low frequency, it's harder to filter. A hanging bridge is just a case where the frequency is very very low. -- These are my opinions. I hate spam. ___ 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.
