nsayer@kfu.com said: > Yes, that’s true. Given the facilities I have available with the present > hardware, I don’t believe I have much choice. I am not confident that I > could tell the difference between noise in the phase detection system and > PPS jitter variations that small. If the PA6H receiver gave sawtooth > corrections, I’d be able to do better. It would be interesting to look at the data to see if you can find the sort of pattern that a sawtooth correction would help and where a hanging bridge might cause confusion. If the bridge isn't hanging, the data samples should be spread over a range that is the clock period of the GPS unit. Round that up to 100 ns. I doubt if you will see that with a PC. On the other hand, you can get the same sort of pattern with a PPS over USB. That would be a ms wide and easy for a PC to get time stamps much finer grained than that. -- These are my opinions. I hate spam.

> It would be interesting to look at the data to see if you can find the sort Hi Hal, There's lots of examples of sawtooth patterns at: http://leapsecond.com/pages/MG1613S/ In particular there's this monster: http://leapsecond.com/pages/MG1613S/tic-72-hour.gif It's simple for a microprocessor-based GPSDO with its TIC to realize when it's getting too lost in a hanging bridge. There are a number of ways around the problem. My favorite is gluing a resistor on top of the GPS chip and pumping a few tens of mW through it when you want the bridge to stop. Here's the proof-of-concept: http://leapsecond.com/pages/vp/heater.htm /tvb ----- Original Message ----- From: "Hal Murray" <hmurray@megapathdsl.net> To: "Nick Sayer" <nsayer@kfu.com> Cc: "Discussion of precise time and frequency measurement" <time-nuts@febo.com>; "Hal Murray" <hmurray@megapathdsl.net> Sent: Monday, July 18, 2016 9:41 PM Subject: Re: [time-nuts] How does sawtooth compensation work? > > nsayer@kfu.com said: >> Yes, thatâ?Ts true. Given the facilities I have available with the present >> hardware, I donâ?Tt believe I have much choice. I am not confident that I >> could tell the difference between noise in the phase detection system and >> PPS jitter variations that small. If the PA6H receiver gave sawtooth >> corrections, Iâ?Td be able to do better. > > It would be interesting to look at the data to see if you can find the sort > of pattern that a sawtooth correction would help and where a hanging bridge > might cause confusion. > > If the bridge isn't hanging, the data samples should be spread over a range > that is the clock period of the GPS unit. Round that up to 100 ns. I doubt > if you will see that with a PC. > > On the other hand, you can get the same sort of pattern with a PPS over USB. > That would be a ms wide and easy for a PC to get time stamps much finer > grained than that. > > > -- > These are my opinions. I hate spam. >

On Mon, 18 Jul 2016 22:01:01 -0700, you wrote: >> It would be interesting to look at the data to see if you can find the sort > >Hi Hal, > >There's lots of examples of sawtooth patterns at: http://leapsecond.com/pages/MG1613S/ > >In particular there's this monster: http://leapsecond.com/pages/MG1613S/tic-72-hour.gif > >It's simple for a microprocessor-based GPSDO with its TIC to realize when it's getting too lost in a hanging bridge. There are a number of ways around the problem. My favorite is gluing a resistor on top of the GPS chip and pumping a few tens of mW through it when you want the bridge to stop. > >Here's the proof-of-concept: http://leapsecond.com/pages/vp/heater.htm > >/tvb Universal timer/counters and equivalent time sampling DSOs can have this problem when their timebase ends up synchronized with the signal they are measuring. Some carefully modulate their timebase to prevent this. When I was testing my Garmin 18x against my Racal-Dana 1992, I could see it happen when the outside temperature was just right.