Hi Ok, let’s back up a bit. The market for “timing” GPS modules is in GPSDO’s and similar devices. Your local network hub or cell tower is very much in a fixed location. They don’t put them in backpacks. Survey in and position lock is how it’s done,
The sawtooth is the error between the arbitrary ( locked to the TCXO) PPS edge and the “real time” of the PPS edge. The reason it is commonly called sawtooth is the shape of the data that comes out went plotted vs time. The sawtooth can get into a problem known as a hanging bridge when the “tooth” reverses in mid transition. If you look at the section under “timing (page 79)” in the uBlox manual you will find all the fun stuff that makes the T different. One of the timing messages includes the time offset between the pps output and the real GPS time solution. Page 351 and after are the time related commands. The stuff back around page 358 looks like it’s got the sawtooth data in it. Using the sawtooth information involves running it into either a control loop ( the normal case in a GPSDO ) or into some sort of controlled delay line ( far less common ). You need the information every second to feed into the loop along with your measured phase information. There are tons of information about all of this in the archives. There are also a lot of posts that probably will do a more in depth job of bringing you up to speed on all the various terms and issues. Bottom line is that with the sawtooth correction applied, you can get down to below 1x10^-9 at one second on your plot. The T version will automatically output the magic message with the data in it. Bob > On May 20, 2018, at 10:06 PM, Gary E. Miller <g...@rellim.com> wrote: > > Yo Bob! > > On Sun, 20 May 2018 19:26:33 -0400 > Bob kb8tq <kb...@n1k.org> wrote: > >> The “big deal” features on the T series are the ability to do single >> satellite timing > > Which I always thought was pointless, that only works for a fixed > antenna. Any GPS in a fixed position lab will have a good rooftop > antenna with clear skyview. > >> and the auto output of the sawtooth correction >> information. Cranking sawtooth correction into your data will move >> the line down most of the way to the “JL” line. > > Except that requires a post process step, so not useful for real time. > > I just looked at the 'U-blox 8 Receiver Description' and it makes no > mention of sawtooh anything. Is that in a different doc? > > I'll also test Surevey-In mode to see how much that helps. > > RGDS > GARY > --------------------------------------------------------------------------- > Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 > g...@rellim.com Tel:+1 541 382 8588 > > Veritas liberabit vos. -- Quid est veritas? > "If you can’t measure it, you can’t improve it." - Lord Kelvin > _______________________________________________ > 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.
