On 2012-03-19, Alby VA <alb...@empire.org> wrote: > On Mar 19, 2:45?am, unruh <un...@invalid.ca> wrote: >> On 2012-03-19, David J Taylor <david-tay...@blueyonder.co.uk.invalid> wrote: >> >> >> >> >> >> >> >> >> >> >> Hi all, >> >> >> I was doing some GPS research and found this site with lots of GPS's and >> >> accessories. ?Just thought I'd pass it along. >> >> >>http://www.gpssensors.com/ >> >> >> I don't know which ones are timing GPS's. >> >> >> Sincerely, >> >> >> Ron >> >> > Ron, >> >> > The one I recognise as being a timing GPS with PPS and suitable for NTP is >> > one which isn't one that page, but here: >> >> > ?https://www.starlite-intl.com/Detail.asp?pid=2320 >> >> > Same company. ?US $61 >> >> Certainly the 18xLVC has a PPS pulse, as does the 18x-5 OEM which is a >> 5PPS. It give about 1us accuracy, not 10ns which is what some might call >> timeing GPS. But that 1ns is pretty useless for computer timing, since a >> computer really cannot use better than about 1us accuracy. > > > > I'm getting 1us accuracy from my Sure GPS once I did the proper Mods > per David Taylor's notes.
As per my comment. The interrupt processing/clock reading time on a PC is of the order of 1us. Note that on the Sure, the process of converting to an RS232 signal means that the PPS signal is of the order of 1us accuracy ( the signal processors are not the worlds fastests chips) The actual PPS signal at the PPS pin has a rise time of about 10ns, and the Sure has a normal sawtooth timing signal, so that would indicate a few 10s of ns accuracy from the Sure, but the conversion to RS232 washes that out (and the interrupt processing time on your computer washes that out as well). > > URL: http://godzilla.empire.org > > > assID=0 status=0415 leap_none, sync_uhf_clock, 1 event, > event_clock_reset, > version="ntpd 4.2.6p5@1.2349-o Mon Feb 20 22:00:33 UTC 2012 (1)", > processor="amd64", system="FreeBSD/9.0-RELEASE", leap=00, stratum=1, > precision=-19, rootdelay=0.000, rootdisp=0.401, refid=PPS, > reftime=d311cdf2.ee1ec49a Mon, Mar 19 2012 11:23:30.930, > clock=d311cdfe.0179ea2d Mon, Mar 19 2012 11:23:42.005, peer=21829, > tc=4, mintc=3, offset=0.000, frequency=-24.622, sys_jitter=0.002, > clk_jitter=0.002, clk_wander=0.001 > > > _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
