Harald Brinkmann wrote: > This is my setup: > > I am using a Navilock NL-320U connected to a small Linux box running ntp > 4.2.4p4-44.1 that came with the openSuSE 11.0 distribution. This is > supposed to supply a time service to the local network without the use of > external network ntp servers purely from the received GPS signal. > > I know that using a USB connection is not optimal, but the achieved accuracy > is fine for my needs. > > Last Saturday (2008-08-02) I noticed for the first time that the time off > the GPS unit was one second behind the DCF time, which I monitor on a > separate radio clock. A reboot of the system did not help. On Sunday > (2008-08-03) everything was back to normal. I noticed the same effect again > on Friday evening (2008-08-08) and through yesterday (2008-08-09), but > everything seems fine today (2008-08-10). > > I added a network server to my ntp configuration to double check the effect. > This is how the output "ntpq -p" looks like when everything is fine: > > remote refid st t when poll reach delay offset > jitter > ============================================================================== > LOCAL(0) .LOCL. 10 l 19 64 377 0.000 0.000 > 3.906 > *GPS_NMEA(0) .GPS. 3 l 22 64 377 0.000 14.902 > 3.906 > xptbtime2.ptb.de .PTB. 1 u 422 1024 377 66.375 -8.106 > 5.216 > > And this is the output when I observe the one second lag: > > remote refid st t when poll reach delay offset > jitter > ============================================================================== > LOCAL(0) .LOCL. 10 l 33 64 17 0.000 0.000 > 3.906 > *GPS_NMEA(0) .GPS. 3 l 30 64 17 0.000 -978.27 > 11.515 > xptbtime2.ptb.de .PTB. 1 u 31 64 17 67.160 1.002 > 3.906 > > Looking at the raw NMEA output, the UTC info in there also seems to be one > second slow. > > In all of this I presume the PTB time to be correct. > > My question is, has anyone else observed this and how can I fix this? > > Thanks > > Harald >
It sounds as if the GPS receiver you have was designed for navigation rather than timing! Timing receivers typically have a Pulse Per Second (PPS) output and use a binary protocol rather than NMEA to transmit the time to a serial port. Using the proper tool for the job should solve many of your problems. _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
