On 2011-07-12, Michael Eder <[email protected]> wrote: > We are using a Garmin GPS 16x. I should clarify these are platforms in the
18x I presume. > middle of the ocean so the sole time source is the GPS and PPS. Are they really waterproof enough to leave them out in the salty ocean? > We have measured the time delta between the GPS and the PPS and the GPS > while delayed to process the NMEA string has a relatively low jitter and is > quite reliable. What is "relatively low" for you? 10 ms? 1usec? > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Rob > Sent: Tuesday, July 12, 2011 1:25 PM > To: [email protected] > Subject: Re: Single GPS/PPS time source gets marked as a > falseticker > > Michael Eder <[email protected]> wrote: >> Hi Folks, >> >> For our buoy deployments we have GPS and a highly accurate oscillator >> conditioned by the GPS PPS. Unfortunately when we let this run for >> longer periods we see both the GPS and PPS being marked as false >> tickers. There is a lot of information on the web about this, but I >> have not found a definitive solution. What is the best way to configure > NTP when you only >> have a GPS NMEA string and pulse per second? In our situation it is >> feasible that the NMEA may not be always be available while the PPS >> is, we are seeing a problem when both the NMEA and pulse seem to be >> working properly. > > Are you using gpsd? > If so, please use the binary protocol for the GPS receiver in use instead of > NMEA. NMEA often has problems with the timestamps. > (in fact, NMEA says the timestamps are time-of-fix which does not have to be > the current time but can be some time in the near past) > > I see you already have been tweaking the NMEA time to compensate for > problems. This does not work well with gpsd. When you have a systematic > time offset for NMEA you should try to solve it either by stopping the use > of NMEA or by fixing the problem in the receiver with a firmware update. > > E.g. there is a recent Garmin receiver that has unusable NMEA time. > > _______________________________________________ > questions mailing list > [email protected] > http://lists.ntp.org/listinfo/questions _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
