Hi …. except… A navigation GPS doesn't care much about the time solution. Updating the location is a much higher priority than updating the time. The typical "solution" is to let the time estimate coast for a while and update it much less often than the location.
Bob On Dec 28, 2012, at 7:18 PM, Magnus Danielson <[email protected]> wrote: > On 28/12/12 23:35, Bob Camp wrote: >> Hi >> >> The GPS does an estimate against the local crystal frequency. It generates >> the PPS off of it's estimate. The less often it updates the estimate the >> more odd things you see as the crystal drifts. > > A typical GPS off the shelf solves the position solution every second, having > a 1 Hz report rate. This includes clock corrections. Some GPSes is capable of > higher report-rates. > >> Of course, the crystal can have trouble all it's own. If the crystal has a >> rapid rate of frequency change over a narrow temperature range, the GPS >> simply can't keep up with the crystal. > > Most GPS receivers only have TCXOs, and even if tossing in an OCXO, excessive > heat can throw the frequency and hence the GPS solution way of the mark. For > many GPS reference stations, rubidiums is used to steer the internal clock, > and the quality of that lock can affect how well it tracks it and have > secondary frequency issues. > > So, it comes as no surprise that the GPS module is temperature sensitive. The > metrology labs measure and compare the temperature stability of various > GPS-receivers, > > There are also filters that can provide temperature effects, but the TCXO is > where it usually hurts most. > > Cheers, > Magnus > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
