Hal Murray <[email protected]> wrote: > It uses the SiRF chip set. There is no PPS. The timing > on the NMEA strings is bad to horrible. > > If anybody has figured out how to get good timing out of the > SiRF units, please clue me in.
The NMEA protcol is unsuitable for accurate timing. There often is not even a spec for the delay between calculating a fix and sending the NMEA data for a given device, and this delay often varies according to internal priorities and scheduling. Also note that the time field in NMEA packets is a "time of fix" and not a "current time". There are SiRF units that output PPS and the timing is no problem with those. But they do not seem to exist with USB interface. (probably because there is no way to send the PPS signal over USB with accurate timing) You need an RS232 model, that puts the PPS on DCD or CTS. At least the SiRF chips send reasonably long PPS pulses, that can be transmitted over RS232 without external pulse stretcher (as some Trimble devices do require) _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
