[ntp:questions] Suggested gps devices for use as a time sourcefor ntpd

Jason Rabel jason at extremeoverclocking.com
Wed Aug 8 02:27:51 UTC 2007


> >NMEA doesn't give you well-defined (or even ill-defined)
> >time markers. It has to be PPS.
>
>NMEA does give well defined time markers.  They just have more
>jitter than a PPS signal.

I think we could all agree that NMEA sentence accuracy can vary greatly
between receivers. Like the old Jupiter 8 receivers when operating in NMEA
mode were often 1 second behind, sometimes jumping to 2.

There is no guarantee of timing accuracy from any GPS receiver
specifications I have read about their position & time output info, be it in
NMEA or a native binary mode. It can only be assumed that it will be before
the second mark.

Sysplex on the other hand usually does have accompanying information stating
that the <CR> at the end of the line is sent within X amount of the time
mark.

Jason




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