[ntp:questions] Using Garmin GPS-III+ as Time source

Nero Imhard nim at pipe.nl
Mon Nov 24 08:27:10 UTC 2008


Unruh schreef:

> If it provides an nema output then you probably can use it to
> discipline your clock to of order 10-20ms.

What does "probably can" mean exactly?

It only works if the temporal relation between an emitted NMEA sentence
and the time it contains is either formally specified or can be
determined empirically. The former is almost never the case, the latter
may often seem to work, but yields a low level of confidence.

As long as I see receivers with highly variable time offsets for their
NMEA, I have to regard NMEA as unusable for refclocks. I even consider
it unsuitable for "numbering the seconds" of a PPS source, but I own a
specimen of a particularly crappy GPS receiver in this respect ;-)

N




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