[Lowfer] Use of NMEA strings for GPS 1 pps time tagging

[Dave Brown]

I am only just coming up to speed on this but-
It appears that time tagging the1 pps output of a GPS rx from data in the
NMEA string is not always as straightforward as it may seem. Not all rxs
behave the same in the way - most, but not all, tag the immediately previous
1 pps leading edge. As well, a particular rx can have a variable delay
between the 1 pps leading edge and the corresponding NMEA string output,
depending on several factors that can/will change, even at a fixed site.
 So the possibility exists for there to be varying integral second
differences between the GPS derived time at various QTHs-depending on the
hardware used. Clever software can evidently sort these issues and allow a
reliable 'time' output to be produced.
This is proving to be a rather interesting subject and I would welcome
feedback from others who may have more input to offer. In particular this
has ramifications for Africam -any comment, Bill?

73
 Dave, ZL3FJ