[time-nuts] Sawtooth correction: next or previous PPS
Hal Murray
hmurray at megapathdsl.net
Tue May 22 01:13:45 UTC 2018
holrum at hotmail.com said:
> One thing to look out for when messing with sawtooth messages is the
> question of does the message come out before or after the PPS pulse... good
> look finding the answer in the receiver documentation...
Has anybody asked the manufacturers?
This should be easy to see if you record the PPS offset referenced to a good
clock and compare that to the reported offset. If the frequency is stable
and you are getting a sawtooth (rather than a bridge) then a point on a
corrected graph next to the jump in the sawtooth will look good if you have
it right or be off by a clock cycle if you have it wrong.
holrum at hotmail.com said:
> "After" seems to be the most common answer. That makes hardware/delay line
> compensation rather tricky. ...
The slides from Tom Clark and Rick Hambly's VLBI talk (page 29) show a before
setup.
http://www.gpstime.com/files/TOW/tow-time2015.pdf
You said "most common". That implies there are both types. (or
documentation errors) We should make a list of which GPS modules do it which
way.
--
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