Hi All,
So I've been playing with some timing hardware here, and have noticed
something rather curious. I have two otherwise identical Lea-6T GPS
modules, configured exactly the same. These units are tied to the same
antenna, with a splitter with the same length cables running to each
unit. They were given the same survey coordinates. Initially there was
not any appreciable difference between the PPS outputs. The outputs
were on average within about one nS of each other. However after a day
or two they started to display a difference of about 21nS between the
PPS outputs. This is also evident in the GPSDO output, as the phase of
the 10Mhz is also skewed by 21nS or so.
A few days ago I started a 48 hour survey. The came up virtually
identical coordinates at the end of that survey. After the survey the
phase is still 21nS different.
At this point, my only thought is the GPS splitter. It's DC coupled to
one unit, and AC coupled to the other. It is possible there are some
delays on one output vs. the other due to the blocking caps and bypass
inductor in the splitter. I've tried swapping the GPSDO units on the
splitter, so we'll see what happens there.
Can anyone offer any insight as to why the two units may have a
different PPS output timing? It's not really a problem, more of a
curiosity and mildly academic exercise.
Thanks,
Dan
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