On 03/13/2013 09:05 PM, David wrote:
This brings up something that I have wondered about for a while.
The Garmin GPS18x (and many other receivers) specify the PPS output as
within 1uS but does that mean it wanders around over say 12 or 24
hours within 1uS of GPS Time or does it mean something else? I can
easily see the granularity of the PPS output but that is obviously not
what the specification refers to.
If it's anything like the ancient Motorola receivers I purchased off
fleabay on the mistaken assumption that they were UT+, it might have a
1uS phase skip every 20s or so. In other words, after a random number of
seconds the PPS (and all subsequent PPS) will be exactly 1uS early. The
idea being that it loosely tracks UTC/GPS, but jumps whenever it gets
too far away. Totally useless for timing but at least they were cheap.
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