[time-nuts] GPS orthodontics: sawteeth & hanging bridges - theeffect of time averaging

Tom Van Baak tvb at leapsecond.com
Thu Dec 21 13:41:00 EST 2006


> To explore this I used TAC32 to record the 1 pps sawtooth
> correction message from a Motorola M12+ receiver for
> about 1 hour, during which time many bridges occurred (1).
> Excel's statistical toolbox was then used to examine
> the data.

Brooks,

That's really nice work.

Are you sure, though, that doing the statistics on the
correction data itself is equally as valid as statistics
on the measured 1PPS hardware output? Something
doesn't seem quite right with your premise, but I can't
put my finger on it just yet.

When I take a couple of hours of M12+ 1PPS data
(not sawtooth corrections) I get the following standard
deviations:

1 second raw samples: 10.40 ns
then removing small linear frequency offset,
1 second samples:  9.36 ns
30 second averages: 9.62 ns
300 second averages: 10.0 ns

Did I do something wrong? PHK, what do you think
about this?

/tvb




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