[time-nuts] GPS noise reduction

Tom Van Baak tvb at LeapSecond.com
Sun Apr 6 02:02:34 EDT 2008


One more thing, maybe I missed this earlier in the thread, but
can you really call it "sawtooth correction" when you apply a
receiver reported correction (with 1 ns granularity) to a 1PPS
signal (with 9 ns RMS or +/- 15 p-p jitter) as coarsely measured
by a 100 MHz TIC (with 10 ns resolution)?

I haven't done the math, but it seems like it's at least an order
of magnitude less precise of a correction than the normal case
where one makes ns or sub-ns measurements and then applies
a ns-resolution correction in software. This is what both Tac32
(for Oncore) and Tboltmon (for Thunderbolt) do when you use
one serial port for the GPS receiver and another serial port for
a 53131/2 time interval counter.

It just seems the small ns-level corrections from your receiver
get rather lost in the large 10 ns resolution of your TIC. More
like a staircase than a sawtooth, perhaps?


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