| Re: [chrony-users] gpsd, pps and chrony |
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On Tue, 5 Apr 2011, Miroslav Lichvar wrote:
On Mon, Apr 04, 2011 at 09:25:01PM +0100, Ed W wrote:
(They also have a 20hz GPS with decent sensitivity and a GPS/GLONASS
hybrid board...)
And exactly what would a 20Hz buy you?
20 times more samples could improve the stddev of the calculated mean up to
factor sqrt(20). It would also allow shorter polling interval.
That assumes that the primary errors are gaussian statistical in nature, which
I doubt (eg, the sawtooth nature over 10s of seconds of the gps-utc offset on
most receivers, and the ionospheric correction error, which is highly
correlated over times on the order of hours. And if your receiver has an
amplifier in the chain with us response time, all the averaging in the world
will not improve that. Ie, the number of outputs per second is not, I believe,
a limitation, especially since the computer itself takes so long (usec) to
respond.
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William G. Unruh | Canadian Institute for| Tel: +1(604)822-3273
Physics&Astronomy | Advanced Research | Fax: +1(604)822-5324
UBC, Vancouver,BC | Program in Cosmology | unruh@xxxxxxxxxxxxxx
Canada V6T 1Z1 | and Gravity | www.theory.physics.ubc.ca/
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