[time-nuts] Using a UBlox NEO-6 GPS module for calibrating a PIC microprocessor based timer.

[Attila Kinali]

On Sun, 1 Dec 2013 18:49:55 -0000
"David J Taylor" <david-taylor at blueyonder.co.uk> wrote:

> You are right that I simplified things.  The sawtooth effect will have (over 
> a long term) a uniform distribution with a width equal to 
> 1/<sampling-frequency>.

I'm not so sure about the uniform distribution. The u-blox histogram
is not so clear on that. But yes, my first approximation would also
be a uniform distribution with added (Gauss-like)roll off at the edges.

> 
> I appreciate your better knowledge on the "GPS jitter".  Certainly a poor 
> antenna location is to be avoided, and the serial output could be used to 
> give some indication of the general GPS quality (e.g. by looking at signal 
> strength, number of satellites, and precision of fix, in general terms).

Unfortunately, it's not so easy. Multipath does not necessarily lead
to poor reception. And even if it does, you cannot conclude from the
reapearance of a satelite that the multipath is gone. I'm also not
sure how uncertainties of position relate to timing jitter in navigational
receivers. One can assume that l/c = t, but this is just a worst case
assumption and my uninformed guess would be that the jitter is actually
lower than that.


				Attila Kinali

-- 
1.) Write everything down.
2.) Reduce to the essential.
3.) Stop and question.
		-- The Habits of Highly Boring People, Chris Sauve