Bob,
The sawtooth is generated by the granularity of the GPS receiver clock
not being synchronous with the recovered PPS. The receiver program can
calculate the correction to be applied to the next PPS and outputs it in
a message, bu only in timing receivers, this is not a useful thing in
navigation receivers and I think that it cannot be calculated using the
satellites' position, it is a receiver "defect".
Why don't you buy a timing receiver? An used Motorola Encore M12+
timing receiver can be bought by $35 or less (ebay items 290656401551 or
301131583613. The seller is a known Time Nuts supplier). An UT+ or GT+
even for quite less.
Regards,
Ignacio EB4APL
On 21/03/2014 20:28, Bob Stewart wrote:
I've gotten my PLL mostly working, but, since I'm using a nav receiver, it looks like I
may want to see if I can do a poor-man's sawtooth correction based on GPS position
changes. Has anyone done this or have a reference for a project that has? It would seem
to me that only the East-West movements would be a factor, but I dunno. As a beginning,
I was just going to plot lat and lon deltas from "gpsd" data to see what
correlates to the phase error jumps I'm seeing, unless this path has already been tread.
I don't expect the accuracy that would be afforded by a real timing receiver.
Bob - AE6RV
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