Re: PPS and NMEA same source not combined

My pleasure, lol
Thanks for the help guys I am much better educated now.  I have read loads out there on the net but much of it seems to be guess work.  It was nice to get some good info from the horses mouth.

Mike.



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On 19 Mar 2023, at 20:20, Bill Unruh <[email protected]> wrote:

Well, not at the offsets but the offsets and the statistical standard
deviation. and also depends on the number of sources. There is a voting system
in place as well. That is why one should always have an odd number of sources,
so "good ones" can outvote "bad ones". The PPS offset and spread will (almost) always be within the spread of the
internet sources, but the NMEA could well be outside because of systematic
errors. It will tend to have large spread because of the variability of
getting its sentences out. But the PPS should have a very small spread (micro
to namnoseconds) and lie within the spread of the internet sources (unless
your internet connection is very assymmetric).

Doing this made me look at mine and discover that the PPS source seems to have
died yesterday. Thanks.


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 |____ [email protected]
Canada V6T 1Z1 ____|____ and Gravity ______|_    theory.physics.ubc.ca/

On Sun, 19 Mar 2023, Rob Janssen wrote:

[CAUTION: Non-UBC Email]

True, but an NMEA source is not an accurate local source.  A PPS source is.
So the hierarchy is:
1 - PPS source
2 - internet source(s)
3 - NMEA source

And chrony correctly determines that, after looking at the reported offsets.

On 3/19/23 21:00, Mike Smith wrote:
Rob,
Yes I kind of understand your thinking and I was about to agree but surely if you have a more accurate local source, using that would be preferable?
Mike.


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