[time-nuts] Four hour cycle in GPS NMEA jitter

Kiwi Geoff geoff36 at gmail.com
Tue Mar 21 19:24:16 EDT 2017

> https://goo.gl/photos/JZhBbFKFzkBAykti6
> Why would a GPS module produce jitter with a pattern like this?

Trent, I must admit I have not seen such a four hour "spike" before in
the NMEA latency, however a clue may be that the GPS ephemeris
(broadcast by the SV's) orbit description is valid only for a "4 Hour
Period" - before the SUN and Moon and other factors make it too

I did a Google search for

telit ephemeris gps "4 hour"

and found that the TELIT appears to have some algorithm that enhances
somehow the ephemeris. Maybe your 4 hour spike (which appears to be
for 4 seconds each time) is evidence of your TELIT doing some extra
homework involving the ephemeris - just a guess on my part.

Regards, Geoff (Christchurch , New Zealand)

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