[time-nuts] Four hour cycle in GPS NMEA jitter
Kiwi Geoff
geoff36 at gmail.com
Wed Mar 22 15:28:39 EDT 2017
On 3/22/17, Trent wrote:
> https://goo.gl/photos/JZhBbFKFzkBAykti6
> Why would a GPS module produce jitter with a pattern like this?
Trent, I decided to R.T.F.M. (read the fantastic manual ;-)
It looks like that in your Telit module, there is a mode called
-----------------------------------------------
Client Generated Extended Ephemeris (CGEE)
CGEE data is always generated for a prediction interval of three days:
- Consists of 18 blocks of 4-hour EE data blocks
- Updated when a newly visible satellite is acquired
- Updated when new broadcast ephemeris is received from a tracked
satellite and the current
EE data block is nearing expiration
- On average, it takes 1.2 seconds per satellite for the receiver to
calculate CGEE
-----------------------------------------------
So I think that is the cause of your 4 Hour NMEA latency issues, when
your Telit module is creating a new EE (Extended Ephemeris) data set.
>From a quick glance at the manual, it looks like this mode can be
turned off with:
AT$GPSIFIX=0
That "should" remove your 4 hour NMEA latency issues (fingers crossed).
Regards, Geoff ( Christchurch , New Zealand )
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