[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:


That "should" remove your 4 hour NMEA latency issues (fingers crossed).

Regards, Geoff  ( Christchurch , New Zealand )

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