[time-nuts] Thunderbolt GPS rollover

bg at lysator.liu.se bg at lysator.liu.se
Sun Jun 10 22:16:10 UTC 2012


Hi again Mark,

> Most GPS receivers base their rollover point from their data of
> manufacture/firmware creation/etc.   The week rolls over 1024 weeks after
> that.   They tend to not be dependent upon when the actual GPS week rolls
> over.  Better receivers have ways of inferring the actual week after a
> rollover occurs...  it appears that the Thunderbolt does not do this.
> Also,  most GPS receivers do not cease to work after a rollover...  they
> just report a bad date.
>
> From the Thunderbolt manual:
> The first week number roll-over will occur as August 21, 1999 (GPS)
> transitions to August 22, 1999 (GPS). The ThunderBolt adjusts for this
> week rollover by adding 1024 to any week number reported by GPS which is
> less that week number 936 which began on December 14, 1997. With this
> technique, the ThunderBolt will provide an accurate translation of GPS
> week number and TOW to time and date until July 30, 2017.

A neat solution to this would be if the time-nuts could reverse engineer
enough of the Tbolt to mod the firmware and fix any upcoming roll-over
issues. Anyone know if Trimble has issued any firmware upgrades to the
general public? Both my Nortel GPSTM 45000-boards have later firmwares
inside than in the printing on the physical board.

--

   Björn




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