[time-nuts] Garmin GPS12XL V3.51

[Forrest Christian (List Account)]

I realize that this doesn't help old receivers, but I'm sort of
surprised that this wasn't addressed as the GPS system has had various
additions made to it such as WAAS.  Even 3-4 bits allocated to this
purpose in one of the datastreams would move us out beyond any
reasonable expectation of the life of the current GPS protocol.

Does anyone know if any of the global GNSS alternatives (aka GLONASS,
etc.) have similar limitations?

On Tue, Apr 9, 2019 at 7:01 AM Tom Van Baak <tvb at leapsecond.com> wrote:
>
> > There's another relatively simple clue in the old GPS signal: the leap
> > second count! A device manufacturer could teach it what the leap second
> > count was at manufacturing time, and how to predict a lower bound on the
> > leap second count in the future (with a suitable safety margin / fudge
> > factor) which should allow it to live a bit more than 20 years.
>
> The idea was proposed 20+ years ago, Trimble even has a patent on it. Details here:
>
> http://leapsecond.com/notes/gpswnro.htm
>
> But it turns out not to work. Earth rotation is too difficult to predict 20, 40, or 60 years into the future. There was talk that the GPS receiver failures in 2015 were related to this algorithm. Look for any threads with subjects like: TS2100, TymServe 2100, 1995 rollover, Trimble ACE, Heol Design in:
>
> http://lists.febo.com/pipermail/time-nuts_lists.febo.com/2015-May/
> http://lists.febo.com/pipermail/time-nuts_lists.febo.com/2015-June/
>
> /tvb
>
> ----- Original Message -----
> From: "Tony Finch" <dot at dotat.at>
> To: "Discussion of precise time and frequency measurement" <time-nuts at lists.febo.com>
> Sent: Tuesday, April 09, 2019 4:08 AM
> Subject: Re: [time-nuts] Garmin GPS12XL V3.51
>
>
> > Leo Bodnar <leo at leobodnar.com> wrote:
> >
> >> Assume that the device does not have any reliable long term non-volatile
> >> memory that you can update.
> >
> >> In the absence of any clues your only reliable piece of knowledge is
> >> that the cold start date is somewhere after the date of manufacturing
> >> or, most often, firmware compilation date.
> >
> > There's another relatively simple clue in the old GPS signal: the leap
> > second count! A device manufacturer could teach it what the leap second
> > count was at manufacturing time, and how to predict a lower bound on the
> > leap second count in the future (with a suitable safety margin / fudge
> > factor) which should allow it to live a bit more than 20 years.
> >
> > Tony.
> > --
> > f.anthony.n.finch  <dot at dotat.at>  http://dotat.at/
> > Gibraltar Point to North Foreland: Northeasterly 5 or 6, occasionally 7 in
> > south. Moderate. Showers at first in south. Good, occasionally moderate at
> > first.
> >
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-- 
- Forrest