[time-nuts] Garmin GPS12XL V3.51

[Adrian Godwin]

The references I found in those archived postings explain that the problem
was that the GPS receiver had been 'fixed' in 2011 but that the fix only
worked until 2015. The solution was to replace the receiver.

I wasn't able to find any discussion of why the fix lasted such a short
time, but it seems far too short to be due to variation in the rate of leap
second insertions.

Assuming that the reason for that algorithm's failure is correct though, it
implies that leap second insertion rate might vary by at least 13
insertions in 20 years in order that an estimate of week counter cycles
produced from leap second count would be wrong.

This carries a further implication that the 7 bit count of leap seconds
will last not for 175 years but half that or perhaps worse. Or, if the
problem is with a lower than assumed rate of insertions, better.

How much variation in the rate of leap second insertion is there?

On Tue, 9 Apr 2019, 14:01 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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