[time-nuts] Garmin GPS12XL V3.51

[Tom Van Baak]

> 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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