[time-nuts] Failure mode in GPS receivers

[bg at lysator.liu.se]

On Sun, December 17, 2006 21:34, Bruce Lane said:
> Good day,
>
> *********** REPLY SEPARATOR  ***********
>
> On 17-Dec-06 at 21:25 bg at lysator.liu.se wrote:
>
>>On Sun, December 17, 2006 20:54, Poul-Henning Kamp said:
>>> In message <200612171136230661.088C8673 at 192.168.42.129>, "Bruce Lane"
>>> writes:
>>>>Fellow clock-tickers,
>>>>
>>>>       In the group's experience, what's the most common failure
>>>> mode for GPS receivers, especially older ones, that could stop them
>>>> from hearing the sats?
>>>
>>> Antenna damage.
>>
>>Did not a hardcoded GPS-week limitation strike quite a lot of older Datum
>>stuff?
>
> 	In a word... huh?
>
> 	Methinks I'd better go do some googling... Unless you'd care to expand on
> that? ;-)

Wording could have been better. Seach for GPS week rollover. The GPS
satellites send a datastream to all receivers telling them the time and
where the satellites are. To know the date you have a GPS-week, that is 10
bits long. Week #1 started Jan 1 1980.

well read more on tvb's site.

Some receivers half fixed this problem by adding 1024 weeks to any GPS
week lower than some safe number - say a few weeks before the engineer
wrote that code in the receiver firmware.


--

   Björn