[time-nuts] Epoch rollover ?

k4cle at aol.com k4cle at aol.com
Sat Oct 22 18:30:10 EDT 2011



Connected by DROID on Verizon Wireless

-----Original message-----
From: Bruce Lane <kyrrin at bluefeathertech.com>
To: time-nuts at febo.com
Sent: Fri, Oct 21, 2011 20:44:07 GMT+00:00
Subject: Re: [time-nuts] Epoch rollover ?

Good day,

*********** REPLY SEPARATOR  ***********

On 21-Oct-11 at 13:18 Dennis Ferguson wrote:

>On 21 Oct, 2011, at 11:53 , k4cle at aol.com wrote:

>> Bruce, the most common cause of a GPS receiver getting the date
>incorrect is due to cross-correlation.  And cross-correlation is usually
>the result of too much gain in the GPS antenna's LNA.

	(snippage)

	I would be more likely to believe this if the setup had not been working
just fine for the last four years. ;-)

	No, based on what I've read, I'm definitely inclined to believe it's a
1024-week rollover thing.

	(more snippage)

>Some of the heuristics I've heard of are these (or maybe combinations of
>these):
>
>- Assume the date must be more recent than when the firmware was
compiled.
>  By itself this leaves the device with a 1024 week rollover problem,
but
>  the 1024 weeks are counted from the date the firmware was compiled
rather
>  than from the GPS epoch.

	(still more...)

	This idea fascinates me, as it is, potentially, the easiest to correct
AND the unit itself is vintage mid-90's. This would also explain why the
thing stayed working for a while after the last 1024-week roll.

	I think I'll pull out the firmware, see if I can find the compile date
in a dump of the EPROM, change said date, and put the whole thing back
together. At worst, I'll end up with the same situation I have now. At
best, it'll fix it.

	No matter what, I'll post the results. Dennis, thanks much! I hadn't
even considered that line of thinking.




Bruce Lane, Owner & Head Hardware Heavy,
Blue Feather Technologies (http://www.bluefeathertech.com)
Assoc. member, AZA & AAZK for many moons.
"Salvadore Dali's computer has surreal ports..."


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