[time-nuts] GPS Week 1536 causing problems?

Hal Murray hmurray at megapathdsl.net
Tue Jul 7 03:49:24 UTC 2009


> Providing an RTC has benefits, especially when considering
> week-rollover  issues, since when the receiver wakes up it has no idea
> of date at all,  pulling in the RTC time and date is a sufficient
> hint, and adjusting  with detailed info from the GPS is a trivial
> extention. Then adjusting  the RTC is not a hard thing to do every
> once in a while. The same  problem could also be solved using EEPROM
> space. A byte would suffice.

My comment about batteries was thinking of non-rechargable ones.  There is no 
reasonable way to open the unit to replace a battery.  What's the lifetime of 
a rechargeable battery?  I guess it doesn't matter much if the capacity 
decreases a lot as long as the unit can recover when the battery is dead.

My model of a GPS receiver is that it uses the time and ephemeris data to 
predict the frequencies to listen on.  It needs to correct for Doppler.  
That's assuming the position hasn't changed (much).

How long is an ephemeris good for?  If it's too stale or the RTC has drifted 
too much then it might as well start cold.


-- 
These are my opinions, not necessarily my employer's.  I hate spam.







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