GPS Lock on times

Donald · Posted: Mon Oct 10, 2005 11:36 am Post subject: GPS Lock on times

If a guru would pop up and explain the reasons behind the various "Lock on times" I'm sure many of us would like to know...

(I am not refering to variations due to urban canyons etc - assume perfect positioning and in sight of most 'visible' sats.)

EG:
1) COLD. When the GPS unit is new, the lock on time takes quite a time to sort itself out. Say several minutes or more.

2) WARM (ish). After initial lock on from new, daily lock on is shorter, say in the region of 1 minute.

3) WARM. Used it say, an hour ago, Lock on is a few seconds.

4) HOT. Lost GPS lock in tunnel - re-aquire sats in 2 - 3 seconds

5) COLD (Again) - Not used GPS for some time, it reverts to long lock on as per 1) above....

Why does it vary so much???
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Axim X50 & TT5, Arkon CM820 powered mount with built in sirf2 gps
Axim 5 sans GPS Rx
Ford Focus 2L Ghia, Wife, kids, dog, cats, mortgage, bank manager & taxman to support, debts, windows need painting - (I cut the grass! - its rained - it needs

lbendlin · Posted: Mon Oct 10, 2005 1:33 pm Post subject:

The receiver needs to have a basic understanding of where to expect the satellites. This base data (Almanach/Ephemeris) is aging when the receiver is not in use, and additionally the backup battery on the receiver only holds for two - three days.

So when the base data is gone you're back tot he cold start scenario, which can take anything from 5 minutes to eternity. Especially when you are driving while the receiver is trying to receive the base data you are making it very hard for the poor little box - that's when we say better be stationary with good sky view.
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Pocketgps · Posted: Mon Oct 10, 2005 10:36 pm Post subject:

Not up to date, but have a look At This

Donald · Posted: Wed Oct 12, 2005 10:39 pm Post subject:

Thanks both of you - It now slots into place. I must admit, I have been trying to reconcile the timings for some time.

Regards
_________________
Axim X50 & TT5, Arkon CM820 powered mount with built in sirf2 gps
Axim 5 sans GPS Rx
Ford Focus 2L Ghia, Wife, kids, dog, cats, mortgage, bank manager & taxman to support, debts, windows need painting - (I cut the grass! - its rained - it needs

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