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post #9 of (permalink) Old 26th June 2007
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I suppose the windscreen must be attenuating the signal to some degree. It's just that the theory goes that Sirfstar III is sensitive enough to be able to use the lower strength signal.

Having said that, the signal is still weakened, and maybe that means that even Sirfstar III loses some of the signal.

But aside from the signal strength, there are three things that can seriously lengthen the time it takes for a sat-nav to achieve a lock:
1) Out of date almanac data, possibly for satellites that are no longer in range. This shouldn't really be a problem if the unit's only been off for a few hours, but if it's a matter of days, then it can be an issue.
2) The unit has been switched on in a significantly different location to where it was switched off (the stored almanac data is incorrect for the new location, and it takes the unit a while to figure that out.
3) The unit is trying to acquire a GPS lock in a moving vehicle. (It's much harder for it to reconcile its position when that position is constantly changing.)

Combine any of the above with the attenuating effect of the windscreen, and I suppose lengthy lock times are to be expected. The more factors you combine, the longer it's likely to take to acquire a lock. It's an achievement that Sirfstar III works at all. My 700 with Sirfstar II rarely gets a lock in the Lag without the external aerial.
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Last edited by Horatio; 26th June 2007 at 01:32 PM.
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