GPS sensitivity

Alastair Johnson alastair at
Mon Oct 27 16:48:32 CET 2008

Stefan Monnier wrote:
> The FR is the first device I use with a GPS, so I don't know what's
> considered as "normal" w.r.t GPS function.  I find that my FR's GPS
> never works inside a building (e.g. at home), and even outside in the
> streets of Montreal, it seems to only be able to get a first fix if I'm
> in a somewhat open area (i.e. not in a street but on a place, in
> a park), and also it seems to rarely if ever be able to get a first fix
> when it's in my pocket.
> Is that normal?  My FR does have the capacitor in the µSD slot and it
> has a fairly recent kernel (don't know if that means it has the software
> fix that "stops the µSD clock when possible", does it?)

It's a little tricky to describe 'normal' since the movement of the sats 
gives some inherent variability. Getting the first fix also requires 
significantly more signal than maintaining a fix once acquired, and it 
seems to help being stationary when doing it. I don't know how limited 
the view of the sky is in Montreal, but 'urban canyon' effects have long 
been a problem for GPS systems due to limited view of the sky (can't see 
enough sats) and multiple reflected signals. That said, since the SD 
clocking fixes were added to the kernel I find the Freerunner usually at 
worst as quick as my Garmin Gecko at getting a fix, and substantially 
better at keeping it. The Freerunner will often keep a fix indoors when 
the Gecko hasn't a hope. OTOH the Gecko is hardly state of the art now, 
so expectations may be different.

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