[OSM-talk] fwd: Two thirds of mobile users want driving ANDwalking navigation

Apollinaris Schoell aschoell at gmail.com
Tue Feb 16 18:38:19 GMT 2010


On 16 Feb 2010, at 9:46 , Dave F. wrote:

> John Smith wrote:
>> On 17 February 2010 01:40, John F. Eldredge <john at jfeldredge.com> wrote:
>> 
>>> Frequently you can't get a position fix at all, if the building has much metal in its structure.  I can't get a position fix from inside my house unless I am near a south-facing window, probably due to a metallic-foil vapor barrier in the attic.
>>> 
>> 
>> It has little to do with the material it's made of, it's all about how
>> much mass an object has, the more mass the more it will absorb RF.
> Is this correct?
> 

No

> I assumed the reason I had trouble getting reception on board trains 
> because of what their roofs were screened with. 
> I can't believe they'd put much mass up there.
> 

even a thin metal film will filter almost all GPs signals. older GPS units with SirFII chips don't work in cars with metal coated windshields and need an external antenna. reception from the side or backside is not enough.
newer with SirFIII or similar quality chip will work

> Cheers
> Dave F.
> 
> 
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