>Peter wrote:
>
>   "The funny part being that they won't work even
>    inside the attic of a wood thatched house"
>
>Do you have the antennas pointed up? <grin>
>
>There has to be a reason - since in my wood-frame
>house my old '94 era Magellen will lock and display
>position *inside* - as will several JRC OEM GPS
>modules that I've worked with.
>
>I have found that the 'thermal reflective plastic
>window film' (I believe they use some sort of
>vapor-deposited metal on this co-called 'plastic')
>>used on the windows of tall modern office buildings
>won't pass a GPS signal - I had to look for a break
>in the 'plastic' in order to test GPS devices in the
>office!

Any timber is a good absorber of RF signals, even down to HF. The New
Zealand Forestry Service used to have mobiles on their vehicles somewhere in
the 5-8MHz region IIRC, and noticed significant reductions in signal
strength out in the pine forests. The actual losses will depend on a number
of other factors such as moisture content, and exact wood type, but it will
always be there.

A typical microwave absorption (not a power load) consists of a wedge shaped
piece of wood in a lump of waveguide. I have often figured that the best way
to make a stealth motor vehicle to minimise detection by traffic speed
cameras is to have the panels covered by wedges of a nice soft wood like
balsa, shaped into wedges that would act as waveguide beyond cut-off at the
relevant frequencies :) OK the car would look odd, but you wouldn't get many
traffic tickets. :)

If you are able to receive the GPS signal inside your house then the
cladding on the house must be something other than wood.

There is of course another gotcha in all this. I am not sure what the
absorption frequency of water is, but I suspect that the GPS transmissions
are not in this range, as it would foul up location finding in wet weather
if it was, and as this is a military originated system, I suspect they would
choose a frequency with minimal losses under these conditions.

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