Someone's 'theory':

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

Real world:

Brick veener exterior (MORE absorptive/reflective to
uW's than wood), standrard wood framing, roofing of
4'x8' plywood sheets topped  with 'composition'
shingles -

- and GPS receivers are *fully* able to function.

Your example involving 'pine forests' involves a
LOT more in the way of lossy material which a
typical land-mobile 2-way system would and see
using terrestrially-bound just barely above
the surface-of-the-earth signals.

    "Any timber is a good absorber of RF signals, even
     down to HF."

Any truth to the rumor that old hams used to use
wood sticks dipped in parafin (sp?) as spacers
on their open-wire twin-lead feedlines?

I guess there're no thruth to the rumor that lumber
used in construction if kiln-dried to some single-digit
moisture value either ...

I need an explnation, too, as to how I can pick up SW
as well as AM broadcast band signals equally inside
and outside inside of my house too.

(It seems that 'mother nature' is un-informed as to the
proper behavior of EM waves in an urban environemnt.)

Okamura, where are you when we need you?

Jim

----- Original Message -----
From: "Alan B. Pearce" <A.B.Pearce@RL.AC.UK>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Tuesday, July 16, 2002 2:28 AM
Subject: Re: [OT]: BGMicro GPS recievers


> >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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