Satellite Signals

[Footpounds]

All of the reading I have done on GPS satellite signals state that the signals will penetrate plastic, windows, cloth, and other light materials. Why then can I receive signals in my house? I live in a one story home with a plywood roof with composite shingles (a regular suburban home). The signals that I am receiving are from satellites that are directly overhead or that are just slightly off from being directly overhead. I just turned on my GPSr and got a lock on 4 birds from my living room. What's the deal?

[+Redwoods Mtn Biker]

Do you still get signals when the roof is wet? See...

 

http://gpstracklog.typepad.com/gps_tracklo...cloud_cove.html

 

Rich Owings

www.MakeYourOwnMaps.com

www.GPStracklog.com

 

"We were desert mystics, my friends and I, poring over our maps as others do their holy books." - Edward Abbey

[Footpounds]

I don't know if the signals still come through when my roof is wet. That was really not my point. The bigger issue is why they are coming through WOOD and SHINGLES.

[Neo_Geo]

They're probably bouncing off of objects outside and being reflected inside through the windows. See MULTIPATH ERRORS.

[Footpounds]

That makes sense except for the fact that my aluminum blinds are closed. If your theory was correct then it would be even more mysterious as the signals would be passing through metal. I know my experience is not unique! Come on, surely this must be a common occurence! Hasn't someone out there noticed this and come up with a rational explaination?

[peter]

They come through my roof (plywood and spanish tiles on top) just fine too, and they also make it through typical fiberglass boat construction. Most materials are not good absorbers of microwaves, but anything with a high water content (incl. people) or metal will block the signals.

 

As a general rule, anything that will heat up readily in a microwave oven will also absorb the GPS signals although the frequencies are a little different (1.5 GHz for GPS and a little over 2 GHz for ovens).

 

So as long as the wood and shingles on your roof are dry they'll pass the signals ok, but of course insulation with a metal foil layer would block them.

 

The physical reason why things with water absorb the signals is that water molecules are highly polarized with the oxygen end having a negative charge and the end with the two hydrogens having a positive charge. When the GPS signals go through water the oscillating electrical field of the microwaves cause the water molecules to rotate back and forth and this absorbs energy from the signals.

[Footpounds]

Peter, THAT is the kind of intelligent explaination I was looking for! I knew there had to be a logical reason for what I was seeing. Thanks a bunch for your reply!