<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by MeLike2Travel:
I don't know too much about the technical aspects of GPS units. It seems to me that it would be difficult to use them in the plane. But then again, a friend of mine says he can get a signal inside his apartment, even when he's not next to the window. Is that even possible?
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Unlikely. Bear in mind that the power output of a GPS satellite for the public L1 signal is about 26W; the antenna gain is quite high, so imagine a 30W spotlight focussed on the earth from 21,000km away and you get some idea of how weak the signal is by the time it arrives.
You can hinder most handhold GPS receivers just by putting your hand over the antenna, in my experience. I would be extremely surprised if you could acquire enough satellites to get a position fix indoors.