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There are two pieces to the equation. First is the antenna gain. The 
second is the sensitivity of the electronics used in the receivers. The 
GPS signal is very weak - less than 10^-16 watts per Hz. It is well 
below the ambient microwave radiation background noise on the earth. It 
uses encoding to allow the receivers to see it. The current batch of 12 
channel commerical GPS receivers are not very sensitive. Even with a 
optimal 1/4 wave antenna you don't get the gain you should because of 
the receivers.

The good news is there is a trend for the use of GPS in indoor 
applications. Try using your GPS inside - it won't work. In order to get 
one that work inside you need about 100 times more signal strength 
delivered to the decoders (see 
http://www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=149220 ). 
I expect we will see the development of affordable high gain antennas 
and more senitive receiver technology in the near future, and with 
Gallieo (Eurpoean navagational satellite system) coming on line and 
receivers designed to use both systems. These advances will eventually 
filter down into the inexpensive commerical outdoor units and solve many 
of the problems the current crop has.

But currently with my GPS I don't even think about messing with it in 
the forest when the foliage is out - it can process the signal.

Truman

April wrote:

> This is true of any GPS unit and it not a problem specific to the
> Forerunner.  I haves not had a moment's trouble with satellite
> reception when not in the woods (i.e., riding along the roadside), so
> I have not experienced "marginal" results in that instance.
>
> When I am going to be in an area that I know (or think) will have
> problems with satellite reception, I also use an external antenna that
> works in most of the conditions I have had it in. There is a runner in
> NC that uses an external antenna with great success in areas that he
> couldn't pick up a signal without the external antenna.
>
> http://www.pc-mobile.net/gpsant.htm
>
> BTW, even if there is no satellite reception, the 301 will still
> record heart rate data.
>
> April
> Nashville, TN
>  
>
>  


--

“It doesn't matter how beautiful your theory is, it doesn't matter how 
smart you are. If it doesn't agree with experiment, it's wrong” Richard 
Feynman



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