Here's a link for those interested in some of the technical details of
satellite radio

http://makeashorterlink.com/?Q1715285B

This info is almost three years old, but it will give you some basic
information about how the system
works, including an early link budget for XM's system. You will notice
that in some areas (places like large cities, tunnels, etc) repeaters
are used
to ensure coverage. In addition, most satellite systems of this type
have *some* link margin to allow
for reasonable in-building penetration loss, which is a function of
location, construction materials, frequency
of operation, etc.

RK