This excerpt taken from the SIRI 10-K filed Mar 10, 2009.
Our Satellite Radio Systems
Our satellite radio systems are designed to provide clear reception in most areas despite variations in terrain, buildings and other obstructions. Subscribers can receive our transmissions in all outdoor locations where the satellite radio receiver has an unobstructed line-of-sight with one of our satellites or is within range of one of our terrestrial repeaters. We continually monitor our infrastructure and regularly evaluate improvements in technology.
The FCC has allocated the portion of the S-band located between 2320 MHz and 2345 MHz exclusively for satellite radio. Each of SIRIUS and XM uses 12.5 MHz of this bandwidth to transmit its respective signals. Uplink transmissions (from the ground to our satellites) use 12.5 MHz of bandwidth in the 7060-7072.5 MHz band.
Our satellite radio systems have three principal components: