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Satellite radio in the United States was born in 1992 when the U.S.
Federal Communications Commission (FCC) allocated a spectrum in
the "S" band (2.3 GHz) for nationwide broadcasting of satellite-based
Digital Audio Radio Service (DARS). In 1997, two companies received
licenses for digital satellite radio initiatives. CD Radio (Now Sirius
Satellite Radio) and American Mobile Radio (now XM Satellite Radio).

Headquartered in New York City, Sirius uses PAC encoding
technology and digitizes their signal, at near CD quality meaning that
there is very little loss of quality from the original source track. Sirius
programming is delivered to its subscribers via 3 high power, Loral
SS/L-1300 commercial satellites in an inclined elliptical orbit around
the Earth. Unlike most satellites, which use geostationary orbits
22 300 miles above the Earth, the unique higher Sirius Radio satellite
inclined orbit allows a somewhat larger coverage area.

The Sirius satellites have an average elevation angle of about 60
degrees as opposed to approximately 45 degrees for geostationary
satellites. This higher elevation allows them clearer line of sight and
fewer obstructions such as buildings and trees. The 3 satellites slowly
orbit the Earth approximately 100 degrees apart and employ a "hand-
off" method, meaning that only 2 of the 3 satellites are active at any
given time to avoid interference as Sirius is only allocated 2 different
frequencies. One of the satellites over the U.S. will use frequency A
and the other will use frequency B. As each one of the satellites leave
the footprint of the continental U.S., they deactivate and hand-off
their signal to another satellite which has just re-activated and is just
entering the footprint of the continental U.S. Each of the 3 satellites
spend approximately 16 hours over the continental United States,
with at least one satellite over the United States at any given time.

satellite coverage

The inclined orbit also means that many areas of Canada and Mexico
are covered better by its satellite footprints. Sirius also has a forth
redundant satellite on the ground ready to be launched in case one
of its three primary satellites should fail. The Sirius satellites cover the
entire continental United States as well as many areas of Canada and
Mexico. Sirius also uses a number of land based repeaters, located
throughout the U.S., mostly in major sites that have tunnels and
large buildings that can block out satellite reception. By default, your
Sirius radio receiver will "listen" for the signal on the satellite
frequencies. If it is not able to receive them, it will automatically
switch to terrestrial mode and listen for the signal from a repeater.
Once the satellite signal has been re-established, it will switch back
to satellite mode. Additionally, Sirius has recently announced a
partnership with the Canadian Broadcasting Corporation and
Standard Radio Inc., that would allow Canadians to subscribe to a
Canadian satellite radio version of Sirius, with Canadian English and
French channels. This application is currently before the CRTC for final

You won't usually have to worry about pointing your satellite antenna
as it will automatically acquire the satellite lock as long as you have a
clear view of the southern sky. The Sirius signal is capable of
penetrating some objects, such as some wood roofs, however steel,
concrete and abundance of trees can interfere with the signal.

XM radio delivers its satellite radio programming to its subscribers via
4 of the worlds most powerful commercial satellites, currently in
geostationary orbit 22 300 miles above the Earth. The 2 active XM
radio satellites are Boeing HS-702's and are aptly named "Rhythm"
and "Blues". "Rhythm" and "Rock" are currently positioned at 85
degrees West Longitude, servicing mostly the western half of the
United States. "Blues" and "Roll" are currently positioned at 115
degrees West Longitude, servicing mostly the eastern half of the
United States. Together these 4 satellites offer nationwide U.S.
coverage and beyond. The footprint from the XM Radio satellites
extend approximately from Mexico City, Mexico to more than a couple
hundred miles into Canada and approximately 100 miles off both the
east and west coasts. This allows people travelling into Canada or
Mexico to enjoy uninterrupted coverage. Monitored and controlled
by Telesat Canada, the satellites broadcast their signals back down
to Earth using the L band radio frequencies (950-1450 MHZ). Rhythm
and Blues as well as Rock and Roll are designed to broadcast using
different frequencies to avoid interference and use a variety of
methods to minimize dead spots including spacial, time and frequency

Because the signals are so much more powerful that other satellite
signals, such as satellite television broadcasts, XM radio needs only
small omni directional antenna located on the vehicle or home. The
antennas are similar to GPS or satellite telephone antennas in that
they contain a number of small, flat arrays that collect the signal and
do not require pointing like traditional satellite antennas. They need
only have a clear line of sight to the satellite.

In many U.S. urban cities where large buildings and tunnels can
interfere with the XM signal, XM radio also supplements their signal
with terrestrial transmitters. Your XM receiver will automatically switch
from the satellite to the terrestrial broadcast if available to maintain
the highest quality broadcast possible. Recently, XM Radio began
broadcasting current weather the traffic conditions of many major U.S.
cities as well, allowing listeners to stay updated.

XM radio programming is available throughout the continental United
States. The satellite footprint, however extends further north and
south and residents of Canada and Mexico have reported excellent
reception in most areas. A U.S. mailing address is required to receive
XM Radio programming.

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