What is Satellite TV?
Conceptually, satellite television is a lot like broadcast television.
It's a wireless system for delivering television programming directly to a
viewer's house. Both broadcast television and satellite stations transmit
programming via a radio
signal (see How
Radio Works for information about radio broadcasting).
Broadcast stations use a powerful antenna to transmit radio waves to
the surrounding area. Viewers can pick up the signal with a much smaller
antenna. The main limitation of broadcast television is range. The radio
signals used to broadcast television shoot out from the broadcast antenna
in a straight line. In order to receive these signals, you have to be in
the direct "line of sight" of the antenna. Small
obstacles like trees or small buildings aren't a problem; but a big
obstacle, such as the Earth, will reflect these radio waves.
If the Earth were perfectly flat, you could pick up broadcast
television thousands of miles from the source. But because the planet is
curved, it eventually breaks the signal's line of site. The other problem
with broadcast television is that the signal is often distorted
even in the viewing area. To get a perfectly clear signal like you find on
cable, you have to be pretty close to the broadcast antenna without too
many obstacles in the way.
Satellite television solves both of these problems by transmitting
broadcast signals from
satellites
orbiting the Earth. Since satellites are high in the sky, there are a lot
more customers in the line of site. Satellite television systems transmit
and receive radio signals using specialized antennas called satellite
dishes.
Satellites are higher in the sky than TV
antennas, so they have a much larger "line of sight"
range.
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The television satellites are all in geosynchronous orbit,
meaning that they stay in one place in the sky relative to the Earth. Each
satellite is launched into space at about 7,000 mph (11,000 kph), reaching
approximately 22,200 miles (35,700 km) above the Earth. At this speed and
altitude, the satellite will revolve around the planet once every 24 hours
-- the same period of time it takes the Earth to make one full rotation.
In other words, the satellite keeps pace with our moving planet exactly.
This way, you only have to direct the dish at the satellite once, and from
then on it picks up the signal without adjustment, at least when
everything works right. (See
How
Satellites Work for more information on satellite orbits.)
At the core, this is all there is to satellite television. But as we'll
see in the next section, there are several important steps between the
original programming source and your television.
