Satellite TV
Introduction
A satellite is an object that orbits around another object in space. The satellites that
concern us transmit television directly to the consumer. These satellites require a special
orbit, so a little information about orbits is a good place to start in understanding satellite
television basics.
The time it takes for a satellite to complete an orbit depends upon its distance from the
object that it orbits. The moon is a natural satellite that is 238,328 miles from Earth. It takes
27.32 days for the moon to complete one orbit of the Earth. The space shuttle operates in a low
Earth orbit. The shuttle orbits less than 200 miles to about 350 miles above the Earth. The
average time for the space shuttle to complete an orbit around the Earth is about 90 minutes.
The moon takes longer to complete an orbit of the Earth because it is much further from the
Earth than is the space shuttle. The type of orbit that is required of the satellites that
transmit television signals to the Earth lies between these two extremes.
In order for a satellite to be used for television transmission, it must "hang" over one
spot above the Earth. The types of orbits described so far would require a receiving dish that
is constantly moving, in order to keep up with the transmitting satellite.
Satellite television satellites are in a geosynchronous orbit that exactly matches the speed
that the Earth spins. When a satellite is in a geosynchronous orbit, the satellite appears to
be stationary when viewed from the ground. In order to accomplish a geosynchronous orbit, a
satellite must be directly over the equator and about 22,300 miles from the Earth.
This area around the Earth is often called the Clarke Belt. Satellites maintain proper
positioning in the Clarke Belt with onboard fuel. Ground stations constantly monitor these
satellites to make any adjustments that are necessary to keep a satellite in it's orbital slot.
The television signals transmitted by a satellite are quite different from the television or
radio signals that are broadcast over the air. The particulars of a satellite TV signal are
beyond the scope of this small article, but there are some basics that you should know. Satellite
TV is transmitted by microwaves. Microwaves don't behave like the lower frequency radio waves of
off-air television or radio, which can bounce off obstructions, clouds, and the ground.
Microwaves are strictly line of sight. In order for a satellite dish to receive a signal, there
can be no obstruction between the transmitting satellite and the receiving satellite dish. The
very first thing that a prospective dish owner should do is perform a site survey in order to
ensure that there are no obstructions blocking the satellite(s) of interest. Because microwaves
are highly directional, the satellite dish and associated components must be properly aligned.
Satellite television in the USA is divided into two major types. The first major type is TVRO. TVRO satellite systems have a large dish which is movable. The movable dish enables a TVRO system to view programs on the many satellites that are positioned in the Clarke Belt. TVRO satellite systems are also called BUD, Big Dish, C-Band, and Full View satellite TV. Just remember that if the dish is large (usually 6 - 12 feet across) and it moves, it is a TVRO satellite system. To find out more about TVRO satellite systems go to TVRO Basics.
The second major type of satellite TV is DBS. DBS systems have a small dish (18 inches to 3 feet across) that does not move. In the US there are currently 2 major types of DBS satellite systems. Each DBS system requires it's own special receiving equipment and has it's own programming line up. The 2 major types of DBS systems are DIRECTV and DISH Network. To find out more about DBS satellite systems go to DBS basics.
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