About Satellite Dish Theory
Although satellite dishes may seem fantastically high tech, the principles behind them are actually rather straightforward. Instead of sending a signal over an electric wire like cable does, a satellite transmitter sends it through the air, bouncing it off of a satellite put into orbit for just that purpose. As long as nothing is blocking the satellite, a dish can receive the signal from anywhere in the world.
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Significance
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Satellite dishes are used for all sorts of communication. They have been used for satellite television since the 1990s, and more recently for Internet, radio and other uses. Satellite dishes can transfer any information that can be sent via cables, but they have some advantages over cables. With a dish, the signal is sent directly to the house with no need for miles of cables. As long as there is a communications satellite in the sky and a clear line of site, the antenna can send and receive signals.
Design
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A satellite dish is a type of parabolic reflector. A parabolic reflector has a special shape designed to focus radio signals at its focal point. Conversely, signals broadcast from the reflector's focal point will bounce off the reflector and be directed straight ahead. At the focal point is a receiver called an LNB, or low-noise block converter. This receives microwave signals and converts them into electric signals which the television, computer or other device can use. In two-way satellite dishes such as those used for satellite Internet, the LNB also broadcasts a signal which is bounced off the parabolic reflector and sent in a straight line.
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Function
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A satellite transmitter first broadcasts an encrypted signal toward a geosynchronous satellite -- a satellite which is always at the same point in the sky. The transmitter itself is a large parabolic antenna, much like the satellite dish that eventually receives the signal. The signal contains programs from all the channels the satellite provider offers with a special digital passkey to stop people who haven't subscribed from watching them. The satellite rebroadcasts the signal, sending it out in all directions. The satellite dish is pointed toward the satellite, so it receives the signal. The signal is focused into the LNB, changed into an electronic signal, and then sent down a coaxial cable to the receiver in the house. The receiver decrypts, or unscrambles, the signal and lets you change channels and operate the satellite TV.
Benefits and Drawbacks
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Satellite dishes have many benefits over cable. They allow people in rural areas without cable providers to receive television service, and often offer superior picture and sound quality. Satellite services offer hundreds of channels, whereas some local cable services do not. On the downside, satellite service can be expensive. Buying and installing a satellite dish is costly, and the service is typically more expensive than cable. Additionally, many people view satellite dishes as an eyesore. Finally, service can sometimes be disrupted by bad weather, and a good storm or freeze can damage a satellite dish.
Size
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Originally, satellite dishes were big, bulky things. The older TVRO dishes are often called big ugly dishes, or BUDs, and for good reason. They could be as big as 12 feet in diameter. They were designed to pick up free stations with much weaker signals, and had to be large enough to compensate. Sometimes, these dishes led to neighborhood disputes and zoning ordinances, since they were considered eyesores. Modern dishes are much smaller -- usually anywhere from 1 1/2 to 2 1/2 feet.
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