When satellite television first hit the market in the early 1990s, home dishes were expensive metal units that took up a huge chunk of yard space. In these early years, only the most die-hard TV fans would go through all the hassle and expense of putting in their own dish. Satellite TV was a lot harder to get than broadcast and cable TV.
Today, you see compact satellite dishes perched on rooftops all over the United States. Drive through rural areas beyond the reach of the cable companies, and you’ll find dishes on just about every house. The major satellite TV companies are luring in more consumers every day with movies, sporting events and news from around the world and the promise of movie-quality picture and sound.
Satellite TV offers many solutions to broadcast and cable TV problems. Though satellite TV technology is still evolving, it has already become a popular choice for many TV viewers.
PROBLEMS WITH BROADCAST TV:
Conceptually satellite TV is a lot like broadcast TV. 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.
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 TV 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 TV thousands of miles from the source. But because the planet is curved, it eventually breaks the signal’s line of sight. The other problem with broadcast TV 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.
The Satellite TV Solution:
Satellite TV solves the problems of range and distortion 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 sight. Satellite TV systems transmit and receive radio signals using specialized antennas called satellite dishes.
The TV satellites are all in geo synchronous 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.
SATELLITE TV SYSTEM:
Early satellite TV viewers were explorers of sorts. They used their expensive dishes to discover unique programming that wasn’t necessarily intended for mass audiences. The dish and receiving equipment gave viewers the tools to pick up foreign stations, live feeds between different broadcast stations, NASA activities and a lot of other stuff transmitted using satellites.
Some satellite owners still seek out this sort of programming on their own, but today, most satellite TV customers get their programming through a direct broadcast satellite (DBS) provider, such as DirecTV or DISH Network. The provider selects programs and broadcasts them to subscribers as a set package. Basically, the provider’s goal is to bring dozens or even hundreds of channels to your TV in a form that approximates the competition, cable TV.
Unlike earlier programming, the provider’s broadcast is completely digital, which means it has much better picture and sound quality. Early satellite television was broadcast in C-band radio — radio in the 3.7-gigahertz (GHz) to 6.4-GHz frequency range. Digital broadcast satellite transmits programming in the Ku frequency range (11.7 GHz to 14.5 GHz).
There are five major components involved in a direct to home (DTH) or direct broadcasting (DBS) satellite system: the programming source, the broadcast center, the satellite, the satellite dish and the receiver.
- Programming sources are simply the channels that provide programming for broadcast. The provider doesn’t create original programming itself; it pays other companies (HBO, for example, or ESPN) for the right to broadcast their content via satellite. In this way, the provider is kind of like a broker between you and the actual programming sources. (Cable TV companies work on the same principle.)
- The broadcast center is the central hub of the system. At the broadcast center, the TV provider receives signals from various programming sources and beams a broadcast signal to satellites in geosynchronous orbit.
- The satellites receive the signals from the broadcast station and rebroadcast them to Earth.
- The viewer’s dish picks up the signal from the satellite (or multiple satellites in the same part of the sky) and passes it on to the receiver in the viewer’s house.
- The receiver processes the signal and passes it on to a standard TV.
SATELLITE TV PROGRAMMING:
Satellite TV providers get programming from two major sources: national turnaround channels (such as HBO, ESPN and CNN) and various local channels (the ABC, CBS, Fox, NBC and PBS affiliates in a particular area). Most of the turnaround channels also provide programming for cable TV, and the local channels typically broadcast their programming over the airwaves.
Turnaround channels usually have a distribution center that beams their programming to a geosynchronous satellite. The broadcast center uses large satellite dishes to pick up these analog and digital signals from several sources.
Most local stations don’t transmit their programming to satellites, so the provider has to get it another way. If the provider includes local programming in a particular area, it will have a small local facility consisting of a few racks of communications equipment. The equipment receives local signals directly from the broadcaster through fibre-optic cable or an antenna and then transmits them to the central broadcast center.
The broadcast center converts all of this programming into a high-quality, uncompressed digital stream. At this point, the stream contains a vast quantity of data — about 270 megabits per second (Mbps) for each channel. In order to transmit the signal from there, the broadcast center has to compress it. Otherwise, it would be too big for the satellite to handle. In the next section, we’ll find out how the signal is compressed.
SATELLITE TV SIGNAL:
Satellite signals have a pretty long path to follow before they appear on your TV screen in the form of your favorite TV show. Because satellite signals contain such high-quality digital data, it would be impossible to transmit them without compression. Compression simply means that unnecessary or repetitive information is removed from the signal before it is transmitted. The signal is reconstructed after transmission.
Standards of Compression:
Satellite TV uses a special type of video file compression standardized by the Moving Picture Experts Group (MPEG). With MPEG compression, the provider is able to transmit significantly more channels. There are currently five of these MPEG standards, each serving a different purpose. DirecTV and DISH Network, the two major satellite TV providers in the United States, once used MPEG-2, which is still used to store movies on DVDs and for digital cable television (DTV). With MPEG-2, the TV provider can reduce the 270-Mbps stream to about 5 or 10 Mbps (depending on the type of programming).
Now, DirecTV and DISH Network use MPEG-4 compression. Because MPEG-4 was originally designed for streaming video in small-screen media like computers, it can encode more efficiently and provide a greater bandwidth than MPEG-2. MPEG-2 remains the official standard for digital TV compression, but it is better equipped to analyze static images, like those you see on a talk show or newscast, than moving, dynamic images. MPEG-4 can produce a better picture of dynamic images through use of spatial (space) and temporal (time) compression. This is why satellite NTV using MPEG-4 compression provides high definition of quickly-moving objects that constantly change place and direction on the screen, like in a basketball game.
Source: howstuffworks.com and youtube.com
Ravi teja ( MGIT ECE 3rd year)
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