Satellite TV

Satellite Television
 Satellite television is television delivered by the means of communications satellite and received by a satellite dish and set-top box. In many areas of the world it provides a wide range of channels and services, often to areas that are not serviced by terrestrial or cable providers.
 Satellite television is television delivered by the means of communications satellite and received by a satellite dish and set-top box. In many areas of the world it provides a wide range of channels and services, often to areas that are not serviced by terrestrial or cable providers.
 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.
 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.
 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.
 Satellites are higher in the sky than TV antennas, so they have a much larger line of sight range.
 The TV 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.
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 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 ).
The Components
 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.
 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.
Cable: Satellite's Biggest Contender
With emerging technologies in each service, the hardest decision in TV viewing is no longer just what channel to watch -- it's what service to choose.
CABLE Advantages
 Cable : Advancements in digital cable provide improved audio and picture quality with additional channels at a lower cost than satellite. You can also access cable channels from multiple rooms in your house fairly easily.
CABLE Disadvantages
 Cable : Cable has limited access in rural areas, and you should prepare for increased service costs as your provider updates its equipment. Your service costs are also subject to local taxes.
SATELLITE Advantages
 Satellite : Satellite offers movie-quality audio and picture display with hundreds of channels. This service is readily available in rural and urban areas and provides access to more digital and high definition programming.
SATELLITE Disadvantages
 Satellite : It is expensive to purchase all the equipment at the outset (and you can't typically rent it). If you want to access satellite TV in multiple rooms, be prepared for extra fees. Also, satellite TV is subject to weather-related malfunctions.
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.
Satellite Dish
 When the signal reaches the viewer's house, it is captured by the satellite dish. A satellite dish is just a special kind of antenna designed to focus on a specific broadcast source. The standard dish consists of a parabolic (bowl-shaped) surface and a central feed horn. To transmit a signal, a controller sends it through the horn, and the dish focuses the signal into a relatively narrow beam.
 The dish on the receiving end can't transmit information; it can only receive it. The receiving dish works in the exact opposite way of the transmitter. When a beam hits the curved dish, the parabola shape reflects the radio signal inward onto a particular point, just like a concave mirror focuses light onto a particular point.
Satellite Receiver
 It de-scrambles the encrypted signal. It takes the digital MPEG-2 or MPEG-4 signal and converts it into an analog format that a standard television can recognize. It extracts the individual channels from the larger satellite signal. It keeps track of pay-per-view programs and periodically phones a computer at the provider's headquarters to communicate billing information.
The Black-and-White TV Signal
 In a black-and-white TV, the screen is coated with white phosphor and the electron beam "paints" an image onto the screen by moving the electron beam across the phosphor a line at a time. To "paint" the entire screen, electronic circuits inside the TV use the magnetic coils to move the electron beam in a "raster scan" pattern across and down the screen.
Color TV Screen
 A color TV screen differs from a black-and-white screen inthree ways:
o There are three electron beams that move simultaneously across the screen. They are named the red, green and blue beams.
o The screen is not coated with a single sheet of phosphor as in a black-and-white TV. Instead, the screen is coated with red, green and blue phosphors arranged in dots or stripes. If you turn on your TV or computer monitor and look closely at the screen with a magnifying glass, you will be able to see the dots or stripes.
o On the inside of the tube, very close to the phosphor coating, there is a thin metal screen called a shadow mask. This mask is perforated with very small holes that are aligned with the phosphor dots (or stripes) on the screen.
How does Satellite Television work?
 Satellite TV works by broadcasting video and audio signals from geostationary satellites to satellite dishes on the Earth's surface. These geostationary satellites orbit the earth in a region of space known as the Clarke Belt, which is approximately 22,300 miles above the equator. Each of these satellites carries a number of transponders. These transponders each carry a signal back to the Earth. These signals are typically on C Band, Ku Band, or Ka Band. The band of a signal describes, in broad terms, the frequency of the signal. After travelling over twenty thousand miles, these signals are received by a satellite dish.
 This dish can be as small as 18" across, or it can be 9‘ or larger across. The purpose of the dish is to act as a collector and a reflector. The dish collects the signal and reflects it towards the feedhorn. The feedhorn receives the reflected signal and sends it to the LNB. The LNB amplifies the signal and converts it to a frequency more suitable for transmission over a cable. In satellite terminology, that cable is known as the IFL. The LNB transmits the signal over the IFL to the satellite receiver. The satellite receiver then sends the signal to your television set.

for GenSci 3

University of Saint La Salle
Bacolod City

College of Arts and Sciences

An Environmental Science Reading in Partial Fulfillment of the Requirements of the Course General Science III - Environmental Science




Submitted by:
Jim Austin M. Tolentino
ABCO2




Submitted to:
Dr. Jessica Villarosa
GenSci 3


http://www.sciencedaily.com/releases/2009/11/091109142129.htm