Satellite Television

Television is a widely used telecommunication medium for transmitting and receiving moving images, either monochromatic (black and white) or color, usually accompanied by sound. “Television” may also refer specifically to a television set, television programming or television transmission. The word is derived from mixed Latin and Greek roots, meaning “far sight”.

Commercially available since the late 1930s, the television set has become a common communications receiver in homes, business and institutions, particularly as a source of entertainment and news. Since the 1970s the availability of video cassettes, laserdiscs, DVDs have resulted in the television set frequently being used for viewing recorded as well as broadcast material.

Until 2000s broadcast TV programs were generally recorded and transmitted as an analog signal, but in recent years public and commercial broadcasters have been progressively introducing digital television broadcasting technology.

The first satellite television signal was relayed from Europe to the Telstar satellite over North America in 1962. The world’s first commercial communication satellite, called Intelsat, was launched into synchronous orbit on April 6, 1965.

Satellite television, like other communications relayed by satellite, starts with a transmitting antenna located at an uplink facility. Uplink satellite dishes are very large, as much as 9 to 12 meters in diameter. The increased diameter results in more accurate aiming and increased signal strength at the satellite. The uplink dish is pointed toward a specific satellite and the uplinked signals are transmitted within a specific frequency range, so as to be received by one of the transponders tuned to that frequency range aboard that satellite. The transponder “retransmits” the signals back to Earth but at a different frequency band (a process known as translation, used to avoid interference with uplink signal), typically in the C-band (4-8 GHz) or Ku-band (12-18 GHz) or both. The leg of the signal path from the satellite to the receiving Earth station is called the downlink.

The downlinked satellite signal, quite weak after traveling the great distance, is collected by a parabolic receiving 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 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 not transmit information; it can only receive it. The receiving dish works in the exact opposite way of the transmitter.

The central element in the feed horn is the low noise blockdown converter, or LNB. The LNB amplifies the signal bouncing off the dish and filters out the noise. The LNB passes the amplified, filtered signal to the satellite receiver inside the viewer’s house. The end component in the entire satellite TV system is the receiver. The satellite receiver demodulates and converts the signals to the desired form.

Текст был сокращен, проверить упражнения.