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Information about Satellite TV

Satellite TV ,Satellite communication,satellite antenna,Direct Broadcast Satellite, Television Recieve-Only Satellite

Satellite TV

Satellite TV is television delivered by way of orbiting communications satellites located 37,000 km (22,300 miles) above the earth's surface. The first satellite television signal was relayed from Europe to the Telstar satellite over North America in 1962. The first domestic North American satellite to carry television was Canada's Anik 1, which was launched in 1973.

Satellite television, like other communications relayed by satellite, starts with a transmitting antenna located at an uplink facility. Uplink satellite dishes are directed toward the satellite that their signals will be transmitted to, and are very large, as much as 9 to 12 meters (30 to 40 feet) in diameter. The increased diameter results in more accurate positioning and improved signal reception at the satellite. The signal is transmitted to devices located on-board the satellite called transponders, which retransmit the satellite signal back towards the Earth at a different frequency. The satellite signal, quite weak after travelling through space, is collected by a parabolic receiving dish, which reflects the weak signal to the dish's focal point and is received, down-converted to a lower frequency band and amplified by a device called a low-noise block downconverter, or LNB. Direct broadcast satellite dishes use an LNBF, which integrates the feedhorn with the LNB.

A new form of satellite antenna, which does not use a directed parabolic dish and can be used on a mobile platform such as a vehicle, was recently announced by the University of Waterloo. The signal, now amplified, travels to a satellite receiver box through coaxial cable (RG-6 or RG-10; cannot be standard RG-59) and is converted by a local oscillator to the L-band range of frequencies (approximately). Special on-board electronics in the receiver box help tune the signal and then convert it to a frequency that a standard television can use.

There are two primary types of satellite television distribution

1) Direct Broadcast Satellite

Direct broadcast satellite, (DBS) also known as "direct to home" is a relatively recent development in the world of television distribution. "Direct broadcast satellite" can either refer to the communications satellites themselves that deliver DBS service or the actual television service. DBS systems are commonly referred to as "minidish" systems. DBS uses the upper portion of the K u band.
Modified DBS systems can also run on C Band satellites and have been used by some networks in the past to get around legislation by some countries against reception of Ku Band transmissions.
DBS systems are generally based on open standards such as MPEG2 DVB-S but may include proprietary encryption and decryption/reception equipment, most often in the form of a television set-top signal descrambling box called an IRD (Integrated Receiver Decoder). This measure assures satellite television providers that only authorised, paying subscribers have access to Pay TV content but at the same time can allow free to air channels to be viewed even by the people with standard equipment available in the market.

2) Television Recieve-Only Satellite

Television receive-only satellite, or TVRO, refers to satellite television reception equipment that is based primarily on open standards equipment. This contrasts sharply with direct broadcast satellite, which is a completely closed system that uses proprietary reception equipment. TVRO is often referred to as "big dish" satellite television. TVRO systems are designed to receive analog satellite signals from both C-band and K u -band satellite television or audio signals. TVRO systems tend to use larger rather than smaller satellite dish antennas, since it is more likely that the owner of a TVRO system would have a C-band-only setup rather than a K u -band-only setup. Additional receiver boxes allow for different types of digital satellite signal reception, such as DVB / MPEG-2 and 4DTV.

Parabolic Earth Station antennas receive signals from a single satellite at a time. Simulsat is a quasi-parabolic satellite earthstation antenna that is capable of receiving satellite transmissions from 35 or more C and Ku Band satellites simultaneously.
Direct broadcasting satellites which can be received by what are known in Chinese as little ears have had a major role in breaking the government monopoly of information on Mainland China. Although met with frequent and generally unsuccessful efforts to regulate them, satellite dishes are fairly common in urban China. Satellite television has also played an important role in broadcasting to expatriate communities such as Arabs, and overseas Chinese.
Published: 2006-05-31
Author: trupti modi

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