Who Invented Electricity Article

Satellite Television

Geo stationary satellites are satellites that are positioned about 36,500 kilometers or 22,300 above the Earth�s equator, in a region called the Clarke�s belt and rotate at the same speed as the Earth and hence appear stationary to an observer on the Earth. Satellite television receives TV signals that are beamed from the Earth and reflected from these satellites on to a TV dish. These orbiting satellites have capacity to carry several hundred TV channels through their �transponders� and enable a viewer to receive them anywhere on the Earth.

These transponders operate in various signal bands like C band, Ka band, Ku band etc. These bands are comparable to VHF, UHF etc. frequency bands of radio signals. The TV signals from the satellites are received through dish antennas usually parabolic in shape as small as 18 inches or as large as 9 meters in diameter. These dish antennas gather the signals and reflect on to the feedhom, the focal point of the parabolic dish. LNB or Low Noise Block receives these signals, amplifies them and converts the frequency for transmission over a cable. The signals are then received by the satellite receiver at the other end of the cable and converted into a form that can be played over the television set.

Digital satellite televisions introduced into the market recently permit handling large no. of TV channels with equal no. of satellite bandwidth. Satellite televisions are provided with standard as well as high definition format resolution as per latest ATSC standards.

There are a variety of satellite TV services offered in different countries around the world. DirecTV and Dish Network are the two of the biggest satellite providers in the U.S. and operate in the Ka and Ku band respectively. Superstar and the National Programming Service offer TV signals in the C band. The satellite TV signals can be received in three modes � directly by the viewer, received by affiliated local TV stations and thirdly by central receivers for distribution through cable systems. Television Read Only (TVRO), Direct Broadcast Satellite (DBS), Direct Satellite System (DSS) and Free to Air (FTA) are the four types of satellite television in operation at present in the U.S.

TVRO carries unencrypted satellite signals and provides both free to air and paid for programs and is called the �big dish�. Free to Air (FTA) signals can be received by anyone having the necessary receiver even without subscribing to any of the satellite TV vendors. DirecTV owns DSS for distributing audio and video signals. DBS allows receiving signals with small dishes directly. Installation fees and monthly subscription fees need to be paid by the subscriber for receiving subscription only satellite television signals.