Direct-broadcast satellite television
Direct-broadcast satellite television (DBSTV) also known as Direct-to-home television (DTHTV) is a method of receiving satellite television by means of signals transmitted from direct-broadcast satellites. All the major services including DirecTV, Dish Network, Bell TV, Shaw Direct, and Sky use direct-broadcast satellites. Signals are transmitted using Ku band and are completely digital which means they have high picture and stereo sound quality.
Prior to the arrival of DBS services in the early to mid-1990s signals were sent from fixed service satellites on the C-band analog and received with television receive-only systems, which had more disadvantages to DBSTV including the requirement of large satellite dishes.
There are five major components in a DBS satellite system: the programming source, the broadcast center, the satellite, the satellite dish, and the receiver. Satellites used for transmission of television signals are generally in either naturally highly elliptical (with inclination of +/-63.4 degrees and orbital period of about twelve hours, also known as Molniya orbit) or geostationary orbit 37,000 km (23,000 mi) above the earth's equator. Satellite television, like other communications relayed by satellite, starts with a transmitting antenna located at an uplink facility. Uplink facilities transmit their signals typically in the C-band frequency range due to their resistance to rain fade. As a result, uplink satellite dishes are very large, often as much as 9 to 12 metres (30 to 40 feet) 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 then converts the signals to Ku band, a process known as "translation," and transmits them back to earth to be received by home satellite stations.
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