A Historical Look At Satellite Television by devid johnson
Satellite television is TV broadcasted and delivered via a communications satellite device in geostationary orbit 22,000 miles above the Earth. This contrasts with conventional terrestrial television and cable television, providing a broader range of channels and services comprised of subscription-only services and a basic package of channels. The satellite maintains a specific position in space. Signals are beamed up to the satellite from an Earth station, then relayed back down again to be received by a dish. Satellites can deliver both analogue and digital services.

The first satellite television signal was transmitted from Europe to the Telstar satellite over North America in 1962. The first geosynchronous communication satellite, Syncom 2 was launched in 1963. A device called Early Bird, the world’s first commercial communication satellite, was launched into synchronous orbit on April 6, 1965. In 1967 the Soviet Union created ORBITA, the first national network of satellite television. This device was employed on the principle of using the highly elliptical Molniya satellite for re-broadcasting and delivering of TV signal to ground downlink stations. Canada created geostationary Anik 1, the first domestic North American satellite to carry television in 1972. Launched in 1974, the world saw the first experimental educational and Direct Broadcast Satellite ATS-6 come into being. In 1976, Ekran, the first Soviet geostationary satellite to carry Direct-To-Home television was successfully launched.

Satellite television functions much like other communications relayed by satellite. The communication starts with a transmitting antenna based at an uplink facility. Uplink satellite dishes are quite large, as much as 9 to 12 meters (30 to 40 feet) in diameter. The increased diameter controls more accurate aiming and increases signal strength from the satellite. The uplink dish is aimed at a specific satellite and the uplinked signals are transmitted within a specific frequency range, which is then received by one of the transponders tuned to that frequency range aboard that satellite. To avoid interference with the uplink signal, the transponder ‘retransmits’ the signals back to Earth at a different frequency band, (typically in the C-band and/or Ku-band. The segment of the signal path from the satellite to the receiving Earth station is called the downlink.

A prototypical satellite has up to 32 transponders for Ku-band and up to 24 for a C-band only satellite, or more for hybrid satellites. Standard transponders each have a bandwidth between 27 MHz and 50 MHz. Each geo-stationary C-band satellite needs to be spaced 2 degrees from the next satellite (to avoid interference). For Ku the spacing can be 1 degree. This means that there is an upper limit of 360/2 = 180 geostationary C-band satellites and 360/1 = 360 geostationary Ku-band satellites. C-band transmission is prone to terrestrial interference while Ku-band transmission is susceptible to rain (as water is a prime absorber of microwaves).

The downlinked satellite signal, quite weak after traversing such a large distance, is contained by a parabolic receiving dish, which returns the weak signal to the dish’s focal point. A feedhorn, which is a device mounted on brackets at the dish’s focal point, is essentially the flared front-end of a section of waveguide that collects the signals at or near the focal point and ‘conducts’ them to a probe or pickup adhered to a low-noise block downconverter or LNB. The LNB intensifies the relatively weak signals, filters the block of frequencies in which the satellite tv signals are transmitted, and converts the block of frequencies to a lower frequency range in the L-band range.
About the Author
Written by David Johnson. Find more information on Satellite TV Offers as well as Direct TV Promotions