Satellite television
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Satellite Television
Satellite television is television delivered by way of communications satellites, as compared to conventional terrestrial television and cable television. In many areas of the world satellite television services supplement older terrestrial signals, providing a wider range of channels and services, including subscription-only services.
History
The first satellite television signal was relayed from Europe to the Telstar satellite over North America in 1962. The first geosynchronous communication satellite, Syncom 2 was launched in 1963. The world's first commercial communication satellite, called Early Bird, was launched into synchronous orbit on April 6, 1965. The first national network of satellite television, called Orbita, was created in Soviet Union in 1967, and was based on the principle of using the highly-elliptical Molniya satellite for re-broadcasting and delivering of TV signal to ground downlink stations. The first domestic North American satellite to carry television was Canada’s geostationary Anik 1, which was launched in 1973. ATS-6, the world's first experimental educational and Direct Broadcast Satellite, was launched in 1974. The first Soviet geostationary satellite to carry Direct-To-Home television, called Ekran, was launched in 1976.
Technology
Satellites used for television signals are generally in either highly-elliptical (with inclination of +/-63.4 degrees and orbital period of about 12 hours) or geostationary orbit 37,000 km (22,300 miles) above the earth’s equator.
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 (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 'retransmits' the signals back to Earth but at a different frequency band (to avoid interference with the uplink signal), typically in the C-band and/or Ku-band. The leg of the signal path from the satellite to the receiving Earth station is called the downlink.
A typical satellite has up to 32 transponders for Ku-band and up to 24 for a C-band only satellite, or more for hybrid satellites. Typical transponders each have a bandwidth of about 36 to 50 Mbit/s. 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 susceptible to terrestrial interference while Ku-band transmission is affected by rain (as water is an excellent absorber of microwaves).
The downlinked satellite signal, quite weak after travelling the great distance (see inverse-square law), is collected by a parabolic receiving dish, which reflects the weak signal to the dish’s focal point. Mounted on brackets at the dish's focal point is a device called a feedhorn. This feedhorn is essentially the front-end of a waveguide that gathers the signals at or near the focal point and 'conducts' them to a low-noise block downconverter or LNB. The LNB converts the signals from electromagnetic or radio waves to electrical signals and shifts the signals from the downlinked C-band and/or Ku-band to the L-band range. Direct broadcast satellite dishes use an LNBF, which integrates the feedhorn with the LNB. (A new form of omnidirectional 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 L band signal, now amplified, travels to a satellite receiver box, typically through coaxial cable (RG-6 or RG-10, etc.; cannot be standard RG-59). The satellite receiver then converts the signals to the desired form (outputs for television, audio, data, etc.). Sometimes, the receiver includes the capability to unscramble or decrypt; the receiver is then called an Integrated receiver/decoder or IRD.
Categories of usage
There are three primary types of satellite television usage: reception direct by the viewer, reception by local television affiliates, or reception by headends for distribution across terrestrial cable systems.
Direct to the viewer reception includes direct broadcast satellite or DBS and television receive-only or TVRO, both used for homes and businesses including hotels, etc.
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 "mini-dish" systems. DBS uses the upper portion of the Ku 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 proprietary transport stream encoding and/or encryption requiring proprietary reception equipment. Service providers sometimes license several manufacturers to provide equipment capable of receiving the proprietary streams. This equipment typically uses a smart card as part of the decryption system or conditional access. 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 (FTA) channels to be viewed even by the people with standard equipment available in the market.
Commercial DBS services: The first commercial DBS service, Sky Television plc (now BSkyB), was launched in 1989. Sky TV started as a four-channel free-to-air analogue service on the Astra 1A satellite, serving the United Kingdom and Republic of Ireland. By 1991, Sky had changed to a conditional access pay model, and launched a digital service, Sky Digital, in 1998, with analogue transmission ceasing in 2001. Since the DBS nomenclature is rarely used in the UK or Ireland, the popularity of Sky's service has caused the terms "minidish" and "digibox" to be applied to products other than Sky's hardware. BSkyB is controlled by News Corporation.
PrimeStar began transmitting an analog service to North America in 1991, and was joined by DirecTV Group's DirecTV, in 1994. At the time, DirecTV's introduction was the most successful consumer electronics debut in American history. Although PrimeStar transitioned to a digital system in 1994, it was ultimately unable to compete with DirecTV, which required a smaller satellite dish and could deliver more programming. DirecTV eventually purchased PrimeStar in 1999 and migrated all PrimeStar subscribers to DirecTV equipment. In 2003, News Corporation purchased a controlling interest in DirecTV's parent company, Hughes Electronics, and renamed the company DirecTV Group.
In 1996, EchoStar's Dish Network went online in the United States and, as DirecTV's primary competitor, achieved similar success. AlphaStar also launched but soon went under.
Dominion Video Satellite Inc.'s Sky Angel also went online in the United States in 1996 with its DBS service geared toward the faith and family market. It has since grown from six to 36 TV and radio channels of family entertainment, Christian-inspirational programming and 24-hour news. Dominion, under its former corporate name Video Satellite Systems Inc., was actually the second from among the first nine companies to apply to the FCC for a high-power DBS license in 1981 and is the sole surviving DBS pioneer from that first round of forward-thinking applicants. Sky Angel, although a separate and independent DBS service, uses the satellites, transmission facilities, & receiving equipment used for Dish Network through an agreement with Echostar. Because of this, Sky Angel subscribers also have the option of subscribing to Dish Network's channels as well.
In 2003, EchoStar attempted to purchase DirecTV, but the U.S. Department of Justice denied the purchase based on anti-competitive concerns.
Free DBS services: Germany is likely the leader in free-to-air DBS, with approximately 40 analogue and 100 digital channels broadcast from the SES Astra 1 position at 19.2E. These are not marketed as a DBS service, but are received in approximately 12 million homes, as well as in any home using the German commercial DBS system, Premiere.
The United Kingdom has approximately 90 free-to-air digital channels, for which a promotional and marketing plan is being devised by the BBC and ITV, to be sold as "Freesat". It is intended to provide a multi-channel service for areas which cannot receive Freeview, and eventually replace their network of UHF repeaters in these areas.
India's national broadcaster, Doordarshan, promotes a free-to-air DBS package as "DD Direct +", which is provided as in-fill for the country's terrestrial transmission network.
While originally launched as backhaul for their digital terrestrial television service, a large number of French channels are free-to-air on 5W, and have recently been announced as being official in-fill for the DTT network.
In North America (USA, Canada and Mexico) there are over 80 FTA digital channels available on Intelsat Americas 5, the majority of them are ethnic or religious. Other popular FTA satellites include AMC-4, AMC-6, Galaxy 10R and SatMex 5. A company called GloryStar promotes FTA religious broadcasters on IA-5 and AMC-4.
Television receive-only
Television receive-only, 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 and digital satellite feeds of both television or audio from both C-band and Ku-band transponders on FSS-type satellites. 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 Ku band-only setup. Additional receiver boxes allow for different types of digital satellite signal reception, such as DVB/MPEG-2 and 4DTV.
The narrow beam width of a normal parabolic satellite antenna means it can only 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, these small 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. [1]
References
[1] Wikipedia
http://en.wikipedia.org/wiki/Satellite_television
