TV - Satellite - Inglês
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.
- 1 History
- 2 Technology
- 3 Standards
- 4 Categories of usage
- 5 Satellite television by continent and country
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 1972 . 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.
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 (4–8 GHz) and/or Ku-band (12–18 GHz). 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 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 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 traveling 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 flared front-end of a section of waveguide that gathers the signals at or near the focal point and 'conducts' them to a probe or pickup connected to a low-noise block downconverter or LNB. The LNB amplifies 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. The evolution of LNBs was one of necessity and invention.
The original C-Band satellite TV systems used a Low Noise Amplifier connected to the feedhorn at the focal point of the dish. The amplified signal was then fed via very expensive 50 Ohm impedance coaxial cable to an indoor receiver or in other designs fed to a downconverter (a mixer and a voltage tuned oscillator with some filter circuitry) for downconversion to an intermediate frequency. The channel selection was controlled, typically by a voltage tuned oscillator with the tuning voltage being fed via a separate cable to the headend. But this simple design evolved.
Designs for microstrip based converters for Amateur Radio frequencies were adapted for the 4 GHz C-Band. Central to these designs was concept of block downconversion of a range of frequencies to a lower, and technologically more easily handled block of frequencies (intermediate frequency).
The advantages of using an LNB are: cheaper cable could be used to connect the indoor receiver with the satellite TV dish and LNB; and the technology for handling the signal at L-Band and UHF was far cheaper than that for handling the signal at C-Band frequencies. The shift to cheaper technology from the 50 Ohm impedance cable and N-Connectors of the early C-Band systems to the cheaper 75 Ohm technology and F-Connectors allowed the early satellite TV receivers to use, what were in reality, modified UHF TV tuners which selected the satellite television channel for down conversion to another lower intermediate frequency centered on 70 MHz where it was demodulated. This shift allowed the satellite television DTH industry to change from being a largely hobbyist one where receivers were built in low numbers and complete systems were expensive (costing thousands of Dollars) to a far more commercial one of mass production.
Direct broadcast satellite dishes are fitted with an LNBF, which integrates the feedhorn with the LNB.
The satellite receiver demodulates and 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. The cable connecting the receiver to the LNBF or LNB must be of the low loss type RG-6 or RG-10, etc. It cannot be standard RG-59.
(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. )
Analog television distributed via satellite is usually sent scrambled or unscrambled in NTSC, PAL, or SECAM television broadcast standards. The analog signal is frequency modulated and is converted from an FM signal to what is referred to as baseband. This baseband comprises the video signal and the audio subcarrier(s). The audio subcarrier is further demodulated to provide a raw audio signal.
If the signal is a digitized television signal or multiplex of signals, it is typically QPSK.
The conditional access encryption/scrambling methods include BISS, Conax, Digicipher, Irdeto, Nagravision, PowerVu, Viaccess, Videocipher, and VideoGuard. A large number of these schemes are known to be ineffective, however.
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 broadcast via 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.
The term Television receive-only, or TVRO, arose during the early days of satellite television reception to differentiate it from commercial satellite television uplink and downlink operations (transmit and receive). This was before there was a DTH satellite television broadcast industry. Satellite television channels at that time were intended to be used by cable television networks rather than received by home viewers. Satellite TV receiver systems were largely, constructed by hobbyists and engineers. These TVRO system operated, mainly, on the C band frequencies and the dishes required were large typically over ten feet in diameter. Consequently 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. The higher frequency Ku-band systems tend to be Direct To Home systems and can use a smaller dish antenna because of the higher power transmissions and greater antenna gain.
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.
Satellite television by continent and country
South African-based Multichoice's DStv is the main digital satellite television provider in sub-Saharan Africa, broadcasting principally in English, but also in Portuguese, German and Afrikaans. Canal Horizons, owned by France's Canal+, is the main provider in French-speaking Africa. Another entrant into the satellite television circuit in Africa is MyTvAfrica, a subsidiary of Dubai based Strong Technologies. Satellite television has been far more successful in Africa than cable, primarily because the infrastructure for cable television does not exist and would be expensive to install since majority of Africans cannot afford paid cable television. Furthermore, maintaining a cable network is expensive due to the need to cover larger and more sparsely populated areas though there are some terrestrial pay-TV and MMDS services.
In Canada, the two legal DBS services available are Bell Canada’s ExpressVu and StarChoice. The CRTC has refused to license American satellite services, but nonetheless hundreds of thousands (up to a million by some estimates) of Canadians access or have accessed American services — usually these services have to be billed to an American address and are paid for in U.S. dollars. Whether such activity is grey market or black market is the source of often heated debate between those who would like greater choice and those who argue that the protection of Canadian firms and Canadian culture is more important.
In October 2004, Quebec judge Danièle Côté ruled Canada's Radiocommunication Act to be in direct violation of the Canadian Charter of Rights and Freedoms, insofar as it bans reception of unlicensed foreign television services. The judgment gave the federal government a one-year deadline to remedy this breach of the Constitution. However, this contradicts prior Supreme Court of Canada decisions and, at last word in late 2004, was expected to be appealed.
In addition, Canadian satellite providers continue to be plagued by the unquestionably black market devices which "pirate" or "steal" their signals as well as by a number of otherwise completely lawful devices which can be reprogrammed to receive pirate TV.
One cable TV CEO (Karl Péladeau of Québecor, which owns Vidéotron) is on public record as demanding conditions be placed on the CRTC license issued to Bell ExpressVu, due to BEV’s reputation for vastly inferior security compared to its cable rivals and Shaw Cable–owned StarChoice.
Although there are no official statistics, the use of American satellite services in Canada appears to be declining as of 2004.
Some would claim that this is probably due to a combination of increasingly aggressive police enforcement and an unfavourable exchange rate between the Canadian and U.S. currencies. As the U.S. dollar has been declining as of 2005 versus other international currencies, the decline in DirecTV viewership in Canada may well be related not to a cost difference as much as to the series of smart card swaps which have rendered the first three generations of DirecTV access cards (F, H and HU) all obsolete.
Latin America’s main satellite system are SKY Latin America, which has approximately 1.4 million subscribers in each of Brazil and Mexico and DirecTV Latin America, which provides service to the rest of the Americas, with a total of approximately 1.3 million subscribers. Pay-TV is not popular among Latin American because fees are expensive in PPP terms.
In 1975 RCA created Satcom 1, the first satellite built special for use by the three national television networks. At the same year, HBO leased transponder of Satcom and began transmission of television programs via satellite to cable systems. Owners of cable systems paid $ 10 000 to install 3-meter dishes to receive TV signal in C-band. In 1976 Taylor Howard built an amateur system, which consisted of a converted military surplus radar dish and a satellite receiver designed and built by Howard, for home receiving of TV signal from satellite. Taylor's system could be used for receiving TV programs both from American and Soviet communication satellites.
In 1991 Primestar launched as the first the first North American DBS service. Hughes’s DirecTV, the first national high-powered upper Ku-band DBS system, went online in 1994. The DirecTV system became the new delivery vehicle for USSB. News Corporation currently holds a 38% stake, which it is in the process of selling to Liberty Media. In 1996, EchoStar’s Dish Network went online in the United States and has gone on to similar success as DirecTV’s primary competitor. The AlphaStar service launched in 1996 and went into bankruptcy in 1997. 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. Sky Angel uses Echostar receivers. Primestar sold its assets to Hughes in 1999 and switched off.
In 2004, Cablevision’s Voom service went online, specifically catering to the emerging market of HDTV owners and aficionados, but folded in April 2005, with the service’s “exclusive” high-definition channels currently being migrated to the Dish Network system. Commercial DBS services are the primary competition to cable television service, although the two types of service have significantly different regulatory requirements (for example, cable television has public access requirements, and the two types of distribution have different regulations regarding carriage of local stations).
The majority of ethnic-language broadcasts to North America are carried on Ku band free-to-air; the largest concentration of ethnic programming is on Galaxy 25 at 97° W. GlobeCast World TV offers a mix of free and pay-TV ethnic channels in the internationally-standard DVB-S format, as do others. Home2US Communications Inc. also offers ethnic programming, the platform is on AMC-4 at 101° W, with several ethnic channels as well as free and pay-TV. Several U.S.-English language network affiliates (representing CBS, NBC, ABC, PBS, FOX, the CW (formerly the WB and UPN), i and MyNetworkTV) are available as free-to-air broadcasts, as are the three U.S.-Spanish language networks (Univisión, Telefutura and Telemundo). The number of free-to-air specialty channels is otherwise rather limited. Specific FTA offerings tend to appear and disappear rather often and typically with little or no notice, although sites such as LyngSat do track the changing availability of both free and pay channels worldwide.
The satellite BS-2a was launched in preparation for the start of full scale 2-channel broadcasts. Broadcasting Satellite BS-2a was the first national DBS (direct broadcasting satellite), transmitting signals directly into the home of TV viewers. Attitude control of the satellite was conducted using the 3 axial method (zero momentum), and design life was 5 years. The TV transponder units are designed to sufficiently amplify transmitted signals to enable reception by small, 40 or 60 cm home-use parabolic antennas. The satellite was equipped with 3 TV transponders (including reserve units). However, one transponder malfunctioned 2 months after launch (March 23, 1984) and a second transonder malfunctioned 3 months after launch (May 3, 1984). So, the scheduled satellite broadcasting had to be hastily adjusted to test broadcasting on a single channel.
Later, NHK started regular service (NTSC) and experimental HDTV broadcasting using BS-2b on June, 1989. Some Japanese producers of home electronic consumer devices began to deliver TVsets, VCRs and even home acoustic systems equipped by built-in satellite tuners or receivers. Such electronic goods had a specific BS logo.
On April, 1991, Japanese company JSB started pay TV service while BS-3 communication satellite was in use. In 1996 total number of households that receive satellite broadcasting exceeded 10 million.
The modern two satellite systems in use in Japan are BSAT and JCSAT; the modern BS digital service uses BSAT satellites, while other system of digital TV broadcasting SKY PerfecTV! uses JCSAT satellites.
In Europe, DBS satellite services are found mainly on Astra satellites and Hotbird (operated by Eutelsat.) BSkyB (known as Sky) serves the UK. Sky Italia, Canal Digitaal and UPC being the main providers in Italy, the Netherlands and Central Europe.
The overall market share of DBS satellite services in 2004 was 21.4% of all TV homes, however this highly varies from country to country. For example, in Germany, with many free-to-air TV-stations, DBS market share is almost 40%, and in Belgium and the Netherlands, it’s only about 7%, due to the widespread cable networks with exclusive content.
The first Soviet communication satellite, called Molniya, was launched in 1965. By November, 1967 the national system of satellite television, called Orbita was deployed. The system consisted of 3 highly elliptical Molniya satellites, Moscow-based ground uplink facilities and about 20 downlink stations, located in cities and towns of remote regions of Siberia and Far East. Each station had a 12-meter receiving parabolic antenna and transmitters for re-broadcasting TV signal to local householders.
However, a large part of Soviet central regions were still not covered by transponders of Molniya satellites. By 1976 Soviet engineers developed a relatively simple and inexpensive system of satellite television (especially for Central and Northern Siberia). It included geostationary satellites called Ekran equipped with powerful 300 W UHF transponders, a broadcasting uplink station and various simple receiving stations located in various towns and villages of Siberian region. The typical receiving station, also called Ekran, represented itself as a home-use analog satellite receiver equipped with simple Yagi-Uda antenna. Later, Ekran satellites were replaced by more advanced Ekran-M series satellites.
In 1979 Soviet engineers developed Moskva (or Moscow) system of broadcasting and delivering of TV signal via satellites. New type of geostationary communication satellites, called Gorizont, were launched. They were equipped by powerful onboard transponders, so the size of receiving parabolic antennas of downlink stations was reduced to 4 and 2.5 meters (in comparison of early 12- meter dishes of standard Orbita downlink stations).
By 1989 an improved version of Moskva system of satellite television has been called Moskva Global'naya (or Moscow Global). The system included a few geostationary Gorizont and Express type of communication satellites. TV signal from Moscow Global’s satellites could be received in any country of planet except Canada and North-West of the USA.
Modern Russian satellite broadcasting services based on powerful geostationary buses such as Gals, Express, Yamal and Eutelsat which provide a large quantity of free-to-air television channels to millions of householders. Pay-TV is growing in popularity amongst Russian TV viewers. The NTV Russia news company, owned by Gazprom, broadcasts the NTV Plus package to 560,000 households, reaching over 1.5 million viewers.
United Kingdom and Ireland
The first commercial DBS service in the United Kingdom, Sky Television, was launched in 1989 and used the newly launched ASTRA satellite, providing 4 analogue TV channels. The channels and subsequent VideoCrypt video encryption system used the existing PAL broadcast standard. This gave Sky a distinct advantage over the winner of the UK state DBS licence, BSB.
In the following year, after many delays, BSB was launched, broadcasting five channels in D-MAC format and using the EuroCypher video encryption system which was based heavily on the General Instruments VideoCipher system used in the USA. While the BSB system was technologically more advanced than the PAL system and one of the main selling points of the BSB offering was the Squarial, an expensive flat plate antenna and LNB. Sky's system used conventional and cheap dish and LNB technology.
The competition between the two companies was fierce and bidding wars over the UK rights to movies. Sky kept costs to a bare minimum, operating from an industrial park in Isleworth just outside of London. BSB had expensive offices in London (Marco Polo House). The two services subsequently merged to form British Sky Broadcasting (BSkyB) though the new BSkyB was really Sky. The technologically more advanced BSB D-MAC/EuroCypher system was gradually replaced with Sky's VideoCrypt video encryption system.
By 1999, following the launch of several more satellites (at 19.2°E by SES Astra, the number of channels had increased to around 60 and BSkyB launched the first subscription-based digital television platform in the UK, offering a range of 300 channels broadcast from the Astra satellites at 28.2°E under the brand name Sky Digital. BSkyB’s analogue service has now been discontinued, with all customers having been migrated to Sky Digital.
The first satellite service specifically set to the Nordic region was TV3 which launched in 1987. With the launch of Astra 1A, getting the TV3 channel got easier. The first Nordic-specific satellite, Tele-X, was launched in 1989. The services directed at Scandinavia were then scattered among several satellites. In 1993, the former BSB satellites were bought by a Swedish and a Norwegian company, respectively. These two satellites were renamed Thor 1 and Sirius 1, moved to new positions and started broadcasting services intended for people in the Nordic region. With the launch of additional Thor and Sirius satellites later in the 1990s, Astra and other satellites were abandoned by the Nordic services with almost all Nordic satellite television migrating to the Sirius and Thor satellites.
Initially the basic channels were free-to-air. This caused several rights problems since viewers throughout Europe were able to see very much acquired English language programming as well as sports for free on the Nordic channels, although the channels only held broadcasting rights for specific countries. One way of avoiding that was to switch from PAL to the D2MAC standard, hardly used anywhere outside the Nordic region. An unencrypted channel could still be seen in all the Nordic satellite homes, so eventually all channels went encrypted (several of them only being available in one country).
There are two competing satellite services: Canal Digital (Norwegian Telenor) and Viasat (Kinnevik). Canal Digital launched in 1997 and was digital from the start, broadcasting from Thor. Kinnevik had been operating an analogue subscription service since the late 1980s, but waited until the year 2000 before launching a digital service. All analogue services from Thor and Sirius will have ceased in 2006, when the three remaining Danish channels go digital-only. The competition between Viasat and Canal Digital has caused some homes in Scandinavia to have to buy two set-top boxes and have two subscriptions to get the full range of channels. Viasat doesn't provide their own channels (TV3, TV3+, ZTV, TV1000 and the Viasat-branded channels) on the Canal Digital platform. Canal Digital does however have exclusive distribution of channels from SBS Broadcasting, Discovery, TV2 Denmark and Eurosport; for several years the Swedish SVT and TV4 channels were also exclusive to Canal Digital.