Satellite television
Satellite television is a service that delivers television programming to viewers by relaying it from a communications satellite orbiting the Earth directly to the viewer's location.[1] The signals are received via an outdoor parabolic antenna commonly referred to as a satellite dish and a low-noise block downconverter.
A satellite receiver then decodes the desired
Modern systems signals are relayed from a communications satellite on the
Early systems used
Different receivers are required for the two types. Some transmissions and channels are unencrypted and therefore free-to-air, while many other channels are transmitted with encryption. Free-to-view channels are encrypted but not charged-for, while pay television requires the viewer to subscribe and pay a monthly fee to receive the programming.[6]
Satellite TV has seen a decline in consumers since the 2010s due to the
Technology
The satellites used for broadcasting television are usually in a
Satellite television, like other communications relayed by satellite, starts with a transmitting antenna located at an
A typical satellite has up to 32 Ku-band or 24 C-band transponders, or more for Ku/C hybrid satellites. Typical transponders each have a bandwidth between 27 and 50 MHz. Each geostationary C-band satellite needs to be spaced 2° longitude from the next satellite to avoid interference; for Ku the spacing can be 1°. This means that there is an upper limit of 360/2 = 180 geostationary C-band satellites or 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 at this particular frequency). The latter is even more adversely affected by ice crystals in thunder clouds. On occasion, sun outage will occur when the sun lines up directly behind the geostationary satellite to which the receiving antenna is pointed.[11]
The downlink satellite signal, quite weak after traveling the great distance (see
The original C-band satellite television systems used a low-noise amplifier (LNA) connected to the feedhorn at the focal point of the dish.[15] The amplified signal, still at the higher microwave frequencies, had to be fed via very expensive low-loss 50-ohm impedance gas filled hardline coaxial cable with relatively complex N-connectors to an indoor receiver or, in other designs, a downconverter (a mixer and a voltage-tuned oscillator with some filter circuitry) for downconversion to an intermediate frequency.[15] 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 design evolved.[15]
Designs for microstrip-based converters for amateur radio frequencies were adapted for the 4 GHz C-band.[16] Central to these designs was concept of block downconversion of a range of frequencies to a lower, more easily handled IF.[16]
The advantages of using an LNB are that cheaper cable can be used to connect the indoor receiver to the satellite television dish and LNB, and that the technology for handling the signal at
In the United States, service providers use the
The satellite receiver or
A practical problem relating to home satellite reception is that an LNB can basically only handle a single receiver.[20] This is because the LNB is translating two different circular polarizations (right-hand and left-hand) and, in the case of K-band, two different frequency bands (lower and upper) to the same frequency range on the cable.[20] Depending on which frequency and polarization a transponder is using, the satellite receiver has to switch the LNB into one of four different modes in order to receive a specific "channel".[20] This is handled by the receiver using the DiSEqC protocol to control the LNB mode.[20] If several satellite receivers are to be attached to a single dish, a so-called multiswitch will have to be used in conjunction with a special type of LNB.[20] There are also LNBs available with a multi-switch already integrated.[20] This problem becomes more complicated when several receivers are to use several dishes (or several LNBs mounted in a single dish) pointing to different satellites.[20]
A common solution for consumers wanting to access multiple satellites is to deploy a single dish with a single LNB and to rotate the dish using an electric motor. The axis of rotation has to be set up in the north–south direction and, depending on the geographical location of the dish, have a specific vertical tilt. Set up properly the motorized dish when turned will sweep across all possible positions for satellites lined up along the geostationary orbit directly above the equator. The dish will then be capable of receiving any geostationary satellite that is visible at the specific location, i.e. that is above the horizon. The DiSEqC protocol has been extended to encompass commands for steering dish rotors.[citation needed]
There are five major components in a satellite system: the programming source, the broadcast center, the satellite, the
Satellite television, like other communications relayed by satellite, starts with a transmitting antenna located at an
The downlinked satellite signal, weaker after traveling the great distance (see
The reason for using the LNB to do the frequency translation at the dish is so that the signal can be carried into the residence using cheap
An LNB can only handle a single receiver.[20] This is due to the fact that the LNB is mapping two different circular polarisations – right hand and left hand – and in the case of the Ku-band two different reception bands – lower and upper – to one and the same frequency band on the cable, and is a practical problem for home satellite reception.[20] Depending on which frequency a transponder is transmitting at and on what polarisation it is using, the satellite receiver has to switch the LNB into one of four different modes in order to receive a specific desired program on a specific transponder.[20] The receiver uses the DiSEqC protocol to control the LNB mode, which handles this.[20] If several satellite receivers are to be attached to a single dish a so-called multiswitch must be used in conjunction with a special type of LNB.[20] There are also LNBs available with a multi-switch already integrated.[20] This problem becomes more complicated when several receivers use several dishes or several LNBs mounted in a single dish are aimed at different satellites.[20]
The
Analog television which was distributed via satellite was usually sent scrambled or unscrambled in
Later signals were digitized television signals or multiplex of signals, typically
The
Sun outage
An event called sun outage occurs when the sun lines up directly behind the satellite in the field of view of the receiving satellite dish.[24] This happens for about a 10-minute period daily around midday, twice every year for a two-week period in the spring and fall around the equinox. During this period, the sun is within the main lobe of the dish's reception pattern, so the strong microwave noise emitted by the sun on the same frequencies used by the satellite's transponders drowns out reception.[24]
Uses
Direct-to-home and direct broadcast satellite
Direct-to-home (DTH) can either refer to the communications satellites themselves that deliver service or the actual television service. Most satellite television customers in developed television markets get their programming through a direct broadcast satellite (DBS) provider.[25] Signals are transmitted using Ku band (12 to 18 GHz) and are completely digital which means it has high picture and stereo sound quality.[2]
Programming for satellite television channels comes from multiple sources and may include live studio feeds.
Most systems use the
Some countries operate satellite television services which can be received for free, without paying a subscription fee. This is called
The
India's national broadcaster, Doordarshan, promotes a free-to-air DBS package as "DD Free Dish", which is provided as in-fill for the country's terrestrial transmission network. It is broadcast from GSAT-15 at 93.5°E and contains about 80 FTA channels.
While originally launched as
In North America (United States,
Television receive-only
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 the primary method of satellite television transmissions before the satellite television industry shifted, with the launch of higher powered DBS satellites in the early 1990s which transmitted their signals on the Ku band frequencies.[3][33] Satellite television channels at that time were intended to be used by cable television networks rather than received by home viewers.[34] Early satellite television receiver systems were largely constructed by hobbyists and engineers. These early TVRO systems operated mainly on the C-band frequencies and the dishes required were large; typically over 3 meters (10 ft) in diameter.[35] Consequently, TVRO is often referred to as "big dish" or "Big Ugly Dish" (BUD) satellite television.
TVRO systems were designed to receive analog and digital
The narrow beam width of a normal parabolic satellite antenna means it can only receive signals from a single satellite at a time.
History
Early history
In 1945 British
The first public satellite television signals from
The world's first commercial communications satellite, called
The first in a series of Soviet geostationary satellites to carry
Beginning of the satellite TV industry, 1976–1980
The satellite television industry developed first in the US from the
In the US, PBS, a non-profit public broadcasting service, began to distribute its television programming by satellite in 1978.[55]
In 1979, Soviet engineers developed the Moskva (or
Early satellite television systems were not very popular due to their expense and large dish size.
TVRO/C-band satellite era, 1980–1986
By 1980, satellite television was well established in the
Originally, all channels were broadcast in the clear (ITC) because the equipment necessary to receive the programming was too expensive for consumers. With the growing number of TVRO systems, the program providers and broadcasters had to scramble their signal and develop subscription systems.
In October 1984, the
Videocipher II used analog scrambling on its video signal and Data Encryption Standard–based encryption on its audio signal. VideoCipher II was defeated, and there was a black market for descrambler devices which were initially sold as "test" devices.[75]
1987 to present
By 1987, nine channels were scrambled, but 99 others were available free-to-air.[72] While HBO initially charged a monthly fee of $19.95, soon it became possible to unscramble all channels for $200 a year.[72] Dish sales went down from 600,000 in 1985 to 350,000 in 1986, but pay television services were seeing dishes as something positive since some people would never have cable service, and the industry was starting to recover as a result.[72] Scrambling also led to the development of pay-per-view events.[72] On November 1, 1988, NBC began scrambling its C-band signal but left its Ku band signal unencrypted in order for affiliates to not lose viewers who could not see their advertising.[76] Most of the two million satellite dish users in the United States still used C-band.[76] ABC and CBS were considering scrambling, though CBS was reluctant due to the number of people unable to receive local network affiliates.[76] The piracy on satellite television networks in the US led to the introduction of the Cable Television Consumer Protection and Competition Act of 1992. This legislation enabled anyone caught engaging in signal theft to be fined up to $50,000 and to be sentenced to a maximum of two years in prison.[77] A repeat offender can be fined up to $100,000 and be imprisoned for up to five years.[77]
Satellite television had also developed in Europe but it initially used low power communication satellites and it required dish sizes of over 1.7 metres. On 11 December 1988, however, Luxembourg launched Astra 1A, the first satellite to provide medium power satellite coverage to Western Europe.[78] This was one of the first medium-powered satellites, transmitting signals in Ku band and allowing reception with small dishes (90 cm).[78] The launch of Astra beat the winner of the UK's state Direct Broadcast Satellite licence holder, British Satellite Broadcasting, to the market.
Commercial satellite broadcasts have existed in Japan since 1992 led by
In the US in the early 1990s, four large cable companies launched
On March 4, 1996, EchoStar introduced Digital Sky Highway (Dish Network) using the EchoStar 1 satellite.
In addition to encryption, the widespread availability, in the US, of DBS services such as PrimeStar and DirecTV had been reducing the popularity of TVRO systems since the early 1990s. Signals from DBS satellites (operating in the more recent
In a return to the older (but proven) technologies of satellite communication, the current DBS-based satellite providers in the US (Dish Network and DirecTV) are now utilizing additional capacity on the Ku-band transponders of existing FSS-class satellites, in addition to the capacity on their own existing fleets of DBS satellites in orbit. This was done in order to provide more channel capacity for their systems, as required by the increasing number of High-Definition and simulcast local station channels. The reception of the channels carried on the Ku-band FSS satellite's respective transponders has been achieved by both DirecTV & Dish Network issuing to their subscribers dishes twice as big in diameter (36") than the previous 18" (& 20" for the Dish Network "Dish500") dishes the services used initially, equipped with 2 circular-polarized LNBFs (for reception of 2 native DBS satellites of the provider, 1 per LNBF), and 1 standard linear-polarized LNB for reception of channels from an FSS-type satellite. These newer DBS/FSS-hybrid dishes, marketed by DirecTV and Dish Network as the "SlimLine" and "SuperDish" models respectively, are now the current standard for both providers, with their original 18"/20" single or dual LNBF dishes either now obsolete, or only used for program packages, separate channels, or services only broadcast over the providers' DBS satellites.
On 29 November 1999 US President Bill Clinton signed the Satellite Home Viewer Improvement Act (SHVIA).[85] The act allowed Americans to receive local broadcast signals via direct broadcast satellite systems for the first time.[85]
Legal
The 1963 Radio Regulations of the International Telecommunication Union (ITU) defined a "broadcasting satellite service" as a "space service in which signals transmitted or retransmitted by space stations, or transmitted by reflection from objects in orbit around the Earth, are intended for direct reception by the general public."[86]
In the 1970s some states grew concerned that external broadcasting could alter the cultural or political identity of a state leading to the
See also
- Cable television
- List of direct broadcast satellite providers
- Television receive-only
- Satellite television by region
- Commercialization of space
- Free-to-air
- Microwave antenna
- Molniya orbit
- Murphy v Media Protection Services Limited
- Satellite dish
- Satellite subcarrier audio
- Smart TV: provides television via internet connection
- SMATV
- Television antenna
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External links
- Media related to Satellite television at Wikimedia Commons
- Digital Satellite Television by Chris Muriel (June 21st, 2000)