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. 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 television program for viewing on a television set. Receivers can be external set-top boxes, or a built-in television tuner. Satellite television provides a wide range of channels and services. It is usually the only television available in many remote geographic areas without terrestrial television or cable television service.

Modern systems signals are relayed from a communications satellite on the X band (8–12 GHz) or K_u band (12–18 GHz) frequencies requiring only a small dish less than a meter in diameter. The first satellite TV systems were an obsolete type now known as television receive-only. These systems received weaker analog signals transmitted in the C-band (4–8 GHz) from FSS type satellites, requiring the use of large 2–3-meter dishes. Consequently, these systems were nicknamed "big dish" systems, and were more expensive and less popular.

Early systems used analog signals, but modern ones use digital signals which allow transmission of the modern television standard high-definition television, due to the significantly improved spectral efficiency of digital broadcasting. As of 2022, Star One C2 from Brazil is the only remaining satellite broadcasting in analog signals.

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.

Satellite TV is being affected by the cord-cutting trend where people are shifting towards internet based streaming television.

Technology

The satellites used for broadcasting television are usually in a geostationary orbit above the earth's equator. The advantage of this orbit is that the satellite's orbital period equals the rotation rate of the Earth, so the satellite appears at a fixed position in the sky. Thus the satellite dish antenna which receives the signal can be aimed permanently at the location of the satellite and does not have to track a moving satellite. A few systems instead use a highly elliptical orbit with inclination of +/−63.4 degrees and an orbital period of about twelve hours, known as a Molniya orbit.

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 re-transmits the signals back to Earth at a different frequency (a process known as translation, used to avoid interference with the uplink signal), typically in the 10.7-12.7 GHz band, but some still transmit in the C-band (4–8 GHz), K_u-band (12–18 GHz), or both. 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 K_u-band or 24 C-band transponders, or more for K_u/ 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 K_u 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 K_u-band satellites. C-band transmission is susceptible to terrestrial interference while K_u-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.

The downlink satellite signal, quite weak after traveling the great distance (see path loss), is collected with 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 or collector. The feedhorn is a section of waveguide with a flared front-end 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 (LNB). The LNB amplifies the signals and downconverts them to a lower block of intermediate frequencies (IF), usually in the L-band.

The original C-band satellite television systems used a low-noise amplifier (LNA) connected to the feedhorn at the focal point of the dish. 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. 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.

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, more easily handled IF.

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 L-band and UHF was far cheaper than that for handling the signal at C-band frequencies. The shift to cheaper technology from the hardline and N-connectors of the early C-band systems to the cheaper and simpler 75-ohm cable and F-connectors allowed the early satellite television receivers to use, what were in reality, modified UHF television tuners which selected the satellite television channel for down conversion to a 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 only small numbers of systems costing thousands of US dollars were built, to a far more commercial one of mass production.

In the United States, service providers use the intermediate frequency ranges of 950–2150 MHz to carry the signal from the LNBF at the dish down to the receiver. This allows for the transmission of UHF signals along the same span of coaxial wire at the same time. In some applications ( DirecTV AU9-S and AT-9), ranges of the lower B-band and 2250–3000 MHz, are used. Newer LNBFs in use by DirecTV, called SWM (Single Wire Multiswitch), are used to implement single cable distribution and use a wider frequency range of 2–2150 MHz.

The satellite receiver or set-top box demodulates and converts the signals to the desired form (outputs for television, audio, data, etc.). Often, the receiver includes the capability to selectively unscramble or decrypt the received signal to provide premium services to some subscribers; the receiver is then called an integrated receiver/decoder or IRD. Low-loss cable (e.g. RG-6, RG-11, etc.) is used to connect the receiver to the LNBF or LNB. RG-59 is not recommended for this application as it is not technically designed to carry frequencies above 950 MHz, but may work in some circumstances, depending on the quality of the coaxial wire, signal levels, cable length, etc.

A practical problem relating to home satellite reception is that an LNB can basically only handle a single receiver. 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. 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". This is handled by the receiver using the DiSEqC protocol to control the LNB mode. 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. There are also LNBs available with a multi-switch already integrated. 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.

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.

There are five major components in a satellite system: the programming source, the broadcast center, the satellite, the satellite dish, and the receiver. "Direct broadcast" satellites used for transmission of satellite television signals are generally in geostationary orbit above the earth's equator. The reason for using this orbit is that the satellite circles the Earth at the same rate as the Earth rotates, so the satellite appears at a fixed point in the sky. Thus satellite dishes can be aimed permanently at that point, and do not need a tracking system to turn to follow a moving satellite. A few satellite TV systems use satellites in a Molniya orbit, a highly elliptical orbit with inclination of +/-63.4 degrees and an orbital period of about twelve hours.

Satellite television, like other communications relayed by satellite, starts with a transmitting antenna located at an uplink facility. Uplink facilities transmit the signal to the satellite over a narrow beam of microwaves, typically in the C-band frequency range due to its resistance to rain fade. Uplink satellite dishes are very large, often as much as 9 to 12 metres (30 to 40 feet) in diameter to achieve accurate aiming and increased signal strength at the satellite, to improve reliability. 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 K_u band, a process known as "translation," and transmits them back to earth to be received by home satellite stations.

The downlinked satellite signal, weaker after traveling the great distance (see path loss), is collected by using a rooftop parabolic receiving dish (" satellite dish"), which reflects the weak signal to the dish's focal point. Mounted on brackets at the dish's focal point is a feedhorn which passes the signals through a waveguide to a device called a low-noise block converter (LNB) or low noise converter (LNC) attached to the horn. The LNB amplifies the weak signals, filters the block of frequencies in which the satellite television signals are transmitted, and converts the block of frequencies to a lower frequency range in the L-band range. The signal is then passed through a coaxial cable into the residence to the satellite television receiver, a set-top box next to the television.

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 coaxial cable. To transport the signal into the house at its original K_u band microwave frequency would require an expensive waveguide, a metal pipe to carry the radio waves. The cable connecting the receiver to the LNB are of the low loss type RG-6, quad shield RG-6, or RG-11. RG-59 is not recommended for this application as it is not technically designed to carry frequencies above 950 MHz, but will work in many circumstances, depending on the quality of the coaxial wire. The shift to more affordable technology from the 50ohm impedance cable and N-connectors of the early C-band systems to the cheaper 75ohm technology and F-connectors allowed the early satellite television receivers to use, what were in reality, modified UHF television tuners which selected the satellite television channel for down conversion to another lower intermediate frequency centered on 70 MHz where it was demodulated.

An LNB can only handle a single receiver. 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 K_u-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. 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. The receiver uses the DiSEqC protocol to control the LNB mode, which handles this. 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. There are also LNBs available with a multi-switch already integrated. This problem becomes more complicated when several receivers use several dishes or several LNBs mounted in a single dish are aimed at different satellites.

The set-top box selects the channel desired by the user by filtering that channel from the multiple channels received from the satellite, converts the signal to a lower intermediate frequency, decrypts the encrypted signal, demodulates the radio signal and sends the resulting video signal to the television through a cable. To decrypt the signal the receiver box must be "activated" by the satellite company. If the customer fails to pay his monthly bill the box is "deactivated" by a signal from the company, and the system will not work until the company reactivates it. Some receivers are capable of decrypting the received signal itself. These receivers are called integrated receiver/decoders or IRDs.

Analog television which was distributed via satellite was 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.

Later signals were digitized television signals or multiplex of signals, typically QPSK. In general, digital television, including that transmitted via satellites, is based on open standards such as MPEG and DVB-S/ DVB-S2 or ISDB-S.

The conditional access encryption/scrambling methods include NDS, BISS, Conax, Digicipher, Irdeto, Cryptoworks, DG Crypt, Beta digital, SECA Mediaguard, Logiways, Nagravision, PowerVu, Viaccess, Videocipher, and VideoGuard. Many conditional access systems have been compromised.

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. 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.

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. Signals are transmitted using K_u band (12 to 18 GHz) and are completely digital which means it has high picture and stereo sound quality.

Programming for satellite television channels comes from multiple sources and may include live studio feeds. The broadcast center assembles and packages programming into channels for transmission and, where necessary, encrypts the channels. The signal is then sent to the uplink where it is transmitted to the satellite. With some broadcast centers, the studios, administration and up-link are all part of the same campus. The satellite then translates and broadcasts the channels.

Most systems use the DVB-S standard for transmission. With pay television services, the data stream is encrypted and requires proprietary reception equipment. While the underlying reception technology is similar, the pay television technology is proprietary, often consisting of a conditional-access module and smart card. This measure assures satellite television providers that only authorized, paying subscribers have access to pay television content but at the same time can allow free-to-air channels to be viewed even by the people with standard equipment available in the market.

Some countries operate satellite television services which can be received for free, without paying a subscription fee. This is called free-to-air satellite television. Germany is likely the leader in free-to-air with approximately 250 digital channels (including 83 HDTV channels and various regional channels) broadcast from the Astra 19.2°E satellite constellation. These are not marketed as a DBS service, but are received in approximately 18 million homes, as well as in any home using the '' Sky Deutschland'' commercial DBS system. All German analogue satellite broadcasts ceased on 30 April 2012.

The United Kingdom has approximately 160 digital channels (including the regional variations of BBC
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