![DirecTVSlimline3RB](https://upload.wikimedia.org/wikipedia/commons/a/a2/DirecTVSlimline3RB.jpeg)
Satellite television is a service that delivers television programming to viewers by relaying it from a
communications satellite
A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. C ...
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 low-noise block downconverter (LNB) is the receiving device mounted on satellite dishes used for satellite TV reception, which collects the radio waves from the dish and converts them to a signal which is sent through a cable to the receiver i ...
.
A satellite receiver then decodes the desired
television program
Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertising, e ...
for viewing on a
television set
A television set or television receiver, more commonly called the television, TV, TV set, telly, tele, or tube, is a device that combines a tuner, display, and loudspeakers, for the purpose of viewing and hearing television broadcasts, or using ...
. Receivers can be external
set-top box
A set-top box (STB), also colloquially known as a cable box and historically television decoder, is an information appliance device that generally contains a TV-tuner input and displays output to a television set and an external source of sign ...
es, or a built-in
television tuner
A tuner is a subsystem that receives radio frequency (RF) transmissions, such as FM broadcasting, and converts the selected carrier frequency and its associated bandwidth into a fixed frequency that is suitable for further processing, usually be ...
. 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
Terrestrial television or over-the-air television (OTA) is a type of television broadcasting in which the signal transmission occurs via radio waves from the terrestrial (Earth-based) transmitter of a TV station to a TV receiver having an ant ...
or
cable television
Cable television is a system of delivering television programming to consumers via radio frequency (RF) signals transmitted through coaxial cables, or in more recent systems, light pulses through fibre-optic cables. This contrasts with broa ...
service.
Modern systems signals are relayed from a
communications satellite
A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. C ...
on the
X band (8–12 GHz) or
Ku 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
Television receive-only (TVRO) is a term used chiefly in North America, South America to refer to the reception of satellite television from FSS-type satellites, generally on C-band analog; free-to-air and unconnected to a commercial DBS prov ...
. 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
A digital signal is a Signal (electrical engineering), signal that represents data as a sequence of discrete space, discrete values; at any given time it can only take on, at most, one of a finite number of values. This contrasts with an analog ...
which allow transmission of the modern television standard
high-definition television
High-definition television (HD or HDTV) describes a television system which provides a substantially higher image resolution than the previous generation of technologies. The term has been used since 1936; in more recent times, it refers to the g ...
, due to the significantly improved
spectral efficiency
Spectral efficiency, spectrum efficiency or bandwidth efficiency refers to the information rate that can be transmitted over a given Bandwidth (signal processing), bandwidth in a specific communication system. It is a measure of how efficiently a l ...
of digital broadcasting. As of 2022,
Star One C2
Star One C2 is a Brazilian communications satellite. It was launched on 18 April 2008 22:17 UTC by an Ariane 5ECA carrier rocket, as part of a dual-payload launch with Vinasat-1. It was built by Thales Alenia Space, based on the Spacebus-3000B3 s ...
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
Free-to-air (FTA) services are television (TV) and radio services broadcast in unencrypted form, allowing any person with the FTA Receiver, appropriate receiving equipment to receive the signal and view or listen to the content without requiring ...
, while many other channels are transmitted with encryption.
Free-to-view
Free-to-view (FTV) is a term used for audiovisual transmissions that are provided free without any form of continual subscription . It differs from free-to-air (FTA) in that the program is encrypted.
Free-to-view vs. free-to-air
The free-to-vi ...
channels are encrypted but not charged-for, while
pay television
Pay television, also known as subscription television, premium television or, when referring to an individual service, a premium channel, refers to Subscription business model, subscription-based television services, usually provided by multichan ...
requires the viewer to subscribe and pay a monthly fee to receive the programming.
Satellite TV is being affected by the
cord-cutting
In broadcast television, cord-cutting refers to the pattern of viewers, referred to as cord-cutters, cancelling their subscriptions to multichannel television services available over cable or satellite, dropping pay television channels or reduc ...
trend where people are shifting towards internet based
streaming television
Streaming television is the digital distribution of television content, such as TV shows, as streaming media delivered over the Internet. Streaming television stands in contrast to dedicated terrestrial television delivered by over-the-air aer ...
.
Technology
The satellites used for broadcasting television are usually in a
geostationary orbit above the earth's
equator
The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...
. 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
Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object.
For a satellite orbiting the Eart ...
of +/−63.4 degrees and an orbital period of about twelve hours, known as a
Molniya orbit
A Molniya orbit ( rus, Молния, p=ˈmolnʲɪjə, a=Ru-молния.ogg, "Lightning") is a type of satellite orbit designed to provide communications and remote sensing coverage over high latitudes. It is a highly elliptical orbit with an ...
.
Satellite television, like other communications relayed by satellite, starts with a transmitting antenna located at an
uplink
In a telecommunications network, a link is a communication channel that connects two or more devices for the purpose of data transmission. The link may be a dedicated physical link or a virtual circuit that uses one or more physical links or sha ...
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
transponder
In telecommunications, a transponder is a device that, upon receiving a signal, emits a different signal in response. The term is a blend of ''transmitter'' and ''responder''.
In air navigation or radio frequency identification, a flight trans ...
s 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),
Ku-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
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
Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water f ...
(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
Path loss, or path attenuation, is the reduction in power density (attenuation) of an electromagnetic wave as it propagates through space. Path loss is a major component in the analysis and design of the link budget of a telecommunication system ...
), 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
A feed horn (or feedhorn) is a small horn antenna used to couple a waveguide to e.g. a parabolic dish antenna or offset dish antenna for reception or transmission of microwave. A typical application is the use for satellite television recep ...
or collector. The feedhorn is a section of
waveguide
A waveguide is a structure that guides waves, such as electromagnetic waves or sound, with minimal loss of energy by restricting the transmission of energy to one direction. Without the physical constraint of a waveguide, wave intensities de ...
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
A low-noise block downconverter (LNB) is the receiving device mounted on satellite dishes used for satellite TV reception, which collects the radio waves from the dish and converts them to a signal which is sent through a cable to the receiver i ...
(LNB). The LNB amplifies the signals and
downconverts them to a lower block of
intermediate frequencies (IF), usually in the
L-band
The L band is the Institute of Electrical and Electronics Engineers (IEEE) designation for the range of frequencies in the radio spectrum from 1 to 2 gigahertz (GHz). This is at the top end of the ultra high frequency (UHF) band, at the lower ...
.
The original
C-band satellite television systems used a
low-noise amplifier
A low-noise amplifier (LNA) is an electronic amplifier that amplifies a very low-power signal without significantly degrading its signal-to-noise ratio. An amplifier will increase the power of both the signal and the noise present at its input, ...
(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
Coaxial cable, or coax (pronounced ) is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric ( insulating material); many coaxial cables also have a p ...
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
Microstrip is a type of electrical transmission line which can be fabricated with any technology where a conductor is separated from a ground plane by a dielectric layer known as the substrate. Microstrip lines are used to convey microwave-frequ ...
-based converters for
amateur radio
Amateur radio, also known as ham radio, is the use of the radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency communic ...
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.
![Universal-euro-sat-lnb](https://upload.wikimedia.org/wikipedia/commons/e/e3/Universal-euro-sat-lnb.jpg)
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
The L band is the Institute of Electrical and Electronics Engineers (IEEE) designation for the range of frequencies in the radio spectrum from 1 to 2 gigahertz (GHz). This is at the top end of the ultra high frequency (UHF) band, at the lower ...
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
DirecTV (trademarked as DIRECTV) is an American multichannel video programming distributor based in El Segundo, California. Originally launched on June 17, 1994, its primary service is a digital satellite service serving the United States. I ...
AU9-S and AT-9), ranges of the lower
B-band
The NATO B band is the obsolete designation given to the radio frequencies from 250 to 500 MHz (equivalent to wavelengths between 1.20 and 0.60 m) during the cold war period. Since 1992 frequency allocations, allotment and assignments are in line ...
and 2250–3000 MHz, are used. Newer LNBFs in use by DirecTV, called SWM (Single Wire Multiswitch), are used to implement
single cable distribution
Single-cable distribution is a satellite TV technology that enables the delivery of broadcast programming to multiple users over a single coaxial cable, and eliminates the numerous cables required to support consumer electronics devices such as tw ...
and use a wider frequency range of 2–2150 MHz.
The satellite receiver or
set-top box
A set-top box (STB), also colloquially known as a cable box and historically television decoder, is an information appliance device that generally contains a TV-tuner input and displays output to a television set and an external source of sign ...
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
In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can deci ...
the received signal to provide premium services to some subscribers; the receiver is then called an
integrated receiver/decoder
An integrated receiver/decoder (IRD) is an electronic device used to pick up a radio-frequency signal and convert digital information transmitted in it.
Consumer IRDs
Consumer IRDs, commonly called set-top boxes, are used by end users and are ...
or IRD. Low-loss cable (e.g.
RG-6
RG-6/U is a common type of coaxial cable used in a wide variety of residential and commercial applications. An RG-6/U coaxial cable has a characteristic impedance of 75 ohms. The term, ''RG-6'', is generic and is applied to a wide variety of ...
,
RG-11, etc.) is used to connect the receiver to the LNBF or LNB.
RG-59
RG-59/U is a specific type of coaxial cable, often used for low-power video and RF signal connections. The cable has a characteristic impedance of 75 ohms, and a capacitance of around 20pF/ft (60pF/m). The 75 ohm impedance matches a dipol ...
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 polarization
In electrodynamics, circular polarization of an electromagnetic wave is a polarization state in which, at each point, the electromagnetic field of the wave has a constant magnitude and is rotating at a constant rate in a plane perpendicular to ...
s (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
{{Unreferenced, date=December 2009
A multiswitch is a device used with a dual or quattro LNB to distribute satellite TV signals to multiple (usually more than four) receivers from a single dish and LNB.
A typical Ku band universal LNB desig ...
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.
![Working satellite television](https://upload.wikimedia.org/wikipedia/commons/1/11/Working_satellite_television.jpg)
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 equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...
.
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 Molniya orbit ( rus, Молния, p=ˈmolnʲɪjə, a=Ru-молния.ogg, "Lightning") is a type of satellite orbit designed to provide communications and remote sensing coverage over high latitudes. It is a highly elliptical orbit with an ...
, a highly
elliptical
Elliptical may mean:
* having the shape of an ellipse, or more broadly, any oval shape
** in botany, having an elliptic leaf shape
** of aircraft wings, having an elliptical planform
* characterised by ellipsis (the omission of words), or by conc ...
orbit with
inclination
Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object.
For a satellite orbiting the Eart ...
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
In a telecommunications network, a link is a communication channel that connects two or more devices for the purpose of data transmission. The link may be a dedicated physical link or a virtual circuit that uses one or more physical links or sha ...
facility.
Uplink facilities transmit the signal to the satellite over a narrow beam of
microwave
Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ra ...
s, 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
transponder
In telecommunications, a transponder is a device that, upon receiving a signal, emits a different signal in response. The term is a blend of ''transmitter'' and ''responder''.
In air navigation or radio frequency identification, a flight trans ...
s tuned to that frequency range aboard that satellite.
The transponder then converts the signals to
Ku band, a process known as "translation," and transmits them back to earth to be received by home satellite stations.
![DTH Satellite Dish - India - IMG 3474](https://upload.wikimedia.org/wikipedia/commons/b/b2/DTH_Satellite_Dish_-_India_-_IMG_3474.jpg)
The downlinked satellite signal, weaker after traveling the great distance (see
path loss
Path loss, or path attenuation, is the reduction in power density (attenuation) of an electromagnetic wave as it propagates through space. Path loss is a major component in the analysis and design of the link budget of a telecommunication system ...
), 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
A feed horn (or feedhorn) is a small horn antenna used to couple a waveguide to e.g. a parabolic dish antenna or offset dish antenna for reception or transmission of microwave. A typical application is the use for satellite television recep ...
which passes the signals through a
waveguide
A waveguide is a structure that guides waves, such as electromagnetic waves or sound, with minimal loss of energy by restricting the transmission of energy to one direction. Without the physical constraint of a waveguide, wave intensities de ...
to a device called a
low-noise block converter
A low-noise block downconverter (LNB) is the receiving device mounted on satellite dishes used for satellite TV reception, which collects the radio waves from the dish and converts them to a signal which is sent through a cable to the receiver ...
(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
The L band is the Institute of Electrical and Electronics Engineers (IEEE) designation for the range of frequencies in the radio spectrum from 1 to 2 gigahertz (GHz). This is at the top end of the ultra high frequency (UHF) band, at the lower ...
range.
The signal is then passed through a
coaxial cable
Coaxial cable, or coax (pronounced ) is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric ( insulating material); many coaxial cables also have a p ...
into the residence to the satellite television receiver, a
set-top box
A set-top box (STB), also colloquially known as a cable box and historically television decoder, is an information appliance device that generally contains a TV-tuner input and displays output to a television set and an external source of sign ...
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
Coaxial cable, or coax (pronounced ) is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric ( insulating material); many coaxial cables also have a p ...
. To transport the signal into the house at its original
Ku band microwave
Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ra ...
frequency would require an expensive
waveguide
A waveguide is a structure that guides waves, such as electromagnetic waves or sound, with minimal loss of energy by restricting the transmission of energy to one direction. Without the physical constraint of a waveguide, wave intensities de ...
, a metal pipe to carry the radio waves.
The cable connecting the receiver to the LNB are of the low loss type
RG-6
RG-6/U is a common type of coaxial cable used in a wide variety of residential and commercial applications. An RG-6/U coaxial cable has a characteristic impedance of 75 ohms. The term, ''RG-6'', is generic and is applied to a wide variety of ...
, quad shield RG-6, or RG-11.
RG-59
RG-59/U is a specific type of coaxial cable, often used for low-power video and RF signal connections. The cable has a characteristic impedance of 75 ohms, and a capacitance of around 20pF/ft (60pF/m). The 75 ohm impedance matches a dipol ...
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
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.
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
{{Unreferenced, date=December 2009
A multiswitch is a device used with a dual or quattro LNB to distribute satellite TV signals to multiple (usually more than four) receivers from a single dish and LNB.
A typical Ku band universal LNB desig ...
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
A set-top box (STB), also colloquially known as a cable box and historically television decoder, is an information appliance device that generally contains a TV-tuner input and displays output to a television set and an external source of sign ...
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
In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can deci ...
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/decoder
An integrated receiver/decoder (IRD) is an electronic device used to pick up a radio-frequency signal and convert digital information transmitted in it.
Consumer IRDs
Consumer IRDs, commonly called set-top boxes, are used by end users and are ...
s or IRDs.
Analog television which was distributed via satellite was usually sent scrambled or unscrambled in
NTSC
The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...
,
PAL
Phase Alternating Line (PAL) is a colour encoding system for analogue television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 ...
, or
SECAM
SECAM, also written SÉCAM (, ''Séquentiel de couleur à mémoire'', French for ''color sequential with memory''), is an analog color television system that was used in France, some parts of Europe and Africa, and Russia. It was one of th ...
television broadcast standards. The analog signal is
frequency modulated
Frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The technology is used in telecommunications, radio broadcasting, signal processing, and computing.
In analog freq ...
and is converted from an FM signal to what is referred to as
baseband
In telecommunications and signal processing, baseband is the range of frequencies occupied by a signal that has not been modulated to higher frequencies. Baseband signals typically originate from transducers, converting some other variable into a ...
. 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
Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency reference signal (the carrier wave). The modulation is accomplished by varying the sine and cosine inputs at ...
. In general, digital television, including that transmitted via satellites, is based on open standards such as
MPEG
The Moving Picture Experts Group (MPEG) is an alliance of working groups established jointly by International Organization for Standardization, ISO and International Electrotechnical Commission, IEC that sets standards for media coding, includ ...
and
DVB-S/
DVB-S2 or
ISDB-S.
The
conditional access
Conditional access (CA) is a term commonly used in relation to software and to digital television systems. Conditional access is that ‘just-in-time’ evaluation to ensure the person who is seeking access to content is authorized to access the c ...
encryption/scrambling methods include
NDS NDS may stand for:
* Low German ( nl, Nedersaksisch, links=no, german: Niederdeutsche Sprache, links=no, ISO 639-2 language code: nds), a West Germanic language native to Northern Germany, Denmark and the Netherlands
* Lower Saxony (german: Niedersa ...
,
BISS,
Conax
Conax develops television encryption, conditional access and content security for digital television. Conax provide CAS technology to pay TV operators in 85 countries. The company has offices in Norway (headquarters), Russia, Germany, Brazil, t ...
,
Digicipher
DigiCipher 2, or simply DCII, is a proprietary standard format of digital signal transmission and it doubles as an encryption standard with MPEG-2/MPEG-4 signal video compression used on many communications satellite television and audio signals. T ...
, Irdeto,
Cryptoworks
In television encryption, Cryptoworks is a DVB conditional access system, developed by Philips CryptoTec but now belonging to Irdeto.
Cryptoworks is used by the following pay TV providers:
* OSN
*Digiturk
*the BFBS satellite service
* UPC Dir ...
,
DG Crypt,
Beta digital,
SECA Mediaguard
The SecA protein is a cell membrane associated subunit of the eubacterial Sec or Type II secretory pathway, a system which is responsible for the secretion of proteins through the cell membrane. Within this system the SecA ATPase forms a translo ...
,
Logiways,
Nagravision
Nagravision (or Nagra Kudelski or simply Nagra) is a company of the Kudelski Group that develops conditional access systems for digital cable and satellite television. The name is also used for their main products, the Nagravision encryption syste ...
,
PowerVu
PowerVu is a conditional access system for digital television developed by Scientific Atlanta. It is used for professional broadcasting, notably by Retevision, Bloomberg Television, Discovery Channel, AFRTS, ABS-CBN, GMA Network, and American For ...
,
Viaccess Viaccess is a conditional access system edit by Orange S.A. There are six versions in use today, Viaccess PC2.3, Viaccess PC2.4, Viaccess PC2.5, Viaccess PC2.6, Viaccess ACS3.x/Prime Sentinel, Viaccess ACS4.1, Viaccess ACS5.0, and Viaccess ACS6.x/A ...
,
Videocipher
VideoCipher is a brand name of analog scrambling and de-scrambling equipment for cable and satellite television invented primarily to enforce Television receive-only (TVRO) satellite equipment to only receive TV programming on a subscription basis ...
, and
VideoGuard
VideoGuard (sometimes referred to simply as ''NDS''), produced by NDS, is a digital encryption system for use with conditional access television broadcasting. It is used on digital satellite television systems - some of which are operated by News ...
. 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
A solar equinox is a moment in time when the Sun crosses the Earth's equator, which is to say, appears directly above the equator, rather than north or south of the equator. On the day of the equinox, the Sun appears to rise "due east" and se ...
. During this period, the sun is within the
main lobe
In a radio antenna's radiation pattern, the main lobe, or main beam, is the lobe containing the higher power. This is the lobe that exhibits the greater field strength.
The radiation pattern of most antennas shows a pattern of "''lobes''" at ...
of the dish's reception pattern, so the strong microwave
noise
Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference arise ...
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
![Dishing out the truth](https://upload.wikimedia.org/wikipedia/commons/b/bd/Dishing_out_the_truth.JPG)
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
Ku 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
In a telecommunications network, a link is a communication channel that connects two or more devices for the purpose of data transmission. The link may be a dedicated physical link or a virtual circuit that uses one or more physical links or sha ...
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
Pay television, also known as subscription television, premium television or, when referring to an individual service, a premium channel, refers to Subscription business model, subscription-based television services, usually provided by multichan ...
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
A conditional access module (CAM) is an electronic device, usually incorporating a slot for a smart card, which equips an integrated digital television or set-top box with the appropriate hardware facility to view conditional access content ...
and
smart card
A smart card, chip card, or integrated circuit card (ICC or IC card) is a physical electronic authentication device, used to control access to a resource. It is typically a plastic credit card-sized card with an embedded integrated circuit (IC) c ...
. 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
Free-to-air (FTA) services are television (TV) and radio services broadcast in unencrypted form, allowing any person with the FTA Receiver, appropriate receiving equipment to receive the signal and view or listen to the content without requiring ...
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
Free-to-air (FTA) services are television (TV) and radio services broadcast in unencrypted form, allowing any person with the FTA Receiver, appropriate receiving equipment to receive the signal and view or listen to the content without requiring ...
satellite television.
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
is likely the leader in free-to-air with approximately 250 digital channels (including 83
HDTV
High-definition television (HD or HDTV) describes a television system which provides a substantially higher image resolution than the previous generation of technologies. The term has been used since 1936; in more recent times, it refers to the g ...
channels and various regional channels) broadcast from the
Astra 19.2°E
Astra 19.2°E is the name for the group of Astra communications satellites co-located at the 19.2°East orbital position in the Clarke Belt that are owned and operated by SES based in Betzdorf, Luxembourg.
Astra 19.2°E used to be commonly k ...
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
Sky Deutschland GmbH, branded as Sky, is a German media company that operates a direct broadcast satellite Pay TV platform in Germany, Austria and Switzerland (through Sky Switzerland). It provides a collection of basic and premium digital sub ...
'' commercial DBS system. All German analogue satellite broadcasts ceased on 30 April 2012.
The
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
has approximately 160 digital channels (including the regional variations of
BBC #REDIRECT BBC #REDIRECT BBC
Here i going to introduce about the best teacher of my life b BALAJI sir. He is the precious gift that I got befor 2yrs . How has helped and thought all the concept and made my success in the 10th board exam. ...
...
receiver is required for certain high definition television services). Most of these channels are included within the
", which is provided as in-fill for the country's terrestrial transmission network. It is broadcast from
service, a large number of French channels are free-to-air on satellites at 5°W, and have recently been announced as being official in-fill for the DTT network.
In North America (United States,
(with the majority being ethnic or religious in nature). Other FTA satellites include
5. A company called
.
, 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
frequencies.