Glossaire

Regional designation covering Asia and the Pacific. 

Eutelsat market segment providing satellite connectivity for commercial, business and government aircraft.

The network links that carry traffic between an access network or remote site and the core network.

Satellite connectivity used to extend, reinforce or restore telecom networks between remote access sites and core infrastructure.

A rapidly deployable mobile satellite backhaul solution used to restore or add temporary network capacity.

Eutelsat service area covering satellite television distribution, contribution, managed platforms and video innovation.

Satellite connectivity services for business jets and other non-airline civil aircraft.

The ability to maintain or restore essential operations during disruption, supported by resilient or backup connectivity.

Connectivity that links mobile cell sites to the operator's core network using terrestrial or satellite links.

Satellite connectivity services for passenger airlines and commercial aircraft operations.

Shared internet access delivered to communities through a satellite backhaul connection and local Wi-Fi network. 

The delivery of live or recorded audiovisual content from an event or production location to a broadcaster, studio or distribution centre.

Maritime connectivity solutions for cruise ships and ferries, supporting operations, passenger services, welfare and entertainment.

Secure, resilient and assured satellite communications for defence users and missions.

Efforts to expand affordable, meaningful access to digital connectivity, skills and services for underserved people and communities.

Television broadcasting delivered by terrestrial transmitters using digital standards.

Television or radio services transmitted by satellite directly to viewers' receiving dishes and set-top equipment.

Satellite connectivity rapidly deployed to support communications after disasters and during humanitarian operations. 

An authorised partner that sells or distributes Eutelsat connectivity services to end customers.

Satellite distribution that delivers television services to terrestrial transmitters, cable headends and IP networks.

A family of open technical standards for digital television transmission by satellite, cable, terrestrial and IP networks. 

The DVB standard for first-generation digital satellite television transmission.

A digital satellite transmission standard offering improved capacity and performance compared with DVB-S. 

During the equinoxes of March and September, the sun passes across the plane of the equator, which means that it is on the same plane as the geostationary orbit. Due to the rotation of the earth, this alignment means that the earth obstructs the sun for certain periods and the solar panels cannot generate energy. The duration of the satellite eclipse gradually changes as the equinox approaches, building up to a maximum of 70 minutes on the day itself. During these periods the satellite's storage batteries are used instead of the solar panels so that the satellite can continue to function normally. 

An on-screen guide that provides programme schedules and metadata and helps viewers discover and select content.

Eutelsat market segment providing fixed and mobile connectivity for organisations, remote operations and underserved communities.

The commercial name used by Eutelsat for its satellite communications activities and corporate website.

The listed holding company of the Eutelsat Group.

The name historically used for Eutelsat’s connectivity business combining GEO and OneWeb LEO capabilities.

Linear-style streaming channels delivered over the internet and funded by advertising.

Maritime connectivity solutions for fishing vessels, supporting operations, safety, crew welfare and data exchange. 

Eutelsat's French satellite platform for receiving digital terrestrial television channels and related services in areas served by satellite. 

Eutelsat market segment providing secure and resilient satellite connectivity for civil government, security, defence and humanitarian missions. 

Satellite connectivity for government-operated aircraft and airborne missions.

A video format with higher spatial resolution than standard-definition television.

Video technology that supports a wider range of brightness and colour, producing more detailed highlights and shadows on compatible displays.

Eutelsat's flagship video neighbourhood at 13° East, served by the HOTBIRD satellite system.

A high-dynamic-range television format designed for broadcast workflows and backward compatibility with standard-dynamic-range displays.

Internet and data connectivity provided to aircraft, passengers and operational systems during flight.

Delivery of broadcast or video content from satellite into an internet-protocol distribution network.

Eutelsat brand associated with high-capacity satellite broadband services and satellites.

A Eutelsat very-high-throughput satellite serving broadband, mobility and government connectivity markets. 

User terminals, antennas and related hardware used to access the OneWeb low Earth orbit network.

Television programming delivered according to a scheduled channel feed.

Eutelsat-operated platforms that support the aggregation, processing and distribution of television or video services.

Eutelsat market segment providing satellite connectivity for vessels, offshore operations and maritime users.

Regional designation covering the Middle East and North Africa.

Maritime connectivity services for commercial cargo and merchant vessels.

The standards group responsible for widely used audio and video coding formats; the term is also commonly used for formats based on its standards.

Delivery and consumption of video content across multiple device types, such as televisions, computers, tablets and smartphones.

Short-duration satellite capacity and services used for live events, news, sports or other temporary broadcast requirements.

Maritime connectivity solutions for offshore support and supply vessels.

A satellite's payload is the element that enables it to fulfill its mission, i.e. for a communications satellite, the reception and processing of signals and their retransmission back to earth. The payload includes the satellite antennas and transponders but not the control, propulsion and electrical power equipment, which is part of the satellite platform (physical structure).

The platform is where all the satellite pointing control, thermal regulation, propulsion and power supply functionality is located. The pointing control equipment has sensors to notify the satellite's orientation to the ground in order to maintain it correctly pointed to the earth. Steering usually employs a chemical or sometimes an electrical propulsion system. In a chemical propulsion system, the platform, in addition to the engines (nozzles), contains tanks of propellant and a pressurising gas (typically helium) which drives the propellant towards the engines. The satellite is powered by photovoltaic cells to convert sunlight into electricity. The solar cells are situated on the satellite's "skin" (in the case of spin-stabilised satellites) or on deployable solar panels. The energy produced by solar cells is stored in batteries. 

The amount of electrical energy fed into or taken from a device or system in a specified time, expressed in Watt or dBW. The signal strength on the uplink or downlink of a satellite communications system is quantified by the power of the radio wave radiated by the transmit antenna.

Enterprise connectivity solutions for retail and financial locations, supporting transactions, applications and business continuity.

Eutelsat's electronic programme guide service helping viewers discover satellite television channels and programmes.

Broadband internet access delivered by satellite to households and small or medium-sized businesses.

Government satellite communications supporting secure operations, public safety and mission-critical connectivity. 

A documented commitment defining measurable service levels, responsibilities and remedies between provider and customer.

Any adapter that converts an external signal into content that can be displayed on a television screen. The Set-Top Box is connected to the TV set using a Scart socket, for example, or an HDMI.

Eutelsat market segment providing satellite backhaul and transmission services to telecommunications operators.

An online Eutelsat tool for finding channels and reception parameters available via Eutelsat satellites.

Video formats with substantially higher resolution than HD, commonly including 4K and 8K formats

The delivery of television or video channels from broadcasters and content providers to platforms, networks or end audiences.

An established orbital position and satellite coverage environment where many television channels are grouped for efficient reception by a large audience.

Maritime connectivity solutions for yachts and leisure vessels, supporting communications, entertainment, safety and operations.

Unwanted electrical interference from signals that are immediately adjacent in frequency to the desired signal. This can arise due to imperfections in the transmission channel and/or equipment.

The process of optimising the orientation of a satellite antenna's main direction of sensitivity towards the satellite to maximise the received signal level and to minimise the chance of receiving unwanted interference from other satellite systems. A commonly-used alternative expressions is "antenna pointing".

A receiving antenna collects noise from radiating bodies falling within its radiation pattern. For an on-ground receiving antenna, this includes contributions from the sky and from the surroundings (the earth). The combined effect of these noise sources is modelled by an equivalent noise temperature for the antenna, which varies with elevation angle and antenna size.

The measure of the weakening of a signal (loss) that occurs as it travels through a device or transmission medium (e.g. radio waves through the atmosphere, an electrical signal through a cable). Attenuation is usually measured in decibels.

The amount of time that the quality of a telecommunication service or communications link equals or exceeds a specified minimum value. For satellite communication links the availability is usually expressed as a percentage of the average year.

The pointing direction of an antenna measured in the local horizontal plane in a clockwise direction from north. It is the horizontal co-ordinate that is used to align a satellite antenna.

The process of selecting one of two frequency bands (the "low band" or the "high band") for reception of satellite signals. Frequency band switching is implemented in dual-band LNBs by changing the frequency of the local oscillator reference signal that is used to downconvert the received signals to an intermediate frequency (IF).

The range of frequencies used for a particular radio transmission (e.g. 36 MHz). It is the difference between the lowest and highest transmission frequencies used by a signal.

A highly stable radio frequency signal, which is used by earth stations equipped with an automatic (satellite) tracking system. Beacons can be generated on-board the satellite, or transmitted from the ground and relayed through the satellite. When generated on-board the satellite, they are also known as satellite or on-board beacons and sometimes carry telemetry signals. 

A directional concentration of radio-frequency energy transmitted or received by an antenna; its intersection with Earth is the coverage footprint.

A technique that dynamically switches satellite capacity among coverage areas to match changing demand.

A measure of the ability of an antenna to focus signal energy towards a particular direction in space (e.g. towards the satellite for a ground-based transmitting antenna), or to collect signal energy from a particular direction in space (e.g. from the satellite for a ground-based receiving antenna). The beamwidth is measured in a plane containing the direction of maximum signal strength. It is usually expressed as the angular separation between the two directions in which the signal strength is reduced to one-half of the maximum value (the -3 db half-power points).

A transparent satellite payload that receives, amplifies, frequency-converts and retransmits a signal without onboard demodulation or routing. 

An overall measure of the quality of a received digital bit stream. It is the ratio of the number of information bits that are received in error to the total number of bits received, averaged over a period of time.

A collection of digital multimedia services marketed as a single package, often transmitted in a single data stream.

Broadcasting Satellite Service. Typically used to refer to a range of frequencies intended for direct reception of satellite television and entertainment services. These frequencies are subject to internationally-agreed regulations that govern their use and are designed to ensure that all countries are able to offer services of this nature. In Europe, the BSS downlink frequency range is 11.7 - 12.5 GHz.

A microwave frequency range used for satellite communications, valued for wide coverage and resistance to rain fade.

Carrier-to-Noise-plus-Interference-Ratio. A measure of the quality of a signal at the receiver input. It is the ratio of the power of the carrier to the combined power of noise and man-made interference, measured within a specified bandwidth (usually the modulated carrier's bandwidth). It is usually expressed in decibels. The higher the ratio, the better quality of the received signal.

Carrier-to-Interference-Ratio. A measure of the quality of a signal at the receiver input. It is the ratio of the power of the carrier to the power of interference arising from man-made sources, measured within a specified bandwidth (usually the modulated carrier's bandwidth). It is usually expressed in decibels. The higher the ratio, the better quality of the received signal.

Carrier-to-Noise-Ratio. A measure of the quality of a modulated carrier at the receiver input. It is the ratio of the power of the carrier to the power of the noise introduced in the transmission medium, measured within a specified bandwidth (usually the modulated carrier's bandwidth). It is usually expressed in decibels. The higher the ratio, the better quality of the received carrier.

A proportion of the satellite's bandwidth and power which is used to establish one or more communication channel.

A band of radio frequencies assigned for a particular purpose, usually for the establishment of one complete communication link, or a path for an electrical signal. This term is often used interchangeably with Transponder, but in general the channel bandwidth is less than the transponder bandwidth.

Polarisation in which the electric field rotates as the radio wave propagates; commonly described as left-hand or right-hand circular.

The circular orbit at approximately 35,800 km above the equator, where the satellites travel at the same speed as the earth's rotation (Geostationary Orbit) and thus appear to be stationary to an observer on Earth. Named after Arthur C. Clarke who first postulated the idea of geostationary communication satellites.

A traffic classification used to apply different forwarding priorities or service treatments.

Satellites operating within the same geostationary orbital control window and appearing from Earth to occupy the same orbital position.

The reception of satellite television and entertainment services for distribution to a group of the general public at one location (e.g. in a block of flats), or through a distribution system covering a limited area (e.g. a local cable network). The receiving system is usually more complex with a larger antenna than that used for individual (Direct-To-Home) reception.

A system for restricting access to a particular service to authorised users only (e.g. subscribers to a particular digital bouquet, purchasers of individual pay-per-view events), by means of encryption and authorised decoding.

The ability and services that enable people, sites, vehicles and devices to exchange data over communications networks.

The geographic area in which a satellite service can be received at the specified quality using suitable equipment.

Interference caused by the modulation of one carrier affecting another signal. It is usually due to nonlinear device operation, which can be caused by overloading an amplifier, and is worsened by signal power level imbalances (e.g. at the receiver input in the head-end of a cable distribution network).

Used to refer to a signal that has the opposite (orthogonal) polarisation to a given signal.

The ratio of the signal power received (or transmitted) by an antenna on one polarisation (the polarisation of the desired signal) to the signal power received (transmitted) on the opposite polarisation. This ratio is usually expressed in decibels. It is a measure of the ability of the antenna to detect (emit) signals on one polarisation and to reject signals at the same frequency having the opposite polarisation.

The ratio of the signal power received (or transmitted) by an earth station on one polarisation (the desired signal) to the signal power received (transmitted) on the same polarisation but originating from a cross-polar signal. This ratio is usually expressed in decibels. It is a measure of interference from cross-polar signals into the desired signal, which occurs in all practical systems that exploit both orthogonal polarisation. Strictly speaking, the terms "cross-polar isolation" and "cross-polar discrimination" have different meanings but are often used interchangeably.

A general term that is commonly used to describe satellites and satellite systems that broadcast information directly to individual end-users.

The radio link from a satellite to an Earth station or user terminal.

The total or partial obscuring of one celestial body by another. The events that most affect satellites are eclipses of the Sun by the Earth or the Moon, which deprive the satellite of its usual source of power (solar energy) and cause it to cool down rapidly because it is no longer heated by the Sun. The satellite is designed to cope with such extreme events. Normally, there is no effect on the communications services provided by the satellite during eclipse. 

A measure of transmitted radio-frequency power in a given direction, combining transmitter power and antenna gain; commonly expressed in dBW.

The angle measured in the local vertical plane between the satellite and the local horizon. It is the vertical co-ordinate that is used to align a satellite antenna.

A differentiated-services traffic class designed for low-loss, low-latency and low-jitter forwarding.

The ratio of the maximum gain of a receiving antenna to the receiving system's equivalent noise temperature. This value is usually expressed in dB/K. It is a measure of the ability of an earth station to receive a satellite signal with good quality (high carrier-to-noise ratio). In general, the G/T increases with increasing antenna diameter.

The assignment of fixed amounts of satellite capacity to particular earth stations regardless of their traffic requirements, which may fluctuate over a period of time.

The geographic area on Earth's surface covered by a satellite beam at a defined signal level.

The use of the same frequency resources in sufficiently isolated beams or polarisations to increase satellite capacity.

In general, this refers to any satellite communication service between earth stations located at fixed geographic positions. However, this term is often used to refer to the "unplanned" frequency bands that are not subject to the internationally-agreed regulations that govern the use of the BSS frequencies. The downlink FSS frequencies in Europe are 10.7 - 11.7 GHz and 12.5 - 12.75 GHz.

A circular equatorial orbit at about 35,786 km altitude in which a satellite appears fixed relative to Earth.

Eutelsat's fleet of geostationary satellites providing wide-area broadcast and connectivity services.

A combination of geostationary and low Earth orbit satellite capabilities within one service or network architecture.

An object orbiting the earth at the earth's rotational speed and with the same direction of rotation. The object will appear at the same position in the sky at a particular time each day, but will not appear stationary if not orbiting in the equatorial plane.

The upper part of the Ku-band downlink frequency range, from 11.7 GHz to 12.75 GHz.

A satellite designed to deliver substantially more capacity than conventional systems, often through spot beams and frequency reuse.

Type of linear polarisation where the electric field is approximately aligned with the local horizontal plane at an on-ground transmission or reception point.

A device that accepts a relatively weak input signal and boosts it to a power level that is suitable for transmission over an earth-space link.

The angle between the plane of the orbit of a satellite and the Equatorial plane. A orbit of a perfectly-geostationary satellite has an inclination of 0 degrees.

An orbit that approximates the geostationary orbit but whose plane is tilted slightly with respect to the Equatorial plane, with the consequence that the satellite appears to move about its nominal position in a daily "figure-of-eight" motion when viewed from the ground. Satellites are often allowed to drift into an inclined orbit near the end of their nominal lifetime in order to conserve fuel on-board the satellite, which would otherwise be used to correct this natural drift caused by the gravitational pull of the Sun and the Moon. 

A physical or logical connection through which a partner network exchanges traffic with the Eutelsat network.

Any undesired signal that tends to interfere with the reception of radio waves. It can be caused by transmissions within the same satellite system, by transmissions within other satellite systems that use the same frequencies, or from ground-based sources (e.g. point-to-point radio links, car ignition noise, etc.). 

Mutual interference between signals spaced apart in frequency after non-linear amplification by a common amplifier. In satellite communication systems the phenomenon of intermodulation is usually only significant after the high power amplifier in an earth station or a satellite transponder. It is controlled by means of the IBO/OBO of the amplifier.

A network of connected physical devices that collect, exchange or act on data.

A indoor device accepting signals from at least one LNB, which recovers the original signal from the signal delivered by the LNB. It includes a built-in decoder for reception of services that are protected by a Conditional Access system, subject to authorisation from the service provider. A plug-in "smart card" is often used for authorisation purposes.

A microwave frequency range used for high-capacity satellite communications and broadband services.

A microwave frequency range widely used for satellite television, data connectivity and mobility services.

The terrestrial network location at which traffic from a user terminal enters the partner or Eutelsat terrestrial network.

The time taken for data to travel through a network, usually measured as one-way or round-trip delay.

An Earth orbit below approximately 2,000 km altitude; LEO constellations can provide low-latency, wide-area connectivity.

An elliptically- or circularly-polarised wave, in which the electric field vector, observed in any fixed plane normal to the direction of propagation, whilst looking in the direction of propagation, rotates with time in a left-hand or anticlockwise direction.

Describes a wave in which the electric field vector, observed in any fixed plane normal to the direction of propagation, maintains a constant direction with time. With linear polarisation, the earth station and satellite antennas of a particular earth-space link must be precisely aligned so that their reference polarisation directions coincide, in order to obtain maximum reception quality.

The lower part of the Ku-band downlink frequency range, from 10.7 GHz to 11.7 GHz.

The difference in decibels between the C/(N+I) achieved at the receiver input under clear sky conditions to the minimum C/(N+I) required for just acceptable transmission quality.

Refers to the multiplexing of a number of digital channels (video programmes, audio programmes and data services) into a common digital bit stream, which is then used to modulate a single carrier that conveys all of the services to the end user. The single carrier supports multiple communication channels, hence the phase "multiple channel per carrier". The term MCPC is frequency used in the context of DVB systems, where the composite digital signal is referred to as a Transport Stream.

A network, service or solution that uses more than one orbital regime, such as GEO and LEO, to combine complementary performance and coverage characteristics.

Generally refers to the use of multiple antenna beams on board the satellite to cover a contiguous geographical area, instead of a single wide-area beam. Multibeam architectures are often considered for satellites operating in the Ka-band, which is characterised by narrower beamwidths with respect to the Ku-band. Single, wide-area beams predominate in the latter.

DVB conditional access option based on a detachable Conditional Access (CA) module, which is supplied by the service provider to each subscriber. The CA module is connected to the subscriber's IRD via a standardised interface (the DVB Common Interface). Multicrypt has the advantage that the same IRD can be used to receive services from providers using different and incompatible conditional access systems.

The ability of a network to maintain or rapidly restore service when components, routes or external conditions fail.

A logically separated network configuration that assigns routing, capacity or service characteristics to a partner or use case. 

Any undesired electrical disturbance in a circuit or communication channel. When combined with a received signal, it affects the receiver's ability to correctly reproduce the original signal.

Any satellite orbit in which the spacecraft does not remain fixed relative to a point on Earth, including LEO and MEO. 

The assignment of variable amounts of satellite capacity to particular earth stations according to their fluctuating traffic requirements (according to demand).

Eutelsat's low Earth orbit satellite constellation providing high-performance, low-latency connectivity.

A satellite's assigned location or longitude in the geostationary arc, commonly expressed in degrees East or West.

Any emission on a frequency or frequencies outside the bandwidth of a signal which results from the modulation process. Out-of-band emissions are a potential source of interference to other services and need to be carefully controlled.

An outage is said to occur when the quality of a telecommunication service or communications link falls below a specified minimum value for acceptable communications performance.

The purchasing of programmes and services by a television viewer or service user on an individual basis (e.g. televised coverage of a sports event).

A physical network location where networks interconnect or users access a provider's network. 

The elevation and azimuth angles which specify the direction of a satellite from a point on the earth's surface.

A value which quantifies the amount by which an antenna is misaligned with the satellite's position in space (see Alignment). This is either expressed as an angular error, or as a loss in signal strength with respect to the maximum that would be achieved with a perfectly aligned antenna.

The orientation or rotation of a radio wave's electric field; satellite systems use linear or circular polarisation to separate signals and reuse spectrum.

Techniques used to manage network traffic and prioritise applications to meet defined performance requirements.

A satellite payload that demodulates and processes signals onboard before remodulating and retransmitting them.

A device that amplifies or augments incoming electrical signals and retransmits them towards the earth station(s) at a different frequency. In the satellite context, the term "repeater" usually refers to all Payload equipment, with the exception of the satellite antennas.

Right-hand polarised wave. An elliptically- or circularly-polarised wave, in which the electric field vector, observed in any fixed plane normal to the direction of propagation, whilst looking in the direction of propagation, rotates with time in a right-hand or clockwise direction. 

Signal-to-Noise Ratio. A measure of the quality of an electrical signal, usually at the receiver output. It is the ratio of the signal level to the noise level, measured within a specified bandwidth (typically the bandwidth of the signal). It is usually expressed in decibels. The higher the ratio, the better quality of the signal. See also C/N.

An artificial spacecraft placed in orbit to relay communications, observe Earth, navigate or perform other missions.

The use of satellites and associated ground systems to transmit voice, video and data.

A radio link between a transmitting earth station and a receiving earth station through a communications satellite. A satellite link comprises one uplink and one downlink.

Eutelsat's combined space and ground infrastructure used to deliver multi-orbit communications services.

The operation of a power amplifier, most often a satellite TWTA, at its maximum output power level ("saturated" power level).

In SCPC systems, each communication signal is individually modulated onto its own carrier which is used to convey that signal to the end user. A number of similar carriers share a common satellite transponder and use a unique portion of its bandwidth. Each carrier supports a single communication channel only (e.g. one-half of a voice circuit), hence the phrase "single channel per carrier".

The radiation pattern of a satellite antenna that has been designed so that its footprint follows the boundary of a specified geographical area (the area of service provision) as closely as possible. Shaped beams maximise the antenna gain over the service area and reduce the likelihood of interference into systems serving other geographical areas.

Simultaneous transmission of an identical programme or service using two or more standards or transmission media. Used to refer to a technique pioneered by Eutelsat for transmitting one broadcast analogue FM television carrier and one digital television carrier in a single satellite transponder that would normally only support the FM TV carrier.

DVB conditional access option based on a commercial agreement between service providers, which allows access to a common population of proprietary IRDs. The IRD hardware is usually specific to the conditional access system and cannot be used to receive services delivered by service providers that are not party to the agreement.

Collective television reception and distribution system serving a local population of users collocated in a block of flats, a hotel or other group-housing complex. SMATV systems use one or more high quality, centrally located antenna to receive the satellite signals, plus UHF and/or VHF antennas to receive local terrestrial broadcast services. The satellite and terrestrial signals are distributed to the end-users via a dedicated cable distribution network. Several different cable distribution architectures are possible.

A satellite whose payload resources and coverage can be reconfigured through software to adapt capacity to changing demand.

The satellite capacity and in-orbit infrastructure used to provide a communications service.

A satellite beam focused on a relatively small geographic area, enabling higher power and frequency reuse.

Any emission on a frequency or frequencies outside the bandwidth of a signal including harmonic emissions, parasitic emissions, intermodulation products and frequency conversion products. Spurious emissions are a potential source of interference to other services and need to be carefully controlled.

An antenna beam that can be repointed by mechanical and/or electrical means. Usually used to refer to relatively narrow satellite beams that can be steered over a part or the whole of the portion of the earth's surface that is visible from the satellite's orbital position.

Sun-Satellite Conjunction can cause a large increase in the noise received by an earth station that is pointed towards the satellite, which degrades the signal quality and can even cause the signal to be lost for a short time. Whilst this is an unavoidable physical phenomenon, it does not affect the relatively small antennas that are used for individual and collective reception of broadcast television and entertainment services.

The transmission of coded signals towards a satellite to initiate, modify or terminate equipment functions on-board the satellite.

Coded radiocommunication from the satellite to the ground for the transmission of data relating to the functioning and configuration of the satellite.

The functions used to monitor a satellite, determine its orbit and send operational commands.

The process of continuously adjusting the orientation of an antenna so that its boresight follows the movements of the satellite about its nominal position. Used in earth stations equipped with large antennas and earth stations operating to satellites in inclined orbit.

A term used to describe satellite systems or satellite transponders that do not alter the basic format of the signals they receive before retransmitting them. A transparent transponder simply converts signals to a lower frequency and amplifies them prior to retransmission, as opposed to regenerative transponders or on-board processing (see Regenerative and OBP respectively).

A satellite payload channel that receives, processes or frequency-converts, amplifies and retransmits radio signals.

An earth station incapable of transmitting to the satellite and intended for the individual or collective reception of television (multimedia) services from the satellite.

The radio link from an Earth station or user terminal to a satellite.

Type of linear polarisation where the electric field is approximately aligned with the local vertical plane at an on-ground transmission or reception point.

A high-throughput satellite designed to provide exceptionally large aggregate capacity, typically using many spot beams and extensive frequency reuse.

A logical network that segments traffic over shared physical network infrastructure.

An encrypted logical network that enables secure communication over shared or public infrastructure.

A more precise definition of horizontal linear polarisation. X-polarisation is defined with respect to a particular direction from the satellite towards the earth, allowing precise calculation of the polarisation alignment angle for any given geographic location.

A more precise definition of vertical linear polarisation. Y-polarisation is defined with respect to a particular direction from the satellite towards the earth, allowing precise calculation of the polarisation alignment angle for any given geographic location.

The process and technical requirements for transmitting to, and receiving from, Eutelsat satellite capacity.

An electronic device used to increase the strength (power) of a signal fed into it.

A device for transmitting or receiving radio waves. Also known as an aerial. In satellite communication systems the antenna usually consists of a parabolic reflector and a feedhorn. In a receiving system the reflector focuses radio waves onto the feedhorn for detection and conversion into electrical signals. In transmitting systems the reflector concentrates the radio waves emitted by the feedhorn into a narrow beam aimed towards the satellite.

The total reflective area of a parabolic antenna (dish) over which radio waves are captured or radiated. The effective aperture is smaller than the physical aperture and is related to it by the Antenna Efficiency.

The ratio of the signal strength transmitted towards or received from a particular direction in space by a real antenna to the signal strength that would be obtained with a theoretically perfect antenna of the same physical size. This ratio is usually expressed as a percentage.

The radiation of electromagnetic energy from the feedhorn to the surface of the parabolic reflector of a transmit antenna, or the focusing of electromagnetic energy captured by the reflector of a receiving antenna towards the feedhorn. With perfect illumination no signal energy is lost to the surrounding terrain. In practice there is always some loss.

The ratio of the width of a television picture or television screen to its height. The ratio for conventional television systems is 4:3. In advanced television systems (e.g. widescreen) the ratio is usually 14:9 or 16:9, which better approximate the aspect ratio used in cinema.

A passive device that weakens a signal that passes through it. The amount by which the signal power is reduced is usually expressed in decibels.

A circuit or device that allows only a specified range of frequencies to pass from input to output, rejecting all signals at lower or higher frequencies.

A twist-lock coaxial connector that is commonly used on commercial video equipment and on some brands of satellite receiver.

Earth station transmitter combining signal up-conversion and power amplification in a single unit, normally located directly at the antenna input, or close to it. 

A cable consisting of an inner insulated core of stranded or solid wire surrounded by an outer insulated flexible wire braid. Used principally as a transmission line for radio frequency signals with low loss. Commonly shortened to Coax. Sometimes referred to as screened cable because the outer braid screens the inner conductor from electrical interference.

A circuit or device that restores a coded signal to its original form based on knowledge of the process used to code the signal.

A device that recovers the original signal from a modulated carrier signal, such that the characteristics of the original are faithfully reproduced. Implements the process of Demodulation.

A device that recovers the original signal from one that has been rendered unintelligible by Scrambling.

A device that converts a digital signal (a series of numbers or other characters) into its equivalent analogue form (a continuously-varying signal voltage).

A device that splits a collection of signals into two groups according to the frequency range in which they are located, or combines two groups of signals, each occupying a separate frequency range, into a single collection of signals.

Digital Satellite Equipment Control. A standardised method for two-way communication between devices in satellite reception systems. Information is exchanged between devices interconnected by standard coaxial cable by means of a modulated 22 kHz tone. DiSEqC™ is a trademark of Eutelsat.

Parabolic microwave antenna used for transmitting and/or receiving satellite signals. The term is derived from the shape of the reflector surface, but is taken to mean the whole of the antenna subsystem, including the feedhorn and the antenna structure.

A device for converting the frequency of a signal to a lower frequency.

An antenna system consisting of a reflector, a support structure and two LNBs, each equipped with a separate feedhorn or sharing an integrated feed assembly. The focal point of each feed is set so that the antenna system can receive from two different satellite orbital positions simultaneously. The angular separation between satellite positions is usually around 6 degrees, although other angles are possible.

A feedhorn that can simultaneously receive signals in two different frequency bands, for instance the C-band (4 GHz) and the Ku-band (11/12 GHz).

A ground-based installation that transmits signals to, receives signals from, or communicates through satellites.

The ratio of an antenna's focal length to its diameter. It describes the basic geometric architecture of the antenna, which affects its physical size, its design and its electrical performance.

A standard, low-cost RF connector used to terminate the coaxial cables that interconnect satellite reception equipment (e.g. for connecting the LNB output to the satellite receiver's input).

A device resembling a horn that emits radio waves in a concentrated beam or collects and focuses radio waves that are incident on its aperture. In a receiving system it collects microwave signals reflected from the surface of the antenna. In a transmitting system it directs microwave signals onto the reflector surface for focussing into a narrow beam aimed at the satellite. The feed is mounted at the focus of the parabolic reflector. It is usually designed to match a particular antenna geometry (F/D ratio).

A device that blocks signals or radiation of certain frequencies while allowing others to pass unaltered.

The distance from the reflective surface of an antenna to its focal point, usually measured in the horizontal plane. Incoming satellite signals are directed to the Feedhorn which is normally located at the focal point. See also f/D ratio.

A ground facility that connects a satellite network to terrestrial networks and routes user traffic between them.

The Earth-based infrastructure, systems and operations used to control satellites and connect them with terrestrial networks and users.

A terrestrial facility equipped to communicate with satellites; it may perform telemetry, tracking, control, gateway or service functions.

An amplifier in a (long) transmission line that boosts the strength of a signal to an exploitable level.

An active or passive device that divides a signal into two or more signals containing all the original information. A passive splitter feeds an attenuated version of the input signal to the output ports. An active splitter amplifies the input signal to overcome the splitter loss.

A device that receives and amplifies weak satellite signals at the output of a feedhorn, whilst introducing as little electrical noise as possible in the process. The frequency of the incoming signal is unchanged at the output of the device. The feedhorn is typically a physically separate device.

Equipment mounted near a satellite dish feed that amplifies received signals and converts them to a lower frequency for the receiver.

A device which superimposes the amplitude, frequency or phase of a wave or signal onto another wave or signal (a carrier), which is then used to convey the original signal via a transmission medium (e.g. satellite link).

An antenna having a feedhorn that is offset from the centre of the reflector. It generally offers better performance than a symmetrically-fed antenna because the feed system does not block the main reflector aperture.

A LNB that is slightly displaced with respect to the focal point of the reflector so that it receives signals originating from a different direction to that obtained with an LNB placed at the focal point. A technique used in dual-feed reception systems, which receive signals from satellites located at two different orbital locations.

A dish-shaped antenna that uses a parabolic reflector to focus radio-frequency signals. 

A device that amplifies a weak signal for subsequent processing, which may include further signal amplification. In an SMATV system, it is the amplifier mounted adjacent to an antenna to increase the strength of the signal prior to its processing at the headend.

An LNB providing four outputs simultaneously. It is used to deliver signals received on both linear polarisations (horizontal and vertical) and in both frequency bands (high and low). Each output delivers the signals received on one polarisation and in one frequency band. It is used in collective reception systems to ensure that all services are available to all subscribers, regardless of the service (TV programme) selected by any individual.

The equipment that receives incoming electrical signals or modulated radio waves and converts them into the original audio, video or data signals.

A receiver designed for satellite reception system, which receives modulated signals from an LNA or LNB and converts them into their original form suitable for direct presentation to the user.

Also known as Euroconnector or Peritel. Twenty-one-pin connector commonly used in Europe to interconnect satellite receivers, television sets and other audiovisual equipment (e.g. videocassette recorders).

A device that renders a signal unintelligible and/or randomises its content.

A device that takes an input signal and splits it into two or more identical output signals, each a replica of the input signal but with a different amplitude (typically).

A high power amplifier using solid state technology (i.e. transistors). Used for low and medium power applications.

A satellite ground facility hosting antennas and network equipment that connects satellite capacity with terrestrial networks and services.

A high power amplifier based on tube technology. Normally employed when high output power levels are required.

An LNB that is capable of receiving a signal transmitted on any linear polarisation and at any frequency within the range 10.7 - 12.75 GHz, usually by means of band and polarisation switching.

Any undesired emission resulting from the radiocommunication process, which could potentially interfere with other systems. Formal definition: the combination of spurious emissions and out-of-band emissions.

A device for converting the frequency of a signal into a higher frequency.

Equipment at a customer site, vehicle, aircraft or vessel that connects to the satellite network.

A compact satellite earth station, typically using a small dish, for two-way data, voice or video communications.

A device for converting an analogue voltage waveform into a series of digital numbers so that the signal can be manipulated numerically ("digitally processed").

One of the methods for transmitting information using radio waves by superimposing the information signal onto a radio frequency carrier wave. The amplitude of the carrier wave is varied in accordance with the time-varying amplitude of the input signal. The frequency of the carrier wave remains unchanged.

A system in which one continuously-varying physical quantity (e.g. the intensity of a sound wave) is represented directly by another (e.g. the voltage of an electrical signal) as faithfully as possible.

The process of Modulation, where the modulating wave or signal is analogue and the amplitude, frequency or phase of the carrier wave or signal is varied continuously according to the content of the modulating signal.

A defined interface that allows software systems to exchange data and functions.

An error detection and correction technique based on the transmission of data in discrete packets. A decoder in the receiver detects errors but cannot correct them. Instead it sends a retransmission request to the transmitter which then repeats the transmission.

A carrier signal modulated by a sound signal, where the carrier frequency is slightly higher than the maximum frequency encountered in a video signal. This signal is combined with a video signal and the combination is used to modulate a radio frequency carrier for subsequent transmission over a satellite link. The signal is referred to as a subcarrier because it is itself modulated onto a carrier.

The range of frequencies occupied by the source electrical signal that is to be transmitted over a radiocommunications link. It is the frequency band occupied by an analogue or data signal prior to modulation and frequency conversion, or after frequency conversion and demodulation. For example, the baseband of a video signal extends from 0 Hz to about 5 MHz.

A technique that controls an antenna array to focus radio-frequency energy in selected directions, improving coverage and reducing interference.

The process of converting the frequency of an entire block of radio frequency signals received from the satellite to a lower intermediate frequency (of around 1 GHz). This permits subsequent processing of the signals within a satellite receiver, including selection of the desired signal from the available block of signals.

A pure frequency signal that is used to convey information through a transmission channel. The key characteristics of the carrier signal (frequency, amplitude or phase) are varied according to the content of the information. These variations are detected at the receiver and are used to reconstruct the original signal.

A technique allowing multiple users to simultaneously share a common transmission bandwidth. Each user transmits continuously, generating a controlled level of interference into other users. Each transmitter is assigned a unique signature, or code, which is combined with the useful information at the transmitter. The receiver is able to recover the desired information and reject unwanted information by means of this unique code.

The process of deliberately adding redundant information to a message at the transmit end of a transmission link so that errors can be detected and corrected at the reception point. The term "channel" is used to indicate that the encoding is specifically related to the transmission channel and to distinguish it from any other encoding used in the system (e.g. for digital image compression).

The colour information of a television picture. It is also used to refer to the modulated colour component of a PAL, SECAM or NTSC television signal.

The ratio of the number of bits in a data stream that carry useful information to the total number of bits, including those added for error correction purposes. For example, a code rate of ¾ indicates that ¾ of the bits carry useful information and ¼ of the bits are used to detect and correct errors in the receiver, after which time they are discarded.

A signal obtained by subtracting the brightness (luminance) information of a television picture from the primary colour information (red or blue). Two colour difference signals (red and blue) are conveyed in a PAL, SECAM or NTSC picture. The third (green) can be deduced in the television receiver from these two colour difference signals and the brightness information.

A digital technique for reducing the information needed to represent a still image, a moving image or an audio signal without undue impact on the subjective quality of the processed material. The most important information is retained, whilst repeated or unnecessary information ("redundant" information) is discarded. Such techniques are used to reduce the capacity needed to store and/or transmit photographic, video and audio information.

Interference received in one communication channel from signals conveyed by other communication channels.

A baseband television signal containing the picture information (luminance and chrominance) plus all the synchronization signals necessary to display a fully-locked television picture.

A reduction in the amplitude of the higher frequency portions of a frequency modulated signal (e.g. analogue television) and its accompanying noise after transmission via a radio link. De-emphasis is used in conjunction with a complementary Pre-Emphasis device in the transmitter so that their combined effect on the signal is neutral. The pre-/de-emphasis process improves the signal-to-noise ratio for high frequency signal components and thus the overall quality of the received signal.

The process of restoring a coded signal to its original form based on knowledge of the encoding process.

The act or process by which an output wave or signal is obtained from a carrier wave or signal, where the recovered wave or signal has the characteristics of the original modulating wave or signal. The reverse process of Modulation.

The extraction of multiple distinct messages or signals from a single composite signal ("multiplex").

The process of Modulation, where the modulating wave or signal is digital and the amplitude, frequency or phase of the carrier wave or signal is varied in discrete steps according to the content of the modulating signal.

A signal that represents information using discrete values, enabling robust processing, compression and transmission.

The process of converting the frequency of a signal to a lower frequency. Downconversion is performed at the reception point to permit the recovery of the original signal. See also Upconversion and Frequency Conversion.

Radiation produced, or the production of radiation, by a radio transmitting station, which can be an earth station or a satellite.

The process of converting a message into a code that is designed to achieve a particular purpose (e.g. error detection and correction, bit rate reduction).

The process of "locking" a signal using secret information so that it can only be deciphered by an authorised recipient who is in possession of the appropriate secret "key". This process is used in Conditional Access systems as a mechanism for controlling and managing subscribers to a particular service or range of services.

The process of reconstructing digital information that has been corrupted in the data transmission process. There are two basic variants of error correction: FEC and ARQ. Error correction requires the detection of erroneous data based on observation of the received data. 

The process of detecting erroneous digital information after data recovery in the receiver. Erroneous information usually results from transmission errors. Error detection exploits the properties of a code applied to the data in the transmitter.

Conditional access system used mainly with the D2-MAC television transmission standard.

A system in which signals are each allocated a unique portion of a shared frequency range. Each individual signal is modulated and translated in frequency so that it occupies the correct frequency segment of the composite signal spectrum and does not interfere with the other signals sharing the same band of frequencies. Individual signals are recovered from the composite signal by filtering. FDM is used, for example, to convey multiple television signals in a cable distribution system. 

A method allowing multiple carriers to share a single satellite transponder or range of frequencies. The transponder bandwidth is divided into sub-channels, each of which is allocated to a particular earth station (carrier). The earth stations transmit continuously and the transponder conveys several carriers simultaneously at different frequencies.

An error detection and correction technique based on the addition of a code to the signal at the transmitter. A decoder in the receiver detects and corrects errors making use of the properties of this code. The amount of coding information added to the original signal is quantified by the Code Rate.

One of the principal methods for transmitting information using radio waves by superimposing the information signal onto a radio frequency carrier wave. The frequency of the carrier wave is varied in accordance with the time-varying amplitude of the input signal. The amplitude of the carrier wave remains unchanged

One complete TV picture, composed of two fields and a total of 525 and 625 scanning lines in NTSC and PAL systems, respectively.

The number of cycles of a periodic signal per second, measured in hertz (Hz).

The process of altering the frequency of a signal so that it is suitable for transmission or other processing.

In radio communication systems, frequency conversion from baseband to the transmission frequency, and from the reception frequency to baseband, is usually carried out in two or more stages. Any frequency obtained after a frequency conversion that does not correspond to the baseband, the transmission frequency or the reception frequency is known as an intermediate frequency. In satellite reception systems the term IF is often used to refer to the frequency range in which the LNB delivers the signals it receives from the satellite (950 - 2150 MHz) to the IRD.

The process of scanning a single image ("frame") of a moving picture sequence in two sequential stages, where each stage produces a scanned image ("field") comprising one-half of the total number of horizontal lines used in the scanning process. The lines of each field alternate. It is a technique that is used in conventional television systems (e.g. PAL) to reduce the transmission bandwidth by exploiting the properties of the human eye.

A group established by the International Organization for Standardization (ISO) that developed a widely-used international standard for the coding of still pictures. The term "JPEG" is often used to refer to the coding method itself, which reduces the information needed to represent the picture with good quality.

The brightness information of a television picture. It is also used to refer to the brightness component (Y signal) of a PAL, SECAM or NTSC television signal.

The frequency range from approximately 1 to 300 GHz, covering the frequency range suitable for satellite communications.

The process of varying a carrier signal to encode information for transmission.

A widely-used video compression standard. See MPEG.

The simultaneous sharing of a common transmission bandwidth by multiple users. In satellite communications, it usually refers to the shared use of one or more transponders by multiple earth stations.

A signal that comprises multiple distinct signals or messages, usually for the purposes of transmission via a common communications channel.

The use of a common communications channel for sending two or more messages or signals (e.g. multiple digital television programmes on a single digital carrier, or "multiplex"). Multiplexing is the process of combining multiple signals into a composite signal that is suitable for transmission via the common communications channel.

An antenna made of multiple radiating elements whose relative phases are controlled to steer the beam electronically.

Electromagnetic frequencies used for wireless communications, including satellite links. 

A unit of information representing the physical state of a system having one of two values, such as on or off.

Number of bits of information transferred or transmitted every second.

Alternative expression for bit/s.

A sequence of bits processed as one unit of information. A byte is a digital "word" normally consisting of eight bits.

Units used to express the Figure of Merit or G/T of an earth station, with the dimensions of 1/kelvin, expressed on the decibel logarithmic scale.

The relative gain of an antenna with respect to an equivalent isotropic antenna, expressed on the decibel logarithmic scale.

The power of a signal in watts, expressed on the decibel logarithmic scale.

Power of a radio wave incident on a surface area of one square metre, measured in watts and expressed on the decibel logarithmic scale.

A unit for comparing two currents, voltages or power levels based on a logarithmic scale. It is used particularly for expressing the difference between very large and very small values (expression: R = 10*log10(r), where r is the linear ratio and R is the ratio in dB).

A range of frequencies used for transmission or reception of radio waves (e.g. 10.7 GHz to 12.75 GHz).

A particular distribution of electromagnetic radiation with frequency, which is characteristic of the source of the emission. In satellite communication systems, the spectrum of a transmitted signal depends upon the modulation scheme employed. The term "frequency spectrum" is also used more generally to refer to a continuous range of frequencies.

Unit of frequency equal to 1,000,000,000 Hz.

High Definition TV has a screen ratio of 16:9, and is normally provided with 5.1 independent channels of CD-quality stereo surround sound (also referred to as AC-3). The video signal enables an increased image resolution by offering up to 1080 active lines and 1920 pixels per line, instead of the 576 lines and 720 pixels per line provided by the PAL TV standard. The increased resolution at progressive scan instead of interlaced makes the picture extremely sharp.

The SI unit of frequency, equivalent to one cycle per second. The frequency of a periodic phenomenon that has a periodic time of one second.

Information transfer rate, equal to 1,000 bit/s.

Basic SI unit of thermodynamic temperature.

Unit of frequency equal to 1,000 Hz.

Information transfer rate, equal to 1,000,000 bit/s.

Unit of frequency equal to 1,000,000 Hz.

Unit of data transmission rate for a radio link, equal to 1,000,000 symbol/s. Can be directly related to the bandwidth required to establish the transmission link (e.g. 33 MHz for a transmission rate of 27.5 Msymbol/s).

A unique signal state of a modulation scheme used on a transmission link, which conveys one or more information bits to the receiver.

The number of symbols transmitted every second.

Coordinated Universal Time. A time-scale which forms the basis of a coordinated dissemination of standard frequencies and time signals throughout the world.

SI unit of power, equal to 1 joule/second.