pinkhelmets
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]]Satellites in Space[[
TV broadcast satellites are placed in orbit directly above the equator at a height of around 36000km. They travel through space at the same speed the earth's rotation - so to us on the ground the satellite appears to be stationary. This is known as a geo-synchronous (or geo-stationary) orbit.
Ground controllers fire on-board jet thrusters occassionally to keep the satellite in the specified position in space. This is the major factor in determining the 'life' of a satellite, as onboard fuel does eventually run out.
In Europe the orbital location of a satellite on the Clark Belt is given by the number of degrees to the East or West of due South (for example: Astra 1 = 19.2°E, Hispasat = 30°W). This is the Azimuth.
]]The Clarke Belt[[
The idea of geo-stationary satellites was first suggested by Arthur C Clarke in an article written for Wirless World magazine in October 1946.
The region in space occupied by these satellites is commonly referred to as 'The Clarke Belt'
]]Getting signals to and from the Satellite[[
Television and radio programme signals are sent from the various originating studios to an Earth up-link station. From there the gathered 'bouquet' of programmes is transmitted into space using a dish aimed at the orbiting spacecraft. This is known as the 'up-link'. The frequency is about 14GHz (in Europe)
The satellite receives these signals, amplifies them and transmits them back towards earth on a different frequency. This work is done by a transponder. This 'down-link' operates at about 11GHz (in Europe), in the so-called Ku microwave band).
A group of satellites in the same orbital position (such as Eutelsat's 'Hotbird') may have a combined total of more than 70 transponders. A transponder rebroadcasts 1 analogue TV channel or as many as 14 digital TV channels (this depends on the digital compression techniques used:- lower compression = less channels = better pictures).
This kind of broadcasting is known as DTH (Direct-to-Home broadcasting).
Each satellite has a massive array of solar cells. Some satellites are cube-shaped and have huge wing-like solar cell arrays extending from the main body, while others are cylindrical and have their entire surface coated with solar cells. The cells convert sunlight into electricity to operate the satellite, providing power for the transponders and to maintain the charge on the standby batteries for the times when the satellite is in the shadow of the Earth.
The satellites used for radio and television broadcasting are not usually owned by the broadcasting companies.
Broadcasters lease the technical facilities from the satellite owner. In Europe the two major satellite providers are Eutelsat and SES-Astra.
The earth stations required to send the programmes up to the satellite (called the 'up-link') are provided by a variety of organisations in many many different countries. Some of these are commercial organisations (eg BT in UK) and some are government agencies (eg national PTT authorities).
TV broadcast satellites are placed in orbit directly above the equator at a height of around 36000km. They travel through space at the same speed the earth's rotation - so to us on the ground the satellite appears to be stationary. This is known as a geo-synchronous (or geo-stationary) orbit.
Ground controllers fire on-board jet thrusters occassionally to keep the satellite in the specified position in space. This is the major factor in determining the 'life' of a satellite, as onboard fuel does eventually run out.
In Europe the orbital location of a satellite on the Clark Belt is given by the number of degrees to the East or West of due South (for example: Astra 1 = 19.2°E, Hispasat = 30°W). This is the Azimuth.
]]The Clarke Belt[[
The idea of geo-stationary satellites was first suggested by Arthur C Clarke in an article written for Wirless World magazine in October 1946.
The region in space occupied by these satellites is commonly referred to as 'The Clarke Belt'
]]Getting signals to and from the Satellite[[
Television and radio programme signals are sent from the various originating studios to an Earth up-link station. From there the gathered 'bouquet' of programmes is transmitted into space using a dish aimed at the orbiting spacecraft. This is known as the 'up-link'. The frequency is about 14GHz (in Europe)
The satellite receives these signals, amplifies them and transmits them back towards earth on a different frequency. This work is done by a transponder. This 'down-link' operates at about 11GHz (in Europe), in the so-called Ku microwave band).
A group of satellites in the same orbital position (such as Eutelsat's 'Hotbird') may have a combined total of more than 70 transponders. A transponder rebroadcasts 1 analogue TV channel or as many as 14 digital TV channels (this depends on the digital compression techniques used:- lower compression = less channels = better pictures).
This kind of broadcasting is known as DTH (Direct-to-Home broadcasting).
Each satellite has a massive array of solar cells. Some satellites are cube-shaped and have huge wing-like solar cell arrays extending from the main body, while others are cylindrical and have their entire surface coated with solar cells. The cells convert sunlight into electricity to operate the satellite, providing power for the transponders and to maintain the charge on the standby batteries for the times when the satellite is in the shadow of the Earth.
The satellites used for radio and television broadcasting are not usually owned by the broadcasting companies.
Broadcasters lease the technical facilities from the satellite owner. In Europe the two major satellite providers are Eutelsat and SES-Astra.
The earth stations required to send the programmes up to the satellite (called the 'up-link') are provided by a variety of organisations in many many different countries. Some of these are commercial organisations (eg BT in UK) and some are government agencies (eg national PTT authorities).