6. Television satellites

Satellites in geosynchronous and geostationary orbit can illuminate entire continents with their antennas. This coverage makes it an ideal platform for broadcasting television (and radio).

 

A television satellite has a large number of 'transponders'. These receive the original television signal from an earth station, amplify it to high power then broadcast it to customers on the ground. These are called 'Direct Broadcast Satellites' or DBS.

When a satellite is constructed, it includes a number of spare transponders to allow for failures over the lifetime of the satellite. Although this does put the launch cost.

The earth stations are usually owned and operated by the satellite company itself whilst the television companies rent the channels they need.

Satellites can broadcast hundreds of channels because each transponder has a very wide bandwidth. Compression is also used to squeeze even more tv channels within the bandwidth available.

Satellites signals come in two forms. Namely 'free-to-air' which means anyone with the right set-top box can view the programmes. 'Freesat' is a free-to-air television service run by the BBC and ITV. It offers over 150 channels including HD tv.

The other type is an 'encrypted' paid service such as Sky. Subscribers pay a monthly fee to view these channels. For example, on offer are movie channels, children's tv, foreign channels, sports.

Another option is 'pay-per-view' where you just pay to see a particular film or programme.

In order to view a satellite channel, you need an satellite dish fitted to the outside wall or roof that points to the satellite. This picks up the signal, amplifies it and sends it to a set-top box. The set-top box converts the signal to a standard television signal.

The most well known system in the UK are the Astra satellites. But using a recent satellite magazine to count how many others were visible over the horizon - there were 51 other TV satellites in view. If you had the correct antenna, line of sight and decryption cards there are thousands of tv channels available in many languages - Polish, Czech, French, Portuguese, German, Arabic etc.

 

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Click on this link: Television satellites.