Communication Satellites

Section 1 of 6Waves used for communication

Radiation	Examples of use
Radio waves	Bluetooth, terrestrial television, local radio stations
Microwaves	Mobile phone masts, wireless internet, communication satellites
Visible light or infrared	Optical fibres

Section 2 of 6Types of satellite orbit

Geosynchronous

• Geosynchronous Takes 24 hours to orbit the Earth, the same time the Earth takes to turn once.
• It returns to the same position above the Earth once a day, so it is in contact with a given base station only once every 24 hours.

Geostationary

• Geostationary Also has a 24 hour orbit, but stays directly above the equator and travels in the same direction as the Earth spins.
• It therefore stays above one fixed point on the surface and is in constant contact with its base station.

Uses

• Uses Geostationary satellites are used for telecommunications and for television broadcasts.

Section 3 of 6Sending a signal round the world

1Ground station transmits

• Ground station transmits A base station sends a microwave signal up to a satellite.

2Satellite receives

• Satellite receives The satellite picks up the signal and amplifies it.

3Relay

• Relay The signal is passed on to another satellite, or sent straight back down.

4Receiving station

• Receiving station A base station in another region receives the microwaves and passes on the information.

Section 4 of 6Why three satellites

Global coverage

Line of sight

• Line of sight Microwaves travel in straight lines and do not bend round the curved Earth, so one satellite sees only part of the surface.

Spacing

• Spacing Three geostationary satellites spaced evenly around the equator can each cover a region, with overlaps between them.

Linking stations

• Linking stations A signal can pass between satellites, so base stations on opposite sides of the Earth can communicate.

Section 5 of 6Key terms

Term	Meaning
Satellite	An object that orbits a larger body, such as the Earth.
Geostationary orbit	An orbit above the equator with a 24 hour period, so the satellite stays above one point on the Earth.
Geosynchronous orbit	An orbit with a period of 24 hours, matching the Earth's rotation.
Orbital period	The time taken to complete one orbit.
Base station	A ground station that sends signals to and receives signals from satellites.

Section 6 of 6Exam technique

1

Saying a geostationary satellite does not move: it does move, at the same angular speed as the Earth's rotation.

2

Confusing the two typesonly geostationary satellites are above the equator and always in contact.

3

Describing the satellite signal as radio waves from the base station: satellite links use microwaves.

4

Thinking one satellite is enough for global coverage: at least three are needed.

5

Giving an orbital period of one hour or one year instead of 24 hours.