Communication Satellites (WJEC GCSE Physics: Combined Science)

• Many important methods of communication rely on long wavelength electromagnetic radiation, including:
  • Bluetooth, terrestrial television signals & local radio stations (using radio waves)
  • Signals from mobile phone masts, wireless internet & communication satellites (using microwaves)
  • Optical fibres (using visible or infra-red waves)

• Communication satellites orbit the Earth and can communicate with base stations on the Earth's surface to relay information around the Earth
• There are two different types of communication satellites:
  • Geostationary satellites
  • Geosynchronous satellites

Different Types of Communication Satellites

Geostationary and geosynchronous satellites orbiitngs around the Earth

Geosynchronous Satellites

• The orbital period of a geosynchronous satellite is 24 hours which is in sync with the orbit of the Earth
• A geosynchronous satellite will be in the same position above Earth once every 24 hours
  • It is therefore only in communication with a base station on the surface of Earth once every 24 hours

Geostationary Satellites

• A geostationary satellite also has a geosynchronous orbit, i.e. it takes 24 hours to orbit the Earth
• A geostationary satellite:
  • Remains directly above the equator and orbits in the same direction as the Earth spins
  • Therefore, it always orbits at the same point above the Earth’s surface
  • Is in constant communication with its base station

A Geostationary Satellite in Orbit

Geostationary satellites orbit the Earth every 24 hours above a fixed position on the Earth's surface

• Geostationary satellites are used for telecommunication and television broadcast
• Base stations on Earth send the microwave signals to satellites which relay them back to the desired locations
• A minimum of 3 satellites located around the Earth is required for global coverage
• Signals can be transmitted across the globe by travelling between ground base stations via satellites

Using Geostationary Satellites to Transmit Information

Information can be transmitted across the Earth using three geostationary satellites