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Science

Sound and light

Communicating with waves: radio waves and microwaves

Radio waves, microwavesmicrowaves: Electromagnetic radiation with a frequency between that of visible light and radio waves., visible light and infrared can all be used for communication. You should know some typical examples of these, and associated hazards.

Radio waves

Radio waves are used to transmit television and radio programmes. Television uses higher frequencies than radio.

A radio programme receiver does not need to be directly in view of the transmitter to receive programme signals. Diffractiondiffraction: The spreading out of waves when they pass through a gap or around an obstacle. allows low-frequency radio waves to be received behind hills, although repeater stations are often used to improve the quality of the signals.

The lowest frequency radio waves are also reflected from an electrically charged layer of the upper atmosphere, called the ionosphere. This means that they can still reach receivers that are not in the line of sight because of the curvature of the Earth's surface.

microwaves pass through the atmosphere, radio waves relected through a charged layer of the upper atmosphere, signal received even though transmitter and receiver are not in the line of sight

Microwaves and radio waves in the atmosphere

Microwaves

A picture showing a mobile phone mast on a brick bulding

A mobile phone mast - an example of a microwave transmitter

Microwave radiation can also be used to transmit signals such as mobile phone calls. Microwave transmitters and receivers on buildings and masts communicate with the mobile telephones in their range. Some people think that mobile phones, which transmit and receive microwaves, may be a health risk. This is not accepted by everyone, as the intensity of the microwaves is too low to damage tissues by heating, and microwaves are not ionising.

Certain microwave radiation wavelengths pass through the Earth's atmosphere and can be used to transmit information to and from satellites in orbit. Satellite television signals use microwaves.

Watch

There is concern that microwave radiation from mobile phones and masts may be harmful to health. You may wish to view this BBC News item (2006) about this issue.

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