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Question:

What type(s) of electromagnetic waves are used for communication?

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The radio and microwave spectrum is divided into frequency bands.

The higher the frequency of the wave:

• the more information they carry.• the shorter their range• the less they spread out (diffract)

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Wave bands

Waveband Frequency range Use

Microwave +3000 MHz Satellite TV, phones

UHF (ultra-high frequency)

300-3000 MHz Terrestrial TV, Mobile phones

VHF(very high frequency)

30-300 MHz Local Radio, emergency

services

MF(medium

frequency)

300 kHz – 3 MHz National Radio (analogue)

LF(low frequency)

Less than 300 MHz International Radio (analogue)

Radio waves are not absorbed strongly by walls, which is why radio (and television) signals can be received indoors.

In some areas, the reflection of waves off other buildings or hills can actually lead to improved radio reception.

Tall objects, like buildings and hills, can prevent radio waves travelling directly from a transmitter, but this is not always a problem.

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Higher frequency radio waves (3–30

MHz) are reflected off the ionosphere high in the atmosphere. These sky waves are used for international and amateur radio.

The ionosphere is stronger in the summer than winter so you can listen to radio stations from a greater distance.

Low frequency (up to 3 MHz) radio waves travel along the Earth’s surface and can travel hundreds of miles. These ground waves are used for local and national radio.

ionosphere

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Microwaves are very high frequency radio waves (over 30

MHz).

This means that they can be picked up by satellites and transmitted over very large distances right round the Earth.

Unlike other radio waves, they are not reflected by the ionosphere but pass straight through and into space.

ionosphere

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In your own words:

1.Describe the difference between using radio waves and microwaves for communication.

2.Explain how the ionosphere is used for communication. Draw a diagram to support your explanation.

Think about other methods of sending a signal between two locations.

Optical fibres are increasingly being used for communications instead of traditional copper wires.

They are cheaper.

Optical fibres have a number advantages over copper wires:

They are thinner and lighter.

Signals can travel further.

Not affected by electromagnetic signals so no interference.

Several digital signals can be carried by one fibre.

Signals do not weaken as much while they travel.

More secure – they are almost impossible to bug.

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Are you now able to….

I still feel unsure. I need some more help to understand.

I feel ok. I need to do some more work to check my understanding.

I am happy and feel I understand and can explain the main points.