Electromagnetic Spectrum
Wave Properties
Radio Waves
Reflection and Refraction

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Communication Systems

Composition of Communication Systems

Communication systems can be broken down in to several components, each with its own specific function. The table below explains these key components and what they do.

Encoderconverts information to a form that can be sent.
Modulatorvaries the wave carrying the signal.
Decodertranslates information to a form that can be understood.
Storagewhere information is held.
Transmittersends signals from one place to another.
Receiverpicks up the signal that has been sent to it.
Transducerchanges signal from one form to another.
Amplifierincreases the amplitude of a signal.

The diagram below demonstrates a system by example of speech.

communication system of speech comprising transmission, encoder, modulator, receiver and decoder.

Transmitting and Receiving

A common method of transmission is fibre optic cables, they are simply wires that carry light. They are used for internet transmission and there are huge networks under the oceans.

The signal along these is digital. A digital signal is either 'on' or 'off' compared to an analogue signal which has a variety of different values.

Signal quality can be reduced in transmission by attenuation where the signal becomes weaker with distance from losing energy. Or noise where the amplitude is distorted.

comparison of digital and analogue signals

Because of attenuation the signal must be amplified by repeaters, but in an analogue signal this means the noise is also amplified and hence the resultant signal received is of poorer quality.

However because of the simplicity of a digital signal it can undergo regeneration to it's original form. It is for this reason that digital signals are seen as better than analogue.

Storage: Computer Disks

As explained above, digital information is either 'on' or 'off' and so could be represented as either 1 or 0, this forms the basis of binary code that is used as the basis for computing.

A CD has a series of bumps on it that represent 1 or 0, these are read using light. See the diagram below.

basic diagram of a CD

The diode laser emits a small beam of concentrated light (laser beam) on to the disk surface. This is then reflected back and can be detected by the photodiode by a change in the intensity of the light reflected. This is why if there is a scratch on your CD surface it could interfer with the quality.