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Communication

There are various forms of electromagnetic radiation that can be used to communicate between two places.

All forms of electromagnetic radiation suffer from attenuation this is the loss of energy with distance. Attenuation reduces the signal as the travels from the transmitter and receiver. The signal needs to be amplified every so often by 'repeater' stations.

(a) Radio
We are all familiar with radio communication long wave (1500m) to FM (wavelength about 3m). You will also now probably use DAB (Digital Audio Broadcasting).

 


(b) microwaves used for satellite links and mobile phones. Using microwaves rather than cables for sending signals is that you don't have to get permission to transmit a signal across someone else's land. However some people may object to having a mobile phone mast near their house.

A disadvantage is that the path between stations must be clear and free from obstacles 'line of sight' and microwaves are also affected by weather particularly rain (microwaves are absorbed by water see Microwave ovens). Microwave dishes are often placed in groups on a tower in cities and these towers have become a familiar feature on city skylines. The photograph is of the Post Office tower in London.
(c) infra red used for relatively short distance communication in remote controllers for TVs, CD players and computer mice. Infra red lasers are used to send beams down optical fibres. Communication by infrared is interference free and it is therefore used in high security local communication networks. Most of the new mobile phones and Pocket PCs now have an infrared (IRDA) port and so this can now be used to transmit information between the two devices.


One advantage of infrared over microwaves is that the transmitters are smaller because the wavelength of infrared radiation is smaller than that of microwaves. The main disadvantage is that the attenuation is greater because of the higher frequency. It is for this reason that infrared is only used over short distances.


(d) light
Communication with visible light is becoming more common. Laser generated pulses carrying the information are sent down a thin glass fibre.

See: Electromagnetic spectrum Electromagnetic spectrum
 

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© Keith Gibbs 2020