analogue transmission

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A method of sending information over long distances by encoding it as an analogue signal. This involves modulating a continuous beam of charged electromagnetic particles (most commonly radio waves but also microwaves and visible light sent through fibre-optic cables). Analogue signals are so called because they are modulated in ways that are directly proportional (analogous) to changes in the source material they encode, and their modulations consist of smooth transitions between states (slopes) rather than the abrupt changes (steps) which are characteristic of digital signals. There are three main disadvantages of analogue transmission systems as compared with digital transmission: firstly, analogue processes encode both wanted and unwanted information (or noise) into the signal itself, so analogue transmission suffers from artefacts such as audio ‘hiss’ and picture ‘snow’. Secondly, analogue signals are continuous temporal segments which are transmitted in real time: consequently the frequency occupied by a particular analogue signal which is regularly sent has to be allocated in advance for that single purpose. In the case of radio, television, and mobile phones, this allocation relates to the licensing of specific frequency bands (or channels) within the electromagnetic spectrum. Thirdly, analogue signals cannot be compressed: consequently media that encode a large amount of information (such as television) require a correspondingly large amount of signal bandwidth. See also spectrum scarcity; transmitter.

Subjects: Media Studies.

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