09-02-2013, 03:15 PM
Fiber optics
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CONTEMPORARY TRANSMISSION MEDIA
Twisted Pair Cables and Coaxial Cables are the two most commonly used transmission media.
Twisted Pair Cabling is a type of wiring in which two conductors of a single circuit are twisted together for the purposes of cancelling out electromagnetic interference from external sources; mainly from the neighbouring pairs.
It was invented by Alexander Graham Bell.
LIMITATIONS: TWISTED PAIR CABLE
Twisted Pair cables have a high susceptibility towards the electromagnetic interference.
It greatly depends on the pair twisting schemes staying intact during the installation. As a result, twisted pair cables usually have stringent requirements for maximum pulling tension as well as minimum bend radius. This relative fragility of twisted pair cables makes the installation processes quite cumbersome, yet important.
PHOTOPHONE
Graham Bell invented this shortly after patenting telephone, in around 1880.
Speech was transmitted by modulating a light beam which travelled through the air to the receiver.