Communications

MODERN COMMUNICATIONS DEVICES give almost instant access to almost any information, almost anywhere in the world. Most work using electricity and magnetism,and some use light too. Telephones and televisions rely on converting sounds or pictures into electrical signals, which are sent long distances through wires at high speed — the speed of light, 300,000 kilometres per second. Information can also be converted from electrical signals into pulses of electromagnetic waves – laser light – and sent along fibre-optic cables. Or it is changed into radio waves and sent to local networks. or up to satellites in space and thenback down to Earth again. The light or radio signals have to be converted into el signals before they can be turned back into sounds or pio again.

An optical fibre is a rod of glass or similar transparent material, which is thinner than a hair and can flex or bend. It is contained ina protective sheath that also separates it from other optical fibres around it. The fibre carries information as coded flashes of laser light. Because these hit the inside of the surface of the rod at a very shallow angle, they bounce off or reflect back into the rod, by total internal reflection. This means the laser pulse Zig-zags along the inside of the fibre, even is bent. The flashes carry information in digital form. As with electrical information, a flash or pulse is 1 in binary, and no flash or pulse (a gap) is 0. The digital information can represent numbers, letters, words, sounds and pictures. Thousands of optical fibres are bundled together in one casing as a fibre-optic cable. In the last 170 years, electrical information has revolutionized the way we communicate.Long – distance or telecommunication networks can pass messages around the would in seconds.These amazing achievements all started with the electric telegraph, which developed into the modern telex system. The telephone network has now developed to carry pictures, computer date, electronic mail and many other forms of information. A mobile phone sends and receives messages by radio waves.The radio waves travel to and from a transceiver (transmitter receiver) station which connects the calls into the standard telephone network Countries are divided up into different areas called cells, and each cell has its own transceiver station.in an area where a lot of people live, there are many small cells because the are likely to be many people using mobile phones. In sparsely populated areas, the cells are larger. A “mobile” is a low-power radio transmitter-receiver. It has a mouthpiece to change sound waves into electrical signals (like a microphone), and an earpiece to change electrical signals into sound Waves (like a loudspeaker). The transmitter-receiver only needs to send and pick up waves from the neatest cel tower, which is Usually just a few kilometres away. However hills or tall buildings may block the radio signals. Also, in areas where the Fel towers are farther apart the signals may be too weak to travel to and from the phone.