Copyright © 2007 Dorling Kindersley
Mobile communications allows direct radio contact with people on the move, connecting them immediately, even in an emergency. Radio was originally invented more than a century ago as a way of communicating with ships. Transistors and microchips now make it possible to get powerful radio equipment into cars and small boats. Unlike a MOBILE PHONE, mobile communication does not rely on the fixed telephone network.
Fire, police, and ambulance services all have their own radio networks. Some can handle data, such as maps, as well as speech. Messages are sent out from a central transmitter to several vehicles, all of which use one channel to reply – so communications have to be short, and are not private.
Mobile phones use radio and landlines to transmit calls. A call is picked up by a nearby base station, which passes the call through landlines to another base station or to a fixed telephone. Base stations are low-powered, so they do not interfere with each other, allowing millions of people to talk using only a few frequencies.
A pocket-sized mobile phone contains more than one computer as well as a microwave radio transmitter and receiver. When you switch it on, the phone finds the nearest base station and logs on so that the system knows where it is. If you start to move out of range, the phone finds another base station and, if necessary, retunes itself.