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.
