A boy holds a 1980s mobile phone, nicknamed "the brick". Mobile phones are radio telephones in which calls are routed through a network of radio aerials, or masts, linked to the main public telephone network. (Landline phones, which carry calls along electrical cables, work in a completely different way.) A mobile phone sends and receives calls without any wire connections. Instead, it uses electromagnetic waves to send and receive the sounds that would normally travel down wires. The first hand-held mobile phone call was made in 1973, using a handset that weighed about a kilogram (more than two pounds).
When you speak into a mobile phone, a tiny microphone in the handset converts the sounds of your voice into a pattern of electrical signals. A microchip inside the phone digitizes them (turns them into strings of numbers). The digital signal is carried by a radio wave and beamed out from the phone's aerial. The radio wave travels at the speed of light until it reaches the nearest radio aerial.
The first mobile phone calls were made from cars in 1946. The phones were composed of vacuum tubes and other heavy equipment, and weighed over 36 kg (80 lb).
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