The word “radio” means communicating with radio waves, which are part of the electromagnetic spectrum. Radio has a huge range of applications. It is used in the telephone network for mobile telephones and links in the network, for broadcasting, for two-way radio communications as used by the emergency services, and for remote control of machines. “Radio” also means the media of radio, in which music and speech from radio stations are transmitted by radio waves, and are picked up by radio receivers.

The existence of radio waves was confirmed in 1888 by the German physicist Heinrich Hertz, but it was the Italian Guglielmo Marconi who, in 1896, was the first to make long-distance radio transmissions. In 1901 he transmitted Morse code across the Atlantic. Two-way radio communications using Morse code began in the early twentieth century, and radio broadcasting began in the 1920s.

On their own, radio waves do not carry any information. To make an electrical signal, such as one representing sound, into a radio signal, the electrical signal is used to shape another signal, called the carrier wave. The shaped carrier signal is sent to a transmitter, where it creates radio waves.

The shaping process is called modulation. So that radio signals from different transmitters do not interfere with each other, they are sent using carrier waves with different frequencies. The whole family of radio waves is divided into sections called wavebands. Each waveband is reserved for a different form of communication. A radio receiver detects radio waves of the right frequency and demodulates them to get back the original electrical signal.

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