Radio

A radio tower.

Radio is a way to send electromagnetic signals over a long distance, to deliver information from one place to another. A machine that sends radio signals is called a transmitter, while a machine that "picks up" the signals is called a receiver. (A machine that does both jobs is called a "transceiver".) When radio signals are sent out to many receivers at the same time, it is called a broadcast.

Television also uses radio signals to send pictures and sound. Radio signals can start engines moving so that gates open on their own from a distance. (See: Radio control.). Radio signals can be used to lock and unlock the doors in a car from a distance.

Sound can be sent by radio, either through Frequency Modulation or Amplitude Modulation.

History of radio

Many people believe that an Italian man named Guglielmo Marconi invented radio, because he was the first person to send radio waves. However,engineer Nikola Tesla made the first practical radio that sent audio (sound) signals.

Uses of radio

Radio was first created as a way to send messages between two people, but it is now used to listen to music, news and Entertainers. This is known as "talk radio." Radio shows were used before there were TV programs. In the 1930s the US President started sending a message about the country every week to the American people. Companies that make and send radio programming are called radio stations. These are sometimes run by governments, and sometimes by private companies, who make money by sending advertisements during the programme. Other radio stations are run independent and supported by local communities. These are called community radio stations. In the early days manufacturing companies would pay to send complete programmes by radio. These were often plays or dramas. Because companies who made soap often paid for plays and dramas, these were called "soap operas".

Radio can still be used to send messages between people. Talking to someone with a radio is different than "talk radio". Citizen's band radio, amateur radio use radio. Policemen, firemen and other people who help in times of trouble use radio to communicate (talk to each other). It is like a mobile phone, (which also uses radio signals) but the distance two people can talk between is shorter and both people must have a radio which can send messages. There is no cost when someone buys the machine, so it is used when often sending messages often between two places, like a policeman and his office.

Satellite radio

Television waves and radio waves have lower frequencies and longer wavelengths than microwaves. They are used to transmit television and radio programmes. Television uses higher frequencies than radio.

A radio programme receiver does not need to be directly in view of the transmitter to receive programme signals. For low frequency radio waves diffraction can allow them to be received behind hills, although repeater stations are often used to improve the quality of the signals.

The lowest frequency radio waves are also reflected from an electrically charged layer of the upper atmosphere, called the Ionosphere. This means that they can reach receivers that are not in the line of sight because of the curvature of the Earth's surface.

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