Radio
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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.
Many people believe that an Italian man named Guglielmo Marconi invented radio, because he was the first person to send radio waves. Engineer Nikola Tesla made the first practical radio that sent audio (sound) signals, but most people do not know that he did this.
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. 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.
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.
[change] Satellite Radio
There is now a new machine, satellite radio. This machine sends digital signals first sent to a satellite in space, up in the sky above the earth (it is an electronic machine like a mirror) and bounced back to Earth. Someone must have a special radio to listen to satellite radio. To get music on a satellite radio people must pay money every month. Satellite radio have many different channels, music, sports and talk, which do not have advertisements. That is why money must be paid every month, because other radio stations make their money by selling advertising. The sound on the satellite radio is very good. It is like on a CD compact disc, maybe even better. There are two satellite radio services in the US: XM Satellite Radio and Sirius Satellite Radio. The old way of sending radio messages is called terrestrial radio, this comes from the Latin language word, "terre" which means "earth", so as not to mix it up with satellite radio from the sky. Europe has digital radio as well, but does not use satellites to send the signal.
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