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 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, sometimes through Frequency Modulation (FM) or Amplitude Modulation (AM).

You can listen to shortwave radio stations here: http://websdr.ewi.utwente.nl:4625