Radio

Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connected to an antenna which radiates the waves. They can be received by other antennas connected to a radio receiver; this is the fundamental principle of radio communication. In addition to communication, radio is used for radar, radio navigation, remote control, remote sensing, and other applications.

Different radio systems use different modulation methods:

• Amplitude modulation (AM) – in an AM transmitter, the amplitude (strength) of the radio carrier wave is varied by the modulation signal
• Frequency modulation (FM) – in an FM transmitter, the frequency of the radio carrier wave is varied by the modulation signal
• Frequency-shift keying (FSK) – used in wireless digital devices to transmit digital signals, the frequency of the carrier wave is shifted between frequencies
• Orthogonal frequency-division multiplexing (OFDM) – a family of digital modulation methods widely used in high-bandwidth systems such as Wi-Fi networks, cellphones, digital television broadcasting, and digital audio broadcasting (DAB) to transmit digital data using a minimum of radio spectrum bandwidth.