Radio communication: is the transmission of signals or messages by wireless by the radio transmitter. The radio transmitter emits a continuous career wave of definite constant amplitude and frequency. The sound impulses are converted into electrical impulses by means of a microphone. The career wave is modulated and these impulses superimposed upon it. The radio receiver is turned or adjusted to this modulated wave. The received Signal or wave is amplified and then rectified by transforming the alternating current induced in a conductor by the modulated wave into direct current by the rectifier. The current after further amplification is passed through a loudspeaker in the receiver which produces sounds injected at the transmitter.