For AM (amplitude modulation) the transmitted carriers amplitude is forced to vary in proportion to the amplitude of the intelligence that you wish to transmit. Where as for FM (frequency modulation) the transmitted carriers frequency is forced to vary in proportion to the amplitude of the intelligence that you wish to transmit. Detectors in the receivers are used to recover the intelligence. AM systems are much more susceptible to random noise caused primarily by severe weather and low signal strength at the receiver. FM systems are pretty much immune to noise because FM detectors do not respond to amplitude variations in the carriers. However FM transmitters requires a wider frequency bandwidth for transmission than does AM transmitters. Standard television transmitters use two carriers per channel. The sound carrier is frequency modulated and the picture carrier is amplitude modulated. The tv receiver is designed to receive both carriers. It also has two separate detectors, one for sound and one for picture. The picture information is routed to the picture picture tube and the sound is routed to the speaker(s).
(SOURCE = Yahoo!7 Answers ;)---jks, wikipedia.)
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