Frequency modulation

Frequency modulation (FM) is a form of modulation which represents information as variations in the instantaneous frequency of a carrier wave. (Contrast this with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant.)

Related Topics:
Modulation - Information - Frequency - Carrier wave - Amplitude modulation - Amplitude

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In analog applications, the carrier frequency is varied in direct proportion to changes in the amplitude of an input signal. Digital data can be represented by shifting the carrier frequency among a set of discrete values, a technique known as frequency-shift keying.

Related Topics:
Analog - Amplitude - Digital - Data - Frequency-shift keying

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FM is commonly used at VHF radio frequencies for high-fidelity broadcasts of music and speech (see FM broadcasting). Normal (analog) TV sound is also broadcast using FM. A narrowband form is used for voice communications in commercial and amateur radio settings. The type of FM used in broadcast is generally called wide-FM, or W-FM. In two-way radio, narrowband narrow-fm (N-FM) is used to conserve bandwidth. In addition, it is used to send signals into space.

Related Topics:
VHF - Radio frequencies - High-fidelity - Broadcasts - Music - Speech - FM broadcasting - Narrowband - Voice - Amateur radio

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FM is also used at intermediate frequencies by most analog VCR systems, including VHS, to record the luminance (black and white) portion of the video signal. FM is the only feasible method of recording to and retrieving from magnetic tape without extreme distortion, as video signals have a very large range of frequency components -- from a few hertz to several megahertz.

Related Topics:
VCR - VHS - Luminance - Hertz - Megahertz

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FM is also used at audio frequencies to synthesize sound. This technique, known as FM synthesis, was popularized by early digital synthesizers and became a standard feature for several generations of personal computer sound cards.

Related Topics:
Audio frequencies - FM synthesis - Synthesizers - Personal computer - Sound card

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