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frequency modulation:see modulationmodulation,
in communications, process in which some characteristic of a wave (the carrier wave) is made to vary in accordance with an information-bearing signal wave (the modulating wave); demodulation is the process by which the original signal is recovered from the wave
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transmission or reception of electromagnetic radiation in the radio frequency range. The term is commonly applied also to the equipment used, especially to the radio receiver.
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a method of modulating oscillations, in which the frequency of the high-frequency carrier oscillations is varied over time according to a law that corresponds to the signal being transmitted. A feature of frequency modulation is its high immunity to noise. Frequency modulation is used for high-quality transmission of information: in radio broadcasting (in the very-high-frequency band), for the audio signal of television programs, in voice-frequency telegraphy, in radiotelephone communications, and in other fields.
frequency modulation[′frē·kwən·sē ‚mäj·ə‚lā·shən]
Contrast Amplitude Modulation.
frequency modulation(1) An earlier magnetic disk encoding method that places clock bits onto the medium along with the data bits. It was superseded by MFM and RLL.
(2) Varying the frequency of the waves of a carrier in order to transmit analog or digital data. Frequency modulation (FM) is widely used in audio transmission, not only for its namesake FM radio, but for the audio channels in television. See modulation and carrier.
|Vary the Angle|
|In FM modulation, the frequency of the carrier wave is varied by the incoming signal. In this example, the modulating wave implies an analog signal.|
|Digital Frequency Shift Keying (FSK)|
|For digital signals, frequency shift keying (FSK) uses two frequencies for 0 and 1 as in this example.|
A Sad Tale of FM Origins
FM radio was invented in the early 1930s by Edwin Howard Armstrong, who years earlier had made a fortune selling RCA his amplifier technology. When he asked RCA to license his FM in 1933, RCA turned it down and pursued its own research. Seven years later, RCA offered him USD $1 million for outright purchase, but Armstrong declined. He was angry at the long hiatus and thought the offer too low. Later, Armstrong sued for patent infringement when he discovered RCA was using his technology, but RCA's legal tactics kept him at bay for so many years that the patents expired. Fighting the company also depleted his wealth. In 1954, Armstrong wrote a note to his wife, walked over to his bedroom window and jumped 13 stories to his death. Eventually, his wife received millions in back royalties from the company.