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Fessenden, Reginald Aubrey

devised radio amplitude sound

(1866–1932) Canadian–US physicist: devised amplitude modulation for radio transmission.

Born and educated in Canada, Fessenden’s first job was in Bermuda but in 1886 he joined laboratory in New Jersey. Then he moved in 1890 to Edison’s great rival, Westinghouse, for 2 years and then to academic life at Purdue and later at Pittsburgh; in 1900 he moved to the US Weather Bureau and then back to industry.

Before 1900 he began to work on radio, which and others were using to transmit messages by sending signals mimicking code. Fessenden sent out a continuous signal or ‘carrier wave’ at a steady high frequency and varied the amplitude of the waves to correspond to the sound waves of voices or music. At the receiver, these amplitude modulations could be reconverted to reproduce the sound. By Christmas Eve 1906 he was able to broadcast what was probably the first sound programme in the USA. He also devised the ‘heterodyne effect’ to improve amplification, and established two-way radio communication between the USA and Scotland. He was second only to Edison in the number and variety of his patents (over 500) and like him he was involved in many lawsuits. Modern radio is largely based on the work of Marconi, Fessenden, (who devised the triode) and , who devised frequency-modulated (FM) transmission.

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