Radio

A Thumbnail History of Electronics

IV. Radio
Speech transmission using a spark transmitter was demonstrated by Fessenden in 1900 but was too noisy; in 1906 he broadcast the first program of speech and music using 50 KHz generated by an alternator. Fessenden also discovered the heterodyne principle of mixing a low frequency signal with the high frequency carrier. The 1913 discovery by De Forest and Armstrong of regenerative feedback and how to use the triode as an oscillator made commercial radio possible. Armstrong’s invention of the superheterodyne receiver in 1917 and FM in 1933 brought radio into the modern era. However, the technical triumphs were marred by years of bitter patent suits between all the participants and led to great personal tragedies.

Reginald Aubrey Fessenden (1866-1932) was a Canadian-American who first worked for Edison. In 1900, while working for the U.S. Weather Bureau, he developed the ideas of continuous wave transmission and amplitude modulation and the heterodyne principle to permit speech transmission. After 1902, he directed the development of a one kilowatt, 50 kHz alternator to replace the spark transmitter, and invented an electrolytic detector for continuous waves. In December 1906 he realized the first radio-telephonic broadcast. Fessenden held hundreds of radio patents and also invented a variety of devices which included the radio compass and the fathometer. He was described as "a stormy and colorful figure" and for years he was deeply involved in a series of litigations against his patents.
Edwin Howard Armstrong (1890-1954) was a junior engineering student at Columbia in 1912 when he invented regenerative feedback and electronic oscillators. Although a later corporate suit brought by De Forest, led to the courts decision in favor of De Forest, the engineering community has continued to regard Armstrong as the inventor. Then in 1917 while serving in the army, Armstrong invented the superheterodyne receiver which is the basis for virtually all modern radio and radar communication systems. This patent was not disputed and Armstrong became a millionaire. Armstrong’s third invention was the superregenerative detector. Then, in 1933 Armstrong obtained a series of patents covering his invention of (wideband) FM, a new system of radio communication. The radio industry, with a vested interest in AM, had no interest in FM and Armstrong had to build the first station himself. FM slowly gained acceptance, but Armstrong, impoverished and embroiled in more patent suits, committed suicide.
Louis Alan Hazeltine (1886-1964) became head of the Electrical Engineering Department at Stevens Institute of Technology in 1917; this was the department which had awarded him his bachelor’s degree only eleven years before. During World War I, he designed a radio receiver for the U.S. Navy. In 1922, Hazeltine invented the "neutrodyne" receiver to eliminate the squeaks and howls of the early radio receivers. The Hazeltine amplifier neutralized the grid-to-plate capacitative coupling which was a cause of oscillation in triode amplifiers. The neutrodyne was the first commercial receiver suited to general public broadcast reception. By 1927 some ten million of these receivers were being used by listeners in the U.S.
Harold Stephen Black (1898-1983) worked, after graduation from Worcester Polytechnic, for a department of Western Electric Company which later became Bell Telephone Laboraotories. For six years he pursued a seemingly futile project to improve the distortion characteristics of amplifiers. In a storied incident, the answer was conceived in a creative flash during a commuter ride on a ferry in 1927. He wrote the equations on a blank page in his daily newspaper. Although at first it seemed paradoxical, negative feedback effected an extraordinary performance in amplifier performance.

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