Development of Radio.

Founded on the work of such men as James Clerk Maxwell, Heinrich R. Hertz, and Guglielmo Marconi, radio technology advanced rapidly in the first decade of the century. In 1901 Reginald A. Fessenden invented a high-frequency alternator (a device that produces alternating current) to produce a continuous radio wave instead of the spark-generated pulses Marconi had managed in his Morse code transmission. Fessenden also discovered a way to modulate the amplitude of radio waves, and on Christmas Eve 1906 he broadcast the first voice radio transmission. That same year Lee De Forest invented the triode vacuum tube, or audion. Edwin H. Armstrong in 1912 used the audion to create a "regenerative circuit" by which incoming radio signals could be amplified to such a degree that they could be played over audio speakers. (The early history of radio was rampant with lawsuits. Armstrong's invention was soon challenged in...