Out of the Archives: ‘Hazy’ and the Neutrodyne

While to modern eyes these carefully crafted boxes may look more like furniture than leading edge technology, they played a key role in the commercial success of radio. Up until the early 1920s, tuned radio frequency (TRF) receivers had two major defects. First, they were difficult for people at home to operate, as each circuit had to be individually tuned to the same frequency. Second, when all the circuits were tuned together, they were prone to oscillating, which caused unpleasant squeals and whistles that marred the radio experience for listeners — until Stevens Professor Louis Alan Hazeltine, Class of 1906 Sc.D. (Hon.) 1933, developed a solution.

Hazeltine, a child prodigy in mathematics, graduated from high school at age 16 and from Stevens at age 20. Following a brief stint at General Electric, he returned to Stevens as an assistant in the Department of Electrical Engineering in 1907 and became an instructor in 1908. Affectionately known as “Hazy” by his students, Hazeltine steadily rose through the faculty ranks, becoming a full professor and head of the department in 1917.

The 1920 Stevens Link yearbook describes Hazy as “work[ing] twelve hours a day, seven days a week, when a problem presents itself for a solution.” His dogged determination paid off in the 1922 invention of the neutrodyne — a TRF receiver with neutralizing circuits added to each amplification stage, canceling out feedback and preventing the oscillation that caused audio interruptions. Three large dials on the front panel simplified tuning for home listeners. His neutrodyne patent was licensed through the Hazeltine Corporation to more than 20 companies that produced and sold the device at an affordable price. By 1927, it was estimated that more than 10 million neutrodynes had been sold in North America — significantly increasing radio’s popularity and making Hazeltine a wealthy man.

Though the neutrodyne was replaced by the superheterodyne radio receiver in the 1930s, Hazeltine’s influence lived on through his namesake corporation, which produced defense electronics into the 1980s.

— Erin Lewis

Collage of images of the neutrodyne and coverage from 1937Bottom and left: The neutrodyne and its components; Stevens professor Louis Alan Hazeltine (center); and coverage of his winning of the Armstrong Medal from the Radio Club of America in 1937 (right).Photos: Michael Marquand, Historic Items: Archives & Special Collections, Samuel C. Williams Library.