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Radio Electronics: The Genius behind FM Radio

One of the great inventors in the history of radio electronics was an engineer named Edwin H. Armstrong. Born in 1890, he was fascinated with electrical technology from a very young age. At the age of 14, he started experimenting with wireless radio circuits, building an antenna in his family’s backyard that was more than 100’ tall.

He made his first major contribution to radio technology while he was a junior at Columbia University in 1912. His invention was a circuit that amplified incoming radio signals by feeding them back though the amplifier tube in what came to be called a regenerative circuit.

The regenerative circuit was an important early breakthrough in radio technology that for the first time allowed radio to be heard through a speaker rather than with headphones.

During World War I, Armstrong invented another type of radio receiver, which he called the superheterodyne circuit.

The basic principal of the superheterodyne circuit is that a radio signal broadcasting at a high frequency — say 1,500 kHz, can be combined with a nearby frequency from an oscillator — say, 1,560 kHz, in such a way that the original signal could also be detected at 60 kHz — the difference between the original signal’s frequency (1,560 kHz) and the oscillator’s frequency (1,500 kHz).

The superheterodyne circuit may be one of the most important electronic circuits ever invented. It's still used in nearly all radio receivers to this day.

His third great invention came in 1933, when he created a method for transmitting radio signals that wasn't subject to interference from atmospheric disturbances like lightning. His new system was called frequency modulation, or FM radio.

Armstrong patented his inventions, but his patents were challenged or ignored by the titans of radio. He lost his lawsuit to protect his patent for his regenerative circuit in 1934 because the justices of the Supreme Court didn't understand how the circuit worked, and the industry challenged his FM radio patents and used his technology freely throughout the 1940s and 1950s.

Finally, in 1954, ill and broke from his legal battles, Armstrong committed suicide by jumping from his high-rise apartment window.

Eventually his widow, Marion, won a series of patent lawsuits and was awarded damages of $10 million.

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