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What’s the Difference Between AM and FM Radio?

The role of radio in our society has changed dramatically over the years, but the technology behind it remains important to this day. Historically, radio was an important source of news and events, and as it became more common in households, it provided families with entertainment at home. Once TV entered the spotlight in homes, radio stations expanded their musical broadcasts and shared new music with listeners everywhere.

Today, we can still hear everything from news, talk shows and sports recaps to jams old and new when we tune in to our favorite radio stations, and with apps and satellite radio, we can listen in from nearly anywhere. Keep reading to learn about the difference between AM and FM radio technology and the National Inventors Hall of Fame® inventors behind each one.


How Do AM and FM Radio Work?

Every radio station sends out a carrier wave (or carrier signal) with variables including amplitude and frequency. When a station plays music or begins any other kind of broadcast, the sound waves are converted into electrical signals that reach our radios via the carrier wave. Depending on whether a radio station is AM (amplitude modulation) or FM (frequency modulation), the carrier wave changes either the amplitude or the frequency.

In an AM radio station, the carrier wave’s amplitude, or the height of the wave, changes. In an FM radio station, the frequency, or the number of wave cycles completed in a certain amount of time, changes while the amplitude stays the same.

Because electrical signals can affect a carrier wave’s amplitude, AM radio tends to emit more static in comparison to FM radio. FM radio also offers greater bandwidth, resulting in more nuanced sound quality.


Who Invented AM Radio?

Hall of Famer Reginald A. Fessenden was born in Quebec, Canada, and had been fascinated with the idea of wireless telegraphy from childhood. He later went to the U.S. to work with Thomas Edison and George Westinghouse. There, he investigated wireless radio communication with the U.S. Weather Bureau.

On Christmas Eve 1906, Fessenden transmitted the first radio broadcast from Brant Rock Station, Massachusetts, which could be heard by ships off at sea – a song played on the violin and a passage read from the Bible.

Previously, wireless broadcasts had consisted of dots and dashes used as code rather than the human voice and music Fessenden was able to share. However, with Fessenden’s invention of AM radio, he put into practice the idea of mixing two high-frequency signals to carry the audible low frequency of the human voice – a major breakthrough in radio capabilities!


Who Invented FM Radio?

Born in New York City, Hall of Famer Edwin Howard Armstrong earned a degree in electrical engineering from Columbia University in 1913. While in college, he invented a regenerative circuit, the first amplifying receiver and the first reliable continuous-wave transmitter.

During World War I, Armstrong served in the U.S. Army Signal Corps laboratories in Paris, where he invented the superheterodyne circuit to amplify weak, high-frequency electromagnetic waves.

By 1933, Armstrong had developed a solution for a static-free radio broadcast. His new system, known as wide-band frequency modulation, varied radio wave frequency over a wide band of frequency rather than a narrow band. Its improved radio signals helped make FM radio a great place to hear our favorite tunes clearly. In fact, Armstrong’s inventions were so impactful that every modern radio or television still makes use of one or more of his developments to this day!


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