Marconi in context
Guglielmo Marconi is the name most people attach to radio, and his contribution was real. From the mid-1890s he built practical wireless telegraph systems, found backers, set up companies and showed the world that signals could cross the sea. He shared the 1909 Nobel Prize in Physics with Karl Ferdinand Braun. But Marconi worked alongside, and often built on, the efforts of Oliver Lodge, Nikola Tesla, Alexander Popov, Jagadish Chandra Bose and others, and credit for particular ideas is still argued over. Marconi’s strength was engineering and commercial determination more than any single new principle.
His systems sent Morse code using spark transmitters. They were good at one thing, sending dots and dashes, and they were not suited to carrying speech or music. The story of this article begins where that technology leaves off.
From Morse to voice: amplitude modulation
To carry sound, a transmitter needs a steady radio wave, called the carrier, whose strength is varied in step with the sound. That is amplitude modulation, or AM. Reginald Fessenden and others experimented with it in the early 1900s, and the vacuum tube, associated with Lee de Forest and John Ambrose Fleming among others, made practical transmitters and amplifying receivers possible.
AM became the standard for the first broadcasting stations in the 1920s. It carries well over long distances, especially at night, and receivers can be simple. Its weakness is that anything that adds electrical noise changes the strength of the signal. Lightning, electric motors and car ignition systems all produced static that the receiver could not tell apart from the program.
Armstrong and the idea of frequency modulation
Edwin Howard Armstrong was already well known before FM. As a young man he developed the regenerative circuit (around 1912), and he is credited with the superheterodyne receiver design (around 1918) that is still the basis of most radios, although a French engineer, Lucien Lévy, made competing claims. Armstrong spent the early 1930s on the static problem.
Instead of varying the strength of the carrier, frequency modulation varies its frequency, the number of waves per second, in step with the sound. Because most noise affects strength rather than frequency, a receiver that ignores strength changes can reject much of the static. Early on, a number of engineers believed this could not work well. John R. Carson had argued in a 1922 analysis that narrow frequency modulation offered no clear advantage. Armstrong’s insight was that a much wider band would give much better noise rejection, at the cost of using more of the radio spectrum. He received patents in 1933 and demonstrated his system to engineers in 1935, showing a clear, quiet signal.
The fight over adoption
The wider channels meant FM had to operate at higher frequencies than AM stations, which required new transmitters and new receivers. Established companies had heavily invested in AM and in a rapidly growing television effort, and Armstrong’s relationship with RCA, which had at first supported his tests, turned sour. Armstrong built his own station in New Jersey in the late 1930s, and a small number of FM stations began broadcasting around 1939 to 1941.
In 1945, the Federal Communications Commission moved the FM band to a new range of roughly 88 to 108 MHz. Supporters of the decision cited interference concerns, while Armstrong and his allies argued it favored established interests. The change made existing FM sets and transmitters obsolete overnight and slowed the new service. Armstrong also spent years in patent litigation with large companies. He died in 1954, and his widow continued the lawsuits, which were eventually settled in her favor, according to most accounts.
How FM finally took over
FM radio remained a minority service in the United States through the 1950s and 1960s, partly because few people owned FM receivers and AM stations drew the advertising. Several developments changed that.
- Stereo broadcasting: FM stereo was approved in the United States in the early 1960s and suited the growing market for high-fidelity recordings.
- Music formats: FCC rules in the 1960s pushed stations that owned both AM and FM outlets to program them separately, and album-oriented music found a home on FM.
- Receivers: FM was built into car radios and cheap portable sets, and the transistor made them small.
FM overtook AM in total listening in the United States in the 1970s, by most estimates. Europe followed a somewhat different path, with broadcasters there adopting FM in the 1950s and building national networks. In many countries FM became the default for music, while AM continued for news, talk and long-distance reception. Both are examples of how engineering choices and regulatory ones interact. The better signal did not win on technical merit alone, since decades of lobbying, rules and consumer habits mattered. Engineers still draw on ideas from the Second World War, such as improved circuitry developed alongside radar detection, to refine receivers.
FM today
FM still carries a large share of the world’s radio listening, even as digital audio broadcasting, internet streaming and satellite radio compete with it. Modern FM chips are built into many smartphones, though not all are enabled for users. Compact silicon chips made tuners inexpensive and reliable. FM’s reputation for musical clarity helped to shape the popular music sound of the late twentieth century, because the listening experience was close to the sound of the record itself.
Marconi, Armstrong and others are best understood as links in a chain. Marconi proved that wireless could be commercial, early voice experimenters showed it could carry speech, and Armstrong improved the quality of what was carried.