It was around this time that the word "radio", derived from its use of radiated signals, came into wide usage. Inspired by visions of the future presented in pulp magazines such as Modern Electronics, first published by Hugo Gernsback in 1908, American children everywhere started buying radio kits in much the same way they later would build plastic model airplanes.

High fidelity came to radio in 1915 thanks to an amplifying speaker that its inventor, Danish émigré Peter Laurits Jensen called Magnavox, Latin for "Great Voice".

Almost anyone could set up a radio transmitter and send signals, and many did, creating a radio Tower of Babel. In 1919, Assistant Secretary of the Navy Franklin Roosevelt advised that, in the interest of national security, the radio business should be organized and standardized.

On October 17, 1919, most radio patents voluntarily were transferred to a new company owned by several major radio companies. The new entity was called the Radio Corporation of America (RCA). In charge of the commercial side of the new entity was the self-proclaimed hero of the Titanic reports, David Sarnoff. Sarnoff was not a scientist but a visionary and would remain the best-known and most influential figure in the world of consumer electronics and communications for nearly 50 years.

In October 1920, Pittsburgh radio amateur and Westinghouse employee Dr. Frank Conrad started broadcasting music. Conrad's ad hoc evening programs were so popular that his employers took an interest, setting up a studio for him in the building and dubbing the operation KDKA, the first commercial radio station. The first commercial radio broadcast was the Warren G. Harding-James Cox presidential election returns on November 2, 1920, heard by a few thousand enthusiasts in the Pittsburgh area. The resulting publicity of the success of these commercial broadcasts, the beginning of Prohibition, speakeasies and the music of the Jazz Age sparked a rush to start radio stations and music broadcasting. By 1923 there were more than 500 radio stations nationwide. Radio soon became a hobby and obsession for dancing to the latest songs on the hit parade, getting the latest news and thrilling to the latest exploits of the era's great sports figures such as Babe Ruth, Jim Thorpe, Jack Dempsey, Bill Tilden and Red Grange.

Although popular, radios were still cumbersome affairs. Early radios did not have speakers–they required headphones. They ran on batteries since most homes still did not have built-in electricity. They also had awkward tuning mechanisms.

In the early 1920s, most of these problems were solved. The boombox boomed in 1923–portable radios with built-in horn speakers and a handle–and lasted until 1927, when most radios could operate on AC house current rather than batteries.

Several other famous names and well-known companies were born during radio's adolescence. For instance:

• In the early 1920s, Powell Crosley Jr., horrified at the high cost of radio sets, produced the first low-priced, mass-market radio, the $9 Crosley Harko. By 1922, Crosley was the world's leading radio manufacturer.
• That same year, Atwater Kent began manufacturing so-called "bread-board" component radios with parts built into beautiful wooden consoles. By the late 1920s, Atwater Kent Radio was one of the country's leading manufacturers.
• In 1923, Eugene McDonald Jr. founded Zenith and James Lansing founded the first speaker company that would bear his name, JBL (the other would be Altec-Lansing).

One hundred thousand radios were sold in 1922, at an average cost of $50 each. Thanks to the portable boom, by 1924, the annual factory dollar volume of radios had multiplied tenfold to $50 million. Radio became as ubiquitous in American homes as bathtubs were.

In fact, the consumer electronics business was known as the radio business for decades afterward. There were inexpensive radio models that required headphones, there were fancy and expensive furniture models, and every type of configuration and price in between existed. By the end of the decade, most radios were all electronic and had one-knob tuning and higher-fidelity conespeakers.

The idea of including a radio in a car first was solved by lugging along a battery-powered portable radio designed to be carried in a car. In the early 1920s, a 20-year-old inventor named William Lear, who later would go on to invent the eight-track cassette and the luxury jet plane that bears his name, along with his sometime partner and friend Elmer Wavering, invented and perfected what many believe to be the first practical car radio. In 1924, Lear sold the rights to his invention to Paul Galvin's Galvin Manufacturing Company. In 1929, Galvin unveiled the "Motorola", short for "motor Victrola", the first practical car radio. Wavering would become president of Motorola 40 years later.

Popular radio maker Philco, founded by William Balderston, also produced early car radios. A few years later, Ross Siragusa formed the Continental Radio and Television Corp. to capitalize on the radio boom. The company, later renamed Admiral, would become one of the dominating brand names in the early days of television two decades later. By the end of the 1930s, 20 percent of all cars had built-in car radios installed at the car factory.

The golden age of radio spanned a 21-year period, from Conrad's founding of KDKA in 1920 until America's entry into World War II. During those years, 100 million radio receivers of increasing sophistication, quality and size, for home, car and travel, were sold by such companies as RCA, Zenith, Emerson, Crosley, Atwater Kent, Philco, Motorola and Admiral.

This growth was fueled by new radio retail stores, none more prominent than those found in the area that became known as Radio Row centered on and around Cordlandt Street in lower Manhattan. Hundreds of small radio and, later, TV retailers, starting with City Radio and Furst Radio in 1921, soon filed the six square block area that included Cortlandt, Dey, Greenwich, Washington and Liberty Streets and West Broadway. Metro Radio, Leotone radio, Rand Radio, North Radio, Harrison Radio, Niagara Radio Supplies, Eugene Blan the Radio Man, Arrow Radio, SUN Radio, G and G Radio, Leeds Radio, Gross Radio, Terminal Radio, Magna and Center Electronics, Mike Krantz, Short Wave Radio, Bernie Briggs Television and Radio and others formed a electronics bazaar of radio knobs, vacuum tubes, breadboards, antenna kits and hi-fi stereo and TV equipment.

Many stores had speakers mounted above their doors, creating a cacophony of sound before the days of noise regulations. Radio Row, with store after store filled with surly salesman and endless supplies of the most popular and arcane electronics gear available, was the premier radio and electronics marketplace in the world until the entire area was bulldozed to make way for the World Trade Center in 1966.

During radio's formative period in the mid-teens and 1920s, all radio broadcasts were on the AM band. In 1922, American mathematician John Carson theorized a higher quality frequency modulated (FM) scheme. In 1933, Edwin Howard Armstrong patented the static-free FM radio technology. But because FM required an entirely new infrastructure and equipment for both broadcast and receiving, few radio companies were interested.

After a brief fling at RCA in the mid-1930s, Armstrong left RCA because Sarnoff had focused his attention on television. Armstrong was forced to create FM himself, founding the first FM radio station at his alma mater, Columbia University, in 1941.