History Made Every Day™

Lee De Forest, the American inventor of the vacuum tube, broadcasts a live performance of Enrico Caruso from the Metropolitan Opera. The broadcast over a telephone transmitter could be heard only by the small number of electronics hobbyists who had radio receivers. De Forest started regular nightly concerts in 1915, increasing interest in radio receivers, which at the time depended on the vacuum tubes manufactured by De Forest's company.

Many discoveries in the field of electricity led to the development of radio. In 1873, British physicist James Clerk Maxwell published his theory of electromagnetic waves. Inventor David Edward Hughes discovered that if one passed those waves through the junction of a steel point and a carbon block, it would conduct a current. In 1879, he showed how radio signals could be received from a transmitter hundreds of yards away. People had already been transmitting long-distance messages with light rays through a heliograph, but radio was more versatile because its waves could travel farther and could be amplified.

Italian electrical engineer and inventor Guglielmo Marconi is traditionally recognized as the inventor of the radio for his 1896 invention, which transmitted signals over more than a mile. The following year, he transmitted signals from land to a ship that was sailing nearly 20 miles off shore. Soon, France and England began using the invention to communicate with each other, even during rainstorms, and by 1905 ships often used radios to communicate with stations on shore. Marconi's work earned him a share of the 1909 Nobel Prize in Physics.

Radio developed quickly after World War I, and amateur operators using short-wave radios made the first transatlantic radio transmission in 1921. Short-wave radio is still used today during emergencies when other modes of communication are rendered useless, and more than 1.5 million people around the world are licensed ham-radio operators. Development in radio (from high-tech equipment to extremely high frequency communication systems) has made space exploration possible, including the Apollo lunar-landing missions. Radio waves of different lengths have diverse characteristics and are identified by their frequencies (for instance, shorter waves have higher frequencies, or numbers of cycles per second). One cycle per second is called a hertz, in honor of German radio genius Heinrich Hertz. Commercial radio stations are broadcast on frequency modulation (FM) or amplitude modulation (AM) and are assigned bandwidths by the Federal Communications Commission.