The next big step was finding a way to manipulate radio waves so they could carry more than dots and dashes. Switching from pulses to continuous waves provided the key. Reginald Fessenden, a Canadian autodidact, invented a way to transmit voice and music by altering the intensity of waves—called amplitude modulation—thus creating AM radio. (Amplitude modulation superimposes a varying audio wave onto a radio wave with a fixed frequency: Where the audio wave peaks, the modulated radio wave is at its highest intensity, and where the audio wave has a trough, the radio wave is at its lowest intensity.)
Fessenden ultimately earned money and fame from his invention. On the other hand, American radio engineer Edwin Howard Armstrong, regarded by many radio cognoscenti as the greatest of them all, is today almost forgotten. He noticed that by varying wave frequency instead of amplitude, stations could avoid the interference that often corrupted AM transmissions. The result was frequency modulation—FM radio. (In this case, a peak in the audio wave is represented by an increase in the frequency of the radio wave, while a trough is represented as a decrease in frequency.) A lifetime of patent lawsuits crushed Armstrong emotionally, and he committed suicide in 1954.
Although its commercial potential today seems obvious, broadcasting was actually kick-started by amateurs: “By the 19-teens, ham radio operators were everywhere,” Douglas says. The hams—a term coined as a slur by professional telegraph operators—“were sending homework and football scores and news in Morse code, and then they went to World War I and found out about vacuum tubes.” Thanks to the amplifying power of the newly invented vacuum tubes, hams started sending audio everywhere. “You could just set up a transmitter and start broadcasting stuff,” says radio industry consultant Rick Ducey, formerly the head of research for the National Association of Broadcasters. “That’s all it took.”
Westinghouse engineer Frank Conrad generally gets credit for transmitting the first regular AM broadcasts in the United States from his East Pittsburgh garage (although stations in San Jose, Detroit, and elsewhere were also active). His show aired every Wednesday and Saturday—some sports scores, some talk, but mostly music. When Conrad ran out of records, he struck a deal with a local store to supply him with more in return for on-air promotions. These are believed to be the first radio ads. But by the mid-1920s, so many people were doing it, the industry “needed a traffic cop,” Ducey says.
To bring some order to the growing number of broadcasters who were appropriating their own radio wavelengths, or frequencies, the government created the Federal Radio Commission. That agency, later re-formed as the Federal Communications Commission (today’s FCC), assigned specific frequency bands to different users. In 1920 Conrad applied for and received a license from the Commerce Department for radio station KDKA. Radio broadcast licensing was born, and a virtual real estate boom—the competition for slices of the radio band—began. The amateurs who stayed amateurs soon found themselves being moved by regulators to less desirable locations farther up the radio spectrum. Roughly speaking, lower frequencies are cheaper to use than higher frequencies because they require less precise equipment, an important consideration for an industry that wanted to market radio receivers to the masses.
Soon the armed forces also wanted their slice of the radio spectrum. Military use of radio communications may have begun at Tsushima, but after World War I it expanded enormously. Governments started to understand radio’s immense potential, not only for communications but also as a weapon: radio detecting and ranging, better known as radar.
Radar began with the observation that lightning gives off a radio signal, and Scottish engineer Robert Watson-Watt, working as a meteorologist, thought he could exploit this phenomenon to warn pilots of approaching storms. Using a directional antenna, he found he could scan the skies and pick up lightning. Then he realized that if he transmitted radio pulses as well as listened to them, he could bounce a signal off a target—an approaching aircraft, for example. By measuring how long it took for echoes to return to the antenna, he could know not only the bearing of the target but also its range.