November 2, 1920: KDKA, the first commercial radio station in the United States, goes on the air in Pittsburgh. July 1, 1941: WBNT, the first commercial TV station, starts broadcasting. April 3, 1973: Martin Cooper of Motorola makes the world’s first cell phone call.
Radio has transformed society three times, not to mention giving birth to the entire field of electronics. Perhaps no invention of modern times has delivered so much while initially promising so little. When radio arrived at the end of the 19th century, few thought that “wireless” communications, in which intangible signals could be sent through the air over long distances, would be competitive in a world dominated by the telegraph and telephone. The early inventors studied the work of Scottish physicist James Clerk Maxwell, who had formulated a set of equations—“Maxwell’s equations”—that expressed the basic laws of electricity and magnetism, but as a purely theoretical exercise in understanding how nature works. His equations explained light as one form of electromagnetic radiation and predicted that there should be many other forms, invisible to the human eye. In the 1880s the German physicist Heinrich Rudolf Hertz validated Maxwell’s laws by detecting radio waves—fundamentally similar to light but with wavelengths a million times longer. “Maestro Maxwell was right,” Hertz said, but he concluded that the existence of these other waves was “of no use whatsoever.”
Frequency Allocation in the United States
Image courtesy of the National Telecommunications and Information Administration
Fortunately, other scientists and engineers saw the radio spectrum not as a curiosity but as a tool for a new kind of communication. The principle behind radio transmission is simple. Electrons moving through a wire create a magnetic field. Place another wire near the first and electrons will start to move in the second wire too. The signal travels between the wires because the magnetic field formed by the first wire—the transmitter—creates an electric field in space, which in turn creates a magnetic field, and so on, moving outward at the speed of light. When the second wire—the receiver—picks up that signal, the field is converted back into the motion of electrons, detectable as an electric current. In order to carry information, the transmitted signal has to vary over time. The easiest way to do this is simply to stop and start the current in the first wire, sending a message as a series of pulses. The flamboyant Serbian-born engineer Nikola Tesla followed that approach and transmitted a radio signal across a short distance in 1893. Soon after, Italian inventor Guglielmo Marconi accidentally discovered that grounded antennas could send signals more than a mile instead of a few hundred yards. He had inadvertently been using Earth to propagate a radio signal close to the ground. With further refinements, he found a way for ships to talk to each other using Morse code—the quintessential pulsed signal—and in 1896, just 21, he traveled to England and set up a radio company, British Marconi.
World events quickly proved the value of this work. In 1905 the Japanese navy all but destroyed the Russian fleet at the Battle of Tsushima, in part because of radio equipment the Japanese bought from Marconi. And in 1912, after ships responding to the sinking Titanic’s distress signals rescued 711 passengers, maritime authorities required every seagoing vessel to have a wireless operator listening around the clock. But Marconi’s vision proved limited. He saw the airwaves as useful for point-to-point traffic between ships at sea and other clients untethered by cables, but that was about it. Marconi “took radio to the marketplace, but he never had the idea of broadcasting,” says Susan J. Douglas, a radio historian at the University of Michigan.
