Communicating With Electromagnetic Waves
How did radio communications develop?
An electromagnetic wave with no changes in amplitude or frequency carries no information—it cannot be used for communication. The first method of using these waves to communicate was to switch them on and off in regular patterns. Letters were represented by a combination of long and short pulses using what is called Morse Code after Samuel S.B. Morse, who developed the code to transmit information over wires (the telegraph).
In 1895 Guglielmo Marconi (1874–1937), a twenty-year-old Italian inventor, created a device that transmitted and received electromagnetic waves over a 1-kilometer (3,280 foot) distance. Later improvements to his antenna and the development of a crude amplifier enabled him to receive a British patent for his wireless telegraph. In 1897, he transmitted signals to ships 29 kilometers (18 miles) from shore and in 1901 he was able to send wireless messages across the Atlantic Ocean. As a result of Marconi’s work on radio transmitters and receivers, he was the co-winner of the 1909 Nobel Prize in physics. Over the next decade transmitters and receivers were improved enough that they could be installed in ocean-going ships.
Voice communication over the telephone had existed since 1876, but if the distance was to be extended, the voices had to be amplified to be heard. In 1906 Lee DeForest invented a vacuum tube amplifier he called the Audion. It took until 1915 for a radio receiver to be sold using Audions. In 1916 DeForest had developed an Audion-based transmitter that allowed dance music to be transmitted 40 miles. A number of other experimental stations demonstrated music by radio—then called wireless. A large number of radio amateurs made significant advances. When the United States entered World War I in 1917 all stations not owned by the government were shut down and it became illegal for people to listen to any radio transmission.
During the war, radio was used to communicate between ships and between land and the ships. After the war, amateurs were forced to use only one wavelength, 200 meters (1,500 hertz). Wavelengths shorter than that were thought to be useless for government use. One amateur was able to send signals 3,000 miles. In 1921 transatlantic voice transmissions were made. Companies began to use radio for specialized needs, like to send time information to jewelers to allow them to set their clocks. From 1919 through 1921 radio was mostly used to transmit musical concerts. The first transmission of a football game occurred in November 1919. By 1922 newspapers had developed radio stations transmitting news, weather reports, crop reports, and lectures. Large companies such as General Electric, Westinghouse, AT&T, and RCA. began to be involved in developing commercial broadcasting.
From 1922 to 1923, as the number of stations grew without regulation, chaos reigned. In 1928 the government announced new assignments in the frequency band 550 to 1,600 kHz. Many more assignments were added after World War II, but these regulations are still in use today.