Communications: From Carrier Pigeons to Telephones and Radio (1876–1976)

Abstract

As mentioned in the abstract of Chap. 13, communications technology, at least since semaphores, has been powered by electricity. At first, the messages were coded by groups of long and short interruptions in a sound (dots and dashes). The big step was voice transmission on a wire, using the same principle as sound transmission through the air, i.e., by varying signal intensity and frequency of a signal (audio modulation or AM). This method was applied, at first to wireless (radio) transmission. Later, a better method (frequency modulation, FM) was introduced in the 1930s. The transmission of pictures (TV) was accomplished by combining AM and FM, using higher frequencies and converting a picture into a sequence of “pixels” (like “dots” in Morse code) whose differences in frequency and intensity correspond to colors and brightness. Subsequent innovations in telecommunication are primarily to increase the information-carrying capacity of the system, by utilizing higher and higher frequencies.