Radio is transmission of signals where no wires are required and which uses the modulation of electromagnetic waves with frequencies below that of the visible light. Although it was Nikola Tesla who first demonstrated the feasibility of wireless communications in 1893, Guglielmo Marconi, an Italian inventor, was the first to develop workable radio communication. In Italy, he sent and received his first radio signal in the year 1895. Lots of experimentations were carried out with the radio, but it was in the early 1930s, when amateur radio operators invented single sideband and frequency modulation. And by the end of the decade, they were established commercial modes.

In 1954, Regency introduced a pocket transistor radio, the TR-1, powered by a "standard 22.5 V Battery". However in 1960, Sony introduced its first transistorized radio, which was small enough to fit in a vest pocket, and was able to be powered by a small battery. Over the next 20 years, except for very high-power uses, transistors replaced tubes almost completely. In the early 1990s, amateur radio experimenters were using personal computers with audio cards to process radio signals and in the year 1994, the U.S. Army launched an aggressive, successful project to construct a software radio that was to become a different radio on the fly by changing software.