Radio

Radio is the use of electromagnetic waves to send information through space without a connecting wire. It began as wireless telegraphy in the 1890s, grew into voice and music broadcasting in the early 1900s, and now carries everything from AM and FM stations to emergency and weather communications. No single person invented radio, and the question of who deserves the credit has been argued in laboratories, patent offices and courts.

History of radio

Radio grew out of nineteenth-century physics. James Clerk Maxwell’s theory of electromagnetic waves led Heinrich Hertz to produce such waves in a laboratory, although Hertz did not think his experiment had any practical use.

In 1892 the physicist William Crookes suggested that these waves could carry telegraph messages, using transmitters and receivers tuned to the same wavelength. A year later Nikola Tesla proposed sending signals with adjustable high-frequency oscillations, in a lecture at the Franklin Institute in Philadelphia.

In 1895 the young Italian experimenter Guglielmo Marconi sent wireless signals over about a mile and a half at his father’s estate near Bologna. In 1896 he took his apparatus to England, where he was granted what the Nobel Foundation calls the world’s first patent for a system of wireless telegraphy. In 1897 he formed a company to sell the technology, and in 1899 he linked England and France across the English Channel.

In December 1901, by the Nobel Foundation’s account, Marconi sent the first wireless signals across the Atlantic Ocean, from Poldhu in Cornwall to St. John’s in Newfoundland, a distance of about 2,100 miles. This showed that radio waves were not blocked by the curve of the Earth. Regular transatlantic commercial service opened in 1907 between Glace Bay in Nova Scotia and Clifden in Ireland.

Voice came next. On Christmas Eve 1906 Reginald Fessenden transmitted the first program of music and speech, sent from Massachusetts and received as far away as Virginia. In October 1920 Westinghouse received the first US broadcasting license for station KDKA in Pittsburgh, which held the first scheduled public broadcast on 2 November 1920.

Inventor and origins of radio

Radio has no single inventor. Marconi built the first widely successful wireless business and shared the 1909 Nobel Prize in Physics with the German physicist Ferdinand Braun. Others, including Oliver Lodge and Tesla, had published or patented closely related ideas about tuned circuits before Marconi’s key patent.

The dispute reached the US Supreme Court in 1943, in Marconi Wireless Telegraph Co. of America v. United States. The Court affirmed that the broad claims of one Marconi patent, No. 763,772, were invalid because earlier work, above all a patent held by John Stone Stone, had already disclosed the same invention. The opinion also described earlier tuning designs by Lodge and Tesla.

The ruling dealt with the validity of specific patent claims. It did not decide who first sent a wireless message, and Justice Felix Frankfurter dissented in part from the finding of invalidity.

Fessenden is credited with the first voice broadcast and with developing amplitude modulation, while Edwin Armstrong later invented important receiver circuits and frequency modulation. Radio is best understood as a layered invention with many contributors.

How radio works

A radio transmitter turns sound into an electrical signal and uses it to modify a steady carrier wave at a chosen frequency. An antenna sends the modulated wave into the air, where it travels at the speed of light.

A receiver’s antenna picks up many waves at once, and a tuned circuit selects the one at the desired frequency. The receiver then removes the carrier and turns the remaining signal back into sound.

Amplitude modulation, or AM, varies the strength of the carrier. It tends to pick up static from sources such as lightning, which is why the sound can be noisy. Frequency modulation, or FM, varies the frequency of the carrier instead. Armstrong used it by the 1930s to improve sound quality, although AM stayed dominant for years afterward.

Tuning made crowded airwaves workable. Marconi’s 1900 patent No. 7777 covered tuned, or syntonic, telegraphy, and Armstrong’s regenerative and superheterodyne circuits later made receivers far more sensitive by using electron tubes.

Types of radio

Wireless telegraphy was the earliest form. It sent Morse code between stations, and it was especially valuable for ships. Broadcast radio sends one program from a station to any listener in range, usually on the AM or FM bands.

Engineers also built point-to-point links. Between 1923 and 1926 Marconi’s team developed a short-wave beam system for long-distance communication, and the first beam station, linking England and Canada, opened in 1926. In 1932 a microwave radiotelephone link began operating between Vatican City and the papal summer residence at Castel Gandolfo.

Impact of radio

Radio changed shipping first. Operators sent messages to shore, and in an emergency a radio could be the only way to contact rescue ships.

Broadcasting then created a mass audience. By the 1940s radio carried news, sports, dramas, comedies, soap operas and commercials, and President Franklin Roosevelt used his fireside chats to address Americans during the Great Depression and World War II. By the 1930s a radio was the single most popular optional item in cars.

The transistor, demonstrated in 1947, shrank radios until they could go almost anywhere. It also made it possible to combine AM and FM in a single small set. Radio also helped prepare the ground for television, which borrowed its programming model.

Uses of radio today

Radio remains a major source of information and entertainment in spite of competition from television and the internet. For many listeners it is still the main way to hear music and talk programs.

The wider radio spectrum is used by fixed and mobile services, broadcasting, amateur radio, space research, emergency telecommunications, meteorology and satellite navigation, according to the International Telecommunication Union. Its Radiocommunication Sector describes the spectrum and satellite orbits as natural resources in growing demand, and it works to keep services free of interference through the Radio Regulations, which are revised at world radiocommunication conferences. The same principle of sending information over a wavelength carried through air also underlies mobile networks and Wi-Fi.

Editorially reviewed by Specialty Digest Editorial TeamLast reviewed November 4, 2026Researched and drafted with AI assistanceReport an issue