20th century

Developments in the early 20th century (1900-1959):

Aircraft used commercial AM radio stations for navigation. This continued through the early 1960s when VOR systems finally became widespread (though AM stations are still marked on U.S. aviation charts).
In the early 1930s, single sideband and frequency modulation were invented by amateur radio operators. By the end of the decade, they were established commercial modes.
Radio was used to transmit pictures visible as television as early as the 1920s. Standard analog transmissions started in North America and Europe in the 1940s.
In 1954, Regency introduced a pocket transistor radio, the TR-1, powered by a "standard 22.5V Battery".

Developments in the latter half of the 20th century (1960-1999):

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In 1960, Sony introduced their first transistorized radio, small enough to fit in a vest pocket, and able to be powered by a small battery. It was durable, because there were no tubes to burn out. Over the next twenty years, transistors replaced tubes almost completely except for very high power uses.
In 1963 color television was commercially transmitted, and the first (radio) communication satellite, TELSTAR, was launched.
In the late 1960s, the U.S. long-distance telephone network began to convert to a digital network, employing digital radios for many of its links.
In the 1970s, LORAN became the premier radio navigation system. Soon, the U.S. Navy experimented with satellite navigation, culminating in the invention and launch of the GPS constellation in 1987.
In the early 1990s, amateur radio experimenters began to use personal computers with audio cards to process radio signals. In 1994, the U.S. Army and DARPA launched an aggressive, successful project to construct a software radio that could become a different radio on the fly by changing software.
Digital transmissions began to be applied to broadcasting in the late 1990s.

The 20th century lasted from 1901 to 2000 in the Gregorian calendar. Many people confuse the 20th century and the years nineteen hundreds (1900s).

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The first benefit to come from radio telegraphy was the ability to establish communication between coast radio stations and ships at sea. A company called "British Marconi" was established to make use of Marconi's and others' patents. This company along with its subsidiary American Marconi, had a stranglehold on ship to shore communication. It operated much the way American Telephone and Telegraph operated until 1983, owning all of its own equipment and refusing to communicate with non-Marconi equipped ships. Many inventions improved the quality of radio, and amateurs experimented with uses of radio, thus the first seeds of broadcasting were planted. Around the turn of the century, the Slaby-Arco wireless system was developed by Adolphus Slaby and Georg von Arco (later incorporated into Telefunken).

On Christmas Eve, 1906, Reginald Fessenden used an Alexanderson alternator and rotary spark-gap transmitter to make the first radio audio broadcast. From Brant Rock, Massachusetts, Fessenden made the transmission. Ships at sea heard a broadcast that included Fessenden playing O Holy Night on the violin and reading a passage from the Bible.

In 1909, Marconi and Karl Ferdinand Braun were awarded the Nobel Prize in Physics for "contributions to the development of wireless telegraphy". Later, though, Tesla's patent (number 645576) was reinstated by the U.S. Supreme Court (1943), shortly after Tesla's death. This decision was based on the fact that prior art existed before the establishment of Marconi's patent. The decision may have enabled the U.S. government to avoid having to pay damages that were being claimed by the Marconi Company for use of its patents during World War I (though, these people ignore Tesla's prior art).

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Wireless telegraphy using spark-gap transmitters quickly became universal on large ships after the sinking of the RMS Titanic in 1912. The International Convention for the Safety of Life at Sea was convened in 1913 and produced a treaty requiring shipboard radio stations be manned 24 hours a day. A typical high-power spark gap was a rotating commutator with six to twelve contacts per wheel, nine inches to a foot wide, driven by about 2000 volts DC. As the gaps made and broke contact, the radio wave was audible as a tone in a crystal set. The telegraph key often directly made and broke the 2000 volt supply. One side of the spark gap was directly connected to the antenna. Receivers with thermionic valves became commonplace before spark-gap transmitters were replaced by continuous wave transmitters.

The 1920s saw the development of a more modern vacuum tube, constructed by Westinghouse engineers (after Westinghouse bought DeForest's and Armstrong's patent). The first known radio news program was broadcast August 31, 1920 by station 8MK, the unlicensed predecessor of WWJ (AM) in Detroit, Michigan. Regular wireless broadcasts for entertainment commenced in 1922 from the Marconi Research Centre at Writtle near Chelmsford, England. Early radios ran the entire power of the transmitter through a carbon microphone.

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While some early radios used some type of amplification through electric current or battery, through the mid 1920s the most common type of receiver was the crystal set. In the 1920s, amplifying vacuum tubes revolutionized both radio receivers and transmitters.

Inventions of the triode amplifier, generator, and detector enables audio radio. The invention of amplitude-modulated (AM) radio, so that more than one station can send signals (as opposed to spark-gap radio, where one transmitter covers the entire bandwidth of spectra) was pioneered by Fessenden and Lee de Forest.

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Radio

History of radio

Discovery and development