The most common type of receiver before vacuum tubes was the crystal set, although some early radios used some type of amplification through electric current or battery. Inventions of the triode amplifier, motor-generator, and detector enabled audio radio. The use of amplitude modulation (AM), with which more than one station can simultaneously 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.
To this day there is a small but avid base of fans of this technology who study and practice the art and science of designing and making crystal sets as a hobby; the Boy Scouts of America have often undertaken such craft projects to introduce boys to electronics and radio, and quite a number of them having grown up remain staunch fans of a radio that 'runs on nothing, forever'. As the only energy available is that gathered by the antenna system, there are inherent limitations on how much sound even an ideal set could produce, but with only moderately decent antenna systems remarkable performance is possible with a superior set.
During the mid 1920s, amplifying vacuum tubes (or thermionic valves in the UK) revolutionized radio receivers and transmitters. John Ambrose Fleming developed an earlier tube known as an "oscillation valve" (it was a diode). Lee De Forest placed a screen, the "grid" electrode, between the filament and plate electrode. The Dutch engineer Hanso Schotanus à Steringa Idzerda made the first regular wireless broadcast for entertainment from his home in The Hague on 6 November 1919. He broadcast his popular program four nights per week until 1924 when he ran into financial troubles. On 27 August 1920, regular wireless broadcasts for entertainment began in Argentina, pioneered by the group around Enrique Telémaco Susini, and spark gap telegraphy stopped. On 31 August 1920 the first known radio news program was broadcast by station 8MK, the unlicensed predecessor of WWJ (AM) in Detroit, Michigan. In 1922 regular wireless broadcasts for entertainment began in the UK from the Marconi Research Centre 2MT at Writtle near Chelmsford, England. Early radios ran the entire power of the transmitter through a carbon microphone. In the 1920s, the Westinghouse company bought Lee De Forest's and Edwin Armstrong's patent. During the mid 1920s, Amplifying vacuum tubes (US)/thermionic valves (UK) revolutionized radio receivers and transmitters. Westinghouse engineers developed a more modern vacuum tube.
The question of the 'first' publicly-targeted licensed radio station in the U.S. has more than one answer and depends on semantics. Settlement of this 'first' question may hang largely upon what constitutes 'regular' programming.
It is commonly attributed to KDKA in Pittsburgh, Pennsylvania, which in October 1920 received its license and went on the air as the first US licensed commercial broadcasting station. (Their engineer Frank Conrad had been broadcasting from his own station since 1916.) Technically, KDKA was the first of several already-extant stations to receive a 'limited commercial' license.
On February 17, 1919, station 9XM at the University of Wisconsin in Madison had already broadcast the first human speech to the public at large. That station is still on the air today as WHA.
9XM sent music over the air two years earlier, was originally licensed in 1914 and sent its first transmission in 1916.
On August 20, 1920, at least two months before KDKA, E.W. Scripps's WBL (now WWJ) in Detroit started broadcasting. It has carried a regular schedule of programming to the present.
There is the history noted above of Charles David Herrold's radio services (eventually KCBS) going back to 1909.
Broadcasting was not yet supported by advertising or listener sponsorship. The stations owned by manufacturers and department stores were established to sell radios and those owned by newspapers to sell newspapers and express the opinions of the owners. In the 1920s, Radio was first used to transmit pictures visible as television. During the early 1930s, single sideband (SSB) and frequency modulation (FM) were invented by amateur radio operators. By 1940, they were established commercial modes.
Westinghouse was brought into the patent allies group, General Electric, American Telephone and Telegraph, and Radio Corporation of America, and became a part owner of RCA. All radios made by GE and Westinghouse were sold under the RCA label 60% GE and 40% Westinghouse. ATT's Western Electric would build radio transmitters. The patent allies attempted to set up a monopoly, but they failed due to successful competition. Much to the dismay of the patent allies, several of the contracts for inventor's patents held clauses protecting "amateurs" and allowing them to use the patents. Whether the competing manufacturers were really amateurs was ignored by these competitors.
These features arose:
Commercial (United States) or governmental (Europe) station networks
Federal Radio Commission
Federal Communications Commission
CCIR
Birth of the soap opera
Race towards shorter waves and FM
The earliest radio stations were simply radio telegraph systems which did not carry audio are not listed. The included first radio station encompass AM and FM stations; these include both commercial, public and nonprofit varieties found throughout the world.
In 1933, FM radio was patented by inventor Edwin H. Armstrong. FM uses frequency modulation of the radio wave to minimize static and interference from electrical equipment and the atmosphere, in the audio program. In 1937, W1XOJ, the first experimental FM radio station, was granted a construction permit by the FCC. In the 1930s, standard analog television transmissions started in Europe, and then in the 1940s in North America.
In 1943, Tesla's patent (number 645576) was reinstated as holding priority in the "invention" of modern radio by the U.S. Supreme Court shortly after Tesla's death. The validity of the patent was never in question in the case. This decision was based on the fact that prior art existed before the establishment of Marconi's patent. Ignoring Tesla's prior art, 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 (as, it is speculated, the government's initial reversal to grant Marconi the patent right in order to nullify any claims Tesla had for compensation).