Editing History of radio (section)

==Technological development==

===Amplitude-modulated (AM)===
The invention of amplitude-modulated (AM) radio, which allows more closely spaced  stations to simultaneously send signals (as opposed to spark-gap radio, where each transmission occupies a wide bandwidth) is attributed to [[Reginald Fessenden]], [[Valdemar Poulsen]] and [[Lee de Forest]].

=== Crystal set receivers ===
[[File:NBS 120 Set.jpg|thumb|left|In the 1920s, the [[Copyright status of works by the federal government of the United States|United States government publication]], "''Construction and Operation of a Simple Homemade Radio Receiving Outfit''", showed how almost any person handy with simple tools could a build an effective [[crystal radio]] receiver.]]

The most common type of receiver before vacuum tubes was the [[crystal radio|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 (radio)|detector]] enabled audio radio. The use of [[amplitude modulation]] ([[AM radio|AM]]), by which soundwaves can be transmitted over a continuous-wave radio signal of narrow bandwidth (as opposed to spark-gap radio, which sent rapid strings of damped-wave pulses that consumed much bandwidth and were only suitable for Morse-code telegraphy) was pioneered by Fessenden, Poulsen and Lee de Forest.<ref>{{Cite book|last=Basalla|first=George|title=The Evolution of Technology|publisher=Cambridge University Press|year=1988|pages=44}}</ref>

The art and science of crystal sets is still pursued as a hobby in the form of simple un-amplified radios that 'runs on nothing, forever'. They are used as a teaching tool by groups such as the [[Boy Scouts of America]] to introduce youngsters to electronics and radio. As the only energy available is that gathered by the antenna system, loudness is necessarily limited.

===Vacuum tubes===
[[File:First vacuum tube AM radio transmitter.jpg|thumb|The first commercial AM [[Audion]] [[vacuum tube]] [[Transmitter|radio transmitter]], built in 1914 by [[Lee De Forest]] who invented the Audion ([[triode]]) in 1906]]
During the mid-1920s, amplifying [[vacuum tube]]s revolutionized [[radio receiver]]s and [[transmitter]]s. [[John Ambrose Fleming]] developed a vacuum tube [[diode]]. [[Lee de Forest]] placed a screen, added a [[Control grid|"grid" electrode]], creating the [[triode]].<ref>{{Cite web|title=Vacuum Tube Radio |url=https://www.nps.gov/features/safr/feat0001/virtualships/vrmovies/muvr2hs11.htm|website=nps.gov|access-date=2020-05-27}}</ref>

Early radios ran the entire power of the transmitter through a [[carbon microphone]]. In the 1920s, the [[Westinghouse Electric (1886)|Westinghouse company]] bought Lee de Forest's and [[Edwin Armstrong]]'s patent. During the mid-1920s, Amplifying [[vacuum tube]]s revolutionized [[radio receiver]]s and transmitters. Westinghouse engineers developed a more modern vacuum tube.

The first radios still required batteries, but in 1926 the "[[battery eliminator]]" was introduced to the market. This tube technology allowed radios to be powered through the grid instead. They still required batteries to heat up the vacuum-tube filaments, but after the invention of [[Hot cathode|indirectly heated vacuum tubes]], the first completely battery free radios became available in 1927.<ref>[https://books.google.com/books?id=IAjtEeVtXqAC&dq=Canadian+inventor+E.S.+Rogers+1925+1926+1927+Battery+Eliminator+indirectly+heated+vacuum+tubes&pg=PA67 The Race for Wireless: How Radio was Invented (or Discovered?)]</ref>

In 1929 a new screen grid tube called UY-224 was introduced, an amplifier designed to operate directly on alternating current.<ref>[https://books.google.com/books?id=hygDAAAAMBAJ&dq=A.C.+screen+grid+tube+UY-224+1929&pg=PA71 Popular Science Aug 1929]</ref>

A problem with the early radios was fading stations and fluctuating volume. The invention of the [[superheterodyne receiver]] solved this problem, and the first radios with a heterodyne radio receiver went for sale in 1924. But it was costly, and the technology was shelved while waiting for the technology to mature, and in 1929 the Radiola 66 and Radiola 67 went for sale.<ref>[https://www.saturdayeveningpost.com/sep-keyword/late-1920s/ late 1920s Archives | The Saturday Evening Post]</ref><ref>[https://www.wshu.org/vintage-radio/2014-06-11/a-radio-for-the-great-depression A Radio for the Great Depression – WSHU]</ref><ref>[https://books.google.com/books?id=Ck9IGgEFeeoC&dq=Radiola+66+superheterodyne+1929&pg=PA340 Radiola: The Golden Age of RCA, 1919–1929]</ref>

===Loudspeakers===
In the early days one had to use headphones to listen to radio. Later loudspeakers in the form of a horn of the type used by phonographs, equipped with a telephone receiver, became available. But the sound quality was poor. In 1926 the first radios with electrodynamic loudspeakers went for sale, which improved the quality significantly. At first the loudspeakers were separated from the radio, but soon radios would come with a built-in loudspeaker.<ref>[https://books.google.com/books?id=tsT9kq4m_G8C&dq=Radiola+Model+104+Tractrix+horn+magnets&pg=PT323 Audio Engineering Explained]</ref>

Other inventions related to sound included the automatic volume control (AVC), first commercially available in 1928.<ref>[https://californiahistoricalradio.com/wp-content/uploads/2021/12/CHRS-Journal-Volume-8-No.-6-1984-Nov-Dec.pdf JI f()IU 112~ A\ IL – California Historical Radio Society]</ref> In 1930 a tone control knob was added to the radios. This allowed listeners to improve imperfect broadcasting.<ref>[https://books.google.com/books?id=sygDAAAAMBAJ&dq=%22Radio+Now+Has+Tone+Control%22&pg=PA84 Popular Science des 1930]</ref>

The [[magnetic cartridge]], which was introduced in the mid 20's, greatly improved the broadcasting of music. When playing music from a phonograph before the magnetic cartridge, a microphone had to be placed close to a horn loudspeaker. The invention allowed the electric signals to be amplified and then fed directly to the [[broadcast transmitter]].<ref>[https://books.google.com/books?id=3u-bCgAAQBAJ&dq=1925+paper+not+only+summarized+the+state+of+the+art+but+also+presented+a+new+loudspeaker+design&pg=PA159 Dawn of the Electronic Age: Electrical Technologies in the Shaping of the Modern World, 1914 to 1945]</ref>

===Transistor technology===
[[File:Vintage Regency TR-1 4-Transistor Radio, Mandarin Red, Made in USA, Introduced In 1954 (8622359295).jpg|thumb|upright|The [[Regency TR-1]], which used [[Texas Instruments]]' [[NPN transistor]]s, was the world's first commercially produced [[transistor radio]] in 1954. Size: 3×5×1.25 inch (7.6×12.7×3.2 cm)]]

Following development of [[transistor]] technology, [[bipolar junction transistor]]s led to the development of the [[transistor radio]]. In 1954, the Regency company introduced a pocket transistor radio, the [[Regency TR-1|TR-1]], powered by a "standard 22.5 V Battery." In 1955, the newly formed [[Sony]] company introduced its first transistorized radio, the [[TR-55]].<ref name="pbs">{{cite web |url=https://www.pbs.org/transistor/background1/events/tradio.html |title=Transistor Radios |year=1999 |publisher=ScienCentral (pbs.org)|access-date=2018-02-03}}</ref> It was small enough to fit in a [[Waistcoat|vest]] pocket, powered by a small battery. It was durable, because it had no vacuum tubes to burn out. In 1957, Sony introduced the TR-63, the first mass-produced transistor radio, leading to the mass-market penetration of transistor radios.<ref name="Skrabec">{{cite book|last1=Skrabec| first1=Quentin R. Jr. |url=https://books.google.com/books?id=2kc69qrid9oC&pg=PA195|title=The 100 Most Significant Events in American Business: An Encyclopedia|date=2012|publisher=ABC-CLIO|isbn=978-0313398636|pages=195–97}}</ref> Over the next 20 years, transistors replaced tubes almost completely except for high-power [[transmitter]]s.

By the mid-1960s, the [[Radio Corporation of America]] (RCA) were using [[metal–oxide–semiconductor field-effect transistor]]s (MOSFETs) in their consumer products, including [[FM radio]], television and [[amplifier]]s.<ref name="Harrison">{{cite book|last1=Harrison|first1=Linden T.|url=https://books.google.com/books?id=03JmxpE39N4C&pg=PA185|title=Current Sources and Voltage References: A Design Reference for Electronics Engineers|date=2005|publisher=Elsevier|isbn=978-0080455556|page=185}}</ref> [[Metal–oxide–semiconductor]] (MOS) [[large-scale integration]] (LSI) provided a practical and economic solution for radio technology, and was used in [[mobile radio]] systems by the early 1970s.<ref name="Zeidler">{{cite journal|last1=Zeidler|first1=G.|last2=Becker|first2=D.|date=1974|title=MOS LSI Custom Circuits Offer New Prospects for Communications Equipment Design|url=https://books.google.com/books?id=TihQAAAAYAAJ|journal=Electrical Communication|publisher=[[Western Electric Company]]|volume=49–50|pages=88–92|quote=In many fields of communications equipment design, MOS LSI custom built circuits provide the only practical and economic solution. (...) A complete list of all applications is beyond the scope of this paper since new MOS developments are constantly being initiated in the various technical areas. Typical examples of completed and present MOS developments are:<br />— crosspoints<br />— multiplexers<br />— modems<br />— mobile radios}}</ref>

===Integrated circuit===
The first integrated circuit (IC) radio, P1740 by [[General Electric]], became available in 1966.<ref>[https://worldradiohistory.com/Archive-Electronics-World/60s/1966/Electronics-World-1966-11.pdf Electronics World (November, 1966, Vol. 76, No. 51. p. 44)]</ref>

===Car radio===
The first car radio was introduced in 1922, but it was so large that it took up too much space in the car.<ref>[https://techhistorian.com/first-car-with-radio/ The First Car With a Radio – Techhistorian]</ref> The first commercial car radio that could easily be installed in most cars went for sale in 1930.<ref>[https://www.thewellnews.com/fourth-estate/can-am-radio-be-saved-should-it-be/ Can AM Radio Be Saved? Should It Be? | The Well News]</ref><ref>[https://mashhua.com/detail/2070 Entrepreneur – Founder Of Motorola – Paul Galvin]</ref>