Original content: Copyright © 2000, 2001, 2002, 2003 Museum of American Heritage
Trademarks are the property of their owners
| 1805 | Theory of induced current: Michael Faraday (England) and Joseph Henry (US) each individually developed the theory that a current flowing in one wire could induce a current flow in another wire not physically connected to the first wire. |
| 1820 | Hans Christian Oersted (Denmark) showed that a current flowing in a wire sets up a magnetic field around that wire. A changing current causes a changing magnetic field which in turn can cause a changing current to flow in an adjacent wire. This principle, electromagnetic induction, explained the observations of Faraday and Henry. |
| 1864 | James Clerk Maxwell (Scotland) publishes a set of equations describing the propagation of electromagnetic waves through space at the speed of light. |
| 1883 | Edison (US), seeking the cause of blackening of incandescent lamps, discovers current flow inside an evacuated bulb. The "Edison effect", current flow in a vacuum between a heated wire and a positively charged electrode, demonstrates electron flow through a vacuum. |
| 1887 | Heinrich Hertz (Germany) builds a spark gap transmitter and a tuned pickup loop receiver to transmit and receive electromagnetic waves. He was also able to verify Maxwell's prediction that radio waves travel at the speed of light. |
| 1895 | Guglielmo Marconi (Italy) demonstrated the use of electromagnetic waves for long distance communication, resulting in the first practical wireless telegraph system. He also discovered that the range of wireless communication improved substantially with increased antenna elevation and the use of a grounded connection to the antenna. |
| 1899 | Marconi sends the first wireless telegraph message across the English Channel. |
| 1900 | Invention of crystal detector. The first model was a steel needle resting on a carbon block. Subsequent designs used a thin metal probe, or whisker in contact with a crystal of lead sulfide or carborundum. |
| 1901 | Marconi sends a wireless signal (the letter "s") between Cornwall, England and St. John's, Newfoundland |
| 1903 | Valdemar Poulsen (Denmark) develops the arc transmitter, capable of generating a relatively clean radiofrequency signal. The Poulsen transmitter was widely used until the 1920s, when it was displaced by vacuum tube designs. |
| 1904 | Sir John Fleming (England) develops the vacuum diode based on the Edison effect. The device serves as a radio wave detector and is the first practical vacuum tube. |
| 1906 | Reginald Fessenden (US) transmits the first radio voice message using a transmitter powered by a 1000 watt alternator (ac generator) rotating at 20,000 rpm and a water cooled carbon microphone connected between the transmitter and the antenna. |
| Lee De Forest builds the first vacuum tube triode, demonstrating modulated current flow resulting from varying the signal to a control grid electrode in a vacuum tube. His "Audion" is the first practical electronic signal amplifier and the foundation for the electronic age to come. | |
| 1914 | Regenerative detector design: An invention of Edwin Armstrong that greatly increased the sensitivity of radio receivers, albeit at the cost of much finicky tuning for proper operation. Misadjusted, it could radiate a signal interfering with the operation of other nearby receivers. |
| 1918 | US Army operates a 1,000,000 watt Poulsen arc transmitter in radiotelegraph service. This transmitter operated at a 15 kHz frequency, the about the same as used in modern communications to underwater submarines. |
| Introduction of superheterodyne receiver, a superior design that eventually became the standard design for radio receivers. | |
| 1922 | Introduction of high power vacuum tubes capable of operating radio transmitters at 50,000 watt levels and higher frequencies. |
| Cone-type loudspeaker, which replaced individual headsets and allowed an entire family to listen to a broadcast together. | |
| 1924 | Introduction of battery eliminator, an AC powered electronic device that supplied the voltages needed to operate a radio receiver. |
| 1927 | AC operation of radio receivers, eliminating the cumbersome batteries or battery eliminators previously required. This event was enabled by the design of vacuum tubes with separate elements for electron emission (cathode) and for heating the cathode. Now only an AC line cord was required to power the radio receiver. |
| 1929 | Invention of the four element vacuum tube (tetrode), allowing substantial increases in power levels handled by small vacuum tubes and improvements in audio fidelity. |
| 1933 | Edwin Armstrong patents frequency modulation. |
| 1938 | General Electric markets first FM receiver for consumer use. |
| 1948 | Invention of transistor. It begins to displace vacuum tubes in radio receivers during the decade of the 1950s. |
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page last updated: February 18, 2003 Original content: Copyright © 2000, 2001, 2002, 2003 Museum of American Heritage Trademarks are the property of their owners |
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