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Radiocommunication
RADIO is the technology of using radio waves to carry information, such as sound, by systematically modulating properties of electromagnetic energy waves transmitted through space, such as their amplitude , frequency , phase , or pulse width . When radio waves strike an electrical conductor , the oscillating fields induce an alternating current in the conductor. The information in the waves can be extracted and transformed back into its original form. Radio
Radio
systems need a transmitter to modulate (change) some property of the energy produced to impress a signal on it, for example using amplitude modulation or angle modulation (which can be frequency modulation or phase modulation ). Radio
Radio
systems also need an antenna to convert electric currents into radio waves , and radio waves into an electric current. An antenna can be used for both transmitting and receiving
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Electromagnetic Radiation
In physics , ELECTROMAGNETIC RADIATION (EM RADIATION or EMR) refers to the waves (or their quanta, photons ) of the electromagnetic field , propagating (radiating) through space carrying electromagnetic radiant energy . It includes radio waves , microwaves , infrared , (visible) light , ultraviolet , X- , and gamma radiation. Classically , electromagnetic radiation consists of ELECTROMAGNETIC WAVES, which are synchronized oscillations of electric and magnetic fields that propagate at the speed of light through a vacuum . The oscillations of the two fields are perpendicular to each other and perpendicular to the direction of energy and wave propagation, forming a transverse wave . The wavefront of electromagnetic waves emitted from a point source (such as a lightbulb) is a sphere . The position of an electromagnetic wave within the electromagnetic spectrum could be characterized by either its frequency of oscillation or its wavelength
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Heinrich Hertz
HEINRICH RUDOLF HERTZ (German: ; 22 February 1857 – 1 January 1894) was a German physicist who first conclusively proved the existence of the electromagnetic waves theorized by James Clerk Maxwell 's electromagnetic theory of light . The unit of frequency — cycle per second — was named the "hertz " in his honor. CONTENTS* 1 Biography * 1.1 Death * 2 Scientific work * 2.1 Meteorology * 2.2 Contact mechanics
Contact mechanics
* 2.3 Electromagnetic waves * 2.4 Cathode rays * 3 Nazi
Nazi
persecution * 4 Legacy and honors * 5 See also * 6 References * 7 Further reading * 8 External links BIOGRAPHYHeinrich Rudolf Hertz
Hertz
was born in 1857 in Hamburg
Hamburg
, then a sovereign state of the German Confederation
German Confederation
, into a prosperous and cultured Hanseatic family
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Electrostatic Induction
ELECTROSTATIC INDUCTION, also known as "electrostatic influence" or simply "influence" in Europe and Latin America, is a redistribution of electrical charge in an object, caused by the influence of nearby charges. In the presence of a charged body, an insulated conductor develops a positive charge on one end and a negative charge on the other end. Induction was discovered by British scientist John Canton in 1753 and Swedish professor Johan Carl Wilcke in 1762. Electrostatic generators , such as the Wimshurst machine , the Van de Graaff generator and the electrophorus , use this principle. Due to induction, the electrostatic potential (voltage ) is constant at any point throughout a conductor
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Electromagnetic Induction
ELECTROMAGNETIC or MAGNETIC INDUCTION is the production of an electromotive force (i.e., voltage) across an electrical conductor due to its dynamic interaction with a magnetic field . Michael Faraday is generally credited with the discovery of induction in 1831, and James Clerk Maxwell
James Clerk Maxwell
mathematically described it as Faraday\'s law of induction . Lenz\'s law describes the direction of the induced field. Faraday's law was later generalized to become the Maxwell-Faraday equation, one of the four Maxwell\'s equations in James Clerk Maxwell's theory of electromagnetism. Electromagnetic induction
Electromagnetic induction
has found many applications in technology, including electrical components such as inductors and transformers , and devices such as electric motors and generators
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Édouard Branly
ÉDOUARD EUGèNE DéSIRé BRANLY (23 October 1844 – 24 March 1940) was a French inventor, physicist and professor at the Institut Catholique de Paris . He is primarily known for his early involvement in wireless telegraphy and his invention of the Branly coherer around 1890. CONTENTS * 1 Biography * 2 Coherer
Coherer
* 3 Honours * 4 Legacy * 5 See also * 6 References * 7 External links and resources BIOGRAPHYHe was born on 23 October 1844. Édouard Branly
Édouard Branly
died in 1940. His funeral was at the Notre Dame cathedral in Paris and was attended by the President of France
President of France
, Albert Lebrun . He was interred in Père Lachaise Cemetery in Paris
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Photophone
The PHOTOPHONE is a telecommunications device that allows transmission of speech on a beam of light . It was invented jointly by Alexander Graham Bell
Alexander Graham Bell
and his assistant Charles Sumner Tainter on February 19, 1880, at Bell's laboratory at 1325 L Street in Washington, D.C.
Washington, D.C.
Both were later to become full associates in the Volta Laboratory Association , created and financed by Bell. On June 3, 1880, Bell's assistant transmitted a wireless voice telephone message from the roof of the Franklin School to the window of Bell's laboratory, some 213 meters (about 700 ft.) away. Bell believed the photophone was his most important invention
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Alexander Graham Bell
ALEXANDER GRAHAM BELL (March 3, 1847 – August 2, 1922) was a Scottish -born scientist, inventor, engineer, and innovator who is credited with patenting the first practical telephone . Bell's father, grandfather, and brother had all been associated with work on elocution and speech and both his mother and wife were deaf, profoundly influencing Bell's life's work. His research on hearing and speech further led him to experiment with hearing devices which eventually culminated in Bell being awarded the first U.S. patent for the telephone in 1876. Bell considered his most famous invention an intrusion on his real work as a scientist and refused to have a telephone in his study. Many other inventions marked Bell's later life, including groundbreaking work in optical telecommunications , hydrofoils , and aeronautics
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Communication System
In telecommunication , a COMMUNICATIONS SYSTEM is a collection of individual communications networks, transmission systems, relay stations, tributary stations, and data terminal equipment (DTE ) usually capable of interconnection and interoperation to form an integrated whole. The components of a communications system serve a common purpose, are technically compatible, use common procedures, respond to controls, and operate in union. Telecommunications is a method of communication (e.g., for sports broadcasting , mass media , journalism , etc.). A COMMUNICATIONS SUBSYSTEM is a functional unit or operational assembly that is smaller than the larger assembly under consideration..
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Terminal Equipment
In telecommunication , the term TERMINAL EQUIPMENT has the following meanings: * Communications equipment at either end of a communications link , used to permit the stations involved to accomplish the mission for which the link was established. * In radio -relay systems, equipment used at points where data are inserted or derived, as distinct from equipment used only to relay a reconstituted signal . * Telephone
Telephone
and telegraph switchboards and other centrally located equipment at which communications circuits are terminated.SEE ALSO * Customer-premises equipment * Data
Data
terminal equipment , an end instrument that converts user information into signals for transmission or reconverts the received signals into user informationREFERENCES This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C"
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Microphone
A MICROPHONE, colloquially nicknamed MIC or MIKE (/ˈmaɪk/ ), is a transducer that converts sound into an electrical signal . Microphones are used in many applications such as telephones , hearing aids , public address systems for concert halls and public events, motion picture production, live and recorded audio engineering , sound recording , two-way radios , megaphones , radio and television broadcasting, and in computers for recording voice, speech recognition , VoIP , and for non-acoustic purposes such as ultrasonic sensors or knock sensors . Several different types of microphone are in use, which employ different methods to convert the air pressure variations of a sound wave to an electrical signal. The most common are the dynamic microphone , which uses a coil of wire suspended in a magnetic field; the condenser microphone , which uses the vibrating diaphragm as a capacitor plate, and the piezoelectric microphone , which uses a crystal of piezoelectric material
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Loudspeaker
A LOUDSPEAKER (or LOUD-SPEAKER or SPEAKER) is an electroacoustic transducer ; which converts an electrical audio signal into a corresponding sound . The most widely used type of speaker in the 2010s is the DYNAMIC SPEAKER, invented in 1925 by Edward W. Kellogg and Chester W. Rice . The dynamic speaker operates on the same basic principle as a dynamic microphone , but in reverse, to produce sound from an electrical signal. When an alternating current electrical audio signal is applied to its voice coil , a coil of wire suspended in a circular gap between the poles of a permanent magnet , the coil is forced to move rapidly back and forth due to Faraday\'s law of induction , which causes a diaphragm (usually conically shaped) attached to the coil to move back and forth, pushing on the air to create sound waves . Besides this most common method, there are several alternative technologies that can be used to convert an electrical signal into sound
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Coherer
The COHERER is a primitive form of radio signal detector used in the first radio receivers during the wireless telegraphy era at the beginning of the 20th century. Its use in radio was based on the 1890 findings of French physicist Edouard Branly and adapted by other physicists and inventors over the next ten years. The device consists of a tube or capsule containing two electrodes spaced a small distance apart with loose metal filings in the space between. When a radio frequency signal is applied to the device, the metal particles would cling together or "cohere", reducing the initial high resistance of the device, thereby allowing a much greater direct current to flow through it. In a receiver, the current would activate a bell, or a Morse paper tape recorder to make a record of the received signal
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Lee De Forest
LEE DE FOREST (August 26, 1873 – June 30, 1961) was an American inventor, self-described "Father of Radio", and a pioneer in the development of sound-on-film recording used for motion pictures. He had over 180 patents, but also a tumultuous career—he boasted that he made, then lost, four fortunes. He was also involved in several major patent lawsuits, spent a substantial part of his income on legal bills, and was even tried (and acquitted) for mail fraud. His most famous invention, in 1906, was the three-element " Audion " (triode ) vacuum tube , the first practical amplification device. Although De Forest had only a limited understanding of how it worked, it was the foundation of the field of electronics , making possible radio broadcasting , long distance telephone lines, and talking motion pictures , among countless other applications
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Radio Transmitter Design
A radio transmitter is an electronic device which, when connected to an antenna , produces an electromagnetic signal such as in radio and television broadcasting, two way communications or radar . Heating devices, such as a microwave oven , although of similar design, are not usually called transmitters, in that they use the electromagnetic energy locally rather than transmitting it to another location. DESIGN ISSUESA radio transmitter design has to meet certain requirements. These include the frequency of operation , the type of modulation , the stability and purity of the resulting signal, the efficiency of power use, and the power level required to meet the system design objectives. High-power transmitters may have additional constraints with respect to radiation safety, generation of X-rays, and protection from high voltages
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Radio Transmitter
In electronics and telecommunications a TRANSMITTER or RADIO TRANSMITTER is an electronic device which produces radio waves with an antenna . The transmitter itself generates a radio frequency alternating current , which is applied to the antenna. When excited by this alternating current the antenna radiates radio waves. In addition to their use in broadcasting , transmitters are necessary component parts of many electronic devices that communicate by radio , such as cell phones , wireless computer networks , Bluetooth enabled devices, garage door openers , two-way radios in aircraft, ships, spacecraft, radar sets and navigational beacons. The term transmitter is usually limited to equipment that generates radio waves for communication purposes; or radiolocation , such as radar and navigational transmitters
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