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Superheterodyne Receiver

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== Superheterodyne Receiver<br>  ==
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== Superheterodyne Receiver ==
  
In radio broadcasting, a transmitting antenna sends out electromagnetic waves that carry the radio program. A radio antenna may pick up these electromagnetic waves. The free electrons in the metal antenna are jostled back and forth by the passing radio wave. Converting the tiny currents created by this jostling into the speech or music of the radio program is the job of a radio receiver.  
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[[Image:Edwin Armstrong 0251.jpg|thumb|right|Edwin H. Armstrong]]
  
There are many different ways a radio receiver can perform this conversion. Reginald Fessenden was the first to apply one of these methods, called the heterodyne principle, to wireless communications in 1901. Fessenden coined the term heterodyne from the Greek words for other and force. The heterodyne principle is based on a well-known sound phenomenon where the combination of two different audio tones of frequencies A and B results in an oscillation with the frequency A minus B. This phenomenon is exploited every day in the tuning of pianos.
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[[Image:Radiola Ad 0153.jpg|thumb|right|RCA Radiola Super-Heterodyne]]
  
Fessenden suggested that the heterodyne principle be employed in a radio receiver by mixing the incoming radio-frequency wave with a locally generated wave of slightly different frequency. The combined wave then would drive the diaphragm of an earpiece at the frequency of the audio. For example, mixing a 101 kHz input with 100 kHz generated by the receiver yields a frequency of 1 kHz, which is in the audible range. Lacking an effective, inexpensive local oscillator, Fessenden could not make a practical success of the heterodyne receiver. Later, however, electron tubes effectively filled the role of the oscillator and led to the building of functional heterodyne receivers during the World War I.
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[[Image:Superheterodyn.jpg|thumb|right|Superheterodyne receiver block diagram]]
  
The basic scheme for radio receivers of today was invented by Edwin H. Armstrong in 1918. Building on Fessenden’s earlier heterodyne technique, Armstrong's scheme is known as the superheterodyne method, and its ability to boost weak signals made it possible to reduce the size of antennas dramatically. Armstrong applied for a patent on 30 December 1918, which was issued on 8 June 1920. Armstrong exploited the heterodyne principle in a different way in his superheterodyne receiver, however. The essential idea was to convert the high-frequency signal to one of intermediate frequency by heterodyning it with an oscillation generated in the receiver. The intermediate-frequency signal was then amplified before the detection and amplification that usually occurs in receivers. Armstrong shared the credit for the superheterodyne with others who worked largely independently. Of special note were Lucien Lévy in France and Walter Schottky in Germany. RCA marketed the superheterodyne beginning in March 1924. It was more sensitive than the heterodyne and could be tuned by turning a single knob. Not long after RCA began licensing other manufacturers to make the superheterodyne, it became the standard type of radio receiver.  
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In [[Radio|radio]] broadcasting, a transmitting antenna sends out electromagnetic waves that carry the radio program. A radio antenna may pick up these electromagnetic waves. The free electrons in the metal antenna are jostled back and forth by the passing radio wave. Converting the tiny currents created by this jostling into the speech or music of the radio program is the job of a [[Radio|radio]] receiver.
  
Armstrong went on to other achievements. In 1922, he introduced the super-regenerative circuit, which was widely used in special-purpose receivers, such as police radios, ship-to-shore radios, and radar systems. In the late 1920s and early 1930s, he almost single-handedly developed wide-band FM technology.<br><br>
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There are many different ways a radio receiver can perform this conversion. [[Reginald A. Fessenden|Reginald Fessenden]] was the first to apply one of these methods, called the heterodyne principle, to wireless communications in 1901. [[Reginald A. Fessenden|Fessenden]] coined the term heterodyne from the Greek words for "other" and "force." The heterodyne principle is based on a well-known sound phenomenon where the combination of two audio tones with frequencies A and B results in an oscillation equal to frequency A minus B. This phenomenon is exploited in the tuning of pianos.
  
[[Category:Communications]] [[Category:Radio_communication]] [[Category:Communication_equipment]] [[Category:Receivers]]
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[[Reginald A. Fessenden|Fessenden]] suggested that the heterodyne principle be employed in a radio receiver by mixing the incoming radio wave with a locally generated wave of slightly different frequency. The combined wave then drives the diaphragm of an earpiece at the frequency of the audio. For example, mixing a 101 kHz input with a 100 kHz signal generated by the receiver yields a frequency of 1 kHz, which is in the audible range. Lacking an effective, inexpensive local oscillator, [[Reginald A. Fessenden|Fessenden]] could not make a practical success of the heterodyne receiver. Little more than ten years later, however, electron tubes effectively filled the role of the oscillator and led to the building of functional heterodyne receivers during World War I.
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The basic scheme for radio receivers of today was patented by Lucien Lévy in 1917 (French patent or Brevet 493,660) and reduced to practice by [[Edwin H. Armstrong|Edwin H. Armstrong]] a year later.  Many others--including [[John Hogan|John V. L. Hogan]], Alexander Meissner, Harold J. Round, Georg von Arco, and Paul Laüt--made contributions or, in Walter Schottky's case, conceived of it independently (Deutsche Republik Patent 368937).  Built on [[Reginald A. Fessenden|Fessenden’s]] earlier heterodyne technique, the essence of the superheterodyne circuit is to convert the high-frequency signal to one of intermediate frequency by heterodyning it with an oscillation generated in the receiver. The intermediate-frequency signal is then amplified before the detection and amplification that usually occurs in receivers. The superheterodyne circuit has the ability to boost weak signals significantly and makes it possible to reduce the size of antennas dramatically.
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While Lévy had applied superheterodyne technology for the purpose of encoding messages during the war, Armstrong exploited it to improve reception in a radio receiver, which became commercially important as the general public in the United States and western Europe began embracing broadcast news and entertainment in the early 1920s.  [[RCA (Radio Corporation of America)|RCA]] marketed the superheterodyne beginning in March 1924. It was more sensitive than the heterodyne receiver and could be tuned by turning a single knob. Not long after RCA began licensing other manufacturers to make the superheterodyne, it became the standard circuit for [[Radio|radio]] receivers.
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[[Edwin H. Armstrong|Armstrong]] went on to other achievements. In 1922, he introduced the super-regenerative circuit, which was widely used in special-purpose receivers, such as police [[Radio|radios]], ship-to-shore radios, and [[Radar|radar]] systems. In the late 1920s and 1930s, he developed and commercialized wide-band [[FM Radio|FM technology]].
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== Further Reading ==
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Alan Douglas, [http://antiqueradios.com/superhet/ "Who Invented the Superheterodyne?"]  
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[http://findingaids.cul.columbia.edu/ead/nnc-rb/ldpd_4078687/summary Edwin H. Armstrong Papers]
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Walter Schottky, [http://www.nonstopsystems.com/radio/article-superhet.pdf "On the Origin of the Super-Heterodyne Method," Proceedings of the I.R.E. 14 (Oct. 1926)]
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[[Category:Communications]]
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[[Category:Communication_equipment]]
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[[Category:Receivers]]
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[[Category:Radio_communication]]

Revision as of 13:00, 19 April 2012

Superheterodyne Receiver

Edwin H. Armstrong
Edwin H. Armstrong
RCA Radiola Super-Heterodyne
RCA Radiola Super-Heterodyne
Superheterodyne receiver block diagram
Superheterodyne receiver block diagram

In radio broadcasting, a transmitting antenna sends out electromagnetic waves that carry the radio program. A radio antenna may pick up these electromagnetic waves. The free electrons in the metal antenna are jostled back and forth by the passing radio wave. Converting the tiny currents created by this jostling into the speech or music of the radio program is the job of a radio receiver.

There are many different ways a radio receiver can perform this conversion. Reginald Fessenden was the first to apply one of these methods, called the heterodyne principle, to wireless communications in 1901. Fessenden coined the term heterodyne from the Greek words for "other" and "force." The heterodyne principle is based on a well-known sound phenomenon where the combination of two audio tones with frequencies A and B results in an oscillation equal to frequency A minus B. This phenomenon is exploited in the tuning of pianos.

Fessenden suggested that the heterodyne principle be employed in a radio receiver by mixing the incoming radio wave with a locally generated wave of slightly different frequency. The combined wave then drives the diaphragm of an earpiece at the frequency of the audio. For example, mixing a 101 kHz input with a 100 kHz signal generated by the receiver yields a frequency of 1 kHz, which is in the audible range. Lacking an effective, inexpensive local oscillator, Fessenden could not make a practical success of the heterodyne receiver. Little more than ten years later, however, electron tubes effectively filled the role of the oscillator and led to the building of functional heterodyne receivers during World War I.

The basic scheme for radio receivers of today was patented by Lucien Lévy in 1917 (French patent or Brevet 493,660) and reduced to practice by Edwin H. Armstrong a year later. Many others--including John V. L. Hogan, Alexander Meissner, Harold J. Round, Georg von Arco, and Paul Laüt--made contributions or, in Walter Schottky's case, conceived of it independently (Deutsche Republik Patent 368937). Built on Fessenden’s earlier heterodyne technique, the essence of the superheterodyne circuit is to convert the high-frequency signal to one of intermediate frequency by heterodyning it with an oscillation generated in the receiver. The intermediate-frequency signal is then amplified before the detection and amplification that usually occurs in receivers. The superheterodyne circuit has the ability to boost weak signals significantly and makes it possible to reduce the size of antennas dramatically.

While Lévy had applied superheterodyne technology for the purpose of encoding messages during the war, Armstrong exploited it to improve reception in a radio receiver, which became commercially important as the general public in the United States and western Europe began embracing broadcast news and entertainment in the early 1920s. RCA marketed the superheterodyne beginning in March 1924. It was more sensitive than the heterodyne receiver and could be tuned by turning a single knob. Not long after RCA began licensing other manufacturers to make the superheterodyne, it became the standard circuit for radio receivers.

Armstrong went on to other achievements. In 1922, he introduced the super-regenerative circuit, which was widely used in special-purpose receivers, such as police radios, ship-to-shore radios, and radar systems. In the late 1920s and 1930s, he developed and commercialized wide-band FM technology.

Further Reading

Alan Douglas, "Who Invented the Superheterodyne?"

Edwin H. Armstrong Papers

Walter Schottky, "On the Origin of the Super-Heterodyne Method," Proceedings of the I.R.E. 14 (Oct. 1926)