(Difference between revisions)
 Revision as of 21:30, 19 July 2010 (view source)← Older edit Revision as of 19:21, 12 June 2013 (view source)Newer edit → (13 intermediate revisions by 5 users not shown) Line 1: Line 1: − == Superheterodyne Receiver
== + == Superheterodyne Receiver  == − [[Image:Edwin Armstrong 0251.jpg|thumb|right|Edwin H. Armstrong]] + [[Image:Edwin Armstrong 0251.jpg|thumb|right|Edwin H. Armstrong]] −

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.

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 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.

+ [[Image:Superheterodyn.jpg|thumb|right|Superheterodyne receiver block diagram]] −

[[Reginald A. Fessenden|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, [[Reginald A. Fessenden|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.

+ 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 receiver. −

+ 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. 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 also exploited in the tuning of pianos. −

[[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 early 1930s, he almost single-handedly developed wide-band [[FM Radio|FM technology]].

+ 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 construction of functional heterodyne receivers during World War I. −

+ The basic scheme for superheterodyne radio receiver circuits of today was patented by Lucien Lévy (French patent or Brevet 493,660, filed 4 August 1917, granted 19 August 1919; and Brevet 506297, filed 1 October 1918, granted 27 May 1920), which he developed from Paul Laüt's earlier heterodyne technique. [[Edwin H. Armstrong|Edwin H. Armstrong]] reduced this to practice a year later, applying for [http://www.google.com/patents/US1342885 U.S. patent 1,342,885] on 30 December 1918, which issued on 8 June 1920. Working in Germany, Walter Schottky also conceived of it independently ([http://worldwide.espacenet.com/publicationDetails/originalDocument?CC=DE&NR=368937C&KC=C&FT=D&ND=&date=19230212&DB=&locale=de_EP Deutsche Reich Patent 368,937], filed 19 June 1918, granted 12 February 1923). Many others--including [[John Hogan|John V. L. Hogan]], [[Alexander Meissner|Alexander Meissner]], Harold J. Round, Georg von Arco, and Paul Laüt--made contributions. −

## Revision as of 19:21, 12 June 2013

Edwin H. Armstrong

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 also 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 construction of functional heterodyne receivers during World War I.

The basic scheme for superheterodyne radio receiver circuits of today was patented by Lucien Lévy (French patent or Brevet 493,660, filed 4 August 1917, granted 19 August 1919; and Brevet 506297, filed 1 October 1918, granted 27 May 1920), which he developed from Paul Laüt's earlier heterodyne technique. Edwin H. Armstrong reduced this to practice a year later, applying for U.S. patent 1,342,885 on 30 December 1918, which issued on 8 June 1920. Working in Germany, Walter Schottky also conceived of it independently (Deutsche Reich Patent 368,937, filed 19 June 1918, granted 12 February 1923). Many others--including John V. L. Hogan, Alexander Meissner, Harold J. Round, Georg von Arco, and Paul Laüt--made contributions.

Built on earlier heterodyne techniques, the essence of the superheterodyne circuit is to convert a 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 first commercially to improve reception in a radio receiver. This 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.