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1918 __ The superheterodyne receiver
Edwin Armstrong (1890-1954)
Comment : In 1918 Armstrong developed the superheterodyne receiver that incorporated the first local oscillator and intermediate frequency modules. The "superhet" as it is sometimes called qualifies a receiver able to function over a range or band of frequencies. The word "heterodyne" means "beating", a technique producing a beating or heterodyne frequency by mixing two or more signals in a nonlinear device such as a vacuum tube, a transistor, or a diode mixer. The incoming frequency is converted to a fixed intermediate frequency (I.F.) where amplification and filtering are provided. In a typical AM receiver, this IF is set on 455 Kc and usually on 10.7 Mc for FM VHF receivers. The "superhet" uses a local oscillator called a variable frequency oscillator (V.F.O.) to maintain a constant difference between its beating frequency and the received frequency to get a constant I.F. n addition, in 1922 Armstrong created the superregenerative receiver, a simplified superheterodyne that improved the gain while simplifying the adjustment of the receiver. The "regen" as it was called was qualified as a receiver "unsurpassed in comparable simplicity, weak signal reception, inherent noise-limiting and AGC action and, freedom from overloading and spurious responses", nothing less. In fact the "regen" used an oscillating detector receiver that we will encounter in all V/UHF rigs in the '20s to the '50s, and that is still used today in children's walkie-talkies, and some receiver kits. The "regen" radios took the most of very few components. However, as parts became easier to obtain, the "superhet" replaced it in all radio activities. I will not learn you that the superheterodyne receiver is the most common receiver in use today. (Thierry Lombry, “The History of Amateur Radio”)
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