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A 5-tube superheterodyne receiver manufactured by Toshiba circa 1955 Superheterodyne transistor radio circuit circa 1975. A superheterodyne receiver, often shortened to superhet, is a type of radio receiver that uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original carrier frequency.
Block diagram of a superheterodyne receiver. The dotted line indicates that the RF filter and local oscillator must be tuned in tandem. The superheterodyne receiver, invented in 1918 by Edwin Armstrong [10] is the design used in almost all modern receivers [11] [9] [12] [13] except a few specialized applications.
An important and widely used application of the heterodyne technique is in the superheterodyne receiver (superhet). In the typical superhet, the incoming radio frequency signal from the antenna is mixed (heterodyned) with a signal from a local oscillator (LO) to produce a lower fixed frequency signal called the intermediate frequency (IF) signal.
For example, a key component of a superheterodyne receiver is a mixer used to move received signals to a common intermediate frequency. Frequency mixers are also used to modulate a carrier signal in radio transmitters .
The name superheterodyne was a contraction of supersonic heterodyne, to distinguish it from receivers in which the heterodyne frequency was low enough to be directly audible, and which were used for receiving continuous wave (CW) Morse code transmissions (not speech or music).
Image response (or more correctly, image response rejection ratio, or IMRR) is a measure of performance of a radio receiver that operates on the superheterodyne principle. [1] In such a radio receiver, a local oscillator (LO) is used to heterodyne or "beat" against the incoming radio frequency (RF), generating sum and difference frequencies.
RCA also vigorously prosecuted patent infringers. This situation helped propel RCA to the forefront of radio manufacturers in the 1920s due to the higher efficiency of the superhet circuit- a situation which lasted until the patents expired in the early 1930s, at which time a flood of low-cost superheterodyne receivers hit the market.
Local oscillators are used in the superheterodyne receiver, the most common type of radio receiver circuit. They are also used in many other communications circuits such as modems, cable television set top boxes, frequency division multiplexing systems used in telephone trunklines, microwave relay systems, telemetry systems, atomic clocks, radio telescopes, and military electronic ...