Automatic gain control (AGC) is an electronic system found in many types of devices. Its purpose is to gain control of a system in order to maintain some measure of performance over a changing range of real world conditions. Look up Electronic in Wiktionary, the free dictionary Electronic can refer to many things: Objects related to electronics The band Electronic. ... For the Macintosh operating system, which was called System up to version 7. ...

A very common and typical example is the AGC used in AM radio. Such a receiver is essentially linear - that is, the output is proportional to the input. This is a necessary requirement because the information content of the signal is carried by the changes of amplitude of the carrier frequency. If the circuit were not linear, the modulation could not be recovered with reasonable fidelity. However, the strength of the signal received will vary widely, depending on the range to the transmitter, signal path attenuation, and so on. The AGC circuit keeps the receiver in its linear operating range by measuring the overall strength of the signal and automatically adjusting the gain of the receiver to maintain a constant level of output. When the signal is strong, the gain is reduced, and when weak, the gain is increased, or allowed to reach its normal maximum. Amplitude modulation (AM) is a form of modulation in which the amplitude of a carrier wave is varied in direct proportion to that of a modulating signal. ... The word receiver has a number of different meanings: In communications and information processing, a receiver is the recipient (observer) of a message (information), which is sent from a source (object). ... The word linear comes from the Latin word linearis, which means created by lines. ... Amplitude is a nonnegative scalar measure of a waves magnitude of oscillation. ... Carrier frequency is the fundamental frequency used in both amplitude modulation and frequency modulation i. ... Modulation is the process of varying a carrier signal, typically a sinusoidal signal, in order to use that signal to convey information. ... For the financial services company, see Fidelity Investments. ... Crystal Palace transmitter, London A transmitter is an electronic device which with the aid of an antenna propagates an electromagnetic signal such as radio, television, or other telecommunications. ... Attenuation is the decrease of the amount, force, magnitude, or value of something. ...

It is usually not advantageous to reduce the gain of the front end of the receiver, which has benefits for both the amount of noise in the signal, and performance in the presence of strong signals, such as blocking rejection. In their most general meanings, the terms front end and back end refer to the initial and the end stages of a process flow. ... In general usage, noise can be considered data without meaning; that is, data that is not being used to transmit a signal, but is simply produced as an unwanted by-product of other activities. ...

AGC is also found in many types of tape recorder, including basic cassette decks and VCRs, the object being to record to tape a good quality signal but one that does not saturate the tape and cause distortion and other problems, even if the signal to be recorded varies in level. Video copy control schemes such as Macrovision exploit this, inserting signal spikes which will be ignored by most televisions but cause the deck's AGC to overcorrect and corrupt the recording. In general, a tape recorder, tape deck, cassette deck or tape machine is any device that records a fluctuating signal by moving a strip of magnetic tape across a tape head, which is a strong electromagnet. ... For the meaning of cassette in genetics, see cassette (genetics). ... The video cassette recorder (or VCR, less popularly video tape recorder) is a type of video tape recorder that uses removable cassettes containing magnetic tape to record audio and video from a television broadcast so it can be played back later. ... In everyday speech, to distort something is to force it out of its natural shape. ... Macrovision is a company that creates electronic copy prevention schemes. ...

See also

• Squelch
• Companding