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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.
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 .
AGC is also found in many types of tape recorderIn general, a tape recorder tape 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. Current flowing in the coils of the electromagnet cause the magne, 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 distortionIn telecommunication and signal processing, the term distortion has the following meanings: #In a system or device, any departure of the output signal waveform from that which should result from the input signal waveform's being operated on by the system' and other problems, even if the signal to be recorded varies in level. Video copy control schemes such as MacrovisionMacrovision is a company that creates electronic copy prevention schemes. Macrovision is notable for its video copy prevention scheme of the same name. A VHS videotape or DVD (no laserdisc or video CD players implement it) encoded with Macrovision will ca exploit this, inserting signal spikes which will be ignored by most televisionSee TV (disambiguation) for other uses and Television (band) for the rock band Television is a telecommunication system for broadcasting and receiving moving pictures and sound over a distance. The term has come to refer to all the aspects of television ps but cause the deck's AGC to overcorrect and corrupt the recording.