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© 2008 The McGraw-Hill Companies

22

9-2: Superheterodyne Receivers

Automatic Gain Control

The output of a demodulator is usually the original modulating signal, the amplitude of which is directly proportional to the amplitude of the received signal.

The recovered signal, which is usually ac, is rectified and filtered into a dc voltage by a circuit known as the automatic gain control (AGC) circuit.

This dc voltage is fed back to the IF amplifiers, and sometimes the RF amplifier, to control receiver gain.

AGC circuits help maintain a constant output level over a wide range of RF input signal levels.

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