CAG , Automatic Gain Control, AGC.
Definition
Due to the distance that a receiver is placed from the transmitting station, as well as other causes, it is subject to the reception of strong and weak signals and of course to different outputs in the audio stage. To avoid this dependency, the current of the emitter or the collector of the IF amplification step can be modified according to the amplitude of the input signal. Since transistors are devices that operate by current, to modify this, the control stage must provide part of its own current. This in turn means that power is needed.
The control voltage is almost invariably obtained from the second detector ; therefore this stage must supply the control power. In general it is desirable for the CAG to act on the IF to prevent overloads and to maintain a reasonably constant signal at the input of the second detector. It is almost never used in the mixing step since the operation of this is a critical function of its point of operation.
The control of the emitter current in an IF amplifier , in this case the AC voltage is applied to the base, so that the changes that result in the base direct current are amplified, appearing as major changes in the current of transmitter. When the input signal is strong, a voltage is applied to reduce the emitter current and the gain of the stage. Conversely, when the signal is weak, the applied voltage is reduced, allowing more emitter current to flow and increasing the gain. By reducing the emitter current, the collector current is also reduced, and therefore, the amplitude of the signal developed at the output of the tuned circuit.
