ARRL Technician Practice Exam

What is the function of automatic gain control (AGC)?

1. To increase transmission power

2. To modulate the output signal

3. To keep received audio relatively constant

4. To filter out unwanted frequencies

The correct answer is: To keep received audio relatively constant

The function of automatic gain control (AGC) is to keep the received audio relatively constant. AGC is a system used in receivers that automatically adjusts the gain of the incoming signal to maintain a consistent level of output, regardless of variations in the strength of the received signal. This is particularly important in radio communications, where signals can vary due to distance, obstructions, atmospheric conditions, or interference. With AGC, the receiver can ensure that the audio output remains at a comfortable listening level, preventing sudden changes in volume that could occur if the signal strength fluctuates. This enhances the clarity of the received audio, making it easier for operators to understand the transmitted information, especially during weak signal conditions. In contrast, increasing transmission power does not relate to AGC since it is focused on signal reception rather than transmission. Modulating the output signal is part of the process of generating signals rather than managing received signals, and filtering out unwanted frequencies addresses different types of interference rather than adjusting the volume level of the signal. Therefore, keeping audio output consistent is the primary role of automatic gain control in a radio communications context.