In a radio receiver with simple AGC

Solution (By Examveda Team)

Automatic Gain Control (AGC): In a radio receiver, AGC is a circuit that automatically adjusts the gain of the receiver to maintain a relatively constant output level despite variations in the input signal strength. This ensures a consistent audio level whether the radio station is close or far away.

Option A: An increase in signal strength produces more AGC
This statement is correct. A stronger input signal produces a larger output from the detector stage (the part of the receiver that extracts the audio signal from the received radio frequency). This larger output leads to a higher AGC voltage. The higher AGC voltage then reduces the gain of the earlier stages (typically the RF and IF amplifiers) to compensate for the stronger signal, thus maintaining a relatively constant output level.

Option B: The audio stage gain is normally controlled by the AGC
This statement is incorrect. The AGC primarily controls the gain of the RF and IF amplifier stages, which precede the detector and audio stages. The audio stage gain is usually fixed or controlled independently to optimize its performance for the audio signal. Controlling the audio stage with AGC could lead to distortion or unwanted effects.

Option C: The faster the AGC time constant the more accurate the output
This statement is incorrect. The AGC time constant represents the speed at which the AGC voltage changes in response to signal strength variations. A very fast time constant would quickly adjust the gain for rapid signal fluctuations, but could also cause the output to be unstable and respond to noise or interference, leading to a less accurate, potentially "pumping" or fluctuating output. A slower time constant, although resulting in slower response to signal changes, provides a smoother and more stable output. The optimal time constant is a compromise between response speed and stability.

Option D: The highest AGC voltage is produced
This statement is incorrect. The AGC voltage is designed to maintain a certain output level. While a stronger signal *does* produce a higher AGC voltage initially, the system is designed to *limit* how high that voltage can get to prevent saturation and distortion. The goal is not to generate the highest possible AGC voltage, but rather the appropriate voltage to provide consistent audio output.