What is the role of Automatic Frequency Control (AFC) in a radio receiver?

• A. AFC automatically corrects small drifts in local oscillator frequency to maintain tuned frequency.
• B. AFC increases the amplitude of the signal.
• C. AFC demodulates the data.
• D. AFC filters out noise.

Answer: (A)

AFC keeps the receiver locked to the station by automatically correcting small changes in the local oscillator frequency so the tuned frequency stays put. In a typical superheterodyne design, the incoming signal is mixed with a local oscillator to produce an intermediate frequency. If the local oscillator drifts due to temperature, aging, or other factors, the intermediate frequency shifts and the desired signal slides out of the filter’s passband, making reception unstable. AFC uses a signal derived from the detector (or a reference tone) to sense this detuning and applies a small correction to the local oscillator, nudging it back to the correct value. This keeps the tuned frequency stable, so the signal remains centered in the filter and demodulation stays consistent. It isn’t about increasing amplitude (that’s automatic gain control), isn’t the demodulation process, and isn’t primarily about filtering noise.