What does AFC control in frequency modulation transmitter and receiver circuits?

AFC, or Automatic Frequency Control, plays a crucial role in maintaining the stability of the oscillator frequency in both transmitters and receivers in frequency modulation circuits. The primary purpose of AFC is to ensure that the oscillator remains locked to the desired frequency despite variations such as temperature changes, component drift, or frequency shifts caused by signal conditions.

In frequency modulation systems, maintaining oscillator stability is essential for accurate modulation and demodulation of signals. If the oscillator drifts from its intended frequency, it can lead to distortions, degraded signal quality, and difficulties in demodulation at the receiver end. AFC continuously monitors the output frequency and adjusts it automatically to keep it aligned with the reference frequency, thus ensuring consistent performance.

While other options like amplitude stability, phase stability, and frequency modulation itself are important in communication systems, they do not specifically represent the primary function of AFC. Amplitude stability is more relevant to ensuring that signal strength is consistent, phase stability relates to the timing alignment of signal waves, and frequency modulation refers to the technique of modulating the frequency of a carrier signal itself.