Which system enhances oscillator stability in FM communications?

Automatic frequency control (AFC) enhances oscillator stability in frequency modulation (FM) communications by maintaining the oscillator frequency at a fixed and accurate level. In FM systems, a stable carrier frequency is crucial for reducing distortion and ensuring clear signal transmission.

AFC continuously monitors the output frequency of the oscillator and adjusts it whenever a deviation occurs due to factors like temperature fluctuations or component aging. This real-time adjustment means that the frequency remains locked to the intended transmission frequency, thereby minimizing drift and maintaining the integrity of the communication signal.

The other options, while relevant to communication systems, do not serve the specific function of enhancing oscillator stability in the same way. Amplitude modulation, phase modulation, and frequency modulation themselves describe various methods of encoding information onto a carrier wave but do not specifically address the adjustments needed to keep the oscillator stable.