Amplitude limiting in FM demodulation is used to ensure what characteristic of the signal?

• A. It ensures that frequency deviation reflects phase changes while amplitude remains constant
• B. It makes amplitude remain constant but has no effect on FM
• C. It improves sensitivity by reducing noise
• D. It reduces the carrier frequency

Answer: (A)

Amplitude limiting is used to make FM demodulation rely on frequency changes rather than amplitude changes. In FM the information is carried by the instantaneous frequency, which comes from how fast the carrier’s phase is changing. The limiter clips or stabilizes the signal so the envelope stays constant, removing amplitude fluctuations that could masquerade as frequency variations. With a constant amplitude, the detector’s output reflects the actual phase (and thus frequency) deviations caused by the modulating signal, not any amplitude wander. That’s why the observed frequency deviation corresponds to the phase changes, while amplitude remains steady. The other ideas don’t describe what the limiter does: it doesn’t keep amplitude varying, it isn’t primarily about improving sensitivity in isolation, and it doesn’t change the carrier frequency.