What determines the amount of deviation of an FM signal?

The amount of deviation of an FM (Frequency Modulation) signal is primarily determined by the amplitude of the modulating signal. In FM, the frequency of the carrier wave is varied in accordance with the instantaneous amplitude of the modulating signal. The greater the amplitude of the modulating signal, the more the carrier frequency is deviated from its resting frequency.

This relationship is rooted in the fundamental principle of FM, where changes in the amplitude of the modulating signal dictate how much the carrier frequency will shift away from its original value. Therefore, if the amplitude of the modulating signal increases, the deviation increases, leading to a wider frequency swing. Thus, the correct answer reflects the core concept of how FM transmission works by linking the deviation directly to the amplitude of the signal driving the modulation.

When considering the other options, while the frequency of the modulating signal and aspects like the phase can influence the characteristics of the FM signal, they do not determine the amount of deviation in the same direct manner as the amplitude does. This clarification helps in understanding how FM radio communication operates effectively.