What frequency modulation (FM) primarily indicates in a signal?

Frequency modulation (FM) primarily indicates changes in the frequency of the carrier signal as opposed to its amplitude or phase. In FM, information is encoded in the variations of the frequency, which means that as the amplitude of the modulating signal changes, the frequency of the carrier signal changes accordingly.

This type of modulation is particularly beneficial for broadcasting and communication because it is more resilient to noise, making FM signals clearer and more stable than amplitude modulation (AM) signals. While other forms of modulation, such as amplitude modulation, focus on changing the strength of the signal, FM allows for fluctuations in frequency to correspond to the information being transmitted, resulting in high fidelity and reduced interference.

The other options refer to different aspects of signal modulation. For example, amplitude changes reflect AM where the amplitude varies but frequency remains constant. Signal phase changes are related to phase modulation (PM), while signal wave changes are a broad and less specific description not limited to a particular modulation technique. Therefore, the focus on frequency changes accurately characterizes FM.