What does the frequency deviation in FM indicate?

The frequency deviation in frequency modulation (FM) refers to the extent to which the instantaneous frequency of the carrier wave shifts from its resting value, known as the carrier frequency. This deviation is a critical parameter in FM communication as it directly correlates with the amplitude of the modulating signal.

When the modulating signal varies, it causes the carrier frequency to deviate above and below its nominal frequency. The greater the amplitude of the modulating signal, the larger the frequency deviation will be. This is fundamental in FM broadcasting, as it helps define the amount of information carried by the signal. The relationship between the modulating signal and the resulting frequency shifts is essential for understanding how FM works, influencing bandwidth and the quality of the received signal.

The other options discuss different aspects of modulation. One refers to amplitude modulation, which is not applicable to FM. Another concerns sidebands, which are indeed a product of modulation but do not define frequency deviation. Lastly, signal strength is related to power levels rather than frequency shifts. These distinctions highlight why the correct answer emphasizes the frequency's shift relative to its carrier frequency as a key characteristic of frequency modulation.