What is Frequency Deviation in FM?

Frequency deviation in frequency modulation (FM) refers to the maximum deviation of the carrier frequency from its center frequency. In FM, the carrier signal's frequency is modulated or varied in accordance with the amplitude of the modulating signal (usually an audio signal). The frequency deviation determines the range over which the carrier frequency varies.

The modulating signal, which carries the desired audio or information, causes the instantaneous frequency of the carrier signal to deviate above and below its center frequency. The amplitude of the modulating signal determines the extent of this deviation. The frequency deviation is typically specified in terms of hertz (Hz) and represents the maximum distance the carrier frequency moves away from its center frequency.

In FM broadcasting, for example, the standard frequency deviation is often limited to a certain value, such as ±75 kHz. This means that the carrier frequency can deviate by up to 75 kHz in either direction from its center frequency. The frequency deviation affects various aspects of FM transmission, including the bandwidth required to transmit the signal, the signal-to-noise ratio, and the overall fidelity of the audio being transmitted.

It's worth noting that the frequency deviation is related to the modulation index (β), which is the ratio of the frequency deviation to the modulating signal frequency. The modulation index determines the degree of frequency modulation applied to the carrier signal and affects the spectrum and bandwidth requirements of the FM signal.