What is the modulation index of an FM signal?

The modulation index for Frequency Modulation (FM) is defined mathematically as the ratio of the maximum frequency deviation to the frequency of the modulating signal. This index helps determine the bandwidth and sideband distribution of the transmitted signal. To calculate it, you simply divide the peak deviation of the carrier frequency by the frequency of the audio (or data) signal that is doing the modulating. A higher modulation index means the carrier is being pushed further from its center frequency relative to the speed of the audio waves. Common distractors try to trick you by inverting this ratio, such as dividing the modulating signal frequency by the deviation, or by incorrectly bringing the overall transmitted bandwidth into the calculation. Remember the simple formula: Deviation ÷ Modulating Frequency.