What is meant by the term modulation index?

The term modulation index specifically refers to the ratio between the frequency deviation of a frequency modulated (FM) signal and the frequency of the modulating signal itself. In frequency modulation, the modulation index indicates how much the carrier frequency varies in response to the input or modulating signal. A higher modulation index signifies a greater frequency deviation, which can enhance the signal's sensitivity to the changes in audio or data being transmitted. This is crucial for ensuring that the receiving equipment correctly interprets the variations encoded in the carrier wave.

Understanding the modulation index is essential in designing and analyzing FM transmission systems, as it directly influences the bandwidth of the transmitted signal and its overall accuracy in representing the original information. The other choices do not accurately describe this concept, as they refer to different aspects of modulation or signal properties that do not align with the formal definition of modulation index.