How does the modulation index of a phase-modulated emission relate to RF carrier frequency?

In phase modulation, the modulation index is a crucial parameter that indicates the extent of phase variation in relation to the amplitude of the modulating signal. The modulation index is defined as the ratio of the phase deviation of the carrier signal to the frequency of the modulating signal.

The key point here is that the modulation index is inherently independent of the RF carrier frequency. While the carrier frequency is a critical aspect for determining the overall performance and characteristics of the transmission, the modulation index itself is solely calculated based on the modulating signal's characteristics—specifically, its frequency and phase deviation.

This means that regardless of whether the RF carrier frequency is high or low, the modulation index remains unchanged as long as the modulation characteristics (phase deviation and modulating frequency) are consistent. Therefore, the relationship of the modulation index to the RF carrier frequency is that it does not depend on it, making this the correct statement.