How does the modulation index of a phase-modulated emission vary with RF carrier frequency?
It increases as the RF carrier frequency increases
It decreases as the RF carrier frequency increases
It varies with the square root of the RF carrier frequency
It does not depend on the RF carrier frequency✓Correct answer
Explanation
In phase modulation the index is the peak phase shift in radians, and that shift is set by the amplitude of the modulating signal alone. Moving the same modulator to a higher or lower carrier frequency does not change how many radians the phase swings, so the index does not depend on carrier frequency.