Question
How does the modulation index of a phase-modulated emission vary with RF carrier frequency?
Answer Options
- A) It increases as the RF carrier frequency increases
- B) It decreases as the RF carrier frequency increases
- C) It varies with the square root of the RF carrier frequency
- D) It does not depend on the RF carrier frequency
Correct Answer: D
Explanation
Phase Modulation (\text{PM}) is a type of angle modulation where the phase of the carrier is varied in proportion to the modulating signal’s amplitude. The resulting modulation index for a \text{PM} signal is determined solely by the characteristics of the modulating signal and the sensitivity of the phase modulator.
Unlike \text{FM} created through frequency multiplication, the modulation index of a phase-modulated emission does not depend on the RF carrier frequency. If the carrier frequency is multiplied or divided, the modulation index (the phase change) remains constant. This is a key difference between \text{PM} and \text{FM} in transmitters, as \text{PM} is often used to generate wideband \text{FM} through carrier multiplication.
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