🔍 Key Concepts

• Phase modulation (PM) definition: how the carrier’s phase angle changes with the modulating signal • Expression for PM modulation index: it is related to the maximum phase deviation (in radians) produced by the modulating signal • Distinguish dependence on modulating signal (frequency/amplitude) versus RF carrier frequency

💭 Think About

• Think about what quantity is actually being varied in phase modulation: is it the carrier frequency itself or the instantaneous phase angle? • If you increase only the RF carrier frequency, leaving the same modulating signal and same phase-deviation constant, what happens to the maximum phase deviation? • Compare with frequency modulation (FM): in FM the modulation index involves frequency deviation and modulating frequency; ask yourself whether PM ties directly to the RF carrier frequency in a similar way.

✅ Before You Answer

• Write down or recall the formula for PM modulation index in terms of maximum phase deviation; check if carrier frequency appears anywhere in that expression. • Ask: does changing just the RF carrier frequency (keeping modulating signal and phase-deviation constant the same) change the size of the phase swing in radians? • Verify whether the dependence (if any) should be direct, inverse, or independent of RF carrier frequency based on your formula.