Power of an FM Signal

Power of an FM (Frequency Modulated) Signal

1. FM Signal Form

An FM signal is written as:

s(t) = A_c cos(ω_c t + β sin(ω_m t))

Where:

• A_c = carrier amplitude
• β = modulation index
• ω_c, ω_m = carrier and message frequencies

2. Total Power of FM Signal

P_FM = A_c² / (2R)

This is the same as carrier power.

3. Important Concept

• FM does not change amplitude
• Only frequency varies
• Power depends only on amplitude, which is constant

4. Power Distribution in FM

• Total power is constant
• Distributed among:
• Carrier
• Infinite sidebands (theoretical)
• As β increases:
• Carrier power decreases
• Sideband power increases
• Total power remains constant

• Total power is independent of modulation index (β)
• No power wastage like AM
• More efficient than AM

Summary

• FM Power Formula: P = A_c² / (2R)
• Power remains constant
• Only distribution changes