Which of the following statements is true for FM?

Analysis:

The amplitude Ac is constant in a phase-modulated or a frequency-modulated signal. RF power does not depend upon the modulation index.

A general expression for a phase or frequency-modulated signal is:

\(\phi(t)=A_ccos[ω_ct+g(k_k,m(t))]\)

m(t) = the modulating signal

ωc = Carrier frequency

kk becomes kc for FM and kp for PM.

The average power (Pavg) is given by:

\(P_{avg}=\frac{A_c^2}{2}\) (Always)

We observe that the transmitted power is independent of the modulation index in case of FM.

Transmitted power in AM is given by:

\({P_t} = {P_c}\left( {1 + \frac{{{\mu ^2}}}{2}} \right)\)

Pc = Carrier Power

∴ We conclude that If the modulation index increases, transmitted power increases in case of AM and is unchanged for FM.