Question

$\text{When both the amplitude and the frequency of a sinusoidal message signal are doubled,}\text{the modulation index will be doubled in}\text{1. Amplitude modulation}\text{2. Frequency modulation}\text{3. Phase Modulation}\text{Select the correct answer using the codes given below:}$

• A. $\text{1,2 and 3}$
• B. $\text{2 and 3 only}$
• C. $\text{1 and 3 only}$
• D. $\text{2 only}$

Answer 1

The correct option is C $\text{1 and 3 only}$

$\text{Let,}m\left(t\right)=A_{m}cos\left(2\pi f_{m}t\right)\text{For AM,}{\mu }_{AM}=k_a{A}_m\text{For FM,}{\beta }_{FM}=k_f\frac{A_m}{f_m}\text{For FM,}{\beta }_{PM}=k_p{A}_m\text{So, when both}{A}_m\text{and}{f}_m\text{are doubled,}{\mu }_{AM}\text{and}{\beta }_{P}M\text{wil be doubled and}{\beta }_{P}M\text{will remain be unchanged}$