question_answer

(i) Define modulation index. (ii) Why is the amplitude of modulating signal kept less than the amplitude of carrier wave?             

Answer:

                (i) Modulating index for an AM wave is defined as the ratio of change in the amplitude of the carrier wave to the amplitude of the original carrier wave. \[\text{ }\!\!\mu\!\!\text{  =}\frac{\text{Change in the amplitde of carrier wave}}{\text{Amplitude of the original carrier wave}}\] \[=\frac{{{A}_{m}}}{{{A}_{c}}}\] (ii) When \[{{A}_{m}}\] exceeds \[{{A}_{c}}\], the carrier is over-modulated\[{{A}_{c}}(\mu >1),\], which causes distortion during reception. That is why \[{{A}_{m}}\] is kept less than \[{{A}_{c}}\].