An amplitude modulated wave is as shown in Fig. 15.4. Calculate (i) the percentage modulation, (ii) peak carrier voltage and, (iii) peak value of information voltage.


From the figure, we have

Maximum voltage,


Minimum voltage,


We know that




where Vc and Vm are the peak voltage (voltage amplitude) of carrier signal and message signal respectively.


Adding equation (1) and equation (2), we get




Subtracting (2) from (1), we get




(i) Now, the modulation index is given by:



(ii) Peak carrier voltage ,


(iii) Peak value of information,


1