Write three important factors which justify the need of modulating a message signal. Show diagrammatically how an amplitude modulate wave is obtained when a modulating signal is superimposed on a carrier wave.    

Three factors for the need of modulating a message signal:

a) Size of the antenna or aerial should be /4.

b) Effective power radiated by an antenna should be close to 
c) Interference of signals from different transmitters. Inorder to avoid the interference of the signals, high frequency is required which can be acquired by modulation.