(a) Give three reasons why modulation of a message signal is necessary for long distance transmission. (b) Show graphically an audio signal, a carrier wave and an amplitude modulated wave.

(a) Modulation is necessary because of following reasons :
(i) Reduction in the height of antenna
(ii) Avoids mixing of signals
(iii) Increases the range of communication
(iv) Multiplexing is possible
(v) Improves the quality of reception