Give reasons 

a) For ground wave transmission , size of antenna should be comparable to the wavelength  of signal eg -  

b) Audio signals converted into electromagnetic waves are not transmitted as such directly .

 

c) The amplitude of modulating signal is kept less than that of carrier wave.

 

(a) The size of the antennas should be atleast λ/4 for high efficiency of signal radiation. This is because ground wave propagation is possible for radio waves of frequency band 540 kHz to 1600 kHz. If the band signal frequency is 15 kHz, the height of the antenna would be 5000 which is impossible. 

(b) To transmit audio signal converted to electromagnetic signal, an antenna of atleast size 15 km is needed. This impractical and also signals of different transmitter would mix up. 
(c ) Modulation index,μ = V_m/v_c and its value should be less than 1.

 Thus, the amplitude of the modulating signal is kept less than the carrier waves so that no distortion occurs in the modulated wave.