(a) Size of the antenna or aerial : For transmtting a signal antenna should have a size comparable to the wavelength of the signal (at least `lambda//4` in dimension ) . For an electromagnetic wave of frequency 20kHz , the wavelength `lambda` is 15 km. Actually such a long antenna is not possible to construct and operate. Hence direct transmission of such base band signals is not practical.
(b) Effective power radiated by an antenna : A theoretical signals is not practical .
(length l) shows that the power radiated is proprtional to `( l// lambda)^(2)` .This implies that for the same antenna length the power radiated increases with decreasing `lambda` i.e., increasing frequency . Hence the effective power radiated by a long wavelenth base band signal would be small .For a good transmission we need high powers and hence this also points out to the need of using high frequency transmission.
(b) (i) there is very less noise in frequency modulation.
(ii) Range of requency modulation is larger .
