$A$ transmitting antenna of height $20 \,m$ and a receiving antenna of height $h$ are separated by a distance of $40 \,km$ for satisfactory communication in line-of-sight $(LOS)$ mode. The value of $h$ is (Given: radius of Earth is $6400 \,km$). (in $\,m$)

Given the electric field of a complete amplitude modulated wave as $\vec E = \hat i E_c (1 + \frac{E_m}{E_c} \cos \omega_m t) \cos \omega_c t$,where the subscript $c$ stands for the carrier wave and $m$ for the modulating signal. The frequencies present in the modulated wave are:

$A$ sinusoidal wave $y(t) = 40 \sin(10 \times 10^6 \pi t)$ is amplitude modulated by another sinusoidal wave $x(t) = 20 \sin(1000 \pi t)$. The amplitude of the minimum frequency component of the modulated signal is ...........

The height of a $T.V.$ tower is $75 \ m$. What is the maximum distance in $km$ up to which $T.V.$ transmission can be received (in $.98$)? (Radius of the Earth $= 6.4 \times 10^6 \ m$).

For an amplitude modulated wave,the maximum and minimum amplitudes are found to be $10 \ V$ and $2 \ V$ respectively. Then the modulation index is

The advantages of optical fiber communication over a two-wire transmission line or coaxial cable are . . . . . . .