If the sum of heights of transmitting and receiving antennas in line of sight communication is $h$,then the height of the receiving antenna,to have the maximum range,is

$A$ transmitting antenna is kept on the surface of the earth. The minimum height of the receiving antenna required to receive the signal in line-of-sight at $4\,km$ distance from it is $x \times 10^{-2}\,m$. The value of $x$ is (Let radius of earth $R = 6400\,km$).

The bandwidth of an audio signal is approximately:

$A$ wave is represented as $e = 10 \sin(10^8 t + 6 \sin(1250 t))$. The modulation index is:

In amplitude modulation of waves,the maximum amplitude is $30 \text{ mV}$ and minimum amplitude is $5 \text{ mV}$,then the modulation index is

The heights of the transmitting and receiving antennas are $33.8 \ m$ and $64.8 \ m$ respectively. The maximum distance between the antennas for satisfactory communication in a line of sight mode is (Radius of the earth $= 6400 \ km$) (in $km$)