$A$ $TV$ transmission tower of height $h$ covers a range of distance $d$. By how much will the range change if the height is increased to $3/2 h$?

The ratio of the maximum amplitude to the minimum amplitude of an amplitude-modulated wave is $4$. What is the modulation index of this wave?

The maximum frequency of transmitted radio waves above which the radio waves are no longer reflected back by the ionosphere is . . . . . . ($N=$ maximum electron density of the ionosphere, $g=$ acceleration due to gravity).

The height of a transmitting antenna at the top of a tower is $25 \; m$ and that of the receiving antenna is $49 \; m$. The maximum distance between them for satisfactory communication in $LOS$ (Line of Sight) is $K \sqrt{5} \times 10^{2} \; m$. The value of $K$ is $\dots$ [Assume radius of Earth is $64 \times 10^{5} \; m$] (Calculate up to the nearest integer value).

The transmission loss per kilometer in an optical fiber is approximately...........$dB$.

In a modulation process where the pulse duration varies with the modulating signal,it is called ......