The frequency suitable for beyond-the-horizon communication using sky waves is

$A$ transmitting antenna at the top of a tower has height $32\, m$ and the height of the receiving antenna is $50\, m$. What is the maximum distance between them for satisfactory communication in line of sight $(LOS)$ mode? ........$km$

In a communication system,a repeater is used to extend the range of transmission. It is a combination of:

Audio signals cannot be transmitted directly over long distances because:

Which of the following is the disadvantage of $FM$ over $AM$?

$A$ carrier wave $60 \sin(2\pi \times 10^6 t)$ is modulated by a signal $15 \sin(300\pi t)$. The modulation index is: (in $\%$)