If the amplitude of an audio signal is half the amplitude of the carrier wave,what is the modulation index?

$A$ 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 $\,m$)

The maximum distance up to which $TV$ transmission from a $TV$ tower of height $h$ can be received is proportional to

If a $TV$ transmission is broadcast from a $TV$ transmitter tower of height $h$,then the maximum distance of this transmission is proportional to the height $h$ of the tower as.........

When the angle of incidence is $74^{\circ}$,the critical frequency of the $F$ layer is $50 \text{ MHz}$. What is the Maximum Usable Frequency $(MUF)$ in $\text{ MHz}$ (in $.5$)?

What are the primary causes of signal attenuation in an optical fiber?