The size of the antenna required for a carrier wave of frequency $3 \text{ MHz}$ is: (in $\text{ m}$)

In a frequency modulated wave:

What is the modulation index of an over-modulated wave?

$A$ carrier wave of peak voltage $10 \,V$ is used to transmit a message signal. What should be the peak voltage of the modulating signal in order to have a modulation index of $80 \%$ (in $\,V$)?

$A$ 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 characteristic impedance of a coaxial cable is of the order of .......... $\Omega$.