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

$A$ carrier wave of peak voltage $16 \text{ V}$ is used to transmit a signal. If the modulation index is $75 \%$, the peak voltage of the modulating signal is (in $\text{ V}$)

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

$A$ carrier wave of peak voltage $14\,V$ is used for transmitting a message signal. The peak voltage of the modulating signal required to achieve a modulation index of $80\%$ will be.......$V$

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).

In an amplitude modulated wave for an audio frequency of $500 \, \text{cycles/second}$, the appropriate carrier frequency will be ........ $\text{cycles/second}$.