$A$ modulating signal is a square wave,as shown in the figure. If the carrier wave is given as $c(t) = 2 \sin(8 \pi t)$ volts,the modulation index is:

$A$ message signal is super-imposed with a carrier signal. The resulting modulating signal $C_m(t)$ is given by $C_m(t)=A_1 \sin \left(\omega_1 t\right)+A_2 \sin \left(\omega_2 t\right)-A_2 \sin \left(\omega_3 t\right)$,where $\omega_2 < \omega_1 < \omega_3$. The modulation index and the angular frequency of the message signal respectively,are

The mathematical form of an $AM$ wave is given by $e = 50 (1 + 0.5 \sin(2\pi \times 5 \times 10^{3} t)) \sin(31.4 \times 10^{6} t) \text{ V}$. For the given $AM$ wave,the carrier frequency is ....... and the modulating frequency is .......

In which of the following is the remote sensing technique $NOT$ used?

$A$ ground receiver station is receiving a signal at $5\, MHz$ transmitted from a ground transmitter at a height of $300\, m$,located at a distance of $100\, km$ from the receiver station. Given: Radius of Earth $R = 6.4 \times 10^6\, m$,$N_{\max}$ of ionosphere = $10^{12}\, m^{-3}$. Identify the mode of propagation.

When the receiving antenna is on the ground,the range of a transmitting antenna of height $980 \ m$ is (Radius of the earth $= 6400 \ km$) (in $km$)