An antenna is a device:

Which one of the following is not classified as pulse modulation?

$A$ $TV$ transmission antenna is $40 \ m$ tall. How much service area can it cover if the receiving antenna is at the ground level? (Radius of the Earth $= 6400 \ km$)

$A$ signal of $0.1 \, kW$ is transmitted in a cable. The attenuation of the cable is $-5 \, dB$ per $km$ and the cable length is $20 \, km$. The power received at the receiver is $10^{-x} \, W$. The value of $x$ is ....... .
$[\text{Gain in } dB = 10 \log_{10}(\frac{P_0}{P_i})]$

$A$ carrier wave of peak voltage $12 \, V$ 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 $75 \%$? ...... $V$

The height of the transmitting antenna is $180\,m$ and the height of the receiving antenna is $245\,m$. The maximum distance between them for satisfactory communication in line of sight will be .......... $km$ (given $R = 6400\,km$).