What is the minimum height of an antenna required to transmit a radio signal of frequency $20 \text{ MHz}$?

$A$ radar has a power of $1 \ kW$ and is operating at a frequency of $10 \ GHz$. It is located on a mountain top of height $500 \ m$. The maximum distance up to which it can detect an object located on the surface of the earth (Radius of earth $= 6.4 \times 10^6 \ m$) is ....... $km$.

$A$ $TV$ transmission tower of height $h$ covers a range of distance $d$. By how much will the range change if the height is increased to $3/2 h$?

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.........

For the output of an $AM$ detector circuit to follow the envelope of the carrier wave,which condition must be satisfied? ($T_c$ is the time period of the carrier wave.)

What type of modulation is employed in India for radio transmission?