For effective radiation of a wave with a frequency of $20 \text{ MHz}$,what should be the length of the antenna in $m$?

What should be the height of the transmitting antenna and the population covered if the television telecast is to cover a radius of $150 \, km$? The average population density around the tower is $2000 \, / km^2$ and the value of $R_e = 6.5 \times 10^6 \, m$.

The heights of the transmitting and receiving antennas are $33.8 \ m$ and $64.8 \ m$ respectively. The maximum distance between the antennas for satisfactory communication in a line of sight mode is (Radius of the earth $= 6400 \ km$) (in $km$)

$A$ 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 $\,m$)

$A$ $500\, Hz$ modulating voltage fed into an $FM$ generator produces a frequency deviation of $2.25\, kHz$. If the amplitude of the voltage is kept constant but the frequency is raised to $6\, kHz$,then the new frequency deviation will be.......$kHz$.

The maximum distance up to which $TV$ transmission from a $TV$ tower of height $h$ can be received is proportional to