An $FM$ broadcast transmitter,using a modulating signal of frequency $20\,kHz$,has a deviation ratio of $10$. The bandwidth required for transmission is $.......kHz$.

$A$ transmitting and receiving antenna have a height of $d$ meters each. The maximum distance between them for satisfactory communication in Line-of-Sight $(LOS)$ mode is $2d$ kilometers. If the radius of the Earth is $6400 \text{ km}$, then the value of $d$ is: (in $\text{ m}$)

$A$ diode detector is used to detect an amplitude modulated wave with $60\%$ modulation,using a capacitor of $250 \ pF$ in parallel with a resistor of $100 \ k\Omega$. What is the maximum modulation frequency that can be detected by this circuit?

$A$ $TV$ tower has a height of $150 \ m$. If the population density around the $TV$ tower is $10^3 \ km^{-2}$, then the population covered by the tower is (Radius of the earth, $R = 6.4 \times 10^6 \ m$). (in $\text{lakh}$)

For an amplitude modulated wave,the maximum and minimum amplitudes are found to be $10 \ V$ and $2 \ V$ respectively. Then the modulation index is

For sky wave propagation of a $10\, MHz$ signal, what should be the minimum electron density in the ionosphere?