The need for modulation is

The signal obtained at the output of a microphone is of which type?

The maximum usable frequency $(MUF)$ in the $F$-region layer is $x$,when the critical frequency is $60 \, MHz$ and the angle of incidence is $70^\circ$. Then $x$ is ....... $MHz$.

$A$ $TV$ transmission tower antenna is at a height of $20\, m$. Suppose that the receiving antenna is at:
$(i)$ ground level
$(ii)$ a height of $5\, m$.
The increase in antenna range in case $(ii)$ relative to case $(i)$ is $n\%$.
The value of $n$,to the nearest integer,is .....$\%$

The process of superimposing a signal frequency (i.e.,audio wave) on a carrier wave is known as:

The maximum amplitude of an amplitude modulated wave is $16 \,V$, while the minimum amplitude is $4 \,V$. The modulation index is