In a communication system operating at a wavelength of $800 \,nm$, only $1 \%$ of the source frequency is available as signal bandwidth. The number of channels accommodated for transmitting $TV$ signals of bandwidth $6 \,MHz$ is

$A$ transmitting antenna can cover an area of $6.4\pi \times 10^9 \ m^2$ when used for broadcasting. If the signal is transmitted to another antenna,which is at a distance of $100 \ km$ from this antenna,what should be the minimum height of the receiving antenna for satisfactory communication in line-of-sight mode (in $m$)? (Assume the radius of the Earth $R = 6400 \ km$)

For television broadcasting,the frequency employed is normally in the range of,

Which of the following is $NOT$ a reason for why we need modulation in communication systems?

The maximum frequency of transmitted radio waves above which the radio waves are no longer reflected back by the ionosphere is . . . . . . ($N=$ maximum electron density of the ionosphere, $g=$ acceleration due to gravity).

Indicate which one of the following systems is digital.