For a television network,$5 \times 10^5$ channels are granted. If the central frequency of the microwave link is $25 \text{ GHz}$ and the allotted bandwidth for each channel is $2 \text{ kHz}$,then what percentage of the link is used for the network (in $\%$)?

What is the frequency range of signals that can be transmitted using a $Twisted\, pair\, wire$?

The frequency of a carrier wave is $1 MHz$. It is modulated by a wave of frequency $10 kHz$. If their amplitudes are $10 V$ and $0.5 V$ respectively,what are the modulation index and the frequencies of the $USB$ and $LSB$?

The relationship between the maximum electron density $(N_{max})$ of the ionosphere and the critical frequency $(f_c)$ is given by:

Match List-$I$ with List-$II$:

List-$I$	List-$II$
$A$. $AM$ Broadcast	$I$. $88-108\,MHz$
$B$. $FM$ Broadcast	$II$. $540-1600\,kHz$
$C$. Television	$III$. $3.7-4.2\,GHz$
$D$. Satellite Communication	$IV$. $54-890\,MHz$

Choose the correct answer from the options given below:

The transmitting antenna placed at the top of a tower has a height of $45 \ m$ from the ground. The distance between receiving and transmitting antennas is $40 \ km$ and the radius of earth is $6400 \ km$. The minimum height (in $m$) at which the receiving antenna is to be placed for satisfactory communication in $LOS$ mode, is