In radio broadcasting,the transmission of sound waves is of the type.............

In satellite communication,the uplink frequency band used is

$A$ transmitting antenna has a height of $320\, m$ and that of the receiving antenna is $2000\, m$. The maximum distance between them for satisfactory communication in line-of-sight mode is $d$. The value of $d$ is $\ldots \ldots \, km$.

The frequency suitable for beyond-the-horizon communication using sky waves is

We do not transmit low frequency signals to long distances because:
$(a)$ The size of the antenna should be comparable to signal wavelength,which is impractical for a signal of longer wavelength.
$(b)$ Effective power radiated by a long wavelength baseband signal would be high.
$(c)$ We want to avoid mixing up signals transmitted by different transmitters simultaneously.
$(d)$ Low frequency signals can be sent to long distances by superimposing them with a high frequency wave.
Therefore,the most suitable options are:

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 $\%$)?