The digital signals are used for transmission in communication systems. They are

What is the minimum height of an antenna required to transmit a radio signal of frequency $20 \text{ MHz}$?

The height of a $TV$ tower is $150 \ m$. If the population density in the area covered by the $TV$ tower is $50 \ \text{lakhs}$, then the population density around the $TV$ tower is ....... $km^{-2}$. (Radius of the Earth is $6.4 \times 10^{6} \ m$)

$A$ wave is represented as $e = 10\,(1 + 6\, \sin(50t)) \sin(10^8t)$. The modulation index is:

In $AM$,the cent percent modulation is achieved when

In frequency modulation,........