In a modulation process where the pulse duration varies with the modulating signal,it is called ......

$A$ $TV$ tower has a height of $100 \ m$. The average population density around the tower is $1000 \ \text{per} \ km^2$. The radius of the earth is $6.4 \times 10^6 \ m$. The population covered by the tower is:

The ionosphere acts as a reflector for which frequency range?

The process of the loss of strength of a signal while propagating through a medium is known as:

If the highest frequency modulating a carrier is $5\, kHz$,then the number of $AM$ broadcast stations accommodated in a $90\, kHz$ bandwidth are ....... .

$A$ basic communication system consists of:
$(a)$ Transmitter
$(b)$ Information source
$(c)$ User of information
$(d)$ Channel
$(e)$ Receiver
The correct sequence of the arrangement is: