A signal of $$5$$ $$kHz$$ frequency is amplitude modulated on a carrier wave of frequency $$2$$ $$MHz.$$ The frequencies of the resultant signal is/are :

A radar has a power of $$1kW$$ and is operating at a frequency of $$10$$ $$GHz.$$ It is located on a mountain top of height $$500$$ $$m.$$ The maximum distance upto which it can detect object located on the surface of the earth (Radius of earth $$ = 6.4 \times {10^6}m$$) is :

This question has Statement - $$1$$ and Statement - $$2$$. Of the four choices given after the statements, choose the one that best describes the two statements.
Statement -$$1$$ : Sky wave signals are used for long distance radio communication. These signals are in general, less stable then ground wave signals.
Statement -$$2$$ : The state of ionosphere varies from hour to hour, day to day and season to season.

Consider telecommunication through optical fibres. Which of the following statements is not true?