In satellite communication, the uplink frequency band used is :

A transmitting antenna is kept on the surface of the earth. The minimum height of receiving antenna required to receive the signal in line of sight at $$4 \mathrm{~km}$$ distance from it is $$x \times 10^{-2} \mathrm{~m}$$. The value of $$x$$ is __________.

(Let, radius of earth $$\mathrm{R}=6400 \mathrm{~km}$$ )

A message signal of frequency $$3 ~\mathrm{kHz}$$ is used to modulate a carrier signal of frequency $$1.5 ~\mathrm{MHz}$$. The bandwidth of the amplitude modulated wave is

A carrier wave of amplitude 15 V is modulated by a sinusoidal base band signal of magnitude 3 V. The ratio of maximum amplitude to minimum amplitude in an amplitude modulated wave is