If the length of an antenna is $150 \,cm$,the transmission frequency is . . . . . . $MHz$. (Speed of light in vacuum $= 3 \times 10^8 \,ms^{-1}$)

The modulation index used in amplitude modulation of a message signal of peak voltage $10 \,V$ is $0.5$. By how much should the peak voltage of the carrier signal be changed, so as to obtain the modulation index of $0.8$, keeping the peak voltage of the message signal the same as before?

Which of the following statements is $NOT$ true regarding communication through optical fibers?

$A$ message signal of peak voltage $12 \ V$ is used to amplitude modulate a carrier signal of frequency $1.2 \ MHz$. The amplitude of the side bands is (in $V$)

$A$ $100\, V$ carrier wave is made to vary between $160\, V$ and $40\, V$ by a modulating signal. What is the modulation index?

Which of the following elements is doped to a fiber amplifier in an optical fiber communication system?