The wavelength of the carrier waves in a modern optical fiber communication network is close to ........ $nm$.

$A$ person tries to broadcast with the same antenna both the signals at $10^7 \,Hz$ and $10^6 \,Hz$. If the receiver at some distance has to receive an equal strength for both the frequencies, then the broadcaster has to approximately increase the signal strength at $10^6 \,Hz$ to $10^7 \,Hz$ by

The characteristic impedance of a coaxial cable is typically ...... .

$A$ carrier wave of peak voltage $15 V$ is used to transmit a message signal. What should be the peak voltage of the modulating signal in order to have a modulation index of $80\%$ (in $V$)?

Three signals related to amplitude modulation are shown in the figure. The correct assignment of the signals is

The physical sizes of the transmitter and receiver antenna in a communication system are