In a communication system,the process of superimposing a low-frequency signal on a high-frequency wave is known as:

Which type of medium is used for optical communication?

The height of a transmission antenna is $49 \,m$ and that of the receiving antenna is $64 \,m$. What should be the maximum distance between them for line of sight transmission (in $\,km$)?

Which of the following is the communication channel in case of radio communication?

$A$ speech signal of $3 \text{ kHz}$ is used to modulate a carrier signal of frequency $1 \text{ MHz}$ using amplitude modulation. The frequencies of the sidebands will be:

$A$ carrier wave of peak voltage $10 \,V$ 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 $\,V$)?