Which type of medium is used for optical communication?

$A$ bandwidth of $6 \, \text{MHz}$ is available for $A.M.$ transmission. If the maximum audio signal frequency used for modulating the carrier wave is not to exceed $6 \, \text{kHz}$,the number of stations that can be broadcasted within this band simultaneously without interfering with each other will be ..... .

In amplitude modulation,if a message signal of $5 \ kHz$ is modulated by a carrier wave of frequency $900 \ kHz$,then the frequencies of the side bands are

For transmitting a signal of frequency $1000 \text{ kHz}$, the minimum length of the antenna is (in $\text{ m}$)

If multiple waves with modulation indices $n_1, n_2, n_3, ...$ modulate a carrier wave,what is the total modulation index of the resulting wave?

$A$ message signal of frequency $14 kHz$ is used to modulate a carrier of frequency $900 kHz$. The frequencies of the sidebands are: