Long range radio transmission is possible when the radio waves are reflected from the ionosphere. For this to happen,the frequency of the radio waves must be in the range:

$A$ 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 ..... .

Which of the following is not a natural source of electrical noise?

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

$A$ signal of $100 \,THz$ frequency can be transmitted with maximum efficiency by

For an amplitude-modulated wave, the audio frequency is $500 \, \text{cycles/second}$. What is the actual carrier frequency in $\text{cycles/sec}$?