In digital communications, why are modulations necessary for signals that travel over high-frequency channels?  Answer:  If a baseband digital signal (with a lower frequency) wants to travel over a...

In digital communications, why are modulations necessary for signals that travel over high-frequency channels?

 Answer:

 If a baseband digital signal (with a lower frequency) wants to travel over a high-frequency channel, it must be carried by a sinusoidal carrier. In other words, the signal has to modulate carriers of higher frequencies so that the data signals can be conveyed via the channel.