Question

A separate high freq. wave (i.e. carrier wave) is needed in modulation why ?

Answer 1

Hey there!

A separate high freq. wave (i.e. carrier wave) is needed in modulation because we cannot change any of the characteristics (amplitude, frequency or phase) of the audio  signal as this would change the message to be communicated. So keeping the audio signal same, the amplitude  of freq. or phase of the high freq. carrier wave is modified in accordance with the modulating (i.e. audio  signal) signal.

Good day!

Answer 2

Answer:

If every signals gets into own frequency range then we can transmit multiple signals simultaneously over a channel

Explanation:

Another use is transfer signal from smaller antenna