High - Frequency Carrier Necessity
This is an extremely basic question about RF and you should read a book in this subject.

Basically:


High frequency modulation is used to reduce antenna size without increasing the radiated power. This means smaller antennas for the same information transfer.
The voltage entering the antenna is an analog modulated digital signal. This means that to obtain a digital signal from the analog input a DEMOULATOR is required.


I hope this guide in the right way.