High - Frequency Carrier Necessity

Question

let's consider a basic scheme of a receiver.

Now I have two questions:

1. I was told that the presence of the mixer is important since it is useful to delete the carrier frequency of the received signal. In fact, it is very difficult to work (i.e. amplify, filter etc) with high frequencies and so deleting it will be very useful. But now I have a previous question: why should we impress our signal to a high - frequency carrier, during transmission (and cannot use directly the frequency of our signal)?
2. In this picture I see an analog voltage entering the antenna, and a digital voltage exiting the envelope detector. My question is: when we speak of digital transmission, is the voltage entering the antenna digital or analog?

Answer 1

This is an extremely basic question about RF and you should read a book in this subject.

Basically:

1. High frequency modulation is used to reduce antenna size without increasing the radiated power. This means smaller antennas for the same information transfer.

2. 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.