let's consider a basic scheme of a receiver.
Now I have two questions:
- 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)?
- 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?