Why does an analogue signals quality decrease after amplification?
When you amplify an analogue signal you amplify both the signal and the noise which does not improve the signal to noise ratio. However, with digital signals you don’t amplify the signal but you would rather detect the signal and generate a new signal that is a copy of the original signal, this is why we call them repeaters rather than amplifiers. While analogue signals are affected from the noise and interference when they are transferred over a noisy channel, digital signals are not much affected because the only case for an error to happen is when the noise is large enough to make the repeater read the zero logic as one or read the one logic as zero, but this is not usually the case because noise is usually weak.
