In HF the limiting noise is not receiver generated unlike in microwaves and (ideal) capacitors and inductors don't generate noise: resistors and active componen

In HF the limiting noise is not receiver generated unlike in microwaves and (ideal) capacitors and inductors don't generate noise: resistors and active components do. However a sharp notch is a real pain to make in analogue domain. Lots of stages, temperature changes the component values, and things get bulky.