My simple understanding is that a parabolic dish focuses radio waves to a receiver. It is obvious that any parabola focuses visible light and heat, so I assume that it focuses all radio wavelengths too. So evidently the design of the receiver determines which wavelengths it is sensitive to.
How is such a receiver designed in radio telescopes?
What properties of the receiver determine the wavelengths it is sensitive to?
Is the sensitivity range electronically adjustable?
Why aren't different receivers used so that the same parabola, for example the huge Arecibo dish, could be used for all wavelengths? (Or is it?)
What importance does the size and material of the parabola have for the sensitivity to different radio wavelengths?