What determines which frequency range a radio telescope has?

Question

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?

Answer 1

A parabola does indeed focus over a broad frequency range. The lower limit is determined by the dish diameter, the upper by the construction (mesh size, parabolic accuracy etc.).

The collector placed at the focal point may be a simple dipole or other fixed frequency antenna, or more commonly, a waveguide that leads the collected signals to a low noise amplifier and receiver. The physical dimensions of the antenna or waveguide set the operating frequency range of the antenna system. More than one range may be tuned by means of multiple switched collectors.

The receiver is fundamentally no different to any other receiver; a tuning element selects the signals of interest which are then detected and amplified.