If I remember correctly from one of my visits there they're mainly monitoring radio emissions from gas clouds. Yes, on open evenings one could get close to all the equipment, including going into the optical telescope domes. Some radio telescopes can be large (for example, Jodrell Bank) but they're usually ground mounted. They can be multiple antennae linked together, like the square kilometre array in South Africa, or the world wide network of radio telescopes that imaged a black hole - or more accurately, the material surrounding it; what was published as a picture was 'false colour' or radio frequencies translated into the optical spectrum frequencies.
Michael Ixer ● 27d