That is my simple small dish setup using currently used sat TV frequencies. I think the big ones used lower frequencies (C band ?) and I believe are good for making Hydrogen line receivers if you can find one (more popular in the US I think)
It’s not just amateurs using off-the-shelf communications hardware to do radio astronomy, incidentally.
On a larger scale, I believe the Australian SKA Pathfinder (ASKAP) is built out of standard 12-metre dishes that are used by telecoms companies. Of course, the detectors and mounts needed to be bespoke, though.
Many years ago now we had a Society visit to the home of John “Radio” Smith, which was near to Rudgwick in West Sussex/ He had a very large Ex Radar Ariel which was in the range of 20 to 25ft size. This was guarded by his Bees !!!!!