If you have a Ham license that gives you permission on the right bands, and you are careful to only transmit on those bands, then it's legal. There are power &

If you have a Ham license that gives you permission on the right bands, and you are careful to only transmit on those bands, then it's legal. There are power & frequency rules, among others. It'd be a pretty big DIY project, and quite possibly unable to be done due to physics of the dish preventing you from shifting over to the legal (Ham licensed) frequency. It's not on-face illegal to build radio equipment though.