What you need used to be commonly available, don't know if they still are or not? - the ones we used to use (for upconverting a VHF relay system to UHF) were called 'T-Verters' or 'Tele-verters'. They were wideband, and converted the entire VHF spectrum to UHF.
The frequencies used and critical layout means it's not really a DIY project.