Assuming you're talking about airwave stuff, you would want a HDTV to SDTV converter system and then to pump the output of that into something like the Blonder-

Assuming you're talking about airwave stuff, you would want a HDTV to SDTV converter system and then to pump the output of that into something like the Blonder-Tongue AM60-550 and then amplify the output of that into an antenna. If you keep the output pretty low and use unsaturated channels in your location you'll probably be fine, but you mess up a little bit and in theory the FTC could knock on your door. That being said, people use setups like this for art installations with old school tvs all over the place, so it's likely not a big deal as long as you're not setting up a pirate tv station or something