Looking at tivimate, it's not clear how I'd use it.

I have a TV tuner card, and have an antenna plugged into it.

How do I get tivimate to make use of it...? I'm sensing there's another piece in the middle that I'm missing.

Yeah, it's not for you. Tivimate is for IPTV. If I were just using antenna I'd have no problem using Jellyfin for it since there are not that many channels I would have active anyway, and I live between two major TV markets so I get plenty of OTA.