I have kind of the same problem that you do. I have a stereo/CD/DVD/TV Tuner head unit (like for a car) and small 8" LCD screen. I put a regular car antenna on the side of my tear. The radio/tv tuner has an input for a regular car antenna plug and one for a coax cable (like on the back of a VCR or TV. I bought one of these:
and now I'm trying to find (or make?) a short wire/adapter with a car radio type antenna plug on one end and a coax connector on the other.
I think you said that you bought a TV antenna to start out with, so maybe your solution will be in reverse to mine?