I was able to hear some of the traffic using my Baofeng F8HP with a stock rubber ducky antenna, so you don't need much on the receive side. At least when the ISS is close to you. Not sure what the window is as far as how far removed it can be from directly overhead, and yet still be able to receive that signal with a small antenna like that.

What it takes to hit the repeater I'm less sure. I've heard it can be done with an HT like mine, but I'm guessing that's only possible when it's directly overhead, or very near so. That said, I'd be happy to find out that I'm wrong about that.