Ok, think I found out the problem. I have a Hirschmann Hit Auta 5091 antenna. Since I have owned the car, the antenna never worked (I suspect this was/is the one that came with the car). I took it out of the car, and noticed that it was wired to an external resistor, but w/o a wiring diagram, I was still flying blind. I finally did manage to find a wiring diagram online, and when I hooked it all up, nothing worked. The 5091 has 3 wires coming out of the unit; then into an external resistor, and then 2 wires out (and a ground). Needless to say, they are all different colors. So, a dead unit (no surprise), and a replacement on order.