We just did this. :DHenry,
Go to Radio shack and get the plug, some 14G or so wire, and what ever kind of battery clip you want. They have a ton of them and the people there can probably help you find the correct size, but usually they have a bunch of them hanging there to test fit with.
I am using a 9V battery clip that I wired to a round plug.
The polarity is marked on the AC adapter that came with the receiver.
It worked great for us with just the little 9V range was fantastic with that big antenna.
In fact we even hooked the antenna up to my cheap Radio shack receiver and got a fantastic picture.
Fly Fast....Live Slow...