I bought a 5.8GHz Wireless Audio-Video Transmitter/Receiver the other day. It works fine (for a 1 level house) if you connect say a VCR (Tx) and TV (Rx).  However when I connect it too my PC at the SVideo out, the quality is fairly poor on the TV no matter what the distance. I've also had to "force" my nvidia card into "TV detect" mode, it doesn't automatically detect the svideo port being used like it does with a TV.
I am using a GForce 6800 Ultra (with the latest drivers).

Any suggestions as to why this is going on? Any tests I can do?