I have a Satellite SKY dish, and also UHF and a VHF antenna. Im setting up an htpc, using an HVR-2200 for freeview terrestrial. Do i need a diplexer for the vhf & uhf before I go into the tuner card, or do I only have the uhf going in?
If you are only wanting to watch Freeview|HD (and maybe Prime) then you only need a UHF aerial and have no need for the VHF aerial or a diplexer. If you wanted to tune in VHF channels as well you would need a diplexer.
As Steve says, and preferably if you can get by without the VHF antenna all the better, all it will do is put noise in the system which is not good for DTT reception. The sooner you pull all that old bit alloy off your roof the better off you will be.