This is going to vary market to market.

You can enter your address at www.titantv.com this will give you a listing of all HDTV in your with Local number, and broadcast channel (i.e. Chicago WGN is Channel 9, but HD is broadcast on CH 19)

The other thing to do is to call the station and ask them what channel they are broadcasting their HD signal on.

most are broadcast inthe UHF band.