I'm sure this is a dumb question, but that hasn't stopped me before. Also, please understand I'm not trying to get anything I haven't paid for, but on the other hand I don't want to not get something I'm legally entitled to just because I don't know about it. So here goes: I currently have regular SD programming from Comcast. If I were to sign up for HD programming from them, would they begin sending a different kind of signal to my house, or just enable me to access a signal that's coming in already?