This is strange. I just re-tuned my DVD recorder, and I think I am picking up some OTA channels with it, even though I don't even have an antenna attached, just a coax cable. All of the OTA channels are the HD versions of the channels, but any sub-channels are in SD. It's strange. 
Crash course in technology:
You might be picking up what's called QAM channels...all digital cable channels are in reality sub-channels of the original 125, then mapped to big numbers. Most providers provide in-the-clear QAM with local digital (meaning you get HD channels), and possibliy some bonus channels (if you're lucky).
Also, you can have only one HD channel per OTA station currently...two makes the picture look like shit (not joking).
I know what the QAM channels here are; they're on channels 71.1 through 71.11.
These other channels I'm picking up, like 8.x, 21.x, 27.x, and 33.x all correspond to the OTA frequencies these channels are on. Plus, unlike the QAM channels I'm getting, these OTA channels have digital blocky noise to them. Furthermore, the channels that have their transmitters further away tend to be cutting out more. Also, last night, which was a clear/partly cloudy night, I could pick up the channels a lot better that I can now in the rain and fog.
