exploring the 20-30 local HD channels in your market
20-30?!?
I can get, maybe, four (notably, neither CBS or FOX), and then only with the largest directional antenna available. At least according to AntennaWeb. Real-world experience with a smaller interior antenna would seem to confirm that. (Yes, there are subchannels, but very little additional programming on them. It's mostly SD copies of the main subchannel and then news/weather.)
And I'm hardly in the boonies. Raleigh is like the 50th largest MSA in the country (out of something like 1000 total). And I'm inside the city limits.