I've been somewhat intrigued by this possibility for some time. I played around with my cable hookup, and I discovered that if I bypass the cable box and go direct into my TV, I get a bunch of channels that cable doesn't offer me. So I have it set up both ways, and I get switch between them with my remote. And I'm guessing that some of that is relayed HDTV via digital OTA. I kinda wish I knew more about it.
I live about 45 miles from Mount Tom, where there are a bunch of transmitters at the top. But it's almost line-of-sight. If I walk about a half mile up hill, I can see a beautiful view of Mt. Tom from the parking lot of a restaurant.
I've seen the antennas at Walmart, but I have no basis for judging between amplified and passive, multidirectional and unidirectional. I don't want to waste money. I guess, given Walmart's return policy, I could buy one, try it out, and take it back if I'm not satisfied. But I'd like a better plan than that if I can find one.
Correction: The coax cable delivers both digital and analog channels. no guessing about it. The TV set has both a digital tuner and and an analog tuner connected to the coax antenna input. When the raw cable is plugged into the antenna input, and the TV does a channel search, it comes up with about 2 dozen analog channels and lots of digital channels. Some content is delivered in both an analog channel and a digital channel.