Well, I guess I need to fix the "free" aspect of this first. The DTC-100 cost me about $400.00 about 3 to 4 years ago. I have been doing HD for a while. Many TV's now-a-days come with HD receivers built into them, so this cost might not be an issue. If your TV is HD "ready", you probably don't have a receiver/tuner. If your TV has a tuner and the tuner has an antenna-in that is for HD reception, all you need is RG-59 and an antenna. Reasonably good antenna's will run you $100.00. At my old house, I had TERK antennas on the side of the house. The house had aluminum siding and it still worked great believe it or not. The TERK's are nice because you can put them on the outside of your house and they don't standout. Draw back is they are very directional... so I had 2.
As for my distances, as the crow flies, 20 to 30 miles from house to broadcasting tower. I have towers east, north and west... nothing on the south. NBC, ABC and CBS are clustered in the same area, but with slightly different offsets. FOX is more northeast than east. I have a few other no-name HD feeds from other areas of the compass coming in too.
I have to remember the specific antenna I have... probably will have to look at the box later.
Basically, HD reception comes in on UHF, and the antenna I have does both UHF and VHF. I get all the analog (VHF 2-13) several HD feeds on UHF (14 - 69).
Now, they sell antennas for different ranges and purposes. You must first figure out what stations you want to bring in, location of the towers and distances. Once you know that, you can figure out what type of antenna you need. The antenna's are color coded to make it easier.
Use the link below to figure out what towers are in your area, what they are broadcasting. This will give you an idea on what antenna you need.
http://www.antennaweb.org/aw/welcome.aspx
Here is a nice FAQ on HDTV too.
http://www.avsforum.com/hdtvfaq/HDTV-FAQ.htm
They make antenna's that are very directional, but awesome working. I have two TERK's that I am not using at this point. A TV55 and a TV50. Since the RCA DTC-100 has two external antenna inputs, I would point one oneway and the other the anotherway. I am now using one of those standard antennas with something like 110 elements on it. These type of not so directional dependant, but don't have the distance of some of the others.
Some antennas cover a perfect circle for say.... 30 miles. Others cover a fat oval area say... 50 miles, but remember... OVAL coverage. Draw an oval around your house covering the towers that are clustered. Others have a skinnier oval coverage, but they cover out say... 70 miles. I am making up number to give you an idea on how they work. Use the antennaweb link to figure out the color code you need, then go get the color coded one from BestBuy, CircuitCity, RadioShaft, Lowes, HD even the web.
http://www.avsforum.org is the best place for any and all HD questions. I would be more than happy to discuss HD with anyone as it is yet another of my hobbies.
And lastly.... antenna ampliphiers. Sometimes they help you, sometimes they cause more problems than they are worth. A buddy of mine needed the ampliphier to get a bunch of channels, but for FOX, he was too close to the tower and when he had the amp on, his reception was crap. If he turned the amp off, it was fine. Just food for thought.
Antenna pointing requires PATIENCE. You either get the station or you don't. No such thing as getting "snow" on an HDTV feed.
If you have questions, let me know and I'll try and answer the one's I can.