Hello, Big Picture Big Sound,
I am currently building a new home. I had the electrician place six cable outlets in various locations in the home for the purposes of high-speed internet and television viewing. All the cables lead to a central panel in the basement.
I would rather install an outdoor antenna for over-the-air TV and HDTV, rather than paying the cable company extra money for programming I don't watch (that also currently lacks local HD channels). My question is, can I integrate a UHF-antenna's signal to the cable distribution if the cable company is using it for high-speed internet? If so, what is the best approach?
Congratulations on your impending new home. You must be very excited. Most of my power wires have been in the walls since 1930, so I envy all that shiny new copper wire!
In terms of your question, the answer is "it depends." If the central panel that you describe includes a splitter or distribution amplifier where the end plugs of each of the six cables are labeled and independently accessible, then you should have no trouble identifying which cable goes where. And in this case, all you'd need to do would be run one additional coax cable up to your roof to plug into the roof antenna, plug the inside end of this cable into the input jack of a 4-way or 6-way splitter in the basement (possibly an amplified splitter, depending on the quality of your over-the-air signal), then plug the ends of the cables that you know will be used for televisions into the outputs of this splitter. In this case you would plug only the specific cable you intend to use for your cable modem into the cable company feed coming into the house.
If, however, you are intending to use one of these six cable outlets (let's say, the one in your living room) for both a cable modem and over-the-air antenna reception, then you're probably going to run into problems with interference. Cable TV signals and over-the-air TV signals share the exact same frequencies, so the cable TV signals coming into your house over that cable wire are going to interfere with the signals you're trying to pick up from your OTA antenna.
You can split off the line to go to the cable modem (that's simple) but if you try to use any kind of filter to filter out the cable TV signal from your cable feed (once the signals have been combined), you'll damage the over-the-air reception as well. If your cable company filters out the cable TV signals from your line before it comes into your home (via a trap or filter on the pole outside), then you may be OK combining the cable and over the air feeds, but you're still introducing the possiblity of interference.
With satellite service, you can use something called a "diplexer" to combine satellite and OTA feeds over a single coax cable, and split them back out at the other end with another diplexer with fairly minimal signal loss. You can do the same thing with satellite and cable service, in case you want to get your local programming from your local cable broadcaster, but use satellite for the rest of your channels. But with cable and over-the-air broadcasts, you can't use a diplexer because of the shared broadcast frequencies.
If the walls are not closed up yet, then consider adding a separate coax feed to the room where you intend to have your cable modem so you can have a line dedicated to the modem and use those other 6 outlets for the over-the-air antenna feeds. You can only hook up one cable modem per account, so this should only affect one of your six outlets. Then you'd use the distribution panel/splitter in the basement to route your over-the-air antenna signal all over the house.
If the walls are closed up, then consider just drilling one hole through the outside wall into the specific room where the cable modem is going to be placed (assuming this is a room with an external wall) and use this for the cable modem feed. You can then distribute the internet connection throughout your house using a router and cat5 cable or Wi-Fi.
Hope that helps and good luck with the construction!