There's a big change coming in the way some of us get our TV signals. If you get some or all of your channels using an antenna, your viewing routine may be disrupted on Feb. 17, 2009. That's the deadline for all full-power TV stations in the U.S. to switch from analog broadcasts to 100% digital broadcasts. "Digital" is the "D" in DTV, and when TV stations flip the switch, all old-fashioned analog TVs that aren't connected to a digital converter box will no longer be able to tune in local broadcasts because those broadcasts will be digital.

DTV ≠ HDTV
Some people confuse DTV (digital TV) with HDTV (High-Definition TV), but they're not the same. DTV is a general term covering all over-the-air digital broadcasts. There are two basic types: medium-quality standard-definition TV (SDTV) and high-quality HDTV. In other words, while HDTV is always digital TV, digital TV isn't always HDTV.

The major TV networks produce nearly all of their primetime programs in HDTV, and they look terrific, but most daytime programming is standard definition. SDTV is about the same quality as a DVD, so the picture is sharp and clear - a big improvement over typical analog TV, but not as sharp and detailed as HDTV. Even after the February switchover, we'll still probably see HDTV at night, SDTV during the day. And it may take several years before local news and other programs make the jump to HDTV.

A converter box only delivers standard DTV
If you plan to continue watching over-the-air broadcasts on your analog TV, you'll need to connect a digital converter box between your antenna and TV. And you'll need one for each analog set you plan to keep using. With a converter box, you'll be able to watch standard-definition DTV on your old set, but not HDTV. Your old TV isn't capable of displaying an HD picture, and the converter box isn't capable of feeding HD signals to a TV.

To watch over-the-air HDTV broadcasts in true high-def, you need an HDTV tuner. This tuner can either be inside a TV or in a separate tuner box. The thing is, if you connect an HDTV tuner to your old tube TV, you still won't see an HD picture, for two reasons: your old TV's screen can't show all of the detail in HDTV images, and your old TV lacks the newer HD-capable connections (like component video and HDMI). Most HDTV tuners also include conventional connections that work with older TVs, and when you use these connections, the tuner box downconverts the HD signal to SD. So, the picture you'd see would be good, just not great.

Satellite and cable offer HDTV as a premium service
If you get your TV service from a cable or satellite provider, you won't need to worry about getting a converter box because your cable/satellite box will take care of everything. But, you still need to be aware of the difference between HDTV and SDTV because cable and satellite also offer both types of signals. If you stick with the same channel selections you currently get, chances are you'll be getting SDTV signals.

To get true HDTV picture quality, you generally have to pay a higher monthly subscription fee for HD channels, and you need to get an HD-capable box from your service provider. And, of course, to see the kind of picture that makes people rave about HD, you need a TV that can actually display a crystal-clear HDTV image.