HDTV - What's it all about?

With all the hype about HDTV, if you are new to the subject you are probably looking for some simple answers. One of the first things people ask us is about the difference between analog television, digital television and high definition television (HDTV). Put simply, the quality of the picture is ultimately what it's all about. There are two standards being used in the US today: analog, or NTSC, and digital ATSC signals.

Standard NTSC signals are broadcast in a 4:3 format. (This means that if you have a really big TV screen that is 40" wide, it will by default be 30" high.) NTSC signals deliver 480 lines across your screen in an "interlaced scan" format. What this means is that the screen first draws the image's odd lines, one at a time sequentially from top to bottom and then goes back to fill in the even lines in the same way. Each pass takes 1/60th of a second, so that the whole process takes 1/30th of a second. You might think this would cause a bit of a flicker, but in fact the process is so fast that it is not the human eye does not detect it. You will see this process referred to as "480i", meaning 480 interlaced.

The digital ATSC standard differs in that it starts with the same 480 lines but presents them using the much better "progressive" scanning method, permitting the entire picture to be drawn sequentially from top to bottom without the odd/even interlacing. Call it a trick of the eye or not, the picture simply looks much better. The screen format is also wider - 16:9 instead of 4:3, giving the ability to provide programs in a wide screen or "letterbox" mode.

But there's even more good news. What we just described is referred to as, you guessed it, 480p, but the beauty of the ATSC standard is that it allows for even more lines to be added - up to 1080, capable of a total resolution of a bit over 2 megapixels for those of you who know about digital cameras. The three major sizes being broadcast today are 480p , 720p and 1080i. These last two are both in the category of "high definition" and are broadly used in HDTV broadcasting.

Note: There is a lot of debate over which is better, 720p or 1080i, since the "i" is an interlaced standard. Don't worry about it! They both provide an excellent picture quality.

There are the basics. Beyond that there is the interesting reason behind why all this came to be - money! And you thought it was just so you could enjoy your evening TV programs more, did you? Well, that too, but the real driving factor is that we are rapidly running out of bandwidth in this country, and digital signals simply take up less room than analog. We need more bandwidth, not only for enhanced services commercial suppliers are chomping at the bit to provide, but also for the growth of emergency services. The sale of this bandwidth will generate a lot of much needed cash - a windfall for the government. And the new emergency services will enable us to better react in disasters and provide life-saving services on a daily basis.

The plan is to move everyone to the new ATSC standard by the beginning of 2007. There is still some dispute about that date, but it's going to happen sometime in the not too distant future. All the new digital stations coming on line will be allocated slots in the current UHF band. You remember UHF - that's channels 14-69. For example, WSB Channel 2, the Atlanta ABC affiliate, is now broadcasting WSB-DT simultaneously at 39.1, the digital equivalent of UHF channel 39. This will enable us to eventually close down the old analog channels completely, as they are replaced by the superior quality digital channels everywhere. So, if you have a tuner capable of picking up ATSC signals, they are already there - free for the asking off the air if you have the proper antenna.

So there you have it - we've come full circle in a way. Years ago we used to fiddle with antennas to try to get our TV's to pick up something interesting. Then came cable and later satellite, both of whom are fitting into the DTV/HDTV picture quite nicely as well, but now we have unlimited free access to this terrific technology with the simple addition of an antenna!

For a detailed list of digital stations live right now, plus lots of information on antennas how to select them, you should visit Antennaweb. Like digital TV signals, it's free!