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Originally Posted by glatt
If I have a roof-top antenna strapped to my chimmney, will that stop working well, since the bars will be spaced at the wrong wavelength?
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HDTV, NTSC and even FM radio are radio signals. Antennas are tuned to radio frequencies with little concern for that signal content.
But digital TV signals are picky. To appreciate the problem, consider a TV with a ghost image. IOW a signal is received directly AND another signal is received by being reflected. Same signal arrives twice - at slightly different times.
So what does the digital TV do? It has two copies of digital information combined in one signal. Which should it use? How does it know which signal to reject? To a TV, the image and its ghost are one digital signal - now confused.
To rush to HDTV, the US decided to implement a first option available - 8-VSB - so as to protect Zenith, the only remaining US TV manufacturer. It was a decision based in politics - not in engineering. As a result, the US standard is different and inferior to standards (COFDM) used in Europe, Japan, Australia, etc. The US standard is less resilient to ghosting meaning that US TV will not operate properly even in moving vehicles.
See the Sinclair Broadcasting lawsuit as a last ditch attempt to implement better standards found elsewhere. Their tests in Baltimore revealed reception of COFDM was better than 8-VSB at two sites and that reception difficulties were due to the presence of strong static signal reflections, or "multipath."
Now for your antenna. HDTV uses the same UHF frequencies of analog TV. An HDTV antenna is simply a better (high gain) UHF antenna to reject more ghosts and to get a stronger signal. High gain means the antenna is more directional. More elements (crossbars) on an antenna create a narrower (higher gain) reception angle.
Ghosting is even why interior antennas don't work well with digital TV. Even the phenomenal bowtie antenna is not very directional - is poor at rejecting ghosts.
So how do you know if a signal is defective? In analog TV, you could see both ghosting and little white dots indicating noise - a loss of signal. But digital TV either compensates for that ghosting or noise, OR you have a stopped image. If signal is lost too long, then it appears as no broadcaster on that frequency (channel).
Cable companies are just licking their chops. Many consumers will give up early on their antenna and finally conceded to more expensive digital cable service.
Current antennas are tuned both to VHF and UHF frequencies. VHF frequencies will be assigned to other services (ie cell phones) in a few years. It was to happen long ago. But HDTV sales were not sufficient. Currently Best Buy and Circuit City are throwing TVs out the door in a price war. Large numbers of new TVs suggests the shutdown of VHF TV channels will occur in 2009. Meanwhile, Zenith is now a foreign manufacturer.
IOW, while analog TV is available, then use that TV to get a good UHF antenna - no ghosts and no little white spots. Then your antenna will be ready for HDTV.