Cover Image: June 2005 Scientific American Magazine See Inside

The Multipath to Clarity

Receiving HDTV over the air takes luck and lots of patience















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In the antenna world, bigger is often better, so I also tried something more radical and not particularly aesthetic: an outdoor UHF antenna, used indoors. Called a four-bay bow-tie antenna, it spans about two feet by three feet--among the more compact types of roof antenna. (Even so, you had better have an exceptionally understanding family.) Sure enough, it enabled me to pick up WNBC.

Still, reception was sporadic. I would stand in the corner of the room, moving the cumbersome antenna slightly this way and that as the receiver teased me with moments of signal lock. At other times, I located a sweet spot and left the antenna in place, only to lose the channel when the weather changed.

In January I suddenly picked up WCBS with my Silver Sensor pointed south. Then came WWOR, followed by WNYW after I put the antenna on top of a couple of boxes stacked on a speaker. Finally, I could pick up all the channels being transmitted from the Empire State, albeit with some effort. Something had changed. I looked down the avenue and saw an apartment tower going up a few blocks south. New York City's ever changing skyline had redirected HDTV toward me, at least for the moment.

I live on the 11th floor, and I cannot imagine that those closer to street level will be able to pick up local stations reliably, a fact that could be important once broadcasters cease analog transmissions. At that time they will give up channels 52 to 69. Four of those will go to public safety; the others will be auctioned off for wireless services. The target turn-off date is December 31, 2006, on the condition that 85 percent of the market served by the broadcasters can get digital (2009 or 2010, realistically). Unfortunately, the 85 percent figure counts those who have the equipment even if they cannot receive DTV because of multipath distortion. In sticking with 8-VSB, the FCC gambled that improving technology would save the day.

It is shaping up to be a smart bet, as receivers get better: first-generation models handled ghosts that lagged the main signal by no more than 10 microseconds and were no stronger than half the main signal. New circuitry made by LG Zenith can cope with time differences of 90 microseconds and multipath signals as strong as the main one, the company claims. Its performance convinced Sinclair to drop its objections to 8-VSB. As of this past March, however, LG had not offered these units for sale.

New antennas may also help. Dotcast, based in Kent, Wash., designed an active E-field antenna, which is being marketed by Winegard Company and Terk Technologies. It looks like a mini version of the radar antenna on vintage aircraft carriers. A special amplifier inside boosts only the electric field signal picked up by the antenna, Dotcast says, while ignoring other radio-frequency waves. The narrow, 27-inch-long Dotcast antenna, which should be available this year for about $120, is supposed to function as well as a five-foot-long roof antenna.

HDTV does not transform the viewing experience the way TiVo and DVDs do. And there are growing pains. On WCBS football games, some on-screen graphics did not show up. A space shuttle launch momentarily appeared during a high-def broadcast of ABC's Desperate Housewives (it was not a lame sex joke). But once you see the clarity and color and hear the digital 5.1 sound, there's no turning back. I want my HDTV. I just wish it were easier to get.



This article was originally published with the title The Multipath to Clarity.



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