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DTV: It Really Works!

Believe it or not, we're almost a decade along with the transition to digital terrestrial television

So I performed the most appropriate test I could think of — comparing a 4th-generation LG LST-4200A set-top receiver to the Samsung and OnAir GT boxes in real time, by rotating the antenna slowly away from the desired transmitting tower to introduce multipath and echoes.

I ran the coaxial feed from my rooftop antenna into the Samsung DTB-H260F set-top box, and then looped it into the LG LST-4200A. A cable from the LG tuner's loop-out connection went to my spectrum analyzer for monitoring of each received 8VSB waveform. (The OnAir GT was tested separately with the antenna positions repeated.) Reception was verified on my Princeton AF.30HD reference CRT monitor.

The results? I was able to turn the rooftop UHF yagi antenna as much as 50 degrees off-axis from the ideal heading for each DTV station, yet still receive the signal with no drop-out on either of the 5th-generation tuners. In contrast, the LG tuner had significant dropout or no signal reception at all with these same antenna headings, depending on the severity of the multipath. For one of my tests, I turned the antenna to an 80-degree heading to pick up stations from New York City, positioning the Philadelphia DTV stations 130 degrees to the rear and side of the antenna. Even so, I still picked up three DTV stations from Philadelphia and one from Allentown with no dropout at all.

In short, the ATSC system has gone from a “works on paper, but not in the field” concept to a mainstream DTV transmission and reception standard over the past 10 years. In fact, MPEG stream analysis software bundled with the OnAir GT tuner showed that most DTV stations had their time and date set correctly, were actually transmitting some form of electronic program guide (EPG) information and closed captioning, and had few MPEG packet ID errors.

So what's next for VSB? Apparently, LG is well into developing a 6th-generation version, but that might be all we'll see for a while. That's because the original patents on VSB were issued to Zenith in 1992 and will expire in 2009 —about the time the transition from analog to digital TV is scheduled to take place.

To sum up, the terrestrial VSB system has finally reached the point where it's competitive with direct-broadcast satellite (DBS) in terms of reliability, and competitive economically with cable delivery of DTV. Now, the task is to get mainstream users to put it to work as an alternative, inexpensive source for SDTV and HDTV program content.

Maybe we do need to call it “wireless HDTV!”

Pete Putman is a contributing editor for Pro AV and president of ROAM Consulting, Doylestown, PA. Especially well known for the product testing/development services he provides manufacturers of projectors, monitors, integrated TVs, and display interfaces, he has also authored hundreds of technical articles, reviews, and columns for industry trade and consumer magazines over the last two decades. You can reach him at pete@hdtvexpert.com.



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