HDTV advisory group gives VSB good marks for cable

Electronic News, Sept 26, 1994

WASHINGTON--The FCC Advisory Committee on Advanced Television Service last week said that the vestigial sideband (VSB) technology proposed for a transmission subsystem performed well in cable environments during field trials conducted during the summer.

Although the "Grand Alliance" in high-definition TV selected Zenith Electronics' vestigial sideband (VSB) technology as its digital transmission subsystem earlier this year (EN, Feb. 21), some cable system operators have claimed it is inadequate for their modulation needs (EN, April 21).

The FCC advisory committee conducted three months of field tests this summer in Charlotte, N.C., on the Grand Alliance's eight-level VSB broadcast transmission technology and 16-VSB cable transmission technology. The results, the FCC group said, indicate that the 8-VSB transmission system performance was significantly better than NTSC. "In the UHF band, satisfactory reception was found at 92 percent of locations compared to 76 percent for NTSC. In the VHF band, transmissions were received satisfactorily at twice as many locations as NTSC," according to the group.

In addition, the 8-VSB system was said to have performed well under the real world conditions of multipath, impulse noise and other propagation phenomena, and in a limited indoor reception testing.

The FCC advisory group said "cable test results were equally encouraging." "At sites where cable connections meet FCC specifications, a significant power margin above receiver noise was measured. Even at cable sites not meeting FCC specifications, directly fed receivers were able to operate above the necessary threshold," the group said.

CableLabs, the cable industry's research consortium, participated in the cable system tests and analyzing the results. Charlotte also will be the site of final system verification field testing.

"The field test results show that the digital HDTV transmission technology proposed by the Grand Alliance performs well in real-world conditions," said Richard Wiley, advisory committee chairman.

The tests were designed to compare the Grand Alliance system's broadcast coverage and cable robustness to the performance of the current analog television system, NTSC. "This is an important milestone as we move another step closer to recommending a system to the commission," Mr. Wiley said.

Prior to the FCC decision, GI and Zenith earlier this year had cross-licensed their respective modulation technologies; General Instrument had pushed its QAM transmission subsystem during earlier testing.