As the digital television rollout lumbers along, many broadcasters have questioned the efficacy of the 8-VSB modulation scheme. But for viewers of NBC affiliate WOOD-TV in Grand Rapids, Mich., 8-VSB is working all too well.
Since July, over-the-air viewers in Muskegon, Mich., on Michigan's southwest coast, have complained of snowy or unwatchable pictures on WOOD-TV, which is owned by LIN Television and broadcasts on ch. 8 in Grand Rapids. WOOD-TV was still looking for the source of the problem in August, when the AT & T cable system in Muskegon reported interference in its reception of the signal affecting some 40,000 cable subscribers.
The problem wasn't in Michigan, however. Instead, it was on the other side of Lake Michigan, where WMVS-DT Milwaukee has been transmitting a high-powered DTV signal since March on digital ch. 8. While Milwaukee represents another DMA, wmvs-dt's 1,200-foot tower is only 82 miles away from the Muskegon viewers on Michigan's coast. In between are the waters of Lake Michigan, which can combine with summertime weather to create atmospheric conditions that allow for unusually powerful signal propagation.
"There's nothing to stop that signal," says Mike Laemers, WOOD-TV director of engineering. "Their tower is right on the [western] lake-shore, and our viewers are right on the [eastern] lakeshore. Ten to 15 miles inland from Muskegon, it's not a problem." He estimates that 60,000 cable and off-air viewers in Muskegon were affected.
There hasn't been any interference problem in Muskegon since late August, when WMVS-DT agreed to cut its transmission power by 75% to make sure wood-tv's broadcasts of the Olympics and season-opening prime time shows proceed uninterrupted. In the meantime, WOOD-TV is looking for a long-term solution.
"We're looking at various alternatives, including putting up some sort of translator in the area, feeding the cable headends with microwave or putting up a different antenna at the cable headend," says Laemers. He doesn't think using fiber to deliver the signal is feasible, because western Michigan isn't fiber-rich. And Laemers is afraid to use a microwave channel when the 2 GHz spectrum, which is used for ENG signals, is already being squeezed by the FCC for auction purposes.
David Felland, WMVS-DT director of operations and engineering, says that WMVS-DT had been operating at its authorized power, and had even installed a directional antenna to minimize interference to wood-tv.
Felland says that there are WMVS-DT viewers who can no longer receive the signal. "We hope they would take immediate steps to rectify the receiving station on their end."
Doing so will cost a minimum of hundreds of thousands of dollars, according to LIN President Gary Chapman. In a speech to the Federal Communications Bar Association last month, Chapman also suggested the wood-tv/wmvs-dt situation is "a sharp warning" that digital interference into analog signals may be greater than expected.