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11.08.2002
Originally featured on BroadcastEngineering.com
Sign of the times: More DTV interference

Did the FCC take a technological shortcut and fail to thoroughly test in advance for interference problems from DTV signals? Camden County, NJ, and its neighbors think so.

The area’s police communications system is being jammed by 24-hour-a-day digital television signals from WCVB-DT in Needham, Mass. The Courier Post newspaper of Cherry Hill, NJ, reports that interference is “threatening public safety by drowning out calls from officers to central dispatch in certain kinds of weather.”

Camden County, whose system operates on the same frequencies as the TV station, has appealed to the FCC for help, but so far no solution has been found, the newspaper said. Neighboring counties, which are also experiencing or anticipating similar interference, has joined the FCC appeal.

The local police department said the problem has the potential to leave an officer in the middle of a dangerous situation with no way to call for backup or ask for help. “Losing communications even for the shortest of times could be dangerous for the public and our officers,” said Chris Ferrari, police chief of Oaklyn, one of 31 Camden County communities served by the central communications center.

Normally, the report said, WCVB-DT's signal travels about 50 miles. Under certain atmospheric conditions, however, it can extend to hundreds of miles. Police officials blamed the interference on a weather condition known as tropospheric ducting, which usually occurs on summer nights. Layers of warm and cool air create a kind of “duct” that traps radio transmissions, allowing them to travel hundreds of miles without breaking up--in this case about 270 miles.

WCVB-DT began broadcasting a digital signal on Channel 20, 506 through 512 megahertz, in 1998. But the problem did not occur until this year when the station began around-the-clock DTV broadcasts.

The problem should have been anticipated, Mike Keller, chief engineer at the station, told the newspaper. “I think what happened here is somebody underestimated,” Keller said. “There's nothing new here. Skip and bouncing of signals has been going on forever.”

He said WCVB-DT is willing to work with local police officials, but added the station is operating within the parameters of its license and “there's not much it can do.”

Camden blames the FCC for not having planned better in its efforts to transfer all TV stations from analog to digital broadcasts. The FCC should have known atmospheric conditions could cause a station signal in Boston to travel this far south, county officials told the newspaper.

An FCC spokeswoman professed ignorance of the Camden problem, but said the commission expected the move to digital television to be a painless one.

For more information visit www.courierpostonline.com/news/southjersey/m110102a.htm.

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