Noncommercial KERA-TV Dallas-Fort Worth is collaborating with Minneapolis-based transmitter manufacturer ADC to test new technology designed to reduce the interference between DTV signals and services on adjacent channels.
ADC's software, called Bandwidth Enhancement Technology, is aimed at the more than 300 DTV assignments that have adjacent NTSC channels either below or above them or have other special interference considerations with cable systems, FM radio, radio astronomy installations, or police and fire department communications. Those DTV channels include 2, 4, 5, 6, 7, 13, 14, 36, 38 and 51, according to ADC Marketing Manager Rich Schwartz.
Bandwidth Enhancement Technology is designed to move information from one part of a 6-MHz DTV channel to another, allowing less than the full 6 MHz to be used. But the system doesn't reduce the 19.4-Mb/s DTV throughput, says Schwartz: "The signal is narrowed by as much as 400 kHz without losing any information."
North Texas Public Broadcasting, which operates KERA-TV, plans to start testing Bandwidth Enhancement Technology next month when it launches a low-power DTV signal in Dallas. The station has received ch.14 as its digital assignment, which as the lowest channel in the UHF band is immediately adjacent to two-way radio frequencies used by emergency services and businesses. The station will use an ADC transmitter to generate the DTV signal, which will be radiated from its existing NTSC tower.
"When the FCC gave us this channel, we knew it would be difficult to operate it at full power without causing some interference to land mobile users," says KERA-TV Chief Engineer Rick Owen. "ADC has written custom software for the digital exciter that allows the 8-VSB signal to be attenuated as much as possible at the end of the band, behind the FCC mask of specifications."
Owen isn't sure that KERA-DT won't lose a slight part of its usable data rate by using Bandwidth Enhancement. But that's what the tests are for.
"We may lose some megabits," he says. "But our main concern is just to coexist with the land mobile users."
ADC has performed laboratory tests of Bandwidth Enhancement with both professional and consumer DTV receivers, Schwartz says, noting that all tested so far have had no problem identifying signals run through the system.