Published: TV Technology magazine Issue: 9 March 98 Old Ideas May Bring Relief to Stations by Joe Fedele MIAMI Have you seen your DTV power allocation yet? Several stations that have seen are worried they may not be capable of transmitting a strong enough digital signal into their core market. The controversy over just how much power each DTV station will be able to use has raised many eyebrows. It was also one of the key issues resolved by the FCC’s February 18th DTV allotment up- date. Prior to the allotment table release, a large number of UHF broadcasters wrestled with the thought of transmitting a meager 50 kW of ERP, which had been previously mandated by the FCC in its original ruling. Without sufficient power, many stations whose viewing audience is on the fringes of the Grade B coverage area might not see a picture at all. The battle between UHF broadcasters and the FCC was outlined in an earlier article (see the Oct. 23, 1997 issue of TV Technology titled “Viacom Seeks Increase in Power”) that detailed Viacom’s attempt to have minimum power limits raised to 250 kW for all DTV stations. The newly released table addressed many of those concerns by allowing broadcasters to increase their power up to a 200 kW limit, provided that the change does not result in more than a 2 percent increase in interference to other stations. But even this was not enough for some who see a stark contrast to the 1 mW (megawatt) allocations provided to VHF stations. In recognition of those concerns, the FCC also agreed to allow broadcasters to increase UHF power levels to 1 mW, provided that interference is limited to only 2 percent and that beam tilt antennas are employed to limit coverage to the station’s service area. The concept of using beam tilt antennas to increase power while maintaining service coverage stems from a petition filed late last year by the Association of Local Television Stations (ALTV). But unlike the Viacom proposal, which would raise the minimum only 7 dB and potentially in- crease interference with other stations, the ALTV proposal called for a 13 dB increase (1 mW) with- out adding interference. SENDING STRONG SIGNALS Jim Hedlund, president of ALTV, stated in a Nov. 25 letter to FCC Chairman William Kennard that “American consumers are unlikely to purchase new digital television sets if their favorite UHF stations are unable to transmit sufficiently strong signals in the digital world.” He went on to say that the ALTV proposal would “permit DTV stations to increase power to 1 mW, provided that tilt beam antennas and/or other technologies are employed to prevent any incremental visible interfer- ence [to other DTV stations].” At the core of the ALTV proposal was the age-old concept of manipulating antenna beam tilt in order to better focus a station’s field strength within their allocated contour, without actually ex- ceeding it. The idea is to provide more power density at the viewer’s end to insure good reception. Contrary to the FCC’s assertion that most receive antennas would be located outdoors, Del Parker, vice president of engineering for the Sinclair Broadcast Group (SBG), headquartered in Baltimore, explained that its findings have shown that TV reception is an “inside service.” Nat Ostroff, vice president of technology for SBG and the technical architect of the ALTV plan, explained that signal penetration through the buildings becomes a critical issue with indoor anten- nas. “You need that extra power to punch through the walls,” he added. The theory behind beam tilt centers on a station’s coverage pattern with regard to its field contour and the horizon. “VHF stations are able to point their antenna beams at the horizon,” he said. “But UHF stations must ensure that the radiation center of their antenna is aimed inside the station’s cov- erage area so they do not exceed the prescribed FCC field intensities at their contour’s edge.” The ALTV plan, according to Ostroff, would allow stations to avoid interference at the edge of the contour. “Beam tilt for a typical antenna on a 1,000-foot tower is about 0.5 to 1 degree for many NTSC stations,” he said. “Our plan would increase the average DTV station’s tilt to about 3 degrees. This would allow them to increase their power to up to 1 mW without causing interference to adja- cent markets.” Ostroff predicted that most of the beam tilt would be facilitated through electrical, rather than me- chanical means. “Mechanical tilt can be made to work only on a limited number of antennas, but it is not a universal solution,” he added. With an omnidirectional antenna, for instance, mechanical tilt in the downward direction on one face would cause the opposite end to tilt up towards the horizon. And that would run contrary to any attempts at maintaining the beam within the predicted field contour. But stations that employ direc- tional antennas with a sharp null on one side may be in a better position to utilize mechanical tilt. “We still don’t know how robust the 8-VSB service is going to be,” Parker concluded. “And there will always be a big question as to how effective it will be. Since nobody has been able to com- pletely address this we remain skeptical.” With the FCC’s acceptance of higher power levels now in place, broadcasters can take the next step in determining if Parker’s trepidation about 8-VSB is warranted.