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DTV Stations to Viewers: 'Less Power to You' - TvTechnology

DTV Stations to Viewers: 'Less Power to You'

FCC respite will require upgrades
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FCC respite will require upgrades

WASHINGTON

To hear FCC Chairman Michael Powell tell it, the sputtering DTV transition suddenly is going gangbusters. Admittedly, the numbers he cited at an October MSTV meeting are impressive: HD broadcast network content is up nearly 50 percent in primetime since last year; DTV stations have more than doubled in a year, inching toward the 600 mark; in the top-30 markets, 113 of 119 top-four network affiliates are on the air with DTV; and cable, he boasted, is coming onboard.

Still, if you follow the money during the transition (or the lack of it), it's becoming increasingly apparent that many broadcasters are spending as little as possible in their DTV build-out in order to barely fulfill minimum FCC power requirements. Although about half of today's new digital signals are full-power, in the past year low-power (LP) transmitters are outselling full-power equipment as much as 6-to-1, according to some major manufacturers. But some LP and full-power DTV scenarios are causing technical problems that could portend things to come.

MULTIPLE PATHS

There are at least three LP options available to stations: 1) lowest-cost "throwaway" transmitters that cannot be upgraded; 2) LP3's that include major elements that can be deployed in larger transmitters; 3) larger transmitters that have major elements stripped out to provide an LP solution. Dave Glidden, director of TV transmission products at Harris Corp., says Harris believes "the most cost-effective approach to low power is the second solution. Our Ranger transmitter is cost-optimized for low power, but most major cost elements (exciter, power amplifiers and power supply) can be used within a larger Harris Diamond or Sigma transmitter."

Glidden says despite the FCC's LP rules, many stations have determined their operations will be best served by covering all or most of their service areas. "If broadcasters wish to continue to be a major force ... in their traditional coverage area, they will need to move forward to full power as early as they can possibly afford," he says.

While engineer Lew Zager believes that LP can be a legitimate tool to aid some stations in moving forward with DTV, "Low power was not an FCC option when I was involved with building a digital transmission plant at WETA-TV [a PBS flagship station] more than four years ago - but low power would not have provided WETA with the coverage needed to meet the station's needs and goals." Zager, now senior engineer at PBS's DTV Strategic Services Group, thinks "it holds true even with today's options - there is no question that low power will not be a 'one size fits all solution' for the DTV transition. Low power is a tool that must be carefully considered from an engineering, as well as economic, standpoint," Zager concludes.

"The majority of stations are waiting until the very last minute and they're not too enthusiastic about the transition," says Romeo Castillo, director of sales at KTech, which builds LP DTV transmitters starting at 100 watts. "All the big stations have already made the switch with their deep pockets - but for smaller stations, the transition is a financial burden without a business model that guarantees additional revenue streams." Castillo adds that additional savings are realized with LP equipment in energy bills, real estate costs, additional equipment and financing. Nearly all the transmitters KTech has sold in the past year have been LP, in the range of 100-500 watts.

The LP preference has resulted in some unforeseen, sporadic technical consequences. "There certainly needs to be more studying done on [alleged LP] interference with adjacent channels, but the studies so far indicate there aren't serious problems if the same antenna and TX lines are used. Co-siting may be necessary and desirable in this case," Castillo says. KTech makes the "heart" of its plug-and-play DTV LP transmitter (XMT-100) - including 8-VSB modulator with self-contained real time automatic linear/non-linear precorrection, and PSIP generator.

Adjacent channel problems aside, scattered interference of the analog-digital kind also has cropped up this fall, as more broadcasters have introduced DTV into the realm of nearly 1,600 analog signals. MSTV recently undertook a study to examine some sporadic complaints of analog-DTV problems. By early November, it had interference reports from under a half-dozen sites, all of them near large bodies of water. (One complaint involved WBOC-analog in Salisbury, Md. and WHRO-digital in Hampton Roads, Va. which are more than 100 miles apart.) "At this point," says MSTV President David Donovan, "MSTV intends to examine these situations to determine whether they are isolated instances of interference, or whether the problems are more systemic."

Donovan would not speculate on how long his group's study may last. If the problems do prove to be systemic, further studies-and perhaps time-consuming field-testing - could be in the offing. Some engineers fear that when the growing percentage of LP stations finally goes full power, this could compound the situation. (MSTV also would not comment on a new DTV testing activity it may be working on, in conjunction with NAB, or what implications for transmissions such an initiative might signify.)

Glidden at Harris says among several factors broadcasters should heed when mapping out their initial digital signal plans, "analyze the location of the transmission plant and planned ERP to determine if they have any risk of being interfered with from a much higher analog transmitter operating on an adjacent channel." The FCC's Table of Authorizations, he underscored, was developed with planned DTV ERP's to match a station's Class B analog coverage - not the much lower ERPs required to cover a community of license.

ENHANCED BANDWIDTH

Axcera says it has a solution to the adjacent channel problem with a system it developed called Bandwidth Enhancement Technology (BET). "This actually narrows the bandwidth of the DTV signal in a way that is compatible with 8-VSB receivers," according to Axcera marketing director Rich Schwartz. "It allows sharper filters to be fitted to the transmitter, minimizing adjacent channel interference without compromising signal quality." (The BET system is currently operational on ch. 14 at KERA-DT in Dallas.) Axcera has been selling LP units versus high power at a ratio of about 5 to 1. But Schwartz says "a significant number" of low power sales are for its DT Gateway model that is largely reusable when upgraded with its high-power transmitter (Visionary).

Joe Turbolski, marketing director at Thales, views the growing LP scenario as a double-edged sword. "Since the FCC [low-power] ruling went through a year ago, it changed the ballgame. It does allow stations to get on-air for various reasons, financial or otherwise. However, they may not get full-power [FCC] authorization later, although I haven't seen anything to lead in that direction." Turbolski believes going LP initially at least gives stations "a chance to work with digital sooner." His company's Affinity DVB-T series outsells its full-power offerings at a ratio of up to 7-to-1. Thales packages its standard exciter into low-power units that will not need upgrading later.

Meanwhile, any lack of financial commitment to the transition also prompted FCC Chairman Powell to tell MSTV's DTV fall meeting it "would be a grave error to see the present setback in digital life as either a validation of the old ways, or a rejection of digital change." Powell uses the early, checkered history of the American passenger railroad to further his point on a new industry having to rebound, after an initial burst of enthusiasm, towards eventual success. Ironically, perhaps, passenger rail in the U.S. has been struggling to find a successful business model for decades. DTV proponents hope that will not be their predicament, too.