TECH SPOTLIGHT

What Stations Can Do To Prepare For Repack

While waiting for the FCC to repack the band and hand out new channel assignments, TV stations should not be idle. Here is a list of things they can start doing now to head off trouble later.

Following the FCC’s incentive auctions and subsequent repacking of the TV band, many broadcasters are concerned that they will not be able to find the RF goods and services they will need — tower evaluations and structural designs, antennas, transmitters, transmission lines, tower crews — to make FCC-mandated channel switches ahead of strict deadlines.

But Dan Fallon, senior RF engineer at Dielectric Inc., a major RF equipment supplier, says that the disruption caused by the repacking may not be so bad if broadcasters anticipate problems and plan properly.

In an NAB Show presentation and followup interview with TVNewsCheck, Fallon identified four things broadcasters can start doing today to head off trouble: conducting transmission line sweeps, hiring structural engineers to analyze existing TV towers, beginning tower work and putting up auxiliary antennas on their existing channels.

Only about 10% of the TV antennas in the U.S. are broadband panel antennas, which unlike narrowband pylon antennas, can easily be reconfigured for a new channel assignment. Photo: Dielectric Inc.Broadcasters may be surprised to learn that their existing transmission line might be suitable for other new channels, but they won’t know for sure until they do a line sweep, Fallon says. “I would love to sell miles and miles of transmission line, but that is not practical, given manufacturing capacity and the time frame for the repack.”

While a TV transmission infrastructure is a highly sophisticated system tuned to deliver optimal over-the-air service on a given channel, some components, like transmission line, were designed with enough tolerance to make reuse on a new channel possible, Fallon explains.

“There are excluded channels where flange reflections add up,” he says. “We allow a 3 MHz guard band between where all of that stacks up and where the channel is going to be. That guarantees the VSWR [voltage standing wave ration] will be perfect on the channel the transmission line will be used on.”

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However, just because a manufacturer calls a channel “excluded” doesn’t mean there isn’t the opportunity to use the transmission line with “only a slight degradation of VSWR at the edge. “Before you decide to pull down 1,000 feet of transmission line, measure it. Do it now because even though, for instance, we said it was excluded at ch. 20, it might work,” Fallon says.

Another important preparatory step is to hire a structural engineer to analyze the existing television transmission tower, Fallon says. “Whoever owns the tower needs to get a structural analysis.”

Broadcasters and other tower owners should not simply assume that because a tower was deemed appropriate for the DTV transition that it is in compliance with the latest codes and building standards.

The latest standard (Electronic Industries Alliance/Telecommunications Industry Association RS-222-G “Structural Standards for Antenna Supporting Structures and Antennas”), may require structural reinforcement, Fallon says. “My mechanical engineer summarizes the effect of the Rev. G standard this way: ‘If you are in a high-ice or high-wind area, or both, you probably are going to need some reinforcement.”

Fallon adds that if the analysis reveals reinforcement is required, get started now. “You can get a tower crew today, but maybe you won’t be able to two years from now.”

Don Doty, CEO of tower designer and fabricator Stainless LLC in Lansdale, Pa., cautions that getting the analysis and making reinforcements before a new antenna system is mounted is an aggressive step.

He warns that even slight unanticipated changes in the actual antenna that ultimately is affixed to the tower could affect factors like wind load, thus requiring a new structural analysis and supplemental reinforcements.

According to Fallon, the time between now and when the FCC starts the relocation clock should also be used to put in place an auxiliary antenna used to keep a station on air while its main antenna is modified or replaced.

Fallon also points out that about 90% of the TV antennas in the United States are narrowband pylon antennas, while only 10% are broadband panel antennas. Given their limited channel capacity, it is likely many pylon antennas will need to be replaced, Fallon says.

During the 2009 DTV transition, Fallon notes, many stations chose to hang side-mounted antennas on their towers and left their old analog antennas at the top in place. Some of those stations may be able to put the top-mount antennas back in service depending on final channel assignments, he said.

To stay up to date on all things tech, follow Frank Beacham on TVNewsCheck’s Playout tech blog here. And follow him on Twitter: @TVplayout.


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Ellen Samrock says:

April 25, 2014 at 1:50 pm

There’s not a lot a station can do now unless it is being built now (such as those from the 2009 rural LDTV window). We built ours using broadband antennas and a frequency agile exciter. If we’re repacked anywhere in the UHF band all we need to do is change the mask filter and possibly the power divider. But as soon as the incentive auction was announced and understood the implications of it, we specified equipment that would make moving channels a lot easier and cost effective.


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