BEAUMONT, TEXAS—As we navigate a busy planning period across all phases of the FCC spectrum repack, we are nearing completion on our first two Deerfield Media stations: Fox affiliate KBTV-DT and CBS affiliate KFDM-DT, both in the Beaumont, Texas market.
KBTV has been repacked to UHF Channel 27 from its long-running Channel 40 assignment. This required a new antenna to replace the previous channel-specific antenna, as well as an auxiliary system to continue broadcast operations while the current main antenna was replaced. We opted for Dielectric main and backup systems with an output switch to ensure a seamless cutover after the installation is compete.
AN IDEAL FIT
We selected a TFU-GTH pylon model for the main antenna. This top-mounted steel antenna was the most ideal fit due to its wind load performance for Rev G tower specifications. The Rev G formula considers the unique wind load characteristics for each area of the country, with specifics that include maximum wind speeds and gusts.
We worked closely with the structural engineers at Stainless (tower) and Dielectric to determine the proper design requirements to meet Rev G standards. A tower study determined that the guy wires required retensioning, so we added sub-horizontal member bracing to three tower sections. This reinforcement would also support our new Dielectric antennas, both of which were engineered to withstand the 110 mile-per-hour winds outlined in our local Rev G specifications.
Our existing Dielectric Channel 40 antenna with elliptical polarization has provided excellent coverage, so we opted to use the same vertical-to-horizontal ratio on the new channel 27 TFU-GTH antenna. This essentially futureproofs the installation for ATSC 3.0, when we fully expect to take advantage of the enhanced reception characteristics for mobile services.
FIVE-WEEK WINDOW
We were pleased to retain our existing six-inch rigid transmission line—which has provided us with excellent performance—for our new channel assignment. To make our 1000 kW ERP for Channel 27 with our existing line, we required a power input of 52.1 kW. The TFU-GTH comfortably exceeds that with its 55 kW rated input.
With an approximate five-week window between removing our old main antenna and lighting up the new TFU-GTH, we looked at options to ensured uninterrupted broadcasts. We chose Dielectric’s TFU-WB auxiliary antenna, side-mounted 500 feet above ground level. While its wide cardioid antenna meant that we lost some coverage on the outer market edges, it ensured our signal reached the majority of the local population. A lightweight design with wind load estimated at 75 percent of similar-sized panel antennas ensured we remained well within Rev G standards.
The TFU-WB offers a broadband design from Channels 14 to 51, which gives us plenty of options for the future. One option is to move the antenna to other sites in cases of an emergency. In the meantime, the output switch remains if we ever need to cutover to our backup for maintenance reasons on the main system.
The KFDM project takes place in the same time period as KBTV and follows a very similar plan—a TFU-GTH elliptically polarized antenna, a TFU-WB interim antenna and, in this case, new transmission line—in the move from Channel 25 to Channel 15. The KFDM and KBTV sites have new transmitters equipped with new Dielectric floor-mounted RF systems, which use tunable mask filters in a Constant Impedance configuration to accommodate the higher transmitter power levels.
We also chose Dielectric because of the company’s longevity and reliability. As noted, our previous Dielectric antenna and transmission line performed in top condition for many years, and most recently survived the devastating power of Hurricane Harvey. We needed boats to reach our transmission building, and the KDFM facility was filled with 18 inches of water. It’s a testament to the durability and engineering reliability of Dielectric antennas that they survived such a powerful storm, with no repairs required or disruption to broadcast operations.
Dale Scherbring is regional engineering director for KBTV-DT/KFDM-DT. He can be reached atdjscherbring@sbgtv.com.
For more information on Dielectric, visitwww.dielectric.comor contact Kim Savage at 207-655-8258.
