Dielectric Builds Its Most Compact Combiner Ever for DTV Utah

Complex, space-efficient combining and switching system at DTV Utah transmission facility solves the challenges of adjacent signal combining without performance loss.

Dielectric is celebrating the launch of a unique ATSC 3.0-ready multi-channel combiner and waveguide switching system installed at DTV Utah’s community TV transmission facility. Dielectric won the challenging multi-station repack project because of the quick turnaround of a complex system that met all size and performance specifications, including mask requirements on three adjacent channels in the system, resulting in a clean signal for each of the stations.

DTV Utah is the owner and operator of the facility, which houses transmission systems for nine Salt Lake City-area stations. Eight stations, six of which were repacked to new channel assignments, broadcast from specialized multi-channel antennas (two main and one backup). James and James Consulting managed the project, including the design, integration, and commissioning of the Dielectric system. The owner of the consultancy, Greg James, was a former director of engineering for one of the repacked stations (KSL-DT) and intimately involved with the original DTV Utah facility design.

Side view of the DTV Utah combiner.

Side view of the DTV Utah combiner.

“The DTV Utah site is an interesting mix of public, commercial and independent stations, most of which operate on a common antenna system that changed with the repack,” said James. “The site is located 3500 feet above average ground level (9050 feet above sea level) and transmits across the challenging Wasatch Front terrain, north and south of Salt Lake City, with specialized antennas built for the original system in 1999. We had no way to retune the RF system for all these newly repacked channels, which meant we had to replace the combiner system. Dielectric was the one vendor who could meet all of the challenging requirements across timeline, technical specifications and within space limitations.”

Available space was particularly important, given that the previous combiner, also a Dielectric system, had to remain operable during the transition. The old combiner system and mask filters were in the ceiling of the building and could not be removed. This inspired Dielectric to innovate its most compact combiner to date.

“We had a 17x20-foot space for a tenth transmitter that wasn’t installed, and Dielectric designed a 14x16-foot system that could combine all of our channels and leave room for the tenth transmitter,” said James. “Of most importance, we had to install the combiner before integrating the new repack transmitters. Dielectric was the only company that could deliver such a complex system, and on time.” 

The technical challenges were also substantial, according to James. The three adjacent channels required sharply tuned filters, allowing the full use of each channel’s bandwidth. While the group delay measurement is increased slightly from a more broadly tuned filter, the new GatesAir and Rohde & Schwarz transmitters in the facility provide the necessary correction, making the group delay at the channel edge negligible.”

In addition to the RF, Dielectric provided the waveguide switching on the combiner’s input, allowing for various combinations of main and backup antennas.

“The switching network was complex and had to fit into a small space,” said James. “Dielectric designed a new compact waveguide switch for our requirement. The combiner is not trivial, because switching between three antennas across any combination of transmitters is very complicated to achieve. The performance across all transmitters and antennas is optimized and adaptable to any condition. Overall, the system that was installed and commissioned by Marsand, Inc. offers a very sound and high-performance solution to a unique operating environment.”

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