Multiple Repacked UHFers: Merged Into Common RF Build


A Maine-based tower construction company taking a lead role in the post-Spectrum auction repack antenna replacement process has launched what it is calling “a unique ATSC 3.0-ready multi-channel combiner and waveguide switching system.”

It was installed at DTV Utah’s community TV transmission facility.

Dielectric won the multi-station repack project because of its history of projects that saw the quick turnaround of a complex system meeting all size and performance specifications, including mask requirements on three adjacent channels in the system.

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. Consultancy owner Greg James is a former Director of Engineering for repacked station KSL-5 in Salt Lake City — a Bonneville International flagship property —  and was intimately involved with the original DTV Utah facility design.

“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,” James said. “The site is located 3,500 feet above average ground level (9,050 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.”

In the end, Dielectric proved to be a vendor capable of meeting “all of the challenging requirements across timeline, technical specifications and withinspace 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 located 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 17×20-foot space for a tenth transmitter that wasn’t installed, and Dielectric designed a 14×16-foot system that could combine all of our channels and leave room for the tenth transmitter,” James noted. “Of most importance, wehad 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, James said. 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 Rhode & 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,” James said. “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 very unique operating environment.”