RAYMOND, Maine—Dielectric announced that it has completed a repack project for DTV Utah’s community TV transmission facility, for which it installed an ATSC 3.0-ready multi-channel combiner and waveguide switching system.

The DTV Utah facility houses transmission systems for nine Salt Lake City-area stations. Eight of the stations, six of which were repacked to new channel assignments, broadcast from specialized multi-channel antennas. James and James Consulting managed the project, including the design, integration and commissioning of the Dielectric system.

Requirements for the project called for a system that could transmit from 9,050 feet above sea level and across the Wasatch Front terrain north and south of Salt Lake City with specialized antennas built in 1999. DTV Utah was not able to retune the RF system for all of the repacked channels, which called for replacing the combiner system. In addition, there were mask requirements for three adjacent channels.

Because the previous combiner and mask filters could not be removed from their location, Dielectric designed what it calls its most compact combiner to date, a 14x16-foot system to fit into the available 17x20-foot space while leaving room for a tenth transmitter.

Some of the reported technical challenges had to deal with the three adjacent channels and their need for sharply tuned filters to allow for the full use of each channel’s bandwidth. While the group delay measurement is increased slightly from a more broadly tuned filter, the facility’s new GatesAir and Rohde & Schwarz transmitters provide corrections to make the group delay at the channel edge negligible.

Dielectric’s other contribution to the DTV Utah facility was the waveguide switching on the combiner’s input. This allowed for various combinations of main and backup antennas.

SALT LAKE CITY— In March 2017, DTV Utah began plans on repacking six of its eight DTV Utah Stations that were required to change frequencies as a result of the spectrum auction. DTV Utah, LLC is a television transmitter site located in the Oquirrh Mountains above Salt Lake City, Utah, and was the location of a complex, channel repack project involving nine UHF television stations, with eight of the transmitters combined into a community antenna.

DTV Utah, LLC was formed in 1998 as a nonprofit corporation that owns and operates the community television facility. Greg James of Bonneville International originated the concept of a community site for the new digital service.

“The discussion revolved around the problem created for viewers, if stations were dispersed over a wide geographic area,” James said. “As I thought about multipath in the mountainous area we live in, it made a lot of sense to broadcast from a single location.”

[Read: Eight TV Stations On One Stick Ponder Repack]

Other benefits of co-locating the markets transmitters include economies of scale and reduction of intermodulation interference.

The television stations currently in the DTV Utah group include:

• KSL (Bonneville International)
• KUTV and KJZZ (Sinclair Broadcasting)
• KTVX and KUCW (Nexstar)
• KUED and KUEN (University of Utah)
• KBYU (Brigham Young University)

The DTV Utah site is located 9,000 feet above sea level, with limited access via a 10-mile single-lane dirt road, limited space for construction and a limited seasonal construction window of four months due to weather conditions and road access.

The original DTV Utah site consisted of two four-channel Dielectric combiners, connected to either the main Kathrein antenna, or to an auxiliary antenna through a complex waveguide switching network with five modes of operation. In addition, all eight stations could be combined together and routed to any of the three antennas.

COMPLICATIONS ARISE

It was soon discovered that the original WR 1500 waveguide was not going to pass the new frequencies. The existing Kathrein community antenna also required evaluation to determine if it would perform under the new parameters. The repack design was also complicated by the frequencies that were assigned. Channel 34 (KUTV) and Channel 36 (KUEN) did not require change, but as fate would have it, Channel 35 was assigned to KUCW, creating three adjacent channels and potential intermodulation issues.

Other challenges included transmitter cooling at the thin air of 9,000 feet, transmission line performance, and the requirement to stay on the air while creating a seamless transition to the new channels.

The repack design included a patch panel that provided a path for the N+1 transmitter to replace any of the eight transmitters at the input of the combiner.

Marsand Inc.'s Matthew A. Sanderford, Jr. PE and David Sanderford installed the transmitters while Legacy Electric of Salt Lake City did the electrical work. Tower and antenna work was performed by GTI, America and Burk Technology designed the control system. Climate Control (CCI) handled HVAC.

TRANSMITTERS AND COMBINER

Each station decided on the make and model of the eight new transmitters; Five Rohde and Schwarz THU9evo transmitters and three Gates Air Maxiva UXLT transmitters, including the N+1 transmitter were installed along with one Dielectric combiner and six Dielectric WR1800 waveguide switches for nine different combiner/antenna/test load modes.

Each station purchased their own transmitters based on their own evaluations. “Given the complexity of the project, I suggested one installer for all of the transmitters,” James said. “It would have been a nightmare to schedule different crews on each transmitter. The same was true for electrical, HVAC, and so on.”

The new Dielectric, dual four-port combiner was installed in a very tight 20 x 17 x 9-foot space.

How do you keep your station on the air, while removing your old transmitter and installing the new one? All eight stations were operated at lower power into the auxiliary community antenna through the period of construction and transition. The GatesAir N+1 transmitter was delivered with broadband power amplifiers. As the N+1 was placed on the air, the old transmitter was decommissioned and the new transmitter installed, tuned to the original frequency and tested through the combiner/mask filter to a load.

SEVEN-DAY PROCESS

Each transmitter switch-out took about seven days and the process of bringing each transmitter on line was complex. First, engineers had to run transmitter power at the level that delivered the power calculated to meet ERP requirements of the station, when measured at the dummy load at the output of the combiner. They then had to measure the input power to the combiner hybrid; measure transmitter power out, and calibrate that as 100 percent power. This had to be repeated for each of the four profiles in each transmitter.

A spectrum analyzer was used to perform a power-band measurement on the four combined channels to verify spectrum compliance. As a final step, each station’s reflected power spectrum was recorded to determine a baseline for monthly performance tests.

COMMUNITY ANTENNA REBUILD

The original Kathrein antenna (two Kathrein eight tier by three bay antenna systems—48 panels total), was selected because of the extensive use of the antenna in the Swiss Alps. The temperature extremes at the DTV Utah site are very similar to the Alps, with a thermal swing of over 100 degrees winter to summer (-18F to +85F) Grundy Telecommunications Inc., America, was asked to review the existing Kathrein community antenna system and Kathrein Antenna Works sent an engineer who helped in the evaluation. After band sweeping and physical inspection, engineers determined that the existing antenna system would not perform well for the repack system.

The original tower was custom-built to support the Kathrein 70 x 6-foot radome cylinder. DTV Utah considered replacing the antenna with a different make and model, but structural modifications to the tower would have made replacement cost prohibitive. Kathrein was asked to develop a replacement antenna system … since the radome cylinder supported the antenna, it seemed possible to remove the old antenna system and replace it with a new one.

The next step was demolition and rebuild of the antenna system. Grundy removed main power dividers, cabling harnesses, tier power dividers and panel mounts—some three tons of it—in less than a week. The crew then began installing the new antenna, and six weeks later the rebuilt antenna system was ready for testing.

Katherine field engineers did a proof-of-performance; results were good with the lower antenna showing 28 dB return loss on the lower antenna and 30 dB return loss on the upper; this equates to a VSWR on the upper in the 1.08:1 and the lower antenna at 1.1:1.

OTHER SYSTEMS

For the Burk remote control system, equipment was specified and truth tables developed for interlocking. In some of the modes, reduced power is required. The Burk unit can talk to the transmitters based on the selected mode and ensure that their power levels are correct. If not, the it will shut the offending transmitter down and alert the operator.

Transmission line arc protection was provided by South-Tek Systems, N2-GEN, nitrogen generators.

RESULTS

After a month and a half of construction, all transmitters were installed and operating on the old frequencies. Once all transmitters were installed, commissioned and tested, the new transmitters were retuned to the new frequencies and switched into the refurbished community antenna.

Mario Hieb is a professional broadcast engineer based in the Salt Lake City area.

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WASHINGTON—Eight co-located TV stations in the Salt Lake City market want to stick together in the post-incentive auction channel repack. The station consortium, called “DTV Utah,” shares a tower and transmission facility on Farnsworth Peak, 18 miles outside of Salt Lake City.

“DTV Utah addressed the benefits from both a cost and an interference viewpoint of assigning those members who remain in the repack channel numbers that are close together and high up in the available television band,” the group said in an ex parte filing describing a meeting with Federal Communications Commission officials on Aug. 12. “DTV Utah also expressed concern that its actual cost and interference benefits may not be recognized or accounted for by the general nationwide optimization process adopted by the FCC,” as set forth in its Bidding Procedures Public Notice released Aug. 11.

DTV Utah licensees include KUTV, LLC, for CBS affiliate KUTV; Utah State Board of Regents for KUEN, a noncommercial educational station; Bonneville International Corp., for NBC affiliate KSL-TV; Nexstar Broadcasting, Inc. for ABC affiliate KTVX and The CW affiliate KUCW; University of Utah for PBS member station KUED; Brigham Young University for PBS member station KBYU-TV; and Larry H. Miller Communications Corp. for KJZZ-TV, an independent station.

The consortium formed in 2000 in anticipation of the first digital transition. At the time, the FCC granted the stations even-numbered channel assignments between Channels 34 and 48, enabling interference among the eight stations to be managed at the combiner level in the transmission facility.

Based on those current channel assignments, the members anticipate having to move after the auction. They said preserving the “combined arrangement through optimal channel reassignments will meet some or all of the FCC’s optimization objectives.”

In a previous filing referenced in the Aug. 12 meeting, DTV Utah’s chairman, Jeremy Castro, also noted that if final channel assignments impair the co-location arrangement, “the collective costs for the stations, potentially including new leases and equipment purchases for each of the eight stations and other individual operational expenditures, would certainly exceed that of any costs of preserving the entire DTV Utah group.”

Utah’s terrain presents another problem, Castro said. The mountains surrounding the Salt Lake City market limit where TV transmission facilities can be located. Farnsworth Peak offers the greatest coverage area for the market, and the site has been optimized for DTV Utah’s combined arrangement in terms of “power supply, land use and physical infrastructure,” he said.

Separating the stations may require some of them to move to sites that would not allow them to cover the market without secondary facilities, he said.

DTV Utah is asking for two particular considerations: to be assigned to channels “as close together as possible,” and on channels “higher up in the UHF band.”

The logic behind the requests lay with the stations’ combined technologies. They now use an 8-input combiner designed to perform from 590 to 680 MHz (Channels 34-48). The option of retuning it for “any band plan that repurposes more than 60 MHz is very low,” Castro said. Since the FCC is shooting for up to and possibly more than twice that amount of spectrum, DTV Utah expects to need a new combiner. According to DTV Utah’s discussions with combiner manufacturers, a new combiner would work best on close channel assignments higher up in the UHF band.

DTV Utah stations also share a primary 16-bay array antenna, with each bay comprising five panels. The backup antenna is an 8-bay array with three panels per bay. Both are designed for 470 to 860 MzHz, but DTV Utah’s preliminary assessment is that both antennas can be repurposed “anywhere in the UHF band if DTV Utah is able to retain its combined status.”

The station group submitted its own band plan anticipating three clearing targets in the auction: 60, 84 and 126 MHz. At 60 MHz, four stations would have to be reassigned new channels. At 84 MHz, six would have to move, and at 126 MHz, all eight stations would need to move.

During the Aug. 12, meeting the DTV Utah and FCC reps discussed doing an engineering study on the best way to repack the eight stations. The study would have to be done after the auction, when the FCC releases its channel reassignment Public Notice. The station group also was told it would have to get approval from other stations in the market that might be affected by its proposal.

Additionally, DTV Utah sought clarification on the FCC’s quiet period in which stations participating in the auction are prohibited from communicating about it. The period is to start at the close of the applications window, which has not yet been established.

“DTV Utah pointed out that it would be necessary for its members to continue to conduct business activities” and work with vendors who help maintain the shared facility, KBYU’s Christian A. Fox said in the ex parte filing.


Image “FarnsworthCU” by Milonica, licensed under CC BY-SA 3.0 via Commons