(click thumbnail)The new consolidated DTV tower on Lookout Mountain in Denver stands 730 feet tallDENVER
It took an act of Congress but the long-delayed consolidated DTV tower on Lookout Mountain at the western edge of metropolitan Denver is finally built and in use.
Overseeing the construction effort since December 2007 has been Don Perez, the retired chief engineer from KUSA. Passage of Senate Bill 4092 in December 2006, Perez said, gave the Lake Cedar Group consortium of three TV stations “a blank page to construct whatever we needed to construct on Lookout Mountain to deliver DTV to Denver. But we decided to follow the ODP [original design plan] because we felt it was the right thing to do.”
Sticking to the ODP, he said, meant embedding 80 percent of the new transmission building in the mountainside and anchoring the new 730-foot (AGL) dielectric antenna tower 100 feet lower on the mountain than the base of the building, both done to reduce visibility of the facility. The job was erected by Radian of Canada.
“Anchoring the tower into the cliff of solid rock was quite a feat,” Perez said, “The tower can withstand sustained winds of 110 mph, not just occasional gusts. It’s really an engineering marvel.”
The ODP also called for burying the transmission lines in a tunnel between the building and the tower to avoid any possible winter icefall in high winds.
The final ODP promise will be kept in the summer of 2009 after the DTV transition, Perez said, when crews will remove the analog towers for the three stations from the mountaintop, fully restoring the native landscape.
To handle all the details, Perez relied on project manager Brian Mortimer from Calcon Constuctors in Englewood, Colo., specialists in “difficult” construction projects.
FROM THE GROUND UP
Since most of the three-story building is dug into the mountain with walkouts on one side, Mortimer said, “We blasted out 20,000 cubic tons of bedrock.” The most challenging part was digging a trench, 10-feet wide and 240 feet long, for the sloping conduit tunnel that ran from the bottom floor of the building down to the base of the tower.
(click thumbnail)Calcon Constuctors blasted out 20,000 cubic tons of bedrock and dug a 10-foot-wide by 240-foot-long trench for the sloping conduit tunnel that runs from the bottom floor of the building down to the base of the tower.“Everything in the commonly owned space is 100 percent redundant,” Mortimer said. In case of power loss, Calcon installed two 1.5 mW Cummins diesel generators with tanks holding 20,000 gallons of fuel. Each generator can come online within 12-15 seconds, he said.
“We had a ground-up opportunity to do a lot of good things in the new building,” said Eric Buckland, engineering manager at KCNC-TV, branded as CBS4 in Denver.
Buckland said KCNC installed a Harris PowerCD UHF ATSC IOT transmitter for ERP of 974 kW on assigned channel 35. The station is transmitting ATSC at only 24 kW until the February 2009 transition. As a backup, KCNC in-stalled a Harris DiamondCD solid-state UHF ATSC transmitter, currently operating at 15 kW.
Buckland reiterated the redundancy theme. “We have a Qwest T1 line for STL and TSL along with the BAS mi-crowave system. We have our own four-wire and two-wire phone lines between the station and transmitter in case the Qwest fiber is cut,” he said.
And to keep the power flowing, KCNC installed a 400 KVA UPS to support the primary transmitter and half of the equipment rack. A secondary 150 KVA UPS supports the backup transmitter and the other half of the rack. “We can switch where the power goes,” Buckland said, “so each UPS can support either transmitter or either side of the rack. Each UPS provides 30 seconds of power failure ride-through as the diesel generators kick in.”
KCNC went state-of-the-art for their dual UPS systems, both built by GE and containing Pentadyne flywheels, which operate 24/7 and “avoid the needs for banks of chemical batteries,” he said. The flywheel, suspended on its rotor axle without bearings by magnetic levitation, uses the inertia of the spinning mass to store and generate power kinetically. The Pentadyne UPS flywheel and rotor weigh 50 pounds and spin at 5,200 RPM.
Standing next to KCNC’s dual UPS units is a third GE UPS with a Pentadyne flywheel, a 90 kW unit owned by ABC affiliate KMGH-TV7. “We only have one UPS because CBS4 has more transmitter equipment than we do,” said Rick Craddock, director of engineering at KMGH.
Currently KMGH is using a UHF transmitter operating on low power at 15 kW over channel 17. When analog shuts off next year, Craddock expects FCC approval for analog channel 7 to beome digital channel 7, and KMGH will operate at full power using a Harris Platinum VHF digital transmitter.
MOTHER’S DAY MOVE
Like the other stations in the consortium, KMGH had been transmitting with a low-power ATSC transmitter from atop Republic Plaza in downtown Denver. “We moved all digital operations to Lookout Mountain last May 19, Mother’s Day,” said Craddock.
Like the other two stations in Lake Cedar Group, Craddock said, “we have not yet moved our ENG receive site there. We’re still migrating from our analog tower site a little to the southwest, practically a stone’s throw from the new tower.”
A third station in the new facility, NBC affiliate KUSA-TV9, is broadcsting half power at 500 kW, according to Chief Engineer Ken Highberger. After February 2009, the station will use a Harris VHF Platinum transmitter to move to a full-power 1,000 kW signal on channel 16.
KUSA chose not to use the UPS system chosen by KCNC and KMGH, Highberger said. In fact, they chose not to install any unilateral UPS, relying solely on the diesel generators for the whole facility. “The Harris transmitter already has built-in redundancy,” he noted, “and everything is modular.”
Highberger added that KUSA decided to build up its operations in the new facility incrementally. “We’ve already installed big ticket items like the transmitters. The rest of the equipment, like a Leitch distribution amplifier, is being installed one month at a time. There’s nothing special in our design. We’re sticking with what we know.”
The fourth station on the tower is KTVD, a myNetworkTV affiliate that broadcasts on analog channel 20 but will switch over to digital channel 19 next February.
Perez said that he is just happy the tower finally is built and in operation. “We have a great facility that took longer than any of us wanted, but will serve the community for many years to come,” he said.
