After years of legal delays from community opposition, the consolidated tower facility on Lookout Mountain is finally constructed and broadcasting digital TV to metro Denver.
By Ken Freed
Correspondent, TV Technology
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 actively 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 local TV stations “a blank page to construct whatever we needed to construct on Lookout Mountain to deliver DTV to Denver, but we decided it was best to follow the ODP [original design plan] approved by Jefferson County before the federal act was passed.”
Sticking to the ODP, he said, meant embedding 80 percent of the new transmission building in the mountainside and anchoring the new 734-foot dielectric antenna tower 100 feet lower on the mountain than the base of the building, both actions to reduce visibility of the facility.
“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, doing this 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, which is removing the analog towers for the three stations from the mountaintop and fully restoring the native landscape.
As part of the process, he said, all the stations decided together about what would be common equipment bought by Lake Cedar Group, and what would be up to the stations to buy themselves, such as equipment for their separate rack rooms.
To handle all the details, Perez relied on project manager Brian Mortimer from Calcon Constuctors in Englewood, Colo, specialists in “difficult” construction projects. Mortimer said the Calcon crew ranged from 12 people to 75 people “when we were working at full push from October through December last year, plus there were about 200 subcontractors.” Among these was the tower construction crew from Radiant in Canada.
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, ten 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.
“We were too far from the road and the slope was too steep to use our heavy equipment,” said Mortimer, “so we had to get down there with a back hoe and carry out the rock with a forklift.”
“Everything in the commonly owned space is 100 percent redundant,” Mortimer said. In case of power loss, Cancon installed two 1.5 megaWatt Cummins diesel generators with tanks holding 20,000 gallons of fuel. Each generator can come online within 12-15 seconds, he said, and each can power the entire facility. Whichever unit kicks in first takes over the load and the second unit drops back to idle.
“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 joined the station as chief engineer five years ago to support David Layne, the director of broadcast engineering.
Buckland said KCNC installed a Harris PowerCD UHF ATSC transmitter with two multi-stage depressed-collector inductive output tubes (IOT) for amplified ERP of 974 kW over assigned channel 35. The station currently is covering their DMS by transmitting ATSC at only 24 kW until the February 2009 transition.
As a backup, KCNC installed a Harris DiamondCD solid state UHF ATSC transmitter operating at 15 kW.
Antennas the transmitters are hung separately on the tower, with the secondary antenna 100 feet lower. Buckland declined to say which station’s antenna as the highest one on the tower. “We all agreed not to disclose this, so no one can claim to have the highest antenna. It’s a marketing thing.”
Buckaland reiterated the redundancy theme. “We have a Qwest T1 line for STL and TSL along with the BAS microwave system. We have our own four-wire and two-wire phone lines between the station and transmitter in case the Qwest fiber is cut.”
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 lbs and spins at 5200 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 tthan we do,” said Rick Craddock, director of engineering at KMGH.
KMGH installed a single Harris Platinum VHF digital transmitter, noow 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 become digital channel 7 and operate at full power.
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.”
The third station in the new facility, NBC affiliate KUSA-TV9, also installed a Harris VHF Platinum transmitter for full power on channel 16 at about 1,000 kW. Until the DTV transition, the station is broadcasting half power at 500 kW, said chief engineer Ken Highberger. “I think it’s quite understandable that all the stations chose to go to the same transmitter vendor.”
However, 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.”
Perez said that he just happy the facility finally is built and in operation. “It took us a long time, but we all got to where we’re supposed to go.”
——————————–
Originally Published in TV Technology on 8/20/08. (c) 2008 by Ken Judah Freed
Related posts:
- Place related post plugin php here...
