Four L.A.-area stations send seven signals from one facility
Barring unforeseen complications like weather, four Southern California stations plan to have seven digital and analog signals up and running from Mt. Wilson in time for the November sweeps. What makes their goal slightly different than most stations is that they've pooled their resources to do this on one of the most crowded pieces of real estate in the U.S.
The four stations are KDOC, KJLA, KOCE and KXLA. What they have in common is channel proximity on the public airwaves, the mandated deadline to go digital, and the desire to get the best signal possible at the most economical cost.
KDOC (Channel 56 analog, 32 digital) is an Irvine-based independent run by Golden Orange Broadcasting. KJLA (57, 49) is an independent English-Spanish language station in West Los Angeles. KOCE (50, 48), a PBS station in Huntington Beach, is a service of the Coast Community College District. Los Angeles-based independent KXLA (44, 51) is licensed to Rancho Palos Verdes Broadcasters and features Asian-language TV fare.
Heading up the project is broadcast consultant S. Merrill Weiss, principal of the Merrill Weiss Group.
"We had consulted Merrill Weiss as a project engineer to lead this project and keep all the stations together and deal with all the political issues between the stations," said Ken Brown, chief engineer at KJLA and consulting engineer for KXLA. "He's done an outstanding job."
Among the key technology issues taken on by Weiss was an antenna design for all seven transmitters. This included notching patterns for those that had to accommodate the Mexican coordination with respect to interference issues, and a full, broad-cardioid pattern for those who did not. He provided the basic design and recommended the Australian wireless technology group Radio Frequency Systems to implement the technology.
"What the complex pattern is designed to do is to put one megawatt into the L.A. basin including Orange County," explained Brown, whose station beams as far south as Temecula. "As you start to look beyond Orange County [toward Mexico], the energy that the antenna is putting out is severely reduced-it's all done through phasing cables."
Brown noted that RFS worked hard over the years to produce technology that would "keep the phasing just right and the panels facing correctly," so the pattern wasn't wrongly distorted. He also credits transmitter manufacturer Axcera and site owner American Tower Corp. with "jumping through hoops" to make the project work.
The stations plan to beam 1-megawatt signals and 2 1/2-megawatt analog signals from their communal home on Mt. Wilson -- a three-story building on about 4,000 square feet of property. The first two 1,150 square-foot floors house six transmitters with room for two more; the top floor holds equipment racks for auxiliary equipment as well as a maintenance shop and spare parts storage. One transmitter is located in an adjacent, older building on the site.
There are no walls between the transmitters, which were smaller than any the competitors offered at the time of purchase. Built into the transmitters is a shared remote control system made by Statmon Technologies that cuts down on needed space and wiring requirements. It takes only Ethernet cables and interfaces to monitor the various systems and building operations (generator, power switches, temperature control).
"We have one computer in the entire building that monitors all the common stuff -- the room temperatures, power combiners, airflow -- and everyone can pull [the data] with their own transmitter through the remote-control system," said Brown.
And then there's the space that holds the RF power combiners, channel input filters and mask filters.
Roger Yokum, chief engineer at KOCE, described the power combining system as an "amazing feat of engineering," starting with the most obvious observation: It's ingeniously bridged over the nearby post office due to space constraints.
"All of the weight of the various filters and combining spines that feed the antennas are hung from ceiling girders on custom-built steel structures that are tied to the floor so they don't swing during earthquakes," he said.
The common cooling system -- housed on the roof -- is fully redundant so a transmitter is never totally lost due to a partial shutdown. This "incredible" system, said Yokum, is "comprised of four large heat exchangers."
Each heat exchanger, he explained, has a main pump and a backup; two are used for the first floor, with one pump feeding an A tube, the other a B tube to each transmitter. Liebert Corp. manufactured the exchangers, Axcera did the plumbing.
Outside the building, an ancillary system of 16 beam power supplies (4,000 pounds each) provides high voltage for the IOT beams. Because only eight could fit on the concrete pad adjacent to the building, a steel structure was built six feet above the pad for the other eight, which are staggered on grates so the parts are easier to get to, explained Yokum, who described the Axcera-designed feature as "a shoe-horned operation."
The project enables unique economies of scale beyond those already mentioned.
"We went to bid as a group, so we would all buy the same transmitter and share parts and training, " said KOCE's Yokum. "We got some nice pricing on transmitters, spare parts and test gear-and can share a test rack and rotate maintenance staff."
By late September, the two antennas -- which have panels on three sides of a five-sided column -- were on the top of a 400-foot tower atop the nearly 6,000-foot mountain.
The antennas will be hooked up to the power combining system to initially support seven analog and digital services (KJLA will continue its analog broadcasts elsewhere), with the capacity to support a dozen.
"After the antenna column is installed on the tower, the transmission lines will be hung, the combining system will be tuned to the antenna system and then the system can go on the air," Weiss said.
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