Four Los Angeles broadcasters are ready to go on air this month with shared digital broadcasting facilities atop the city's premier transmission site, Mount Wilson.
The broadband antenna system, designed and manufactured by wireless technology group Radio Frequency Systems (RFS), is initially supporting seven combined analog and digital services, with the capacity to accommodate 12.
The broadband antenna system, designed and manufactured by Radio Frequency Systems (RFS), is initially supporting seven combined analog and digital services, with the capacity to accommodate 12.
For more than four years, broadcast consultant S. Merrill Weiss, of the Merrill Weiss Group, has worked with RFS, infrastructure provider American Tower and transmitter manufacturer Axcera to develop a multi-system digital/analog solution for Los Angeles broadcasters KDOC, KXLA, KOCE and KJLA.
The first stage of the combined system was finished in November 2003. With work that’s been completed recently all seven new services can broadcast from the mountain and share facilities without interfering with each other.
According to Weiss, the ability to control the antenna pattern was essential. In particular, the patterns had to be sculpted so that they reduce towards the Mexican border that’s 129 miles away without losing performance in the city.
"I don't know any way other than using panel antennas, we could have done this without compromising performance," said Weiss. RFS was introduced into the project due to its experience in designing high-power broadband panel arrays, he added.
The resulting RFS solution is composed of dual combined antenna systems with the capacity to accommodate 12 digital or analog services from channel 32 to 56. Two chains of a specially designed high-power directional waveguide combiner, which can be expanded to six modules each, were installed in the first half of 2003. That was followed by raising two stacked 10-level broadband panel arrays and eight associated flexible coaxial feeders in October.
The resulting RFS solution comprises of dual combined antenna systems with the capacity to accommodate a total of 12 digital or analog services from channel 32 to 56.
According to Nick Wymant, RFS project manager, an added challenge was optimizing the rigid line systems between the transmitters and the combiners and flexible coaxial feeders, which are located in different buildings because of the very crowded nature of the site.
"We took great care during the design phase to minimize the reflections that could have occurred due to the large number of components in the rigid feed system," he said. "This involved the development of high-performance broadband elbows, which we tuned to optimize system performance."
Wymant said the system has been run at high-power and that all indications from early testing are that pattern objectives have been achieved. "The antenna coverage is sculpted in all azimuth directions, not just to the southern border," he said. "This is so we don't waste power over the ocean, and can provide solid signal strength to the satellite cities in the west."
"It also would be fair to say," added Weiss, "that the RF system, including all the filters, combiners, and transmission lines, demonstrate superb performance. Indeed, when we turned on several of the transmitters at full power, we at first thought that some of the reflected power meters were defective because they did not even move. It later turned out that the reflected power was just that low."
For more information, please visit: www.rfsworld.com.
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