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.
Four Los Angeles broadcasters are to begin broadcasting DTV signals this month from atop the city’s premier 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.
For more than four years, broadcast consultant S. Merrill Weiss, of the Merrill Weiss Group, has been working 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 combined system, the first stage of which was completed in November 2003, means all seven new services can broadcast from the mountain, sharing facilities without interfering with each other.
The ability to control the antenna pattern was essential, Weiss said, explaining that the patterns had to be sculpted so that they reduce signals towards the Mexican border—just 129 miles distant—without losing any performance in the city. “I don’t know any way, other than using panel antennas, we could have done this without compromising performance,” he said.
The resulting RFS solution comprises dual combined antenna systems with the capacity to accommodate a total of 12 digital or analog services from channel 32 to 56.
The resulting RFS solution comprises dual combined antenna systems with the capacity to accommodate a total of 12 digital or analog services from channel 32 to 56. Two chains of a specially designed high-power directional waveguide combiner—expandable to six modules each—were installed in the first half of 2003; followed by the raising of two stacked 10-level broadband panel arrays and eight associated flexible coaxial feeders in October.
An added challenge, said Nick Wymant, RFS project manager, was optimizing the rigid transmission 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 the desired 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.”
For more information visit: www.rfsworld.com.
