| When four Los Angeles broadcasters set out to build their DTV facilities, they saw similar needs and realized that there would be substantial benefit in joining forces. The Mt. Wilson Group Project was formed to meet those needs. The group is made up of KDOC-DT, KJLA-DT, KOCE-DT and KXLA-DT, all of which serve Los Angeles. The goal of the system design was to combine the analog and digital facilities of all four stations into a single facility on Mt. Wilson. Because it is in an ideal location to serve the Los Angeles basin, it is extremely popular and available floor space and tower space are limited. |
To accommodate the transmission equipment, American Tower built a three-story satellite transmitter building, along with a master combining room and 400ft tower. The high-power digital and analog transmitters are located on the first and second floors of the facility, with the third floor used for auxiliary equipment, a complete maintenance shop and spare parts storage.
To minimize tower space requirements, the plan called for all of the stations to share two broadband panel antennas. Radio Frequency Systems (RFS) designed a combiner/filter system to feed four channels into each antenna during normal operation. The system is also capable of routing any of the channels to either antenna, effectively providing each station with a master and a backup antenna. This arrangement meets the group’s desire for system redundancy. To take advantage of economies of scale, the plan also called for the use of a common transmitter manufacturer, make and model. This would allow for common spare parts, as well as common knowledge between station engineers about the operation and maintenance of the selected transmitter.
The group chose Axcera as the solution. In order to achieve the desired level of redundancy in the transmission system, they installed transmitters for the DTV channels and HP100DAW units for the analog. The transmitters are capable, respectively, of output powers of 50kW average DTV and 100kW peak visual analog. These are dual-IOT transmitters equipped with dual exciters, ensuring a high level of system redundancy. The team worked closely with multiple RF system manufacturers to integrate the complex filter/combining network with the transmitters. They also worked together to ensure that the adaptive correction would continuously optimize the performance of each transmitter, even in the presence of multiple combined channels.
Currently, seven of the eight transmitters are on the air and providing reliable service to the LA basin, with plans to relocate the final analog transmitter to the site in the near future.