Tuesday, March 5, 2013

Catalina's KBRT-740 Relocates

In the news recently has been Christian-format station KBRT-740, owned and operated by Crawford Broadcasting Company. KBRT was a long-time resident of Catalina Island, some 20 miles off the coast of Los Angeles, CA. The station has moved its transmitter operation to the mainland after developing a 27 acre piece of land in the Santa Catalina Mountains in Orange County.

In planning since the new site was purchased in 2008, the FCC granted final planning approval in October of 2011, and building permits were issued the following spring. Work began immediately with the installation of a new underground power service from a location nearly a mile away.

Construction proceeded throughout the summer and fall of 2012, completing in December. Final testing, including transmitter and antenna adjustments were finished in the first weeks of 2013, and the station cut over to the new location on February 28 with an upgraded 50 kilowatt power output.

Scott Fybush published a detailed article on KBRT in a recent issue of Radio World, entitled One of America’s Most Remote AM Sites Signs Off, covering its history. It makes for an interesting read.

Crawford Broadcasting has also posted a gallery of photos with description of the construction of the new site. If you are interested in seeing what goes into the building of a mediumwave tower site, be sure to check it out.

Over the years, KBRT has had to tread a fine broadcast line in order to sandwich their signal pattern between San Francisco's southeast-firing 50KW KCBS-740 and the 20 KHz interference contour for nearby San Diego's 50KW KFMB-760, some 100 miles distant but across a nearly all salt water path. The three tower, 10KW array firing due east from Catalina Island 20+ miles offshore worked well enough during the day, covering the L.A. area quite nicely. However, KBRT's limited night authorization of only 113 watts couldn't compete with San Francisco flamethrower KCBS-740 barreling down the coast after dark, so it chose to operate during daylight hours only.

The recent move to the Santa Catalina Mountains with headquarters in Costa Mesa, CA has not changed KBRT's signal pattern constraints. Using a new four tower array, engineers have cleverly carved out a quite similar pattern which now fires southwest toward the ocean, managing to corral the new and expanded 50KW signal perfectly between San Francisco's KCBS-740 and San Diego's second adjacent channel KFMB-760. The pattern has enlarged some due to the increased power, guaranteeing a little better coverage up and down the coast and inland and still succeeds in not overlapping into the 0.15 mV/m fringe contour area for KCBS.

Below you will find a 0.15 mV/m daytime pattern study generated by Radio Data MW. Both old and new KBRT-740 patterns are superimposed to show their differences. Included are daytime patterns for San Francisco's KCBS-740 (370 miles distant) and Phoenix, Arizona's omnidirectional 1KW KIDR-740 (355 miles distant). The pattern map is based on a ground conductivity of 8 mS/m, average for most of the coastal area. Note that in actuality the pattern over the ocean would be skewed outward beyond what the plot shows due to the high conductivity of the salt water, however this makes a negligible difference to this analysis.

Monitoring 740 KHz from Quartzsite, Arizona (extreme western Arizona along I-10), three stations are apparent near the noon hour on a sensitive truck radio. Strongest and readily copyable is Phoenix's 1KW Spanish language outlet KIDR-740 at 124 miles. Next in strength is the new 50KW KBRT-740 from Orange County at 195 miles, alternately fading up to compete with KIDR, then fading down to just above the noise level. In the background and barely above the noise level, and not generally intelligible, is San Francisco's 50KW KCBS-740 at 557 miles. Using either the Tecsun PL-380 or the Tecsun PL-600 and a 24-inch nulling loop brings up KCBS to a copyable level. Previously, 10KW KBRT-740 from its Catalina Island location (then at 239 miles) was a somewhat difficult catch, usually requiring a nulling loop to remove San Francisco's KCBS signal and enhance signal strength.

I am headed cross country back to the east coast this week. More to come, including the US Mediumwave Pattern Map files. Stay tuned.

KBRT-740 and companions - 0.15 mV/m fringe pattern plot

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