FIELD STRENGTH RESULTS ARE DISAPPOINTING BUT VERY INTERESTING

KFI, 640 kHz, Los Angeles, is considered to be one of the finest AM broadcast facilities in the United States. As many of you know, its Main broadcast tower collapsed on December 19, 2004 after being struck by a private plane (see first URL below). During the almost four year period that the tower was down, KFI operated almost exclusively on its short auxiliary ("Aux") tower that is located just a few hundred feet from its Main tower in La Mirada, CA. KFI has been authorized by the FCC to run up to 25 kW into the Aux tower (second URL, footnote 1).

On September 25, 2008 at approximately 5:10:20 PM PDST, KFI resumed broadcasting on its new Main tower that, for aviation safety reasons, had been shortened a bit relative to the old main tower. (The new tower is equipped with a capacitive top-hat to improve radiation efficiency to compensate for the decrease in height.) Marvin Collins, retired Chief Engineer of KFI, invited our readers to take field strength measurements when KFI switched from its auxiliary tower to its new Main 50 kW tower. We had of course assumed that KFI would be switching from its 25 kW Aux tower to its shiny new 50 kW tower right next door.

Unfortunately, the switch did not come off as expected. The field strength readings were "all over the map" and therefore disappointing. It now appears that for some reason KFI elected to operate from a far-removed auxiliary tower (the "Aux-Aux" tower as we'll call it) instead of from the La Mirada Aux tower just prior to the switch. So, the field strength data varied considerably depending on where each observer happened to be located with respect to the La Mirada Main tower and the mysterious Aux-Aux tower. One observer, apparently close to the Aux-Aux tower, reported a decrease in signal strength when the switch was made (and that was a very important clue) while all of the other measurements showed signal strength gains.

So, just where is the Aux-Aux tower located? Although our efforts to reach KFI's current Chief Engineer have been unsuccessful, the evidence suggests that KFI was broadcasting from the old KTLK (1150 kHz) site just before the switch occurred. In fact, KFI probably used the SW tower in that array (see the second URL below, page 2), and one reader pegged the power level at 10 kW although that figure has not been confirmed by KFI.  The KTLK site is also known as the Montecito site, perhaps because it is accessed via Montecito Drive, and the site is located just a bit east of Dodger Stadium.  So, the Montecito site is almost certainly the mysterious Aux-Aux site mentioned above.

Why did KFI establish the Aux-Aux site in the first place?  Two good reasons come to mind: (a) to protect the erectors of the new Main tower from excessive RFR exposure and (b) to serve as a backup in case the La Mirada Aux tower failed.

Thanks to everyone who submitted signal strength data or even informal listening reports.  Good job!

  http://www.bext.com/_CGC/2004/cgc664.htm

  http://tinyurl.com/KFIauxiliary

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