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Tuesday, August 4, 2015

KEZW-1430 Denver, Colorado

Late last April I passed through Denver, Colorado and got a nice shot of KEZW-1430. The transmitter site sits south of Denver and west of Interstate 25 between the I-470 loop and E. County Line Rd., and just inside Douglas County. The beautiful, in-line symmetrical 5 tower array stands tall against the front range of the Rocky Mountains.

KEZW is the largest radio station in the United States to be powered by the sun. The 100 KW solar array is 300 x 80 ft. and normally dispenses 80 percent or more of the station's daily power requirement. The ground-mounted solar array is 12 tables with 36 panels on each table, surrounded by fencing. Tower lighting has been converted from power-hungary incandescents to LEDs. 85 KW are available from the inverters.

During the design phase, it was decided to forego battery power and simply feed the inverters directly into the power grid. This meant the station would be on the grid during nighttime hours. It also simplified the installation. Concern was also expressed over what effect the solar array might have on the signal pattern. It turned out to be small, and fine tuning of the array solved the differences.

KEZW operates on 1430 KHz with 10 KW daytime and 5 KW nighttime using a Nautel MD-10 transmitter. In the photo below, tower #1 is to the right and tower #5 to the left. During daytime hours, tower#1 is used as a monopole, producing an omni-directional pattern. At night, all 5 towers are fed to push a 9.2 dB gain signal lobe northward at 10 degrees (42 KW equivalent), in-line with the towers and out the right side of the picture.

Curious is the center tower, which appears to be about twice the height as the others. FCC engineering records show all towers, including tower #3 to be 136 electrical degrees tall (the fed portion), which equates to 259.8 ft, or 0.378 wavelength. So, taking this record as true, it means that only the bottom half of the center tower is being fed. It leaves me wondering what the top half is used for, as I see no other hardware on it, though it does appear it could be insulated in the middle.

See the interesting article on KEZW published in Radio World:

http://www.radioworld.com/article/sun-rays-power--kw-am-station/217859

Radio Mag Online also has an interesting artilce on the construction phase:

http://www.radiomagonline.com/deep-dig/0005/kezw-goes-green-with-solar/35230

If you ever get to the Denver area, be sure to take a drive on I-470 west from I-25 and see this impressive array.

KEZW-1430 Denver, Colorado

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