Towering Over Wyoming

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The downtown tower location is ideal for providing low-power signals to a portion of the market in the event power is lost at the main KAML-KDDV transmission site, which currently lacks a generator. A Moseley STL antenna and receiver was installed at the KGWY transmission facility to support the first hop and establish the backup, low-power transmission. From KGWY, the Moseley system transports the KAML-KDDV audio another 15 miles to the main transmission site, where a receiver sits inside the building.

The Moseley STL system is frequency agile, and a backup system sits on a nearby shelf in the event of a failure in the main receiver. Spare HT30 parts share the same limited storage space, with a nearby workbench for maintenance. The Thermo Bond shelter contains and protects this equipment, but the building is nearly at full capacity with little room for new equipment.

The Thermo Bond shelter offers plenty of other benefits though, notably in terms of HVAC design. Although six tons of AC cooling are available in the building, the eastern Wyoming climate is cool enough to limit AC needs to the thick of summer. Thermo Bond installed ventilation to exhaust hot air out of the transmitters and to the outside at each side of the building. When AC is not required in the cooler months, consumer-grade swamp coolers draw in cool air from the outside. In the winter months, the swamp coolers are on thermostats and shut down when the building is cold, as do the exhaust fans over the transmitters. This allows heat to remain in the building when outside temperatures drop as low as 30 degrees below zero.

Final prep

The final step before firing the transmitters was tuning the antenna. ERI made one final trip out to the site, measuring the feed off the antenna with a spectrum analyzer and inserting slugs around the appropriate conductors to achieve proper tuning. KDDV required more adjustments due to an undesirable level of reflected power, but by trial and error, the levels were adjusted appropriately until we were satisfied.

Legend Communications is looking ahead to potential HD Radio installations. The use of a single combined antenna and 4" transmission line for the two analog transmissions minimized the weight today, allowing plenty of load capacity on the tower for two separate antennas and line feeds for HD Radio transmissions tomorrow.

Dozier is director of engineering for Legend Communications and is based in Cody, WY.

Equipment List

Andrew 4" Heliax, ⅞" Heliax, dehydrator, Super Flex jumpers, transmission line hardware, wall feed-thru panel
Bird Wattcher
Burk ARC-16, Auto Pilot
ERI SHPX diplexed antenna with radomes, FM combiner, Lambda mount, Mag Rod, transmission line hardware, tower
Harris HT-30, Digit
Mark 4' STL antenna
Moseley PCL 6020, STL/RPU power divider
Myat rigid transmission line
Omnia 3-FM-Turbo
Scioto 4" copper strap
Thermo Bond building

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