Towering Over Wyoming

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Hoisting the transmission line up the tower.

Hoisting the transmission line up the tower.

Most of the 16' × 28' interior space is reserved for the Harris HT30 transmitters. The transmitters were part of the greater Harris turnkey package, which also included the ERI high-power FM antenna and combining system, a Moseley PCL 6020 STL package, an Omnia 3-FM audio processor (installed at the studio), Andrew transmission line, Myat RF plumbing and connectors, and Bird RF monitoring equipment.

Harris performed a thorough set up of the HT30 transmitters at its facility in Quincy, IL. According to our computers, the transmitters were sharply tuned to frequency and underwent 24 hours of test runs at the facility. Reassembly at the transmission site was simple, requiring basic interconnections between the high voltage systems and main cabinets before installing the tubes and enabling the remote control system. The engineering team currently uses Burk Auto Pilot remote dial-up units to access readings from the transmitters and alert us of unusual status readings. The point-to-point Burk units communicate over subcarrier cards connected to the legacy phone system.

The Harris Digit exciters were set up at the factory to determine the amount of power needed at each station's frequency to drive the IPA modules. We like the fact that the new HT30 design eliminates a driver module that formerly bridged the exciter and IPA. The removal of that stage means the exciter compensates for the 15W to 20W of drive power that is missing now that the exciter runs straight to the IPA. But the benefits include simplification of the transmitter design and maintenance, and the purging of occasional matching problems that sometimes affected the gain.

The combiner integration was more challenging. The transmission equipment was delivered with a host of 3" hard line and extra elbows from Andrew. This equipment was used to build trombones that would address the signal matching delays at the combiner. The trombones added length to the line through a series of loops, which ERI engineers cut to size on-site to synchronize everything. Our chief engineer, Tony Kyriss, used a band saw to cut cleanly through the hard line, and the swivel points in the elbows made the plumbing assembly less complicated.

The combiner feeds into 4" transmission line to the outside and up the tower. We initially looked at 5" line because of concern that the 60kW capacity of the 4" line was cutting it close. The tradeoff was a much lower weight load on the tower and easier line management. ERI ran the line up the tower to the antenna, and looped it in an orderly manner back to the ground. Bird watt meters at the combiner output monitor signal strength out of the combiner and up the transmission line.

The Moseley STL platform provides fixed 950kHz RF transport over two hops. The STL path from the studio is different from the norm, if not unique. Legend Communications also operates KGWY-FM in Gillette, approximately 1,000' across the street from the KAML-KDDV studios. The KGWY studio site has a 500' tower essentially in its backyard, and it is the STL receive site for the first hop.

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