Sierra H: The Transmitter Goes Over the Mountain
Transmitter installation and design
The Flexiva is a single-cabinet design that resembles an equipment rack. The 20kW model is built from two 10kW power blocks, with no external power supply or combining network required. All connectivity is internal. This makes it compact enough to fit four 20kW units in a 22x22-square foot building with other equipment racks, a combiner, dummy loads, air conditioners, service entrances, disconnects, surge suppressors and transfer panels -- and room to spare for engineering service.
The high elevation makes transport a challenge, as previously noted. It's nearly impossible to drive a huge transmitter truck up the mountain, and the Flexiva design allowed me to break the transmitter down into components that I could easily transport. This very much simplified the move-in process, as the rack was the largest piece to transport.
The transmitters, each outfitted with Harris FlexStar exciters, were reassembled onsite. We loaded the cabinet set including power supplies and amplifier modules, and reattached the side doors once each transmitter was in place. A used ERI six-cavity U combiner was repurposed and reconfigured into a more space-friendly T arrangement to bring the entire RF system together.
At the same time we replaced an existing Moseley 6000 STL system with a Harris Intraplex STL HD T1 system. We additionally added Orban 8600FM units for on-air processing, and DaySequerra M2A-FM modulation monitors. The Orbans sound exceptionally nice, and we use AAC encoding on the Intraplex for the best possible audio quality and least amount of delay. It has worked very reliably, with only rare minor interruptions.
We plan to install an Intraplex HD Link 950MHz STL system when the weather breaks, and switch between the two units every 30 days or so. The terrain and distance from the studio involves multiple hops for a 950-based system, and will require some path analysis, new microwave dishes and multiple tower crews.
Exterior work on the tower was limited to re-tuning and double-slug tuning the existing six-bay ERI antenna. The previous engineers had the foresight to consider that the antenna would be diplexed down the road, minimizing equipment and labor costs on antenna and tower changes.
- continued on page 4
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