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Sierra H: The Transmitter Goes Over the Mountain
There is no question that a site this remote requires backup transmitters. It takes three hours to reach the facility on a clear day. The winters here bring snow -- up to 2.5 feet at the time of writing -- and it takes a Snowcat to reach the site. Delivering a completely new system could take days, with devastating effect to a station's bottom line from being off the air.
This left little choice beyond retiring the current transmitters. The Platinum Z was removed, rebuilt and resold as two separate 10kW transmitters. The Nautel removal was a more difficult proposition. The double-wide cabinet, nearly 8' long, was inseparable. We dragged it from the building with a tractor and set it in a pick-up bed for transport down the mountain.
The major requirement for the new transmitter was size versus output power, equally important in both space considerations and the fact that only single-phase electricity is available at the site. This steered us toward solid-state digital transmitters, which would avoid having to add rotary phase converters to make power.
We decided to purchase four Harris Flexiva 20kW transmitters. The Flexivas offered the compact footprint we needed to fit two main and two backup transmitters in a space that traditionally had space for only one transmitter and half a backup.
Though the stations need only 13.5kW from each transmitter to meet licensed power, the 20kW design offers additional headroom for additional services in the future. However, the distance from the studios -- approximately 74 miles -- means that both stations will operate in FM-only configurations for the foreseeable future.
The choice was made, but it wasn't just plug-and-play. There was much advance work required to get the site in order.
Grounding, electrical and HVAC
The fact that the Platinum Z took 14 lightning strikes signified a serious grounding problem. The site is now very well-protected, with bonding rings inside and outside made with four-inch strap, and six chemical grounding rods surrounding the building to mitigate lightning strikes and electrical faults. LEA PowerVantage external surge suppressors provide additional RF system protection.
Most interior electrical work was redone, upgrading from a 400-amp to an 800-amp service. Prior building renters improperly tapped into electrical panels and left wires from previous installations bare and protruding from walls. This asks for trouble in RF environments where non-terminated wires left for dead can resonate RF, producing feedback. They also can attract static electricity and lightning. LEA DS30S inline surge suppressors provide additional interior protection for the new RF systems.
HVAC was itself a project, with modifications to a pair of Bard 6-ton wallmount, single-phase units. Site power is far from stable, and we've encountered interesting problems -- notably that the digital controllers on modern AC units often lock up. Quick power interruptions are often the cause, so we stripped the digital controls and installed mechanical relays. When the power stops, the mechanical controls dial in like timed relays and restart the units after 20 seconds.
While an improvement, the overall AC system still lacks the required redundancy, and a third unit will be added in the spring. This unit will automatically turn on if one of the main units goes south to avoid overheating the building.
- continued on page 3
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