WXPR had been on the air since 1983 with a CSI 12000F tube transmitter, which was upgraded to a 20000F in 1992. It fed a 10-bay Phelps-Dodge antenna of the same 1983 vintage. This setup provided steady, reliable service but aside from the tubes, spare parts were getting difficult or were impossible to acquire and we needed a new linear transmitter to transmit an HD Radio signal.
As a 100kW class C1 FM, we chose the space combining method with an interleaved antenna on our 400-foot tower. We decided this would waste the least amount of electricity and heat. Another attractive aspect of space combining is that the digital transmitter can serve as a backup analog transmitter if the analog needs to be off-line for any significant period.
We selected an eight-bay Dielectric antenna for analog and the four-bay equivalent for digital. Calculated antenna gain and line losses meant we needed 27kW TPO analog. With the digital antenna providing a gain of 2.1 we only needed 500W from a digital transmitter to reach our ERP of 1kW (1 percent of analog).
We started evaluating transmitters last spring. All the familiar names were in the running by the time we sent requests for bids. Most manufacturers responded with products we were comfortable with, but we decided on Nautel. Besides the company's solid reputation, our CE influenced part of the decision. As a retired U.S. Army Signal Corps officer, he appreciated Nautel's years of experience manufacturing to military specifications. In addition, as stewards of a community public radio station, we recognized that we were building for the future, and planning for the next 25 years doesn't necessarily mean going with the lowest bidder.
The final decision
|Performance at a glance|
|Display-based user interface
100-event troubleshooting log
Redundant, hot-pluggable modules
62 percent overall analog efficiency
30 percent overall digital efficiency
Broadband amplifier design
Six operational presets
We chose the for the digital signal. Achieving 27kW analog power meant going with the Nautel Q30 that combines outputs of a standalone Q20 and V10 (20kW and 10kW respectively). Both the V5d and the Q30 use a Nautel M50 exciter, and the SC1 controller handles the balancing of the Q20 and V10's outputs into the combiner.
At the end of July 2006 we placed the order. By early September, Nautel notified us that the shipment was ready. This was a surprise, being three weeks ahead of the date specified in our original bid request.
The shipment consisted of 13 wooden crates weighing almost 4,300lbs. The delivery truck hired in Nova Scotia by Nautel did not have a lift gate, but that turned out to be a blessing in disguise. We had the load transferred to a local moving company at its warehouse, and were glad to have the moving company's equipment, expertise and muscle when unloading the equipment at our site.
Great attention to detail was evident in preparing the containers for shipping. Besides three transmitter cabinets, the crates contained the reject loads, main and spare power modules, main and spare power supplies, exciters, exporter, importer, a variety of connectors, hardware, sections of hard line, wiring assemblies, cable sets, combining kits and a complete set of technical manuals. Every part or component inside each crate was either bubble-wrapped or foamed and sealed in boxes. There was no unpadded or unfilled space in any crate.
Once unpacked, assembly began. The importer, exporter and V5d exciter communicate through three ports of a provided four-port hub. We supplied a rack shelf, KVM switch, keyboard, monitor, mouse and a number of AES-3 cables for audio routing.
An extensive set of manuals accompanied the shipment. The V5d, Q20, V10, exciters, importer and exporter each had individual manuals with sections addressing installation prep, step-by-step installation instructions, operation, maintenance and repair. Nautel owners can join the Nautel Users' Group and have access to all of these manuals and more online.
Individual power supplies and power modules were unpacked and installed. The V5d has one IPA module with its own switching power supply, and four RF power modules each with an individual power supply. Each power module consists of four discrete circuit boards that mate to BNC-type connectors at the rear of their slides within the cabinet. Power and control are applied through a fifth interface board in each module.
Parts and connections were meticulously documented and labeled. Detailed drawings and photographs showed the layout of the cabinets, plumbing and electrical connections. Removable tags in the enclosures guided us to locations where components belonged. Bagged hardware was labeled for specific applications and frequently attached where needed. Ample quantities of spare hardware were provided — all stainless steel.
Assembly, RF plumbing, final electrical and grounding work, and other small but important details took place over several weeks. Our pledge drive was scheduled for the end of October and the tower crew, OK Tower of Medford, WI, was booked for the following Monday, Oct. 30. That week we began the changeover. We would broadcast with our old transmitter at low power from a temporary antenna rigged on another tower on our site.
A look inside the V5d with the amplifier modules on the upper left and the power supplies along the bottom.
As fortune would have it, the CSI transmitter chose this time to fail so we ran a spare RPU extension from the analog STL receiver in the old building to the new, swung the temporary antenna feed line into the new building and commenced broadcasting with the Q30 at low power.
By the middle of the first full week in November the tower crew was finished. The tower was unrigged and the analog increased to full power. However, the new digital STL had less headroom than predicted by the path study and the V5d still languished on the sidelines.
As a work-around, we applied replacement audio from the Danagger Plan B silence eliminator directly to the V5d, and then powered it up. With that, we became the first station in north-central Wisconsin to broadcast an HD Radio signal.
Meanwhile, a 10W STL booster amplifier was ordered. It solved the headroom problem, and five days after reaching full analog power the V5d was simulcasting our main program service at 500W on HD1. An HD2 service is in the works for the spring of 2007.
The V5d performs effortlessly. Reject power behind the circulator is on the order of 2.5W or 3W. Reflected power is barely measurable. We had an initial issue with fail indicators on one of the intermediate power amplifier modules, but it was promptly diagnosed and replaced by Nautel customer support.
I expected to have minor snags and bumps in the road in a project of this scope. There are ancillary parts and devices you don't know you need, and nothing ever goes completely as planned. But that wasn't the case with anything supplied by Nautel. We're extremely pleased, and so are our listeners.
Dan Roberts of Broadcast Connection was the supervising contractor on this job. WXPR Chief Engineer Elmer A. Goetsch, contract engineer Jim Zastrow of Zastrow Technical Services, and broadcast engineer Bob Gorjance were also instrumental in all stages of this project.
Gander is the operations director of WXPR, Rhinelander, WI.
Editor's note: Field Reports are an exclusive Radio magazine feature for radio broadcasters. Each report is prepared by well-qualified staff at a radio station, production facility or consulting company.
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