Field Report: Nautel NV20

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When we started the plan to install HD Radio in 2008, we allowed ourselves a year to meet the deadlines. The 2008 NAB Show was around the corner, so we looked at what manufacturers had available or might be planned. Our needs sounded simple: two stations (KIFM and KBZT), two HD Radio transmitters.

The usual thoughts of tube vs. solid-state were considered, but we had more direct concerns. The transmitter had to be the right size physically and produce 10kW of analog power with digital. Combined solid-state looked likely, but the external combiner presented some space issues. Were we going to have to give up one, maybe two, full-powered analog backups? I did not like that prospect.

A group from Lincoln Financial Media met with Nautel to see the new NV40 solid-state transmitter. After seeing the unit, I began to lose focus on the talk. The talk ended and I said, “Cut that in half and we will get two of them.” Though the comment was not a sale, when Nautel said our end-of-year deadline of having the transmitters on site could be met, the off-the-cuff comment became reality. We took delivery of the first NV20s on Dec. 24, 2008.

Planned installation

Working with pre-installation documentation based on the NV40, our electrician prepared the wiring. When the transmitters arrived, they were a perfect physical fit in our tight space. To the surprise of Nautel I had the first transmitter operating into a dummy load by lunch time. I poked around the Advanced User Interface (AUI) and found the AUI more intuitive to navigate than expected. By the end of the day I had both transmitters running into their respective dummy loads at full TPO of 10kW, analog-only mode. Not bad for a day's work.

Performance at a glance
Occupies less than one square yard
Advanced User Interface software control
Up to 22kW maximum analog
Ethernet accessible
The remote interface wiring to the Burk remote control system was easy to install as the preconfigured interface on the NV20 had all the inputs and outputs I planned to use. We ran our AES audio feeds to the new NVE300 exciters. These exciters are based on the M50 core, but are redesigned to fit within the transmitter.

In a short time we learned how to balance the power modules via their own bias settings to make the HD Radio mask perfect. We discovered that the factory swapped the bias settings between the KIFM and KBZT transmitters by accident. When all was said and done, KBZT was on the air in digital and we had the ability to put KIFM on the air in digital.

The transmitter

The Nautel NV20 is a solid-state FM transmitter capable of running in analog, digital and hybrid modes. The footprint of this box is amazingly small for the power levels attained.

Centered in the front door is the 17" touch-screen AUI display. There are no buttons on the front; all operations are performed through the AUI or with switches accessible on the controller board when the door is open. Ethernet access also displays the same information as the AUI and both run independently.

The remote interface board is buffered by opto-couplers on the controller board. The remote-control wiring is sectioned to eight-pin screw headers making it easy to connect. All remote functions are user-configurable through the AUI.

The reject load assemblies are behind the plate that supports the controller board. Below these are the eight RF power modules. Below these are the 20 power supplies. Two supplies power each hot-swappable power module for redundancy. The other four run the IPAs and the fans, two each. Below these are the low-voltage power supplies, again two each for redundancy.

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