Field Report: Nautel NV40
WYSO is a 50KW non-commercial FM station licensed to Antioch University in Yellow Springs, OH. WYSO serves the Dayton/Springfield, OH, metro providing NPR and a variety of other public radio programming to more than 1 million people. This station has undergone many improvements and upgrades since first going on the air in 1958 as a 10W student station. That history of growth to meet the needs of the public radio audience and fulfill the mission of the University's outreach is culminating this year in two major projects - the construction of new state-of-the art studios, and a new transmitter and antenna that will increase power to improve coverage and maximize the potential audience.
I embarked on the power increase project when a detailed study of the directional antenna pattern revealed the opportunity to increase the coverage area contours toward major population centers. During this time, the Corporation for Public Broadcasting announced that grants would be available to increase IBOC facilities. WYSO broadcasts in digital and continues to explore methods to utilize the capabilities for multiple audio channels and associated data, so increasing the digital coverage was another objective. Studies completed by John Kean and NPR Labs suggested that an IBOC sideband level of -14dBc would come close to achieving coverage parity with the analog signal without causing objectionable interference to either adjacent stations or our own analog signal. Our own studies verified that WYSO could utilize IBOC levels of at least -14dBc, so we now had yet another reason to proceed.
The search commenced for a suitable new transmitter that would be able to produce the required power output at -14dBc in MP3 mode and also be compatible with the many limitations of our transmitter site. The first major site limitation was tower capacity at our leased antenna site, which only allowed a two-bay antenna. With what the directional antenna gain would likely be following range proof measurements, we could need as much as 30kW TPO to make our 50kW ERP goal. The second major limitation was the absence of three-phase power. The current transmitter utilized a Phasemaster to convert from single phase, but that is a compromise in efficiency and results in higher utility costs, as well as creating a potential reliability issue with another single point of failure. In fact, the Phasemaster had a history of two failures resulting in outages. A solid-state transmitter with switching power supplies could resolve that issue.
My initial research was taking place in 2010 at a time when several transmitter equipment manufacturers were responding to the market demand for reliable solid state, lower cost, high power transmitters with smaller footprints by developing or enhancing new lines of high power solid state FM transmitters with elevated IBOC capability. Ability to bring a product to market in a timely fashion became yet another issue.
|Performance at a glance|
|◊ 16 hot-swappable RF power modules with integrated IPA PAs
◊ Redundant IPA power supply
◊ Hot-swappable power supplies
◊ Redundant low-voltage power supplies
The Nautel NV40 turned out to be the only product on the market that would produce the required 30KW TPO at -14dBc IBOC level in MP3 mode, was also solid-state and was capable of operating from single-phase power with switching power supplies. Achieving that power level was possible due in part to its Power Boost peak to average power reduction (PAPR) technology that was proven during independent tests last year conducted by NPR Labs. Additional IBOC gains would also be possible in the future by utilizing asymmetrical sideband capability. The adaptive pre-correction maintains spectral compliance without external filters.
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