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Computer Modeling OK'd

Unanimous Approval Expected on FM Directional Antenna Draft Order

A draft order that would allow FM broadcasters to use computer modeling to verify the pattern of their directional antennas is expected to be unanimously approved at Thursday’s open meeting, FCC and industry officials told us. The final version isn’t expected to be much changed from the draft order, and would allow antenna manufacturers to do the modeling and still require the construction of full-size or scale models the first time the pattern of a particular type of antenna is verified using a particular modeling software.

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Current FCC rules require stations verifying the patterns for FM directional antennas to physically build and take measurements using a full-size model of the antenna or a scaled-down mock-up. Allowing computer modeling instead will vastly decrease the costs for stations buying FM directional antennas, said Edward Schober, Radiotechniques broadcast engineer. Physical modeling can require many hours spent at testing ranges and a sizeable investment. Schober expects most broadcasters using directional antennas will opt for computer modeling whenever possible, he told us.

We envision that this rule change will reduce the cost of designing and building an FM or LPFM directional antenna, savings that should be passed on to the broadcast applicant and thus reduce the cost of station construction,” says the draft order: “A less expensive directional antenna should provide an FM or LPFM applicant with greater flexibility in antenna siting.” The NPRM that teed up the draft order was unanimously approved in November, and the draft order’s release drew little ex parte activity in docket 21-422. The proceeding stems from a June petition from Dielectric, Jampro Antennas, Shively Labs, Radio Frequency Systems and the Educational Media Foundation.

Full-size modeling “is still an option,” said Bill Harland, vice president-marketing for Electronics Research, Inc. (ERI), which operates the country’s only full-size, 50-acre testing range. ERI does computer modeling but was among the only objectors to the FCC’s directional FM proposal. “We do not believe you will get as accurate a picture" as with full-scale models, Harland said. Schober said broadcasters in need of particularly large, expensive and complicated antennas could still opt for the full-size range, and the order would still require modeling “the first time the directional pattern of a particular model of antenna is verified using a particular modeling software,” it said.

ERI argued that moving away from physical modeling would lead to more interference disputes, but the FCC said in the draft order it doesn’t agree. That echoes the position of the vast majority of commenters, who widely supported the FCC proposal. “ERI has an economic motive to continue this core part of their business model which is a huge money generator for them,” said noncommercial educational broadcaster the American Militia Association in an April comment filing. Harland said ERI doesn’t plan to appeal the FCC’s order if it's approved.

The draft order doesn’t specify what software should be used to do the modeling, and requires that the software modeling be performed by only antenna manufacturers, answering concerns about qualifications raised by NAB and other commenters. “As we gain more experience with computer modeling of directional FM antenna patterns, we will explore expanding the range of entities authorized to perform computer modeling beyond manufacturers,” the draft item said. “Given the varying backgrounds of broadcast engineers, we do not wish to codify what constitutes qualifications to perform computer modeling.”