Sometimes a good idea can’t wait. That is apparently the thinking inside the Federal Communications Commission. Just months after a group of antenna manufacturers proposed changes to the agency’s directional antenna performance verification rules, the FCC is poised to adopt the rule at its May meeting.
Four FM antenna manufacturers, including Jampro Antennas, Radio Frequency Systems, and Shively Labs, along with Educational Media Foundation, last June filed a petition with the FCC that proposed stations have the option of verifying the directional antenna pattern through computer modeling, rather than by physical measurements as is required by the current rules. This is done by building a full-size mockup of the antenna and supporting structures or by constructing a scale model of the antenna and structures. The manufacturers pointed out that several broadcasters already use computational modeling in their design processes and then must duplicate that effort – at greater expense – to construct physical models on which to make measurements.
The National Association of Broadcasters got behind the proposal, agreeing with the antenna makers that the approach would cut costs for broadcasters while also providing greater flexibility in transmitter site selection.
In the draft order (MB Docket No. 21-422 ) scheduled to be voted on at the Commission’s May 19 meeting, the FCC goes along with the option of submitting computer-generated proofs of FM directional antenna patterns from the antenna’s manufacturer, in lieu of measured pattern plots and tabulations.
“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,” the FCC says in the draft order. “Additionally, a less expensive directional antenna should provide an FM or LPFM applicant with greater flexibility in antenna siting.” It also notes that what it calls a “modest rule change” will put FM and LPFM directional antenna performance verification on the same footing as AM radio and digital TV where computer modeling to verify directional antenna performance is already allowed.
The FCC has also embraced a proposal by the NAB that several “guardrails” be included , mostly in terms of data provided to the Media Bureau. The draft order details information that the station owner would be required to submit. The list includes such things as who is performing the modeling, information regarding the software used to create the computer model, and a description of the software tools used in the modeling and the procedures applied in using the software – including a description of all radiating structures included in the model.
The Commission is also likely to require that the first time the directional pattern of a particular model of antenna is verified using computer results, the broadcast station will need to submit to both the results of the computer modelling and measurements of either a full-size or scale model of the antenna demonstrating a “reasonable correlation” between the measurements achieved and the computer model results.
Once a particular antenna model or series of elements has been verified, the FCC has tentatively concluded that subsequent applicants using the same antenna model number or elements and the same modeling software may cross-reference the original submission by providing the application file number. “We believe this will provide a sufficient basis to verify that the computer model has been shown correctly to describe the pattern generated by the antenna or elements,” the draft order says.
The Commission has also tentatively decided not to expand the range of entities authorized to perform computer modeling of directional FM antenna patterns beyond antenna manufacturers, noting there was some disagreement among broadcasters if others should be allowed. It says a “more cautious” approach is needed for FMs since there are far fewer directional DTV stations and AM directional patterns are subject to continual verification through sampling that is not possible with FM directional antennas. “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 order says.
The Commission has also embraced the NAB suggestion that broadcasters be allowed to use whatever software they choose, rather than have certain products officially sanctioned. The FCC is also not changing its current policies regarding interference complaints or disputes.