Latin America. Dielectric has launched a new engineering service that allows drone operators to fully and accurately characterize antenna azimuth and lift performance without special FAA exemptions. The service has been successfully tested in beta and is now "in production" at several transmission tower sites.
The new service is a response to a common dilemma faced by drone operators: to fully characterize an antenna's lift pattern, the drone's flight must be performed in the far field of elevation, approximately several thousand feet from the antenna. FAA waiver requests have stalled for more than 18 months in some cases, preventing the drone operator from completing measurements to verify antenna performance.
Less attractive alternatives for broadcasters include close flights, which are required only for azimuth; or less precise and time-consuming terrestrial techniques. Since field measurements are reimbursable for "repackaged" stations in the U.S., the delay in obtaining an exemption from the FAA can result not only in a repackaging project that takes much longer than necessary, but also in the late identification of installation problems.
Dielectric engineers recognized that a new approach was needed. Realizing that no special FAA exemptions were required for drone flights within the shield of the tower structure, Dielectric devised a method to confirm the antenna's far-field elevation pattern, in addition to the azimuth pattern, from the data collected within that shield. This technique has an additional advantage, as far-field measurements are subject to signal reflections, multiple paths, and interference, as are more complicated ground vehicle measurements.
"FAA rules impose several restrictions on flying drones for commercial use. There is a 400-foot altitude restriction on commercial drone flights, unless the operator can fly the drone within a 400-foot radius around a structure and does not fly more than 400 feet above the top of that structure," said John Schadler. Vice President of Engineering at Dielectric. "Unfortunately, waivers for these rules take many months to process and may never be granted due to other restrictions. Our technique solves the problem of getting an exemption beyond the FAA shield. That means there's no need to create flight plans and safety simulations, among other requirements that lengthen the approval process."
Both near-field and far-field measurements allow broadcasters to verify the azimuthal radiation patterns of their TV antennas and confirm that they are radiating as planned and properly oriented in the tower. Dielectric's approach calculates near-field elevation pattern characteristics for comparison with near-field drone measurement data, allowing a near-field measurement to accurately reflect far-field lifting performance.
Flight preparation
Before a drone pilot takes off, Dielectric engineers build a complete virtual model of the entire antenna, including the tower's support structure, based on the final planes of the antenna and tower. Using the company's sophisticated high-frequency modeling software with the virtual model produces a detailed prediction of azimuth and elevation data at a given distance from the tower, at or within the 400-foot FAA limit. That allows for a comparison of the virtual model with the actual near-field measurement, which is, in fact, an out-of-focus representation of what radiation features look like in the far field.
The drone pilot then collects the data and returns it to Dielectric, where engineers export and graph the data about the virtual model. Once compared and confirmed, a report is provided to the end customer, which is usually an engineer of the television station or a consultant representing the station.
Starrett adds that Dielectric has the ability to model any antenna for which it has detailed drawings and data, meaning service will likely be restricted to Dielectric antennas. "Dielectric had more than 80 percent of the repackaging business in the United States over the past three years," Schadler said. "That brings our total number of repackaged antennas sent to 948, so we expect to be pretty busy backing this new service."
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