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Is it recommended to install a 100 KVA 13,800/400 Volts, 3 Phase, 60 Hertz Package Substation beneath the VORTAC Counterpoise Metallic Grids and what will be the effects if the substation is already energized with the VORTAC also in operation?

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    $\begingroup$ This seems like the kind of question that should really be asked of an engineering consulting company, most likely an electrical engineering firm with experience in RF analysis and shielding and, ideally, aviation and its associated regulations—not a bunch of Internet randos. $\endgroup$
    – randomhead
    Jan 12 at 5:45
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No. This is a very bad idea, for the following reasons.

First of all placing a very large chunk of metal under the counterpoise grid will affect the uniformity of the radiation pattern of both the unidirectional and the omnidirectional signals being transmitted by the VOR station.

Secondly there is a risk of coupling RF currents into the substation and the power leads coming into and out of it. This may upset the switching and regulation hardware inside the substation, as well as turning the power leads into antennas, further disrupting the pattern uniformity of the transmitted signals.

Part of the test & qualification process for such a construction project will be to collect RF field uniformity data in the complete 3D space surrounding the VOR all the way out to its maximum intended range in the complete absence of the substation, repeating the test with the substation under the grid but with power disconnected, and once again, with power connected.

Note that there are both commercially-available and freeware antenna simulation software packages available with which the effects of the substation on the VOR signals can be predicted. I recommend that you halt the construction project until after you have run the models and proven to the aeronautics authority that the substation will not perturb the VOR an any way.

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