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A NEC4.2 analysis of the performance of a buried ground rod at the A-C mains entrance of a building shows it be ineffective in removing the common-mode r-f current that can flow along the OD of the shield of a coaxial cable between the transmitter and the input terminals of a dipole antenna.

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A rather common expectation is that bonding the outer surface of the shield of a coaxial cable to a buried ground rod effectively "grounds" that conducting surface at radio frequencies. If that was true, then it would be a good means of removing common-mode currents that can be present in some typical antenna/transmit systems.

The study below is an examination of this, leading to the OBSERVATION it includes for the conditions shown there.

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    $\begingroup$ Nice experiment. Is NEC4 able to simulate a ground spike? I haven't actually used the NEC4 buried wires but I thought it was a "trick" for buried radials, correctly loading them to account for how they work in the ground. A ground rod is quite different. Also with the wire 5 aligned with the dipole, there could be coupling. To be sure, why not repeat the simulation with perfect ground, and a ~5 Ohm resistor to ground at point 4-5-7. Lift wire 5 up a metre or two. $\endgroup$ – tomnexus Jul 13 at 13:28
  • $\begingroup$ Is the mains ground rod different from any other ground rod? $\endgroup$ – Phil Frost - W8II Jul 13 at 14:36
  • $\begingroup$ Yes, NEC4.x is able to analyze antenna systems having buried conductors with results matching both theory and calibrated measurement. And no, the ground rod in my NEC model is no different than any other ground rod for these stated conditions, including its different ESR values for differing frequencies and Earth conductivities. $\endgroup$ – Richard Fry Jul 13 at 15:17

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