Below for some perspective on this topic is a NEC4.2 analysis showing the difference in performance of a 40m, 1/4WL, unloaded, base-fed vertical monopole antenna system when driven against either a 5/8" OD or a 12" OD, copper-clad, 8-ft long ground rod buried in poor Earth (1 mS/m, d.c. 5).
Increasing the ground rod OD up to 12" is the equivalent of modifying the adjacent Earth around a 5/8" OD ground rod to be nearly a perfect conductor of the radial r-f currents in the Earth around the monopole, that flow toward the ground rod.
An improvement in system performance results, but not a very significant improvement.
Increasing the ground rod OD up to 12" is the equivalent of modifying the adjacent Earth around a 5/8" OD ground rod to be nearly a perfect conductor of the radial r-f currents in the Earth around the monopole, that flow toward the ground rod.
An improvement in system performance results, but not a very significant improvement.
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