The suggestion has been made on various ham-related websites that improving the conductivity of the Earth around a ground rod produces a worthwhile improvement in the e-m radiation from a vertical monopole using that ground rod. How effective is that?
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1$\begingroup$ Isn't "improving the conductivity of the Earth around a ground rod" the same thing as "installing radials"? Is there any question that radials are effective? $\endgroup$– Phil Frost - W8IIJul 28, 2020 at 14:36
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1$\begingroup$ I edited my answer to deal with your observation. $\endgroup$– Richard FryJul 28, 2020 at 15:12
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$\begingroup$ How about lowering the earth resistance using Epsom salt (magnesium sulfate) around the rods? See Signal Corps manual MIL-HDBK-419A starting on page 2-59 "2-9 ELECTRODE ENHANCEMENT". Scroll down to the sketch used in many ARRL publications. Sorry I didn't have a link, you'll have too Google it. ALSO, please see my own experience using Epsom salt. $\endgroup$– Mike WatersJul 28, 2020 at 21:01
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$\begingroup$ A quick look at MIL-HDBK-419A prompts some concerns about its usefulness w.r.t. buried rods used as "r-f grounds." The measured data it shows appears to apply to the relatively low-frequency a-c of the utility power distribution grid and lightning protection, while omitting the additional need to provide a low-R path to the Earth for transmit/receive antenna systems operating in their part of the e-m spectrum. $\endgroup$– Richard FryJul 29, 2020 at 9:35
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2 Answers
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Below for some perspective on this topic is a NEC4.2 analysis showing the difference in performance of a 40m, 1/4-wavelength, 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 Earth in that radius area 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.
[Added October 7, 2020]: Improving the conductivity of Earth for several meters around ground rods buried at the base of a vertical monopole (or anywhere else) does almost nothing toward improving the conductivity of the ground plane out to a 1/2WL radius of the base of a vertical monopole.
Regardless of the height of that monopole in physical, free-space wavelengths, minimizing the ESR of the entire ground plane within 1/2WL radius around its base is critical to the radiation efficiency of that antenna system. That ESR is a series circuital element with a large affect on the relative amount of r-f current from the source (transmitter) that will flow along the monopole itself.
RF energy dissipated in the ESR of a set of radials buried in soil is converted to heat, rather than to useful e-m energy radiated into space.
Reference: Ground Systems as a Factor in Antenna Efficiency, Brown, Lewis & Epstein (RCA Labs); Proceedings of the I.R.E., 1937.
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1$\begingroup$ The graphic should say an 0.625" (5/8") ground rod rather than 0.0625", right? $\endgroup$ Jul 28, 2020 at 17:10
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1$\begingroup$ That is right. Thank you for catching my mistake. A corrected NEC graphic now is included in my answer above. $\endgroup$ Jul 28, 2020 at 19:03
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If by improving conductivity, you mean flooding several acres or square miles with ocean (or saltier) sea water (or via natural intrusion near a low lying shoreline or wetlands), or installing a solid copper floor several square wavelengths in size in the parking lot, yes.
But some people have reported improved antenna performance by putting a metal mesh of gopher wire (not too deep) under their lawn, with the vertical antenna grounded in the middle. Probably soldering or crimping adjacent mesh sheets is desirable.
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1$\begingroup$ RE: "If by improving conductivity, you mean flooding several acres or square miles with ocean (or saltier) sea water ..., yes." — My answer addressed and concerned the conductivity of the region of the Earth within a 6" radius of the vertical axis of an 8-ft-long buried ground rod, however. $\endgroup$ Jul 29, 2020 at 9:44
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$\begingroup$ Wouldn't an only 6" radius in non-conductive ground be not much different from just having a larger diameter ground rod (12" iron pipe, etc.)? $\endgroup$– hotpaw2Sep 1, 2020 at 21:34