Purpose and conclusion
This report holds the ground-radial system constant so that soil and water conditions are the changing variables. The reference installation is a quarter-wave vertical with four equal quarter-wave radials laid at the surface or shallow-buried, evenly spaced at 90 degrees. With only four ground-mounted radials, soil conductivity remains a major determinant of loss and stability. Poor soil is expected to impose the greatest loss, good soil less, and salt water the least. These are engineering conclusions, not guaranteed station-specific values.
The available technical literature supports the comparison, but not one universal numerical table for every location. Brown, Lewis, and Epstein measured how radial number and length affect vertical efficiency; Severns measured practical HF radial systems and found four long ground radials to be a weak baseline compared with more extensive systems; his salt-water discussion explains why conductive water changes the result. The graphics keep the installation fixed and present an illustrative relative ground-loss index rather than pretending to provide a universal dB loss for every site.
Fixed installation used for every ground condition
| Item | Held constant |
|---|---|
| Radiator | One quarter-wave vertical at its design frequency. |
| Ground radials | Four equal quarter-wave wires, same conductor and insulation, evenly spaced at 90 degrees. |
| Placement | At the surface or shallow-buried; no added ground screen or extra radial wires. |
| Feed system | Same feedpoint, choke approach, matching method, accepted power, and measurement method. |
| Comparison variable | The effective ground environment: poor, average, good, or salt-water dominated. |
What changes and what does not
A fixed four-radial layout makes the comparison meaningful because it prevents the usual repair—adding more wire—from masking the effect of the site. It does not make the sites electrically identical. Conductivity, permittivity, moisture, waterline geometry, terrain, and nearby conductors change the return-current path and the far-field reflection. Retuning after installation remains necessary because ground condition can also change feedpoint impedance.
| Ground condition | Effect with the same four radials | Practical reading |
|---|---|---|
| Poor terrestrial ground | More return current must use lossy earth outside the small radial field. Loss and seasonal variation are likely highest. | Four radials are a deliberately constrained baseline, not a recommended finished system. |
| Average terrestrial ground | The same wires screen some of the high-current region, but earth remains a material part of the return path. | Expect an improvement over poor ground, but still substantial sensitivity to site conditions. |
| Good terrestrial ground | Lower earth loss and a more favorable ground image improve the result without changing the wire layout. | Better soil helps, but it does not turn four radials into a broad radial field. |
| Salt water or shoreline dominated ground | High conductivity can markedly reduce earth loss and can favor waterward low-angle propagation. | The direction toward water, waterline distance, tide, corrosion, and radial continuity remain important. |
Poor ground with four fixed radials
This is the most demanding condition. The four wires cover only four narrow sectors, so a large fraction of the near-field return region remains lossy soil. Brown, Lewis, and Epstein established that increasing radial number and length improves vertical efficiency; the inverse lesson is especially relevant here. Severns' HF experiments also found a four-long-radial surface system substantially weaker than denser radial systems. Soil moisture changes can make the result move over time, even when the antenna geometry does not.
Average ground with four fixed radials
The radial system is unchanged, so any improvement comes from the earth rather than additional copper. Higher conductivity and favorable permittivity reduce the penalty of current that leaves the radial wires and flows in the soil. Average ground can therefore outperform poor soil with exactly the same four wires. It is important not to overstate the result: the ground quality changes loss, but it does not create a universal takeoff angle or substitute for a more extensive radial field when space allows.
Good ground with four fixed radials
Good terrestrial ground lowers the earth-loss penalty without changing the wire layout. Lower loss and a more favorable ground image improve the result, but four radial wires remain only a small radial system. The graphic shows the source-supported direction of the change: more useful field at lower angles and less loss than the poor- or average-ground cases, using the same four wires.
Salt water with four fixed radials
Salt water is the special case most likely to make a sparse radial system look surprisingly effective. Its conductivity can provide a favorable return environment, especially toward open water. Severns' salt-water analysis cautions against the slogan that beach verticals need no radials: the fixed four wires still provide defined return paths at the feedpoint, and performance depends on how much of the installation is actually coupled to conductive water. The same vertical can behave differently inland and waterward.
How to interpret the loss graphic
The relative ground-loss index is deliberately not labeled in dB. The available research strongly supports the ranking and the physical reason for it, but a precise loss value depends on the frequency, radial-wire dimensions, conductivity, permittivity, moisture, terrain, salt-water coupling, feedline current, and nearby objects. The common scale makes the intended comparison clear: poor ground is the high-loss baseline; average soil improves it; good terrestrial soil improves it further; and conductive water can reduce the earth-loss contribution substantially.
For a site-specific answer, use measured field strength or validated modeling with local ground constants. SWR is useful for retuning, but it is not a measurement of radiated performance.
Measurement plan
Use the same antenna, frequency, accepted power, receiver gain, and receive location for each comparison. First retune for the actual site; then compare calibrated field strength or reciprocal receive measurements over enough samples to reduce propagation noise. Record soil moisture, tide and waterline position at shoreline sites, and any feedline-current observation. On skywave paths, use enough samples to distinguish ground-system change from ordinary propagation variation.
Elevated four radial counterpoise note
A four-wire elevated counterpoise is a useful reference but is not the same physical experiment as four wires on or in the ground. The count can remain four, but height and resonance deliberately shift return current from earth to the wires. The peer-reviewed Christman and colleagues study modeled a four-elevated-radial monopole with strong ground-wave performance. Include this only as a separate geometry comparison, not as evidence that four ground-mounted radials are equivalent.
References
- G. H. Brown, R. F. Lewis, and J. Epstein, Ground Systems as a Factor in Antenna Efficiency, Proceedings of the IRE, 25(6), 753–787, 1937. doi:10.1109/JRPROC.1937.228255.
- R. Severns, N6LF, Experimental Determination of Ground System Performance for HF Verticals, QEX ground-systems series, especially the multiband radial configurations and surface-radial comparisons.
- R. Severns, N6LF, Vertical Ground Systems Over Saltwater, technical report, Antennas by N6LF.
- A. Christman, R. Radcliff, D. Adler, J. Breakall, and A. Resnick, AM Broadcast Antennas with Elevated Radial Ground Systems, IEEE Transactions on Broadcasting, 34(1), 75–77, 1988.
- ITU-R Recommendation P.527, Electrical Characteristics of the Surface of the Earth, for site-appropriate conductivity and permittivity context.