Vertical-Antenna Ground Systems: Radials, Earthing and Lightning

The phrase ground system is too convenient. It can mean the conductive return for antenna current, the protective conductor for an electrical fault, part of a lightning-protection system or an EMC bond between equipment. Those functions can meet at coordinated bonding points, but they are not proved by the same measurement and they must not be substituted for one another.

Start by Naming the Job

• RF return or counterpoise: conductors that carry part of the antenna current at the operating frequency. In a vertical, these may be buried radials, wires on the surface, elevated radials, a conductive roof, the coax exterior or a deliberately engineered combination.
• Protective earthing and bonding: the conductors and electrodes used to limit dangerous touch voltage and provide a fault-current path. Their design belongs to the electrical installation and its applicable code.
• Lightning protection: a coordinated system of air terminations where applicable, down conductors, bonding, earth terminations, separation, cable-entry treatment and surge-protective devices, selected from a lightning-risk assessment.
• RF or EMC bonding: low-impedance interconnection over the frequencies of concern. A bond that looks excellent on a continuity meter can still have significant inductive impedance at HF or during a fast transient.

A conductor can participate in more than one system, but that does not collapse the systems into one. A radial field that improves an antenna measurement is not automatically a compliant protective electrode. A compliant protective conductor is not automatically the antenna’s preferred RF return. A single rod beside the feedpoint is not, by itself, a complete lightning-protection plan.

Where a Ground-Mounted Vertical Loses Power

For a defined reference plane, radiation efficiency is the radiated power divided by accepted power. The missing power can include conductor loss, loading-coil or matching-network loss, and dissipation associated with fields and currents in real ground. The radial system changes how current closes around the base and how strongly the near field drives lossy soil.

Adding or rearranging radials can change more than loss. It can alter feedpoint impedance, current distribution, common-mode current on the feed line and the installed radiation pattern. That is why “the SWR improved” and “the antenna radiates more accepted power” are different findings.

A Ground Rod Is Not an Infinite RF Sink

At HF, a rod and its connection have resistance, inductance, capacitance and soil-spreading impedance. Its effect depends on frequency, dimensions, soil conductivity and permittivity, moisture, nearby conductors and the length and route of the connecting strap or wire. The rod can become one branch of the RF return network; it does not make current vanish into an equipotential earth.

This is why a lone rod is usually a poor replacement for a designed radial or counterpoise system. It can still be required or useful for another job—but calling it a “safety ground” is incomplete unless it is part of the installation’s coordinated, code-compliant earthing and bonding arrangement. Adding an isolated electrode can create dangerous potential differences during a fault or lightning event.

What the Classic Measurements Actually Establish

George Brown, Ron Lewis and Joseph Epstein’s landmark 1937 field-strength work compared specific vertical antennas and buried radial systems around 3 MHz. Their measurements showed that radial number and length affect antenna impedance, earth current and field strength, with diminishing returns in the tested arrangements. Those curves are valuable experimental evidence. They are not a universal lookup table for every amateur-band vertical, soil, radial height and radiator length.

Rudy Severns, N6LF, revisited vertical ground systems for amateur HF use with NEC models, feedpoint measurements, radial-current measurements and controlled relative field tests. His work is especially useful because it states the fixtures, soil assumptions, frequency, geometry and limitations. It also preserves a result that is easy to lose in slogans: how the copper is distributed can matter as much as how much copper is used.

Severns’ programme followed the practical work of Jerry Sevick, W2FMI, and Arch Doty, K8CFU. The continuity is important. Each generation tested a physical arrangement; none supplied a magic radial count that is independent of the installed antenna.

Ground-Mounted Radials Are a Distributed System

A radial lying on or just below soil is strongly coupled to a lossy medium. It is not simply a free-space quarter-wave resonator. Exact quarter-wave cutting is therefore not the normal design objective for a dense ground-mounted field. Length, count, angular spacing, burial depth, insulation, soil properties and the radiator’s electrical height all affect current distribution and loss.

Near the base, radial spacing is small and radial current is generally greatest. Farther out, the conductors spread apart and the field can couple more strongly into the soil between them. That physical picture explains why, for some sparse systems and fixed amounts of wire, increasing the number of shorter radials can outperform making a few wires longer. It does not prove that short radials are always best. Once the inner region is well served, more reach can reduce loss farther out; the crossover changes with the radiator, soil and frequency.

The practical design method is iterative:

• Define the bands, radiator geometry, available radius and total conductor budget.
• Model several realistic soil cases rather than one optimistic conductivity value.
• Compare radial count, length and distribution while keeping the reference plane and accepted power consistent.
• Build a baseline that can be expanded in repeatable steps.
• Measure feedpoint impedance and relative field strength after each change; map radial and feed-line current when the equipment is available.

Rings, meshes or extra conductors near a crowded base can be useful in a designed system, but “more metal near the feedpoint” is not automatically optimal. Connections, corrosion, current sharing and the outer part of the near field remain part of the result.

Elevated Radials Trade Copper for Sensitivity

A small number of elevated radials can form an efficient single-band counterpoise when their lengths, heights, angles and currents are controlled. Severns demonstrated equivalence to a large ground-mounted field under favourable experimental conditions, then documented how sensitive a sparse elevated system can be to asymmetry, nearby conductors and variations in the ground beneath it.

That is the real trade: fewer conductors, but tighter control of the complete installation. A radial that is a little lower, bent around an obstacle or coupled to a fence can change current balance, feedpoint impedance, efficiency and pattern. Multiband operation adds more interactions because each conductor is electrically different on every band.

Elevated radials must also be treated as antenna elements. Keep people and animals away from them, provide mechanical support and strain relief, evaluate RF exposure and touch voltage, and respect electrical and overhead-line clearances. Hiding a live radial at hand height is not a performance shortcut.

Insulation and Burial Are Engineering Choices

For on-ground or shallow-buried radials, insulation changes the immediate dielectric environment and can protect the conductor from direct soil contact. Bare wire can make electrical contact with soil but may corrode faster depending on material, soil chemistry, moisture and dissimilar-metal joints. Either construction can work; neither deserves a universal RF or service-life promise.

Record the conductor material, insulation, joint system, burial depth and soil exposure. Then inspect connections periodically and remeasure the antenna after major seasonal changes. A radial field that looked stable when dry may behave differently after waterlogging, frost, landscaping or corrosion.

Saltwater Changes the Boundary, Not the Need for a Design

Saltwater’s high conductivity can make a shoreline or over-water site exceptionally favourable for a vertical. The result still depends on where the feedpoint sits relative to the water, water depth, tides, radial or counterpoise geometry, corrosion, cable routing and whether the antenna itself expects an external return system.

N6LF’s saltwater note is a useful warning against extracting one headline number. Its often-repeated 0.1 dB observation belonged to a particular self-contained multiband vertical in one comparison with and without a large radial field. The same note describes tide-dependent detuning for a different vertical whose conducting support entered the water. The lesson is geometry and current path—not that every seaside vertical can discard its counterpoise.

Saltwater also does not replace protective earthing, lightning assessment, surge protection or corrosion control. Those remain separate design jobs.

Protective Earth and Lightning Protection Stay Intact

IEC 60364-5-54 addresses earthing arrangements, protective conductors and protective bonding for electrical-installation safety. National rules implement and supplement those requirements. They determine such matters as conductor selection, electrode integration, fault protection and bonding—not an antenna-efficiency experiment.

IEC 62305 treats lightning protection as a system whose design, installation, inspection and maintenance also consider touch and step voltages. ITU-T K.56 shows the same coordinated approach for radio sites: assess risk and integrate the lightning-protection system, bonding, earthing, surge-protective devices and all entering cables. A radial field, an isolated rod or simply disconnecting the coax is not an equivalent substitute.

If a required bond seems to worsen RF behaviour, do not remove it. Find the coupling path and solve the compatibility problem with appropriate routing, bonding geometry, filtering, choking or isolation while leaving protection intact.

Measure the Installed Antenna, Not the Shopping List

A useful radial experiment holds the transmitter, frequency, reference plane and accepted power constant. Change one part of the ground-mounted system at a time, then repeat the original configuration to expose drift. Record soil moisture and weather because the environment is part of the circuit.

• Calibrate at the feedpoint. A VNA reading through an unmatched feed line can hide transformation and cable loss unless the reference plane is moved or de-embedded correctly.
• Measure accepted power. Keep network and feed-line losses separate from the antenna comparison.
• Use relative field measurements. A fixed remote receiving system or calibrated field-strength setup can compare configurations when geometry and propagation remain stable.
• Check current paths. Clamp-on RF current probes can reveal radial-current asymmetry and unintended current on the mast, coax exterior or control cables.
• Repeat A/B/A. Temperature, wind, soil moisture and nearby objects can move results by the same tenths of a decibel being discussed.

Rudy’s field work is a good model of this discipline: calibration at the antenna, repeat runs, stray-coupling checks and explicit limits on what the test could establish. A fixed radial recipe without comparable installation data is a starting hypothesis, not a measured result.

Primary and Authoritative Sources

• Brown, Lewis and Epstein, “Ground Systems as a Factor in Antenna Efficiency,” Proceedings of the IRE—the historical field-strength, impedance and earth-current experiments behind many broadcast-ground discussions.
• Rudy Severns, N6LF, Experimental Determination of Ground System Performance for HF Verticals, Part I—test setup, calibration, relative S21 method and measurement limitations.
• Rudy Severns, N6LF, A Closer Look at Vertical Antennas with Elevated Ground Systems—elevated-radial equivalence under ideal conditions and sensitivity to asymmetry and surroundings.
• Rudy Severns, N6LF, Radial System Design and Efficiency in HF Verticals—soil-, geometry- and conductor-budget-dependent modeling rather than a universal radial recipe.
• Rudy Severns, N6LF, Some Thoughts on Vertical Ground Systems Over Saltwater—current penetration, tide, geometry and corrosion considerations for over-water installations.
• IEC 60364-5-54:2011+AMD1:2021—earthing arrangements, protective conductors and protective bonding for low-voltage electrical installations.
• IEC 62305-3:2024—lightning-protection systems, inspection, maintenance and touch/step-voltage safety.
• ITU-T K.56—an in-force radio-site example of coordinated lightning risk, bonding, earthing, surge protection and cable treatment.

Joeri’s Bottom Line

Do not buy a radial count. Design a current path. For a ground-mounted vertical, put conductor where the installed near-field current makes it useful, then expand and measure until the next increment no longer earns its space, cost and maintenance. For an elevated counterpoise, accept that fewer wires demand tighter control of symmetry, tuning, surroundings and safety.

Most importantly, keep the names honest. The antenna RF return, protective earthing, lightning protection and EMC bonding may need coordination, but none proves the others. When those jobs are separated first, both the antenna measurement and the safety decision become much clearer.

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