Elevated or On-Ground Radials? Follow the Installed Current
Elevated or On-Ground Radials? Follow the Installed Current
Elevated and ground-surface radial systems can both work very well. The useful comparison is not a magic wire count; it is how each installation distributes return current, limits loss, preserves symmetry and survives its surroundings.
RF.Guru working definition: Common-mode current is the non-cancelling phasor-sum current in a specified set of conductors, evaluated at a defined cross-section and using a declared current-direction convention. In the intended differential transmission-line mode, the outgoing and return currents are equal and opposite, so their phasor sum is zero. When they do not cancel, the remaining current must close through another reference or return path—such as the outside of a coax shield, a mast, equipment chassis, station wiring, nearby structures, earth, the operator, or distributed coupling through the environment.
This broader working definition is especially useful in practical antenna systems. On transmit, non-cancelling current on the outside of the coax can make the feedline and connected structures part of the radiating antenna system unless that path is intentional, clearly defined and properly controlled—for example by providing the required return path and placing a suitable common-mode choke at the correct boundary.
I do not choose a radial system from the sentence “four elevated equal sixty on the ground” or “many short radials always win.” Rudy Severns, N6LF, did the harder work: he changed count, length, height and geometry in controlled models and field experiments. His results are valuable precisely because their conditions are visible.
Elevated radials trade wire quantity for tuning and symmetry discipline. On-ground radials trade that tuning sensitivity for more conductors and soil interaction. Neither label decides efficiency before geometry, current and field strength are measured.
What the Radials Are Doing
A ground-referenced vertical needs a return path from the base region back to the source terminal. Without a sufficiently conductive radial structure, some current returns through lossy soil and unintended conductors. The resulting loss, current distribution and pattern depend on frequency, soil conductivity and permittivity, moisture, conductor layout, feedline route and nearby metal.
Radials on or just below the surface are strongly coupled to lossy earth. They normally behave as a distributed network rather than isolated free-space resonators. Elevated radials couple less directly to soil and participate more visibly in the antenna's tuned structure. That distinction explains why the two systems should not be designed by the same rule.
Protective earthing and lightning protection remain separate jobs. A radial fan designed for antenna return current is not automatically an electrical safety electrode or a lightning-current system. Required bonding and protection must follow the applicable installation rules.
What N6LF's Comparison Demonstrated
In his 7.2 MHz Part 3 experiment, N6LF used one 33.5-foot vertical, controlled the feedline with a common-mode choke and compared a 64-wire ground-surface system with smaller ground and elevated arrangements. He repeated the sequence on different days. That work showed that a small elevated set can approach the measured transmission performance of a much larger surface system in the tested geometry.
It did not establish that four elevated wires are universally equal to sixty-four surface wires. With only a few elevated radials, current division becomes sensitive to wire length, height, slope, nearby conductors and feedline coupling. Later N6LF work examined this asymmetry, radial voltage, multiband behaviour and the stabilising effect of additional wires.
The correct conclusion is constructive: elevated systems can use fewer conductors efficiently when they are installed as a controlled, balanced return structure. The smaller the set, the more carefully its current sharing and high RF voltage must be measured.
N6LF also gave a practical recommendation: try twelve or more elevated radials to reduce sensitivity to unequal currents and high Q. I read that as a robustness recommendation, not a threshold below which an antenna cannot work. If the site can support the extra wires safely, that is a useful reason to add them even when a carefully arranged four-wire test already gives a strong signal.
Elevated Radials: Efficient but Exposed
Elevated radials are usually cut near their operating-band resonance and trimmed with the entire antenna assembled. Their electrical length changes with height, wire insulation, droop, ground, vegetation and coupling between wires. In a multiband fan, wires for other bands are not passive scenery; they can couple and carry current.
- Symmetry matters. Unequal angles, heights and surroundings can produce unequal radial currents and pattern distortion.
- Count changes robustness. Adding wires can reduce dependence on one radial and make the return structure less fragile, but no fixed count guarantees the result.
- Touch voltage matters. Elevated conductors may carry substantial RF potential relative to nearby ground, especially at high power. Keep them out of reach and qualify insulation and access control.
- The feedline still matters. A suitable choke can impede an unwanted coax-exterior path, but its position follows the intended return boundary and its installed effect must be measured.
On-Ground Radials: Distributed and Forgiving
Surface or shallow-buried radials are not normally trimmed as free-space quarter-wave resonators. Adding conductors changes the current density and reduces the fraction of near-field energy dissipated in soil, but the improvement diminishes as the local region becomes well served.
Count and length cannot be separated from total wire, radial spacing and soil. For one fixed conductor budget, distributing wire among more directions may improve coverage near the base; at another site, shortening every wire can leave important current regions uncovered. N6LF's measurements are a map of particular geometries, not permission to replace site design with “many short” or “few long.”
The broadcast work of Brown, Lewis and Epstein at about 3 MHz established systematic field-strength trends for defined buried radial systems. It remains foundational, but a broadcast tower, frequency, soil and 120-wire layout are not a drop-in specification for every amateur vertical.
Jerry Sevick, W2FMI, brought that experimental habit into the amateur HF setting. In his 1973 QST article, The W2FMI Ground-Mounted Short Vertical, Figure 2 follows the input resistance of a quarter-wave 40 m vertical as radial count changes, with two radial lengths compared. That is useful evidence about a particular ground system—not a licence to subtract a textbook resistance and declare the remaining loss gone. Sevick's concluding research questions included elevated-versus-ground comparisons as a function of height. N6LF's later work helps answer that practical question with measured transmission performance as well as impedance.
Choose the System That You Can Control
| Design question | Elevated radial system | On-ground or shallow-buried system |
|---|---|---|
| Electrical behaviour | Part of a tuned coupled structure | Distributed conductor/soil network |
| Typical sensitivity | Length, height, symmetry and nearby objects | Soil, coverage, spacing and conductor budget |
| Practical advantage | Potentially strong performance with fewer wires | Mechanically simple and less tuning-sensitive |
| Primary risk | Unequal current and accessible RF voltage | Loss hidden in soil and sparse coverage |
| Proof | Radial-current equality, impedance and field A/B/A | Base-region current distribution, accepted power and field A/B/A |
I choose elevated radials where I can preserve geometry, keep conductors inaccessible and measure current sharing. I choose an on-ground system where traffic, vegetation, supports or multiband complexity would make a small elevated fan unstable. A hybrid installation can work, but then both systems are coupled and must be measured together rather than credited separately.
Measure More Than Feedpoint Resistance
A feedpoint resistance moving toward a textbook radiation resistance does not by itself prove that loss vanished. The radiation resistance, conductor loss, soil loss and unwanted-current paths all contribute at the selected reference plane. Use a power and field ledger instead:
- record calibrated R + jX at the feedpoint with the same geometry for every state;
- control accepted power, matching-network loss and transmitter foldback;
- measure current on each accessible elevated radial, or sample the surface system at repeatable positions;
- map coax-exterior and mast current before and after any choke;
- compare far-enough field strength in fixed directions with an A/B/A sequence;
- record soil condition, weather, radial height, lengths, spacing and uncertainty;
- repeat the powered test long enough to check matching components, connections and conductors thermally.
The best radial system is the one whose return current you can place, measure and keep stable. Elevated and on-ground systems are both engineering tools. Count is an input; controlled current and verified field performance are the result.
Primary and authoritative technical references
- Jerry Sevick, W2FMI — The W2FMI Ground-Mounted Short Vertical, QST, March 1973
- Rudy Severns, N6LF — Ground-System Performance, Part 3: Surface and Elevated Radials
- Rudy Severns, N6LF — Elevated Ground Systems, Part 1
- Rudy Severns, N6LF — Elevated Ground Systems, Part 2
- Rudy Severns, N6LF — An Experimental Look at Ground Systems for HF Verticals
- Rudy Severns, N6LF — Multiband Vertical Ground Systems
Mini-FAQ
- Are four elevated radials always equal to sixty-four on-ground radials? No. A small elevated set performed very well in N6LF's controlled test, but equality depends on frequency, geometry, height, symmetry, feedline control, soil and surroundings.
- Must elevated radials be tuned? Treat them as part of the tuned antenna structure. Trim and verify the complete installation because height, insulation, coupling and nearby objects change their electrical behaviour.
- Must on-ground radials be a quarter wavelength? No. They form a distributed conductor/soil network. Useful length and count depend on current coverage, frequency, soil, available wire and geometry.
- Do more short radials always beat fewer long ones? No. Some fixed-wire-budget experiments favour wider near-base coverage, but shortening every conductor can leave important current regions uncovered. Preserve each experiment's geometry and measure the site.
- Can I compare radial systems from SWR alone? No. Control accepted power and matching loss, then measure current distribution and repeatable field strength. A lower SWR can coexist with higher loss.
- Are elevated radials a safety earth? No. Antenna return conductors, protective earthing and lightning protection have different purposes. Elevated radials can carry hazardous RF voltage and must be kept inaccessible.