When 120 Radials Lose to an Inverted-L EFHW
When 120 Radials Lose to an Inverted-L EFHW
I have repeatedly watched a large radial field give way to an inverted-L end-fed half-wave. The useful question is not which topology wins by name, but which complete installation puts more signal where the operator needs it.
Over the last few years I, ON6URE, have seen the same sequence at least five times. A serious low-band operator lays 120 or more radials under a ground-mounted vertical, uses it for a while, then replaces it with an inverted-L EFHW and prefers the result. That repeated observation is worth investigating. It is not a controlled proof that an EFHW universally beats a monopole.
Engineering principle: compare accepted power, loss and realized pattern at the required frequency, azimuth and elevation. Radial count is only one input to a monopole system; an EFHW label says nothing by itself about transformer loss, return current, common mode or installed pattern.
What Those Five Installations Really Tell Me
The swaps tell me that installation constraints can dominate topology. They may also tell me that one antenna’s pattern suited the paths being judged, that one matching network lost less power, that one feedline carried less unintended current, or simply that the replacement was installed higher or farther from lossy objects.
Contest results, reverse-beacon reports and operator impressions are valuable field evidence, but propagation and receive noise move while the comparison is being made. Unless the antennas are switched rapidly into the same receiver or transmitter chain and observed over enough directions and times, they do not isolate efficiency from pattern or propagation.
So I keep the observation and narrow the conclusion: a 120-radial installation can lose to an inverted-L EFHW in a particular station. The number 120 does not guarantee otherwise.
Why 120 Is a Real Number, Not a Magic Number
The number has serious engineering history. Brown, Lewis and Epstein’s 1937 broadcast work measured antenna resistance, field intensity and radial and earth currents for many combinations of radiator height, radial count and radial length. Their Ground Systems as a Factor in Antenna Efficiency identified a large 120-wire buried system as desirable in its medium-frequency broadcast context.
The current US AM broadcast rule still gives the number a precise boundary. 47 CFR § 73.189 describes 120 buried radials, each 0.35 to 0.4 wavelength long and spaced 3°, as an excellent ground system for a base-grounded broadcast vertical. It also permits demonstrated field strength as evidence when a proposed system departs from the specified minimum.
That is not a promise that any 120 wires of any length, depth, spacing or condition will produce a particular amateur-HF result. The broadcast case includes frequency, field-strength requirements, a nearly complete radial fan, long conductors and a defined base-grounded vertical. A 160 m or 80 m garden installation with shortened, folded, interrupted or corroded wires is a different system.
What N6LF Measured—and What He Did Not
Rudy Severns, N6LF, tested real 7.2 MHz antennas over measured soil, adding 33-foot radials in steps from zero through 64 and measuring both feed-point impedance and relative field strength. In his QEX Part 4 report, most of the improvement in those cases arrived with the first 16 radials. Improvement continued beyond 16, but at a smaller rate; for his quarter-wave vertical, the measured change from eight to 64 radials was about 0.9 dB.
N6LF explicitly warns that those graphs describe his soil, frequency, antennas and measurement geometry. The effect was larger for the shorter, more heavily loaded antennas because their loss problem was larger to begin with. He also showed why feed resistance alone cannot be treated as radiation resistance: radiation resistance, soil loss and conductor or loading loss can all change while the antenna is re-resonated.
His soil comparison does not support a general rule that better soil makes a finite radial field perform worse. In the modeled cases, better soil had lower starting loss, so increasing radial count produced somewhat less improvement than it did over poorer soil. Frequency-dependent conductivity and permittivity, radial length and spacing, radiator height and loading still decide the actual result.
N6LF’s broader radial-system design study also shows that how copper is distributed matters. For a fixed wire budget, more short ground-surface radials can outperform fewer long ones in some cases. A few elevated resonant radials are a different design: they can work very well, but current symmetry, length, height, nearby objects and isolation become critical. Do not exchange “four elevated” and “120 on soil” as if only the count changed.
The Ground-Mounted Monopole Power Ledger
A base-fed monopole closes its RF circuit through the radial and ground environment. A useful feed-point power ledger is:
Paccepted = Pradiated + Psoil + Pradial + Pconductor + Ploading/matching
Radials reduce the electric and magnetic fields that drive loss in nearby soil and provide a lower-loss return structure. The result depends on radial number, length, angular coverage, wire resistance, joints, depth or surface contact, soil parameters and frequency. Short verticals also need loading or top loading; coil loss and the lower radiation resistance of a short structure can make the same ground resistance more damaging.
Do not estimate efficiency by subtracting an ideal 36 Ω from measured feed resistance. N6LF’s measurements show that the radiation-resistance term itself changes with the radial system and antenna adjustment. A low SWR or a plausible resistance is a match result, not a loss audit.
A well-built monopole over a suitable radial field can be excellent, particularly when a low-angle vertically polarized pattern is the target. Nothing in my field observations overturns that.
The Inverted-L EFHW Has Its Own Loss Ledger
An inverted-L EFHW is a roughly half-wave conductor bent into vertical and horizontal sections and fed near a high-impedance end. The end feed normally requires a high-ratio matching network. ARRL’s EFHW construction material, for example, explicitly includes both an impedance transformer and a counterpoise connection. End feeding does not eliminate the second terminal of the RF circuit.
The return current can use an intentional counterpoise, capacitive coupling to the surroundings, the coax shield exterior, station wiring or a combination. A choke can define a boundary, but it also changes that return circuit and may change impedance and pattern. ITU-T K.136 identifies converted common-mode current as current created by cable or network unbalance and warns that unwanted current on a coaxial exterior can affect RF measurements.
The matching network has core, winding and stray-field loss. Its efficiency changes with frequency, transformation ratio, load impedance, construction, flux, voltage, waveform and temperature. The antenna wire and its joints have conductor loss, and the high-voltage feed region needs suitable spacing, insulation and access control. A 1:1 SWR does not prove that the transformer is cool, efficient or seeing the intended impedance.
Measure the finished transformer or matching unit across the operating band and expected complex load. A calibrated two-port or back-to-back fixture can bound insertion loss; a thermal or calorimetric check can expose loss at transmit power. Keysight’s network-analyser calibration guidance explains why the measurement planes and fixture effects must be removed before treating S21 as device loss.
The EFHW trade is not “radials versus no radials.” It is one return system and matching network versus another. If coax exterior becomes part of the radiator, count it in the geometry and current distribution rather than calling the antenna counterpoise-free.
Pattern Can Beat Efficiency in One Direction
A ground-mounted monopole and an inverted-L half-wave do not have the same current distribution or pattern. The vertical and horizontal portions of the L both contribute to the field. Height, bend location, wire direction, slope, soil and nearby conductors set the elevation pattern, azimuth pattern and polarization mix. Exterior-coax current can add another radiating conductor.
That means the antenna producing the stronger report on one path may have higher realized gain in that direction without having higher total radiation efficiency. Conversely, an efficient antenna can put less power toward a chosen path because its pattern is wrong for that azimuth or elevation. The current IEEE Std 145-2025 separates radiation efficiency, directivity, gain and realized gain for exactly this reason.
For a contest station, “better” needs a target: local or DX, azimuth sector, elevation-angle range, transmit or receive, bandwidth, power, available supports and tolerance for common-mode current. Once the target is stated, the field observation becomes testable.
A Fair A/B Comparison
- Freeze the objective. State frequency, bandwidth, target azimuth and elevation, polarization, power, duty cycle and receive-noise goal.
- Document both geometries. Record every conductor, height, radial, counterpoise, feedline route, choke position, bond and nearby structure.
- Set power reference planes. Measure transmitter power, feedline loss, matching-network loss and accepted power at each antenna’s declared feed plane.
- Map common-mode current. Use a characterised clamp current probe around the complete coax at several positions and frequencies. A feedline that radiates is part of the compared antenna.
- Measure the pattern result. Use rapid A/B switching with a stable remote receiver or source, several azimuths and enough repetitions to separate propagation variation from antenna difference.
- Repeat environmental cases. Soil moisture, radial contact, transformer temperature, wind-driven geometry and nearby-object changes can move the result.
Record SWR because the transmitter needs an acceptable load, but do not use SWR as the performance verdict. The useful outputs are loss at each stage, current distribution and realized field in the directions that matter.
My Conclusion After Seeing the Swap Repeatedly
I still take those five-plus replacements seriously. They show that a large radial count is not a warranty and that an inverted-L EFHW can be the better station antenna under real constraints. They do not establish a hierarchy that follows from the antenna names.
Sometimes the monopole loses because its ground and loading losses are too high. Sometimes the EFHW wins because its geometry creates a more useful pattern or because it fits higher and farther from loss. Sometimes an apparently successful EFHW is quietly using the coax as part of the radiator. And sometimes a measured, symmetric, low-loss 120-radial monopole will beat it.
The honest verdict is a complete-system one: measure where the power goes and where the field arrives. The garden does not award points for copper count, and the antenna does not read the label on its transformer box.
Mini-FAQ
- Do 120 radials guarantee that a ground-mounted vertical will outperform an EFHW? No. The count has broadcast-engineering significance, but performance also depends on radial length and coverage, soil, radiator and loading loss, matching loss and the required pattern.
- Did N6LF find that radials stop helping after 16? No. In his measured 7.2 MHz cases, most improvement arrived with the first 16 and smaller gains continued beyond that. He explicitly bounded the result to his antennas, soil and test geometry.
- Does better soil require more radials? Not as a universal rule. In N6LF’s comparison, better soil began with less loss and gained somewhat less from increasing radial count. Frequency, soil parameters and the complete geometry still matter.
- Is an EFHW radial-free? No. Its end-feed circuit still needs a return path, which may include an intentional counterpoise, capacitance, coax exterior or station wiring. Choke placement helps define that path but can change tuning and pattern.
- What is the fairest comparison? Compare accepted power, matching and conductor loss, common-mode current and realized field at the same frequency, azimuth and elevation using rapid repeated A/B measurements.