POTA PERformer, Challenger and Dominator: What the Numbers Prove
POTA PERformer, Challenger and Dominator: What the Numbers Prove
Greg Mihran, KJ6ER, published three practical portable vertical concepts and enough technical detail to invite serious discussion. The useful question is not whether they make contacts. It is which conclusions follow from the models and calculations—and which still need an installed measurement.
Portable HF rewards fast setup, modest weight and an antenna that gets on the air. KJ6ER deserves credit for publishing buildable ideas rather than hiding them behind a photograph and a signal report. That openness also lets us examine the claim chain properly.
The February 2025 KJ6ER Antennas Primer compares the PERformer quarter-wave, Challenger off-centre-fed half-wave, Dominator end-fed half-wave and a two-element Dominator beam. The individual Challenger and Dominator documents add dimensions, transformer choices, counterpoise lengths, SWR arithmetic and NEC patterns.
This is a technical response to those documents. It credits the portable design choices while testing whether the displayed quantities support the broader efficiency, gain and coverage conclusions attached to them.
Start With the Four Different Antenna Systems
The names describe different current-path and matching problems, not a simple ladder from basic to dominant:
| System | Engineering question | Evidence needed |
|---|---|---|
| PERformer | An elevated quarter-wave radiator with two tuned radials. Radial angle may skew the azimuth pattern. | Element currents, feed-line exterior current, installed pattern and repeatability as the surroundings change. |
| Challenger | An asymmetrically fed, approximately half-wave system using a 4:1 transformation and a linked return conductor. | Complex feed impedance, transformer loss, return-path current, conductor loss and installed gain. |
| Dominator | An end-fed, approximately half-wave system using a high-ratio transformer and linked counterpoise. | The same complete-system evidence, with additional voltage, transformer and common-mode boundaries. |
| Dominator beam | A parasitic two-element array built around the driven Dominator geometry. | Both element currents, spacing, loss, front-to-back ratio, installed pattern and uncertainty. |
Each can be useful. Each can also behave differently from a clean model when the tripod, coax, operator, soil and nearby conductors become part of the electromagnetic structure.
The 96% Number Is Mismatch Efficiency
For a real reference impedance, an SWR of 1.5:1 gives:
|Γ| = (SWR − 1) / (SWR + 1) = 0.2
1 − |Γ|² = 0.96
At that reference plane, 4% of the incident power is reflected and 96% is accepted by the load connected there. That is a useful mismatch result. It is not the radiation efficiency of the antenna system.
Accepted power can still be dissipated in a transformer, choke, conductor, joint, ground-coupled return path or unintended feed-line mode. Radiation efficiency instead compares radiated power with accepted power at a declared antenna boundary. Realized gain adds pattern directivity and the stated mismatch condition. These quantities belong in separate columns.
Joeri’s short version: SWR can tell you how much incident power is accepted at one plane. It cannot tell you where that accepted power goes.
Component Loss Does Not Close the System Budget
The Primer lists key component losses and a quantity called structural efficiency. Those figures may be useful inside their stated calculation, but readers must not silently expand their boundary.
A transformer insertion-loss result applies to the exact transformer, fixture, frequency, source and load impedances, power level and temperature used for the test. A choke result applies to the common-mode path and test method used. Neither result measures radiator loss, joint loss, ground coupling, feed-line exterior radiation or the installed far field.
A 4:1 transformer can be a sensible choice when the measured feed impedance calls for it. It avoids the very large transformation used by a conventional high-impedance EFHW network. That does not make every 4:1 implementation lower-loss, and it does not establish the Challenger’s total efficiency. The completed network still needs measured complex impedance, insertion or transducer loss under representative terminations, thermal behaviour and installed current-path checks.
A Counterpoise Is Part of the RF Circuit
“No radials” is a mechanical description only if a linked counterpoise remains necessary. Electrically, the counterpoise carries return current and helps set the impedance, resonance, loss and pattern. Whether we call it a radial, counterpoise or return wire does not change that role.
The coax shield, tripod, operator and nearby conductors may supply additional exterior return paths. A feedpoint choke changes that path; it does not make the rest of the installation disappear. The ARRL’s common-mode current and choke guide makes the practical point: choke behaviour is frequency-dependent and the installed exterior current should be measured before and after the change.
For these portable systems, useful evidence includes a current map along the counterpoise and coax, repeated with several feed-line routes and lengths. If resonance, impedance or field strength changes materially, the external path is part of the measured antenna system.
Half-Wave Is a Geometry, Not a Performance Certificate
A current maximum near the middle of a roughly half-wave conductor is expected standing-wave behaviour. It does not prove a percentage efficiency, a low take-off angle or a global-coverage category.
The linked return conductor and environment help set the electrical length and terminal impedance. A transformer ratio maps the impedance present at the feedpoint; it does not move that feedpoint along the radiator. When the radiator, counterpoise, transformer capacitance, tripod and feed-line exterior interact, the complete structure—not one named element—sets the current distribution.
That is why dimensions should be presented as starting values. Final length belongs to the declared installation and should be accompanied by a complex-impedance sweep and a record of the return-path geometry.
A Polar Plot Is Conditional Evidence
NEC is excellent for comparing controlled geometries and testing sensitivity. Its output is conditional on the wire model, segmentation, conductor properties, feed definition, ground model, loss model, feed line, choke and nearby structures.
A modelled peak value at one elevation angle does not create a general coverage category such as regional, continental or global. Propagation, terrain, ionosphere, frequency, time, noise and the receiving station remain outside that plot. A small change in modelled peak gain may also trade against another elevation or azimuth rather than represent more total radiated power.
The two-radial PERformer geometry can deliberately skew the pattern. The question is whether the skew remains stable after the park has added a picnic table, wet soil, a shelter post and a different coax route. Rudy Severns, N6LF, published extensive elevated-radial modelling and measurement showing why radial height, asymmetry, coupling and environment deserve explicit treatment.
A symmetrical three- or four-radial layout may reduce sensitivity to those perturbations, but it is not automatically superior in every objective. If directionality is the claim, measure the installed azimuth pattern. If repeatability is the claim, repeat the deployment under controlled perturbations.
“I Made Contacts” Proves Function, Not the Headline Number
A QSO demonstrates that the complete path supported communication. It does not isolate antenna efficiency, gain, front-to-back ratio or transformer loss. Propagation and the remote station supply too many uncontrolled variables.
That does not make field operation worthless. It tells us how to design the test:
- declare the band, power, geometry, soil condition, feed-line route and choke arrangement;
- compare against a stable reference antenna with the same transmitter and measurement plane;
- switch rapidly or operate simultaneously where practical, so propagation drift is reduced;
- collect distributions rather than one best report;
- measure feed-line exterior current and transformer temperature alongside the signal result; and
- report uncertainty large enough to include calibration, site perturbation and repeatability.
For a directional claim, fixed receiving sites or a controlled field-strength range around the antenna are more useful than a mixed set of ordinary QSOs. For efficiency, a gain comparison needs a known reference and an adequate pattern or total-radiated-power method.
The Fair Reading of KJ6ER’s Work
The PERformer, Challenger and Dominator are documented portable antenna experiments. Their value is speed, reproducibility of the mechanical concept and a clear invitation to build. The documents also mix quantities that readers may interpret too broadly.
The correct response is not to dismiss the antennas. It is to keep the boundaries visible:
- SWR establishes mismatch at a plane, not radiation efficiency.
- Component loss is one term in a complete power budget.
- A counterpoise and feed-line exterior are possible radiating return paths.
- NEC predicts the declared model, not every picnic-table deployment.
- Peak gain and elevation angle do not by themselves define communication reach.
- Small claimed differences need repeatable measurements with uncertainty.
Build the antennas. Enjoy the activations. Publish the model files and measured current paths. The portable-antenna community becomes stronger when a good idea arrives with enough evidence for someone else to reproduce—and challenge—it.
Primary Technical Sources
- Greg Mihran, KJ6ER: Antennas Primer, February 2025
- Greg Mihran, KJ6ER: Challenger Halfwave Antenna, February 2025
- Greg Mihran, KJ6ER: Dominator Halfwave Antenna, February 2025
- Greg Mihran, KJ6ER: PERformer Antenna, February 2025
- Rudy Severns, N6LF: Experimental Determination of Ground-System Performance for HF Verticals, Part 1
- ARRL QST: Common-Mode Current and Common-Mode Chokes
Mini-FAQ
- Does 1.5:1 SWR mean 96% antenna efficiency? — No. It means 96% of incident power is accepted at that reference plane in the stated system. Radiation efficiency requires a separate loss and radiated-power boundary.
- Can a counterpoise be ignored because it is not called a radial? — No. If it carries RF return current, it helps determine impedance, loss and pattern regardless of its label.
- Does a 4:1 transformer prove the Challenger is more efficient? — No. The ratio may suit the measured load and reduce the required transformation, but the finished transformer and complete antenna system still need loss measurements.
- Can NEC prove the antenna’s field performance? — NEC can predict the declared model and expose trends. The installed result still depends on ground, feed-line routing, choking, nearby objects and construction.
- Do successful POTA contacts prove gain? — They prove the communication path worked. Gain needs a controlled reference, declared direction, repeated measurements and an uncertainty statement.
- Are the PERformer, Challenger and Dominator bad antennas? — That conclusion does not follow. They are practical portable concepts; the point is to keep match, component loss, radiation efficiency, gain and coverage claims separate.