More Hexbeam Power Without a Choke? Think Again.

“More power without a choke” is an appealing result. The radio's output goes up. The transmatch seems happier. Surely the choke was holding the antenna back? Not so fast. A transmitter responds to the load at its own terminals; the beam's job is to produce the wanted field in the wanted direction. Those are connected, but they are not the same measurement.

My objection is to using accidental feed-line participation as the cure for a matching problem. A coax-fed directional array should have an intentional feed arrangement, not an extra radiator whose useful length happens to be the distance to the shack. If removing a choke changes the load substantially, find out which current path changed and repair the match with that boundary under control.

Why the Radio May Deliver More Power

Removing a choke can alter the exterior-current path, antenna input impedance and the impedance presented through the coax. That can change tuner settings or loss and, in a transmitter with mismatch protection, the amount of power reduction. It can also disturb a connector or remove a lossy, damaged or poorly designed assembly. The power indication alone cannot identify which mechanism occurred.

The radio does not detect “Hexbeam capacitance” as an antenna category. Its output stage and protection circuit respond to their actual electrical conditions. The thresholds and behaviour belong to that transmitter; there is no universal rule that LDMOS finals dislike every capacitive load or that a bent antenna must make them distort.

The Yaesu FT-710 manual makes a useful distinction: the internal tuner adjusts the load presented at the radio end of the cable, not the antenna's feedpoint SWR. A happier tuner is therefore evidence about its matching job, not a certificate for the radiation pattern.

Record whether the meter reports forward, reflected or net power, and where it sits. At a correctly measured common reference plane, net travelling-wave power is forward minus reflected power. A radio's display upstream of a tuner and a sensor at the antenna do not report interchangeable quantities.

Removing the Choke Changes the System Boundary

In the intended coaxial mode, current on the centre conductor returns on the inner surface of the shield. A different current can flow on the shield exterior, closing through the antenna, mast, station chassis, protective bonding, other cables, earth and distributed capacitance.

A choke around the complete coax adds complex impedance to that exterior-current path while ideally disturbing the internal differential mode only slightly. Remove it and the coax exterior may carry more current. The feed line can then receive and radiate as part of the installed structure, and the fields from that path combine vectorially with the fields from the Hexbeam elements.

Significant added exterior current makes the effective radiating structure different. In one direction its field may reinforce; in another it may cancel or fill a null. Front-to-back ratio, polarization, elevation response and azimuth response can change. That does not guarantee a wrecked pattern or lower total efficiency. It means an improvement toward one station could be a new lobe rather than a better Hexbeam.

That is why I want the coax excluded from the intended array as far as practical. The benefit is control: element geometry and orientation should set the useful beam, instead of an undocumented cable route adding a field that changes when the installation changes. A choke reduces one coupling path; it neither creates a perfect wall nor eliminates every interaction with the mast and surroundings.

Roy Lewallen, W7EL, separates these currents explicitly in “Baluns: What They Do and How They Do It”: the intended current returns on the inside of the coax shield, while significant outside-shield current makes the feed line part of the radiating or receiving structure. He also makes the crucial boundary clear—if the imbalance current is already small, a balun or choke may produce little useful change.

A Hexbeam Is Not Automatically Capacitive

A Hexbeam uses bent wire elements and mutual coupling to fit a directional array onto a compact support. That geometry does not force every finished antenna to present negative reactance. The feed-point impedance depends on the complete element lengths and spacing, conductor diameter, frequency, feed arrangement, nearby objects, mast, feed line and construction tolerances.

Steve Hunt, G3TXQ's original broadband-Hexbeam analysis treats driver dimensions, reflector resonance and end spacing as different design controls. His multiband matching analysis also shows that inter-element feed connections transform the load. The complete design matters; bent wire by itself is not a diagnosis.

Measure the complex impedance R + jX at a declared reference plane. If the analyzer is at the shack end, the feed line transforms the antenna impedance and adds loss. Moving, adding or removing a choke can change the external current path and therefore the measured impedance. Calling one trace the “true Hexbeam impedance” is meaningful only after the system boundary and common-mode condition are fixed.

On transmit, a different mismatch can change accepted power, tuner loss and transmitter foldback. Higher indicated transmitter output is not automatically higher radiated power in the wanted direction. On receive, the same passive linear structure is reciprocal, but receiver noise, overload and local coupling still determine whether a pattern change improves usable SNR.

Fix the Matching Problem Without Losing the Boundary

Start with the actual antenna instructions and operating bands. The KIO Hexbeam assembly manual recommends a 1:1 common-mode choke and checks of the element connections, wire routing and height-dependent SWR. That is an antenna maker treating feed-line isolation as part of the installation—not as an optional gain penalty. Follow the instructions for the specific antenna rather than transplanting its dimensions or ratings to another build.

I separate the problem into three checks:

If the choked antenna presents an unsuitable load, correct the antenna/feed arrangement or use a suitable matching network within the maker's limits. If a correctly specified choke makes little difference because exterior current is already small, acknowledge that result. My preference is an intentional current boundary, not a claim that every additional ferrite must improve every installation.

Receive Changes Are a Useful Second Clue

Removing the choke may also raise a wanted station, local noise or both. Common-mode pickup is only one possible path: noise can arrive through the intended antenna, finite shield transfer, mast and other cables. ITU-R P.372-17 distinguishes those reception boundaries. A higher S-meter reading is no more conclusive than a higher transmitter-power indication.

For a receive comparison, freeze every receiver setting you can: frequency, mode, resolution or audio bandwidth, preamplifier, attenuation, RF gain, AGC, detector, averaging and display reference. Record the I/Q stream when possible so both configurations can be processed identically.

Use a stable wanted source. A laboratory generator feeding a remote test antenna is better than a fading DX signal. A stable ground-wave beacon can be useful when its level and path are repeatable. If the on-air source varies, switch rapidly and repeat enough cycles to estimate the drift.

Measure the noise in a nearby signal-free interval using the same equivalent noise bandwidth. If the reported “signal” bin contains signal plus noise, subtract powers in linear units before calculating SNR:

Do not subtract dB readings directly to remove noise from a combined signal-plus-noise value. A calibrated receiver or spectrum analyzer is preferable; an S-meter can still support a relative experiment only after its steps, AGC behaviour and repeatability have been characterized.

Clamp Current Is a Separate Record

A characterized current probe around the complete coax measures the net signed RF current through its aperture at that cross-section. Because the intended centre-conductor and inner-shield currents substantially cancel, the reading is normally a useful estimate of exterior-shield current—provided the complete cable is enclosed, the probe is calibrated and no other return conductor shares the aperture.

Record the probe transfer impedance at the test frequency, receiver termination, bandwidth, detector, cable corrections, noise floor and uncertainty. Mark several positions along the coax without rerouting it. Exterior current can form a standing-wave distribution; one convenient point may be a current minimum.

A lower clamp reading after installing the choke shows that net cable current fell at that plane. It does not by itself prove less total radiation, better pattern, lower local-noise pickup or higher SNR. Those are correlated measurements, not synonyms.

Run a Real A/B/A Test

Use two comparisons for two different questions. First keep the commanded drive and declared tuner state fixed to see how the transmitter responds to the changed load; retuned operation is a separate, logged case. Then, within safe equipment limits, compare fields at equal net accepted power at the same defined antenna-system boundary. The first records what the station delivers. The second separates directional antenna behaviour from simply applying more power.

Repeat A/B/A or A/B/B/A cycles and record drift. Do not connect an analyzer to an energized transmitter, touch an active feedpoint or adjust a tower installation while transmitting. Follow the antenna and radio makers' limits, use safe low-power checks first, and never remove protective bonding to make an RF reading look better.

To test a pattern claim, one station is not enough. Use a controlled antenna range, a model validated against installed current and geometry, or multiple stable sources over azimuth and elevation. IEEE 149-2021 treats antenna pattern, gain, impedance, instrumentation, site errors and uncertainty as a complete measurement problem—not as an S-meter anecdote.

Interpret the Combination, Not One Number

A choke can be valuable because it makes the installed system more predictable, reduces an unwanted coupling path or restores the intended pattern. It can also be unnecessary at one frequency, poorly placed, lossy, resonant in the wrong place or bypassed by another cable. “Always fit one” and “it is louder without one” are both incomplete engineering specifications.

Keep the Beam; Fix the Feed System

I would not remove a suitable choke merely to make the power display rise. I would find why the transmitter prefers the unchoked load, then make the intended Hexbeam and feed arrangement work together. Correct an assembly fault, an unsuitable match or a bad choke. Do not let a convenient SWR improvement quietly substitute an undocumented beam-plus-coax antenna for the array you intended to install.

The extra watts may be real, and one path may genuinely get stronger. The engineering advantage I want is more specific: useful directional performance from a controlled current system, with the station cable doing its feed-line job. A suitable choke helps maintain that boundary; it is not supposed to be a dummy load for wanted differential power. Output, accepted power, pattern, receive SNR and unwanted cable current tell different parts of the story.

If you have a documented transmitter-output, impedance and cable-current comparison with the original state restored, send it to RF.Guru. That can explain the surprise instead of merely applauding the wattmeter.

Primary and authoritative technical sources

• KIO Hexbeam assembly manual, page 10—assembly checks, operating-height SWR and the common-mode choke recommendation.
• Steve Hunt, G3TXQ: Broadband Hexbeam in depth and multiband matching—geometry, coupling and feed-interconnection effects.
• Yaesu FT-710 operating manual, printed page 48—the station-side boundary of an internal tuner.
• Roy Lewallen, W7EL: “Baluns: What They Do and How They Do It”—coax inner/outer currents, imbalance-current paths and pattern effects.
• ARRL QST: “Common-Mode Chokes”—whole-coax clamp measurement, position dependence and installed before/after verification.
• ITU-R P.372-17: Radio noise—external noise sources and the boundary between antenna/feeder reception and other cable or screening paths.
• ITU-T K.37 (01/2024)—current EMC guidance for source verification, cabling, screening, filtering, bonding and interference mitigation.
• IEEE 149-2021—antenna pattern, gain, impedance, instrumentation, site-error and uncertainty measurement practice.
• BIPM/JCGM Guides in Metrology—measurement models, repeatability, correlation and uncertainty reporting.

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