Low Feedpoint, Low Height: a Terminated Antenna Is the Smarter Choice

Updated December 25, 2025.

Mount any HF wire antenna low to the ground and you quickly run into a frustrating reality: the antenna stops behaving like it did in the book, the SWR moves around with weather and surroundings, and “good” SWR does not automatically mean “good” radiation. In that specific situation (a low feedpoint and/or low installation height), a terminated antenna is often the better tool, precisely because it trades peak efficiency for stability and predictability.

Why low height is such a problem for HF wire antennas

When a horizontal (or mostly-horizontal) HF antenna is installed close to ground, its near field couples strongly into the real world:

• Soil (not a perfect conductor, and it changes with moisture)
• Nearby objects (fences, gutters, rebar, sheds, rails, wiring)
• Vegetation (seasonal changes, wet leaves, growth)
• Your feed system (coax, mast, station ground, “accidental” return paths)

That coupling changes the antenna’s effective impedance and current distribution. In practice it can mean:

• Resonant antennas detune: SWR shifts after rain, snow, or just a wet lawn.
• Matching becomes “fussy”: good today, annoying tomorrow.
• Pattern becomes less predictable: more energy is soaked up locally and less is launched usefully.

What termination changes

A terminated antenna adds a non-inductive resistor at a strategic point in the structure. That resistor is not there to “improve SWR by magic.” It is there to absorb energy that would otherwise reflect and create strong standing waves.

This single idea has two big consequences:

• Fewer standing-wave peaks and nulls
  The resistor damps sharp resonances (reduces Q). With resonances tamed, the feedpoint impedance doesn’t swing wildly with frequency or small environmental changes.
• More traveling-wave behavior
  Instead of energy bouncing back and forth along the wire (narrow “peaky” resonances), the antenna behaves more like a traveling-wave system over a wider range.

Why termination helps specifically when installed low

A low antenna is an “environment antenna.” Its impedance, losses, and current distribution are constantly pushed around by ground and nearby objects. A high-Q resonant design will show every one of those changes as SWR drift, tuner surprises, and unstable behavior.

A terminated design is deliberately less reactive and less peaky. Because it is already damped:

• Height changes cause smaller SWR swings (less dramatic resonance movement).
• Soil moisture changes cause less detuning drama.
• Nearby-object coupling tends to have less impact on match stability.

The price you pay is real: some power is intentionally dissipated in the termination resistor as heat. But at low height, the environment often steals efficiency anyway. Termination turns “uncontrolled loss + instability” into a known, bounded compromise that stays matchable and repeatable.

Terminated antennas that make sense at low height

Half-rhombic: controlled reflections, consistent direction

A half-rhombic is a traveling-wave style wire antenna that uses termination to control reflections. The philosophy is simple: control reflections, accept some loss, gain predictability. That mindset is exactly what you want when height and surroundings are not ideal.

Terminated folded dipole (T2FD / TFD / WBFD): stable SWR across a wide range

The terminated folded dipole family exists because people needed one antenna that works “well enough” across a wide HF range and stays matchable without constant retuning. The termination damps sharp resonances, which is exactly what helps when the antenna is surrounded by wet ground, fences, roofs, and other coupling.

Practical note: many T2FD/TFD/WBFD variants present a higher feed impedance than a simple 50 Ω antenna, so a transformer is typically used to land in the coax world while keeping SWR manageable.

TermiLoop: terminated stability packaged into a compact end-fed loop

The RF.Guru TermiLoop applies the same terminated traveling-wave principle, but in a compact folded loop geometry designed for real installs where resonant wires get “touchy.” The loop perimeter is typically 26–28 m, yet the practical flattop span stays under about 13–14 m thanks to the fold, with the two legs held at a controlled 20 cm spacing using spreaders. That geometry is not cosmetic: it’s what helps preserve a smooth, repeatable current distribution and a flatter impedance curve.

The defining detail is termination placement. The TermiLoop uses an approximately 500 Ω non-inductive termination placed at a high-voltage, low-current node. This is intentional engineering: termination still damps reflections (so SWR stays smooth), but placing it where current is low means less RF is wasted as heat compared with classic terminated dipole approaches where the resistor sits where current is still significant. Net result: you keep the stability benefit while preserving more radiating current, especially on the low bands.

Feeding is designed to be “tuner-friendly by default.” The TermiLoop uses a 4:1 UNUN at the feedpoint and keeps the feedpoint impedance in a range that modern tuners handle easily. In a representative 6 m-high flattop installation, measured SWR stays under about 3:1 across 160–6 m, which is exactly what you want when your installation height is limited and you refuse to chase tuning surprises after every weather change. Fine-tuning is possible via the far-end clamp/connector, but trimming is typically optional.

Feedline behavior is part of the system: for stable results, route the coax away from the loop at a right angle for the first meters, avoid long parallel runs alongside metalwork, and use deliberate common-mode control. A practical approach is a first choke placed around 0.05λ from the feedpoint (about 8 m as a broadband reference), and a second choke at the shack entry, with enough coax between them to avoid feedline resonance-driven weirdness.

The real trade: stable behavior vs peak efficiency

• A resonant antenna (especially up high) can be more efficient and stronger on a specific band.
• A terminated antenna is usually less efficient, because some energy is intentionally dissipated.
• At low mounting heights, the environment often “takes” dB anyway via ground absorption, detuning, and feedline interaction.

So if you’re forced into a low installation, termination is often the more appropriate engineering choice because it gives you: consistent match behavior, fewer tuning surprises after weather changes, reliable multi-band usability, and predictable general coverage.

Practical guidance for builders

Respect the termination resistor

• Use a non-inductive resistor (or a purpose-built non-inductive termination assembly).
• Give it real power handling margin (heat is the point, so plan for it).
• Weatherproof it properly and keep it away from flammable mounting points.

Use the right feed transformation

• Wideband terminated dipole-style antennas often want a transformer to land cleanly in a 50 Ω coax system.
• Don’t treat the transformer as a “band-aid” ... treat it as part of the antenna design.

Control common-mode early (especially with low feedpoints)

• Add a proper choke where it matters so the coax doesn’t become the “other half” of the antenna. This preserves the stability you’re trying to achieve and reduces unwanted noise pickup.
• Rule of thumb: a first choke around 0.05λ from the feedpoint is a good starting point, then a second choke at the shack entry. Keep coax routing sensible: leave the antenna at a right angle first, and avoid long parallel runs near metal.

Note for QRP operators: “terminated = inefficient” is only half the story

Yes, a terminated antenna burns some RF power in a resistor. That’s the cost of stable wideband behavior. But the leap many people make (“therefore it must be worse than a low EFHW”) is not automatically true, especially when the EFHW is also mounted low and the system is being dragged around by ground coupling and feedline effects.

Why “low SWR” can be a bad sign at low height

• SWR only describes the match. It does not tell you how much power is radiated.
• Loss (ground loss, coupling loss, feedline loss) can make SWR look “better” while performance gets worse.

A low EFHW can waste power too ... just invisibly

• At low height, ground and nearby objects can act like a resistive load in the near field.
• If the coax becomes the return path, common-mode current can heat loss mechanisms and create unstable behavior.

Why termination can be the better QRP outcome when you’re forced low

• Stability keeps your rig honest: many radios reduce power as SWR rises; stable match helps you keep full output.
• Less “tuner surprise”: damped resonances mean fewer dramatic shifts after weather changes.
• Less feedline weirdness: controlled current behavior plus choking helps prevent the coax from becoming part of the antenna.

One-line summary: At low height, the EFHW can still waste power ... just invisibly. Termination wastes some power visibly, but often saves you from larger uncontrolled losses.

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