Antenna Performance: Height, Ground Loss, and Resonance

Many operators wonder why otherwise good antennas underperform when mounted too low or with poor ground arrangements. The answer is in how ground loss interacts with current distribution and resonance. Below, we compare common antenna types at different heights and explain how ground proximity changes efficiency and take-off angles.

Resonant Antennas

Flattop EFHW & Dipoles

For a fundamental half-wave wire, both dipoles and EFHWs have their main current maximum near the middle of the radiating wire. The EFHW feedpoint is near a voltage maximum and current minimum; the end-feed arrangement changes the feed impedance and matching requirements, not the basic current maximum location on the fundamental. On harmonic bands, an EFHW develops multiple current maxima and minima along the wire, so ground proximity should be judged by where those current lobes fall.

• Height relation: Aim for ≥ 0.2–0.25 λ for efficient radiation and stable impedance.
• Ground-loss sensitivity: High, especially when current maxima are close to average or poor soil.
• Pattern impact: Low installs favor NVIS on lower bands; DX low-angle energy is reduced.

Verticals (¼-Wave)

Quarter-wave verticals use the ground system as the return path, so losses there dominate total efficiency.

• Current distribution: Maximum at the base → most sensitive to ground quality.
• Ground system: For ground-mounted, use many short radials (16 minimal 120 best); for elevated only 3-4 are sufficient, use tuned radials to cut loss dramatically.
• Height relation: Raising the feed with properly tuned radials is far more effective than simply making the mast taller.

Resonant Loops (Delta/Quad)

• Height relation: Prefer ≥ 0.2 λ for best take-off; still more tolerant of low heights than dipoles.
• Ground-loss sensitivity: Moderate to low due to the closed current path.

Non-Resonant Antennas

Doublets (Non-Resonant Dipoles)

• Feed: Ladder line + balanced tuner. Current distribution and feedpoint impedance vary with band.
• Height relation: Same physics: keep current maxima off the dirt → target ≥ 0.2 λ.
• Ground-loss sensitivity: High when used too low.

EFOC (End-Fed Off-Center, e.g., 29 m with 4:1)

• Behavior: Semi-resonant on multiple bands; less extreme impedance swings than random wires.
• Height relation: More tolerant than EFHW, yet still affected by ground proximity.
• Ground-loss sensitivity: Moderate.

Rybakoff / 6 m Non-Resonant Vertical

• Current distribution: Often dominated by common-mode currents on the feedline.
• Ground-loss sensitivity: Very high without radials/counterpoise.
• Height relation: Elevation helps, but proper choking and a return path are mandatory for usable efficiency.

Low-Mounted Non-Resonant Loops

• Current distribution: Diffuse and distributed, so no single hot spot near the ground.
• Ground-loss sensitivity: Low–moderate; can function at 0.05 λ for NVIS, albeit with reduced efficiency.

Summary Table

Antenna Type	Resonant?	Current Peak	Height Requirement	Ground-Loss Sensitivity	Efficiency Potential
EFHW / Dipole	Yes	Near mid-wire on fundamental; multiple lobes on harmonics	> 0.2–0.25 λ	High	High if elevated
Vertical (¼-wave)	Yes	Base	Ground level OK w/ radials	Very High	Radial-dependent
Resonant Loop	Yes	Distributed	> 0.2 λ	Moderate	High
Doublet	No	Varies	> 0.2 λ	High	Medium–High
EFOC	Semi	Variable / off-center	> 0.15 λ	Moderate	Medium–High
Rybakoff Vertical	No	Near base + CM	> 0.15 λ + choke	Very High	Low–Medium
Low Delta Loop	No	Distributed	0.05–0.15 λ	Low	Medium–High

Key Takeaways

• Ground loss scales with current near earth. Keep current peaks away from the ground.
• Elevate resonant antennas. ≥ 0.2 λ separates peaks from lossy soil and stabilizes impedance.
• Verticals need radials. Ground or elevated tuned radials are the efficiency lever.
• Loops are forgiving. Closed geometry and distributed current reduce loss sensitivity.
• Non-resonant designs work, but require height and solid matching (balanced tuners, proper chokes).

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