Inverted L Antenna Spacing Guide for HF Performance

Inverted L Antenna Spacing Guide for HF Performance

An Inverted L combines a vertical and horizontal wire section, providing useful NVIS and DX performance depending on layout. But performance drops quickly if the wire is too close to conductive structures like aluminum masts, metal sheds, solar panels, or house walls with rebar. Close spacing can cause detuning, coupling, pattern distortion, and RF feedback issues.

Minimum Distance Recommendations

Keep these clearances between the radiating wire and conductive objects (masts, walls, gutters, etc.):

160 m band (1.8 MHz)

• Horizontal clearance: 5–10 m
• Vertical clearance: ≥ 2–3 m

80 m band (3.5 MHz)

• Horizontal clearance: 3–5 m
• Vertical clearance: ≥ 1.5–2 m

40 m band (7 MHz)

• Horizontal clearance: 2–3 m
• Vertical clearance: ≥ 1.5 m

Even conductive objects within ~0.05 λ can detune the antenna, especially near the vertical section where RF current is highest.

Why Spacing Matters

The vertical leg carries high RF current, making it very sensitive to nearby conductors. Interaction can:

• Shift resonance, making matching unpredictable
• Distort the intended low-angle DX pattern
• Create unwanted common-mode currents and noise pickup
• Cause RF feedback in the shack

Construction Tips

• Use a fiberglass or other non-metallic mast for the vertical leg.
• Avoid routing wire parallel and close to aluminum masts or gutters.
• Keep separation from solar panels and reinforced concrete walls.
• If limited on space, angle the vertical wire slightly outward to maintain clearance.
• Add a high-quality common-mode choke at the feedpoint.

Conclusion

Inverted L antennas are versatile and efficient, but spacing is critical. Following clearance guidelines preserves match stability, pattern consistency, and minimizes coupling or feedback problems. When properly sited, the Inverted L delivers strong NVIS and DX coverage across HF bands.

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