Lowering SWR on 160/80 m Inverted-L EFHW by Sloping the Wire
If your 160/80 m EFHW shows high SWR on 80 m (or even 160 m) despite using a 68:1 transformer, one surprisingly effective trick is to slope the wire.
The Problem
A ~79–82 m EFHW behaves as:
- Half-wave on 160 m: impedance ≈ 2.5–4.5 kΩ
- Full-wave on 80 m: impedance ≈ 6–10 kΩ+
That full-wave effect pushes 80 m end impedance beyond the transformer’s comfort zone, leaving SWR stuck at ~2.5–3.5 or higher.
The Solution: Add Slope
Sloping the horizontal leg of your Inverted L downward lowers the high-voltage end, which:
- Reduces voltage maximum
- Improves capacitive coupling to ground
- Shifts current/voltage distribution
➡ Impedance often drops by 1000–2000 Ω, depending on geometry and soil.
Typical Effects
| Wire Shape | 80 m Impedance Estimate |
|---|---|
| Fully horizontal end | 7–10 kΩ |
| Horizontal with downward slope | 4.5–6.5 kΩ |
| Slope + lower height | 3–5 kΩ |
This brings impedance into the sweet spot for a 68:1 UNUN.
Impact on 160 m
- Slight redistribution of current/voltage
- Better return path stability over poor ground
- SWR improvement modest but noticeable
Radiation Performance
No significant change:
- Horizontal part radiates mostly NVIS on 160/80 m
- Sloping doesn’t alter high-angle pattern
- You keep NVIS utility while improving match
Conclusion
Sloping your EFHW Inverted L is a simple way to:
- Reduce impedance on 80 m
- Slightly improve 160 m SWR
- Keep NVIS coverage intact
Letting your EFHW sag or slope improves matchability without hurting pattern or efficiency.
Mini-FAQ
- Why does sloping lower impedance? — It reduces voltage max and increases capacitive ground coupling.
- Will it change the pattern? — No. High-angle NVIS dominance remains the same.
- Does it help 160 m? — A little. Improvement is modest, but return path stability is better.
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