Lowering SWR on 160/80 m Inverted-L EFHW by Sloping the Wire
If your 160/80 m EFHW has a high SWR on 80 m (or even 160 m) and you’re already using a 68:1 transformer, one surprisingly effective trick is to introduce a slope into the wire.
The Problem
A 79–82 m EFHW is:
- A half-wave on 160 m → typical impedance: 2.5–4.5 kΩ
- A full-wave on 80 m → typical impedance: 6–10 kΩ (or more)
That full-wave condition on 80 m causes very high end-impedance — often above what your transformer can comfortably match. The result? A persistent SWR around 2.5–3.5 or higher on 80 m.
The Solution: Slope the Wire
By sloping the horizontal leg of your Inverted-L antenna downward (even gradually), you reduce the height of the high-voltage end of the wire. This:
- Lowers the voltage maximum slightly
- Increases capacitive coupling to ground
- Alters the standing wave and current distribution
➡ This results in a modest but useful drop in impedance — often a reduction of 1000–2000 Ω or more, 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 the impedance closer to the optimal match zone of a 68:1 UNUN.
And on 160 m?
Even though 160 m sees the antenna as a half-wave, the slope can still have a slight effect:
- It shifts the current and voltage distribution modestly
- On poor ground, it can help stabilize the return path
- You might see a mild improvement in SWR, but it’s less dramatic than on 80 m
Does Slope Affect Radiation Performance?
No, not significantly.
- The horizontal part on 160 and 80 m already radiates mostly NVIS
- A slope doesn’t reduce that — the radiating angle remains steep (near 80°)
- The antenna continues to favor high-angle local/regional coverage
So you get better matchability without harming pattern or efficiency
Conclusion
Sloping the wire in your 160/80 m Inverted-L EFHW is a simple and effective way to:
- Reduce impedance on 80 m
- Slightly improve SWR on 160 m
- Retain full NVIS functionality
For better matching and a more manageable SWR curve, don’t hesitate to let your EFHW sag or slope — it works in your favor.
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Written by Joeri Van Dooren, ON6URE – RF, electronics and software engineer, complex platform and antenna designer. Founder of RF.Guru. An expert in active and passive antennas, high-power RF transformers, and custom RF solutions, he has also engineered telecom and broadcast hardware, including set-top boxes, transcoders, and E1/T1 switchboards. His expertise spans high-power RF, embedded systems, digital signal processing, and complex software platforms, driving innovation in both amateur and professional communications industries.