Lowering Feedpoint, SWR Doesn’t Change on a 160/80 m Inverted-L EFHW
When adjusting an EFHW, many assume raising or lowering the feedpoint — e.g. from 1 m to 2 m — should shift SWR. But what if it doesn’t?
That’s usually a good sign — and it tells you something important about your ground quality.
The Setup: 160/80 m Inverted-L EFHW
- Wire length: 78–82 m
- Bands: 160 m = ½λ, 80 m = 1λ
- Feedpoint height: ~1–2 m
- Matching: 68:1 UNUN + choke
Raise or lower the feedpoint, and SWR hardly moves. Why?
It Means You Have Good Ground
A 160/80 m EFHW needs a return current path via counterpoise or coax shield, capacitively coupled to the earth. That path’s stability depends on ground conductivity:
- Good ground (loam, moist clay): stable capacitive return, low loss → feedpoint height has little SWR effect.
- Poor ground (sand, rock): unstable return, higher loss → SWR sensitive to feedpoint height, counterpoise, coax routing.
The Myth: Low Feedpoint = Poor Radiation
Unlike verticals, an EFHW’s feedpoint is at a voltage maximum and current minimum. Radiation comes from higher-current sections further along the wire. Thus:
- Raising the feedpoint has little effect on efficiency or pattern.
- If SWR is stable, a 1 m feedpoint is perfectly fine — and practical for Inverted-L installs.
What You Might Observe
| Observation | Ground Quality | Notes |
|---|---|---|
| SWR unchanged with feedpoint height | Good ground | Stable capacitive return |
| SWR shifts with feedpoint height | Poor ground | Return path unstable/lossy |
| SWR varies with rain/moisture | Moderate ground | Ground conductivity fluctuates |
Practical Tip
For 160/80 m Inverted-L EFHWs, a 1 m feedpoint is fine on decent ground. If SWR jumps with small changes, suspect poor soil and check your counterpoise and choke.
If feedpoint height changes don’t alter SWR, your ground quality is good — and your EFHW is behaving predictably.
Mini-FAQ
- Does feedpoint height affect SWR? — Not much on good ground. Stable soil conductivity keeps the return path consistent.
- Is a low feedpoint bad? — No. The EFHW feedpoint is a voltage max/current min; radiation comes from further along the wire.
- Why does poor ground cause SWR shifts? — Because unstable capacitive coupling makes the return current path lossy and variable.
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