Why Inverted-L Antennas Beat Ground Verticals on the Top Bands
and Why EFHW Inverted-L Goes Even Further
(Indicative engineering analysis) — Numbers below are typical for backyard installations with limited radials and average to poor soil. Exact values depend on soil σ/ε, geometry, height, and hardware losses.
The Controlling Variable: Ground Loss
For low HF (160/80/60/40/30 m), efficiency is dominated by ground return loss. A ground-mounted ¼-wave vertical concentrates maximum current at the base where the return path is the lossy earth–radial interface. The Inverted-L moves a significant portion of the current onto a horizontal top wire, elevating current away from soil and increasing radiation resistance Rr, which immediately reduces the fractional impact of ground loss Rg.
When an Inverted-L does not beat a ground vertical
With a broadcast-grade ground system (dense screen or ≳120 quarter-wave radials) over good soil, a ¼-wave vertical can approach very high efficiency. Over poor soil, even ≈120 radials are “better but not perfect” — residual Rg remains non-negligible.
Efficiency Equation
The single-port efficiency of the radiator + ground system is approximated by:
η = Rr / (Rr + Rg + Rc)
where Rr is radiation resistance, Rg ground loss, and Rc conductor/junction loss.
Assumptions (typical backyard): 160 m → Rg≈25 Ω, 80 m → Rg≈10 Ω, 40 m → Rg≈5 Ω, Rc≈1 Ω. Values are illustrative, not guarantees.
| Band | Topology | Assumed Rr (Ω) | Assumed (Rg+Rc) (Ω) | η = Rr/(Rr+Rg+Rc) | Relative dB |
|---|---|---|---|---|---|
| 160 m | ¼-wave vertical (base-fed) | 25 | 26 | 0.49 | −3.1 dB |
| 160 m | Inverted-L (base-fed) | 40 | 26 | 0.61 | −2.1 dB |
| 160 m | EFHW Inverted-L (λ/2, end-fed) | 2500 | 26 | 0.99 | −0.0 dB |
| 80 m | ¼-wave vertical (base-fed) | 36 | 11 | 0.77 | −1.1 dB |
| 80 m | Inverted-L (base-fed) | 45 | 11 | 0.80 | −0.9 dB |
| 80 m | EFHW Inverted-L (λ/2, end-fed) | 2500 | 11 | 0.996 | −0.0 dB |
| 40 m | ¼-wave vertical (base-fed) | 36 | 6 | 0.86 | −0.7 dB |
| 40 m | Inverted-L (base-fed) | 45 | 6 | 0.88 | −0.6 dB |
| 40 m | EFHW Inverted-L (λ/2, end-fed) | 2500 | 6 | ≈1.00 | −0.0 dB |
Takeaways — (1) Raising Rr from 25→40 Ω (Inverted-L vs base vertical on 160 m) recovers ≈1 dB. (2) Making Rr ≫ Rg (EFHW) renders ground loss almost negligible across the top bands.
Why EFHW Inverted-L Minimizes Ground Loss
- Physics: A λ/2 end-fed radiator exhibits very high feedpoint resistance (often 2–4 kΩ). With the same Rg, η → 1 because Rr ≫ Rg.
- Current placement: Current maxima are elevated along the wire span, reducing soil-proximate displacement currents.
- Practical matching: Use a high-ratio unun; our current builds use 70:1 (optimized 80/40) and 68:1 (optimized 160/80). 40/20 is under test (optimized for 40 m).
Formula View — EFHW vs Base-Fed
For identical site loss Rg:
ηvertical = Rr,¼λ / (Rr,¼λ + Rg + Rc) ηinv-L = Rr,L / (Rr,L + Rg + Rc) ηEFHW-L = Rr,½λ,end / (Rr,½λ,end + Rg + Rc) ≈ 1
Radiation & Pattern Notes (160–30 m)
- ¼-wave vertical: Low takeoff angles; efficiency hinges on the radial system.
- Inverted-L (base-fed): Retains low angles from the vertical section and adds mid/high-angle energy via the top wire — helpful for regional coverage/NVIS while keeping DX angles strong.
- EFHW Inverted-L: Similar macro pattern to a well-sited Inverted-L, but with markedly lower loss and natural multiband behavior via harmonic half-waves.
Browse engineered models — dual-band 160/80, 80/40 (and soon 40/20), plus 40 m monoband: EFHW Inverted-L Collection.
Mini-FAQ
- Does an Inverted-L always beat a vertical? — Only if the vertical lacks a broadcast-grade ground. With ≈120 full radials on good soil the gap narrows; on poor soil it still isn’t perfect.
- Why is EFHW more efficient? — Its end-feed radiation resistance is orders of magnitude higher than site losses, making Rg almost irrelevant in η.
- What transformer ratios do you use? — 70:1 for 80/40 and 68:1 for 160/80; 40/20 EFHW-L is under evaluation (40 m optimized).
- Is a tuner required? — EFHW-L designs are band-targeted via the transformer and length. A small ATU can tidy up band edges and installation-dependent shifts.
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