End Fed Off Center Antennas: Energy Efficiency and DX capabilities
End‑Fed Off‑Center Antennas: Energy Efficiency and DX Capabilities
EFOC29 (80–10 m)
Flat Top @ 10 m Height
- 80 m: Moderate efficiency (~78%) limited by ground and transformer loss; strong NVIS, weak low‑angle DX at this height.
- 40–10 m: Efficiency rises (~88–96%) as radiation resistance increases and ground loss falls.
- 12 m: Near‑resonant segment → high radiation resistance, low loss, excellent DX; EFHW8010 is compromised on 12 m by comparison.
- 10 m: Slightly less effective but usable; matching typically cleaner than a same‑length EFHW.
| Band | Height / λ | Low‑Angle (<15°) | DX Suitability | NVIS |
|---|---|---|---|---|
| 80 m | 0.125 λ | Weak | Poor* | Excellent |
| 40 m | 0.25 λ | Moderate | Moderate* | Strong |
| 30 m | 0.34 λ | Moderate | Moderate* | Weak |
| 20 m | 0.50 λ | Strong | Excellent | — |
| 17 m | 0.67 λ | Strong | Excellent | — |
| 15 m | 0.89 λ | Very strong | Excellent | — |
| 12 m | 1.11 λ | Very strong | Excellent | — |
| 10 m | 1.30 λ | Moderate | Moderate | — |
* To improve DX on 80/40/30 m, raise the antenna to ≥ 18 m AGL.
At 6 m height, the EFOC29 is more NVIS‑oriented on 80/40 m while keeping strong DX on 20/17/12 m.
| Feature | 10 m Height (Flat Top) | 6 m Height (Flat Top) |
|---|---|---|
| 80 m | Moderate eff., good NVIS | Moderate eff., strong NVIS |
| 40 m | Moderate DX, strong NVIS | Weak DX, strong NVIS |
| 30 m | Moderate DX | Moderate DX |
| 20 m | Excellent DX | Moderate DX |
| 12 m | High eff., excellent DX | High eff., excellent DX |
| 10 m | Moderate DX; usable | Usable DX; slightly more compromised |
EFOC17 (40–10 m)
Flat Top @ 10 m Height
- 40 m: ~85% efficiency at 0.25 λ; decent low‑angle DX with strong NVIS component.
- 30–10 m: Efficiency improves (~90–97%); patterns favor DX as height grows in wavelengths.
| Band | Height / λ | Low‑Angle (<15°) | DX Suitability | NVIS |
|---|---|---|---|---|
| 40 m | 0.25 λ | Moderate | Moderate* | Strong |
| 30 m | 0.33 λ | Moderate | Moderate* | Moderate |
| 20 m | 0.50 λ | Strong | Excellent | — |
| 17 m | 0.58 λ | Strong | Excellent | — |
| 15 m | 0.75 λ | Very strong | Excellent | — |
| 12 m | 0.91 λ | Very strong | Excellent | — |
| 10 m | 1.13 λ | Strong | Excellent | — |
* For stronger DX on 40/30 m, raise to ≥ 15 m AGL.
| Feature | 10 m Height | 6 m Height |
|---|---|---|
| 40 m | Moderate DX, strong NVIS | Weak DX, strong NVIS |
| 30 m | Moderate DX | Weak DX |
| 20 m | Excellent DX | Moderate DX |
| 17/15 m | Excellent DX | Good–Excellent DX |
| 12/10 m | High eff., excellent DX | High eff., excellent DX |
EFOC8 (20–10 m)
Flat Top @ 5 m Height
- 20 m: Near‑resonant wire; at 0.25 λ (~5 m) you’ll see moderate low‑angle radiation with high efficiency.
- 17–10 m: Efficiency continues to improve; excellent DX capability despite the lower physical height as electrical height grows.
| Band | Height / λ | Low‑Angle (<15°) | DX Suitability | NVIS |
|---|---|---|---|---|
| 20 m | 0.25 λ | Moderate | Moderate | Weak |
| 17 m | 0.31 λ | Moderate | Good | — |
| 15 m | 0.40 λ | Strong | Excellent | — |
| 12 m | 0.48 λ | Strong | Excellent | — |
| 10 m | 0.56 λ | Very strong | Excellent | — |
As a rule: more electrical height (h/λ) yields improved low‑angle DX. Raising the flat‑top from 5–6 m to 10 m and beyond systematically strengthens 20–10 m DX while 80/40 m transition from NVIS toward DX only when heights ≥ 0.5 λ are practical.
Mini‑FAQ
- Why does EFOC often beat EFHW? — Off‑center voltage feed improves impedance behavior and current placement, reducing loss and smoothing patterns.
- Is 10 m AGL enough for DX? — Yes for 20–10 m; for 80/40 m DX, aim for ≥ 0.5 λ (≈ 10–20 m higher than typical garden masts).
- Why is 12 m so good on EFOC29? — Near‑resonant segment delivers high radiation resistance and low loss → excellent DX.
- Does transformer loss matter? — Yes. High‑quality cores/windings and proper choking preserve efficiency, especially on low bands.
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