EFHW Verticals on 10m, 12m, and 15m
Why Feeding a Half-Wave from the Bottom is a Bad Idea
End-Fed Half-Wave (EFHW) antennas are popular for multiband use, but many hams try to deploy them vertically for the higher bands — 10 m, 12 m, 15 m — thinking they’ve built a compact DX powerhouse.
Unfortunately, what they’ve often built is a power-hungry radiator with serious inefficiencies.
Feedpoint Position: Voltage Maximum, Current Minimum
In any EFHW, the end of the wire is a high-voltage, low-current point. Radiation, however, is driven by current. So when you install the feedpoint at the base, near ground level, the system suffers:
- Most current is ~¼λ up the wire, typically 2.5–3.5 m for these bands.
- That means most radiation occurs well above the base.
- Low feedpoint height → poor ground clearance → ground loss + reduced far-field efficiency.
By contrast, a monoband 1/4-wave vertical with raised radials has maximum current at the base, right where it counts.
Transformer Losses: Real and Measurable
To match the EFHW's 2.5–3.5 kΩ feedpoint to 50 Ω coax, a 49:1 or 64:1 transformer is used. These introduce core losses, especially at higher frequencies.
Even well-designed EFHW transformers using proper ferrite (e.g. Fair-Rite #43 or #61 and yes even #52) suffer measurable loss at the high-voltage end:
| Band | Transformer Loss | Power Lost |
|---|---|---|
| 15 m | ~1.4 dB | ≈ 28% |
| 12 m | ~1.6 dB | ≈ 32% |
| 10 m | ~2.0 dB+ | ≈ 37%+ |
On 10 meters, over a third of your power never reaches the antenna — it dies as heat in the core.
How High is "Efficient"?
You might think: "I'll just mount the EFHW vertical higher."
That helps — a lot. But here's how high you'd need to go:
| Feedpoint Height | Estimated EFHW Efficiency |
|---|---|
| Ground-mounted | <40% |
| 2 m above ground | ~55% |
| 4–5 m | ~70–75% |
| ≥8 m | 80–90% (comparable to raised 1/4λ) |
To match the efficiency of a simple 1/4-wave monoband vertical with 4 raised radials, your EFHW would need to be:
- At least 8 meters off the ground
- Fed through a high-voltage choke
- Using a low-loss transformer, ideally air-wound or multi-core
By then, you’ve built something far more complex than a monoband vertical… and still not necessarily better.
A Real-World Comparison: 15m Band
| Parameter | EFHW Vertical (3m base) | 1/4λ Vertical + 4x Raised Radials |
|---|---|---|
| Height to Max Current | ~2.7 m | Base |
| Transformer Loss | ~1.4 dB (28%) | None |
| Total Radiating Efficiency | ~55–60% | >90% |
| Radiation Angle | Similar (~20°) | Similar (~20°) |
| Pattern | Omni | Omni |
Verdict: The monoband vertical wins in every key metric — with fewer losses, simpler feedpoint, and better power transfer.
Conclusion
EFHW verticals for 10, 12, and 15 meters are:
- Convenient to install,
- Useful in multiband, low-power portable setups,
- But inefficient for serious DX work unless mounted very high (≥8 m feedpoint) with a low-loss transformer and perfect common-mode suppression.
If you want to get every watt to the ionosphere on these bands, a simple monoband 1/4-wave vertical with 4 raised radials outperforms every time — with less cost, less heat, and more signal.
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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.