Why Your EFHW Is Eating Your Signal – And the EFOC Isn’t
If you think all end-fed antennas are created equal, think again. The EFOC (End-Fed Off-Center) antennas from RF.Guru consistently outperform traditional EFHW (End-Fed Half Wave) antennas – and not just in theory.
Let's break it down.
Transformer Losses: EFOC vs EFHW
Traditional EFHW antennas rely on high-ratio impedance transformers (typically 49:1 or 64:1). These are voltage transformers that often require many turns of wire, which translates into high insertion loss and heating. At 100W, it's not uncommon to lose up to 1.5–2 dB in the transformer alone on some bands.
By contrast, the EFOC uses a 4:1 UNUN. While still a voltage-fed design, the lower turns ratio and improved impedance transformation result in minimal core heating and negligible insertion losses (typically <0.1 dB).
⚠️ Not all EFHWs are created equally
At RF.Guru, we do not offer EFHW antennas for bands below 20 meters. The transformer losses are too severe to justify the use. We also do not use broadband ferrite cores across 80–10 meters: no such material exists that performs efficiently over that range. Instead, we select ferrite materials tailored to the specific frequency bands our monoband EFHWs operate in.We do not use compensation capacitors at all, as they merely mask SWR and do nothing to reduce transformer losses.The comparisons below refer to typical EFHW designs found commercially or in DIY kits using type 43 or 52 ferrites — often promoted as "multiband" or "broadband" but inherently lossy.
Total Losses: Transformer + Feedline
Even when both antennas are usable across 80-10 meters, the EFHW suffers both high transformer losses and coax losses on non-resonant bands. Worse yet: on bands below 17m, the apparent low SWR is often misleading due to a tuning capacitor that masks the mismatch – but does nothing to reduce transformer loss. These are the worst offenders.
Realistic Efficiency Comparison @ 100W Input
| Band | EFHW SWR | EFHW TX Loss (dB) | EFHW Coax Loss (dB) | EFHW Total Loss | EFOC SWR | EFOC Loss (Total dB) |
|---|---|---|---|---|---|---|
| 80m | 2.5:1 | 1.8 | 0.25 | 2.05 dB | 2.0:1 | 0.21 |
| 60m | 5.0:1 | 1.3 | 0.62 | 1.92 dB | 2.2:1 | 0.23 |
| 40m | 2.0:1 | 0.7 | 0.21 | 0.91 dB | 1.8:1 | 0.19 |
| 30m | 3.5:1 | 1.2 | 0.45 | 1.65 dB | 3.5:1 | 0.45 |
| 20m | 1.5:1 | 1.0 | 0.17 | 1.17 dB | 1.4:1 | 0.16 |
| 17m | 4.0:1 | 0.9 | 0.55 | 1.45 dB | 2.9:1 | 0.28 |
| 15m* | 2.8:1 | 1.2 | 0.29 | 1.49 dB | 2.0:1 | 0.19 |
| 12m* | 6.0:1 | 1.4 | 0.77 | 2.17 dB | 3.2:1 | 0.35 |
| 10m* | 1.8:1 | 1.1 | 0.20 | 1.30 dB | 1.6:1 | 0.18 |
*Note: EFHW SWR on 15–10m without a compensation capacitor is typically worse than shown. Many published figures underestimate the mismatch, and real-world transformer efficiency on these bands is lower due to high voltage stress.
Also: Below 17m, transformer losses dominate regardless of whether the SWR appears low. The capacitor masks SWR but cannot fix the poor efficiency, especially on 80m, 60m, and 40m. These losses are real, measurable, and often exceed 50% of input power.
Also note: While the EFOC has low-SWR dips on resonant bands, 30m, 17m, and 12m are typically higher. These are still under 3:1 in most cases, but 30m may occasionally reach 3.5:1, depending on installation.
EFOC Advantage: Real-World Efficiency
- Better matching = lower feedline loss
- Lower transformer ratio = higher efficiency
- Smaller footprint = fewer compromises
- Same usability = all bands from 80-10m
- And a closer physical relationship to λ, resulting in more efficient radiation.
In real-world use, especially with 20–30 meters of coax, the EFOC’s consistent SWR below 3:1 across all bands ensures you’re putting your power where it counts: into the air.
Read more:
Stop burning watts. Ditch the EFHW. Switch to EFOC.
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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.