EFHW Transformer Losses: A Reality Check
End-Fed Half-Wave (EFHW) antennas have grown wildly popular in recent years due to their simplicity and band coverage. But like many trends in amateur radio, popularity doesn’t always align with performance. The often-overlooked reality is that EFHW antennas rely heavily on a high-impedance transformer, and that transformer can become a major source of power loss.
Transformer Losses by Configuration
Below is a realistic loss estimation for several commonly used EFHW transformer configurations. These values assume large 120mm cores (not the standard FT240 size) and proper windings. Losses include core heating and RF dissipation, especially at high turns ratios and lower frequencies.
| Transformer | Material | Bands | Loss (%) | Loss (dB) | Notes |
|---|---|---|---|---|---|
| 68:1 EFHW | 77 | 160/80m | 8–12% | 0.36–0.57 | Used in dual-band 160/80m Inverted-L EFHW |
| 70:1 EFHW | 77 | 80/40m | 6–10% | 0.26–0.46 | Dual-band 80/40m, also used in Inverted-L |
| 49:1 EFHW | 43 | 40/20m | 4–7% | 0.18–0.31 | Typical multiband transformer |
| 49:1 EFHW (Mono) | 43 | 20m only | 2–3% | 0.09–0.13 | Monoband transformer optimized for efficiency |
Why Inverted-L EFHWs Can Be (Relatively) Efficient
While EFHWs are often criticized for transformer losses, the Inverted-L configuration with a significant vertical radiator shifts much of the energy directly into the antenna, reducing the dependence on a lossy radial system. Compared to classic ground-mounted verticals or inverted-Ls with unbalanced current paths, the EFHW-Inverted-L tends to concentrate current in the wire, rather than the ground.
This means:
- Less energy lost in radial/soil interaction
- Radiation is dominated by the vertical element (especially for DX angles)
- The EFHW becomes as efficient or more efficient than a poorly-radialed vertical — until transformer losses dominate
However, once transformer losses exceed ~12–15%, this advantage is negated, and traditional verticals with proper radial systems start to outperform EFHWs, both in ERP and bandwidth.
Flat-Top and Sloper EFHWs: A Low-Loss Alternative
For 40/20 m dual-band or monoband 20 m setups, the horizontal flattop or sloper EFHW is a solid performer when the feedpoint is placed above 10 meters. At this height, radiation is largely above ground clutter and favors moderate-angle takeoff for regional and some DX communication.
- On 20 m, monoband EFHWs exhibit very low transformer losses when matched properly with a 49:1 on 43 material.
- A sloper or horizontal EFHW on 40 m is especially well-suited for NVIS operation, ideal for short to medium range contacts.
- As height increases, takeoff angle lowers — improving DX potential.
These configurations are often more efficient and mechanically easier to deploy than verticals or multi-element arrays in limited-space environments.
Common Misconception: YouTube Loss Measurements
There are many misleading videos online that present transformer loss measurements using flawed setups:
- Dummy loads instead of real antennas
- No proper choking of common-mode return currents
- Ignoring standing waves
- Assuming ideal transmission line match
- Misinterpreting average vs. peak power readings
These issues skew the results drastically. Realistic loss evaluation requires measuring both forward and reflected power under real antenna load, using properly choked lines and observing heating effects in the core.
We cover this topic in detail in another article in our RF.Guru Knowledge Base:
The Back-to-Back EFHW UNUN Transformer Measurement Myth
Summary
EFHWs are not inherently bad — but their efficiency is bounded by the transformer, especially below 14 MHz. For high bands (17–10m), transformer losses often exceed 30% (1.5 dB), which makes them a poor choice compared to off-center fed dipoles, multiband verticals, or resonant monoband antennas.
Understanding and communicating this nuance is essential to avoid disappointment and make informed design decisions.
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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.