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 120 mm cores (not the standard FT240 size) and proper windings. Losses include core heating and RF dissipation, especially at high turns ratios and lower frequencies.

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 ground-mounted verticals or inverted-Ls with unbalanced current paths, the EFHW-Inverted-L tends to concentrate current in the wire rather than the soil.

This means:

• Less energy lost in radial/soil interaction
• Radiation dominated by the vertical element (especially at DX angles)
• Comparable or better efficiency than a poorly-radialed vertical — up until transformer losses dominate

Once transformer losses exceed ~12–15%, the advantage is negated and a vertical with a proper radial system will outperform an EFHW in both ERP and usable bandwidth.

Flat-Top and Sloper EFHWs: A Low-Loss Alternative

For 40/20 m dual-band or monoband 20 m setups, a horizontal flattop or sloper EFHW performs well when the feedpoint is placed above 10 m. At this height, radiation clears ground clutter and favors moderate-angle takeoff.

• On 20 m, monoband EFHWs have very low transformer losses when matched with a 49:1 on 43 material.
• A sloper or horizontal EFHW on 40 m is ideal for NVIS operation and regional work.
• More height = lower takeoff angle and better DX potential.

Common Misconception: YouTube Loss Tests

Many misleading videos online present transformer loss measurements using flawed setups:

• Dummy loads instead of real antennas
• No proper choking of common-mode currents
• Ignoring standing waves
• Assuming perfect line match
• Confusing average vs. peak power

These errors skew results. Realistic evaluation requires forward and reflected power measurement under real antenna load, with proper choking and observation of core heating.

Summary

EFHWs are not inherently poor performers — but their efficiency is fundamentally limited by the transformer, especially below 14 MHz. On higher bands (17–10 m), transformer losses often reach 30% (≈1.5 dB), making them less attractive than off-center fed dipoles, multiband verticals, or resonant monoband antennas.

Understanding these limits helps operators avoid disappointment and design more efficient stations.

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