The End-Fed Half-Wave (EFHW) Antenna

The End-Fed Half-Wave (EFHW) antenna has become one of the most popular and versatile wire antennas in amateur radio — and for good reason. It offers high efficiency, multi-band operation, and can be deployed almost anywhere with minimal equipment.

From compact home installations to lightweight field setups, the EFHW is the perfect “grab-and-go” antenna for operators who value flexibility without compromising performance.

Understanding the EFHW Concept

As its name suggests, the End-Fed Half-Wave antenna is a wire that’s resonant at one-half wavelength of its fundamental frequency and its harmonics. Feeding it at the end, rather than the center like a dipole, makes installation far easier in restricted spaces.

Because it’s a half-wave at resonance, its impedance at the feedpoint is very high — often around 2,500–3,000 ohms. To make it compatible with standard 50-ohm coax, a 49:1 or 64:1 impedance transformer (unun) is used. The result is a simple, resonant, multi-band antenna that often works without an external tuner on harmonic bands.

Impedance and Matching Explained

Many beginners are surprised to learn why an EFHW needs a 49:1 unun. The feedpoint of a half-wave end-fed wire presents very high impedance, and directly connecting 50-ohm coax would result in a poor match and high SWR. The unun transforms the high impedance down to a level your radio can handle. At higher power, the voltage at the feedpoint can reach several hundred volts, so using a properly rated transformer is essential for both performance and safety.

Improving 10m Performance with a Capacitor

While a 49:1 unun works well across 40–20 m, some operators find the SWR on 10 m slightly higher than desired. Adding a small capacitor (typically 10–30 pF) across the secondary winding of the unun can help fine-tune the match for 10 m without affecting lower bands. This creates a small resonant “tweak” that improves SWR and reduces power lost in the coax.

• Start with 10 pF and adjust upwards in small increments.
• Use a high-voltage ceramic capacitor rated for at least 1 kV RF to handle the feedpoint voltage.
• Ensure the capacitor is soldered securely and insulated inside the unun enclosure to prevent arcing.
• This modification is optional; many EFHW users operate 10 m without it, but it can help if you want a smoother match.

Why the EFHW Works So Well

The magic of the EFHW lies in its harmonic resonance. A 40-meter half-wave wire is also a full wave on 20m, 3/2 on 15m, and 2 waves on 10m — making it naturally multi-band without traps, coils, or switches.

When deployed properly, it provides excellent radiation efficiency and a reasonably consistent impedance across multiple HF bands. Many operators find the EFHW outperforms multi-band verticals and even dipoles at similar heights, especially for portable or stealth use.

The radiation pattern varies with height and configuration — low heights favor NVIS coverage for regional contacts, while higher or sloped installations produce low-angle lobes ideal for DX. Low-angle DX is generally best achieved with near-vertical or sloper configurations, while horizontal low installations favor NVIS.

Building an EFHW Antenna

Constructing your own EFHW is straightforward and rewarding. The key component is the transformer, which must handle both high voltage and impedance transformation efficiently.

• Transformer: 49:1 unun (2 primary turns, 14 secondary turns) wound on an FT240-43 toroid; adjust winding for higher bands or power to prevent saturation
• Radiating Wire: 10m (33 ft) of 18-22 AWG copper or enamel wire (for 20m version)
• Enclosure: Weatherproof box with SO-239 connector
• Counterpoise: A short counterpoise or coax shield can serve as a return path; performance varies by installation
• Support: Fiberglass pole, tree, or mast

Once built, trimming the radiator length and adding a small tuning stub can perfect the resonance on your target band.

Practical Installation Tips

EFHW antennas are flexible, but a few tips improve performance:

• Mount the feedpoint high for low-angle DX or keep it lower for NVIS.
• Use insulated supports to prevent arcing at high feedpoint voltage.
• Run the coax away from the operator to reduce RF on the feedline.
• Slopers and inverted-Ls can provide a balance between horizontal and vertical polarization depending on your contact goals.
• Even in tight spaces like attics or balconies, routing the wire creatively can maintain good performance without violating HOA rules.

Deployment Options

EFHW antennas can be installed in several configurations, depending on your operating environment:

1. Sloper: Feedpoint low, end elevated — excellent for DX coverage.
2. Horizontal: Ideal for NVIS and regional communications.
3. Inverted-L: Combines vertical and horizontal polarization.
4. Vertical: Mount vertically for low-angle radiation and omnidirectional pattern.

Each layout offers a slightly different pattern, so experimentation is encouraged. Even in HOA or limited-space environments, the EFHW’s end-fed nature allows creative routing — along fences, attics, or balcony railings.

Maintenance and Longevity Tips

To keep your EFHW performing well for years:

• Choose UV-resistant wire if outdoors; stranded copper or enamel is best.
• Protect the unun in a weatherproof enclosure; use silicone or sealant around connectors.
• Inspect connections and feedline for corrosion periodically.
• Check for frayed wire or insulation damage, especially in windy areas.

Real-World Results and Performance

Many operators report efficient EFHW operation on WSPR and FT8. On 20m, a properly matched EFHW can achieve low take-off angles near 15°, making it suitable for long-distance work with modest power levels.

• 5-watt FT8 contacts from North America to Europe and South America reported by some operators
• 1.2–1.5:1 SWR across 40–10m on harmonic bands with a well-matched unun
• Consistent SNR comparable to dipoles at similar heights
• Compact enough for field operations and stealth home installs