End-Fed Half-Wave Antenna: Build, Theory, and Why It's So Popular

The EFHW has become the default wire antenna recommendation in ham radio and I understand why: multi-band coverage from a single wire with one support point and no tuner needed on most harmonic bands.

I resisted the hype for a year ("it's just a random wire with marketing" — I was wrong) then built one for $35 and immediately retired my fan dipole. Three years later it's still my primary HF antenna.

Why It Works

A half-wave wire fed at its END has very high impedance at the feedpoint — roughly 2000-5000 ohms depending on height and surroundings. Your radio wants 50 ohms. A matching transformer (49:1 unun) steps that down to approximately 50 ohms.

The magic: a wire that's a half-wave on 40m is a full wave on 20m, 1.5 waves on 15m, and 2 waves on 10m. These harmonic relationships mean SWR stays low on ALL those bands without retuning.

One wire → four bands → no tuner.

The Advantages Over a Dipole

Single support point. A dipole needs two elevated supports spread apart. An EFHW needs one high point — the far end can be at ground level or anywhere convenient. The feedpoint is at the low end (near your radio/shack).

For someone with one tall tree: game-changing. For portable ops throwing a line over one branch: perfect.

Multi-band. A single 40m dipole works on 40m (and kinda on 15m with a tuner). A 40m EFHW works on 40m, 20m, 15m, and 10m without a tuner.

Feedpoint at ground level. Coax run is zero length in some installations — the transformer sits at your shack wall, the wire runs up and away. No coax loss.

The Disadvantages (Honest)

Common-mode current. The outer shield of your coax becomes part of the antenna unless you choke it. The transformer needs a return path: a short counterpoise wire (about 0.05 wavelength on the lowest band) or the coax shield itself. Put a choke behind the counterpoise or near the radio, never right at the feedpoint with no counterpoise, or the antenna will not match. Without control of the coax current: RF in the shack, computer interference, weird SWR readings.

Noise. EFHWs are noisier on receive than dipoles in some installations because the feedline coupling picks up local noise. The choke helps but doesn't fully eliminate this.

Not a true resonant antenna on every band. The harmonic relationship isn't perfect — real-world SWR on 15m and 10m is usually 1.5-2.5:1 rather than the ideal 1:1. Still within most radios' tolerance, but not the flat match of a resonant dipole on its design frequency.

The 30m/17m/12m gap. WARC bands aren't harmonically related to 40m. The EFHW presents high SWR on 30m, 17m, and 12m. You need a tuner for those bands.

Building the Transformer (49:1 Unun)

The matching transformer is the critical component. You can buy one ($40-80 from MyAntennas, EARCHI, QRPGuys) or build one for $15-20.

Materials

• FT240-43 toroid core ($8-12)
• 18-20 AWG enameled copper wire (about 8 feet for the winding; thinner wire such as 26 AWG is only for small QRP cores)
• SO-239 connector
• Small enclosure (junction box or 3D-printed)
• 100-150 pF capacitor rated 1 kV or more (optional, across the 50 ohm primary; improves the high-band match)

Winding

The standard design: 3 turns primary, 21 turns secondary on the FT240-43 — a 7:1 turns ratio, which squares to the 49:1 impedance ratio.

1. Wind 21 turns of wire evenly around the toroid (secondary — high impedance side)
2. Wind 3 turns over the first few turns of the secondary (primary — 50 ohm side)
3. Connect primary to SO-239 center and ground
4. Connect secondary to antenna wire terminal and ground
5. Optionally solder a 100-150 pF capacitor across the primary, directly between the SO-239 center pin and ground. It offsets the winding's leakage inductance and improves the match on the high bands.

There's a ratio debate in the community (49:1 vs 64:1 vs other ratios). 49:1 works well for most installations. Don't overthink it.

The Wire

For a 40m half-wave: about 66 feet (a half-wave is roughly 468 / 7.15 MHz; the exact length depends on wire gauge, height, and surroundings). Start at 66 feet and trim.

Wire type: 22-26 AWG for portable (lightweight). 14-18 AWG for permanent (stronger, lower loss). Stranded copper is best for antennas that move in wind.

I use 22 AWG Teflon-coated stranded for portable. 14 AWG stranded THHN for the permanent home antenna.

The Counterpoise

This is where people argue endlessly.

A short counterpoise wire (6-12 feet) connected to the ground terminal of the transformer serves as the "other half" of the antenna system. It carries the return current that the coax shield would otherwise handle.

My approach: ~8 feet of wire laid on the ground or draped. This works consistently for me. A common rule is about 0.05λ on the lowest band. With no counterpoise wire, the coax shield acts as the counterpoise, which only works if there is no choke at the feedpoint.

Try 8 feet first. If SWR is high: experiment with length. If it's fine: leave it.

Installation Options

Sloper (Most Common)

High point at 30-40 feet (tree branch, pole). Wire slopes down to the transformer near the ground. Feedpoint at the low end.

This is my home installation: transformer at the shack wall, wire goes up at 45° to a tree 50 feet away, apex at 35 feet. Works great. Easy to install.

Inverted-L

Wire goes vertical from the transformer for 15-20 feet, then horizontal for the remainder. Good when your support point isn't directly above the feedpoint.

Horizontal

Wire runs horizontally between two supports. Transformer at one end. Requires two elevated points but one can be lower than the other.

Portable (Over a Branch)

Throw line over a branch. Pull wire up. Transformer hangs at chest height. Radio connects directly. My POTA setup — 5-minute deployment.

Tuning

Hook up a NanoVNA or antenna analyzer. Check SWR on 40m, 20m, 15m, 10m.

• 40m high? Wire is too long (trim) or too short (add wire, or adjust counterpoise)
• 20m and above high? Probably common-mode issue — add/improve your feedline choke
• All bands high? Transformer issue, bad connection, or wire touching metal/ground

Most EFHWs tune to under 2:1 on all four bands with minimal adjustment.

Commercial Options

Don't want to build? Fine choices:

• MyAntennas EFHW-8010 (~$120): Covers 80m-10m. Well-built transformer. Popular.
• MFJ-1982HP (~$70): Budget option. 40m EFHW with connector.
• QRPGuys End-Fed (~$30 kit): Simple kit, good documentation.

But honestly — the DIY version performs identically for half the price. The transformer is the only complex part, and it's 30 minutes of winding wire around a donut.

Why It Won

The EFHW dominates portable operating because it solves the "one tree" problem. In a park, on a summit, in a backyard with limited supports — one elevated point plus a wire gives you four bands.

The dipole purists will argue that a dipole is more efficient, less noisy, and better-behaved. They're not wrong (mostly). But the installation flexibility of the EFHW wins in real-world situations where you can't always have two perfectly-spaced supports at ideal height.

Perfect is the enemy of on-the-air.