An EFHW Still Needs a Return Path — 5% λ Isn’t Enough

“Since an EFHW is voltage-fed, the return current is much less and ground losses are minimal. So a small counterpoise about 5% of a wavelength is usually all that's needed.”

That statement sounds tidy—but it leaves out the physics that make end-fed half-wave antennas actually work. Let’s unpack what’s really going on with EFHWs, return current, and ground losses.

An EFHW Still Needs a Return Path

“End-fed” doesn’t mean “one wire only.” The current that leaves the transformer secondary must return somewhere—Kirchhoff’s law still applies. If you don’t define that return (with a counterpoise or equivalent), the outside of your coax becomes it, carrying common-mode current and becoming part of the antenna. That’s why unmanaged EFHWs often cause RF-in-the-shack and pattern distortion.

“Voltage-Fed” Doesn’t Mean Negligible Current or Loss

At the end of a resonant half-wave, impedance is high (a few kΩ), so current is lower than a 50 Ω center feed—but not zero. Example: 100 W into 2.5 kΩ gives about 0.2 A RMS at ~500 V RMS. That same 0.2 A flows through the return path (counterpoise and/or coax). It’s enough to cause heating, loss, or noise pickup if the path runs near lossy ground or inside the shack.

Being “voltage-fed” only means the feedpoint has high impedance, not that return current or losses are small.

Ground Losses Are More Than Just Return Current

Even if the return current is modest, ground losses aren’t automatically minimal. Loss happens wherever the antenna’s electric field couples into lossy surroundings such as soil, walls, or metal structures. At the high-voltage end of an EFHW, the E-field intensity is strongest—so proximity to ground or nearby objects increases dielectric and ground losses dramatically.

Voltage-fed antennas are inherently more prone to such losses because their feedpoint operates at high voltage and low current. That’s why they need space to breathe: mounting them higher above ground and well away from conductive surfaces greatly reduces those losses. The “voltage-fed” nature doesn’t make them efficient—it makes their efficiency more dependent on installation height and surroundings.

What a Short Counterpoise Really Does

The often-quoted “5 % λ” rule can help define the RF reference and reduce coax current, but it’s not a magic fix. On some bands it helps a lot; on others it’s almost invisible. Even with a counterpoise, some common-mode current usually remains unless a choke is added. And because an EFHW is multiband, one fixed-length counterpoise may resonate on one band but not on another.

Best-Practice Setup

• Provide a defined return path. Add a counterpoise around 0.05–0.15 λ on the lowest band. Keep it off the ground and separated from the coax.
• Use a real common-mode choke. Place one at the transformer, and optionally another 0.05–0.15 λ down the coax. Aim for several kΩ choking impedance using #31 or #43 ferrite on a 2.4″ core with adequate turns.
• Mind feedline routing. Keep the first few meters of coax away from and not parallel to the radiator. If the coax doubles as a counterpoise, choke it again where it enters the shack.
• Expect pattern sensitivity. If RF flows on the feedline, the entire geometry defines your pattern and noise pickup. Managing return current makes your antenna predictable.

Quick Numbers

• Typical EFHW load: 2–3 kΩ, matched via 49:1 – 64:1 transformer.
• Feedpoint values at 100 W: I ≈ 0.2 A RMS, V ≈ 500 V RMS → same 0.2 A circulates in the return path.
• Approx. 5 % λ counterpoise lengths: 80 m ≈ 4.3 m · 40 m ≈ 2.1 m · 20 m ≈ 1.1 m · 10 m ≈ 0.54 m.

(Treat these as starting points—verify with real current measurements, not just SWR.)

Bottom Line

• The claim “return current is much less, so ground losses are minimal and 5 % λ is all you need” is an oversimplification.
• An EFHW always needs a defined return. Without one, your coax becomes it—with all the usual side effects.
• Voltage-fed antennas are more sensitive to ground proximity—height and clearance directly affect efficiency.
• A short counterpoise helps, but proper choking and feedline geometry make the real difference.

Measure, don’t assume: a clamp-on RF ammeter on your coax or counterpoise tells the real story.

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