End-fed half-wave (EFHW)

An end-fed half-wave is a wire about a half-wavelength long on its lowest band, fed at the end through a high-ratio unun (typically 49:1, sometimes 64:1). The end of a half-wave is a high-impedance point. The transformer brings that down toward something a 50 Ω radio can live with.

On a wire cut for 40 m, the even and odd harmonics are also high-Z at the feed, so the same length is resonant-ish on 20, 15, and 10 m. “Ish” is doing work: insulation, height, and the bend in an inverted-L all move the dips. That is why you cut long and trim with an analyzer, not a laminated cut sheet from a manufacturer you do not own.

This is the default first-activation wire when you have trees or a mast and you want to skip tuner drama. When the truck is the station and you want low-angle 20–10 m, use 4WAVE. When 66 ft will not fit the AZ, use a random wire. Mast hardware and hitch mounts live on those pages and on Hardware — this chapter is the wire.

Common portable lengths

Give the idea, then measure. Do not treat these as commercial kits.

30, 17, and 12 m often sit off the harmonic ladder. A small tuner can patch them. A wild SWR on a band the wire was never meant for is a different antenna, not a moral failing.

Cut / measure: start a little long. Raise it the way you will actually use it (inverted-L at 20 ft is not the same as a flattop at 8 ft). Sweep with an analyzer at low power. Trim a few inches, sweep again. Stop when the dips you care about are in-band and the SWR is something the radio will accept without an ATU — or accept that 15 m wants a tweak and pack the tuner as a trim, not as the plan.

Counterpoise, choke, common-mode

“End-fed” does not mean “no return.” Current that goes out the wire has to come back. If you do not give it a short counterpoise, it uses the coax shield. That can work. It also means the feedline is part of the antenna, RF shows up on the radio case, and a hand on the paddle gets hot.

Do this:

1. Follow the unun maker on counterpoise length if they specify one. A short wire off the ground lug (often in the 0.05 λ neighborhood on the lowest band) is the usual field fix.
2. Put a common-mode choke (1:1 current balun, ferrite clamp kit, or a coil of coax) at the unun, not only at the radio. The goal is to stop the shield from radiating all the way to the picnic table.
3. If you still have RF in the “shack” (tingles, distorted audio, a laptop that locks up), the choke is in the wrong place or the counterpoise is missing. Fix the antenna. Do not turn the power up.

Height, inverted-L vs flattop, trees vs mast

Height and shape change the pattern more than the next 6 inches of wire.

• Flattop, low (8–20 ft): more high-angle / NVIS. Fine for close-in 40 m. Mediocre for DX on 20.
• Inverted-V on a mast: center (or a point near the unun) up, ends down. A 10 m fiberglass mast is the usual park compromise. Jackite / Sotabeams class — see Hardware and the pack list, not a second mast RTFM here.
• Inverted-L: most of the wire vertical, the rest horizontal to a tree or stake. You pick up some low-angle radiation from the vertical section. Good when you only have one support.
• Trees: a legal throw-line where the park allows it. Do not tie the far end to a monument or a protected tree. Confirm before you throw — ethics.
• Mast when trees are banned: inverted-V or inverted-L off the stick. Guy it. Flag the guys.

Higher is not always better on 40 m if your hunters are 200 miles away. It is better on 20–10 if you want skip. Deploy for the band you will actually CQ on first.

Tuner vs no tuner; SWR vs “it loads”

On the bands the wire is cut for, you should not need a tuner. An internal ATU (G90, KX2) is a trim for 15 m or a wet-wire shift. It is not a plan if 40 m is 8:1.

SWR is a measurement at the radio (or at the unun, if you put the meter there). A 1.5:1 or 2:1 dip in-band is a working EFHW. “It loads” means the tuner found a match. The tuner can match a dummy load. If the analyzer never showed a dip near the band and the tuner is doing all the work, you have a random wire with extra loss — be honest and read random wire.

IC-705 has no HF ATU. Either stay on the resonant dips or pack an external. The 4WAVE chapter has the same warning for a different antenna.

When to pick EFHW vs 9:1 random vs 4WAVE

Chooser on Antennas. Quarter-wave whip theory: Verticals.

Best default for a first park sitting with an IC-705 or KX2: 66 ft EFHW + 10 m mast, 40/20/15/10.

Safety

The feedpoint of an EFHW is a high-voltage node. Keep the unun out of face height. Do not drape the first few feet of wire across a picnic table full of people. Gloves if you are grabbing a wet unun while transmitting — better: do not.

Guy lines and throw-lines do not cross trails, playgrounds, or emergency lanes. Flag what you plant. Night packing is when civilians trip. Full leave-no-trace: Ethics.

Power: start low, sweep, then go to the park’s and the radio’s limit. A 100 W radio into a misbehaving EFHW is an RF-in-the-shack problem, not a DX solution.

Related

• Antenna chooser · Random wire · 4WAVE
• Verticals · Ethics · Hardware

Habits / gotchas / checklist (EFHW)

• ~66 ft starting point for 40 m; cut long, trim with an analyzer as hung.
• 49:1 (not a 9:1). Accidental half-wave on a 9:1 is the other chapter.
• Short counterpoise + choke. If the mic bites, the shield is the antenna — fix that before 100 W.
• Unun out of face height. First few feet of wire not across a picnic table of civilians.
• 15 m may want a tuner trim. 30/17/12 often sit off the harmonic ladder.
• IC-705: no HF ATU — stay on the dips or pack an external.
• Trees banned → mast inverted-V, guys flagged. Monument tie-off is a no.