Efficient Monoband EFHWs on 17–10 m

Most hams believe an EFHW must use a ferrite transformer such as a 49:1. For monoband EFHWs, this is completely unnecessary — and often inefficient. A half-wave wire naturally sits at 3–5 kΩ at the feedpoint, and you can match it far more efficiently with:

• A 600 Ω quarter-wave ladder-line transformer (end-fed Zepp / J-pole family), or
• A compact, high-Q L-match directly at the feedpoint.

Both methods eliminate ferrite losses and preserve the radiator’s full performance.

Cutting the Radiator (Monoband)

Start with a clean half-wave radiator. Trim for resonance before installing any matching network.

Band	Center Freq	Starting Length (½-wave, VF≈0.95)
17 m	18.10 MHz	7.87 m (25.8 ft)
15 m	21.20 MHz	6.72 m (22.0 ft)
12 m	24.95 MHz	5.71 m (18.7 ft)
10 m	28.40 MHz	5.01 m (16.45 ft)

Matching Method A — 600 Ω Quarter-Wave Transformer

A 600 Ω open-wire quarter-wave stub is one of the lowest-loss matching systems possible. It is extremely predictable and handles high power with ease.

¼-Wave Section Lengths (VF≈0.98)

Band	Length (m)	Length (ft)
17 m	4.06 m	13.31 ft
15 m	3.47 m	11.37 ft
12 m	2.94 m	9.66 ft
10 m	2.59 m	8.49 ft

Tap Points — Clear Explanation

At the bottom of the 600 Ω ladder-line stub, the two conductors are physically connected together. This point is called the short, and it is the reference for all tap measurements.

From that short, you simply measure upward along the ladder line. At a certain height above the short, you connect your coax feedline across the two conductors. That connection point is the tap. This is the point where the impedance has transformed to approximately 50 Ω.

Example: “Tap = 0.66 m” means: Measure 0.66 m (2.17 ft) upward from the shorted bottom of the stub — that’s where the coax connects.

Updated Tap-Point Table (Metric + Imperial)

Distances are measured upward from the physical short at the bottom of the stub.

Band	Start Tap (m)	Start Tap (ft/in)	Adjustment Range (m)	Adjustment Range (ft/in)
17 m	0.66 m	2.17 ft (26 in)	0.58–0.75 m	1.90–2.46 ft (22.8–29.5 in)
15 m	0.57 m	1.87 ft (22.4 in)	0.50–0.64 m	1.64–2.10 ft (19.7–25.2 in)
12 m	0.48 m	1.57 ft (18.9 in)	0.42–0.54 m	1.38–1.77 ft (16.5–21.3 in)
10 m	0.42 m	1.38 ft (16.5 in)	0.37–0.48 m	1.21–1.57 ft (14.5–18.9 in)

How to Adjust the Tap

• Move tap upward (farther from the short) → impedance increases.
• Move tap downward (closer to the short) → impedance decreases.
• Find the position with the broadest, cleanest SWR dip around 1:1–1.5:1.
• Small movements of 5–10 cm (2–4 in) can be significant.
• Install a 1:1 choke directly at the tap — without it, coax common-mode alters the match.

Matching Method B — Open-Ended Zepp-Style Feed

A purist implementation of the classic airship end-fed Zepp. One conductor becomes the radiator; the other ends open at the top.

• Option 1: Feed coax at the bottom with a small series air-variable (10–70 pF).
• Option 2: Link-coupler (2–3 turns) inductively coupling into the stub.

This method provides extremely low loss and very high voltage excitation of the radiator.

Matching Method C — Classic L-Match (Feedpoint Box)

An L-match treats the EFHW feedpoint as ~3.5 kΩ and matches it to 50 Ω with a series inductor and shunt capacitor.

Band	Series L (µH)	Shunt C (pF)
17 m	3.65	≈21
15 m	3.12	≈17.8
12 m	2.65	≈15.1
10 m	2.33	≈13.3

Use air-core coils and ≥2–3 kV capacitors for 100 W PEP. Add a 1–2 m counterpoise and a choke at the box.

Why This Beats a 49:1 Transformer

• No ferrite heating or loss.
• True half-wave resonance yields maximum EIRP.
• No bandwidth compression from reactive ferrite behavior.
• Transformerless matching puts RF on the wire, not in the core.

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