Random Wire & End-Fed Antennas

Contents

Section	Topic
1	About this volume
2	Geometry & theory — why end-feeding works at all
3	Random wire — non-resonant length + 9:1 UNUN + tuner
4	End-fed half-wave (EFHW) — resonant length + 49:1 / 64:1 UNUN
5	Long wire — multiple-wavelength designs
6	Sloper and inverted-L — geometric variants
7	Feedpoint impedance, UNUN selection, counterpoise length
8	Radiation pattern
9	Frequency response & SWR curve
10	Best-case use
11	Worst-case use
12	Power handling — and the harmonic-radiation question
13	DIY build — a 40 ft EFHW for 40/20/15/10 m
14	Commercial buys
15	Companion gear
16	Common gotchas and myths
17	Resources

---

1. About this volume

End-fed wires are the single-most-popular HF antenna of the post-2010 amateur era — and for good reason. The combination of a resonant length of wire and a small ferrite-toroid transformer that converts ~2450 Ω at the wire’s voltage-max end down to 50 Ω in one step gives you a “single end-support, one feedline, no center insulator, no radial field” antenna that covers four bands at usable SWR without a tuner. The end-fed half-wave (EFHW) is what you reach for when you want to deploy a real HF station in 90 seconds from a backpack, or when an HOA-restricted lot demands a stealth installation that doesn’t require visible center support. The random-wire-plus-9:1 variant is the all-band RX antenna for any SDR.

This volume covers the family in two parts: resonant end-fed designs (the EFHW and its harmonics — §4), and non-resonant end-fed designs (random wire, long wire, sloper, inverted-L — §3, §5, §6). The dividing line is the transformer ratio at the feedpoint: resonant antennas feed at ~2450 Ω and use a 49:1 (sometimes 64:1) UNUN to step down to 50 Ω; non-resonant antennas feed at ~200–1000 Ω and use a 9:1 UNUN plus a tuner to finish the match.

The UNUN — unbalanced-to-unbalanced impedance transformer, distinct from the BALUN of Vol 6 §3 — is the load-bearing component in every antenna in this volume. Its construction is detailed in Vol 16 §6, and the typical failure mode (core saturation under sustained TX) is what separates the $30 commercial EFHWs from the $300 ones. This volume references those details and treats the UNUN as a known black box where convenient.

Sibling to this volume: Vol 8 (Fixed verticals) — verticals also “feed against ground” and share some of the same physics, but they’re vertical conductors with mandatory radial systems; this volume’s antennas are horizontal (or near-horizontal) wires that can operate without a serious radial system. The two families overlap at the inverted-L (a vertical + horizontal hybrid that uses an end-fed feed point at the base) and at the sloper (a tipped vertical or tipped end-fed half-wave).

2. Geometry & theory — why end-feeding works at all

2.1 The voltage-max end of a half-wave

A half-wave dipole, treated as a standing-wave structure, has current maximum at the center and voltage maximum at the ends. Feeding the dipole at the center sees 73 Ω (low Z, high current); feeding it at the end sees ~2450 Ω (high Z, low current). The numbers are reciprocally related — total power transferred is the same, but the form of the energy (current vs voltage) differs dramatically.

A center-fed dipole’s 73 Ω feedpoint is naturally close to 50 Ω coax and needs only a 1:1 BALUN. An end-fed half-wave’s 2450 Ω feedpoint needs a 49:1 transformer ((50/2450) = 1/49 ratio) to match 50 Ω. That ratio drives the entire end-fed family.

   Half-wave dipole, voltage and current standing waves:

   V_peak  ╱╲                              ╱╲   V_peak
          ╱  ╲                            ╱  ╲
         ╱    ╲                          ╱    ╲
        ╱      ╲                        ╱      ╲
   ────●────────●═══════════════════════●────────●────  ← antenna wire
                  ╲                  ╱
                    ╲              ╱  current peak
                      ╲          ╱
                        ╲      ╱
                          ╲  ╱
                            ●
                       I_peak (at center)
                       Z = 73 Ω

   At the ends: V high, I low → Z very high (~2450 Ω)
   At the center: V low, I high → Z low (73 Ω)

2.2 Why end-feeding is mechanically easier

A center-fed dipole needs three things at the center: a strain-relief mechanism, a coax-shield connection point, and a current BALUN box. All three add weight and complexity at the geometric middle of the antenna, where it’s hardest to support.

An end-fed antenna moves all of those concerns to one end — typically the end nearest the operator. The far end is a single insulator on a halyard. The near end carries the UNUN, the coax connection, and a small counterpoise wire. Mechanically: one heavy fitting at the operator end, one light fitting at the far end.

For a backpack-portable installation, this is a massive simplification:

• Walking into the field with a dipole: carry the wire, two end insulators, a center insulator with BALUN, two halyard lines, plus the coax.
• Walking in with an EFHW: carry the wire, one end insulator, the UNUN with built-in coax connector, one halyard line.

The EFHW kit fits in the side pocket of a daypack. The dipole kit requires careful packing.

2.3 The counterpoise question

A center-fed dipole is electrically self-contained: the two λ/4 halves provide each other’s RF return path through the BALUN. An end-fed antenna has no such symmetry — one end is the radiator, the other end is “where the operator stands.” The coax shield, the operator’s body, and any nearby ground all become potential RF return paths, and which one carries the current depends on geometry and is rarely what the operator wants.

The fix: a counterpoise wire at the UNUN’s ground side. A short wire (typically 5–10% of the radiator’s length) provides a deliberate, controlled RF return path that beats the alternatives (coax shield, operator body). With a properly-sized counterpoise, the coax shield is electrically a “feedline” again rather than “part of the antenna.”

Some commercial EFHW designs claim “no counterpoise needed” — they’re partly right (the antenna works without one) and partly wrong (it works better with one). The difference is typically 3–5 dB on receive and 0.5–2 dB on transmit; the counterpoise is the cheapest improvement available.

3. Random wire — non-resonant length + 9:1 UNUN + tuner

3.1 The “good random” length problem

A random wire — any wire not cut for resonance at any specific band — presents a wide range of feedpoint impedances across HF. At some frequencies the wire is near-resonant and Z is high; at others it’s anti-resonant and Z is low; on the bands in between, it’s somewhere reactive. The match presented to a 50 Ω feedline is wildly variable across HF.

The trick that makes “random wire + tuner” work: the 9:1 UNUN transforms the typical 200–500 Ω feedpoint impedance into a 22–55 Ω range that a typical antenna tuner can handle. Without the 9:1, the tuner sees impedances ranging from 20 Ω to 5000 Ω across the bands — beyond most tuners’ match range. With the 9:1, the range compresses to ~5 Ω to 500 Ω, which any tuner handles.

The “good random” rule is: avoid wire lengths that are integer multiples of a half-wavelength at any operating frequency. At a half-wave length, the feedpoint is at a voltage maximum (very high Z) — the 9:1 can’t tame that, and the tuner sees thousands of ohms.

Recommended “good random” lengths that work well across all of HF (3.5–30 MHz):

Length (feet)	Length (m)	Why it works
29 ft	8.8 m	Not λ/2 on any HF band; clean across 80–10 m
41 ft	12.5 m	Classic “good random”; 80–10 m
53 ft	16.2 m	Slightly longer, more capture area
67 ft	20.4 m	Edges close to 1λ at 14 MHz — caution
84 ft	25.6 m	Long random; needs more counterpoise
124 ft	37.8 m	Very long; for 80m DX

The 41-foot random wire is the canonical recommended length — short enough to fit on most lots, long enough for solid 80m–10m coverage, and at no integer-λ/2 multiple of any amateur band.

3.2 The 9:1 UNUN

A 9:1 UNUN is a transmission-line transformer that transforms 50 Ω at the coax side to ~450 Ω at the antenna side (or 9× any other impedance at the antenna side to its coax-side equivalent). The construction is typically a trifilar winding on a ferrite toroid:

Toroid	Mix	Power	Frequency range	Cost
FT240-43	43	200 W SSB / 100 W CW	1.8–30 MHz	$15 (toroid + wire)
FT240-31	31	500 W SSB / 300 W CW	1.8–30 MHz	$18
FT240-52	52	500 W SSB	1.8–30 MHz	$25
T200-2	iron powder (red)	RX-only	1–60 MHz	$5

The Mix-43 ferrite is the standard for amateur low-power EFHW/random-wire UNUNs because its high loss at HF damps any tendency for the transformer to resonate, giving a flatter response across the band. Mix-31 has lower loss and better high-power handling; iron powder (T200-2) is the receive-only choice (very low loss but core saturation under sub-100W transmit).

Winding: 3-wire trifilar, twisted at 4 turns per inch, wound through the toroid 7–9 turns depending on the target frequency range and power level. See Vol 16 §11 for full instructions and the trifilar-winding shortcut tools.

3.3 The tuner — mandatory for transmit

A random wire + 9:1 UNUN does not present a clean 1:1 SWR on any band — the 9:1 brings the wide-Z range into tuner-reach, but a tuner is still required for transmit. Without one, the rig sees 2:1 to 5:1 SWR across the bands and refuses to output full power.

For receive-only use (SDR + random wire), the tuner is unnecessary. Most SDRs (HackRF, RTL-SDR, Airspy) tolerate 2–5:1 SWR happily for receive; the noise figure and sensitivity loss is minimal.

For transmit-capable use, pair the random wire with a wide-range tuner: LDG Z-100Plus, MFJ-993B, Palstar AT2K, or the built-in tuner of modern transceivers (Yaesu FT-991A, Icom IC-7300 — these handle ~3:1 internally; beyond that you need an external tuner).

3.4 The random-wire’s niche

Three use cases dominate:

• SDR all-band receive: a 41 ft random wire + a $15 9:1 UNUN + 50 ft of cheap RG-58 = a usable HF/MF/LF receive antenna for any SDR. Total cost: ~$40.
• Restricted-installation HF transmit: an attic-strung 41 ft random wire + 9:1 UNUN + tuner = HF coverage from a no-outdoor-antennas installation. Compromise vs an outdoor EFHW, but better than no HF at all.
• Field/portable backup: a random wire is the simplest portable HF antenna possible. When the EFHW UNUN fails, the same wire feeds into a 9:1 UNUN works in a pinch.

4. End-fed half-wave (EFHW) — resonant length + 49:1 / 64:1 UNUN

4.1 The EFHW resonance trick

An end-fed half-wave is cut to exactly λ/2 at the lowest band of operation. At that frequency and its odd harmonics (also some even ones — see below), the antenna is resonant, the feedpoint Z is high (~2450 Ω), and a 49:1 UNUN brings it down to ~50 Ω. The same physical antenna covers multiple bands without a tuner:

• 40 m EFHW (cut to ~66 ft) is resonant on 40/20/15/10 m (the half-wave on 40, the full-wave on 20, the 1.5-wave on 15, the 2-wave on 10).
• 80 m EFHW (cut to ~132 ft) is resonant on 80/40/20/17/15/12/10 m (multiple harmonics).
• 20 m EFHW (cut to ~33 ft) is resonant on 20/10 m.

The key fact: odd half-wave multiples present roughly the same high-Z feedpoint as the fundamental half-wave. The 49:1 transformer handles them all. Even-harmonic resonances exist but at different Z — these often need a tuner.

The EFHW SWR profile for a typical 40 m EFHW with a Mix-43 49:1 UNUN:

Band	Resonance type	Typical SWR	Tuner?
40 m	Fundamental (1× λ/2)	1.5–2.0:1	No
30 m	Off-resonance	4–6:1	Yes
20 m	2nd harmonic (2× λ/2 = full λ)	1.5–2.5:1	No
17 m	Off-resonance	5–8:1	Yes
15 m	3rd harmonic (3× λ/2 = 1.5λ)	1.8–2.8:1	Marginal
12 m	Off-resonance	4–7:1	Yes
10 m	4th harmonic (4× λ/2 = 2λ)	2.0–3.0:1	Marginal
6 m	5th harmonic (5× λ/2 = 2.5λ)	3.0–5.0:1	Yes

The “40-20-15-10” coverage is the EFHW’s signature: four bands on a single feedline without a tuner. With a tuner, the EFHW becomes a near-all-band antenna.

4.2 The 49:1 UNUN

A 49:1 transformer transforms 50 Ω at the coax side to ~2450 Ω at the antenna side. Construction is a trifilar or bifilar+single configuration on a ferrite toroid:

Toroid + winding	Mix	Power	Notes
FT240-43, 2-turn primary + 14-turn secondary	43	200 W SSB / 100 W CW	The standard low-power EFHW UNUN
FT240-31, 2+14 turns	31	500 W SSB / 300 W CW	Higher-power version
FT240-52, 2+14 turns	52	500 W SSB	Newer mix, better low-loss
FT290-43, 2+14 turns	43	1 kW SSB / 500 W CW	The “real legal-limit EFHW” toroid
FT290-31 + FT240-31 in parallel	31	1.5 kW SSB	Top-tier amateur power

The 2+14 turn winding ratio gives the 49:1 transformation (impedance ratio = turn ratio squared, so 14²/2² ≈ 49 if you account for the leakage and the magnetic coupling). Real-world implementations sometimes use 3+21 turns (the same 49:1 ratio with more turns for better low-frequency coverage) or 2+14+compensation-cap (capacitive compensation for the 30 MHz end).

The 64:1 UNUN (3+24 turn variant) is sometimes used for longer EFHW designs (80 m+) where the resonance impedance is slightly higher (~3200 Ω) due to the longer wire’s higher Q.

4.3 EFHW vs EFLW (longer-than-half-wave)

A wire cut longer than λ/2 — say, a full λ at 40 m (~132 ft) — is sometimes called an end-fed long wire (EFLW). The feedpoint Z is higher still (~4000 Ω), and a 64:1 or 81:1 UNUN is the correct transformer. The EFLW has higher gain than the EFHW (it’s collinear with itself) but with more lobing in the pattern.

The dividing line is community convention: “EFHW” means λ/2 at the lowest band; “EFLW” or “long wire” means longer. This volume treats EFHW in §4 and EFLW (multi-wavelength designs) in §5.

4.4 The EFHW’s market success

The EFHW has dominated portable amateur HF since about 2015 because it solves the “I want a quick-deploy HF antenna” problem better than any alternative:

• Single end-support: no center insulator, no center support, no two-tree dipole geometry.
• Multi-band: 40-20-15-10 with no tuner; near-all-band with a tuner.
• Counterpoise tolerance: works “well enough” without one; “better” with a small counterpoise.
• Weight: 65–130 ft of wire + a 200 g UNUN = total package weight ~500 g.
• Cost: $80 commercial; $40 DIY.

The MyAntennas EFHW-8010-1K (the dominant commercial EFHW) sells thousands of units per year and has been the bestselling individual amateur antenna for several years running. The market validates the design.

5. Long wire — multiple-wavelength designs

A “long wire” is a wire that’s electrically multiple wavelengths at the operating frequency. The classical long-wire is fed at one end (like an EFHW) but is several wavelengths long, producing a more directional pattern with multiple major lobes pointing off the wire’s axis.

5.1 Pattern lobes

A wire that’s n half-wavelengths long produces an end-fire pattern with multiple major lobes. The number of lobes is approximately n; the lobes lean toward the wire’s far end as n increases (the cone of maximum radiation narrows around the wire’s axis at very long lengths).

Wire length	Major lobes	Angle to wire	Pattern characteristic
λ/2	2	90° (broadside)	Standard dipole pattern
1λ	4	~54°	Cross-pattern
1.5λ	6	~42°	Multi-lobed
2λ	4	~36°	Major lobes near 36° from wire axis
4λ	4	~23°	Pattern leans toward wire axis
8λ	4	~14°	Strong end-fire
16λ	4	~7°	Near-end-fire (rhombic-like)

For very long wires (8λ+), the pattern resembles a rhombic antenna (a directional terminated diamond-shaped wire used in classic broadcast and military installations). Long-wire HF is a niche use today, but it’s the historical antenna of US Navy and BBC overseas-service broadcasting from the 1930s–60s.

5.2 Modern long-wire applications

Three niches keep long wires interesting:

• Beverage receive antennas (covered in Vol 15 (Receive-only loops & specialty receive antennas)): a long wire (300–1000 ft) terminated in its characteristic impedance at the far end, with the directional pattern oriented for low-noise receive of a specific DX direction. Used by serious 160m/80m DXers.
• Long-wire receive for SDR: a 100+ ft random wire fed at one end via a 9:1 UNUN gives an SDR a very low-noise (because it’s directional and not omnidirectional) receive antenna at low cost.
• Historical broadcast / shortwave receive: a long backyard wire is the canonical “shortwave listening” antenna, often paired with a CommRadio CR-1 or a Drake R-8 receiver.

For transmit-capable amateur use, long wires are mostly historical — the EFHW + 49:1 UNUN is simpler and more flexible. The long wire’s directional gain over an EFHW is real (3–6 dB on the favored direction) but at the cost of being unable to work other directions without rotating the entire wire.

6. Sloper and inverted-L — geometric variants

These two configurations are end-fed/end-loaded variants where the wire takes a non-horizontal path. Both are very popular for low-band (80/160 m) operation where a full-size horizontal antenna is impractical.

6.1 The sloper

A sloper is an end-fed half-wave (or random wire) deployed with one end high and the other end low. The classic configuration: end-fed at the top of a tower or mast, descending at 30–60° to a low support near ground.

                           ●  top: UNUN + coax feedpoint
                          ╱
                         ╱   coax goes down inside or alongside the tower
                        ╱
                       ╱
                      ╱   antenna wire descending at ~45°
                     ╱
                    ╱
                   ●  bottom: end insulator + halyard
   ═════════════════════════════════════════════════ ground

The sloper’s pattern is:

• Vertical polarization in the lower half of the antenna (~50%)
• Horizontal polarization in the upper half (~50%)
• Pattern skewed toward the lower end by 2–5 dB
• Omnidirectional-ish in azimuth (the polarization mix smooths the lobes)

This makes the sloper a useful “directional vertical” for fixed installations where you want a slight gain bias toward one specific direction (a favored DX path, a populated band edge).

6.2 The inverted-L

An inverted-L is a hybrid: a vertical section at one end + a horizontal section at the top. The vertical section is typically λ/8 to λ/4 of the operating band; the horizontal section completes the resonance. Fed at the base of the vertical section (against radials) or end-fed via a UNUN (against a counterpoise).

                    horizontal section (~λ/4 of horizontal wire)
                    ●═══════════════════════════════════●
                    │
                    │
                    │  vertical section
                    │  (~λ/8 to λ/4)
                    │
                    │
                    ●  feedpoint
                    │
                    │
                    │  radials or counterpoise
                    │
              ═════════ ground

The inverted-L’s claim to fame: it’s the textbook 80 m / 160 m antenna for a residential lot. The vertical section provides low-angle radiation (the DX-favoring elevation angle) without needing a full-size vertical’s height. The horizontal section completes the resonant length without consuming additional vertical space.

For 160 m on a 30 ft tower:

• Vertical section: 30 ft (~λ/16 at 1.9 MHz)
• Horizontal section: ~100 ft of horizontal wire at the top
• Total wire: 130 ft (~λ/4 at 1.9 MHz)
• Radial field or 4 elevated radials at the base
• Result: a 160 m DX antenna on a 30 ft tower

The inverted-L is a high-effort, high-payoff antenna — the radial field is mandatory, the geometry is fussy, and the per-band tuning is single-band, but the on-the-air performance for 160 m DX rivals far more expensive commercial verticals.

7. Feedpoint impedance, UNUN selection, counterpoise length

Summary table for selecting the UNUN by antenna type and operating bands:

Antenna	Length	Z_feedpoint	UNUN	Counterpoise length	Power-rating UNUN
Random wire (any HF)	29 / 41 / 53 / 67 ft	200–800 Ω (highly variable)	9:1	50–100% of wire length, or use coax shield	FT240-43, ~100W or FT240-31, ~300W
EFHW for 40 m base	66 ft	~2450 Ω at resonance	49:1 (2+14T on FT240-43)	6–7 ft (10% of length)	FT240-43, 200W
EFHW for 80 m base	132 ft	~2450 Ω at resonance	49:1 (2+14T on FT240-43)	12 ft (10%)	FT240-31 or FT290-43, 500W+
EFHW for 20 m base	33 ft	~2450 Ω at resonance	49:1 (smaller core OK)	3 ft	FT200-43, 100W
End-fed long wire (1.5λ on lowest band)	varies	~3000–4500 Ω	64:1 (3+24T)	10–15% of length	FT240-31, 500W
Inverted-L (160m, fed at base)	130 ft total	~30–50 Ω with radials	1:1 BALUN or direct	Radial field (50+ radials)	Standard BALUN, 1.5kW
Sloper (end-fed half-wave at top)	66 ft for 40m	~2450 Ω	49:1 same as EFHW	5–10% (UNUN-end)	Same as EFHW

The counterpoise length is the most-mistuned variable. Conventional wisdom of “λ/4 counterpoise” is wrong for EFHW — the counterpoise is not a quarter-wave resonator, it’s a short wire that gives the UNUN’s ground side a deliberate RF path. A 5–10% counterpoise (~6 ft for a 40 m EFHW) works at every band the EFHW covers. A long λ/4 counterpoise becomes itself a resonant element and shifts the EFHW’s tuning band-to-band.

8. Radiation pattern

8.1 EFHW at the resonant band

At its fundamental resonance, an EFHW radiates with a pattern essentially identical to a center-fed half-wave dipole: figure-8 broadside to the wire, deep nulls off the ends, peak gain ~2.15 dBi (free-space) or 5–7.8 dBi (over real ground at typical heights).

The reason: the radiation pattern is determined by the antenna’s current distribution and geometry, not by where the feedpoint is. A wire with a half-wave standing-wave current distribution radiates the same pattern whether you feed it at the center or at the end.

8.2 EFHW at harmonic bands

At 2nd harmonic (full-wave, 1λ), the wire’s current distribution has a maximum at the geometric center and the geometric quarters — a different distribution than a half-wave. The pattern fragments into 4 major lobes at ~54° from the wire’s axis.

At 3rd harmonic (1.5λ), 6 lobes at ~42°.

At 4th harmonic (2λ), 4 lobes at ~36° (the lobes lean toward the wire’s axis).

For most amateur operating, the harmonic patterns are “good enough” — the gain is still in the 0–5 dBi range across the lobes, and the propagation conditions don’t care about pattern detail at the 1 dB level. Serious DX contesters who care about pattern matching to the propagation path use directional Yagis (Vol 11) instead.

8.3 Random-wire and long-wire patterns

A random wire’s pattern is “complicated, depends on length and routing, usually omnidirectional in azimuth with broad elevation.” For most operating, this is “fine” — the antenna works, the antenna picks up signal from most directions, the antenna emits signal in most directions.

A long wire’s pattern at high wavelength-count (4λ+) becomes increasingly directional, end-fire, and useful for fixed-direction DX. The Beverage receive antenna (Vol 15) exploits this.

9. Frequency response & SWR curve

9.1 EFHW SWR profile (typical)

A well-built 40 m EFHW with a Mix-43 49:1 UNUN typically shows:

Frequency (MHz)	SWR	Notes
3.50–3.70	5–8:1	Off-resonance, tuner needed
7.00–7.30	1.3–1.8:1	Fundamental — clean
10.10–10.15	5–7:1	Off-resonance
14.00–14.35	1.5–2.5:1	2nd harmonic — clean
18.07–18.17	4–6:1	Off-resonance
21.00–21.45	1.8–2.8:1	3rd harmonic — usable
24.89–24.99	4–7:1	Off-resonance
28.00–29.70	2.0–3.0:1	4th harmonic — marginal
50.00–54.00	3.0–5.0:1	5th harmonic — tuner needed

The “40/20/15/10” four-band coverage is what the EFHW is sold as; in reality there’s a 5th band (6 m) at marginal SWR.

9.2 Random-wire SWR profile

A 41 ft random wire with a 9:1 UNUN shows:

• Highly variable SWR across HF (typically 2–5:1)
• No clean resonances
• Requires a tuner to operate
• Reasonably consistent Z presentation (the 9:1 keeps the tuner-load in the 30–500 Ω range across HF)

The tuner’s job: take whatever the 9:1 presents and convert it to 50 Ω at the rig. Modern tuners with auto-tune do this in 2–5 seconds.

10. Best-case use

• Field-portable HF (SOTA/POTA/Field Day): an EFHW + 49:1 UNUN is faster to deploy than a dipole and doesn’t need a center support. One mast, one halyard, transmit in 90 seconds. The dominant portable HF antenna of the post-2015 amateur era.
• Stealth HF (apartment, HOA, no outdoor antennas): an EFHW invisibly strung in an attic, behind a fence line, or along a property line is a viable apartment-HF antenna. Cross-link to Vol 23 for the stealth playbook.
• SDR receive across HF/MF: a 41 ft random wire + 9:1 UNUN + 50 ft of RG-58 + an SDR = $40 of receive infrastructure that picks up everything from 500 kHz (longwave) to 30 MHz (10 m).
• Backyard HF without center support: when no tree or mast is available for a center-fed dipole, an EFHW between one mast and a ground anchor is the workaround.
• Inverted-L for 160 m / 80 m DX: the standard low-band antenna for residential lots with a small tower.
• Single-feedline multi-band installation: 40-20-15-10 in one antenna without a tuner.

11. Worst-case use

• High-power TX without properly-sized UNUN: small T130-2 cores or under-spec FT240-43 winding will saturate at 200 W on 80 m, producing audible heating and signal distortion. The 1 kW EFHWs ($300+) use FT290 cores precisely because they don’t saturate at sustained power.
• Receivers near broadcast AM stations: the high-Z feedpoint of an EFHW picks up everything, including AM broadcast signals from 0.5–1.6 MHz. Mixing products (IMD) appear at unexpected frequencies and can mask weak signals on amateur bands. The fix: a high-pass filter at the SDR input to roll off below 1.8 MHz.
• Direction-finding receive: the broad, multi-lobed pattern provides no useful nulls. Use a small loop or a Yagi instead.
• 80 m / 160 m DX: the EFHW works, but a proper inverted-L or vertical with full radial system outperforms it by 4–8 dB at low elevation angles.
• Critical-listening receive: for serious weak-signal listening, the EFHW’s broad pattern picks up too much noise. A properly-deployed Beverage or K9AY loop (Vol 15) is the right answer.

12. Power handling — and the harmonic-radiation question

12.1 UNUN core saturation

The UNUN is always the power-handling limit:

UNUN core	Continuous SSB	Continuous CW	Notes
FT240-43, 49:1	200 W	100 W	Standard amateur EFHW
FT240-31, 49:1	500 W	300 W	Higher-power
FT240-52, 49:1	500 W	300 W	Newer mix
FT290-43, 49:1	1 kW	500 W	Serious-power EFHW
Twin FT290-31 stacked	1.5 kW	1 kW	Top-tier
9:1 FT240-43	100 W	50 W	Random-wire low-power
9:1 FT290-43	500 W	300 W	Higher-power random-wire

When a UNUN saturates, three symptoms appear:

1. Audible buzz at the antenna location (the core hum’s frequency component shifts)
2. SWR climbs above 2:1 even on the design band (the transformer ratio fails)
3. Frequency-shifted distortion in transmitted audio (harmonic content increases)

Severe saturation can melt the toroid’s plastic casing or the magnetic-coupling wax. Don’t run sustained-power testing at the UNUN’s rated limit; size up for safety margin.

12.2 Harmonic radiation

End-fed antennas are resonant on multiple harmonics, which is the multi-band feature. They’re also better radiators of harmonic energy from the transmitter than narrowband antennas — if the rig’s low-pass filter doesn’t fully suppress 2nd-harmonic content, an EFHW will gladly radiate it.

This is a real regulatory concern: an FCC-licensed amateur is responsible for spectrum cleanliness, and a 100 W transmitter into an EFHW can spit 0.1% (20 dBc) of 2nd-harmonic signal into the air, which is enough to interfere with nearby commercial services on the harmonic frequency.

The fix: a clean transceiver. Modern Yaesu/Icom/Elecraft rigs have 60–80 dB of harmonic suppression at full power; old QRP rigs (Heathkit HW-9, vintage Kenwoods) can be much worse. If you’re running an old rig into an EFHW, check your harmonic output with a spectrum analyzer or just use an in-line filter (Vol 17).

13. DIY build — a 40 ft EFHW for 40/20/15/10 m

This is the canonical portable EFHW build. About 2 hours of work plus tuning. Total parts cost ~$60 USD.

Scope note. Some “40 ft EFHW” designs are cut for 30 m (not 40 m) and cover 30/20/15/10. This volume’s recipe is for 40 m base (~66 ft of wire), which covers 40/20/15/10. Read the wire length carefully.

13.1 Bill of materials

Part	Specification	Source	Mid-2026 price
Antenna wire	#20 or #18 AWG copper-clad steel (CCS) or insulated stranded, ~67 ft	Wireman 522 (#18 CCS, $0.30/ft) or DX Engineering DXE-ANTW-18B ($0.55/ft)	$20–37
Counterpoise wire	Same as antenna wire, ~7 ft	(same source)	$5
49:1 UNUN core	FT240-43 ferrite toroid	DigiKey / Mouser / Amidon	$12
UNUN winding wire	#14 enamel magnet wire, ~3 m	DigiKey	$3
UNUN enclosure	3D-printed PETG box or PVC pipe stub, ~4″×3″×2″	local print / DIY	$5–10
SO-239 (or BNC) chassis connector	for UNUN’s coax connection	DigiKey	$4
End insulator	Lightweight plastic, dog-bone style	DX Engineering DXE-ISP	$3
Halyard rope	1/8″ Dacron, ~10 m	Synthetic Textiles	$7
Weatherproofing	3M Scotch 130C + 33+	$5
Total			~$64

13.2 Step-by-step construction

Wind the UNUN. Cut 3 lengths of #14 enamel wire, each ~1 m long. Twist the three wires together at 4 turns per inch (or just slightly twist together by hand — the twist is for mechanical stability, not RF-critical). Wind the trifilar bundle through the FT240-43 toroid: 7 turns (each turn passes the bundle through the toroid’s hole once).

Label the three wires A, B, C at one end and A’, B’, C’ at the other.

Connect for 49:1:

• Connect A to the coax shield (this is one of the UNUN’s “ground” terminals)
• Connect A’ (the other end of wire A) to B (the start of wire B)
• Connect B’ to C
• Connect C’ to the antenna wire terminal
• Connect the coax shield (the same wire as A’s ground) to the counterpoise terminal

Then connect:

• Coax center conductor between A and B’ (this is the 50 Ω input)
• Antenna terminal at C’
• Counterpoise terminal at A’s ground

Mount the toroid + connections inside the enclosure with a few zip ties or hot-glue dabs. The connections should be solid solder joints; no twist-cap connectors.

Cut the wire. Cut a 67 ft (20.4 m) length of #18 CCS antenna wire. Trim 1% short of theoretical λ/2 — for 40 m at 7.150 MHz, λ/2 is 67.6 ft, cut to 67 ft for tuning headroom.

Attach to the UNUN. Strip and solder the antenna wire to the UNUN’s antenna terminal. Strip and solder the counterpoise wire to the UNUN’s counterpoise terminal.

Attach the end insulator. At the far end of the antenna wire, terminate to the dog-bone insulator with the standard “loop, double back, wrap, solder” procedure (Vol 6 §10.2).

Attach the halyard. A Dacron rope through the end insulator + a stake at the far support point or a halyard pulley over a branch.

Deploy. Hoist the wire so the UNUN end is at chest height (or higher), the wire extends as a sloper or horizontal toward the far end at ~5–10 m elevation. Connect the coax to the UNUN.

Sweep with the NanoVNA. Look for SWR minimum near 7.15 MHz; should be < 1.8:1. If it’s at 6.95 MHz the wire is too long — trim 2–3 inches off the end. If at 7.35 MHz the wire is too short — start over (cheap to redo).

Test the harmonic bands. Sweep 14.0, 14.3, 21.0, 21.4, 28.0, 28.7 MHz — should all show SWR < 2.5:1 if the UNUN is built correctly. If the harmonic bands show clean SWR but the fundamental does not, the wire length is the issue. If the fundamental is clean but the harmonics are bad, the UNUN is the issue (winding error, wrong toroid mix).

Lock and weatherproof. Apply 3M tape to the UNUN’s enclosure seams and to the antenna’s connection to the dog-bone insulator. The UNUN should be in its plastic/3D-printed enclosure throughout this — no exposed windings outdoors.

13.3 Tuning verification

A successful EFHW build shows:

• 40 m: SWR minimum < 1.8:1 between 7.05–7.20 MHz
• 20 m: SWR minimum < 2.5:1 between 14.05–14.25 MHz
• 15 m: SWR minimum < 2.8:1 between 21.10–21.35 MHz
• 10 m: SWR minimum < 3.0:1 between 28.30–28.60 MHz
• 30/17/12 m: SWR > 3:1 (off-band — normal, use tuner if needed)
• 6 m: SWR 3–5:1 (5th harmonic — marginal, use tuner)

If 40 m is right but 20 m is way off, the UNUN winding is wrong (check the trifilar twist direction). If both bands are off, the wire length is wrong (or the counterpoise length is interfering).

14. Commercial buys

Sorted by tier and use case (USD, mid-2026):

Tier	Model	Bands	Price	Notes
Budget	MFJ-1982LP	80–10 m EFHW	$80	Entry-level commercial EFHW; modest UNUN
Budget	HF Kits EFHW	80–10 m	$90	Dutch maker, solid build
Budget	LNR Trail-Friendly 40/20/10	40/20/10 m	$80	Lightweight, popular for SOTA
Budget	DIY (this volume’s build)	40-10 m	$60	The reference DIY
Budget	Chameleon LEFS-8030	80–30 m	$115	Modular variant
Mid	MyAntennas EFHW-8010-1K	80–10 m	$200	The dominant commercial EFHW. 1 kW rated. The “buy this one” choice.
Mid	MyAntennas EFHW-4010	40–10 m	$150	Smaller variant; same UNUN quality
Mid	Par EndFedz EF-40MKII	40/20/15/10 m	$135	Polished commercial EFHW; well-regarded
Mid	Buckmaster 7-band EFHW	80/40/20/17/15/12/10 m	$230	Buckmaster build quality; 7 bands without tuner
Mid	Chameleon EmComm III	80–6 m	$290	Modular, all-band capable
Premium	MyAntennas EFHW-8010-2K	80–10 m, 2 kW	$400	Premium MyAntennas — handles 1.5 kW continuous
Premium	Wolf River Coil EFHW Pro	80/40/20/15/10 m	$250	Upper-end build, premium components
Premium	Bonito MegActiv MA305FT	active EFHW for SDR	$480	Receive-only with LNA
Premium	Custom-built 1 kW EFHW (per spec)	80–10 m	$350+	Custom-built by experienced builders

What to avoid:

• “1 kW PEP EFHWs” with tiny 1″ toroid cores in pocket-sized 3D-printed boxes — these will saturate under sustained transmit. The “1 kW PEP” rating is short-burst; continuous power is much lower.
• EFHWs without published UNUN specifications (core mix, turn count, power rating) — the UNUN is the antenna’s heart; if the vendor won’t disclose it, the build quality is suspect.
• “Multi-band miracle wires” claimed to work on 80–10 m without a tuner from a single wire — the EFHW’s harmonic coverage is real but limited to 4–5 bands; “all 9 bands no tuner” claims are marketing.

15. Companion gear

• One end support: a tree, a fishing pole, a mast, a flagpole. Single-support requirement is the EFHW’s killer feature.
• Counterpoise wire (5–10% of antenna length): typically pre-attached to commercial EFHWs; carry one for DIY builds.
• Choke balun on the coax 0.05λ from the UNUN: an air-core CMC (10 turns of coax through a 4″ form) or 8× Mix-43 ferrite beads slid over the coax. Suppresses common-mode current on the coax shield.
• Tuner (for non-resonant bands): LDG Z-100Plus, MFJ-993B, internal rig tuner. Most modern HF rigs include adequate tuners for ~3:1 SWR; external tuners cover wider ranges.
• Halyard line (Dacron, NOT nylon): single rope from the far end insulator to a tie-off cleat. About 10–30 ft typical.
• Bag or pouch organizer: keeps the wire, UNUN, halyard, and counterpoise together so the “lost a counterpoise — antenna unusable” failure mode is prevented.
• Lightning protection: same polyphaser + single-point ground as in Vol 6 §12. End-fed antennas are more lightning-prone than horizontal dipoles (they have a high-voltage point), so the lightning-protection step is mandatory for permanent installations.

16. Common gotchas and myths

• “EFHWs don’t need a counterpoise” — a 5–10% counterpoise is highly recommended; without it the coax shield becomes the counterpoise and the rig becomes part of the antenna. The “no counterpoise needed” claim refers to “the antenna still works without it” not “the antenna performs the same.”

• “49:1 works on any wire length” — only if the wire is electrically λ/2 at the lowest band of operation. Other lengths produce different feedpoint impedances and the 49:1 mismatches. The “49:1 EFHW” combination is purpose-built for half-wave resonance.

• “Random wire + 9:1 = multiband miracle” — useful as receive-only; for transmit, requires a tuner that can match a wide Z range across HF. The 9:1 enables tuner matching across HF; it doesn’t itself match.

• “My SWR is 1.0:1 across all bands” — if you’re seeing this on an EFHW, the UNUN has core saturation issues that are flattening the SWR by absorbing reflected power as heat. A “perfect” SWR across all bands is not better; it usually means the UNUN is the limit, not the wire.

• “The EFHW is a half-wave antenna” — at its fundamental band, yes. At harmonics it’s a full-wave / 1.5-wave / 2-wave / 2.5-wave antenna with different pattern characteristics. Knowing the antenna’s electrical state at each band helps interpret real performance.

• “More turns on the UNUN = better” — only up to a point. Adding turns increases low-frequency coverage (the toroid’s inductance must dominate at the lowest band), but too many turns add inter-turn capacitance and reduce high-frequency match. The 2+14 standard is well-optimized for HF.

• “I’ll just hang the EFHW vertically out my window” — works, but pattern is degraded (no horizontal symmetry), coax routing is awkward, and the rig sees common-mode current on the shield. A horizontal or sloping deployment is much better.

• “EFHW is invisible to the FCC inspector” — at 100 W, an EFHW is producing the same signal level as a dipole. The “stealth” aspect refers to physical visibility (the wire is harder to see than a dipole), not RF visibility. Don’t assume an EFHW is “compliant” if your transmissions are illegal — the antenna doesn’t change the physics.

• “The 49:1 UNUN is identical to a 49:1 BALUN” — no. A BALUN is balanced-to-unbalanced (BALanced UNbalanced); a UNUN is unbalanced-to-unbalanced. The EFHW’s “49:1 UNUN” is a transmission-line transformer with both ends unbalanced — the antenna wire and the coax shield. Don’t substitute a BALUN; it doesn’t work for this geometry.

• “Counterpoise length must be λ/4” — false. Counterpoise length is not a resonant element; it’s a short wire (5–10% of antenna length) that gives the UNUN’s ground side a deliberate RF path. A λ/4 counterpoise becomes itself resonant and disrupts the EFHW’s tuning.

• “Random wire works the same as EFHW” — false. EFHW is resonant at multiple bands without a tuner; random wire is non-resonant on every band and requires a tuner. The 49:1 vs 9:1 ratio captures the difference.

17. Resources

• ARRL Antenna Book Ch. 10 (end-fed wires) — the canonical reference.
• Sevick, Building and Using Baluns and Ununs (4th ed.) — the UNUN-design bible.
• AA5TB EFHW pages — the de-facto online reference for amateur EFHW construction.
• N5DUX EFHW calculator — published online tool for EFHW dimensions.
• MyAntennas EFHW tech notes — published UNUN design rationale.
• KB1DIG EFHW guide (online) — beginner’s introduction to EFHW theory.
• W2DU’s Reflections III (3rd ed.) — clarifies the SWR/UNUN-loss confusion that EFHW operators often encounter.
• LNR Precision Trail-Friendly antenna manual — published SOTA-oriented design notes.
• N4SPP EFHW build guide — community-favorite construction walk-through.