Not Every HF Antenna Is a “Compromise”

Not Every HF Antenna Is a “Compromise”

This article covers single-element wire antennas only (160–10 m). Most so‑called “compromises” are not antenna‑type limitations — they are installation mistakes: lossy transformers, high‑SWR coax, poor choking, bad heights or undefined counterpoises. A well‑installed wire does exactly what physics says it should do.

First principles: height, current, and pattern

Radiation is produced by the time‑varying current along the wire. The height of the current‑rich portions controls the elevation angle:

• Raise the current maxima → lower takeoff angle → better DX.
• Keep them low → high‑angle/NVIS.

“Voltage‑fed” vs “current‑fed” changes only matching and return‑path physics — not the fundamental radiation mechanism. Half‑wave wires with the same geometry and height have the same pattern whether fed at the center, off‑center, or at the end.

The EFHW height truth: voltage node ≠ immune to ground

A critical but often misunderstood point:

Because an EFHW uses a voltage transformer at a very high‑impedance point, the feed‑end is extremely sensitive to ground proximity. Ground losses couple far more strongly into a high‑voltage / low‑current node than into a low‑voltage / high‑current point.

Raising only the transformer box doesn’t do much for pattern. Raising the middle of the wire — where current is highest — sets your takeoff angle. But the feed‑end height still matters for efficiency on an EFHW because it controls how hard that high‑voltage node “sees” the ground.

EFHW vs center‑fed/OCF at the same geometry and height: the fundamental‑band patterns are essentially identical; the differences show up in matching loss, ground loss, and common‑mode effects.

Example @ ~6 m height (≈20 ft): Horizontally strung on 40 m (6 m ≈ 0.15 λ) an EFHW’s feed‑end is still a strong E‑field point near ground, so it often incurs more loss than an otherwise identical 200–300 Ω EFOC/OCF using a 4:1 voltage balun (unun) and a proper 1:1 choke. On 20 m (6 m ≈ 0.3 λ) the difference shrinks, but the EFHW feed‑end is still more sensitive to return‑path definition and choking.

EIRP is the score that matters

EIRP = Transmitter power − all losses + antenna gain Two 100 W stations can differ by several dB due to:

• coax loss (especially with high SWR),
• transformer/balun loss,
• ground loss,
• stray return current (TX) from insufficient choking / undefined return paths.

Balanced line stays efficient even with high SWR. Coax does not. On receive, the sibling problem is common‑mode noise pickup (RX), which hurts SNR even though it’s not part of EIRP.

Balanced‑fed wires usually outperform coax + high‑ratio boxes

A doublet with ladder line or an OCF with a 4:1 voltage balun (unun) and a proper choke often preserves more EIRP than a 49:1 EFHW because:

• Ladder line has extremely low HF loss even with high SWR.
• Coax loss rises rapidly with SWR and length.
• Lower ratios (e.g., 4:1) are far easier to make efficient than ~49:1.

If you need to end‑feed, targeting ~200–300 Ω (EFOC‑style) with a 4:1 voltage balun (unun) often yields higher EIRP than a 49:1 EFHW of the same length — especially when the feedpoint must be close to ground.

The same logic applies to ladder‑line‑fed delta loops and other balanced wire geometries: keeping the system balanced with low‑loss line preserves EIRP under mismatch. Even an EFHW can be fed with ladder line and a balanced tuner; in practice, this configuration will outperform any 49:1 box for multiband efficiency when installed and choked correctly.

EFHWs: excellent when engineered well

A well‑built EFHW transformer can achieve:

• ≈93% efficiency
• ≈0.3 dB loss in its sweet spot

Bad cores, poor winding, or operation far from the sweet spot (15/10 m especially) cause multi‑dB losses. Execution matters enormously. EFHWs particularly shine on harmonic pairs (160/80, 80/40, 40/20, etc.) because a half‑wave on the fundamental is also resonant on its integer harmonics — provided the transformer and choke are up to the task.

Builder’s note: bi‑filar or tri‑filar windings on the right ferrite mix for your bands do the heavy lifting. Never use a shunt “compensation” capacitor — there is no reason for it.

Baluns and chokes: protect EIRP and your noise floor

With little or no choking capacity (and/or an undefined return path), two things always happen:

• Stray return current (TX): RF uses the feedline/house as the “other half,” stealing power, warping the pattern, and heating things you didn’t plan to heat.
• Common‑mode noise pickup (RX): The same current path drags household/ambient noise into the receiver.

Both share the same fix: define the return path (counterpoise/elevated radial) and add enough 1:1 choking impedance. For QRO, you need more choking capacity (higher Z_cm and current handling) to keep both effects down. Any product that claims “no choke needed” deserves extra skepticism.

Chokes that actually work (rules of thumb)

• Aim for >5 kΩ choking impedance on the bands of interest; >10 kΩ is better for 80/40 m. A single small core with 10–11 turns or a couple of sleeve beads rarely reaches this.
• Use #31 mix ferrite for 1.8–10 MHz and #43 mix for 7–30 MHz. Stacking cores (e.g., two FT240‑31) and using enough turns yields broad, high impedance.
• Series chokes + measurement: On 30–10 m, two high‑Z chokes in series dramatically improve suppression — verify with an RF current probe/meter. For QRO on 160–40 m, use two in series but space them ~2 m along the feedline to spread heating and broaden the stop‑band.
• Place the first choke at the transformer. If the feedline must run through a noisy environment, add a second choke where the coax enters the shack.

Are EFHWs “noisy”?

They’re only “noisy” when the common‑mode path isn’t controlled. There are two symptoms from the same root cause:

• Stray return current (TX): reduces efficiency and distorts pattern.
• Common‑mode noise pickup (RX): raises your noise floor/SNR.

Define the return path (counterpoise or elevated radial) and choke the feedline, and an EFHW becomes as quiet and efficient as any center‑fed wire on the same site — they’ll sound just the same as a dipole.

Vertical EFHWs, inverted‑Ls, and the “10 m feedpoint” myth

You often hear “EFHW verticals only work if the feedpoint is 10 m up.” That’s not correct — and the underlying reason matters:

The EFHW’s transformer sits at a high‑voltage node, which couples strongly to lossy ground. The closer that node is to ground, the larger the efficiency penalty — faster than for lower‑impedance feeds.

What actually governs performance:

• Ground‑loss environment and wavelength fraction: Height sensitivity tracks ground loss at voltage nodes and height in wavelengths, not a fixed meter value.
• Geometry/dimensions matter: For example, an inverted‑V EFHW with the far end higher than the feedpoint reduces ground coupling at both voltage nodes and often beats a version where the end is near ground at the same apex height.
• Feed impedance choice: The effect is less pronounced with lower‑voltage feeds such as a 4:1‑fed (voltage balun, unun) 200–300 Ω end‑feed (EFOC) or pure current‑fed dipoles/doublets.
• Defined return path + choking: Use a counterpoise or elevated radials and a proper 1:1 choke right at the box.

Ratios vs height (putting it together): A generic 49:1 half‑wave often leaves a strong HV region at the base, so base height drives loss. In contrast, the RF.Guru 160/80 (~68:1) and 80/40 (~70:1) inverted‑L EFHWs are dimensioned so the largest HV antinode lives up the wire; the transformer simply matches the higher R_end that geometry creates. Our 40/20 inverted‑L EFHW (~20:1, in development) follows the same principle with a lower R_end on that geometry. That is why these can run lower than a generic 49:1 while holding efficiency — provided the counterpoise/radials and a high‑Z 1:1 choke are in place. On out‑of‑family bands (not intended to be run anyway), the HV map changes; treat base height conservatively there.

Quarter‑wave verticals & radials (why they often win)

A ¼‑wave vertical places a current antinode at the base (low voltage, high current). Near ground it suffers a ground‑loss penalty, but you can compensate with a good radial field. When radials are done right, a ¼‑wave vertical will usually beat an EFHW vertical for efficiency at similar overall heights — and it can be placed much lower because the base is a low‑voltage node.

• Radial count/length: More and longer is better; practical ranges are 8–16 radials as a starting point, with 16–32 offering a clear improvement. Lengths ≈0.2–0.25 λ are common; mixing lengths helps.
• Elevated radials: Two or four tuned, elevated radials can rival many more on‑ground radials if installed symmetrically.
• Bonding/grounds: Keep RF grounds/radials intentional; avoid letting the feedline become the radial by accident — choke it.

Practical guidance for 160–10 m

• Pick pattern first (NVIS vs DX).
• If you can run ladder line: choose a doublet (or a ladder‑line‑fed loop).
• If end‑feeding: choose a good EFHW or a 200–300 Ω EFOC + 4:1 voltage balun (unun) — especially if the feedpoint must be low.
• For verticals near ground: prefer a ¼‑wave with a real radial field when possible.
• Choke aggressively. Define the return path.

Myth‑busting

• “Every antenna is a compromise.” False — different antennas deliver different, intended patterns. The real compromises are self‑inflicted losses.
• “Voltage‑fed means height doesn’t matter.” False — ground loss hits voltage nodes harder.
• “EFHWs are noisy.” False — the issue is either stray return current (TX) or common‑mode noise pickup (RX) from poor choking/return paths; fix those and they’ll sound like a dipole.
• “4:1 always beats 49:1.” Oversimplified — lower ratios are usually easier to make efficient and are less height‑sensitive near ground, but execution rules.
• “EFHW verticals only work if the feedpoint is 10 m up.” False — no magic threshold; efficiency improves as voltage nodes are raised and the return path is controlled. Also, a ¼‑wave vertical with a proper radial field will generally beat an EFHW vertical and can be installed much lower.

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