Why Our 61° and 120° Delta Loops Crush DX – Even From Just 6 m Height

Our delta loop antennas are anything but average. Every angle, length, and wire has been optimized for real-world DX performance from common 6 m mounting poles. But why do we use 61° leg angles for 6–17 m and a 120° layout for 20 m? And how do they manage excellent low-angle radiation, even when their apex height is under 0.25λ at 20 m?

Let’s dive into the electromagnetic details.

SolidDelta: 61° Design from 6–17 m – Monoband Precision

The 61° bottom-vertex-fed triangle used in our SolidDelta series is no accident:

  • It forms a closed loop of approximately 1λ, just right for monoband operation.
  • The feedpoint impedance sits close to 50 Ω, making direct feed with a 1:1 choke both simple and efficient.
  • With 6 m long aluminium legs, the apex reaches just under 6 m high, which is ideal for low-angle DX radiation from 17 m down to 6 m.

Despite the moderate height (e.g. ~0.25λ on 17 m, up to ~0.9λ on 6 m), the current maxima occur in the vertical legs, not at the apex or the bottom. This gives a broadside pattern with a strong horizontal polarization component, and crucially, the radiation lobe forms between 15–25° at these bands—perfect for long-distance DX.

We use dual top wires with 4 cm spacing to improve efficiency: lowering I²R loss, increasing usable bandwidth, and enhancing radiation symmetry.

DeltaXtrm20: 120° Variant for 20 m – Broader, Lower, Still a DX Beast

For 20 m, a 61° delta with 6 m legs doesn’t provide the needed wire length for resonance. The solution: open the triangle to 120°. The result:

  • A full-wave perimeter maintained.
  • A slightly lower height (~5.2 m), but enough to stay above ground-loss sweet spot.
  • Feedpoint impedance ~110 Ω, transformed losslessly via a 4.1 m 75 Ω coax section (¼ λ) after a 1:1 UNUN.

Even though the height is below 0.25λ, why does it still radiate well for DX?

Because unlike a vertical, the delta loop forms a closed current loop. The fields are balanced, and the current maximums are still in the vertical sections of the triangle. That means ground coupling is reduced, and effective height—from the point of view of radiation—is closer to a 0.3–0.35λ monopole, despite physical height.

In this configuration, there’s also a slight increase in vertical polarization, helping ground-wave and low-angle skip without increasing noise pickup like a classic ¼λ vertical might.

DeltaRex: Multiband 120° Versatility from 40 m to 10 m

The DeltaRex is our multiband solution based on the same 120° geometry. It uses a 4:1 UNUN to feed the loop non-resonantly. Unlike monoband designs, this configuration trades some resonance for flexibility:

  • SWR below 3:1 from 40 m to 10 m, ideal for tuners.
  • NVIS coverage on 60 m and 80 m when mounted low.
  • Can be mounted as low as 0.5 m above ground, especially for NVIS applications—something not practical with resonant designs like the DeltaXtrm20.

Why is this possible? Because in a non-resonant loop, the current distribution adapts to height more flexibly, and the need for precise λ-matching is relaxed. While DX performance increases with height, the DeltaRex can serve both NVIS and DX roles, depending on elevation.

Why the DeltaRex Acts Taller Than It Is

Thanks to its non-resonant loop geometry, the DeltaRex behaves as if it were mounted at nearly double its physical height compared to a traditional dipole. A near-resonant antenna like the EFOC29 performs somewhat better than a dipole at low height, but it still requires more elevation than the DeltaRex to achieve similar low-angle radiation.

Technical Rationale:

Closed-Loop Geometry = Balanced Radiation
The delta loop forms a closed current path, which naturally balances the electric and magnetic fields. This leads to:

      • Lower ground currents
      • Lower sensitivity to ground proximity
      • Reduced common-mode current pickup
      • Reduced return currents
      • Less ground loss and less height dependency

Non-Resonant Operation = Less Height Sensitivity
In a non-resonant loop:

      • Current maxima aren’t fixed at particular nodes like in a dipole or EFHW.
      • The field pattern adapts smoothly with height.
      • You get a more uniform and stable radiation pattern across a wider height range.

Effective Electrical Height
Electrically, the DeltaRex behaves as if it is 0.4–0.5λ above ground, even when mounted physically at just 0.2–0.25λ. This is due to the efficient current distribution and low interaction with lossy ground near the feedpoint.

In short, loop geometry combined with non-resonant feed makes the DeltaRex far more height-forgiving and efficient, especially compared to open-wire designs.

Lambda, Height, and Real-World Take-Off Angles

In all variants, we aim for:

  • A balanced current distribution with minimal ground-loss coupling.
  • Heights between 0.25–0.9λ, which is the sweet zone for DX at each band.
  • Avoiding the need for radials or traps.

A traditional vertical of the same height would suffer from high ground loss, narrow bandwidth, and strong common-mode pickup. Our delta loops don't. Their self-contained geometry, choked feed, and full-wave perimeter ensure superior radiation characteristics.

Summary

Product Angle Band Range Height Polarization Feedpoint Z Matching
SolidDelta 61° 6–17 m ~6 m Horizontal-dominant ~50 Ω Direct 1:1 choke feed
DeltaXtrm20 120° 20 m ~5.2 m Mixed (some vertical) ~110 Ω 1:1 choke + 75Ω ¼λ coax
DeltaRex 120° 40–10 m (NVIS 60/80) 0.5–6 m NVIS or DX, depending on height High-Z (varies) 4:1 UNUN + tuner

Bottom line: Even under 0.25λ, when engineered right, you still get low take-off angles, wide bandwidth, and efficient radiation—without radials, traps, or compromises.
DX doesn't need height. It needs smart design.

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Written by Joeri Van Dooren, ON6URE – RF, electronics and software engineer, complex platform and antenna designer. Founder of RF.Guru. An expert in active and passive antennas, high-power RF transformers, and custom RF solutions, he has also engineered telecom and broadcast hardware, including set-top boxes, transcoders, and E1/T1 switchboards. His expertise spans high-power RF, embedded systems, digital signal processing, and complex software platforms, driving innovation in both amateur and professional communications industries.