Why Wire Delta Loops Lose Efficiency at Higher HF Bands
Delta loops are excellent performers on the low bands. A full-wave loop offers low take-off angles, reasonable gain, and quiet reception. But once you push that same loop up into the higher HF bands, efficiency begins to collapse. Here’s why.
Current Distribution Shrinks
A full-wave loop is resonant at its design frequency. On higher bands, the loop becomes multiple wavelengths long. Current concentrates in just a few short segments, leaving the rest of the wire carrying almost no useful radiation. The result: the effective radiating area is far smaller than the total wire length.
Multiple Lobes, Little Gain
On 20, 17, or 15 meters, a 40- or 80-meter loop behaves like a multi-wavelength polygon. Instead of a clean main lobe, you get many high-angle lobes with deep nulls in between. Forward gain drops, and useful DX angles are lost. The radiation pattern becomes unpredictable and difficult to aim.
Feedpoint Impedance Becomes Chaotic
At its design frequency, the loop has a stable impedance (usually near 100–120 Ω). On harmonics, impedance swings wildly into the hundreds or even thousands of ohms. Matching losses increase, coax losses rise, and tuners struggle.
Ground Losses Dominate
A long wire loop high in the air is still capacitively coupled to ground. As the current paths shorten on higher frequencies, more of the RF energy is dissipated in ground losses instead of being radiated. You’re effectively heating the soil instead of radiating RF.
Material and Mechanical Considerations
Our DeltaRex loop demonstrates how much construction material matters. Using 35 mm aluminum tubing reduces resistive losses compared to thin wire, especially on HF. On the top span, a twin-wire design with 5 cm spacing adds performance and stability. Also note: building the 120° bottom angle is straightforward with metal tubing, but very difficult with carbon or fiberglass masts due to their flex and stress limitations.
So What Works Better on Higher Bands?
- Monoband loops — A dedicated 20 m delta loop offers clean gain and low angles.
- Multiband verticals — With raised radials and proper choking, they outperform large loops on upper HF.
- Fan dipoles or OCFs — Often provide more consistent results on the higher bands than a single oversized loop.
Mini-FAQ
- Can’t I just use a tuner? — Yes, but you’re only matching the impedance. The poor current distribution and multi-lobe pattern remain.
- Is a loop ever good on harmonics? — On some even harmonics, you may get a usable match and pattern, but it’s rarely predictable.
- What about using it as a receive loop? — Loops remain quiet on receive, even on harmonics, so they can still help reduce noise.
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