DeltaRex 80M–6M — Technical Overview
Updated: 2025-08-19 — Technical overview validated against DeltaRex design geometry and feed system.
DeltaRex — Technical Overview
DeltaRex is a rugged, multiband closed-loop TX antenna refined for real-world HF. A tall triangular loop with a dual-wire top span and bottom-vertex feed delivers low loss, stable patterns, and a tuner-friendly match across 40–10 m, with usable NVIS on 60/80 m.
Pre-engineered geometry, stainless hardware, dual-wire top span, and a matched 4:1 UNUN (2.4 kW or 3.6 kW ICAS). Add a quality 1:1 choke ~8 m up the line and you’re on air fast.
Specs at a Glance
| Mechanical | Tall isosceles triangle, 120° bottom vertex; legs 2 × 6 m (Ø35 mm, 2 mm wall, EN AW-6063 T66); dual-wire top (~11 m) with ~5 cm spacing; fittings/base/fasteners in RVS316; total wire length ~22.4 m. |
|---|---|
| Electrical | Feed at bottom vertex; 4:1 UNUN (2.4 kW or 3.6 kW ICAS); typical loop feed Z ~100–120 Ω; 1:1 current choke ~8 m up the feedline (see below); polarization horizontal. |
| Bands | Optimized: 40–10 m | Usable NVIS: 60 m, 80 m | Not supported: 160 m. |
| Power | Up to 3.6 kW ICAS with included UNUN (class dependent) and proper choking. |
For all bolts, screws, and electrical interfaces, apply AL-1100 aluminum paste during assembly to prevent galvanic corrosion and keep contact resistance low in outdoor exposure.
How often? One thorough application at installation is typically sufficient. In harsh coastal or polluted environments, reapply every 2–3 years during a visual inspection, or sooner if you open/retorque joints.
Type: Horizontal-polarized, multiband closed-loop TX antenna
Bands: 40–10 m optimized (usable NVIS on 60/80 m)
Power Handling: Up to 3.4 kW ICAS
Polarization: Horizontal (bottom-vertex feed, dual-wire top)
Operating Bands & Angles
| Band | Mode | Typical Takeoff / Behavior |
|---|---|---|
| 10 m | DX | Low-angle radiator (~8–12° @ ~3–5 m base) |
| 12 m | DX | Clean pattern, wide match window |
| 15 m | DX | Slight multi-lobe (full-wave+) |
| 17 m | DX | Strong gain, balanced lobe |
| 20 m | DX | Full-wave loop — primary band |
| 30 m | DX/NVIS | Mid-angle, tuner-assisted |
| 40 m | DX/NVIS | Efficient half-wave loop |
| 60 m | NVIS | Usable with tuner (sub-resonant) |
| 80 m | NVIS | Sub-efficient but functional |
| 160 m | — | Not supported (perimeter too short) |
Angles are indicative; surroundings and height will nudge results.
Recommended Heights
| Bottom @ | Top Wire | Best Use Case |
|---|---|---|
| 0.5 m | ~5.5 m | Quick install, higher angles |
| 2 m | ~7 m | Lower takeoff, reduced ground loss |
| 4 m | ~9 m | DX & moderate NVIS sweet spot |
| 5 m | ~10 m | Deepest DX angles |
Feed System & Choking
- UNUN: 4:1 (2.4 kW or 3.6 kW ICAS), bottom-vertex feed; typical loop Z ~100–120 Ω → ~25–30 Ω post-transform.
- Choke: Add a quality 1:1 current choke roughly 8 m down the coax (≈0.1λ of the lowest band) if you don’t need 80 m; otherwise ~4 m (≈0.05λ) is sufficient.
- Feedline: Use a minimum 26 m coax run from antenna to shack and add a second choke before the shack entry.
- Routing: Keep coax away at right angles initially; avoid long parallel runs near metal gutters/fences.
Why Two Wires on the Top Span?
At first glance, the dual-wire top span might seem redundant, but it actually functions as a single, wider conductor. By spacing the wires ~5 cm apart, the DeltaRex achieves a wider effective surface area, which lowers the Q of the loop and delivers a broader, flatter SWR curve. This reduces sensitivity to weather, height changes, and narrowband tuning issues. The technique is similar to the “cage effect” often used in high-end Yagis, where multiple parallel wires create lower resistive loss and more stable bandwidth compared to a single thin conductor.
Why This Loop Is an Efficient DX “Compromise”
- Right-sized perimeter vs. λ: ~22.4 m ≈ 0.56λ @ 20 m and ≈ 0.28λ @ 40 m — strong DX geometry without traps or coils.
- Lower ground loss than short verticals: Elevated base & horizontal top reduce soil coupling.
- Dual-wire top span: Lower resistive loss and broader bandwidth over a single wire.
- Noise behavior: Continuous loop path plus proper choke reduce CM pickup into the shack.
VSWR Sweep
(Indicative) — measured at the feedpoint with the 4:1 UNUN and a 1:1 current choke ~8 m up the line (or ~4 m if you intend to use 80 m). Expect small shifts with height and surroundings. Use ≥26 m feedline and a choke before shack entry.
Radiation Patterns
Patterns shown are simplified models for clarity — see why we use simplified models and not NEC. Real-world results vary with soil, height, and surroundings. These plots are for 3 m bottom height.
Use a 1:1 choke ~8 m up the feedline (or ~4 m if you will use 80 m), keep the dual-wire top span evenly spaced, and verify clear air around the top wire for best bandwidth and symmetry. Run ≥26 m of coax to the shack and add a choke before entry.
Mini-FAQ
- Do I need radials? — No. DeltaRex is a closed loop; no ground plane required.
- Do I need a tuner? — Usually not on 40–10 m with an internal ATU. 30 m may need an external tuner depending on height. 60/80 m require an external tuner.
- Where should I place the choke? — ~8 m down the coax (≈0.1λ of the lowest band) if you don’t need 80 m; otherwise ~4 m (≈0.05λ). Always add a second choke at shack entry.
- What feedline length? — Use a minimum 26 m coax run from antenna to shack for stable behavior across bands.
- Power rating? — Up to 3.6 kW ICAS with the supplied 4:1 UNUN and proper common-mode choking.
- Why two wires on the top? — The dual-wire top lowers Q and broadens bandwidth for a flatter SWR curve and better stability.
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