XentrX Technical Overview
Updated: 2025-10-31 — Technical overview validated against XentrX geometry, feed system, and radiation modeling.
The XentrX 40–6 m Off-Center Vertical Dipole is a high-efficiency broadband HF transmit vertical designed for full-band coverage and mechanical robustness. It operates from 40 m through 6 m without traps or coils, using an integrated 4 : 1 UNUN and dual 1 : 1 chokes to maintain balance and isolation across the band. The feedpoint is about 6 m above ground, making it a true low-angle DX antenna.
Supplied as a complete system — just mount, connect, and operate. All key parts are pre-tuned and weather-sealed for long-term reliability.
Specs at a Glance
| Type | Off-center vertical dipole (OCV) — no radials required |
|---|---|
| Coverage | 40 m to 6 m continuous; typical SWR < 3 : 1 except 30 m (~3.4 : 1) |
| Feedpoint Height | ≈ 6 m above ground (typical installation) |
| Feed System | Integrated 4 : 1 UNUN (auto-transformer) + dual 1 : 1 current baluns (top & bottom) |
| Polarization | Vertical — low-angle DX optimized |
| Power Rating | 3.6 kW PEP (1.8 kW CCS) with dual-core UNUN |
| Mechanical | Marine-grade AL-1100 aluminum sections with 60° indexed locking; stainless hardware |
Included Components
- 7.40 m radiator and 4.65 m counterpoise (if ordered with aluminum tubes; otherwise only assembly hardware is included)
- 3 mounting plates
- 2 glass-fiber-reinforced tubes (one for extending a 6 m mast to 7.40 m, one as a center alignment pin between radiator and counterpoise)
- 1 × 4 : 1 UNUN (auto-transformer, dual-core)
- 2 × 1 : 1 current baluns (top and bottom)
- 1 m coax jumper (between the 4 : 1 UNUN and first current balun)
- 8 m coax (between the first and second current balun)
- All stainless hardware and weather-sealed connectors
Operating Bands & Angles
| Band | Primary Take-Off Angle (TOA) | Peak Gain vs 0 dBd | Behavior |
|---|---|---|---|
| 40 m | ≈ 20 – 25° | +1 – +1.5 dBd | Low-angle DX, suppressed high-angle NVIS |
| 30 m | ≈ 17 – 20° | +1.5 – +2 dBd | Strong DX band with smooth azimuth |
| 20 m | ≈ 12 – 16° | +2 – +2.5 dBd | Excellent DX window |
| 17 m | ≈ 10 – 14° | +2 dBd | Split-lobe pattern emerges |
| 15 m | ≈ 10 – 12° | +1.5 – +2 dBd | Multi-lobe but strong low angle |
| 12 m | ≈ 8 – 12° | +1 – +1.5 dBd | DX-friendly with broader coverage |
| 10 m | ≈ 6 – 10° | +0.5 – +1.5 dBd | DX & E-skip capable multi-lobe |
Take-off angles based on feedpoint ≈ 6 m AGL, average ground (εr ≈ 13, σ ≈ 5 mS/m). Azimuth is essentially omni.
Image currents in the soil reinforce radiation near the horizon, producing DX-grade angles < 20°. Extra lobes appear above 17 m but the lowest lobe remains dominant and ideal for long-path or trans-equatorial propagation. For even lower angles, raise the antenna 2 – 3 m or ensure moist ground conditions.
Feed System & Choking
- UNUN: 4 : 1 dual-core auto-transformer rated 3.6 kW PEP / 1.8 kW CCS.
- Chokes: Two 1 : 1 current baluns — one between radiator and feedline, one at shack entry.
- Feedline: Use high-quality 50 Ω coax (≤ 0.8 dB loss @ 30 MHz). Allow 1 – 2 m drip loops each end.
- Optional: Place additional chokes mid-line to further reduce common-mode coupling.
Radiation Patterns
Patterns shown are simplified free-space models at average ground for clarity (40 – 10 m bands).
Mount the feedpoint ~6 m high, ensure the two current chokes are in place (top and bottom), and keep coax runs away from metal surfaces. Add drip loops and a rubber mat under the ballast frame for mechanical damping and strain relief.
Mini-FAQ
- Do I need radials? — No. The XentrX is a true off-center vertical dipole; the lower section acts as a counterpoise.
- What tuner is required? — Most internal tuners handle 40–6 m; 30 m may need an external unit.
- Why two chokes? — They block common-mode currents on TX and cut noise on RX.
- Feedpoint height? — ≈ 6 m AGL yields best DX angles without pattern distortion.
- Power rating? — Up to 3.6 kW PEP (1.8 kW CCS) with the integrated dual-core UNUN.
Interested in more technical content? Subscribe