Optimal NVIS Antenna Heights for Reliable HF Coverage
NVIS (Near Vertical Incidence Skywave) communication is essential for regional HF coverage, especially in mountainous terrain or where line-of-sight paths are blocked. To optimize NVIS propagation, the antenna must radiate at high elevation angles—typically above 60°. One of the biggest levers is the antenna’s height above ground.
Why 0.18 to 0.22 λ?
For NVIS antennas—especially horizontal dipoles or inverted-Vs—the most reliable transmit height is relatively low: about 0.18–0.22 λ. This range produces a strong upward lobe and suppresses low-angle energy that isn’t useful for short-range coverage.
Too low (≲ 0.15 λ) increases ground loss and hurts efficiency; too high (≳ 0.25 λ) flattens the pattern, eroding the NVIS effect. The sweet spot shifts slightly with ground conductivity and nearby objects, but 0.18–0.22 λ is a robust target for most installs.
Recommended Heights by Band
The table shows feedpoint heights that hit ~0.18–0.22 λ for common NVIS bands. For inverted-Vs, set the feedpoint in this range; the ends can slope down safely.
| Band | Frequency (MHz) | Wavelength (λ) | Optimal Height Range (m) |
|---|---|---|---|
| 30 m | 10.1 | 29.7 m | 5.3 – 6.5 |
| 40 m | 7.1 | 42.3 m | 7.6 – 9.3 |
| 60 m | 5.3 | 56.6 m | 10.2 – 12.5 |
| 80 m | 3.6 | 83.3 m | 15.0 – 18.3 |
| 160 m | 1.9 | 157.9 m | 28.4 – 34.7 |
Receive vs. transmit optimization: In practice, operators often observe lower optimal heights for the best receive SNR and slightly higher heights for the best transmit NVIS footprint. This isn’t a violation of the reciprocity theorem; rather, it reflects differences in local noise, ground loss, and ionospheric absorption on the specific day and band. For more on the receive side, see Understanding Optimal NVIS Receive Angles.
Practical Tips
- Supports: Trees or lightweight masts make it easy to hit the target height.
- Ground/soil: Poor soil may benefit from nudging height toward the top of the range.
- Multi-band NVIS: A fan dipole or doublet near the 60 m height (~11 m) is a solid compromise for 80/60/40 m.
- Polarization: Favor horizontal polarization for NVIS. Keep vertical runs short and add a 1:1 common-mode choke at the feedpoint to reduce feedline radiation.
- Avoid high installs: If the goal is regional coverage, avoid heights ≳ 0.3 λ that push energy into shallower angles.
With the right geometry and height, a simple wire delivers dependable regional coverage—perfect for emergency nets, military-style comms, and everyday local QSOs when you need “fill-in” coverage despite terrain.
Mini FAQ – NVIS Antenna Height & Setup
- What height should I use? Aim for ~0.18–0.22 λ at the feedpoint. For 80 m that’s ~15–18 m; for 40 m ~7.6–9.3 m.
- Does polarization matter? Yes—use horizontal antennas (dipole/inverted-V). Vertical antennas favor low angles, not NVIS.
- Can I do NVIS on 20 m? Usually no; MUF and ionospheric conditions rarely support true NVIS at 14 MHz. 80/60/40 m are the staples.
- Should I add a choke? Yes. A 1:1 current choke at the feedpoint lowers noise and improves pattern consistency.
- Is inverted-V OK? Yes—set the feedpoint at the target height; the legs can slope down safely.
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Written by Joeri Van Dooren, ON6URE – RF, electronics, and software engineer; complex platform and antenna designer. Founder of RF.Guru. Expert in active and passive antennas, high-power RF transformers, and custom RF solutions.