Efficient Multiband Verticals with a 4:1 UNUN Explained

Last updated: August 22, 2025.

Efficient Multiband Verticals with a 4:1 UNUN Explained

“Only a vertical of exactly 7.2 m will give a good match” — this Rybakoff myth has misled many hams. In reality, with a 4:1 UNUN, radials, and a choke, lengths like 6 m or 9 m perform just as well — often better.

Capacitive Coupling and Ground Return

A vertical is a radiator above a lossy capacitor — the ground. Matching is about adjusting feedpoint capacitance and current distribution so the impedance lands in the 100–200 Ω zone. That’s where a 4:1 UNUN shines.

Choose a Length for the Bands You Want

• 9 m — ~0.43 λ on 15 m and 0.22 λ on 40 m: covers 15–40 m effectively.
• 6 m — efficient across 10–20 m.

These lengths consistently yield ~100–200 Ω feedpoint impedance across bands. The 4:1 UNUN converts this to 20–50 Ω, easily within tuner range.

Lay Down Proper Radials

For stable SWR and efficiency, use resonant radials, not “random wires.” At least four per band:

• 4 × 10.5 m radials (7 MHz)
• 4 × 5.5 m radials (14 MHz)
• 4 × 3.75 m radials (21 MHz)

This provides consistent return paths and reduces soil dependency.

Feedpoint Tuning: Height & Element Balance

• Height above ground: ~0.1–0.2 λ is ideal. For a 9 m vertical, that’s ~20 cm–1.2 m. Adjusting height shifts SWR dramatically.
• Feedpoint position: Raising the feedpoint 20–30 cm changes current taper and balances multiband response.

You are “tuning the capacitor,” not the element. Optimize return path + balance, not mythical resonances.

Why SWR Drops Into Place

When radiator length, radial system, and feedpoint location align, the real impedance sits at ~100–150 Ω with manageable reactance. A 4:1 UNUN brings this into 20–50 Ω: clean, tunable, efficient.

Kill Common-Mode Current

Add a 1:1 choke ~0.05 λ down the coax:

• ~6.6 m on 80 m
• ~3.5 m on 40 m
• ~1.25 m on 15 m

This prevents the coax from acting as an unintended counterpoise, cleaning up the pattern and reducing RFI.

Conclusion

Stop chasing folklore like “Rybakoff 7.2 m.” A vertical is just a radiator over ground. Pick a length that covers your bands, add radials, and let a 4:1 UNUN and choke handle the rest. The real magic is in the dirt.

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