1/4-Wave Fan Verticals

A 1/4-wave fan vertical is one of those antennas that looks almost too simple to deserve much explanation.

Several vertical wires, rods, or radiator sections of different lengths are connected to the same feedpoint. Each one is cut close to a quarter wavelength for a different band. The coax centre conductor feeds the vertical radiators. The coax shield connects to a common radial or counterpoise system.

That is the whole idea.

No traps. No loading coils. No remote tuner at the base. Just several resonant vertical paths in parallel, with the radial system forming the other half of the antenna.

Electrically, it is easiest to think of it as the vertical cousin of the fan dipole. A fan dipole places several half-wave dipoles in parallel. A fan vertical places several quarter-wave vertical radiators in parallel and completes the system with radials or counterpoises.

The Basic Layout

A typical 1/4-wave fan vertical uses a non-conductive support, such as a fibreglass mast or fishing pole. The longest wire is normally used for the lowest band. There are exceptions, however. The RF.Guru VertX uses a conductive support that is part of the antenna system and includes the 20 metre band as part of that structure.

The VertX deliberately focuses on 20–10 metres. For 40 metres, we prefer an EFHW Inverted-L approach, because it can cover both useful low-angle DX behaviour and higher-angle NVIS-style coverage more effectively in many real-world installations.

At the base, all vertical radiators are connected together and go to the feedpoint centre conductor. The radial field, ground screen, or counterpoise wires connect to the shield side of the feedpoint.

A simple version may use only two bands, for example 40 and 20 metres. A more elaborate version may cover 40, 30, 20, 17, 15, 12, and 10 metres. In our own RF.Guru VertX approach, the design choice is deliberately different: 20–10 metres are handled by the vertical fan system, while 40 metres is better solved with a separate EFHW Inverted-L when both DX and NVIS coverage matter.

The principle does not really care whether the radiators are made from wire, aluminium tube, telescopic whip sections, or a mixture of materials. What matters is that each branch is a separate resonant or near-resonant vertical radiator.

Why It Works

On each band, the radiator closest to quarter-wave resonance tends to present the most useful current path. The other radiators are off resonance and normally carry less current.

In casual language, people often say the antenna “self-selects” the correct element.

That phrase is useful, but it should not be taken too literally. The unused wires do not vanish. They are still present, still coupled, and still capable of moving the resonance of the active element. That is why spacing, wire routing, and final tuning matter.

The system is best understood as a set of parallel resonators. One branch is near resonance on the band of interest, while the others are electrically longer or shorter than ideal. The branch with the best current distribution does most of the radiating.

Starting Lengths

For wire radiators, a useful starting point is:

These are starting values, not final dimensions. Wire insulation, conductor diameter, mast material, nearby wires, feedpoint height, radial layout, and ground conditions all change the final tuning.

Start long. Fold back or trim later. Once the antenna is complete, tune it in its final position, not on the workbench and not with only one radiator attached.

For the RF.Guru VertX, the practical design range is 20–10 metres. The table above is a general quarter-wave reference, not a claim that every band is best solved with the same physical fan-vertical approach.

The Radial System Is the Other Half

A quarter-wave vertical is not a complete antenna by itself. The vertical wire is only one side of the RF system. The return side is supplied by the radial field, ground plane, counterpoise, metal roof, seawater, vehicle body, or whatever conducting structure is connected to the shield side of the feedpoint.

This is where many vertical myths start. A good SWR does not automatically mean a good radial system. Ground loss can make an antenna look easier to match while silently turning RF power into heat.

A lossy radial system may produce a comfortable impedance, but that does not mean the antenna is efficient.

Ground-Mounted Fan Vertical

For a ground-mounted fan vertical, the radials can lie on the soil, be stapled into grass, or be shallow-buried. They do not have to be exactly quarter-wave resonant, because the soil detunes them anyway.

In practice, many shorter radials are usually more useful than only one or two perfectly calculated wires.

Elevated Fan Vertical

For an elevated fan vertical, the radials behave more like tuned counterpoise wires. In that case, they should normally be near quarter-wave length for each band.

A small number of elevated radials can work very well, but they become part of the tuned antenna system and must be treated as such.

Feedpoint Impedance and SWR

A perfect quarter-wave vertical over a perfect ground plane would have a feedpoint resistance around the mid-30-ohm region. Real installations are not perfect. Ground loss, radial loss, wire coupling, feedline interaction, and nearby objects all change what the transmitter sees.

That is why a 1:1 SWR is not always proof of performance.

Sometimes it means the system is well matched. Sometimes it means the ground system is lossy enough to bring the feedpoint resistance closer to 50 ohms. The antenna analyser tells you about impedance. It does not directly tell you how much of your power becomes radiation.

Tuning Sequence

A fan vertical should be tuned as a complete system. Install all intended vertical wires and all intended radials first. Then begin tuning.

• Start with the lowest band and longest radiator.
• Find the SWR dip or impedance minimum.
• If the dip is too low in frequency, shorten the radiator.
• If the dip is too high in frequency, lengthen the radiator or unfold a folded-back section.
• Move upward in frequency, band by band.
• After the highest band is adjusted, repeat the process once or twice.

The repeat pass matters because the radiators interact. Adjusting the 20 metre wire may slightly move 17 or 15 metres. Adjusting the 40 metre wire can affect harmonic behaviour.

This is normal. It is not a fault; it is simply what parallel resonant structures do.

Spacing Between Radiators

The wires do not need to be metres apart, but they should not all be taped tightly together either. Some spacing reduces coupling and makes tuning less frustrating.

On a fibreglass pole, small spreaders or tie-off points can hold the wires a few centimetres away from each other. The exact spacing is not sacred. Consistency and mechanical stability are more important than chasing imaginary precision.

For portable use, convenience often wins. For a permanent installation, better spacing, strain relief, weatherproofing, and a tidy feedpoint plate make the antenna much easier to live with.

Use a Feedline Choke

A fan vertical is an unbalanced antenna, but that does not mean the coax shield should become an uncontrolled extra radiator.

A good 1:1 common-mode choke near the feedpoint helps keep the feedline from becoming part of the antenna system.

Without a choke, the coax outer can act as an accidental radial, an accidental radiator, or both. That may change the tuning, increase RF in the shack, distort the pattern, and make the antenna behave differently when the feedline is moved.

A Short Timeline of the Idea

The 1/4-wave fan vertical belongs to a long tradition of practical amateur-radio experimentation. It is a natural combination of two older ideas: the quarter-wave ground-plane vertical and the parallel-element fan antenna.

That timeline is useful because it avoids both extremes. The fan vertical is not a mysterious new antenna, but neither is modern packaging irrelevant. A good commercial implementation can make an old electrical principle far easier to reproduce reliably.

Why Hams Like Them

A well-built fan vertical has several attractive properties:

• it can be resonant on multiple bands without traps or loading coils
• it is mechanically simple
• it is easy to understand and repair
• it is efficient when the radial system is good
• it is attractive for portable, field-day, POTA, SOTA, and small-garden use
• it can give useful low-angle radiation for DX, especially when compared with very low horizontal antennas

The simplicity is also educational. A fan vertical forces the builder to understand current, radials, feedpoint impedance, common-mode current, and the difference between resonance and radiation efficiency.

Where They Disappoint

Fan verticals are not magic. They are still vertical antennas. They need a return system. They interact with nearby objects. They can pick up local noise. They can put RF on the feedline if the choke and radial system are poor. They may need several tuning passes before all bands behave properly.

The most common disappointments are caused by unrealistic expectations:

• expecting a tiny radial field to behave like a perfect ground plane
• expecting all wires to tune independently
• expecting a 1:1 SWR to prove high efficiency
• expecting the coax shield not to participate when no choke is used
• expecting a vertical in a noisy urban garden to receive like a quiet rural antenna

None of these are failures of the fan vertical principle. They are ordinary antenna-system problems.

Best-Practice Summary

• Use a non-conductive support where possible, unless the conductive support is intentionally part of the design.
• Keep the radiators mechanically stable and reasonably separated.
• Start all radiators slightly long.
• Install the full radial system before tuning.
• Tune from the lowest band upward.
• Repeat the tuning pass because the wires interact.
• Use a proper 1:1 common-mode choke near the feedpoint.
• Do not judge the antenna only by SWR.
• Remember that the radial field is part of the antenna, not an accessory.

The Real Conclusion

The 1/4-wave fan vertical is a beautifully practical antenna. It combines the old fan-antenna idea with the quarter-wave vertical. Several resonant vertical radiators share one feedpoint, and the radial system provides the other half of the RF circuit.

Its appeal is not that it breaks physics. Its appeal is that it uses physics in a simple, visible, and repairable way.

When the radial system is good, the feedline is choked, and the wires are tuned as one coupled system, a fan vertical can be an excellent multiband HF antenna.

Modern commercial versions helped make the idea easier to build and more widely recognised, but the real lesson remains the same: current makes antennas radiate, radials complete the circuit, and SWR alone is never the whole story.

For RF.Guru, that also means choosing the right topology for the right band range. The VertX applies the fan-vertical idea where it makes most sense for a compact vertical system: 20–10 metres. For 40 metres, an EFHW Inverted-L is often the better practical tool because it can provide both DX and NVIS-style coverage from the same general installation concept.

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