Inverted-U Configuration for the EFHW16080

Shallow Inverted-U Layout for an 81 m EFHW160/80 Antenna

An 81 m end-fed half-wave antenna for 160 m and 80 m is often installed as an inverted-L, sloper, or long wire adapted to the available supports. When two elevated supports are available, a shallow inverted-U layout can be a very practical alternative. It keeps the feedpoint near the ground, lifts a useful portion of the wire into the air, and gives a good compromise between regional coverage and low-angle radiation.

This is not a magic layout, and it should not be confused with a full-size vertical over a large radial field. But for real gardens, real supports, and real installations, the shallow inverted-U can be a very effective way to deploy a long 160 m / 80 m EFHW without needing 80 m of straight-line space.

Physical Configuration

The exact geometry depends on the available supports, but the basic idea is simple: the wire rises from the transformer, crosses the property as a raised horizontal or gently sloping section, and then descends toward the far support. The drawing is conceptual, not to scale.

• Total wire length: approximately 81 m
• Transformer: 68:1 UnUn, intended for a nominal high-impedance EFHW feedpoint
• Feedpoint location: near the base of one leg, typically around 1.5–2 m above ground
• First section: slopes upward toward the main span
• Main span: preferably 10–15 m high, or as high as the supports allow
• Far end: slopes downward toward the second support, often ending around 5–6 m above ground
• Site width: commonly 30 m or more, depending on how much of the 81 m wire can be carried in the top span and sloping sections

Visual layout:

     /------------------\
    /                    \
   /                      \
--                          --

Practical note: an 81 m wire cannot always be represented by a simple 30 m drawing. If the available span is shorter, the remaining length must be accommodated by longer sloping sections, diagonal routing, or a gentle non-parallel path. Avoid tight folding or close parallel runs, because those can increase coupling between wire sections and change the current distribution.

Current Distribution: The Important Correction

Because this is an end-fed half-wave antenna on 160 m, the feedpoint is not a high-current point. It is a high-voltage, low-current point. The 68:1 transformer is used because the feedpoint impedance is high, often in the several-kilohm range depending on height, ground, surroundings, and feedline interaction.

On 160 m, the current rises as you move away from the transformer and reaches its main maximum roughly around the middle of the electrical half-wave. In a shallow inverted-U layout, that current maximum will often be located somewhere in the raised section or around the transition between the first sloping leg and the top span, depending on the exact geometry.

The far end of the wire is again a high-voltage, low-current point. So the statement “the current maximum is near the feedpoint” is not correct for a voltage-fed EFHW. That would be more typical of a classic quarter-wave vertical or quarter-wave inverted-L fed against a radial system.

Behavior on 160 m

On 160 m, the 81 m wire behaves close to a half-wave radiator. Since the antenna is still low in terms of wavelength, the horizontal part contributes a strong high-angle component, which helps regional and NVIS-style coverage. At the same time, the sloping sections introduce vertical current components and help support lower-angle radiation than a purely low horizontal wire.

This makes the shallow inverted-U a useful compromise. It will not behave exactly like a tall quarter-wave vertical with a large radial field, and it will not behave like a high horizontal dipole either. It sits between those worlds: part horizontal, part sloping, part vertical, and very dependent on installation height.

For DX on 160 m, height still matters. A top span at 10–15 m is only about 0.06–0.09 wavelength high on 160 m, so the antenna will still produce substantial high-angle radiation. However, compared with a wire lying very low or a heavily compromised ground vertical, the raised inverted-U can be surprisingly effective because more of the useful current is away from lossy ground.

Behavior on 80 m

On 80 m, the same 81 m wire behaves approximately as a full-wave end-fed antenna. The current distribution now has two main current regions rather than one. This creates a more complex radiation pattern, with broader lobes and deeper pattern variation depending on orientation, height, and local coupling.

The 80 m pattern will normally not be perfectly omnidirectional. It can favor certain directions, especially broadside to the main span or along lobes created by the full-wave current distribution. For practical operation, that is not necessarily a disadvantage. It often gives a useful mix of medium-angle and higher-angle radiation, making the antenna usable for both longer-distance contacts and regional work.

DX and NVIS Balance

The shallow inverted-U layout is attractive because it does not force the antenna to be only a DX antenna or only a local-coverage antenna. The sloping and partially vertical sections help lower-angle radiation. The raised horizontal section supports stronger regional coverage. On 160 m and 80 m, where most real-world installations are electrically low, this balance is often more useful than chasing a theoretical perfect pattern that cannot be achieved on the available property.

For local and regional contacts, the horizontal part is beneficial. For DX, the height of the current-carrying sections and the amount of lossy ground coupling become important. Raising the main span, keeping the first sloping section clear of buildings, and avoiding lossy nearby structures will generally help more than obsessing over an exact drawing shape.

Feedline, Counterpoise, and Choking

An EFHW does not need a classic radial field in the same way a quarter-wave vertical does, but it still needs a return/reference system. In many practical installations, the coax shield becomes part of that system. A short ground stake can help provide a local reference and static bleed path, but it should not be described as a magic replacement for all return-current behavior.

For that reason, the feedline should be treated as part of the antenna system unless it is deliberately isolated. A common-mode choke is usually placed near the shack, or at the point where you want the intentional counterpoise section to stop. Placing a choke directly at the transformer can sometimes make the system less stable if no other counterpoise is provided.

In practice, a controlled length of coax shield, followed by a good common-mode choke before the feedline enters the shack, often gives a better and more predictable result than pretending the coax is not involved.

Advantages of the Shallow Inverted-U Layout

• Allows an 81 m 160 m / 80 m EFHW to fit into a more realistic property layout
• Raises a useful part of the antenna away from lossy ground
• Combines horizontal, sloping, and partially vertical radiation components
• Supports both regional coverage and lower-angle DX radiation
• Keeps the transformer and feedpoint accessible near ground level
• Avoids the need for a large 160 m radial field
• Can be easier to deploy than a classic quarter-wave inverted-L with many radials

Important Considerations

• Height still matters: the higher the main span, the better the low-angle potential.
• The feedpoint is high voltage: use proper insulation, strain relief, and spacing from people, animals, and conductive structures.
• The coax shield participates: manage common-mode current deliberately with a suitable choke location.
• Avoid tight wire folding: close parallel wire sections can couple and change the electrical length and pattern.
• Keep the sloping legs clear: nearby metalwork, gutters, fences, trees, and buildings can detune or distort the antenna.
• Expect pattern lobes on 80 m: a full-wave wire is not a simple omnidirectional radiator.

Summary Table

Parameter	Value / Recommendation
Wire length	Approximately 81 m
Transformer type	68:1 UnUn for high-impedance end-fed operation
Feedpoint height	Typically around 1.5–2 m
Main span height	Preferably 10–15 m, higher if available
Far-end height	Often around 5–6 m
Layout width	Site-dependent; 30 m or more is practical, but the full 81 m wire path must be preserved
160 m behavior	Approximate half-wave end-fed antenna with one main current maximum away from the feedpoint
80 m behavior	Approximate full-wave end-fed antenna with two main current regions and a more lobed pattern
Counterpoise behavior	Coax shield and local reference system normally participate
Choke recommendation	Use a common-mode choke near the shack or after the intended counterpoise/feedline section

When to Choose This Layout

• You want one practical antenna for both 160 m and 80 m
• You have two elevated supports but not enough room for a straight 81 m wire
• You want a mix of DX and regional coverage
• You prefer a feedpoint near ground level for easy access and troubleshooting
• You do not want to install a large classic radial field for 160 m
• You can keep the wire reasonably high and clear of nearby structures

Practical Conclusion

The shallow inverted-U is a field-friendly way to deploy an 81 m EFHW160/80 when a straight wire, tall vertical, or full radial field is not realistic. Its strength is not theoretical perfection. Its strength is that it lifts useful current-carrying sections into the air, keeps the installation manageable, and gives a practical balance between top-band DX and regional coverage.

As always with long end-fed antennas, the final result depends on height, routing, soil, feedline length, choking, and nearby structures. But when installed thoughtfully, this layout can be an excellent real-world solution for operators who want serious 160 m and 80 m capability without turning the garden into a radial farm.

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