EFHW Antennas: Inverted L vs Sloper/Flattop on 80/40M
End-Fed Half-Wave (EFHW) antennas remain one of the most flexible choices for 80 m and 40 m operation. Among the most common deployments are the Inverted L and the Sloper/Flattop. Each favors different propagation modes—low-angle DX or high-angle NVIS—depending on installation and height.
The Inverted L Configuration (EFHW8040)
The Inverted L combines a vertical wire section with a horizontal run. On 80/40 m this often means ~10–15 m vertical and the remainder horizontal, forming an “L”.
Advantages for DX
- Low-angle launch: The vertical section enhances shallow elevation angles—ideal for intercontinental DX.
- Space efficiency: Less horizontal real estate; practical on smaller lots.
- Balanced coverage: With a short counterpoise and proper common-mode choking, it supports both DX and some regional work, leaning toward DX.
Advantages for NVIS
- The horizontal portion contributes to high-angle energy on 80 m, especially when the horizontal leg is relatively low compared to wavelength.
Note: EFHW feedpoints are high-voltage; use appropriate clearance and weatherproofing. Add a 1:1 common-mode choke 0.05–0.1 λ down the coax (and another before shack entry if needed) to tame RF on the feedline.
Drawbacks
- Support needs: Requires a mast/tree for the vertical rise.
- Environment sensitivity: End-fed systems interact with nearby structures and the feedline; define the local reference with a short counterpoise (≈0.02–0.05 λ) and good choking.
The Sloper/Flattop Configuration
A Sloper angles downward from a high support; a Flattop runs horizontally between supports. Most of the wire is parallel to ground.
Advantages for DX
- Directional bias (Sloper): Tends to emphasize the downslope direction, useful when you want to favor a specific path.
- Simple deployment: Typically needs just two supports; quick portable setup.
Advantages for NVIS
- High-angle coverage: Horizontal orientation promotes near-vertical incidence—excellent for local/regional links on 80 m.
- Low-height usability: Works well even at 5–10 m AGL, where NVIS is favored.
Installation height dominates behavior: lower flattops increase high-angle energy (better NVIS), while higher flattops (≥0.5λ) begin to form lower-angle lobes on 40 m.
Drawbacks
- Weaker low-angle energy: Without a vertical section, low-angle DX performance is typically reduced versus an Inverted L.
- Directional effects: Sloper bias may not line up with desired DX paths.
Performance Comparison
| Parameter | Inverted L | Sloper / Flattop |
|---|---|---|
| DX Suitability | Excellent (low-angle) | Moderate (slope/height dependent) |
| NVIS Suitability | Moderate | Excellent (high-angle) |
| Install Complexity | Higher (vertical support) | Lower (simple supports) |
| Pattern Bias | Near-omni with proper choking | Directional if sloped; flattop more uniform |
| Space Required | Compact (saves horizontal space) | Needs horizontal span between supports |
When to Choose Each
Choose the Inverted L (EFHW8040) if:
- DX is the priority (especially on 40 m).
- Horizontal space is tight but a vertical support is feasible.
- You can deploy a short counterpoise and proper common-mode chokes for a defined, stable reference.
Choose the Sloper/Flattop if:
- Regional/NVIS coverage on 80 m is your main goal.
- You have room for a horizontal span and want a simpler install.
- You prefer fewer support constraints and a more uniform pattern.
Conclusion
The Inverted L EFHW8040 tends to win on low-angle DX, while Sloper/Flattop EFHWs excel for high-angle NVIS and regional reliability. Match the geometry and height to your coverage goals on 80/40 m, and stabilize EFHW installations with a short counterpoise plus well-placed chokes.
Mini-FAQ
- Do EFHWs still need a choke? — Yes. Place a 1:1 current choke about 0.05–0.1 λ down the coax; add a second before shack entry if needed.
- Does an Inverted L need radials? — No. Use a short counterpoise (≈0.02–0.05 λ) to define the local reference. Full radials tend to morph it into a Marconi vertical and detune the EFHW match.
- Is a Sloper always directional? — It typically favors the downslope direction, but still provides usable coverage elsewhere.
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