EFHW 160/80 Inverted L for OT8M Contest Station 77m with Low Feedpoint

We generally recommend installing the EFHW Inverted L with the highest point at least 15 m above ground for optimal low-angle DX. But this OT8M contest station deployment shows that even with a slightly lower end height, excellent results are possible over good soil with proper grounding and choking.

This is RF.Guru’s EFHW16080 4 kW High Power Inverted L Endfed Halfwave, set up at OT8M. The antenna combines a low feedpoint, efficient geometry, and robust components for reliable 160/80 m contest use.

Configuration Overview

• Antenna: EFHW16080 4 kW Inverted L (68:1)
• Total Wire Length: 77.5 m (trimmed from 81 m for tuning)
• Feedpoint Height: 0.5 m
• Vertical Section: 12 m
• Horizontal Section: ~65.5 m, slightly sloped
• End Height: ~15 m
• Transformer: RF.Guru EFHW16080 4 kW 68:1
• Counterpoise: 1.5–2 m wire to RVS INOX ground stake
• Line Isolator: 9 kW HF +30 dB CMR isolator, 8 m from feedpoint

Design Philosophy

• Keep feedpoint safe and accessible at ground level
• Maximize vertical component for DX on 160 m
• Use long horizontal segment for NVIS coverage on 80 m
• Maintain strong current section at bend for efficient coupling

Use Case: OT8M Measurements

Operator Wim (OT8M) optimized for both bands, with 80 m tuned toward SSB DX. Results:

• 80 m: SWR dip 2.4:1 @ 3.700 MHz (DX window)
• 160 m: SWR dip 3.6:1 @ 1.875 MHz (DX region)

Excellent soil conductivity kept SWR stable even when raising feedpoint height — confirming ground quality effects.

Performance Expectations

• 160 m: 77.5 m length ≈ half-wave at 1.83 MHz. Transformer efficiently handles ~3.6:1 SWR, tuner easily matches.
• 80 m: Operates near 1λ; supports strong NVIS and DX at 3.7 MHz with ~2.4:1 SWR.

Installation Notes

• 68:1 transformer ensures safe 4 kW ICAS operation up to 2.5:1 SWR.
• Feedpoint height variation had negligible impact due to excellent soil conductivity.
• Choke placement (8 m away) prevents coax from acting as a counterpoise.
• Counterpoise wire grounded to stainless peg stabilizes impedance.

This 77.5 m EFHW Inverted L demonstrates that high-performance 160/80 m operation is achievable with a low feedpoint and modest support height. The design balances low-angle DX on 160 with NVIS on 80, making it ideal for contesting and multi-mode operation.

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