Tuning a 160/80m EFHW Inverted L for SSB DX

Purpose-Built for Serious Low-Band DX

The 160/80 m EFHW Inverted L is a full-size antenna (~81 m of wire) designed for maximum performance on the low bands. Minimum vertical support: 15 m, with the remainder forming the horizontal section. More height = shorter horizontal leg, reducing space. When tuned properly, it combines low-angle DX capability on 160 m with NVIS + DX coverage on 80 m.

Why SSB DX is the Priority

SSB requires more power density at low angles to cut through QRM and noise, unlike CW or FT8 which succeed with less power. On 160/80 m, SSB faces:

• Narrow usable bandwidth (often <300 kHz)
• Rapid impedance swings outside resonance
• Strong dependence on height and soil quality

Therefore: tune for SSB DX windows — the mode with the toughest demands.

The Tuning Trade-Off: 160 vs 80 m

Tempted to tune for FT8/CW? Don’t. For SSB DX:

• 160 m: Forgiving. Even at 7:1 SWR, a tuner + good coax adds only ~0.5–0.7 dB loss over 30 m.
• 80 m: Critical. Bandwidth is tight, and mismatch increases loss in coax and transformer cores. Tune here.

Best practice: Tune around 3.75–3.8 MHz for SSB DX. Let the tuner handle 160 m.

Physical Configuration

• ~81 m total wire length
• Vertical section: ≥15 m
• Horizontal section: 81 m – vertical
• Transformer: rugged 68:1, rated for 4 kW ICAS SSB up to ~2.5:1 SWR

Feedpoint & Ground

• Feedpoint height: 1–2 m above ground (radiation unaffected; current is in vertical).
• Counterpoise: short 1–2 m wire to stainless ground peg.
• Choke: ~8 m from feedpoint to block common-mode pickup.
• Transformer: mount low for access and stability.

Bandwidth Management

• Expect nonlinear SWR due to EFHW current distribution + ground coupling.
• Detune slightly from 160 m exact resonance and use tuner there.
• Prioritize SWR dip at 3.75 MHz for 80 m SSB.
• Use analyzer sweeps to track dips — not just lowest SWR across band.

Transformer Stress & Power Handling

• SSB creates high peaks (PEP) with speech processing.
• Core heating, capacitor breakdown, and loss rise under SWR >5:1.
• Stress is higher on 80 m than 160 m, so tune for SSB on 80 m first.

Summary: Best Practices for SSB DX Tuning

• Tune at 3.75–3.8 MHz (SSB DX)
• Use a robust 68:1 transformer
• Place choke ~8–12 m from feedpoint
• Let tuner handle 160 m mismatches
• Don’t obsess over 1.0 SWR — focus on dips & usable BW
• FT8/CW still work fine even if antenna tuned for SSB

Always tune for the mode that demands the most bandwidth and power (SSB). Other modes will still work, but not the other way around.

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