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Electronics & Antennas for Ham Radio

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End Fed Off Center Antennas: Mounting advice

Related reading:
The FD4 Windom Antenna — a deprecated classic and why the EFOC29 is a better choice
Why the EFOC29 design outperforms the EFHW8010 and EFLW37 in multiband operation

When installing a wire antenna, avoid over-tightening the wire. It’s best to leave a slight bend or sag. This prevents excessive tension, protects insulators and support structures, and allows for flexibility during wind or temperature changes. A little slack ensures better longevity and stable performance.

For longer wire antennas, consider using a pulley system with a counterweight. This allows the wire to self-adjust under wind or thermal expansion, maintaining consistent tension without overstressing attachment points. The result is reduced risk of breakage and better long-term stability.

Mounting Advice for EFOC Antennas (EFOC29, EFOC17, EFOC8)

EFOC antennas (End-Fed Off-Center) are near-resonant designs. They generally require lower feedpoint heights than EFHW antennas and can be installed in compact gardens as slopers, inverted-Vs, or inverted-Us. Below are mounting recommendations for:

  • EFOC29 (80–10m)
  • EFOC17 (40–10m)
  • EFOC8 (20–10m)

EFOC29 (80–10m) as a Sloper

  • DX (20–10m): Slope 30–45°, feedpoint 7–10m. Low-angle radiation improves DX.
  • NVIS (80–40m): Steeper slope 60–75°, feedpoint 3–5m. Enhances high-angle NVIS.
  • Multi-band: 45° slope at 5–7m provides balanced performance.

Directivity: Dominant radiation is toward the lower end of the slope. Steeper angles produce more upward NVIS energy.

EFOC17 (40–10m) as a Sloper

  • DX (20–10m): Slope 30–45°, feedpoint 7–10m improves DX efficiency.
  • NVIS (40m): Slope 60–75°, feedpoint 3–5m enhances high-angle NVIS.
  • Multi-band: 45° slope at ~5m balances DX and NVIS.

Directivity: Like the EFOC29, main radiation is toward the slope’s lower end, with NVIS components at steeper slopes.

EFOC8 (20–10m) as a Sloper

  • DX (20–10m): Slope 30–45°, feedpoint 3–5m. Shorter length allows compact installs.
  • Regional: Slope 45–60°, feedpoint 3–4m directs more energy upward for local coverage.
  • Small gardens: Compact size makes it space-friendly while still DX-capable.

Directivity: Sharper directivity toward the lower endpoint due to shorter length. Steeper slope angles add NVIS coverage.

General Alternatives

Inverted V

  • Best for: Balanced NVIS and DX, especially with EFOC29 and EFOC17.
  • Feedpoint: ≥3m, ideally 5–7m for better performance.
  • Pattern: Radiation is strongest broadside to the V plane.

Inverted U

  • Best for: Limited spaces and DX on higher bands (EFOC8, EFOC17).
  • Feedpoint: 3–5m works well due to near-resonance.
  • Pattern: Broadside radiation to the U’s open ends.

Technical Considerations

  • Near-resonant design means less dependency on feedpoint height compared to EFHW.
  • Tuning may still shift with geometry; minor length trimming or tuner use can help.
  • NVIS use: feedpoint heights of 3–5m are adequate on 40m and 80m (EFOC17, EFOC29).

Minimum Ground Clearance

These are minimum recommended clearances. For flat-top use, expect compromised performance. In sloper, V, or U configurations, only the ends may approach these values.

Band Freq (MHz) λ Effective Ground (1/10 λ) Normal Ground (1/20 λ)
80m 3.5 85.7m 8.57m 4.29m
60m 5.3 56.6m 5.66m 2.83m
40m 7.1 42.3m 4.23m 2.12m
30m 10.1 29.7m 2.97m 1.49m
20m 14.2 21.1m 2.11m 1.06m
17m 18.1 16.6m 1.66m 0.83m
15m 21.2 14.2m 1.42m 0.71m
12m 24.9 12.0m 1.20m 0.60m
10m 28.5 10.5m 1.05m 0.53m

Multiple Antennas on One Mast

Condition Recommended Angle Reason
Minimum Angle ≥90° Acceptable isolation for most setups.
Optimal Isolation 180° Max separation, minimal coupling.
Multiband Setup ≥120° Reduces pattern distortion.
Compact Space 45° Works for high freq/directional, but coupling risk.
Resonant Wires ≥120° Reduce interaction due to broad lobes.
Directional (Yagis) ≥90° Narrow patterns tolerate closer spacing.
Cross-Polarized ≤90° Minimal interaction due to polarization.

Mini-FAQ

  • Can I mount EFOC antennas flat-top? — Not recommended; slopers, Vs, or Us are more effective.
  • What is the minimum feedpoint height? — 3–5m is enough for NVIS; raise higher for DX.
  • Do I need a tuner? — Usually not, but small trimming or tuner helps optimize resonance.

Interested in more technical content like this? Subscribe to our updates for deep-dive RF articles and lab notes.

Questions or experiences to share? Contact RF.Guru — we’re happy to help with your setup.

Joeri Van Dooren, ON6URE – RF engineer, antenna designer, and founder of RF.Guru, specializing in high-performance HF/VHF antennas and RF components.

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