End Fed Off Center Antennas: Mounting advice
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) 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.
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