End Fed Off Center Antennas: Mounting advice

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

EFOC antennas (End-Fed Off-Center antennas) differ from EFHW antennas in that they are near-resonant designs and generally require lower feedpoint heights for effective operation. Below are the recommendations for deploying the EFOC29 (80–10m), EFOC17 (40–10m), and EFOC8 (20–10m):

EFOC29 (80–10m) As a Sloper

For DX on Higher Bands (20m, 15m, 10m):
  • Use a slope angle of 30–45° to favor low-angle radiation.
  • A feedpoint height of as low as 5m is sufficient, although raising it to 7–10m enhances performance on higher bands.
For Regional NVIS Communication (80m, 40m):
  • A steeper slope angle (60–75°) improves NVIS radiation by directing energy upward.
  • A feedpoint height of 3–5m works well for NVIS on 80m and 40m.
For Multi-Band Use (80–10m):
  • Use a 45° slope as a balanced compromise.
  • A feedpoint height of 5–7m provides adequate performance for both NVIS and DX across all bands.
Directivity:
  • The dominant radiation is toward the slope’s lower end (downward and outward).
  • Some NVIS energy is radiated upward, especially when the slope is steeper.

EFOC17 (40–10m) As a Sloper

For DX on Higher Bands (20m, 15m, 10m):

  • Use a slope angle of 30–45° for low-angle radiation.
  • A feedpoint height of 5–7m is effective; higher heights (~10m) improve DX performance on higher bands.

For Regional NVIS Communication (40m):

  • A steeper slope (60–75°) enhances upward radiation for NVIS.
  • A feedpoint height of 3–5m is ideal for NVIS on 40m.

For Multi-Band Use (40–10m):

  • A 45° slope provides balanced DX and NVIS performance.
  • A feedpoint height of 5m works well for mixed-use applications.

Directivity:

  • Similar to the EFOC29, the primary radiation is toward the lower end of the slope, with NVIS energy radiating upward if the slope is steep enough.

EFOC8 (20–10m) As a Sloper

For DX (20m, 17m, 15m, 10m):

  • Use a slope angle of 30–45° to favor low-angle radiation for DX.
  • A feedpoint height of as low as 3–5m is sufficient due to the shorter wavelength and the near-resonant design.

For Regional Communication (20m):

  • Steeper slopes (45–60°) can direct more energy upward for local or regional coverage.
  • A feedpoint height of 3–4m works well.

For Limited-Space Installations:

  • The EFOC8’s compact size makes it suitable for small gardens.
  • A 30–45° slope with a feedpoint at 3–5m is effective for most applications.

Directivity:

  • The shorter length of the EFOC8 leads to sharper directivity toward the lower endpoint of the slope, with some upward energy for higher slope angles.

General Alternatives

Inverted V:

  • Best for: Balanced NVIS and DX performance on lower bands ( EFOC29 and EFOC17).
  • Feedpoint Height: A minimum of 3m is sufficient for resonance, but raising it to 5–7m improves overall performance.
  • Radiation Pattern: Equal radiation in both directions perpendicular to the plane of the V.

Inverted U:

  • Best for: Compact spaces and DX on higher bands ( EFOC8 and EFOC17).
  • Feedpoint Height: 3–5m works effectively due to near-resonance.
  • Radiation Pattern: Broadside to the open ends of the U.

Technical Considerations

  • EFOC antennas’ near-resonant design reduces the dependency on feedpoint height for tuning and performance compared to EFHW antennas.
  • Optimal impedance and resonance may still vary slightly with mounting configurations. Using an antenna tuner or adjusting wire lengths can ensure peak performance.
  • For NVIS applications, feedpoint heights as low as 3m are effective, especially on 40m and 80m with the EFOC17 and EFOC29, respectively.

      EFOC Antenna Minimum Ground Clearance

      These are the minimum recommended clearances! When used as a flat-top configuration, performance will be significantly compromised. These values serve as a guideline for the lowest part of the antenna when installed in configurations such as an Inverted L, Inverted V, Sloper, or Inverted U, where the majority of the wire is positioned well above these minimum heights and the endpoints of the wire can be at these minimum clearances.

      Band (Meters) Frequency (MHz) Wavelength (λ) Effective Ground
      (1/10 λ)      		 Normal Ground
      (1/20 λ)
      80m 3.5 85.71m 8.57m 4.29m
      60m 5.3 56.60m 5.66m 2.83m
      40m 7.1 42.25m 4.23m 2.12m
      30m 10.1 29.70m 2.97m 1.49m
      20m 14.2 21.13m 2.11m 1.06m
      17m 18.1 16.57m 1.66m 0.83m
      15m 21.2 14.15m 1.42m 0.71m
      12m 24.9 12.05m 1.20m 0.60m
      10m 28.5 10.53m 1.05m 0.53m

       

      Multiple antennas on the same supporting mast ?

      Condition Recommended Angle Reason
      Minimum Angle ≥ 90° Minimizes coupling and interaction for most setups, providing acceptable isolation.
      Optimal Angle for Isolation 180° Maximizes isolation and minimizes mutual coupling, ensuring independent operation.
      Multiband Setup ≥ 120° Reduces interaction across bands, prevents pattern distortion, and ensures good coverage.
      Compact Space 45° Can work for directional antennas or high frequencies but leads to significant coupling.
      Resonant Wire Antennas (e.g., EFOC, EFHW, Dipoles) ≥ 120° Reduces mutual coupling due to their broad radiation patterns and potential interaction.
      Directional Antennas (e.g., Yagis) ≥ 90° Tolerant of closer spacing because of narrower radiation patterns.
      Cross-Polarized Antennas ≤ 90° Can be closer together as interaction is minimal due to polarization differences.