Tuning Advice for an End-Fed Half-Wave (EFHW) Antenna

An End-Fed Half-Wave (EFHW) antenna is a highly versatile solution for multiband HF operation. Its design makes it resonant on harmonics of the fundamental frequency, allowing it to cover multiple bands with a single wire. Proper tuning is crucial to maximize efficiency and performance across all desired frequencies.

Understanding the EFHW Antenna Design

1. Feedpoint and Transformer:

  • EFHW antennas require a 49:1, 56:1, 68:1 or 70:1 transformer to match the high impedance at the feedpoint to a standard 50-ohm coaxial feedline. (

2. Radiator Length:

The wire length determines the resonance points. For example:

3. Optional Compensation Capacitor:

  • Some EFHW8010 antennas include a compensation capacitor placed at the midpoint of the wire. This capacitor is used to adjust the resonance point of the 80m band, centering the dip more effectively within the band for improved performance.

Steps to Tune an EFHW Antenna

1. Initial Setup

  • Mounting Height: Install the antenna at a height of 10-15 meters for optimal performance across most bands.
  • Clear Area: Avoid nearby structures, trees, or metal objects that may detune the antenna.
  • Feedpoint Placement:

For the EFHW16080 and EFHW8040: (Inverted L placement)

    • Secure the feedpoint to a stable structure at a height of 3–5 meters, and ensure the transformer is properly grounded (whether near the shack or the antenna, it doesn’t matter). Aim for the highest possible elevation, with a minimum height of 15 meters for the 160–80 meter  and at least 10 meters for the 80–40 meter.

2. General Tuning Process

1. Measure SWR Across All Bands:

    • Use an antenna analyzer or SWR meter to check resonance on all desired frequencies.
    • Record the resonant frequency and SWR for each band.

2. Adjust Wire Length:

If the antenna is too long:

If the antenna is too short:

    • Resonant frequencies will appear above the desired bands.
    • Add wire (if feasible)

3. Check Resonance After Each Adjustment:

    • Ensure that adjustments to one band do not negatively affect other bands.
    • For multiband operation, prioritize tuning the most frequently used bands.

4. Add a Common-Mode Choke

To reduce RF interference and feedline radiation:
  • Place a common-mode choke (ferrite beads or a coaxial choke) on the feedline near the shack entrance.
  • This minimizes RF currents on the coax shield, improving overall performance and reducing pickup up rf noise in the shack.

5. Provide a DC ground connection

The EFHW antenna will function without grounding, but grounding is recommended to protect your equipment by directing static buildup to the lowest resistance path instead of your gear. For the inverted L setup (160–80 and 80–40 antennas), it’s best to position the ground connection close to the feedpoint. For antennas installed higher than 10 meters, a ground connection near the shack entrance is sufficient.

Band-Specific Tips

Low Bands (160m, 80m, 40m):

  • These bands require the entire wire length to radiate efficiently.
  • Ensure the antenna height is sufficient to reduce ground losses and maximize radiation. (For 160m at least 15m high)

Mid Bands (20m, 15m):

  • Resonance is typically easier to achieve on these bands due to harmonic alignment with the wire length.
  • Adjust the wire length or transformer placement as needed to optimize SWR.

High Bands (12m, 10m):

  • These bands may show multiple lobes in the radiation pattern due to the antenna’s electrical length.
  • While SWR may rise slightly, performance is generally acceptable without major adjustments.

Common Issues and Solutions

 

Issue Cause Solution
High SWR on all bands Incorrect transformer installation Verify transformer placement
Low efficiency on lower bands Insufficient height above ground Raise the antenna or improve ground plane
RF interference in the shack Common-mode currents on feedline Add a common-mode choke near the transformer or ground the coax cable
Poor performance on high bands Excessive wire length causing detuning Shorten the wire or use a tuner

 

Environmental Considerations

  • Seasonal factors like humidity and vegetation growth can slightly detune the antenna. Recheck SWR periodically.
  • Proximity to ground or nearby structures affects radiation patterns. Adjust the mounting height if needed.

Using an Antenna Tuner

  • While EFHW antennas are resonant by design, an antenna tuner can fine-tune minor mismatches, especially on higher bands.
  • Use a tuner capable of handling the expected power and frequency range.

Conclusion

Tuning an EFHW antenna involves balancing wire length, feedpoint matching, and environmental factors to achieve low SWR and efficient radiation across multiple bands. 

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Written by Joeri Van Dooren, ON6URE – RF, electronics and software engineer, complex platform and antenna designer. Founder of RF.Guru. An expert in active and passive antennas, high-power RF transformers, and custom RF solutions, he has also engineered telecom and broadcast hardware, including set-top boxes, transcoders, and E1/T1 switchboards. His expertise spans high-power RF, embedded systems, digital signal processing, and complex software platforms, driving innovation in both amateur and professional communications industries.