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, 64:1, 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:

• EFHW16080: ~80m long, covering 160m–80m.
• EFHW8040:  ~40m long, covering 80m–40m.
• EFHW4020: ~20m long, covering 40m–20m.
• EFHW4010: ~20m long, covering 40m–10m.
• Less efficient lengths EFHW8010 
  read: Why the EFOC29 Design Outperforms the EFHW8010 and EFLW37 in Multiband Operation
  read: The Challenges of Multiband End-Fed Half-Wave (EFHW) Antennas and Ferrite Losses
  

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 EFHW8010 and EFHW4010 and monoband EFHW60, EFHW30: (Sloper, Flat-Top)

• Position the feedpoint at a height of 6 to 15 meters (higher better performance)

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. Compensation Capacitor Tuning ( EFHW8010 Only)

If your antenna has a compensation capacitor:

1. Start Tuning Higher Bands (40m, 20m, 10m):

• Adjust the wire length to achieve resonance on these bands first.
• Measure SWR with an analyzer and ensure it is below 2:1 for each band.

2. Add Wire for 80m:

• After tuning the higher bands, add the additional wire needed to extend resonance to the 80m band.
• Fine-tune the added length to achieve resonance on 80m without affecting the higher bands.

3. 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:

• • Resonant frequencies will appear below the desired bands.
  • Shorten the wire incrementally (5–10 cm) and re-measure SWR.
• Alternatively, fold back the excess wire instead of cutting it. Secure the folded section with cable ties or tape to allow for further adjustments.  Read more: Folding Back vs. Cutting Wire Antennas: Essential Tips for Optimal Performance

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

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. For EFHW8010 antennas with a compensation capacitor, tuning the higher bands first ensures the best performance before extending resonance to 80m. With proper setup and periodic adjustments, an EFHW antenna provides excellent multiband coverage for both DX and local communication.

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.