When choosing an end-fed antenna for multi-band HF operation, three popular designs come into consideration: the End-Fed Off-Center ( EFOC29), the End-Fed Half-Wave 80-10m ( EFHW8010), and the End-Fed Long Wire 37m ( EFLW37). While all three can be used effectively for HF operation, the EFOC29 design presents several advantages that make it a superior choice for DX performance and efficiency in multiband operation.

However, it is important to note that in dual-band operation (160-80M, 80-40M, 40-20M), the EFHW outperformed both due to its resonant characteristics.

1. Radiation Pattern and Gain

One of the most important factors in antenna performance is its radiation pattern and DX gain at low elevation angles(10–20°), which is critical for long-distance contacts.

• EFOC29: Due to its off-center feed point the current distribution is asymmetrical, which modifies the formation of lobes. This results in more pronounced and optimized lobes for DX propagation at higher frequencies.
• EFHW8010: As a classic half-wave, its current and voltage distribution are well understood, but on higher bands, it exhibits more scattered lobes with deeper nulls, which can lead to inconsistent DX performance in multiband setups. However, in a dual-band configuration (e.g., (160-80M, 80-40M, 40-20M), the EFHW can be extremely effective and the better choice.
• EFLW37: This long wire does not have the same level of resonance control, leading to weaker low-angle radiation, which makes it less effective for DX operation on most bands.

The measured DX gain comparison shows the superiority of the EFOC29, particularly on 20m, 17m, 15m, 12m, and 10m, where it outperforms the EFHW8010 and EFLW37 by 0.5–1.5 dB in multiband use. 

2. Feed Point and Impedance Matching

The feed point location significantly influences antenna impedance and efficiency.

• EFOC29: The 29% off-center feed point provides an impedance that is easier to match compared to a traditional EFHW. A well-designed transformer (typically a 4:1 or 9:1) ensures efficient power transfer with minimal losses.
• EFHW8010: Requires a 49:1 transformer to match the high impedance (typically 2,500–3,000Ω), which results in higher losses due to the extreme impedance transformation ratio, especially in multiband use. However, in dual-band operation, this issue is less pronounced as it remains efficient within two key resonance points.
• EFLW37: Typically matched with a 9:1 unun, it suffers from mismatch issues on several bands, leading to higher SWR on non-resonant frequencies.

This means that the EFOC29 provides a better efficiency and lower loss transformation for multiband operation, translating to more power reaching the antenna instead of being dissipated as heat.

3. Multi-Band Performance and Efficiency

The ideal multi-band antenna should perform consistently across all bands while maintaining good efficiency.

• EFOC29: Offers a better balance between efficiency and bandwidth, allowing stronger DX performance on high bands while maintaining usability on lower bands.
• EFHW8010: While resonant on multiple bands, its pattern becomes chaotic on higher frequencies, reducing DX predictability. 
• EFLW37: Requires a tuner and has lower efficiency due to its non-resonant nature, particularly on higher bands.

4. Noise Immunity and RFI

• EFOC29: With its balanced current distribution, it generally has lower common-mode noise, making it quieter in urban environments.
• EFHW8010: Being a classic EFHW, it is more prone to common-mode noise and RFI issues, especially in compromised installations. 
• EFLW37: Due to its length and random impedance, it tends to pick up more noise and requires a good counterpoise.

Conclusion

For operators seeking the best balance between efficiency, DX performance, and ease of matching in multiband operation, the EFOC29 is the superior choice. Its optimized feed point placement, lower impedance transformation ratio, and enhanced DX gain on higher bands make it an ideal solution for both serious DXers and general HF operators.

However, it is crucial to note that for dual-band operation,(160-80M, 80-40M, 40-20M) the EFHW remains king, as its lobes align well on specific resonant bands.

Compared to the EFLW37, both the EFOC29 and EFHW8010 demonstrate significantly higher efficiency and DX reach.

In summary, if your goal is effective DX communication and a well-balanced HF antenna for multiband use, the EFOC29 design is the way to go. 

Article written by Joeri Van Dooren, ON6URE – RF engineer, antenna designer, and founder of RF.Guru. With extensive experience in active and passive antenna systems, high-power RF transformers, and custom RF solutions, Joeri shares insights into cutting-edge radio communication technologies.