Optimizing the EFOC29 for 160m-10m Band Operation with additional Radials

A 29-meter (EFOC29) end-fed antenna, when paired with a UNUN, can serve as an effective multi-band HF solution. However, its performance on 160m to 10m can be significantly improved by using an optimal radial system. This article explores how to enhance efficiency and reduce impedance variations across these bands while considering the impact of coaxial cable as part of the counterpoise system.

Understanding the Role of Radials and Coaxial Shield

A 4:1 UNUN provides impedance transformation but does not eliminate the need for a counterpoise. In this setup, the coaxial shield acts as part of the counterpoise system, contributing to the overall electrical length.

  • The initial counterpoise includes 12.2 meters of coaxial shield.
  • Additional radials will be connected at the end of the coaxial cable, just before the choke. This also adds the possibility for the 160M band (NVIS only). You can also improve the 80 and 60m band.
  • For difficult bands like 30m and 15m, additional radials will be connected directly from the transformer to improve impedance matching. These radials are independent of the coaxial length.

While a single ground connection may work, a well-designed radial system enhances performance across multiple bands. The impact of radial adjustments is more significant on top bands (160m-80m) due to ground losses, but including radials for all bands helps maintain a stable impedance match.

Revised Radial Lengths Considering Coaxial Shield Contribution

Since the coaxial cable contributes 12.2m to the counterpoise system, radials should be adjusted accordingly. The goal remains to create an effective RF ground using a combination of quarter-wavelength radials and shorter counterpoise elements.

Updated Radial Lengths for 4:1 UNUN

Band Wavelength (m) Quarter-Wave (m) Adjusted EFOC29 Radials (m) Radial Connection Point
160m 160 40 27.8 From the choke
80m 80 20 7.8 From the choke
60m 60 15 2.8 From the choke
40m 40 10 10 From the transformer
30m 30 7.5 7.5 From the transformer
15m 15 3.75 3.75 From the transformer

 

Key Adjustments:

  • The 160m, 80m, and 60m band radials should be connected from the choke.
  • Additional radials for 40m, 30m, and 15m band should be connected directly from the transformer and do not include the coax length in their calculations.

Recommended Radial Configurations

Basic Setup (Minimum Required for Better Performance)

If space is limited, a few radials can significantly improve antenna efficiency:

  • One 27.8m radial (Improves 160m performance, from choke)
  • One 7.8m radial (Enhances 80m, from choke)
  • One 10m radial (Covers 40m, from transformer)
  • One 7.5m radial (Covers 30m, from transformer)
  • One 3.75m radial (Covers 15m, from transformer)

Intermediate Setup (Balanced Performance)

Adding more radials enhances the antenna’s multi-band capabilities:

  • 4 radials of 27.8m (Improves 160m, from choke)
  • 4 radials of 7.8m (Effective for 80m, from choke)
  • 4 radials of 2.8m (Useful for 60m, from choke)
  • 4 radials of 10m (Useful for 40m, from transformer)
  • 4 radials of 7.5m (Useful for 30m, from transformer)
  • 4 radials of 3.75m (Useful for 15m, from transformer)

Elevated vs. Ground Radials

  • Elevated radials (1m or higher) require fewer radials to be effective.
  • Ground radials (laid directly on or slightly buried under the soil) improve performance but benefit from higher numbers.
  • If space is limited, prioritize one long radial (27.8m, from choke) and a few shorter ones (7.8m, 10m, 7.5m, or 3.75m from the transformer).

Conclusion

By incorporating an optimal radial system while considering the coaxial shield as part of the counterpoise, the EFOC29 can provide stable and efficient performance from 160m to 30m.

Even a modest radial setup significantly improves impedance matching and efficiency, while a well-optimized radial field ensures the best radiation characteristics across all bands. Investing in a good counterpoise system will maximize the potential of your 29m end-fed antenna, ensuring a stronger and more reliable signal on HF frequencies.

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.