EFOC29 Get 80m and 30m Under Control: Practical Tips for Better SWR

The EFOC29 is a compact off-center-fed antenna with a 29-meter wire, a 4:1 UNUN, and a 1.2-meter counterpoise implemented via the coax braid, paired with a choke placed at 12.2 meters. It performs well across many HF bands, but users sometimes struggle with high SWR on 80 meters and 30 meters. Here's why that happens and what you can do to fix it.

Why 80m and 30m Are Problematic

• Harmonic mismatch: The 29-meter wire length does not align neatly with 1/2 or 1/4 wavelengths on 80m or 30m.
• Impedance excursions: Feedpoint impedance can drift far outside the comfortable transformation range of the 4:1 UNUN.
• Common-mode coupling: On lower bands, the coax may radiate or pick up noise, distorting the measured impedance.

Reposition the Choke

The factory-recommended 12.2-meter location is a good general compromise, but:

• Try placing the choke closer, for example around 8 meters from the feedpoint.
• Try placing the choke farther away, for example around 14 meters from the feedpoint.
• Optimal choke position varies based on coax length, feedpoint height, wire slope, and local installation conditions.

Reference the Manual for Wire Tuning

The installation manual specifies that the 80m dip is tuned just below 3.5 MHz. Any significant deviation from the intended 29-meter length can degrade the tuning. Trimming or extending the radiator is not advised unless you are intentionally retuning the antenna for a fixed-frequency application.

Height Matters

Feedpoint height and wire geometry can have a significant effect on impedance:

• Raising or lowering the feedpoint by even 1–2 meters can shift the impedance curve.
• Keep the wire as horizontal as possible. Avoid steep slopes, sharp bends, or running the wire close to conductive objects.
• When space is limited, aim for a gradual slope and at least 6–7 meters average wire height.

Avoid Short “80m Stub” Fixes

A short open-ended coax stub is not a proper 80m tuning solution. On 80m, a quarter-wave RG58 stub is roughly 14 meters long when using common solid-PE RG58 with a velocity factor around 0.66, depending on the exact target frequency and cable type. Foam-dielectric coax or other cable types may require a different length.

A 2–3 meter open-ended RG58 stub is therefore not an 80m quarter-wave stub. At 80m it behaves mainly as a short reactive shunt, mostly adding capacitance near the feedpoint. That may move the impedance slightly, but it is not a clean or predictable 80m resonance-stabilizing solution.

Because the EFOC29 is a multiband antenna, adding random coax stubs near the feedpoint can also disturb other bands. A stub, trap, or matching network should only be used after measurement or modeling, and only when you understand which band it is intended to affect.

• Do not add a 2–3 meter open RG58 stub as a general 80m SWR fix.
• For an actual coaxial quarter-wave stub, calculate the length using the target frequency and the cable velocity factor.
• For most installations, choke position, feedpoint height, wire geometry, and tuner range are safer first adjustments.

Final Advice: Don’t Fear 3:1

• Most external tuners can handle 3:1 SWR comfortably, although tuner range varies by model and by impedance.
• Focus on ensuring the antenna radiates well and keeps common-mode noise low.
• Always inspect R and X separately. A high SWR is not always a bad antenna, but it does tell you that the transmitter or tuner is seeing a mismatch.

Summary

If you're struggling on 80m or 30m with an EFOC29, start by moving the choke, double-checking your radiator length, and optimizing the feedpoint height. Avoid adding short coax stubs as a quick fix unless they have been properly calculated and verified. The system is well-designed and usually only needs minor installation tweaks.

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