EFHW vs. EFOC: Two Voltage-Driven Antennas, Two Smart Solutions
End-Fed Half-Wave (EFHW) and End-Fed Off-Center (EFOC) antennas are both voltage-fed wire antennas. While they may look similar at a glance — both typically fed at the very end and both requiring high-impedance transformers — their current distributions, height sensitivity, and operating behavior reveal clear differences.
Rather than one being strictly “better” than the other, they represent two different solutions for two different environments.
EFHW: Precision Tool for Serious DX
The EFHW is a resonant antenna that excels when installed at the proper height. At resonance, it supports a strong current maximum in the middle of the wire and high voltage at the ends. This geometry allows it to radiate efficiently on its fundamental frequency and on its second harmonic — making it highly effective as a dual-band solution (e.g., 40m/20m or 80m/40m).
EFHWs are most effective when:
- Mounted at least half a wavelength above ground for horizontal configurations
- Mounted 3 to 7 meters or higher for vertical or sloped configurations (higher = lower takeoff angle)
- You need sharp low-angle radiation for DX
Their downside? They’re less forgiving. Install them too low or close to obstacles, and performance drops quickly — especially on the second harmonic.
Our recommendation: Stick with monoband or dual-band EFHWs for maximum efficiency. Avoid squeezing in 10m on a 20m+ wire — it will radiate inefficiently due to unfavorable current distribution.
EFHW Advantages:
- Clean low-angle radiation when installed high
- Efficient two-band operation (via full-wave/half-wave harmonic pairing)
- Excellent for portable or stealth DX setups — if height allows
EFHW Limitations:
- Needs height to perform well
- High voltage feedpoint stresses transformer and insulation
- Susceptible to nearby coupling and environment distortion
EFOC: The Forgiving All-Rounder
The End-Fed Off-Center antenna is more of a general-purpose tool. It’s designed for multiband use from a single wire, typically using a 4:1 UNUN. The feedpoint is placed off-center, shifting the current maximum closer to the transformer and reducing feedpoint impedance to more manageable levels.
This current shift makes the EFOC more tolerant of:
- Lower mounting heights (5–8 meters)
- Mounting on or near rooftops
- Non-ideal geometries, like slopers or inverted-L layouts
It may not be a DX beast like a high-mounted Dual Band EFHW, but it’s extremely effective for everyday use, especially when fed with a proper choke and counterpoise.
EFOC Advantages:
- More tolerant of lower height and non-optimal placement
- Easier to match (lower feedpoint impedance)
- Good multiband compromise for casual operators
EFOC Limitations:
- Not ideal for chasing DX at low angles
- Slightly lower efficiency due to current asymmetry
- Can require radiator/counterpoise tuning to optimize
So Which Should You Choose?
| Use Case | Best Choice |
|---|---|
| High DX performance, elevated installation (10m+) | EFHW (mono/dual band) |
| Compact rooftop or balcony deployment | EFOC |
| Efficient dual-band pairing (40/20 or 80/40) | EFHW |
| Ease of tuning, forgiving to install | EFOC |
| Reliable portable multiband use | EFOC |
Bottom Line: Know Your Environment
These antennas are not competing — they’re complementary. The EFHW is a precision antenna for DXers with space and height. The EFOC is a solid multiband performer when you need to compromise on space, height, or simplicity.
They’re both voltage-fed, but their current distribution and impedance behavior are what make or break performance.
When the antenna’s voltage distribution is not symmetrical — particularly in end-fed verticals — the return path may become undefined, causing part of the differential-mode current to divert and flow along the coax shield. This leads to unintended radiation from the feedline, increased local noise pickup, and potential RF-in-the-shack.
Important: This current is often mischaracterized as "common-mode," but what you're actually seeing (and measuring with clamp meters) is unbalanced differential-mode current flowing on the outer shield due to the undefined return path. This current radiates via skin effect — a differential-mode phenomenon — just like any other antenna conductor.
And a final note on measurement: There are no clamp-on meters that can distinguish between common-mode and differential-mode currents. These devices simply detect net RF current on the outside of the coax shield. What they show is energy — and that energy can originate from either mode. The only thing they confirm is: RF is flowing where it probably shouldn't be.
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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.