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3.6kW End-fed Off-Center EFOC17 40-10M
3.6kW End-fed Off-Center EFOC17 40-10M
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The EFOC17 is a multiband end-fed off-center HF wire antenna designed for practical operation from 40m through 10m. It is built for operators who want broad HF coverage in a compact wire format without traps, loading coils, or unnecessary complexity.
What makes the EFOC17 especially flexible is that it can be deployed in two valid ways: as a 2-wire off-center-fed dipole variant, or as the classic EFOC version using the coax system as the short return path. Both approaches work, but they do not use the same choking strategy, so following the correct installation guide matters.
Why this antenna works in real installations
- Integrated 4:1 UNUN helps interface the antenna system to standard 50 Ω station equipment.
- Useful multiband coverage gives straightforward access to 40m, 20m, 15m, and 10m, with 30m, 17m, and 12m often usable with a tuner depending on deployment.
- Two installation methods let you choose the version that best fits your station layout and feedline routing.
- Correct return-current control is part of the design. The 2-wire version needs a hard 1:1 current choke directly at the feedpoint, while the coax-counterpoise version follows its own dedicated guide.
- Rugged outdoor construction makes the EFOC17 suitable for both permanent and semi-portable installations.
Specs at a Glance
| Feature | Specification |
|---|---|
| Application | Multiband HF wire antenna |
| Primary Coverage | 40m, 20m, 15m, and 10m |
| Additional Bands | 30m, 17m, and 12m may require a tuner |
| Antenna Type | End-fed off-center wire antenna |
| Transformer | Integrated 4:1 UNUN |
| Insertion Loss | Less than 0.2 dB |
| Typical VSWR | Typically below 2.5:1 on supported bands with proper deployment |
| Main Radiating Wire | 16.8 m |
| Coax for coax-counterpoise version | Approx. 16 m EXTRAFLEX-BURY-7 |
| Included choke on coax-counterpoise version | Ferrite choke positioned at approximately 3.7 m |
| Connector | SO-239 |
| System Impedance | 50 Ω |
| Enclosure | Rugged UV-resistant polycarbonate housing |
| Antenna Wire | Hard-drawn tinned copper with XLPE sheath |
| Approx. Weight | 650 g |
Power Ratings
| Version | ICAS | CCS | FT8 / FT4 |
|---|---|---|---|
| 2.4 kW version | 2400 W PEP @ VSWR < 2.0:1 | 1200 W PEP @ VSWR < 2.0:1 | 850 W @ VSWR < 1.5:1 |
| 3.6 kW version | 3600 W PEP @ VSWR < 2.0:1 | 1800 W PEP @ VSWR < 2.0:1 | 1250 W @ VSWR < 1.5:1 |
For ICAS and CCS power definitions, see our power rating guide.
Choosing the Correct Installation Method
- 2-wire variant — Use the dedicated off-center-fed dipole installation method with the correct second wire configuration. Follow the EFOC17 off-center dipole installation guide.
- Important for the 2-wire version — Use a hard 1:1 current choke directly at the feedpoint, not farther down the feedline.
- Coax-counterpoise version — Use the classic EFOC installation method where the coax system forms the short return path. Follow the EFOC17 antenna installation guide.
- Included choke on the coax-counterpoise version — A supplied ferrite choke should be installed at approximately 3.7 m. This is a practical baseline choke for around 200 W SSB / 100 W FT8 in a clean installation.
- More difficult installations — For higher power, compromised sites, or challenging feedline routing, a stronger common-mode solution may be advisable. See our high-CMR choke guidance.
Common-mode current matters here
The EFOC17 is not just about wire length. Like other off-center and return-path-managed antennas, performance depends strongly on where the return current is allowed to flow. That is why the 2-wire version and the coax-counterpoise version use different installation logic. Following the right guide is part of getting stable SWR, predictable current distribution, and cleaner on-air behavior.
Included with the Product
The exact contents depend on the selected version, but the EFOC17 platform includes the core antenna hardware needed for deployment.
- Complete tested EFOC17 transformer assembly with integrated 4:1 UNUN
- Outdoor-rated hard-drawn tinned copper antenna wire with XLPE sheath
- Weather-resistant enclosure with SO-239 connection
- For the coax-counterpoise version: approximately 16 m of EXTRAFLEX-BURY-7 coax and the supplied ferrite choke
- For the 2-wire variant: dedicated 2-wire deployment method as described in the installation guide (no coax included)
Mechanical Characteristics
- Core: High-performance ferrite optimized for low loss and stability
- Transformer wire: Heat-resistant PTFE-insulated wire
- Connector: Professional SO-239 connection point
- Enclosure: Polycarbonate, outdoor ready, UV-resistant, and mechanically robust
- Antenna wire: Approx. 2 mm outdoor wire for durable stationary use
Optional Mounting Kit
- 1 x Stainless steel mounting plate
- 2 x Stainless steel U-bolt mast clamps
- 2 x Black nylon tube inlays
- 8 x Stainless steel hex socket cap screws
- 4 x Stainless steel spacers
Helpful Guides & Technical Reading
EFOC17 off-center dipole installation guide
EFOC17 antenna installation guide for the coax-counterpoise version
Why the EFOC17 is the better choice for 40m to 10m operation
EFHW vs. EFOC: two voltage-driven antennas, two smart solutions
Why your EFHW is eating your signal and the EFOC is not
SWR and Installation Reality
Like all wire antennas, the final SWR and operating behavior depend on installation height, surrounding structures, ground conditions, feedline routing, and common-mode current control. Reference measurements are a baseline, not a guarantee. Always check SWR after installation and tune only with the correct variant guide in mind.
Mini-FAQ
- Does the EFOC17 cover 40m to 10m? — Yes. Those are its main target bands, with 30m, 17m, and 12m often available with a tuner depending on deployment.
- What is the difference between the 2-wire version and the coax-counterpoise version? — The 2-wire version uses a dedicated second wire and is installed as an off-center-fed dipole. The coax-counterpoise version uses the coax system as the short return path and follows the classic EFOC method.
- Where should the choke go on the 2-wire version? — Use a hard 1:1 current choke directly at the feedpoint.
- Is the supplied choke enough for every installation? — Not always. It is a practical baseline choke for moderate power in clean installs. More difficult sites can benefit from stronger common-mode suppression.
- Can I use the same installation guide for both variants? — No. Each variant has its own correct deployment method and should follow its own dedicated guide.
- Is this suitable for permanent outdoor installation? — Yes. The EFOC17 is built for durable outdoor use when installed correctly and weather-sealed as needed.
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