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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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EFOC17: Choose the Return Path Before You Raise the Wire
A compact 40–10 m end-fed off-center platform with an integrated 4:1 UNUN. Choose either the coax-counterpoise system or the two-wire off-center-fed dipole and follow the matching manual—because the choke belongs in a different place.
Fulfilment varies with order volume; allow approximately 1–4 weeks for assembly and shipping.
Unroll and measure every delivered wire. Use the manual’s starting dimensions, keep surplus folded back and cut only after installed tuning.
Two Valid Installations, Two Different Choke Boundaries
Approximately 16 m of EXTRAFLEX-BURY-7 coax is supplied. The first 3.7 m of coax exterior is the intended return section; the supplied choke is placed at its boundary.
The long and short wires form an off-center-fed dipole. A hard 1:1 current choke belongs directly at the coax side of the 4:1 feedpoint unit.
A 3.7 m choke position belongs to the coax-return version. The two-wire version requires the choke at the feedpoint so the feedline is not the missing radiator.
A low SWR does not identify the current path. Keep the chosen geometry and choke boundary fixed, then check the complete band sweep and exterior coax current. A tuner can transform impedance but cannot repair uncontrolled feedline participation.
Electrical and Mechanical Summary
| Item | Current specification |
|---|---|
| Primary bands | 40 m, 20 m, 15 m and 10 m |
| Additional bands | 30 m, 17 m and 12 m may require a tuner depending on deployment |
| Transformer | Integrated 4:1 UNUN; published insertion loss below 0.2 dB within the qualified boundary |
| Coax-version radiator | 16.8 m measured starting dimension from deliberately oversize supplied stock |
| Coax-version feed system | Approximately 16 m EXTRAFLEX-BURY-7 and supplied choke at approximately 3.7 m |
| Typical installed VSWR | Below 2.5:1 on supported bands with proper deployment; installation-dependent |
| Connector and enclosure | SO-239 in a rugged UV-resistant polycarbonate housing |
| Approximate weight | 650 g |
Power Versions
| Version | ICAS | CCS | FT8/FT4 |
|---|---|---|---|
| Single core | 2,400 W PEP at VSWR < 2.0:1 | 1,200 W PEP at VSWR < 2.0:1 | 850 W at VSWR < 1.5:1 |
| Dual core | 3,600 W PEP at VSWR < 2.0:1 | 1,800 W PEP at VSWR < 2.0:1 | 1,250 W at VSWR < 1.5:1 |
The supplied coax-version choke has its own boundary. It is a practical baseline for approximately 200 W SSB or 100 W FT8 in a clean installation. Higher transformer ratings do not override the choke, connector, cable, duty-cycle or thermal limits.
Installation Manuals
16.8 m start dimension, 3.7 m return section, choke placement, tuning and safety.
De Nederlandstalige handleiding voor de uitvoering met coax-retourpad.
Wire families and the hard 1:1 current choke directly at the feedpoint.
De Nederlandstalige tweedraadsprocedure en voedingspuntchoke.
Qualify the boundary for actual frequency, power and installation conditions.
Interpret the version label against waveform and duty cycle.
Follow the Current Path, Not Just the SWR
Explore more RF.Guru engineering on off-center antennas, transformers, chokes and installed current paths—and subscribe for new articles.
Join the notification list →Mini-FAQ
- Can both EFOC17 variants use the same guide? No. The coax-return and two-wire OCF versions require different current paths and choke positions.
- Where does the choke go on the coax version? At approximately 3.7 m from the feedpoint.
- Where does it go on the two-wire version? A hard 1:1 current choke belongs directly at the feedpoint.
- Is the supplied wire already cut exactly? No. Measure the deliberately oversize stock and fold the surplus before cutting.
- Does the transformer rating set the whole system rating? No. The weakest component and actual mismatch, duty and temperature set the limit.
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