EFOC8 Antenna Installation and Tuning Guide
EFOC8 Antenna Installation and Tuning Guide
Measure the deliberately oversize wire, establish the intended 2.2 m coax return section, place the supplied choke at its boundary and tune the installed antenna without letting the remaining feedline become an accidental radiator.
RF.Guru working definition: Common-mode current is the non-cancelling phasor-sum current in a specified set of conductors, evaluated at a defined cross-section and using a declared current-direction convention. In the intended differential transmission-line mode, the outgoing and return currents are equal and opposite, so their phasor sum is zero. When they do not cancel, the remaining current must close through another reference or return path—such as the outside of a coax shield, a mast, equipment chassis, station wiring, nearby structures, earth, the operator, or distributed coupling through the environment.
This broader working definition is especially useful in practical antenna systems. On transmit, non-cancelling current on the outside of the coax can make the feedline and connected structures part of the radiating antenna system unless that path is intentional, clearly defined and properly controlled—for example by providing the required return path and placing a suitable common-mode choke at the correct boundary.
The EFOC8 is a compact end-fed off-center antenna for 20 m through 6 m. The integrated 4:1 UNUN handles the intended impedance transformation. The first 2.2 m of coax exterior provides the designed short return path, and the supplied choke defines where that path should end.
Current starting configuration: the effective radiator starts near 7.6 m, while RF.Guru deliberately supplies about 8 m or slightly more so the installer can measure and fold back the surplus. The coax-counterpoise package uses approximately 16 m of EXTRAFLEX-BURY-7 coax and the supplied ferrite choke at approximately 2.2 m from the feedpoint.
Measure the Supplied Wire First
Do not assume the package contains a pre-cut 7.6 m radiator. The cutting machine intentionally supplies extra wire. Unroll it without stretching it, lay it straight, measure from the feedpoint connection end, mark the 7.6 m starting dimension and keep the remaining wire folded back for first tuning. Cut only after the installed measurements are repeatable.
Use the current EFOC8 product page to confirm the selected power and counterpoise version. The product exists with either a coax return path or a separate counterpoise-wire terminal. This guide covers the version supplied with coax and a ferrite choke.
Choose the Physical Layout
A flat top and a sloper are both practical starting layouts. Neither diagram fixes the installed pattern or impedance. Height, slope, bends, nearby metal, soil and cable routing remain part of the antenna system.
Flat top
Keep the radiator as straight, high and clear as the site safely permits. Leave the far-end surplus folded back during commissioning.
Sloper
A sloper can be supported from one high point, but its response depends on the complete geometry and surroundings. Keep its lower end safely out of reach.
Build the Intended Current Path
- Mount the enclosure securely and add strain relief so the SO-239 connector does not carry the wire tension.
- Measure the delivered wire, mark 7.6 m as the initial electrical length and install it with the surplus folded back.
- Route the first approximately 2.2 m of coax as the intentional exterior return section. Keep it away from reachable metal and do not coil it randomly.
- Install the supplied ferrite choke at approximately 2.2 m from the feedpoint.
- Route the remaining coax away from the radiator where practical. Preserve the same routing throughout tuning.
The return section may be horizontal, vertical or sloping, but moving it relative to soil, roofs or conductive supports can change the system. The 2.2 m dimension identifies the designed choke boundary; it does not make every route electrically identical.
Tune the Installed Antenna
Raise the antenna into its final position and begin at low power. Sweep the intended operating ranges rather than checking a single frequency. Use the same reference plane and cable arrangement for every pass.
- Record the complete 20 m response first because it anchors the lowest intended band.
- Check 17 m, 15 m, 12 m, 10 m and 6 m with the same geometry.
- If the response needs to move upward in frequency, shorten the active length in a small step by increasing the fold-back. If it must move downward, unfold available wire.
- Return the antenna to the same installed shape and repeat the full sweep after every change.
- Use a tuner where the installed impedance requires it. Do not use the tuner to hide unstable common-mode behaviour.
The bands interact, and a length change that improves one band can move another. Aim for the operating segments you actually use, not one spectacular minimum displayed by the analyser.
Check the Choke and Power Boundary
The supplied choke is a practical baseline for approximately 200 W SSB or 100 W FT8 in a clean installation. The 2.4 kW and 3.6 kW transformer versions do not make that baseline choke a multi-kilowatt component. Higher power, sustained digital duty or a compromised return path requires a choke qualified for the actual common-mode voltage, current, frequency range and thermal conditions.
A low SWR is not a choke measurement. Where possible, measure net current around the complete coax before and after the choke. Repeat at fixed transmitter power. Strong current below the choke, RF in the shack or large retuning when the feedline moves indicates that the current boundary needs attention.
Mechanical, RF and Weather Safety
- Never install the antenna where a wire, support or tool could contact an overhead power line.
- Keep the radiator and feedpoint out of reach during transmission because high RF voltage can occur.
- Use suitable insulators, supports and strain relief, and do not overtension the wire.
- Disconnect the transmitter before changing the wire, coax or choke position.
- Weather-seal the SO-239 connection and use a drip loop.
- Follow the station’s applicable bonding, surge, lightning and RF-exposure requirements. The ferrite choke is not lightning protection.
Mini-FAQ
- Is the supplied EFOC8 wire already exactly 7.6 m? No. RF.Guru deliberately supplies extra wire. Measure it and mark the 7.6 m starting dimension before folding or cutting.
- Where does the supplied choke go? At approximately 2.2 m from the feedpoint on the coax-counterpoise version.
- Does the first 2.2 m of coax matter? Yes. Its exterior is the intended short return path, so its routing is part of the installed antenna.
- Can the EFOC8 be installed as a sloper? Yes, but height, slope, surroundings and feedline routing affect both impedance and pattern.
- Should I cut the wire to tune it? Begin with fold-back adjustments and cut only after repeated measurements in the final geometry.
- Does the transformer rating apply automatically to the supplied choke? No. The complete system is limited by its weakest component and its actual VSWR, duty cycle, cooling and common-mode stress.