How to Build an Off-Center Fed Dipole (OCFD)

If you’re tired of glowing YouTube thumbnails and antennas that never quite match the hype, the off-center fed dipole (OCFD) is a refreshing reality check. It’s a simple, rugged wire antenna that quietly covers multiple HF bands without fancy traps, motors, or mystery black boxes.

In this guide you’ll build an OCFD you can actually rely on — for casual DX, nightly nets, and emergency communication when the grid is down. We’ll walk through materials, tools, planning, and detailed step-by-step instructions. If you can measure, cut wire, and safely get a line over a tree limb, you can build this antenna in an afternoon.

Expect about 3–4 hours of hands-on work for a first-time build, plus some extra time for tuning with an analyzer. By the end of this article you’ll have a working OCFD on the air, a clear understanding of how it behaves, and a repeatable recipe you can deploy at home, at a bug-out location, or on a family property.

What Is an Off-Center Fed Dipole (OCFD)?

An off-center fed dipole is exactly what it sounds like: a dipole where the feedpoint is intentionally moved away from the physical center. That off-center feedpoint sees a higher impedance than a classic 50 Ω center-fed dipole. With the right 4:1 current balun and feedpoint location, you get several bands with reasonable SWR on a single piece of wire.

Unlike many “random-wire” antennas, the OCFD is repeatable and predictable. A common 80 m design around 135 ft long, fed roughly one-third from one end, gives useful coverage on 80, 40, 20, 17, and 10 meters — often without a tuner on at least one or two bands. Add a tuner and it becomes a very capable all-around HF antenna for the prepared operator.

Materials Needed for a Reliable OCFD

You can build an OCFD from purely generic parts, but specifying real-world components makes life easier. Use this list as a shopping checklist.

Wire, Balun, and Feedline

• Antenna wire: ~135 ft (41 m) of 14–16 AWG stranded, insulated copper wire for an 80 m OCFD. (Example: Davis RF Flex-Weave, DXE-ANTW-400.) For a 40 m-only version, 66 ft (20 m) is plenty.
• 4:1 current balun: Rated for at least 1 kW PEP, HF coverage 1.8–30 MHz. Commercial examples include DX Engineering, Balun Designs, or MFJ 4:1 current baluns.
• Coaxial feedline: 50 Ω coax such as RG-8X for shorter runs, or RG-213 / LMR-400 for permanent and higher-power installations.
• Common-mode choke: Either a dedicated 1:1 choke (ferrite core) or several ferrite beads for the coax near the feedpoint.

Mechanical Hardware

• End insulators (x2): UV-resistant plastic or ceramic units with holes for wire and rope.
• Center support plate or insulator: Small aluminum or fiberglass plate with holes for wire, balun mounting hardware, and a top eye bolt.
• UV-resistant rope or paracord: 3–5 mm diameter, 50–100 ft (15–30 m) total for hoisting and tie-offs.
• Stainless hardware: Nuts, bolts, washers, and eye bolts for attaching the balun and supporting the center insulator.
• Weatherproofing: Self-fusing silicone tape, electrical tape, and outdoor-rated sealant for coax connectors and balun joints.

Optional but Highly Recommended

• Lightning arrestor at the entry point or bulkhead panel.
• Ground rod and strap for station grounding and surge control.
• Line launcher: Throw bag, arborist line, or slingshot to safely get ropes into trees.

Tools Required

Nothing exotic here — just normal hand tools plus something to measure and test RF.

Essential Tools

• Wire cutters and strippers
• Needle-nose pliers and regular pliers
• Cordless drill with small bits (for center plate holes)
• Screwdrivers and nut drivers for the balun hardware
• Soldering iron and solder (if using soldered connectors or joints)

Measuring and Testing

• Measuring tape: At least 50 ft (15 m), though 100 ft makes life easier.
• Antenna analyzer: NanoVNA, RigExpert, or similar preferred for plotting SWR curves.
• Or at minimum a radio + SWR meter capable of low-power tune-up.

Safety and Comfort

• Safety glasses and work gloves
• Ladder (if absolutely necessary — trees and masts are safer when reachable from the ground)
• Headlamp if you’re the “tune it after dark” type

Preparation: Planning Your OCFD Install

Before you cut a single piece of wire, step back and plan. You’re building a core piece of your station, not a throwaway experiment.

1. Pick Your Bands and Length

If you want strong local and regional emergency coverage, you’ll want 80 m or 60 m in the mix. That points you at the 135 ft design. If you mainly operate 40–10 m and have a smaller lot, a 66 ft OCFD is easier to deploy and less visually obvious.

2. Survey Your Supports

Walk your property and look for trees, masts, chimney mounts, or garage corners you can use. Think about:

• Safe distances from power lines (absolutely no guessing here).
• Where coax will enter the shack or radio room.
• How you’ll drop the center support if you need to service the balun.

3. Decide on the Shape

A perfectly flat, level dipole is nice, but real yards rarely cooperate. The good news: OCFDs tolerate bends and slopes quite well.

• Flat-top: Best overall if trees or masts are available.
• Inverted-V: Easier on small lots and sheds snow and ice well.
• Sloper: Handy when you only have one tall support and a lower tie-down point.

Once you’ve sketched your layout and confirmed the length will fit, you’re ready to build.

Step-by-Step: Building Your Off-Center Fed Dipole OCFD

In this section you’ll go from loose wire and parts to a working OCFD. Follow the steps in order and don’t rush the measurements.

1. Step 1 — Measure and Cut the Antenna Wire

   Roll out your wire in a straight line on the ground. Use the measuring tape to mark the total length you chose in the planning stage. For an 80 m build, mark 135 ft; for a 40 m build, mark 66 ft.

   Cut the wire cleanly at the mark. Next, measure from one end to the 33–34% point. On a 135 ft antenna that’s roughly 45 ft for the short leg and 90 ft for the long leg. Cut at that mark so you now have two separate legs: one short, one long.

2. Step 2 — Build the Center Support and Balun Mount

   Take your small plate or center insulator and drill holes for the two legs, an eye bolt at the top, and the balun mounting hardware. Deburr the holes so they don’t cut the wire insulation.

   Mount the 4:1 current balun to the plate using stainless bolts and lock washers. The goal is to have a single, solid assembly that you can hoist by the eye bolt without stressing the coax connectors.

3. Step 3 — Attach the Dipole Legs to the Balun

   Strip about 1–2 inches (2–5 cm) of insulation from the inner ends of each leg. Crimp or solder ring terminals onto each, depending on your hardware. Attach the short leg to one balun output terminal and the long leg to the other.

   Leave a very gentle loop of slack between the ring terminal and the wire entering the center plate. This prevents the balun from becoming a mechanical stress point when the wind kicks up.

4. Step 4 — Install End Insulators and Ropes

   Strip or crimp ring terminals on the far ends of both legs and attach them to end insulators. Tie UV-resistant rope or paracord to each insulator with a strong knot such as a bowline or figure-eight follow-through.

   Make the ropes longer than you think you’ll need. Extra length can always be coiled up; a rope that’s too short usually means another trip up the ladder or tree.

5. Step 5 — Hoist the Antenna to Operating Height

   Using throw line or a line launcher, get a light pilot line over your chosen supports. Pull your main support rope into position and attach it to the center assembly’s eye bolt.

   Raise the center until it reaches your target height — ideally 30–50 ft. Then walk the end ropes out toward your tie-off points, adjusting tension so the wire is neither drum-tight nor sagging onto branches or roofs.

6. Step 6 — Connect Coax and Common-Mode Choke

   Attach your coax to the balun’s SO-239 or terminal block, tightening by hand and then snugging with a wrench if appropriate. Weatherproof the connection with self-fusing silicone tape and a layer of electrical tape.

   Install a 1:1 current choke close to the feedpoint or at the shack entry. This can be a commercial choke balun or several turns of coax through ferrite cores. The choke keeps RF off the outside of the coax and prevents “mystery” RFI issues in the shack.

7. Step 7 — Perform Initial SWR Sweeps

   Connect the coax to your antenna analyzer or to the radio and SWR meter. Start with very low power. Sweep the bands the antenna should cover — for example 80, 40, 20, 17, and 10 m.

   Note the frequencies where SWR dips. On a typical 135 ft OCFD, you’ll see useful minima on several bands without touching the wire. Don’t chase perfection yet; just get a baseline for where things stand.

8. Step 8 — Trim and Fine-Tune the Legs

   If the SWR dips are consistently low in frequency, trim both legs equally — just an inch or two at a time — and repeat the sweep. If 80 m is perfect but 40 m is high, you can remove tiny amounts from the short leg to nudge that band upward.

   Keep notes as you go. When you’re happy with the main bands, stop trimming. A tuner can clean up smaller mismatches without sacrificing valuable bandwidth.

9. Step 9 — Lock Everything Down for Weather

   Once tuning is complete, recheck all mechanical connections. Tie off ropes securely, coil and secure any extra line, and verify the wire can’t rub against sharp edges or metal gutters in high wind.

   Finish weatherproofing the coax connectors and balun. A little extra tape and sealant today means fewer surprises in the next thunderstorm.

Testing and Verifying Your OCFD

With the antenna up and roughly tuned, it’s time to verify performance and catch any hidden problems before you call it “done.”

Baseline Electrical Checks

• SWR sweeps: Use your analyzer to log SWR curves across each band. Save or screenshot the plots so you can compare later after changes.
• Power handling: Start with 10–20 W and gradually increase. Watch SWR for sudden changes, which may indicate arcing or loose hardware.
• Common-mode behavior: If touching the radio or coax changes the SWR noticeably, improve your choke or station grounding.

On-Air Sanity Checks

• Make a few local contacts on your primary band to confirm audio quality and signal reports.
• Use digital modes or beacons to get real-world distance and SNR reports on multiple bands.
• Compare receive noise and signal levels against another antenna if you have one.

Troubleshooting Common Issues

Symptom	Likely Cause	Fix
High SWR on all bands	Bad connection, wrong balun, or water in coax	Check coax continuity, verify balun wiring, inspect and re-seal connectors
Only one band tunes well	Incorrect total length or feedpoint offset	Re-measure legs, adjust short leg length slightly, confirm offset is ~33%
RFI in shack electronics	Common-mode current on coax	Add or improve 1:1 choke, bond station ground, reroute feedline away from devices

Results and Performance: What to Expect

A well-built off-center fed dipole is not magic, but it is honestly good. With decent height and a clean feed system you can expect strong regional coverage on the low bands and solid DX potential on the higher bands.

Band-by-Band Expectations

Band	Expectation	Notes
80 m	Good regional coverage	Best for nets and night-time ragchews; NVIS at modest heights
40 m	Excellent	Daytime regional work and nighttime DX depending on propagation
20 m	Very good	Strong DX band; lobes and nulls appear as height increases
17 & 15 m	Good	Often tune well with a modest tuner; great for DX when open
12 & 10 m	Good to excellent	Can be very effective during high solar activity; patterns become multi-lobed

Compared to a fan dipole or trap dipole, the OCFD trades “perfect” resonance on every band for simplicity and a single span of wire. Compared to many end-fed half-wave (EFHW) designs, it often has a cleaner feed system with fewer RFI surprises, especially when you prioritize a quality current balun and choke.

For radio operators focused on emergency communications and off-grid reliability, the OCFD offers a strong mix of capabilities: one antenna, many bands, no moving parts, and no fragile loading coils to burn out under continuous duty modes.

FAQ — Quick Answers About OCFD Antennas

Do I need a tuner with an off-center fed dipole?

Strictly speaking, no — many OCFDs show low SWR on several bands without one. In reality, a tuner is highly recommended. It lets you safely run your rig on “in-between” frequencies, clean up mismatches as weather and surroundings change, and stretch the antenna onto bands it only barely reaches.

Can I use a voltage balun instead of a current balun?

You can, but you probably shouldn’t. OCFDs are prone to common-mode currents because of their asymmetry. A current balun forces equal and opposite currents on the legs and dramatically reduces RFI, meter weirdness, and “hot mic” symptoms in the shack.

How high does the OCFD really need to be?

More height is almost always better for DX, but don’t let “perfect” stop you. A center height of 30–40 ft already works very well for regional and long-haul communication. Even 20–25 ft is perfectly serviceable for emergency and local work, especially on 80 and 40 metres.

Can I bend or zig-zag the legs to fit my yard?

Yes. The OCFD is very tolerant of bends and “dog-leg” layouts as long as the wire doesn’t run right alongside metal siding or close to power lines. Sharp bends can slightly shift resonance, but the convenience is usually worth it on tight lots.

Next Steps, References & Further Reading

• ARRL Antenna Book and ARRL Handbook sections on multiband wire antennas.
• Manufacturer documentation for your specific 4:1 current balun and common-mode choke.
• Local radio club build nights and online communities where operators share real OCFD layouts and analyzer plots.