How to Build a 40 Meter Dipole Antenna? | 67-Foot Wire Build

A full-size 40-meter dipole measures about 66.9 feet tip to tip, split into two 33.4-foot legs using the 468/f rule.

For the full breakdown, see our best 40 Meter Band Antenna guide.

The 40-meter dipole is the amateur band’s default antenna: two equal wire legs, a center feed point, and one simple formula. When you set out to build a 40 meter dipole antenna, that formula decides whether you finish with a resonant single-band antenna or an afternoon of trimming.

The standard length rule is 468 / f(MHz), giving total length in feet. At 7.0 MHz that’s 66.9 feet, split into two legs of about 33.4 feet each. Builders using insulated wire usually cut a few inches long, then trim to resonance at the frequency they actually operate.

How Long Is A 40-Meter Dipole? The 468/f Length Rule

A full-size 40-meter dipole spans 66.9 feet tip to tip when cut for 7.0 MHz, with each leg at about 33.4 feet. Cut for mid-band and the total drops to roughly 65.5 feet.

On 40 meters the US band runs 7.0 to 7.3 MHz, so the same 67-foot wire can be trimmed to resonate anywhere inside it.

Two build realities shift the math. Insulated wire slows the signal slightly, which pulls resonance lower than the formula predicts — so cut long and trim in small steps. End insulators and the wire’s own end effects push the same direction. Cutting for 7.0 MHz and trimming up toward 7.15 is the most common path. The formula is a starting point, not a promise; every installation sits in slightly different surroundings, which is why the SWR meter earns its place.

How Do You Build And Feed A Dipole?

Build a 40-meter dipole as two identical wire legs joined at a center feed point, with a 1:1 current balun, end insulators, and rope support at both ends.

The parts list is short: two equal wire legs, a center insulator, two end insulators, rope, and a 1:1 current balun.

2. Strip about an inch of insulation on each inner end, then solder or clamp both wires to the center insulator and feed point.
3. Attach an end insulator to each outer tip, tie rope through both insulators, and anchor the ends to supports. This strain relief stops wind fatigue from snapping the wire.
4. Install a 1:1 current balun or choke at the feed point and run coax to the radio. Skip the balun and the coax shield becomes part of the radiating element.
5. Raise the center so the legs hang straight, and keep all wire clear of power lines and nearby metal structures.
6. Check SWR across 7.0–7.3 MHz. If the dip sits below your target frequency, shorten both legs equally and re-test. When the SWR minimum lands where you operate, the build is done.