Antenna Length Calculator

Planning to build your own antenna? This antenna length calculator gives you cutting lengths for the three most popular homebrew designs: the half-wave dipole, the 1/4-wave vertical and the J-pole. First, pick the antenna type. Next, choose a band or type in your own frequency. The lengths update right away in both feet and metric.

Band / preset

Frequency (MHz)

Type any frequency, or pick a preset.

Wire / element factor

0.95 is the classic 468 / f rule. Use 0.97–0.98 for thin bare wire up high.

How to Use the Antenna Length Calculator

Start by choosing a tab at the top of the calculator. Then select a band from the preset list. The list also includes the ACURA AG2NJ repeater frequencies, so you can build a J-pole or vertical tuned for our machines. If you want a different spot in the band, simply type the frequency in megahertz.

The letters in each result match the letters on the diagram. For example, on the dipole, A is the total length and B is one leg. As a result, you can measure straight from the diagram to your wire or tubing.

Half-Wave Dipole

A dipole is the classic first HF antenna. It is two equal wires fed in the middle with coax. The calculator uses the familiar 468 divided by the frequency rule, which equals a wire factor of 0.95. However, thin bare wire hung high in the clear often needs a little more length, so you can raise the factor to 0.97 or 0.98.

1/4-Wave Vertical

A quarter-wave vertical is one upright element with three or four radials at the base. The radials act as the other half of the antenna. In addition, bending them down at about 45 degrees brings the feed point close to 50 ohms. This design works well on 10 meters and up, and it is a favorite for 2 meter base stations.

J-Pole

The J-pole is a half-wave antenna fed through a quarter-wave matching stub. Because it needs no radials, it is a popular build from copper pipe or ladder line for 2 meters and 70 cm. The calculator uses the widely published copper-pipe J-pole formulas. Treat the feed point (D) as a starting spot, and then slide the coax clamps for the lowest SWR.

Cut Long, Then Trim

Every result is a starting point. Height above ground, nearby trees, roof lines and wire size all shift the resonant frequency. So always cut a little long and trim slowly with an SWR meter or antenna analyzer. You can always cut more off, but you cannot add it back.

Have questions about your build? Bring them to the Thursday 7:00 pm ACURA net on any of our linked repeaters. You can also check out our New Hams page or see the Repeater Status Board before you test your new antenna on the air.