OCF Dipole Calculator

Calculate off-center-fed dipole element lengths and feed-point split for ham radio bands.

Off-Center Fed Dipole

A Windom-style multi-band dipole fed away from center. Common feed points are 33% and 43% from one end, usually with a 4:1 or 6:1 balun.

Band

Design Frequency (MHz)

Length Factor (%) Accounts for the typical shortening of a resonant element. Actual length varies with conductor and installation.

Feed Point Position

OCF Dipole Formula

These are the sizing relationships used by this calculator.

Wavelength

lambda (m) = 299.792458 / f(MHz)

Total Length

Total length = lambda / 2 * (Length factor (%) / 100)

Leg Lengths

Short leg = Total length * Feed point ratio; Long leg = Total length * (1 - Feed point ratio)

FAQ

What feed-point options does this OCF dipole calculator support?

It supports the common 33 percent and 43 percent feed-point positions used for Windom-style multi-band dipoles.

Does an OCF dipole still need tuning?

Yes. The calculated lengths are a starting point. Feed-line routing, height, conductor type, and balun choice still affect the final result.

Antenna Calculators

Use these as starting dimensions

Real antennas still depend on environment, conductor diameter, insulation, feed method, and nearby structures. Expect to trim and retune.

Good field workflow

Cut slightly long when possible.
Measure with the feed system you will actually use.
Make small tuning changes and record each one.

Length factor note

This is a starting estimate for the shortening of a resonant element. Conductor size, insulation, mounting height, nearby structures, and feed arrangement can shift the final length.