Dipole Length Calculator

Technical notes & accuracy

Length model.

A half wavelength with a single fixed 0.95 end-effect correction: length = (300 / f_MHz / 2) × 0.95, with each element half of that. This is a first-cut figure, equivalent to the familiar 143/f_MHz metre rule. Cut long and trim to your own SWR minimum.

Wire diameter and insulation are not modelled.

This calculator does not ask for either, because it cannot use either. The length above is a bare-wire figure. Insulated wire needs roughly another 2–5% shortening, and thicker wire lowers the resonant length slightly; neither correction is applied here, so allow for both when you cut.

Feed point impedance.

The free-space textbook figure of 73 Ω for a traditional dipole, reduced by 5% for an inverted V to reflect the drooping legs. It does not vary with height, and a real dipole's feed impedance varies strongly with height over ground.

Height and ground conductivity.

These two reach one place only: they scale the intensity of the 3D pattern by a single attenuation factor, clamped between 0.1 and 1. Because that factor scales every direction equally, it changes the pattern's magnitude but never its shape, and it does not touch the lengths or the impedance above. Ground reflection lobing, the effect that actually makes height matter on HF, is not modelled here.

SWR sweep.

An illustrative curve against a 50 Ω system, from one third to three times the design frequency, using a simple inverse-with-frequency impedance model. It shows the shape of a dipole's narrow usable bandwidth; it is not a prediction of your antenna's measured SWR.

Provenance.

Every formula and constant above is carried over unchanged from the original InnovAntennas dipole calculator, with each expression traced by line number to that source in the page's own script. Nothing has been re-derived, approximated or substituted.