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Off-Center-Fed Dipole (Windom)

Wire Antennas

A dipole fed away from center to find an impedance common to several bands.

Band: HF (e.g. 80/40/20/10 m)
Gain: ~2-4 dBi (band dependent)
Polarization: Horizontal

Photos

Real-world photo of a Off-Center-Fed Dipole (Windom) in use — Real-world example. Source: Wikimedia Commons (CC BY-SA 3.0; Original work: Mikeinc Derivative work: Chetvorno).

Radiation / wave patterns

Idealized radiation pattern of the Off-Center-Fed Dipole (Windom) — Idealized azimuth radiation pattern (illustrative, generated). Radial scale in dB.

How & why it works

By moving the feedpoint to roughly one-third of the way along the wire instead of the center, the off-center-fed dipole lands on a feedpoint impedance near 200 ohms that recurs on several harmonically related bands. A 4:1 balun transforms that to about 50 ohms, giving multiband operation from a single horizontal wire. The asymmetry requires a balun and good common-mode choking to keep RF off the feedline.

Real-world uses

Multiband HF home stations wanting coax feed without an external tuner.