The Impedance-Transformation Properties
of Common 4:1 Balun Types

L. B. Cebik, W4RNL

Baluns, as we commonly construe them in amateur radio, have three main functions. First, they convert an antenna feedpoint or a parallel transmission line from a balanced circuit to a single-ended (sometimes called an unbalanced) configuration, where the single-ended configuration is necessary for cables and equipment using coaxial connectors in which the outer conductor is connected to ground somewhere in the system. Second, we often employ baluns to attenuate common-mode currents to keep them out of equipment and off the surface of coaxial cable braids or sheaths.

Third, we employ some baluns to transform load impedance values to an alternative value. Although there are designs for baluns capable of many impedance ratios (from 1:1 upward), the most usual balun impedance ratio is 4:1. Indeed, the amateur radio marketplace offers dozens of 4:1 units from different makers, with many different styles of construction for many different applications.

Although many measurements exist for the power handling capabilities of existing 4:1 balun, with additional measurements for their ability to attenuate common-mode currents, I have seen no measurements of the impedance transformation properties of baluns across the full HF spectrum from 3 to 30 MHz. The AIM 4170 antenna analyzer unit and associated software provides a convenient method of filling this vacuum, at least partially. The notes in the following series of preliminary measurement reports make a start toward characterizing different types of balun designs with respect to impedance transformation.

Part 1: Essential Background

Part 2: The Dual-Ferrite-Bead HF Balun: Some Preliminary Measurements

Part 3: Voltage Baluns: Some Preliminary Measurements

Part 4: Toroidal Current Baluns: Some Preliminary Measurements

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Updated 04-01-2008.© L. B. Cebik, W4RNL. Data may be used for personal purposes, but may not be reproduced for publication in print or any other medium without permission of the author.

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