Balun is an acronym for BALanced to UNbalanced, which describes certain circuit behavior in a transmission line, source, or load. Most communications applications deal with two-terminal sources, transmission lines, and loads. This includes coaxial cables, open wire lines, and systems working against earth or a ground plane as the ”second conductor.”
Baluns are often selected based on the ratio between 50-ohm coaxial systems and the advertised impedance of another transmission line. As an example, 9:1 baluns are often used to connect the normal 50-ohm impedance of our radios to a 450-ohm transmission line regardless of what the actual impedance is on the line or the impedance of the antenna. Sometimes, this is because designers and end-users fall into the habit of using the same balun others use. Sometimes, it is because of a mistaken idea of what a balun is supposed to do…
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