balancing transformers - aerial matching made simple

balancing transformers elektor october 1984 10-30 A balancing transformer (often called a balun, which is a contraction of ba/anced/unbalanced) is any device used to couple a balanced impedance, for instance an aerial, to an unbalanced transmission line, such as a coaxial aerial feeder cable. balancing transformers are impedance transformation and sym- metry transformation. Textbooks refer to these baluns as quarter-wave matching sections. In such sections, the parallel-connected ends pre- sent an impedance of Z/2, where Z is the characteristic impedance of the cable used in the transformer. This termination of the section is asymmetrical. The series-connected ends present an impedance of 2Z, and the section here is open-circuited and symmetrical. aerial matching made simple Figure 1. Illustrating the principle of a balancing transformer: la) using balanced cable, and lb) using coaxial cable. Z is the characteristic impedance of the cable used. lb An example of a balancing transfo...