4:1 Guanella Current Balun Construction and Measurements

This article details the construction and testing of a 4:1 Guanella current balun, built using two 1:1 current baluns. The author discusses the operating principle, noting that transmission lines are connected in parallel at the low-impedance end and in series at the high-impedance end to achieve a 1:4 impedance ratio. The balun was constructed with FT240-43 toroids, using 2.5mm2 twisted pair cable for 8 turns. Measurements were performed with a 200-ohm resistor, showing satisfactory VSWR and impedance values. The author compares results using 2.5mm2 cable versus 1mm enameled wire, recommending the former for better efficiency. The balun is intended for use with a 20m Deltaloop antenna. The article also touches on the importance of short core-terminal connections and the option of adding a Common Mode Choke (CMC).