4:1 Guanella Current Balun Construction and Measurements

Constructing a 4:1 Guanella current balun involves cross-connecting two 1:1 current baluns. At the low-impedance end, transmission lines from each balun are connected in parallel, while at the high-impedance end, they are connected in series. This configuration allows the device to achieve a 1:4 impedance ratio, effectively transforming a 200-ohm load to 50 ohms. The balun described utilizes FT240-43 toroids wound with 2.5mm2 twisted pair cable for 8 turns, intended for use with a 20m Deltaloop antenna.

Measurements performed with a 200-ohm resistor demonstrate satisfactory VSWR and impedance characteristics across the HF bands. The article compares the performance of 2.5mm2 cable versus 1mm enameled wire, recommending the former for superior efficiency. Emphasis is placed on maintaining short core-terminal connections to optimize performance.

Additional considerations include the option of integrating a separate Common Mode Choke (CMC) for enhanced common mode current suppression, especially if the balun's inherent suppression is not prioritized.