Using ferrite E-cores for baluns

Published on: 2021/10/03

Author: Chavdar Levkov LZ1AQ

E-cores and U-cores are common and cheap since they are used in mass production for various pulse transformers. They can be used with success for baluns especially where the connectors on the cable are already mounted. The advantage is that multiple turns can be winded without the need to unmount the connectors . The material of E cores usually can be used successively up to 15 MHz for common mode baluns. They are very suitable for baluns for control and power supply cables where the requirements for very high common mode impedance are not so big. Junk box source of E-cores might be the old switch power supplies which can be found anywhere.

The following pictures give some examples. Cable ties are used to fix tightly the two sides of the core.

Fig.1 Balun on USB cable with 4 turns. The core is E 32x16x9, 3F3 material from Ferroxcube. 3 cable ties are used to fix the cores.

Fig.2 Fig.3 An example of balun with 8 turns of shielded cable with RCA connectors (the same core) . The adhesive tapefixes additionally the cable ties making this setup very stable. The inductance at low frequencies is 140 uH. The impedance plot is measured between two ends of the shield of the cable.