Which of the following would reduce RF interference caused by common-mode current on an audio cable?
Place a ferrite choke on the cable✓Correct answer
Connect the center conductor to the shield of all cables to short circuit the RFI signal
Ground the center conductor of the audio cable causing the interference
Add an additional insulating jacket to the cable
Explanation
Common-mode current flows in the same direction on all conductors of a cable, so a ferrite sleeve encircling the whole cable adds series impedance to that current while the differential signal, whose currents cancel in the core, is unaffected. That selectivity is exactly what is needed.