Ham Radio General Class Practice Test

Which of the following would reduce RF interference caused by common-mode current on an audio cable?

1. Placing a ferrite bead around the cable

2. Adding series capacitors to the conductors

3. Add shunt inductors to the conductors

4. Adding an additional insulating jacket to the cable

The correct answer is: Placing a ferrite bead around the cable

Placing a ferrite bead around the cable is an effective method for reducing RF interference caused by common-mode currents. Ferrite beads are designed to suppress high-frequency noise by presenting a high impedance to the unwanted RF signals while allowing the desired signals to pass through relatively unaffected. When common-mode currents flow through the audio cable, ferrite beads can absorb the RF energy and dissipate it as heat, thereby minimizing the noise and interference that may affect the performance of the audio system. This approach is commonly used in various types of cables in the field of electronics and ham radio to enhance signal integrity. In contrast, while adding series capacitors might block certain high-frequency signals, their effectiveness in dealing with common-mode currents is not as direct or efficient as using ferrite beads. Shunt inductors could potentially help by providing a low-impedance path for signals at certain frequencies, but they typically require careful tuning and may not adequately address all RF interference issues. Adding an additional insulating jacket may improve the physical protection of the cable but does not inherently reduce RF interference from common-mode currents.