Deep Dive: G4C08
The correct answer is A: Place a ferrite choke on the cable. What would reduce RF interference caused by common-mode current on an audio cable is to place a ferrite choke on the cable. Ferrite chokes block common-mode RF current on cables, preventing it from causing interference. For amateur radio operators, this is a common RFI fix. Understanding this helps when troubleshooting RF interference.
Why Other Answers Are Wrong
Option B: Incorrect. Connecting center conductor to shield doesn't reduce common-mode current - it would short the signal. This doesn't help with common-mode RFI. Option C: Incorrect. Grounding the center conductor doesn't reduce common-mode current - it would short the signal. This doesn't help with common-mode RFI. Option D: Incorrect. Adding insulation doesn't reduce common-mode current - insulation doesn't block RF on the cable. Insulation doesn't help.
Exam Tip
Reduce common-mode RFI on audio cable = place ferrite choke on cable. Think 'F'errite 'C'hoke = 'F'ilters 'C'ommon-mode current. Ferrite chokes block common-mode RF current on cables, preventing interference. Not shorting, not grounding, not insulation - just ferrite choke.
Memory Aid
Reduce common-mode RFI on audio cable = place ferrite choke on cable. Think 'F'errite 'C'hoke = 'F'ilters 'C'ommon-mode. Ferrite chokes block common-mode RF current on cables, preventing interference. Very effective RFI fix.
Real-World Example
Common-mode RF current on an audio cable is causing interference. You place a ferrite choke (toroid) on the cable. The ferrite choke presents high impedance to common-mode RF current, blocking it and preventing interference. This is a very effective RFI fix for common-mode problems.
Source & Coverage
Question Pool: 2023-2027 Question Pool
Subelement: G4C
Reference: 2023-2027 Question Pool · G4 - Amateur Radio Practices
Key Concepts
Verified Content
Question from the official FCC General Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the G4C topic.