General exam question G4C08
Subelement G4, AMATEUR RADIO PRACTICES· Group G4C
Which of the following would reduce RF interference caused by common-mode current on an audio cable?
- A.Place a ferrite choke on the cable (correct answer)
- B.Connect the center conductor to the shield of all cables to short circuit the RFI signal
- C.Ground the center conductor of the audio cable causing the interference
- D.Add an additional insulating jacket to the cable
WhyPlacing a ferrite choke on an audio cable can reduce RF interference caused by common-mode current on that cable. A ferrite choke clamped around an audio cable adds impedance specifically to common-mode current flowing along the outside of the cable's shield, without affecting the wanted differential audio signal, which reduces RFI picked up that way, answer A. Shorting the center conductor to shield would kill the audio signal itself, grounding the center conductor is not how common-mode current is addressed, and an extra insulating jacket does nothing electrically to stop RF coupling.
Published 2026-08-28 · Last updated 2026-08-28 · Question text is verbatim from the 2023-2027 NCVEC Element 3 pool (public domain); the explanation above is original writing, see our methodology.
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