Extra exam question E4E07
Subelement E4, AMATEUR PRACTICES· Group E4E
Which of the following can cause shielded cables to radiate or receive interference?
- A.Low inductance ground connections at both ends of the shield
- B.Common-mode currents on the shield and conductors (correct answer)
- C.Use of braided shielding material
- D.Tying all ground connections to a common point resulting in differential-mode currents in the shield
WhyCommon-mode currents on a shield and its conductors can cause a shielded cable to radiate or receive interference. Shielded cables can radiate or pick up interference when common-mode currents, current flowing in the same direction on the shield and the internal conductors together, are present, since a shield only fully does its job against differential-mode signals and can itself become an unintended radiator or antenna under common-mode conditions, answer B. Low-inductance grounding at both ends and braided shielding are both generally good practices that reduce this problem rather than cause it, and tying grounds to a single point is meant to prevent, not create, unwanted current paths.
Published 2026-08-28 · Last updated 2026-08-28 · Question text is verbatim from the 2024-2028 NCVEC Element 4 pool (public domain); the explanation above is original writing, see our methodology.
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