Practical takeaway
Interference often comes from current flowing where you did not intend it to flow. Grounding, bonding, filtering, and common-mode control are different tools for different paths.
G4C · General question group
RFI, Grounding & Bonding
Interference often comes from current flowing where you did not intend it to flow. Grounding, bonding, filtering, and common-mode control are different tools for different paths.
General exam focus
The explanation below teaches the ideas behind G4C while keeping the important terms recognizable. The Quiz Me button uses the current question-pool wording for this group.
1. Bond equipment to reduce unwanted voltage differences
Short, low-impedance bonding between station chassis helps keep equipment at similar RF potentials. That can reduce RF feedback and common-mode problems, but it is not a substitute for the building’s electrical safety ground.
2. Common-mode current rides on the outside of coax
A balanced antenna fed through an unbalanced system can put RF current on the outside of the feed line. Ferrite common-mode chokes and good feed-system design can reduce that current and the RFI or noise pickup it causes.
3. Fix interference at the mechanism
Low-pass filters, high-pass filters, ferrites, shielding, bonding, and cable routing address different coupling paths. First identify whether the problem is harmonics, overload, common mode, radiation, or conduction.
G4C checklist
- Distinguish electrical safety grounding, RF bonding, and lightning protection.
- Recognize common-mode current on the outside of coax.
- Use ferrite chokes and good bonding to control unwanted RF current.
- Diagnose the coupling mechanism before choosing a filter.
Exam scope: NCVEC 2023-2027 General Class (Element 3), effective July 1, 2023 through June 30, 2027, with February 4, 2026 sixth errata. The current NCVEC pool is the exam authority; explanatory prose here is SPARKA teaching material. NCVEC pool