Basic Qualification · B-008 Interference and suppression · B-008-002-010
One method of preventing RF from entering a stereo set through the speaker leads is to wrap each of the speaker leads:
- Aaround a wooden dowel
- Baround a ferrite core
- Caround a copper bar
- Daround an iron bar
Correct answer: B — around a ferrite core. From the official ISED question bank, verified word for word.
Why
Wrapping speaker leads around a ferrite core works because the ferrite acts as a magnetic sponge that soaks up unwanted radio frequency energy, stopping it from turning into crackling noise in your stereo. The full explanation — and one for every question — is in Pro.
Practise this section
Interference and suppression is section B-008 of the Basic exam: When things interfere: harmonics, overload, RFI to and from your station, filters, ferrites and how to fix the neighbour's TV.
Drill B-008 — free, no account