Basic Qualification · B-003 Station assembly, practice and safety · B-003-013-001
What causes the loud noise heard from an FM receiver in the absence of a signal?
- A The additional gain following the discriminator
- B The nature of atmospheric noise in the VHF range
- C The higher intermediate frequency used in FM receivers
- D The very large gain of stages ahead of the discriminator
Correct answer: D — The very large gain of stages ahead of the discriminator. From the official ISED question bank, verified word for word.
Why
FM receivers use extremely high amplification in the stages before the discriminator to catch weak signals, but this same massive gain also boosts the tiny background hiss present in every electronic circuit. The full explanation — and one for every question — is in Pro.
Practise this section
Building a station safely: power supplies, grounding, RF exposure, lightning, feedline routing, and what a transmitter, receiver and transceiver actually do.