Purpose of a noise limiter in AM broadcast receivers In an AM (amplitude modulation) receiver, what is the primary function of the built-in noise limiter circuit?

Introduction / Context:
AM receivers are particularly vulnerable to impulsive noise sources because such impulses appear as brief, large-amplitude disturbances that the detector will demodulate as loud clicks and pops. A noise limiter is a non-linear circuit that clips or otherwise suppresses these transients before audio detection.

Given Data / Assumptions:

• Standard broadcast AM receiver.
• Presence of impulsive noise sources like automotive ignition, lightning, and switching machinery.
• Limiter operates ahead of or around the detector stage.

Concept / Approach:
Impulse noise produces high-amplitude spikes over a wide bandwidth. A noise limiter (clipper, slicer, or gated device) reduces the amplitude of such spikes to protect the demodulator from large excursions, thereby improving the listener’s experience without substantially affecting normal program peaks.

Step-by-Step Solution:
Identify common impulsive noise sources: ignition systems, lightning, switching motors.Recognize that AM envelope detection converts spikes directly into audible clicks.A limiter clamps or clips these peaks before detection.Hence it mitigates noise from all listed sources.

Verification / Alternative check:
Service manuals show limiter diodes around the detector/IF stages labeled as “noise limiter” or “ANL” (automatic noise limiter), evidencing broad effectiveness against impulses irrespective of origin.

Why Other Options Are Wrong:
Each single source is only part of the picture; the limiter targets any impulsive noise, not just one category. The added option about audio dynamic range expansion is unrelated to the limiter’s clipping function.

Common Pitfalls:
Expecting the limiter to reduce continuous hiss; it is most effective on brief transients, not on wideband thermal noise.

Final Answer:
All of the above