Superheterodyne receiver symptoms and stages: match common issues/features to their likely causes or blocks. List I (Observation) A. IF noise B. Image frequency reception C. Station selector operation D. Excessive hum in audio List II (Likely block / cause) Ganged tuning (RF + local oscillator tracking) Spurious response due to image signal Leaky filter capacitor (power supply/AF stage) Mixer (frequency conversion) stage

Introduction / Context:
In a superheterodyne radio, symptoms such as noise, images, tuning accuracy, and hum each point to characteristic stages. Recognizing these helps troubleshoot quickly during labs and service tasks.

Given Data / Assumptions:

• The receiver uses an RF stage, mixer, IF filters/amplifiers, detector, AF amplifier, and power supply filtering.
• “Image frequency” refers to the undesired frequency that also converts to the IF.
• “Ganged tuning” means mechanically linked variable capacitors for RF and LO tracking.
• Hum generally indicates power supply ripple or bad decoupling.

Concept / Approach:

Map each observation to the stage most directly associated with it: IF noise is strongly influenced by the mixer and early IF chain; images are spurious responses inherent to mixing; station selection relies on RF/LO tracking; hum relates to defective filtering capacitors in the audio/power supply chain.

Step-by-Step Solution:

Verification / Alternative check:

Block-level analysis: the mixer sets the noise figure heavily in many receivers; images appear at f_image = f_signal ± 2 f_IF; ganged tuning alignment restores selectivity; replacing a dried-out electrolytic in the supply typically removes hum, confirming the mapping.

Why Other Options Are Wrong:

• Blaming ganged tuning for hum misattributes an audio/power issue to RF mechanics.
• Connecting images to the audio stage ignores frequency-translation fundamentals.

Common Pitfalls:

Forgetting that front-end RF selectivity prior to the mixer is crucial for image rejection; if RF tracking is off, images worsen, but the phenomenon itself is due to mixing.

Final Answer:

A-4, B-2, C-1, D-3