Coupling used in IF stages of superheterodyne receivers Which type of coupling is typically employed between IF amplifier stages to obtain the desired bandwidth and selectivity response?

Introduction / Context:
Intermediate frequency (IF) strips shape the receiver selectivity and gain. The coupling choice between IF stages strongly influences bandwidth, passband flatness, and skirt selectivity, which determine adjacent-channel rejection and audio fidelity for AM/FM/SSB receivers.

Given Data / Assumptions:

• Superheterodyne topology with a fixed IF.
• Goals include controlled bandwidth and relatively steep skirts.
• Standard IF frequencies and practical transformer Q values.

Concept / Approach:

Double-tuned transformer coupling uses two resonant windings with adjustable coupling, producing a band-pass response that can be shaped for flatter tops and steeper skirts than a single-tuned stage. By adjusting mutual coupling, designers tailor bandwidth and ripple, achieving better selectivity than simple RC or single-tuned coupling.

Step-by-Step Solution:

Verification / Alternative check:

Classic AM and FM receiver IF designs employ cascaded double-tuned transformers or ceramic filters achieving the desired response.

Why Other Options Are Wrong:

Capacitive or RC coupling (a, b) is not selective; single-tuned (d) has narrower, more peaked response and less control; direct coupling (e) provides no band-pass shaping.

Common Pitfalls:

Assuming more stages alone guarantee selectivity; bandwidth and shape factor depend on coupling and filter design.

Final Answer:

Double-tuned transformer coupling