Energy transfer and tuning: Can a parallel tuned (tank) circuit be used to couple energy from one circuit to another at or near its resonant frequency?

Introduction / Context:
Coupling stages in radios, filters, and oscillators often relies on tuned circuits to pass desired frequencies while rejecting others. A parallel resonant (tank) circuit presents a high impedance at its resonant frequency and can be arranged to transfer energy efficiently between circuits with appropriate coupling (inductive or capacitive).

Given Data / Assumptions:

• Parallel L–C network with finite Q.
• Loose to moderate coupling to source and load (transformer or capacitive coupling).
• Operation near the tank's resonant frequency f0.

Concept / Approach:
At resonance, the tank's reactive currents circulate between L and C while the input/output see a transformed impedance that can pass energy selectively at f0. With inductive coupling (mutual inductance between coils) or capacitive tapping, the tank can be used as a frequency-selective interstage coupler, maximizing transfer at f0 and attenuating off-frequency signals. This is the basis of many RF front-ends and IF stages.

Step-by-Step Solution:

Verification / Alternative check:
Classic AM radio IF transformers are parallel tanks with adjustable coupling; sweep responses show a peaked passband centered at f0 with controllable bandwidth.

Why Other Options Are Wrong:
Incorrect: ignores widespread use of parallel tanks in coupling networks.
Series-only / DC-only: coupling by tuned circuits is inherently AC and frequency-selective; DC is blocked or bypassed as designed.

Common Pitfalls:
Over-coupling (excessive bandwidth or double-hump response); under-coupling (weak transfer). Forgetting loading reduces effective Q and shifts tuning.

Final Answer:
Correct