Deep Dive: T6D11
The correct answer is A: An inductor and a capacitor in series or parallel. A resonant or tuned circuit is created by combining an inductor and a capacitor in series or parallel. This LC combination creates a circuit that resonates at a specific frequency, where the inductive and capacitive reactances cancel each other out, creating a frequency-selective response. For amateur radio operators, resonant circuits are fundamental to antenna tuners, RF filters, receiver front-ends, oscillators, and impedance matching networks. The resonant frequency depends on the values of L and C, calculated as f = 1/(2π√LC). Understanding resonant circuits is essential for RF work and equipment design.
Why Other Answers Are Wrong
Option B (A linear voltage regulator): Incorrect. A voltage regulator maintains constant voltage output. It doesn't create resonance or frequency selectivity - it's a DC circuit for voltage control, not a tuned circuit. Option C (A resistor circuit for reducing SWR): Incorrect. Resistors can be used in matching networks, but a simple resistor circuit doesn't create resonance. Resonance requires reactive components (inductors and capacitors), not just resistance. Option D (A circuit for high-fidelity audio): Incorrect. High-fidelity audio circuits focus on wide frequency response and low distortion, not resonance. They're designed to pass all audio frequencies, not to be frequency-selective like resonant circuits.
Exam Tip
Resonant circuit = inductor + capacitor. Think 'L'C circuit = 'L'ooks 'C'ool at one frequency. Regulators control voltage, resistor circuits match impedance, audio circuits pass all frequencies - none are resonant circuits.
Memory Aid
Resonant circuit = Inductor + Capacitor. Think 'R'esonant = 'R'eactive components ('L' and 'C') that 'R'esonate at one frequency. LC combination creates frequency selectivity.
Real-World Example
In your antenna tuner, an inductor and capacitor form a resonant circuit that matches your antenna at a specific frequency. At resonance, the circuit presents the desired impedance, allowing maximum power transfer. By adjusting the capacitor, you change the resonant frequency to match different bands. This LC resonance is what makes the tuner work - it creates frequency-selective impedance matching.
Source & Coverage
Question Pool: 2022-2026 Question Pool
Subelement: T6D
Reference: 2022-2026 Question Pool · T6 - Electrical components
Key Concepts
Verified Content
Question from the official FCC Technician Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the T6D topic.