Question T6D11
From subelement T6 - T6D
Which of the following is a resonant or tuned circuit?
Why is this correct?
A resonant or tuned circuit requires both an inductor and a capacitor, which can be connected in series or parallel. These circuits exhibit resonance at a specific frequency where the reactive effects of the inductor and capacitor cancel each other out. Linear voltage regulators (B) control DC voltage levels, resistor circuits for SWR reduction (C) involve impedance matching but aren't resonant circuits, and high-fidelity audio circuits (D) may contain various components but aren't defined as resonant circuits.
Memory tip
Remember the L-C pattern: resonant circuits always need both inductance (L) and capacitance (C). The key insight is that resonance occurs when inductive and capacitive reactances are equal but opposite, creating either minimum impedance (series) or maximum impedance (parallel) at the resonant frequency.
Learn more
In practical amateur radio operation, resonant circuits form the foundation of antenna tuners, filters, and oscillators. Series resonant circuits present minimum impedance at resonance, making them useful for selecting specific frequencies in filters. Parallel resonant circuits present maximum impedance at resonance, making them effective for rejecting unwanted frequencies. Understanding resonant frequency calculations helps with antenna matching and filter design in station construction.
Think about it
Why do you think a resonant circuit needs both an inductor AND a capacitor, rather than just one or the other?