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LC Circuit Resonant Frequency CalculatorIn alternating current (AC) electronics and radio frequency (RF) engineering, combining an inductor (L) and a capacitor (C) creates a resonant circuit capable of storing and filtering electrical energy at a highly specific frequency. This interactive LC Resonant Frequency Calculator computes the exact oscillation threshold (f) based on your component values, or works in reverse to help you determine the required inductance or capacitance for a target frequency channel. Whether you are tuning an RF antenna impedance matching network, building a bandpass filter for an amateur radio receiver, or designing a tank circuit for an induction heater, automated calculation ensures precise spectral performance. The Fundamental Resonance FormulaResonance occurs in an LC circuit at the exact frequency where the magnetic energy opposition of the inductor (Inductive Reactance, XL) perfectly balances and cancels out the electric energy opposition of the capacitor (Capacitive Reactance, XC). Because XL = XC, the imaginary components of the circuit's total impedance disappear, allowing the circuit to oscillate naturally. The mathematical formula derived from this equilibrium is known as the Thomson equation: f = 1 / (2π × √(L × C)) Where:
Because the product of LC sits inside a square root in the denominator, increasing either the capacitance or the inductance causes a non-linear drop in the overall resonant frequency. To calculate a particular parameter of a circuit (e.g. resonant frequency (f), inductance (L) value or capacitance (C) value) click on the corresponding parameter on the figure and then enter all the necessary values:
This tool also displays inductor and capacitor color codes and SMD (surface mount device) inductor and capacitor codes for calculated values. Tank Circuits vs. Series Resonance
You might also find helpful: La calculadora de frecuencia resonante del circuito LC es una herramienta fácil de usar para determinar rapidamente la frecuencia resonante de un circuito LC (tambien llamado circuito resonante) el cual contiene solo un inductor y un capacitor en paralelo o serie. Formula de frecuencia resonante: f = 1 / (2π × √(L × C)) Para calcular un parametro particular de un circuito (por ejemplo, frecuencia de resonancia (f), valor de inductancia (L) valor de capacitancia (C)) haga clic en el parametro correspondiente en la figura y luego ingrese todos los valores necesarios:
Esta herramienta tambien muestra codigos de colores de inductores y capacitores y codigos de inductores y capacitores SMD (dispositivo de montaje en superficie) para valores calculados. Frequently Asked QuestionsHow do you choose component values if multiple L and C combinations yield the same frequency? While many different pairings of L and C can hit your target resonant frequency, engineers select specific values based on the desired Quality Factor (Q-factor) and circuit bandwidth. A high L-to-C ratio (L/C) results in a high-Q circuit with a very narrow, sharp filtering bandwidth. Conversely, a low L-to-C ratio widens the bandwidth, which is useful when you need to pass a broader range of sideband data along with your carrier signal.
Why does a real-world LC circuit eventually stop oscillating? In physical reality, perpetual motion does not exist in electronics. Every real-world inductor possesses an internal DC resistance inside its copper wire windings, and every capacitor suffers from a small Equivalent Series Resistance (ESR). These resistive losses convert a tiny fraction of the oscillating electrical energy into pure heat during each cycle. To prevent this dampening effect from killing the signal, an active component (like a transistor feedback loop) must continuously inject energy into the circuit.
What happens to electrical energy inside an LC tank circuit at resonance? At the resonant frequency, the circuit acts as an electrical pendulum, endlessly sloshing energy back and forth between two states. The capacitor stores energy within its expanding and collapsing electric field, which it then discharges into the inductor. The inductor uses that current to build up a magnetic field, which subsequently collapses and recharges the capacitor in the opposite polarity. In an ideal circuit, this lossless oscillation would continue forever.
How do I calculate the required inductance if my target frequency and capacitance are fixed?If you know your target resonant frequency (f) and your available capacitor value (C), you can calculate the necessary inductance (L) by squaring both sides of the Thomson equation and isolating L: L = 1 / 4π²f²C. This configuration is highly useful when winding custom magnetic coils to match a specific fixed-frequency radio standard or communications link. How to select a capacitor for an LC tuner circuit at 100 MHz?Example:
How to select inductance for a matching LC network at 2.4 GHz with a chosen small SMD capacitor?Solution using the calculator:
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