Calculator Inputs
Example Data Table
| Inductor | Capacitor | Stray C | Approx Resonance | Common Use |
|---|---|---|---|---|
| 10 µH | 100 pF | 2 pF | 4.98 MHz | RF tuned stage |
| 1 mH | 10 nF | 0 pF | 50.33 kHz | Audio filter test |
| 220 nH | 47 pF | 1 pF | 49.24 MHz | VHF matching check |
Formula Used
The main resonance formula is:
f₀ = 1 / (2π√LC)
Here, L is inductance in henries. C is effective capacitance in farads.
C effective = installed capacitance + stray capacitance
Reactance is calculated with these formulas:
XL = 2πfL
XC = 1 / (2πfC)
For a series tank, the impedance estimate is:
Z = √(R² + (XL - XC)²)
Quality factor estimates use:
Q series = ω₀L / R
Q parallel = R / ω₀L
Bandwidth is estimated as:
Bandwidth = f₀ / Q
How to Use This Calculator
Enter the inductor value and select its unit. Enter the capacitor value and select its unit. Add stray capacitance if the layout, coil, probe, or socket adds extra capacitance. Enter series resistance for coil ESR. Enter parallel resistance for leakage or load damping.
Use the test frequency field to inspect reactance and impedance away from resonance. Use the target frequency field to estimate a new capacitor or inductor value. Press submit. The result appears above the form and below the header. Use the CSV or PDF button to export the same result.
Tank Circuit Resonance in Practice
A tank circuit stores energy in a magnetic field and an electric field. The inductor stores current energy. The capacitor stores voltage energy. At resonance, these two stores trade energy with minimum reactive cancellation. The result is a strong frequency selectivity. This makes the circuit useful in radios, filters, oscillators, matching networks, and tuned sensors.
Why the Resonant Point Matters
The resonant frequency is the point where inductive reactance equals capacitive reactance. A series tank has its lowest impedance near this point. A parallel tank has its highest impedance near this point. The exact behavior depends on winding resistance, dielectric loss, load resistance, and stray capacitance. A calculator gives a clean starting value, but real parts still need bench trimming.
Quality Factor and Bandwidth
Quality factor, called Q, shows how sharp the tuning is. A high Q circuit has a narrow pass band and higher circulating energy. A low Q circuit is wider and more damped. Bandwidth is estimated by dividing resonant frequency by Q. This estimate helps compare coils, capacitors, and loading choices before building the circuit.
Using Advanced Inputs
This tool includes installed capacitance and optional stray capacitance. Stray capacitance often comes from coil turns, boards, sockets, and probes. Even a few picofarads can shift high frequency tanks. The test frequency field lets you inspect reactance away from resonance. Target frequency fields estimate the needed capacitor or inductor for retuning.
Design Checks
Use realistic resistance values. A perfect zero resistance gives unrealistic Q. Include coil ESR for series work. Use leakage or load resistance for parallel work. Keep voltage ratings above expected peak values. Remember that circulating current may exceed source current in high Q tanks. After calculation, verify the circuit with a meter, signal generator, or network analyzer.
Result Recording
Record every input unit with the result. Unit mistakes are common in LC work. Millihenries, microhenries, nanofarads, and picofarads can look similar during hurried tests. Save exported reports for later comparison. Compare the target values with standard part values. Then choose the closest safe component or use a trimmer. For transmitters, add margins for heat, voltage stress, and current stress. For receivers, watch noise and unwanted coupling. Document changes after each test.
FAQs
1. What is a tank circuit?
A tank circuit is an inductor and capacitor network. It stores energy back and forth between magnetic and electric fields. It is often used for tuning, filtering, oscillation, and frequency selection.
2. What does resonant frequency mean?
Resonant frequency is the point where inductive reactance and capacitive reactance are equal in size. At this point, the circuit becomes strongly frequency selective.
3. Why include stray capacitance?
Stray capacitance comes from wiring, coil turns, sockets, and measuring probes. It adds to the installed capacitor. It can noticeably shift high frequency resonance.
4. What is Q factor?
Q factor measures tuning sharpness. A higher Q means narrower bandwidth and stronger circulating energy. A lower Q means wider response and more damping.
5. What is bandwidth in this calculator?
Bandwidth is estimated by dividing resonant frequency by Q. It gives a practical half-power range estimate for comparing tank circuit selectivity.
6. Can this calculator tune a real coil exactly?
It gives a strong starting point. Real coils may include losses, nearby metal, temperature drift, and parasitic effects. Final tuning should be verified on the bench.
7. What resistance should I enter?
For series analysis, enter coil ESR or total series loss. For parallel analysis, enter leakage, load, or equivalent parallel damping resistance.
8. Why are CSV and PDF exports useful?
Exports help save calculations for lab notes, reports, and comparisons. They are useful when testing several coils, capacitors, or target frequencies.