Resonant Frequency Calculator

Use the Resonant Frequency Calculator to calculate the resonant frequency from the inductance and capacitance

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The formula for the resonant frequency of a circuit shows that the same frequency will always be obtained as long as the product of the inductance (L) and capacitance (C) is constant. The relation between the two for a fixed frequency is called the L/C ratio. The resonant frequency formula is:

$latex F=\frac{1}{2\pi\sqrt{LC}}&s=3$

L = Inductance in Henrys (H)
C = Capacitance in Farads (F)
F = Frequency in cycles per second (C.P.S.) or Hertz (Hz)

These units may be inconvenient when dealing with radio frequencies. An alternative formula is:

$latex F=\frac{10^6}{2\pi\sqrt{LC}}&s=3$

L = Inductance in microhenrys (µH)
C = Capacitance in picofarads (pF)
F = Frequency in kilocycles (kc) or kilohertz (kHz)

Example: Find the resonant frequency of a circuit with an inductance of 3.2 µH and capacitance of 970pF

$latex F=\frac{10^6}{6.28\sqrt{3.2*970}}=\frac{10^6}{6.28*55.71}&s=3$

$latex =\frac{10^6}{350.05}=2856.667\; kc&s=3$

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Using the Resonant Frequency Calculator

Inductance: Input the inductance and select your preferred units

Capacitance: Input the capacitance and select your preferred units

Frequency: The calculated resonant frequency is displayed in the red cell

Selecting units: You can choose your preferred units of measurement through selecting the units cells and clicking the arrow to display a list of available options

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Reference: ARRL – The Radio Amateur’s Handbook

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