Electronic – Why is the LC circuit resonant frequency way off

oscillatorresonance

I'm very new to oscillators but very keen to learn more so I connected this very simple circuit:

enter image description here

where the voltage source is my signal generators and I have an oscilloscope connected across the capacitor.

Here is a picture:

enter image description here

The formula to calculate the resonant frequency is:

$${\displaystyle f_{0}={\frac {\omega _{0}}{2\pi }}={\frac {1}{2\pi {\sqrt {LC}}}}\,.}$$

My inductor has a value of 100uH, and the capacitors is 100uF, so the formula gives the resonant frequency of around 1.6kHz. For a parallel LC circuit, this should give the highest impedance for the circuit, so therefore the voltage reading on the oscilloscope should be the highest at this frequency.

However, this is not what I'm observing. The highest voltage seems to be at around 4.7kHz:

enter image description here

It has about 440mV volt peak to peak (the signal generator is set to 2V) while around the calculated resonant frequency:

enter image description here

The voltage is around 340mV peak to peak, much lower value. For higher voltages than 4.7kHz, the reading is smaller again.

So what am I misunderstanding/doing wrong? I understand that a basic LC circuit is not an ideal filter, but how is the measured resonant frequency so different from the calculated one?

Best Answer

Another consideration is that electrolytic capacitors are completely inappropriate for this application. Their capacitance changes significantly with applied voltage. They are leaky, with high ESR and very low linearity.

Ceramic capacitor is much more appropriate for this application. Film capacitors are better yet.