I'm very new to LC circuits and signal generators but I would like to learn more about them. I have a capacitor which I do not know the exact value. But it is in the range of pF. Therefore I decided to build an LC tank circuit and use resonance to find my capacitance value. Before I put an unknown capacitance into the circuit, I bought some known capacitors and inductors to test my circuit. I used 470pF film capacitor and 680µH inductor and 10kohm resistance for providing damping and a diode for the test circuit. According to the formula, I should see the resonance around 281 kHz. You can see my circuit in the attachment. I feed the circuit with square wave and I used Agilent 33220 function/arbitrary waveform generator (up to 20MHz).
I saw something that I believe was resonance behavior but the oscilloscope reading was unstable. I checked the cables, signal generator, and oscilloscope (I connected directly signal generator to oscilloscope and applied sin and square wave with a certain frequency and saw the value that I applied on the oscilloscope screen). They are working.
What could be the reason for unstable reading? What do you think?
P.S. I read couple of things in the forum and saw suggestions such as using 0.01 µF capacitor. I have already ordered it but I think the problem is not the capacitor.
Link for the unstable reading: https://www.dropbox.com/scl/fi/35f8w2o0eyvagf29a1cn4/20230809_164401.mp4?rlkey=7ajpvt5ub804clisixep9kdbw&dl=0