Measured Q factor of LC circuit does not correspond with calculated and simulated
My LC circuit consists of:
L= 33,4 uH R= 0.3 Ω C=32,63 nF
Not quite true; there is also the 50 ohm impedance of the signal generator parallel loading the LC. You would need to drive this circuit differently i.e. with a current source if you wanted to measure Q factor: -
Resonant frequency is at 152.524 kHz and the 3 dB point is at 153.241 kHz. The upper and lower 3 dB bandwidth is therefore 1.434 kHz and the Q is centre frequency divided by bandwidth is: -
$$\dfrac{152.524}{1.434} = 106.36$$
In my opinion, the problem is just with measurements setup, but I do not know how to use a function generator for LC circuit, which has variable impedance.
Correct.
Three things to consider
- Component tolerances.The values you have selected might not physically be those values. There can easily be +-10%
- The inductor will have resistance to help dampen out the oscillation
- The ring-down method requires you to excite the circuit at its resonance frequency. Your L-C has a resonance at 1.6MHz while you have excited it at ~40KHz
0,3 Ohm resistance maybe isn't true at higher frequencies due the skin effect. But the connection to the signal generator should be kept very loose to prevent its 50 Ohm to affect the result. Insert a capacitor in series with the signal generator. Try one which has 100 x bigger reactance than the LC parts in the resonant circuit at the interesting frequency range. I guess you can use about 150pF.
You can try to disconnect one end of the 36.2nF capacitor, charge the cap with DC and then connect it again with mercury switch or other non-bouncing method. The voltage of the LC circuit (=decaying sine) can be stored to an oscilloscope. You can decide the actual resonant freq and Q from the decaying sine.
ADD after getting the wire thickness and length of the coil: It's not skin effect who pulls the Q down. Assuming the measurement is properly performed there's left "other losses". I guess your coil is too near some lossy material. Try to keep it far away everything including paper, wood, unknown plastics etc. Let it hang in the air.