measuring LC resonance on scope

[electrolust]

I never know where to post my questions!  I feel like all of them are beginner questions.

Anyway, I would like to measure the resonant frequency (kHz range) of a parallel LC circuit.  I watched Alan's (w2aew) #55 video and the theory and technique seems pretty easy.  The total capacitance is in the 100nF range.  Therefore, the 11-15pF probe capacitance is neglible and I can just probe across the inductor, yes?

It seems so obvious but it's worthwhile to verify my understanding.

If OTOH the total capacitance were say in the 50pF or even 100pF range, then the probe capacitance becomes significant and I'd have to put an op amp follower in the circuit to look at its output, yes?  Or use a lo-z low-capacitance probe technique, yes?

To the best of my understanding, the R of the probe (10M per my expectation) doesn't come into play for resonance but rather just determines the current at the resonant frequency.  And so if I did have to use a lo-z probe, I would want to set the signal generator to also be lo-z output.

[StillTrying]

I don't know about down to 50pF on the LC circuit, but you can do it with a SG and 2 resistors of about 5k6. Connect both resistors to the top of the LC, drive one from the SG, and watch for the peak in amplitude with the scope on the other resistor. It works even if the SG is a square wave.

[w2aew]

I never know where to post my questions!  I feel like all of them are beginner questions.

Anyway, I would like to measure the resonant frequency (kHz range) of a parallel LC circuit.  I watched Alan's (w2aew) #55 video and the theory and technique seems pretty easy.  The total capacitance is in the 100nF range.  Therefore, the 11-15pF probe capacitance is neglible and I can just probe across the inductor, yes?

It seems so obvious but it's worthwhile to verify my understanding.

If OTOH the total capacitance were say in the 50pF or even 100pF range, then the probe capacitance becomes significant and I'd have to put an op amp follower in the circuit to look at its output, yes?  Or use a lo-z low-capacitance probe technique, yes?

To the best of my understanding, the R of the probe (10M per my expectation) doesn't come into play for resonance but rather just determines the current at the resonant frequency.  And so if I did have to use a lo-z probe, I would want to set the signal generator to also be lo-z output.

You might also get something out of these videos, even though some are talking about self-resonance, the theory applies to LC circuits too:

[danadak]

Daves video might be useful -


https://www.eevblog.com/2012/12/08/eevblog-396-bode-plotting-on-your-osciloscope/


Regards, Dana.