Anti Resonance in an LC Tank

Thread Starter


Joined Jul 7, 2011
I am tuning an LC tank to resonance and driving the AC source with a 2n7002.

I am achieving resonance at a much lower frequency than my target frequency. I read in the tutorials that this may be due to series inductive resistance dominating the LC causing it to dampen and resonate at a lower frequency.

I tried to counter this effect, as it says in the tutorial, with a series resistance on the capacitor. This sort of worked but after trying various axial resistors I decided to try a trim pot.

Now the resonant frequency is too high. (I am monitoring the current to see when it drops to its lowest point. This is how I am determining resonance.)

I know that the f=1/2*pi*sqrt(LC) is a non-linear equation and I am wondering if this is why I am getting a "jump" in resonant frequencies rather than a smooth linear transition?

I hope this make sense!