Strange resonance in inductor

Discussion in 'General Electronics Chat' started by avatar3, Mar 30, 2010.

1. avatar3 Thread Starter New Member

Mar 30, 2010
2
0
I have a Scope plugged to a 100 mH inductor and I observe these weird sinusoidals whenever I touch the circuit with a metal object. The effect is also seen when I poke with my finger but it is less pronounced. There is nothing else apart from the inductor and the scope in the circuit. The frequencies of the sinusoidals are about 83 KHz. I figure this is some kind of resonance so I compute C=36 pf using resonance frequency equation "f = 1/(2pi*sqrt(LC))". That is only my hypothesis but it can't be right. Does anyone have a better theory? The link to my video is right below. http://www.youtube.com/watch?v=mh9eggF4jbA thanks

2. davebee Well-Known Member

Oct 22, 2008
539
46
Could you sketch your complete circuit? Nothing fancy, but if you could include all the connections, including clipleads, scope probes, etc., it may help.

I've seen any number of odd things in sensitive analog rf circuitry, from internal resonances to picking up local radio stations (the nearby 100 kHz LORAN station is a frequent source of interference to sensitive circuits) which is why circuit designers so often specify building analog circuits on a full ground plane with lots of decoupling capacitors.

3. avatar3 Thread Starter New Member

Mar 30, 2010
2
0
I made a quick sketch but I don't know how to upload the image. I don't have a website to post it either. The inductance is connected to the scope with alligator clips. My inductor is in a little box and the wires I plugged in the box have the alligator clips at their other ends. I don't think my sketch will be very usefull anyway. Can I email it to you?

4. davebee Well-Known Member

Oct 22, 2008
539
46
It would be better to get a picture up here in the forum so everyone else could have a look at it, but even a verbal description might be good enough.

I watched the utube video again but cannot quite make out the circuit - what does the red cliplead connect to? Where does the scope ground lead connect? Where is the inductor itself in the video?