# [TCML] HELP Oscilloscope coil tuning! BIG TOPIC!

Mon Apr 20 18:52:22 MDT 2009

Ok, so I just got back from the lab on campus. I was playing with the
new digital scopes which I am going to be able to use to tune the new
coil im building. Ya Universities! Heres the thing... I'm no stranger to
coiling, but a newbie when it comes to using the scope. Can someone very
carefully explain process to me... That is, correct what ever it is that
im doing wrong. First off visit this link on my server to see a diagram
I made real quick in paint to show you my setup.

http://host.atomiklan.com/tesla/scope1.png            (Note: The
frequency on the multimeter means nothing, just a visual aid)

Ok so in this first image, im attempting to obtain the operating
frequency of the secondary coil with toroid. Correct me if im wrong, but
the toroid, secondary coil, air, and ground acts like a inductor
capacitor circuit hence the frequency. The toroid forms a capacitor with
earth using air as a dielectric. Is it possible to measure the frequency
of the coil without the toroid? Im assuming yes... but pointless. Ok so
to make replies simple and easy i'll number all my questions at the

Ok so back to the setup. Here are my understood steps to tune the coil...

1:    I should use the tesla geometry formulas for an inductor and
topload to get the general area of the frequency of the secondary and
toroid so I dont have to sweep the entire range of signal generator.
2:    Attach the signal generator to the bottom of secondary.
3:   Turn on below area of expected resonance.
4.   Hang oscilloscope probe near secondary coil.
5.   Raise frequency on signal generator and watch scope till the
amplitude of sine wave maxes. At this point this is the frequency of
coil. If you pass this by continuing to raise frequency, the sine wave
amplitude should drop again till you reach another resonance point.
6.   Read the frequency where sine wave was max on the multimeter. (The
multimeter was only in setup to get a digital readout of analog signal
generator.)

Ok, now that we have the secondary coils resonate frequency, its time
for the primary tank circuit.

Diagram: http://host.atomiklan.com/tesla/scope2.png             (Note:
The frequency on the multimeter means nothing, just a visual aid)

1:   Disconnect the transformer and any filiters. You should only have
the sparkgap, capacitor, and primary in the circuit.
2:   Bridge the sparkgap.
3:   Wire sparkgap, capacitor, and primary in series like normal.
4:   Attach oscilloscope probe to one end of primary and im assuming the
ground of probe to tap point??? You should use a 10K ohm resistor on
probe in this setup.
5:   Attach signal generator in same manner. One to end of primary, and
other end to tap point. Then adjust the tap point on primary till you
achieve the exact same frequency as above.

Ok so my questions.

1. Can the secondary frequency be found without the toroid? Or is this
pointless?

2. When getting secondary frequency, do i leave the alligator clip on
probe attached to ground, or nothing?

3. What settings should I set on the signal generator as far as strength?

4. When I tried testing this setup today with a test coil, when i varied
the frequency, the amplitude went up but never peaked at the "correct
frequency". It would just keep increasing no matter what setting I set
it on. What am I doing wrong here?

5: Am I missing something as far as using the scope correctly?

6. In regards to tuning the primary, is my setup correct as far as where
to connect everything?

7. Do I use the 10K built into probe or do i need another resistor?

8. The scope probe goes on one end of primary with... where/what does
the other connect to? Ground of probe to other end of primary? Other end
of primary into another port on scope?

Thanks everyone for all your help!

Hopefully this will clear up any confusion using scopes not only for me
but others as well.

Thanks,
Andrew Robinson