[TCML] Tesla Coil tuner - scope traces questions

["Ryckmans, Thomas" <Thomas.Ryckmans@xxxxxxxxxx>]

Hello,

 

I've used a signal generator to try and tune my small coil. Because of
the small secondary (Diameter=70 mm, about 480 turns, 15 turns/cm, 32 cm
height; measured L is 3.5 mH; top load a bit more than 7 nF and coil
self capacitance 5 nF) resonance frequency is quite high - about 760 kHz
calc and 833 kHz measured using a source. 

I am using http://deepfriedneon.com <http://deepfriedneon.com>  to
calculate values
 
thanks for having a look!
 
For all measurments, secondary and primary were physically separated
 

1.	Here is a picture of my scope's trace when off resonance (1)

http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#518789176
5716440722
<http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#51878917
65716440722> 

 

 

then I tuned the signal generator until I got (2):

http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#518789179
1486244514
<http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#51878917
91486244514> 

 

 

strange looking wave form. It collapsed very near that frequency but I
could not take a picture. Is this the resonance frequency? Removing the
secondary and reading the scope I got 833 kHz.

 

Then I kept my source at 833 kHz and plugged in the primary in parallel
with the tank caps and shorted spark gap. My salt water caps is now 11.6
nF and my primary is inside diameter 110 mm, tube 8mm diameter, side to
side spacing 10 mm as per bartb recommendations - I did rebuilt the
whole primary]. 

 

Calculated inductance is 

1.3 microH for 2.5 turns, 

1.9 microH for 3 turns

2.6 microH for 3.5 turns

3.4 microH for 4 turns

 

And to reach "around" 833 kHz with my 11.6 nF cap I would need a bit
more than 3.5 turns.

 

Now for measurments:

 

When tapping at 2 turns I get trace (3) with amplitude about 2.5 squares
x 50 mV = 125 mV

http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#518789180
8666113714
<http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#51878918
08666113714> 

 

 

at 3 turns (Picture 4)  I get amplitude 4.4 squares at 50 mV = 220 mV

http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#518789181
7256048322
<http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#51878918
17256048322> 

 

 

And at 4 turns I get picture (5)  3.6 squares at 50 mV = 180 mV

http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#518789175
7126506114
<http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#51878917
57126506114> 

 

 

So I think I should get correct tuning between three and four turns...

 

Is this analysis correct? 

 

Are these traces the ones I should expect? 

 

I thought I would get a much more marked effect around resonance!

Also - what is the origin of the small spikes in the three last traces,
especially picture 5? 

 

Is this what is called ringing? I estimate the frequency of the small
spikes to be around 8 MHz or so...

And why is the amplitude so low? My source delivers about 4 volts
without load

 

Many thanks for your comments - as usual

 

Thomas

 

 

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