[TCML] Oscilloscope Tuning, Need help, please look

[Antonio Carlos M. de Queiroz]

Andrew Robinson wrote:
>      Looking again for more help with scope tuning. After a fairly 
> successful afternoon in the lab I think we may actually be getting 
> somewhere with this, but could some veterans out there confirm our 
> results please. Might be helpful for any new guys out there too so 
> take a look! What we're going for here is either you looking at it and 
> laughing at how far off we are, or actually (hopefully) telling us 
> we're on the right path. The link below is for a PDF doc we created 
> describing our results. There are some questions in there too. Any 
> help would be greatly appreciated!
>
> http://host.atomiklan.com/tesla/report.pdf
>
As Paul already said, the two frequencies below and above the main 
resonance don't have relation with the coil. Maybe some external 
interference. The signal generator in this test shall use a sinusoidal 
signal, although any waveform will produce similar results. The main 
resonance is where it should be. Two or more extra resonances are easy 
to find, somewhat below 3 and 5 times the first resonance.
An interesting test to make is as follows:
Connect the oscilloscope at the bottom of the coil, looking at the 
output of the signal generator, that has a nonzero output resistance, 
probably 50 ohms. At the first resonance you will see a dip in the 
signal level, as well as in the second, third, and so on, resonances.
Set the signal generator to the second resonance, and slide a finger 
along the coil (pointing directly to the coil). The dip is reduced due 
to the detuning caused by the extra capacitive loading, but you will 
notice that there is a point where the dip reappears, at about  2/3 of 
the length of the coil.
Set the generator to the third resonance and repeat the procedure. You 
will find two points where the dip reappears, at about 2/5 and 4/5 of 
the length. With some care you can repeat the procedure at higher 
resonances, finding more points where the dip reappears.

Antonio Carlos M. de Queiroz