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Re: Resonate or Not ?



Original poster: Finn Hammer <f-h@xxxx>

This can get quite involving at first try.

You have to plan the coil, roughly at least.
This involves deciding upon a secondary diameter, length and winding pitch which all join together into setting the coils own resonance due to it`s inductance and capacitance.
Next you select a topload, which gets tucked into the field of the coil, extending and smoothing the boundries up there where voltage is high, and increases the capacitance, thus lowering the resonance frequency of the secondary system.


You now select your primary system, coil and capacitor, so that they resonate at the same frequency as the secondary. It is still coustom to build the coil as the adjustable part, to allow tuning, but this is only due to tradition:
In the dark ages, Tesla coil builders would toil with unknown materials and secret tecniques to produce their most prized posessions: the tesla coil capacitor.
Nowadays they just go and buy some off the shelf capacitor and group them to suit their needs. Therefore the cap can have any size, and tuning by the capacitor is equally as feasible.
(Heck, some coils these days have only one turn on the primary, and this turn is made so mechanically elaborate that tapping it would be hardly possible, so tuning by the primary capacitance is the design approach.)
http://home5.inet.tele.dk/f-hammer/prires.jpg


Anyway, to determine with any certainty, that these 2 systems are operating in tune, you need instruments: An oscilloscope and an oscillator (function generator).
Attaching the function generator to the bottom lead of the secondary coil will produce enough voltage on a bare probe hanging 1 metre from the coil`s top, to produce a trace on the scope. Remember to ground the scope to steady the display. Sweeping the function generator up to, and past the resonant frequency you will see, that the amplitude of the secondary rizes significantly at the resonant frequency. Note this frequency down on paper.
Now hook the generator and scope across the cap of the primary system, and sweep like before. You`l get a similar reaction, and need to either tap the coil to get resonance at the same frequency as the secondary, or change cap value.
When you have seen this, using instruments, you _Know_ the coil is operating in tune.


But you have to realize that the streamer also acts as a capacitive extension of the toroid, and is certain to pull the resonant frequency further down, during streamer discharge. Therefore it is coustumary to tune the primary system 6-8% lower than the secondary, to aim at this expected drop in secondary operating frequency.

Hope this helps,
Cheers, Finn Hammer

Tesla list wrote:

Original poster: "Christopher" <cpfortun@xxxxxxxxxx>

Hi all....

How do you determine if a tesla coil is operating at true resonance or not? What are the things that a person should observe when buiding a coil unit....to ensure that it operates at resonance.....without force driving the unit ?
Thanks to all responses
Chris