Hi Belfior. The length of wire, the diameter of the wire, spacing between turns, and the dimensions of the coil
will all affect the self resonant frequency of a coil. The self resonant frequency of a coil depends on the
coils's inductance and the coil's self capacitance. You can use a signal generator and an oscilloscope to measure
the self resonant frequency of a coil fairly closely, but it is not quite that straight forward. Close proximity of other conductive objects
to the coil and connecting other wires and components to the coil will all affect the coil's self resonant frequency,
as doing this alter's the total capacitance seen by a coil, which will alter the frequency the coil resonates at. So you
can measure a coil's self resonant frequency alone by itself when it is not connected to anything, but as soon as you
you move the coil close to other circuit components and connect it into a circuit that self resonant frequency
will typically change to some degree.
You can use this online tesla coil software to help calculate approximate coil resonant frequencies.
Click the 'Load Sample Coil' button in the top right of the grid, to load some sample coil parameters,
and you can play around with the 'Insert values for the Secondary Coil' section to match your intended coil
parameters and then click the 'Run JAVATC' button below the first grid section to calculate the
approximate secondary coil resonant frequency in that sort of configuration. This should be fairly ballpark,
but the exact resonant frequency of a coil will depend on other factors as well, as I mentioned above.
To figure out what the various parameters do in JavaTC, picture a standard tesla coil arrangement and it should
start to make more sense after you play around with the program a bit. Remove any top loads from the configuration
(toroid, sphere, disc, cylinder), as they will lower the resonant frequency of the secondary coil if used.
JAVATC
http://www.classictesla.com/java/javatc/javatc.htmlIf you connect a capacitor in series or in parallel to a coil, you can use an online calculator like this one:
Resonant frequency calculator
http://www.1728.org/resfreq.htmAlso, you can possibly use a GDT (gas discharge tube) in place of a sparkgap, and you can purchase them
for different desired breakover voltages, but they can potentially overheat under continuous high current
use, so their suitability will depend on requirements. Also, a GDT may or may not be suitable
for use in a Kapanadze type of device, as that is still anyone's guess at this point.
Here's a picture
of a common type of GDT:
http://www.littelfuse.com/~/media/electronics/images/gas_discharge_tubes/littelfuse_gdt_gtca28_image.jpg.jpg
