Re: The equation used to calculate the resonant frequency of a secondary coil

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br> 

Tesla list wrote:

 > Original poster: robert & june heidlebaugh <rheidlebaugh-at-desertgate-dot-com>
 >
 > Adam: You were given a formula. The problem is you dont know the self
 > capacitance so tables based on experimentation is required, I use spaced
 > wire so I can only wind a coil to approximat size and test the results, The
 > self capacitance of close wound coils dosen't apply. Use the prograns
 > provided by the Tesla list for best results.

The "self-capacitance" of a coil with many turns is practically the
capacitance of metal foil cylinder in free-space divided by 2, so
the usual Medhurst formula should apply, even if the coil is not
close-wound, at least as long as the winding is uniform.

A convenient formula for the self-capacitance of a solenoidal coil is:
C=r*(11.26*(h/r)+16+76.4*sqrt(r/h)) pF
And for the inductance:
L=u0*Pi*N^2*r/((h/r)+0.9) H
r=radius (m), h=height (m), N=turns, u0=Pi*4e-7.
Add to C the capacitance of the terminal, discount a reasonable fraction
of the sum due to shielding effects (without precise calculations is
useless to say more than this about how much to discount...), and
calculate the resonance frequency as (as several already mentioned):
f=1/(2*Pi*sqrt(L*C))

The result will be easily correct within 10% or less.
The several programs mentioned in the list can do these calculations,
and with better precision.

Antonio Carlos M. de Queiroz