Wheeler's Formula for Inductance

   L(uH) = (r^2) * (N^2) / (9*r + 10*h)

where:
   r = coil RADIUS in inches
   N = number of turns
   h = coil height in inches




Another useful formula is Medhurst's formula for self capacitance of
a coil.




Medhurst's formula:    C  = K x D

where:  C = capacitance in picofarads
        K = constant which depends on the ratio of the coil height to diameter
        x = means multiply K times D
        D = solenoidal coil diameter in centimeters
        H = coil height in centimeters

        H/D       K
        5.0     0.81
        4.5     0.77
        4.0     0.72
        3.5     0.67
        3.0     0.61
        2.5     0.56
        2.0     0.50
        1.5     0.47
        1.0     0.46



Now that you know the inductance and self capacitance of your
secondary coil you can determine the resonant frequency by applying
the resonant frequency formula:

                1
   f =  --------------------
                 __________
         2 pi   / L C

    f = frequency in cycles per second
    L = circuit inductance in henries
    C = circuit capacitance in farads
   pi = 3.141592654



This is remarkably accurate for most secondary coils. You can also determine
your resonant frequency after adding a toroid by adding the toroid's 
capacitance to the Medhurst value.

If you are just interested in computing self-resonant frequencies
there is another formulad which I have found useful and generally accurate.
Its not quite as accurate as the above method.


The formula is:
                 (1/5)
    29.85 x (H/D)
F = -------------------
     N x D


where
F= self resonant frequency in Mhz of an isolated coil 
H= coil height in meters
D= coil diameter in meters
N= total number of turns

Make sure the top line reads " (H/D) to the 1/5 power"


Mike Hammer