Capacitance of toroids

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Original poster: "Adriano Mollica" <adriano.mollica@xxxxxxxxxxx>

Hello to everyone,

I almost finish the construction of my TC, but i have a little problem.
I need a top load of 29pF, than i think is ok, and i'm going to make it by
using a extensible aluminium pipe, that is pretty cheap and easy to put in a
toroid shape.

My question is, how can i calculate the capacitance of that toroid i'm gonna
build?

i found on internet two different way to calculate it, but  both use only
two parametes witch are , in one case: internal diameter and external
diameter, or in the other case: external diameter  and size of the pipe.
 And of course, i obtained 2 quite different measurements. What i need, is a
formula that use all three parameters toghether: inside diameter(d) ,
external diameter(D), and size of the tube(x).

do you know the answer?

thanks, Adriano