"Is it then possible to somehow estimate the capacitance provided by this or another antenna?" - snazzy

Well yes, it is - and its not difficult... Dewster produced a spreadsheet recently, Theremin_simulation_v3_2012-04-28.xls , but I cannot find this..

But the essential formula he gave was:

From:

"Physics of the Theremin" by Kenneth D. Skeldon, Lindsay M. Reid, Viviene McInally, Brendan Dougan, and Craig Fulton, 1998 (PDF)

Antenna capacitance above a ground plane:

Cant = 2*pi*epsilon0*L / (ln(2*L/D)-k) <- Corrected

where:

L = length of antenna in meters

D = diameter of antenna in meters

epsilon0 = permittivity of free space = 8.85E-12 Fm^-1

k is a constant depending on how far above the ground it is mounted

k = 0.4 for almost at ground level.

Extra capacitance for the above antenna due to a hand in proximity:

Chand = pi*epsilon0*L / (10*ln(4*x/D))

where:

L = length of antenna in meters

D = diameter of antenna in meters

x = distance from hand to antenna in meters

epsilon0 = permittivity of free space = 8.85E-12 Fm^-1

To get total capacitance for antenna with hand at any given distance, add antenna and hand capacitances.

**I think that to compute the antenna capacitance (without taking the hand capacitance) all you need is:**

**2*PI()*e*L / (ln(2*L / D) -k))*10^12**

**L = Length of antenna in metres**

**D = Diameter of antenna in metres**

**e = 8.85E-12 **

**k = 0.4**

**The result should be antenna capacitance in pF.**

**If you calculate the antenna capacitance for the EM using the above, you should be able to mess with length and diameter values for whatever antenna you want to substitute, so that you get the same capacitance.**

Fred.

Dewster - Please correct me if Im wrong about the above - I am not sure about the 2*PI() in the formula.. This formula was lifted from your spreadsheet but doesnt fit the formula in the text.