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Re: Self Capacitance formulas

In a message dated 96-01-12 12:24:27 EST, you write:

>Hi Ed,
>
>	Mark R. posted the self capacitance formula due to Medhurst
>in a previous post. If you use this formula in conjuction with standard
>inductance formulas for soleniods (like Wheeler's), you can compute 
>the self resonant (no top terminal) frequency of most coils. I have found
>that it works very well for predicting most of Malcolm's measured 
>frequencies. 
>
>	If you want to read a little more of Medhurst try:
>"HF Resistance and Self-Capacitance of Single-LAyer Solenoids" by
>R.G. Medhurst, Wireless Engineer, Vol 2, p35, Feb 1947
>*Note: the range of frequencies he used does not allow his Q formulas
>to work at normal Tesla coil frequencies.
>
>
>	If you are just interested in computing self-resonant frequencies
>there is another method which I have found useful and generally accurate
>to about 10% for all coil sizes -  space wound or not. Its limitation is
that
>it probably shouldn't be used for aspect ratios (Height/Diameter)<1.
>
>The formula is:
>                 (1/5)
>    29.85 x (H/D)
>F = -------------------
>     N x D
>
>(hope the ascii came out)
>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"
>Note that the frequency is a very weak function of the
>aspect ratio (H/D), but a fairly strong function of the number of turns
>and the diameter.
>
>	This is an adapation of the formula for Helical Antennas found
>in Reference Data for Radio Engineers. A form of this equation also
>appears in both of the Corum brother's books:
>"Vacuum Tube Tesla Coils" and "TC Tutor"
>
>Incidentally, they incorrectly attribute the analysis of the helix to 
>Kandoian and Sichak. These guys actually just made a simplification of the 
>formula derived earlier by JR Pierce (1947) and Franz Ollendorf (1925).
>------------------------------------------------------------------
>I have a list which has more complete references.
>
>-Ed Harris

Ed,

Thanks,  Ed Sonderman