Re: 8-9 RFI noise thoughts. (comment on Medhurst)

• To: tesla-at-pupman-dot-com
• Subject: Re: 8-9 RFI noise thoughts. (comment on Medhurst)
• From: "Jim Lux" <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Thu, 26 Aug 1999 11:57:01 -0600
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

> It surprises me that the 1/4 wave school haven't found a way of 
> calculating resonator frequency without using arcane formulae 
> incorporating fifth powers and suchlike. However, it is also notable 
> that Medhurst's formula incorporates either a tabulate factor or
> a function which is also complex in order to generate the factor vs 
> H/D curve from whence the factor values may be derived.  So 
> perhaps it's not that surprising after all ;)

I once tried to analytically derive the expression for the capacitance of a
cylinder above a ground plane. You can treat it either as coaxial tubes
that flare or as a series of rings spaced apart (with an image below the
ground plane). In either case, it gets very messy, very fast, and a
tabulated empirical measurement (like Medhurst) is probably the best way to
go, short of numerical analysis (like Terry has done). Given that
construction tolerances in real world situations are on the order of a
percent or so, it does no good to have an analytical expression accurate to
infinite digits.

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