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K0CQ   > TECHNI   07.06.06 04:21l 23 Lines 1104 Bytes #999 (0) @ WW
BID : 23989_W0AK
Read: GUEST DL1LCA
Subj: Re: Capacitor dielectric (VK2ZRG)
Path: DB0FHN<DB0THA<DB0HDF<DB0ERF<DB0FBB<DB0BI<DB0NOS<DB0EA<DB0RES<ON0AR<
      N9ZZK<W4JAX<N4ZKF<N0KFQ<WC0M<KQ0I<W0AK
Sent: 060603/1756Z @:W0AK.#CIA.IA.USA.NOAM #:23989 [Des Moines] $:23989_W0AK
From: K0CQ@W0AK.#CIA.IA.USA.NOAM
To  : TECH@WW

Lots  of  these formulae are based on empirical  measurements  or 
simplification  of more complex formulae often involving  inverse 
hyperbolic  transcendental  functions. In nearly every  case  the 
simplified  formulae  are  only valid over  a  limited  range  of 
dimension  (or  dimension  ratios in the  cases  of  transmission 
lines).  When  a formula has a square root or  log  function  its 
probably one of those simplified formulae.

An example is the formulae for a two wire transmission line. Most 
references  show  276  log10  (2S/d).  This  formula  causes  the 
conductors   to  intersect  at  about  200   ohm   characteristic 
impedance. The more complex formula seems correct down to a  very 
low impedance because the conductors don't touch until  virtually 
zero  impedance.  At  least  the formula  fits  the  endpoint  of 
conductor  contact  better and above 250 ohms or so  matches  the 
simpler formula. The more correct but less convenient formula  is 
120 inverse hyperbolic cosine (D/d).

73, Jerry, K0CQ @ W0AK.#CIA.IA.USA


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