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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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