[TowerTalk] Guy wire interaction - the devil is in the details

[Guy Olinger, K2AV]

>From Thu, 8 Apr 1999 22:17:50 -0400:

>I measured on a HP-4291B.
>
>I just double checked by grid-dipping a small 1 uH inductor placed 
>across the insulator (that way I don't need to get near the insulator 
>with test leads or a test fixture). The inductor dipped at 52.4 MHz 
>with the insulator and grip. Substituting a 9 pF capacitor caused a 
>dip at 54 MHz.

Just exactly what I would have done. Dippers may be a pain, but they
certainly can confirm the [octave, order of magnitude, general
neighborhood, approximate value] of a capacitor or inductor. It *will*
be around 9-12 pf. While that is a killer in the middle of an other
wise resonant HF conductor, at the ends of a long section, it will
move the resonant frequency a lot. 

Next time I model guywires, I'm going to use a single conductor on
EZNEC and put a 12 pf load where the breaks go. That may explain a few
things.
 
>> IMO...HOG WASH.
>
>You are welcome to your opinion.
>
>My opinion is, I'd never use longer guy lines near higher frequency 
>antennas. Banking on a table being correct that doesn't account for 
>end-capacitance, no matter how many years its been out, is not a 
>good choice.
>
>It seems reasonable to me the model should allow for end 
>capacitance. Food for thought anyway.
>
>73, Tom W8JI
>w8ji@contesting.com

73, Guy
--. .-..

Guy Olinger, K2AV
k2av@qsl.net
Apex, NC, USA

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