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Re: [TowerTalk] inverted L tower mounting

To: "" <>
Subject: Re: [TowerTalk] inverted L tower mounting
From: "Jim Brown" <>
Date: Sat, 23 Feb 2008 13:15:00 -0800
List-post: <">>
On Sat, 23 Feb 2008 13:29:58 -0500 (EST), 

>Unfortunately, you're likely to have parasitic effects between 
>vertical and your two towers, both of which may be resonant near 
>160 meters. 

Good point -- that can certainly happen, but to do much, it 
requires more than 130 ft of vertical or near vertical conductor 
(or maybe 100-110 ft with the top loading of a beam). There's a 
much greater liklihood of resonance with an 80M/75M vertical. 

I agree with Frank -- if the dimensions are in the ballpark, you 
should do some modeling. Ah, you say -- the NEC software costs 
money. Yeah, it does. But how much would you spend on the 
antennas? How much is your time to build them worth?  I have 
W7EL's EZNEC5 Plus package, and I've learned a lot from it.

Another point -- the feedlines to any other wires (like that 
inverted vee you mentioned) should also be considered as parastic 
elements. Luckily, there's a VERY effective way to take them out 
of the game. Simply add some good coax chokes as "egg insulators" 
in the feedlines to break up the resonances. See my Coax Choke" 
tutorial and Power Point for details. The PPT has  few screen 
prints from an NEC model showing the feedline interaction, and how 
the chokes can kill it.


Jim K9YC


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