[TowerTalk] Inv L Directivity

[Gene Smar]

TT:

     I would imagine most of us model an Inv L with the flattop wire going in the +X direction on the Cartesian coordinate system used by EZNEC, etc.  Depending on the vertical/azimuthal slice you select to display, you might end up plotting the max TOA towards the RIGHT of the plot.  This is actually 180 degrees from the +X axis.  Hence the mixup in perceived directivity.  (It happened to me when I modeled an L for this thread a few days ago.)  


73 de
Gene Smar  AD3F

From: David Gilbert <xdavid at cis-broadband.com>
Date: 2007/08/31 Fri PM 05:40:19 CDT
To: TOWERTALK at contesting.com
Subject: Re: [TowerTalk] Inv L Directivity


Could you guys maybe have it reversed?  Every time I've modeled an 
Inverted-L with EZNEC the directivity is in favor of the direction AWAY 
from the top loading wire.  The only exception I've found seems to be if 
I assume perfect ground, in which case there doesn't seem to be any 
significant directivity.

To be sure, the "directivity" doesn't represent much forward gain in any 
case, and in fact compared to a full quarter wave vertical it seems that 
the pattern is simply reduced in the direction of the wire ... not 
actually enhanced in the direction away from it.  But the "front/back" 
looks like maybe a couple of db which might be worth knowing in some 
situations.

73,
Dave   AB7E





john at kk9a.com wrote:
> There is enhanced radiation in the direction of the top loading wire, 
> however it is not worth worrying about.  It is about 1db with a 1/4 wl 
> inverted "L" that is 1/8 wl. high.
>
> John KK9A
>
>
>
>
> To: towertalk at contesting.com
> Subject: [TowerTalk] Inv L Directivity
> From: Craig Clark <jcclark at wildblue.net>
> Date: Fri, 31 Aug 2007 13:33:58 -0400
> List-post: <mailto:towertalk at contesting.com>
>
>   
>>    8. Re: Topband: INV L Directionality
>>
>>     
>
> G3XAP wrote a number of articles in RadCom (RSGB magazine) about this
> question.
>
> December 1973 p 842 "160m dx from suburban sites"
>
>
> November 1977 p 858 "The G3XAP directional antenna from the
> lower                               frequencies"
>
> Ashton's conclusion was there is enhanced radiation in the direction
> of the top loading wire. His antenna used a 40-60' vertical element
> and a 130' top loading wire. To get omni-directional performance, he
> added more top loading wires.
>
>
>
>
>
> 73, Craig Clark, K1QX 
>
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