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@cis-broadband.com>
Date: 2007/08/31 Fri PM 05:40:19 CDT
To: TOWERTALK@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@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@contesting.com
> Subject: [TowerTalk] Inv L Directivity
> From: Craig Clark <jcclark@wildblue.net>
> Date: Fri, 31 Aug 2007 13:33:58 -0400
> List-post: <mailto:towertalk@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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>
>
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