[TowerTalk] Inverted L Question

[Les Kalmus]

Dennis,

I had the same problem with a similar configuration of inverted L.
I measured the antenna at the base with an MFJ259B and used the readings 
as input to the matching formulas given by ON4UN, which accompany the 
4th edition of Low Band DXing.
After a bit of work, and to my surprise, one configuration suggested by 
the formula was a series capacitor followed by a parallel capacitor 
between the coax and antenna.
The result was a near perfect match. I later refined the capacitor 
settings with an AIM4170 which showed a bit of additional tweaking was 
needed.
I was never able to run more than 400-500 watts into the antenna. Since 
this matching network was put in place, I can run full legal limit.
You need to do this kind of analysis and try the math to see which 
values are needed in which kind of network. It's much easier to run the 
numbers first than do it by trial and error.

73, Les W2LK


DENNIS BRICKEY wrote:
> I realize this is not a tower question, but the antenna gurus hang out here.  Hopefully some bandwidth can be tollerated for an antenna question. 
>
> I am working on a 160 meter inverted L and having some difficulty getting the match correct.  I'd appreciate any input. 
>
> 175' total wire length.....100' vertical 75' sloping horizontal 
>
> 23 (qty) 130' radials. 
>
> Fed with 75 ohm cable hardline through a variable capacitor. 
>
> I've trimmed and extended the vertical section and adjusted the cap with each length change.  The low swr point is always 2.8:1.  Essentially the only thing changing is how 
>
> much the capacitor meshes.  
>
> I started with 16 radials and thought adding more would help the match, but it has not changed. 
>
> Any Ideas? 
>
> All advice appreciated. 
>
> Thanks, 
>
> Dennis N4DD
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