My radial field consists of 55 radials, 75' to 150' in length, buried 0.5" to
1" deep. My coax feedline, encased by a 1.25" gray pvc conduit, is 12'' deep
and 80' long. It passes beneath several radials between the shack and the
antenna base.
I don't use a common-mode choke at the base feedpoint of my inverted L, where
the only matching element is a series-connected capacitor to cancel out the
inductive reactance of the antenna's total length of 170'.
I am willing to insert a common-mode choke, but don't know what to measure
beforehand to learn if one is needed. Nor do I know what changed indications
to look for after such a choke has been installed.
I'd be grateful for any advice.
73,
Charles, W2SH
> From: w9ac@arrl.net
> To: topband@contesting.com
> Date: Fri, 27 Jan 2012 10:20:16 -0500
> Subject: Re: Topband: T Vertical feed
>
> > This is a terrible error in logic. Current on the radials will divide
> > based on the impedance of each radial. If the feedline happens to be
> > a "pathological" length its (outer) shield can carry *all* of the
> > antenna return current.
>
> To Joe's point, I don't think we want the feedline to become a radial. It
> also seems that placement of the line should occur under the radial field
> and not on top of it, but I have not seen any studies that compare
> measurements. Anyone have this data? My initial thought for base-fed
> verticals is to use a CM choke at the base and also at the perimeter of the
> radial field, unless by placing the line under the field significantly helps
> to reduce coupling to the line.
>
> Paul, W9AC
>
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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