Topband: T Vertical feed

[DAVID CUTHBERT]

I had considered this case and it is valid with lossless GND or in free
space. But over lossy ground one resonant "radial" with many short radials
carries the about the same current.

While not entirely accurate this can be explored in NEC-2 by placing the
radials close to S-N GND.

Dave WX7G
On Jan 27, 2012 8:21 AM, "Paul Christensen" <w9ac at arrl.net> wrote:

> > 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
>
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