Topband: Shunt Fed Tower Info

[R. Kline]

I used to have  a 3 element KLM 40M beam, and I grounded the elements
directly to the boom by adding  small straps that were connected to the
existing strap (that joins the 2 element halves).  Regarding the driven
element, this wasn't possible, although I did directly ground the coax side
of the matching/balun assembly.  Perhaps what Tom suggests would be
worthwhile for the driven element (although the high reactance should be at
7 MHz - not 14 MHz).  In that case,  2 networks would likely be needed (one
for each half element), or perhaps a balanced network could be constructed.
The important thing would be to have a low impedance path to  the boom at
1.8MHz for all of the insulated elements.

73,
Riki, 4X4NJ

----- Original Message -----
From: "Tom Rauch" <w8ji at contesting.com>
To: <Cqtestk4xs at aol.com>; <topband at contesting.com>
Sent: Monday, August 04, 2003 3:27 PM
Subject: Re: Topband: Shunt Fed Tower Info


> > concerned about the height of the tower being used as a radiator.  A
rough
> guess
> > is that the top loading of the tower by the boom of the KLM 40 meter
> antenna
> > would make the tower around 230 feet or so.
>
> I see two problems Bill. First, a half-wave grounded structure is
> anti-resonant when grounded. Grounding detunes the entire structure. That
> means you can excite it with current, which is a good thing when you have
a
> four square around it.
>
> You could sectionalize the tower, run a wire up the side and feed it a few
> feet away, or detune the tower somehow. (Or it may not be half-wave
> resonant, and then it would work.)
>
> The other problem is the antennas. Insulation in the elements can be an
> issue at high power. I'd ground the elements through an inductor that is
> several hundred ohms reactance on 14MHz.
>
> 73 Tom
>
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