What distance from the tower is a good rule of thumb for the cage wires?
Three is the minimum, would four be "better", as in easier to match, provide
better isolation?
Pondering this for a 48' mast for 80M, as I don't think I have enough on top to
make it useful on 160...
Julius Fazekas
N2WN
Tennessee Contest Group
http://www.k4ro.net/tcg/index.html
http://groups.google.com/group/tcg1?hl=en
Tennessee QSO Party
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Elecraft K2 #4455
Elecraft K3/100 #366
Elecraft K3/100 #1875
--- On Tue, 7/13/10, Herb Schoenbohm <herbs@vitelcom.net> wrote:
> From: Herb Schoenbohm <herbs@vitelcom.net>
> Subject: Re: Topband: Spam:****, Re: Shunt-fed tower vs. T-vertical
> To: r_bakalov@yahoo.com
> Cc: topband@contesting.com
> Date: Tuesday, July 13, 2010, 11:11 AM
>
>
> Rudy Bakalov wrote:
> > If the cage does the radiation, does that mean that
> the cage has to be the entire length of the tower? That
> would be a no-go for me as there will be 2 additional
> rotating yagis on the tower, at 68' and 31'.
> >
>
> No the cage can be shorter and actually end at the 30 foot
> level...but
> you will have to check the base impedance to design the
> proper match.
> > I have LOTS of space. How far from the tower should
> one end of the T be to avoid the interaction?
> >
> At least more than a half wave to reduce interaction
> especially if the
> tower is at or near resonance the way it is...or less if
> you can
> decouple it at RF.
>
> > Also, if I remember correctly from my physics classes,
> perpendicular wires (top of the T and the tower) do not
> interact; what kind of interaction did you experience that I
> should be aware of?
> >
> >
> > The horizontal wires of the "T" are not doing much of
> the radiation
> > due to the cancelation effect. That is why a T is a
> great antenna as
> > the horizontal radiation is minimized. The
> imblance that is sure to
> > occur is by the close spaced support metal tower in
> terms of a
> > wavelength or less.You could conceivably detune the
> tower at 1.8 but
> > this gets complicated. There are lots of papers,
> i.e. NAB and IEEE on
> > detuning large metal structures such as power line
> supports to
> > minimize the interaction. But IMHO the best
> thing for you is to go
> > with your tower as you should be able to deal with the
> match presented
> > even with a shorter cage below the bottom beam.
>
> Herb, KV4FZ
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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