[TowerTalk] Re: tt

[James White]

Years ago before Hurricane Andrew we had a 3 element wire beam up about 50
feet - suspended between two towers and a bunch of tall pine trees that
Andrew later removed...

First a coaxially fed dipole (hardwired from the split in the coax - no
balun, etc) with a  was hung and once it was just right as far as
tuning/trimming its length it was taken down...

We then made a director 5% shorter .15 w/l ahead of it, and a reflector 5%
longer .2 w/l behind it ...very crude approach not taking into account any
sort of feed point affects, etc. - but:

It worked Very Well!  Three rope "booms" were used of equal dimension were
used - a middle and one at the tips of the wire elements, to maintain
uniform spacing of the elements...then the whole mess was pulled up
taught....took a whole weekend to get the thing tensioned just right but it
was well worth it...

sometimes it doesn't pay to get too complex!

73,

Jim, K4OJ



----- Original Message -----
From: <n4kg@juno.com>
To: <TOWERTALK@contesting.com>; <tleaf@hotmail.com>
Sent: Monday, January 08, 2001 7:53 AM
Subject: [TowerTalk] Re: tt


> I am posting this question and answer to TowerTalk
> since they may be of interest to the readership.
> See below.  N4KG
>
> On Mon, 08 Jan 2001 "Ted Leaf" <tleaf@hotmail.com> writes:
>
> > Hi Tom,
> >
> > My inverted V, apex at 25', is trimmed to my center freq with a 1:1
> > SWR--which is about what the books say--50 ohms.
> >
> > Was wondering why the V beam is 30 ohms.
> >
> > I don't recall what a V beam looks like.  Please explain.  And isn't
> > the  standard rule that reflectors are about 10% longer?
> >
> > 73, Aloha
> > Ted Leaf, K6HI
> > Kona, Hawaii
> > <tleaf@hotmail.com>
> >
> A stand alone inverted vee will be close to 50 ohms.
>
> The feed impedance of Yagi's is lower, depending
> on tuning and spacing of the parasitic elements
> whether the elements are straight or inverted V style.
> (see W2PV Yagi Antenna Book or similar)
>
> There is a chapter in the W2PV book showing
> the effect (gain and F/B) versus parasitic element
> tuning from +/- 2% through 7%.  A good rule of
> thumb is 5% longer for the reflector and 5%
> shorter for the director.  Beyond that, gain drops.
> Closer tolerances produce higher gain but less
> bandwidth and of course the dimensions are
> much more critical (i.e. you better be right!)
>
> de  Tom  N4KG
>
>
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