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[TowerTalk] Re: V Beam

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Subject: [TowerTalk] Re: V Beam
From: (Jim Reid)
Date: Wed, 16 Jul 1997 18:58:45 -1000
Aloha and Thank you to Brian and all the others who responded
with help and advice,

Brian sent along exactly the needed "code" to get AO going
to optimize the V's.  So I spent lots of hours today fiddling
with various compromise leg lengths,  angles, and whatever else
seemed possible.

Now,  of course,  several other issues arise!  I decided,  after
a few runs,  that optimizing for VSWR on these V's is probably
important.  The tuner I intend to use in a very old E F Johnson
KW Matchbox,  the paint looks pretty good!  The manual xerox
copy of a copy,  say's the box can match 50 to 2000 ohms line
impedance at the box terminals.  Now, is this a statement about
just the "real" part of the Z,  or also the reactive part?  I
was astonished about how wildly the Z varied with wire length in
the V's with a fixed angle.  I tried optimizing on the basis of
wire length,  as my angles are fixed by the available trees!
So I fixed the angle in the optimization.

I made the VSWR (to a 450 ohm line) at least 50% important,
with the gain then 50% important,  and forget F/B,  as I am not
going to terminate the V's.  Here in Hawaii,  and my situation, is
such that the V's will "face" South,  so want both short and long
path coverage at the same time. Most guys out here say the long path
to Eu and Asia is best;  lots of water going South!

I played with the program a long time until the VSWR's, well at least
no more than 5 or 6 to one to a 450 ohm line on 80,  40, 10,  20
and 15,  worked out pretty well.  Best leg length for the angle I can
manage, about 39 degrees on all legs,  is 462 feet.  Can get more gain
with longer legs,  but the higher band performance drops greatly.

Am I making a mistake optimizing for VSWR so the tuner can accommodate
the V-Z resulting from the installation?

Even fiddled with un-equal leg lengths;  seems to not compromise
anything very much!

This project is getting more and more interesting!

73,  Jim,  KH7M

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