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[TowerTalk] vertical modeling

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Subject: [TowerTalk] vertical modeling
From: (Frank T. Brady)
Date: Mon, 8 Dec 1997 00:56:02 -0800 (PST)

 I'm ready to begin experimenting with the telescoping mast/vertical I
bought recently:

* I want it to double as the support for a wire antenna between it and the
same mast type about 140 feet away.

* I'm erecting it above the leach lines of our septic system in the hope
that it will cut down on return current losses. 

* I want to use it mainly on 40 (and 20 if possible) and I would like to try
various physical and electrical radiator lengths (like maybe 5/8 wavelength).

 I described the project to N5SU in Dallas.  He has a 52' aluminum tower
vertical that puts out a GREAT signal on 40 meters. He warned me to watch
out for coupling between the wire antenna flattop and/or feedline and the
vertical.  He and others also said that galvanized steel isn't a good rf
conductor, so I should add a bonding strap between each section.

So my questions are:

Will a galvanized steel mast be less efficient than an aluminum radiator?

Are there vertical modeling programs that would help me pick the best length
between 44' and, say, the max of 61 feet or so that I could attain with a
whip attached to the top of the mast?  The mast will be guyed at all
sections and the whip would (hopefully) ride safely atop the mast.

Can modeling determine whether or not coupling may occur and whether or not
it would be detrimental or perhaps just be an influence on the length like a
capacitive hat?

Will the vertical interact/couple with the open wire line dropping
vertically from the center of the wire antenna - a minimum of 70 feet away?
I can separate them more if modeling information dictates.

Although I'm only going to be running 100w for quite some time, If trying to
load this on 20 considerably complicates things, I'd prefer to put 20 off
for awhile.  In any case, optimum 40m operation is the primary goal.

If any of you know of modeling programs or personal experience that can help
me before I sink the concrete guy anchor pads for these two masts, I'd
greatly appreciate it.

73s and seasons greetings,
Frank T. Brady - W0ECS
Wildomar CA

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