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[TowerTalk] Shortened 40m Rotatable Dipole

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Subject: [TowerTalk] Shortened 40m Rotatable Dipole
From: (Charlie Ocker)
Date: Mon, 24 Mar 1997 14:23:25 -0600
I'm looking for some feedback on an idea that I have for feeding a Shortened 
Rotatable Dipole.

I now have mechanical construction data (i.e. element taper schedule) for the 
aluminum tubing that I have on hand that will yield a dipole element that 
withstand the weather here in Northern Illinois.  Thanks again to those 
for your invaluable assistance.

There are many ways to feed and match a shortened dipole element, such as 
inductive center loading, inductive loading coils out some distance from the 
center, linear loading, etc.  All of these will work, each has it's advantages 
and disadvantages.  I am concerned about the mechanical aspects of these 
methods, i.e. weight, weatherproofing, etc, and of ease of access of the 
matching network for tuning.  This dipole will be mounted about 10' or so above 
my TH6, thereby making it a bit difficult to adjust.

So, here is my idea:

Feed the dipole with a short length (no more than 15') of SHIELDED balanced 
made from two identical lengths of RG213.  Any recent edition of the ARRL 
Antenna Book describes such a line.  Bring the end of this short run of 
balanced line to a weatherproof box mounted on the tower.  Inside this box will 
be a balanced L-network or similiar, and a balun for 50 ohm coax feed to the 
shack.  An article by Rich Measures, AG6K, in Feb. 1990 QST details such a 
matching network.

I'd appreciate any comments, pro or con, on this idea.

Thanks in advance,

Charlie  N9CO

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