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[TowerTalk] shunt-fed tower question

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Subject: [TowerTalk] shunt-fed tower question
From: "Richard W. Harris" <>
Date: Tue, 16 Aug 2005 16:03:04 -0600
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I have never done this but am willing to try to shunt-feed my 72-foot
3-section motorized crankup tower to try to get on 160M.  I was told by
someone that I would have trouble doing this if my tower is not
insulated from the base.  I've been reading the ARRL antenna handbook
and Low Band DXing by ON4UN and from the figures I see and the text I
have read I have never heard about having the tower insulated from the
base.  Here is what I have and also what I am interested in doing.  Any
help would be appreciated:


My setup consists of:

72 ft 3-section motorized crankup

12-element  7-band antenna at 74 ft (for 10-40M)

Tower is anchored in a block of concrete 4' x 6' x '9'deep with 3 large

Currently there is no wire connection from tower to earth ground


I have plenty of room in 3 directions to run ground radials out between
80 and 125 feet.  The 4th direction has a small building about 6 feet
west of the tower.


I was planning on running wire on all three legs of the tower to insure
good section electrical connection and then connecting the tower base to
the ground radial system I have not yet installed.


My coax for the beam and rotor control cable will be run inside the
tower and then into a 3" conduit underground to the shack about 90feet
from the tower.


I was planning on dropping a vertical wire from the top of the tower to
ground and using a dip meter to measure electrical length and then plan
the remainder of the installation based on the measurements I get.  I
have a couple of good vacuum variable caps for the gamma or omega match
to allow me to tune for 80M or 160M if this is possible with my setup.


My tower is not insulated from the base and this is my biggest question
but any help/suggestions would be appreciated.  I was a bit confused by
the comment that my tower needs to be insulated from the base.  Is this

Thanks and 73,

Richard - KJ7CU 




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