If they are all in the same plane, either on the ground or elevated, then
there should be no advantage to adding baluns... and in my opinion may make
some things worse. Think about it this way, a vertical with a radial system
is an unbalanced system to start with. The whole purpose of the radial
system is to act as the 'other half' of the dipole, essentially collecting
the current that must get back to the coax shield to balance out the current
from the center conductor going to the vertical. What difference is there
in the current flowing on the shield back to that vertical feed point from
the current on the radial right next to it? Indeed if the voltage induced
on that radial is choked from flowing to the feed point where does it go? I
would say either into heat in the choke or back through the soil to whatever
other path it can find... in either case it is a lossier path than direct to
the feedpoint.
As far as chokes at other points, I would only do that if you have problems
with rf pickup on the line going to the radio. If there is enough rf trying
to go back through the station ground to cause problems then you likely have
a bigger problem.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net
-----Original Message-----
From: Jim Bowman [mailto:ks1j@arrl.net]
Sent: Monday, November 21, 2011 22:37
To: towertalk@contesting.com
Subject: [TowerTalk] Current Balun and 2 El Phased Vertical
I'm erecting a two element phased vertical for 80 meters. Each element has
30 radials underneath. I've prepared the quarter-wave lines for each but
prior to connecting I wondered if a current balun at the feed point was in
order. I have seen various and differing articles regarding baluns for
verticals but most seem to indicate that it is good practice to use them to
avoid the feed line from behaving like another radial. But what about this
situation? Wouldn't baluns conceivably mess up the element phasing?
Along the same vein, the coax length from the transmitter to the phase box
will be about 60' or 70'. Would a common mode balun at the transceiver end
or phase box end serve any purpose?
All these lines would be run along the ground.
73
Jim KS1J
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