[TowerTalk] Off Center Fed Antennas

[Patrick Greenlee]

I have a 270 ft Carolina Windom off center fed dipole.  The short end is up 
46 ft above the surrounding grade and
the other end is up about 25 ft. It is fed via 50 ohm coax and a 4:1 balun.

It performs fairly well on 160, 80, 40, 20, 17, 15, 12, and 10.
I never hear anything on 6 so I don't bother.
I don't do 30 or 60, but probably could with this antenna.
I use the LDG 1000 watt Pro II automatic tuner and usually get matches 
better than 1.3:1

My Flex 5000A gives me 100 watts or so and I sometimes use my Tokyo High 
Power
linear amp to put out 1000 watts pep. If there was ever an opportunity for 
RF in the shack to be a problem
it is with a radio cabled to a computer sitting next to the linear.  All my 
equipment is bonded together to a common point and
wide braid from that common point directly to a hole in the slab floor with 
an 8 ft ground rod.

I have no RFI problems whatsoever.

If I separate all the equipment, disconnecting their individual ground 
braids
I still have no RFI/RF in the shack problems. I haven't tried that 
experiment with the amp and won't, not seeing a reason.

I have a remote coax switch to select other antennas
(including a barn top mounted and guyed radialless Hy-Gain Hy-Tower vertical 
modified to work 160, 80, 40, 20, 17, 15, 12, 10)
and likewise have no RF in the shack problems.

My last RF in the shack problems was running an Atlas 350XL through a manual 
tuner Into the insulated backstay of my sailboat
where the ham shack was the navigators station and had you operating about 
2-3 feet from the wire out the back of the tuner to about 10 ft from the
about 30 degree off vertical random length wire (insulated backstay). You 
could draw sparks from the mike to your mouth if you turned up the output 
much past 100 watts.

I did fine with that maritime mobile setup even though the mast was aluminum 
and all that standing rigging must have had some interesting effects.  I did 
not notice any effect when sheeting in the boom (also aluminum) closer to 
the backstay.

I'm sure there are folks who have problems with RF in their shack with this, 
that, or the other antenna arrangement but it is not necessarily a fault of 
the antenna type. Luckily there is a plethora of alternatives and if you 
can't make a particular one work for you, then use something else but don't 
condemn the Carolina Windom because you have problems with it, as it works 
fine for many of us.

Patrick  AF5CK

-----Original Message----- 
From: Tony Rogozinski
Sent: Tuesday, June 04, 2013 4:40 AM
To: towertalk at contesting.com
Subject: [TowerTalk] Off Center Fed Antennas
Ib ve been using a Carolina Windom here at my Virginia QTH as well as my new 
QTH in Colombia and the results have frankly been pretty
spectacular.  It works good on all bands, thru a tuner b  surprisingly well. 
Been on the air since 1957 so Ib m not a newbie and have used
many antennas over the past 56 years.  From a very marginal QTH here in the 
Blue Ridge I worked 122 countries using 100 Watts during
CQWW CW 2011 b  single band 15 meters!
Obvioulsy I want to put up yagis for the higher bands asap but that wire has 
done yoemans work for me.

Tony
W4OI/HK1AR

From: Jim Brown <jim at audiosystemsgroup.com>
To: towertalk at contesting.com
Sent: Monday, June 3, 2013 11:22 AM
Subject: Re: [TowerTalk] One more dipole-balun question


On 6/3/2013 6:32 AM, John Geiger (AF5CC) wrote:
> Given this new revelation, that it is a off center fed dipole, what is now 
> the best balun for the twin lead to coax junction?

Off-center fed antennas are a really bad idea, primarily because they
make the feedline a part of the antenna. This puts RF in the shack,
increases the likelihood of RFI to your neighbors, and picks up noise to
interfere with the stations you're trying to work.? A common mode choke
could solve this problem, BUT:? the off-center feed places a very high
common mode voltage across the choke, making it likely to fry.

73, Jim K9YC



Tony W4OI/HK4AR

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