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Author Topic: Center feed VS Off Center feed Bi Pole  (Read 1357 times)
KJ6TSX
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Posts: 116




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« on: March 18, 2012, 12:30:53 PM »

I am changing my long wire antenna into a center feed or off center feed dipole antenna, I am 10 feet short of coax being able to connect in the exact center of a 1/2 wave for 80 meters, will feeding 10 feet off center make a big difference? I am using a 1:1 balun
Thanks
George
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N4UM
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Posts: 440




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« Reply #1 on: March 18, 2012, 01:04:49 PM »

It probably won't make a big difference.  In fact you may even wind up with a better match if fed off center - particularly if the antenna is fairly close to the ground.  I don't think you will need the balun.
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K1ZJH
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Posts: 886




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« Reply #2 on: March 18, 2012, 01:07:12 PM »

Coax is relatively cheap, I'd splice in a short section using connectors and a barrel fitting.

If you do go with a balun, use a current balun, it will try to force equal currents on each
leg of the antenna.  You feedpoint impedance will change by moving the feed off of center
on a resonant antenna.

Pete
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WX7G
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Posts: 5908




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« Reply #3 on: March 18, 2012, 01:40:26 PM »

At a height of 30' the input impedance of the center fed halfwave (3.75 MHz) is 50 ohms. Fed 10' off center it is 52 ohms.

It will work just fine.

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W4VR
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« Reply #4 on: March 18, 2012, 02:11:30 PM »

Why don't you go one step further and feed it like a typical OCF.  You'll be able to use the antenna on several bands.
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KJ6TSX
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Posts: 116




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« Reply #5 on: March 18, 2012, 04:19:29 PM »

Well
I center feed the dipole and got a 1:1 match on 3.9Mh, But I guess the band is dead today I can't hear anyone...
Thanks
George
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