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Balanced Vs Unbalanced refers to the VOLTAGE on the conductors with respect to ground, ground ultimately being earth. The CURRENT is balanced in both coax and parallel feedline. Any current flowing on the outside of the shield of the coax is unwanted common mode current.
It's all about the antenna! Build the antenna. Put up a bigger antenna, put up a better antenna, you can never over achieve when it comes to antennas! 
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In a balanced line neither conductor is connected to ground or chassis - chassis is ground. Coax has the shield connected to the chassis at the transceiver and my or may not be grounded at the antenna. That alone makes it an unbalance line.
73
Bob
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 Originally Posted by WB8NQW
In a balanced line neither conductor is connected to ground (chassis). A 3 conductor microphone cable (XLR termination) has a balanced pair of audio wires not connected to ground (chassis) and a grounded conductor usually a shield of some kind.
Coax is unbalanced because the shield is connected to ground (chassis) on at least one end and maybe both ends. I don't believe that skin effect or whether the current is on the inside surface or outside surface has anything to do with balanced or unbalanced.
More to the point, each wire on a balanced circuit carries an inverted copy of the other wire. This means that any outside signal imposed on the wire via induction will be imposed on both wires by the same amount.
Shielded wires, on the other hand, rely on the shield to keep external signals from causing unwanted noise on the signal. The grounded half of a shielded wire also typically carries the ground potential of a device, along with the signals of all of the other equipment connected to that common ground. Since the shield is both ground and part of the audio circuit, differences in ground voltage at the ends of the cable can also induce hum on the circuit. This is why when I was a stage musician and audio engineer, I always fed the sound equipment from the same gang box and used direct boxes (baluns, really) with ground-disconnect switches.
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Originally Posted by K5JYD
Coax is called unbalanced . Why ?
Because it has yet to receive needed mental health care? 
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Originally Posted by N9XV
Just hold the coax in the middle, then it will be balanced
Simple test: If a two-conductor transmission line can be buried with no ill effects, it is unbalanced.
73, Cecil, www.w5dxp.com
Random length "tuned feeders" usually de-tune an antenna system (thus requiring a tuner).
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Why is coax unbalanced?
It's a yin yang thing.
73, Steve, NL7W
Not in but around Palmer, Alaska
"Those who give up their liberty for more security neither deserve liberty nor security."
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- Ben Franklin
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Only if it resides in a red state. 
“Put your works into the hands of the Lord, and your purposes will be made certain." - Proverbs 16:3
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- Galatians 6:7
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Originally Posted by W5DXP
Simple test: If a two-conductor transmission line can be buried with no ill effects, it is unbalanced.
I have some vintage 300-ohm TV cable that has a aluminum foil sheath. It can buried. Is it balanced or unbalanced line?
Is twin axial coax balanced or unbalanced?
Pete
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Originally Posted by K1ZJH
I have some vintage 300-ohm TV cable that has a aluminum foil sheath. It can buried. Is it balanced or unbalanced line? Is twin axial coax balanced or unbalanced?
It is shielded balanced line that has THREE conductors. I specifically said "two conductors" for my test.
73, Cecil, www.w5dxp.com
Random length "tuned feeders" usually de-tune an antenna system (thus requiring a tuner).
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