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Re: [TowerTalk] current balance in ladder line?

Subject: Re: [TowerTalk] current balance in ladder line?
From: Steve Hunt <>
Date: Wed, 19 Jan 2011 09:03:11 +0000
List-post: <">>
The problem is that the moment we attach a feedline to the feedpoint we 
have the potential for unbalancing the currents because there's another 
path for the antenna CM current to take.

It's very instructive to model an OCFD in EZNEC. Place it in Free Space, 
so there's no influence from nearby objects etc. Feed it with a length 
of perfectly balanced twin-feed orthogonal to the dipole; then see the 
massive differences you can get in the dipole leg currents at certain 

Steve G3TXQ

On 19/01/2011 05:09, jimlux wrote:
> On 1/18/11 8:46 AM, Andy wrote:
>>> Why is the current into the antenna balanced?
>> Well, it isn't always.  You are right to question that assumption.
> If there's only two terminals, the current is, by definition, balanced
> at that point.
> What might not be balanced is the current *distribution* and any
> currents that are induced on nearby objects (e.g. the outside of the
> shield of the feedline, or common mode current in a balanced line)
>> An OCF (off-center fed) dipole does not have balanced currents at the
>> feedpoint,
> Not true, from basic circuit theory.  *at the feedpoint* the current
> into one terminal will be exactly the opposite of the current into the
> other terminal.
> What's not symmetric is what happens after that.  The current
> distribution will likely not be symmetric, so any conductor in the
> vicinity will see a different contribution from the two sides, and, so,
> will have some current induced in it.
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