Hi Marsh,
And the currents from antenna to ground? Does them count?
http://g4kno.com/antennas/balunsAndAntennas/images/Fig6.jpg
[http://g4kno.com/antennas/balunsAndAntennas/images/Fig6.jpg]
"Therefore, in the equivalent circuit, there are unequal impedances on either
side and the system is unbalanced"
Thank you
73, Maximo
________________________________
De: marsh@ka5m.net <marsh@ka5m.net>
Enviado: lunes, 20 de marzo de 2017 14:06
Para: 'Máximo EA1DDO_HK1H'; 'jimlux'; towertalk@contesting.com
Asunto: RE: [TowerTalk] current balun question
Maximo,
There is something called Kirchhoff's current law that says all of the
current delivered to the load must return to the source.
A common mode choke, sometimes referred to in error as a 1:1 balun, can add
impedance to the outside surface of the coax shield. We want that impedance
to be high in R and low in jX.
If the current at the antenna feedpoint is 1 amp on the center conductor,
the sum of the currents on the inside and outside of the coax shield will be
1 amp. We want the current on the outside of the coax shield to be zero. A
common mode choke can help.
If you are interested in this and want to know more about the theory, I
suggest http://g4kno.com/antennas/balunsAndAntennas/balunsAndAntennas.html
[http://g4kno.com/images/kompozer.jpg]<http://g4kno.com/antennas/balunsAndAntennas/balunsAndAntennas.html>
Baluns and antennas -
g4kno.com<http://g4kno.com/antennas/balunsAndAntennas/balunsAndAntennas.html>
g4kno.com
Most of us realise that it's a good idea to use a balun when feeding a balanced
antenna from unbalanced feedline. There have been some good articles on ...
Marsh, KA5M
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
Máximo EA1DDO_HK1H
Sent: Monday, March 20, 2017 7:57 AM
To: jimlux <jimlux@earthlink.net>; towertalk@contesting.com
Subject: Re: [TowerTalk] current balun question
Hi Jim, thanks to come back to me.
I understand your point, but...
Let me try with an example.
At the antenna feed point;
I1 = 1
I2 = 2
I3 = 0
In this case, the choke placed at feed point, has low work to do as I3 = 0.
Is the choke balancing I1 and I2 ?
Thanks
Maximo
________________________________
De: TowerTalk <towertalk-bounces@contesting.com> en nombre de jimlux
<jimlux@earthlink.net>
Enviado: lunes, 20 de marzo de 2017 12:47
Para: towertalk@contesting.com
Asunto: Re: [TowerTalk] current balun question
On 3/20/17 4:34 AM, Máximo EA1DDO_HK1H wrote:
> Guy, my question is NOT about common mode current.
>
> Is NOT about how much impedance a choke provide.
>
>
> My only question is to know if (and how) a "common mode choke" is able to
balance different "differential currents".
>
>
> Do you remember the famous I1, I2 and I3? Where I3 is the common mode
current the choke suppress.
>
> So ,my question is about I1 and I2.
>
> If I1 and I2 are different values at feed point, Is a choke balancing
them? Make them equal values into the coax (not antenna side, only coax
side) ?
>
> Or a choke has no effect in I1 and I2 differential mode currents?
>
>
Yes it does force them the be equal..
Think of the two wires as a and b, so the current in one wire is Ia and the
current in the other wire is Ib.
Ia = -Ib (because there's no where else for the current to go)..
Say that a is connected to the center pin, which is I1, and b is connected
to the outer shield, the currents are I2 (inside the coax) and
I3 (outside the coax)
So Ib = I2+I3
if we force I3 to zero (by putting a big impedance in that leg) then Ib=I2
so I1=-I2, which is what you want.
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