[TowerTalk] current balun question

Máximo EA1DDO_HK1H ea1ddo at hotmail.com
Mon Mar 20 08:57:29 EDT 2017

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 ?



De: TowerTalk <towertalk-bounces at contesting.com> en nombre de jimlux <jimlux at earthlink.net>
Enviado: lunes, 20 de marzo de 2017 12:47
Para: towertalk at 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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