[TowerTalk] current balun question

Máximo EA1DDO_HK1H ea1ddo at hotmail.com
Mon Mar 20 03:12:36 EDT 2017


Hi Jim,


Below you are talking about to force to near zero the common mode currents, but I am talking about differential mode currents.

Does a choke force differential mode currents to be balance?


For example, a OCF dipole, where both branches are different length, with not same differential currents at feedpoint. And let's say, zero common mode currents.

Is a choke forcing those different "differential currents" to same level into the coax?


Thank you


73, Maximo


________________________________
De: TowerTalk <towertalk-bounces at contesting.com> en nombre de Jim Brown <jim at audiosystemsgroup.com>
Enviado: martes, 14 de marzo de 2017 17:19
Para: towertalk reflector
Asunto: Re: [TowerTalk] current balun question

On Tue,3/14/2017 12:41 AM, Máximo EA1DDO_HK1H wrote:
> Same question in a different way is; Is the current choke forcing to
> balance differential currents?

Hello Maximo,

An effective common mode choke forces current to near zero at the point
where it is placed. IF it placed at the feedpoint, it will force current
in the sides of the antenna to be equal AT THE FEEDPOINT. In effect, it
disconnects the feedline from the antenna as an element of the antenna.

If the same choke is placed near the shack, the feedline IS part of the
antenna, with it's electrical length equal to its physical length, with
the choke forcing the common mode current to near zero at the point
where it is placed in the feedline.

By "effective," I mean a choke that has a very high common mode
resistive impedance at the operating frequency.

73, Jim K9YC


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