[Elecraft] 9:1 Balun

[Matt Zilmer]

Excellent explanation, Joe.

Thanks,

matt W6NIA


On 1/31/2017 12:12 PM, Joe Subich, W4TV wrote:
>
> On 1/31/2017 2:16 PM, Fred Jensen wrote:
> > A bal-un is a transformer.  Technically, it has two windings on a
> > ferromagnetic core material which for RF is typically some flavor of
> > ferrite, usually in the form of a toroid.
>
> Most common baluns are *not transformers* as the energy does not pass
> solely from input to output by magnetic coupling.  In fact, I would
> hazard a guess that *none* of the devices advertised/sold as baluns
> are transformers.  Yes, many of the inexpensive 4:1 "baluns" - the
> voltage type (auto-transformer) baluns - may qualify due to the
> magnetic coupling between windings but they are *not* baluns in that
> they do not provide a balanced to unbalanced transformation (they are,
> in your terms an "un-un").
>
>> In the classic case, a balanced load [e.g. center of a half-wave
>> wire] becomes unbalanced [coax, shield grounded] by the bal-un.
>
> Again, NO!  The balanced load is not "unbalanced" by the balun.  A
> properly designed balun *keeps the system balanced* by preventing
> current from flowing on the "third wire" (the *outside* of the coax)
> which would otherwise "unbalance" the system.
>
> Due to skin effect, a properly terminated coaxial cable is a three
> wire transmission line.  The center conductor and *inside* of the
> shield form one circuit (which is "balanced" due to the laws of
> physics) and the *outside* of the shield carries "unbalanced" (or
> common mode) current due to any difference in potential between
> the ends of the cable or induced currents from external fields.
>
> 73,
>
>    ... Joe, W4TV
>
>
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-- 
Always store beer in a dark place.  - R. Heinlein

Matt Zilmer, W6NIA
[Shiraz]