[Elecraft] 9:1 Balun

[Fred Jensen]

This list is a lot like being male and married ... no matter what you do 
or say, you're going to be told you're wrong. [:-)

> 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").
We were at our previous QTH on 5 acres for 38 years and I had a lot of 
time and space to experiment with antennas.  I had or had used 6 
different baluns.  All were transformers.  I currently have one on my 
HOA-Stealth wire.  It too is a transformer.  I also have an unused one 
in the garage that is an autotransformer with the shield carried through 
to one of the terminals on the "other" side.  It is an Un-Un, but it has 
a 4:1 turns ratio [16:1 impedance transformation] as well.

While transformers are not the only way to build a bal-un or un-un, 
that's 7 bal-uns and 1 un-un, all transformers.

One can build a balun from transmission line since a transmission line 
will act as a transformer.  They're frequency dependent of course, and 
typically used at VHF and up.

Incidentally, one of the transformer baluns with an SO-239 connector 
carried a rating of "10 KW, 11 KV."  I don't think I'd want to stuff 
10KW into that connector. [:-)  I still have it, I'll never use it 
again, I'll give it away if anyone wants it.
>
>> 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.

Did not intend to say that, English can be seriously difficult when 
describing something.  Let's see if I can re-word that to better convey 
the meaning ...

"The balanced side of the balun is balanced, and it stays that way.  
That's half the point of all this drivel [the other half is impedance 
transformation].  They sometimes use standoff's or such for the balanced 
connection.  Once you go through the balun toward the transmitter, you 
get an unbalanced connection for the unbalanced coax, usually an 
SO-239.  The balun thus allows a balanced load [e.g. the center of a 
wire] to remain balanced when fed with an unbalanced transmission line." 
That should help.

> 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.

Yep, that fact has been discussed multiple times here.

73,

Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County