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
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