Roy Lewallen wrote:
Gene Fuller wrote:

Yes, I have a copy of your article, and I have actually read it. I
think I even understand it. I took a fresh look just before I made my
first post in this thread. The schematic for Sevick's Guanella 4:1
balun is exactly the same as your figure A3-4.

Then I'm puzzled by your statement that if an antenna is completely
symmetrical, no balun is necessary. The very first two figures in the
article and accompanying text show this isn't true. Of course, if you
have a symmetrical antenna AND the feedline is placed symmetrically AND
you have a truly balanced tuner, then there will be no common mode
current and a balun won't do anything. Maybe that's what you meant.

Roy,

If I said that no balun is necessary then I apologize. I certainly did
not intend to say or imply such a thing. I do believe, however that a
single core balun would serve well if the antenna is balanced by design
and by its environment.

The question is how the single core balun performance degrades as the
antenna becomes less balanced through, for example, an asymmetrically
placed feedline. It seems difficult to analyze that problem, and
experimentation would be required.

73,
Gene
W4SZ

Gene Fuller wrote:

If I said that no balun is necessary then I apologize. I certainly did
not intend to say or imply such a thing. I do believe, however that a
single core balun would serve well if the antenna is balanced by design
and by its environment.

The question is how the single core balun performance degrades as the
antenna becomes less balanced through, for example, an asymmetrically
placed feedline. It seems difficult to analyze that problem, and
experimentation would be required.

I agree completely that there's no good way to analyze what will happen.
While you can model a 1:1 current balun with EZNEC or other NEC-based
programs, and an ideal transformer with NEC (or simply multiply reported
impedances with EZNEC), combining them for a model of a transforming
current balun, there's no way I know of to model even an ideal voltage
balun. And as I mentioned earlier, a real transformer is far, far from
ideal when terminated with the kinds of impedances you see in a real
antenna, particularly a multiband one.

You would indeed have to experiment. But it's easy to make quantitative
measurements of common mode current as I showed in the balun article. So
you can make good comparisons of one method over another for your
particular setup. I'd certainly be cautious of trying to extrapolate
what you found to other situations, though.

Roy Lewallen, W7EL