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.

The only question I have is regarding the issue of two cores vs. one
core. I have no doubt that grounding one of the high impedance leads can
lead to improper choking action with a single core. In the completely
balanced case the single core should work perfectly. So what happens in
a more typical case where the antenna is in an unbalanced environment,
but not fully shorted to ground on one side?

It's absolutely true that the test I proposed is a worst case, much more
severe than any realistic application. But I'm sorry, I don't believe
there is a "typical" case -- there are much too many variables involved.
In many situations, a balun isn't used at all and the result is entirely
satisfactory. Others take rather heroic effort to keep the common mode
current tolerable.

There are a number of designs out there for single core 4:1 "current
baluns", all essentially the same, including the Elecraft balun. I have
not tried to perform any measurements, so I have no idea whether these
designs typically work or typically fail. That was the foundation of my
original comment and question.

Sorry, I've never seen or measured one. It would be great if someone
would run some balance tests and see how effective it is.

By the way, there seems to be a pervasive myth that a 4:1 balun or
transformer used in an antenna system actually effects a 4:1 impedance
transformation. You can make one look wonderful by terminating it with
the design impedance (typically 200 ohms resistive) and looking into the
input. But anyone wanting to have a real eye-opening experience should
measure the impedance of a multi-band antenna on several bands, then
look at the impedance at the input of that "4:1" transformer when
terminated with the actual impedance it sees. That's not to say the
transformer doesn't do something, or even that it might present an
impedance that's more (or less) favorable for a tuner to match. But
you'll find that the transformation ratio is often not only far from
4:1, but the transformer also introduces considerable reactance. Whether
this helps or hurts when it comes to matching is something of a crap shoot.

Roy Lewallen, W7EL