Oop, looks like I done hit de tar baby.

Gene Fuller wrote:

I have read your comment about the requirement for two cores for many
years, and I am still puzzled. In the ideal case the balun action is
performed by transmission line transformers, and the flux induced in the
core by the differential current is minimal. The core primarily affects
frequency response and common mode choking action.

It's true that the flux induced by the differential current is minimal
in a transmission line transformer. If, in fact, the balun is wound with
coax as I usually make them, the flux induced by the differential
current is zero because the differential field is entirely inside the
shield.

And it's true that the core affects common mode choking action. The
common mode choking action is exactly what the function of a balun is --
that's how it effects equal and opposite (purely differential mode)
currents on the two transmission line conductors. In other words, that's
how it produces balance and prevents feedline radiation.

So the flux from the common mode component of the current is the very
thing we need to look at when we evaluate baluns.

According to his books, Jerry Sevick has designed, analyzed, built, and
measured many single core 4:1 current baluns. He never mentions the
problem you allude to.

I don't know which edition you have. I have only the first and second; I
believe there was a third. In the first edition, it was clear that
Sevick didn't understand the purpose of baluns or how they accomplished
it. So I discount anything he wrote about baluns in the first edition.
But he figured it out some time between the first and second editions,
so there's some credible information in the second. A number of the 4:1
baluns he shows are indeed wound on a single core. And he dutifully
reports their frequency responses when terminated in a correct impedance
load (seldom the case in a real antenna application). But nowhere do I
see any measurement of their ability to do the primary job of a balun:
to balance the feedline currents. So there's no way of knowing whether
any or all of the many "current" baluns he constructed actually perform
the function of a current balun.

A way to qualitatively check to see if a balun is really acting like a
current balun is to connect a load across the output. Short one terminal
of the output to the "ground" terminal of the input, and measure the
impedance looking in. Then disconnect that short and short the other
output terminal to the "ground" terminal of the input and measure it
again. You can do this with an antenna analyzer or impedance bridge. A
perfect current balun will show the same, correct impedance in both
tests. A perfect voltage balun will show very different impedances.
There should be a way to get a quantitative measure of the longitudinal
(common mode) impedance from this test, but I don't have time to dig it
out just now.

I'd like to add that not long ago I encountered a claim of a 4:1 current
balun on a single core. It was indeed -- it was a conventional, as
opposed to a transmission line, transformer, although it was wound in a
way that made it resemble a transmission line transformer. And it had a
fairly decent bandwidth, although a transmission line transformer is
inherently much broader and doesn't couple differential flux into the
core. So a 4:1 current balun can be constructed on a single core. But I
don't know how a 4:1 transmission line current balun can.

What is happening here?

A whole lot of things could be happening. If an antenna is perfectly
symmetrical, a voltage balun will do the same job as a current balun.
For an explanation why, see
http://eznec.com/Amateur/Articles/Baluns.pdf. So a lot of the "current
baluns" might well be voltage baluns. I seldom see anyone actually test
the current balancing properties of baluns, and without this, there's no
telling what's been constructed.

I haven't looked carefully at Sevick's single core 4:1 "Guanella"
baluns. They might be voltage baluns, or they might be conventional
transformers -- bifilar windings don't automatically create a
transmission line transformer. I don't see any test he ran to verify
that they're functioning as current transformers or for that matter as
transmission line transformers. In a transmission line transformer, the
differential current always has a transmission line path to follow. Some
connections can split the wires carrying a differential current apart,
in which case you no longer have a transmission line transformer.

If you know of a topology which produces a transmission line 4:1 current
balun, I'd be very interested. You could use the same simple analysis
method used in the balun article to show that it really is what you think.

Mike Coslo wrote:

I'm not sure myself, Gene. I've wound single core 4:1's, I've bought
at least 2 of them. I've also been told variously they don't work, and
can't even be made.

Just what IS happening here?

You probably made 4:1 voltage baluns, which worked well enough in your
applications. Where a voltage balun is really a bad idea is when your
antenna system isn't symmetrical. In an effort to balance the voltages
on the two output terminals, it creates unbalanced currents. The
difference between them becomes a common mode feedline current. This is
also explained in the balun article.

.. . . Here Uncle Remus paused, and drew a two-pound yam out of the ashes.

"Did the fox eat the rabbit?" asked the little boy to whom the story had
been told.

"Dat's all de fur de tale goes," replied the old man. "He mout, an den
agin he moutent. Some say Judge B'ar come 'long en loosed 'im - some say
he didn't. I hear Miss Sally callin'. You better run 'long."

Roy Lewallen, W7EL

Not sure how you measured it, but you do realize that the bslun needs
to be terminated in it's appropriate imepdances (load) for you to
measure it's response over frequency. Without the loads, the capacitive
portion will dominate due to the winding cap and it will peak at a very
low frequency. With terminations, the response will broaden out
(remember? s^2+R/Ls+ 1/LCwhere R/L = wo/Q).

Oy Vey, my head hurts after reading all this, and it is spinning,
spinning, and the blood in my veins is transforming into chili...
Maybe that is why I have converted my balanced antennas to 600 ohm feed
and built my own link coupled, balanced tuners... Because chillun' if
youse look at the so called balanced tuners everyone is peddling these
days, dey haint... hey, I read Huck Finn when I was a kid, also

So, let us summarize...
I suspect that most will agree that using a B A L U N to coaxial feed
an unbalanced load, such as a Zepp, or a ground mounted vertical, is
not a good idea...
I suspect that most will agree that that using a B A L U N to coaxial
feed a mostly balanced load, i.e. dipoles, inverted vees, yagi-uda's,
etc. can be a good idea - depending...
Where I suspect the water gets muddy is when we carelessly
intellectually speaking mix the functions of a choke balun with an
impedence transformer...

As Roy has pointed out, having both magnetic activities on the same
core will allow mixing of the core flux and possibly probably even
degrade the functioning of one or both... Notice that Sevik has
designs that use two or more cores to separate the functions of
transforming impedence and of choking common mode current.. And that he
has no hesitation in series connecting two or more devices to get to
the final result desired...

Probably, the cleanest way to doing both a transformation of impedence
and of balance is to use one or more UNUN's in series to reach the
desired impedence, and then series a 1:1 BALUN designed for that
impedence level... If you still lie awake at night worrying about
current on your feedline, the add a solenoid wound, coaxial choke below
the whole mess...
Or go back to wire feed...

denny / k8do

Denny wrote:
Because chillun' if
youse look at the so called balanced tuners everyone is peddling these
days, dey haint... hey, I read Huck Finn when I was a kid, also

Even the MFJ balanced tuners feed the common-mode
currents directly through the tuning caps where
they encounter a 1:1 choke-balun on the input of
the network. That's not much difference from using
an unbalanced tuner with the choke on the output.
Your link coupling is a better solution although
a fixed number of turns in the link probably won't
work 3-30 MHz.
--
73, Cecil http://www.w5dxp.com

Single band tuners... Link ratio is tuned to the antenna impedence...
All hand made parts including the variable caps... Only ones in the
world and like nuttin you ever saw before... Works like gangbusters...
Just a little hobby to keep me out of bars and from shooting dice on
street corners...

denny

Cecil Moore wrote:


Your link coupling is a better solution although
a fixed number of turns in the link probably won't
work 3-30 MHz.

"Denny" wrote in message
oups.com...
Single band tuners... Link ratio is tuned to the antenna impedence...
All hand made parts including the variable caps... Only ones in the
world and like nuttin you ever saw before... Works like gangbusters...
Just a little hobby to keep me out of bars and from shooting dice on
street corners...

denny

Cecil Moore wrote:


Your link coupling is a better solution although
a fixed number of turns in the link probably won't
work 3-30 MHz.

I remember a tuner like that from the Air Force ham club. When you changed
bands you unplugged a coil and its link. Fed a big 80M thru 10M LPA.
Balanced feedline from the tuner to outside and up the tower was made of
1/2 inch copper tubing. I was impressed , but then again it didnt take that
much to impress me back then.