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

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.

Please help a newbie. Can I get a good definition of "common mode"?
I've been reading ARRL pubs but can't seem to get my head around this
concept.

With humility,
john

jawod wrote:
Please help a newbie. Can I get a good definition of "common mode"?
I've been reading ARRL pubs but can't seem to get my head around this
concept.

First understand differential currents as occur in
transmission lines. The two differential currents
in the two wires are equal in magnitude and 180
degrees out of phase. This is the ideal case for
a transmission line and differential currents
average out to zero, i.e. equal currents flowing
in opposite directions.

Common-mode currents are the currents left over
when the average of the total currents is not zero.
Icm = (I+ + I-)/2

From the IEEE Dictionary: "common mode signal -
The average value of the signals at the positive
and negative inputs of a differential input waveform
recorder. Vcm = (V+ + V-)/2"
--
73, Cecil http://www.w5dxp.com

"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.

jawod wrote:
Please help a newbie. Can I get a good definition of "common mode"?
I've been reading ARRL pubs but can't seem to get my head around this
concept.


The best explaination of this I have ever seen is contained in W1HIS
..pdf article on yccc.org concerning common mode chokes. Dont let your
head hurt. It is a big download but well worth the read. Chuck is a
retired prof at MIT and did AR commuity a great service by publishing
this. Transmission line vs. common mode is addressed in the early
stages of this read. If you get hooked on this chunk of info like I did
because of receive improvements and TVI redux be sure to read the
footnotes. There is a wealth of info contained in the footnotes.

To give you some idea of the degree of improvement in receive noise
floors....I am using a 33 foot vertical mounted 12 feet up with some
elevated radials. I feed this with a Johnson Matchbox and 450 window
line. Receive noise floor improved by 7 to 10 db after installing 3
common mode chokes in the feedlines. 1 at the feedpoint, one at the
entry and one at the exciter.

I cannot imagine how much money I would have to spend in improved
antennas and hardware to yield that kind of noise redux.

Here is the link:
http://www.yccc.org/Articles/W1HIS/C...S2006Apr06.pdf

BTW. The reason why I started this search on common mode choking was to
reduce rfi in the shack. My installation is meant to offer minimum of
tvi by being careful with my antenna placement which in my case means
having it 12 feet above my transceiver. Not only did the rfi go away
but all my rfi issues subsided on my entertainment devices as well. No
complaints from neighbors either. On smallish city lots with open door
entertainment systems makes it hard to be a good neighbor. This helped
a bunch.

Best and good reading, Chas W7MAP/5