On 9/13/2010 2:36 PM, Owen Duffy wrote:

My modelling experience is that other things like connection to
ground, and open ends to conductors have more influence on the
location of a standing wave pattern than typical common mode chokes.

I have created a simple model of a Carolina Windom at 7MHz, assuming
that the device at the dipole feedpoint is a 4:1 voltage balun with
negligible common mode impedance, the isolater is 1000+j0 (your
nomination), and a feedline configuration that demonstrates that the
isolator has not caused a minimum in the common mode standing wave
pattern at that point.

A pic of the current distribution is at
http://www.vk1od.net/lost/Clip043.png .
...

Common mode chokes can be made pretty easily to have an impedance of
more than 1k ohm. Both modeling and measurement show this is usually
adequate in typical installations to drop common mode current to very
near zero at the choke location. But you can easily have substantial
current a quarter wavelength on either side of it.

Didn't work for this case, the current minimum is about half wave
between the isolator (left hand blue square) and the dipole, and the
common current entering the shack (right hand blue square) is quite
large.

Apologies, there was an error in the model... I hadn't installed the
source properly. I have replaced the pic at
http://www.vk1od.net/lost/Clip043.png . The situation is a little
different, but the isolator does not force a current minimim at its
location, and the common mode current flowing at the shack is large.

Owen

A "4:1 voltage balun with negligible common mode impedance" isn't a
common mode choke, and can't be expected to reduce the common mode
current at its location. If that's what the Carolina Windom uses, I
wouldn't be at all surprised to find in practice what you see in the model.

In no way is a voltage balun a common mode choke or "isolator". When a
load is asymmetrical with respect to ground, a voltage balun actually
*forces* a common mode current to exist at its insertion point. Forcing
equal voltages into unequal impedances results in unequal currents in
the two conductors. The difference between the two is the common mode
current. That's why I've tried for a very long time (at least since the
publication of my balun article in 1985) to educate people that voltage
baluns are not the things to use in antenna systems.

My comments were strictly regarding the properties and uses of common
mode chokes (current baluns), not voltage baluns.

Roy Lewallen, W7EL

On 13 sep, 16:07, Owen Duffy wrote:
lu6etj wrote :

I agree with Cecil, Owen, I do not see nothing strange on have common
mode current in one part of the line and not in the other, ideal choke
it is an open circuit to RF currents.

Miguel,

There are two issues.

Firstly, if the common mode choke (or isolator) is physically small with
respect to wavelength, and there is common mode current on the line
immediately adjacent on one side of it, why is there not an almost equal
common mode current on the other side... or explain the current path that
allows the first mentioned current AND that complies with Kirchoff's
Current Law.

Secondly, the common mode 'conductors' are coupled conductors. I see that
Roy has dealt with that, so I will leave it at that.

For these reasons, it is naive to think that a practical common mode
choke has such extremely high impedance that the common mode current
through the choke is zero, or even near to it. Even if it did drive
common mode current to zero or near zero at that point, that does not
mean there is no common mode standing wave, just that a node exists at
that point.

Ask yourself how whether the use of a common mode choke (isolator) to
effectively reduce common mode current between the common mode choke and
the tx don't also reduce common mode current between the common mode
choke and the dipole feed point.

Owen

Owen

It is obvious, we are talking about different things. External fields
always will induce common mode currents in conductors, then it is
virtually impossible completely remove it. We will have commond mode
currents in our line if our ham neigbourhood turn on his TX or our
wife talk near with her celluar phone too.

When I talk about interrupt common mode current with choke I am not
thinking in prevent all possibles external induction fields over the
section of line isolated with the choke but in interrupt the current
flow that would have in this point if not were the device placed. In
that sense no puntual devices can avoid induction laws. Also, a good
isolator it is a capacitor and always will allow displacement
currents.

From electromagnetic point of view the inductor field beyond the
isolator or ideal choke it is the same that any other external field.
Not work either if as isolating device I installed five meters of
optical fiber and a pair of transducers :)
Do you search for a TL incapable to induce external fields?, then we
are not talking about baluns, perhaps we could talk about EM shieding
of the TL.
Similar situation if we install a perfect balun and run the TL paralel
to the antenna, common mode current not depends.

73

Miguel LU6ETJ

On 13 sep, 17:17, John Smith wrote:
On 9/13/2010 1:01 PM, Owen Duffy wrote:

...
I might note here that a Trask 4:1 current balun is not a Guanella current
4:1 balun, they have quite different connections. The argument that Trask
makes in support of his design on a single core does not apply to the
Guanella design.

Owen

You might want to note that to Trask, he thinks it IS a current balun
... since it has the appearance of two 1:1 current baluns used on a
single core, I tend to agree with his take on it.

Regards,
JS

Owen

It is obvious, We are talking about different things. Fields always
will induce common mode currents in conductors, then it is virtually
impossible totally remove it. We also will have commond mode currents
in our line if our ham neigbourhood turn on his TX or our wife talk
near with her celluar phone...
When I (or "we") talk about interrupt common mode current with choke
(or isolator) I am not thinking in prevent all possibles induction
fields over the conductors. The goal is interrupt a current that would
have in a point if the device (choke) it was not there (neither you
hope for ideal behavior, we must be consecuent).
In this sense no puntual devices can avoid induction laws. Also, a
good isolator it is a capacitor and always will allow displacement
currents.

From electromagnetic point of view the inductor field beyond the
isolator it is functionally similar to any other external field. Even
if you install a five meter optical fiber with a pair of tranducers
isolator betewen a line section you can not prevent electromagnetic
coupling. Similar situation if we buy our ideal balun and then we run
our line parallel to antenna :)

Do you search for a TL incapable to induce external fields?, then we
are not talking about baluns, perhaps we could talk about EM shieding
of the TL.

73

Miguel LU6ETJ

On 9/13/2010 3:07 PM, Owen Duffy wrote:
John wrote in news:i61i8h$png$4
@news.eternal-september.org:

http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=16722

The source is actually
http://www.saunalahti.fi/hohtola/ham...ndom-balun.htm , presented
the the DXZONE front.

Both baluns shown are current baluns, ie devices with a high common mode
impedance.

One of the advantages claimed of the Carolina Windom is the contribution
of feedline radiation.

If that was your objective, you would not employ devices (such as the
current baluns in the referenced article) that reduce the commom mode
feedline current.

Of course, the objective is a specious one. If you wanted to minimise
participation by the feedline as a radiator and pickup (especially noise,
since it is often closer to some noise sources), then you might use an
effective current balun. Indeed, more that one would probably be needed
for an OCF dipole.

Owen

Yes, that is why I said I didn't run the windom in the first place,
complete circle, completed perfectly ...

Regards,
JS

On Sep 13, 12:47*pm, Roy Lewallen wrote:
The difficulty with having common mode current on one side of an
"isolator" or common mode choke (current balun) is that it creates a
field which couples to the line on the other side, generating a common
mode current on the other side.

Since I don't know how robust the Carolina Windom isolator is, my
following statement may or may not apply to the Carolina Windom.

The above problem goes away *if* the choking impedance is high enough
to *cause* a common-mode standing-wave current node (minimum) at the
choke because the net magnetic field is then near zero on both sides.
The same thing happens when a well-designed trap is placed in a
dipole. The high impedance of the trap at the parallel resonant
frequency causes a standing-wave current node and reflects the forward
wave back toward the feedpoint instead of allowing current to flow
through it into the rest of the wire. Here's the current distribution
on a trapped antenna. Note how the trap impedance causes a standing
wave current node at the trap.

http://www.w5dxp.com/trap.JPG
--
73, Cecil, w5dxp.com

On Sep 13, 2:07*pm, Owen Duffy wrote:
For these reasons, it is naive to think that a practical common mode
choke has such extremely high impedance that the common mode current
through the choke is zero, or even near to it.

Nobody said the Carolina Windom choke was that robust - just that it
is possible to design a choke with a high enough impedance to cause a
common-mode standing-wave node at the choke.

Even if it did drive
common mode current to zero or near zero at that point, that does not
mean there is no common mode standing wave, just that a node exists at
that point.

There is a common-mode standing wave on one side of the choke and not
on the other because the very high choking impedance reflects the
common-mode traveling wave on one side of the choke back toward the
source of the forward wave. I took a trapped dipole and dropped a wire
from one end to mininec ground. The standing-wave current is free to
flow through the choke and establish a standing-wave on the other side
- but it doesn't. Here is what a robust isolator is supposed to do to
the common-mode standing-wave current.

http://www.w5dxp.com/trapgnd.JPG

Again, I am not saying the Carolina Windom isolator is that good -
just demonstrating a principle that you seem to be missing above.
--
73, Cecil, w5dxp.com

On Sep 13, 5:19 pm, Owen Duffy wrote:
The NEC model I posted
shows that a 1k isolator (common mode choke) is not effective for that
purpose.

Here's a model of a Carolina Windom on 20m with a 2k choke (isolator)
20 feet down the coax from the antenna feedpoint at a height of 50
feet. The maximum current on the coax braid above the isolator is 0.72
amps. The maximum current on the coax braid below the isolator is 0.14
amps. The radiation pattern is close to the advertised one for 20m.

http://www.w5dxp.com/carwin20.JPG
--
73, Cecil, w5dxp.com

On 9 sep, 16:26, lu6etj wrote:
On 6 sep, 13:14, Wimpie wrote:



On 6 sep, 14:30, John Smith wrote:

On 9/6/2010 5:08 AM, Cecil Moore wrote:

...
The one I remember was about the Carolina Windom 4:1 voltage balun at
the feedpoint and the 1:1 choke-isolator 20' down the coax. The
original Windom was fed, Marconi style, against ground.
--
73, Cecil, w5dxp.com

I have a "weird thing" about windoms ... I just don't trust an antenna
which "manipulates" RF on the feedline in "beneficial" ways and has a
religious cult following ... insane quirk of mine, really. lol *Now I
don't have the room ... moved again.

If the wife had her way, we would move to Montana next to a favorite
sister and brother ... there we would have the room! lol

Regards,
JS

Hello John,

When the feed line goes to a clean environment (for example a ground
provision far from the shack feed line radiation may not be a problem,
but it isn't my favorite. *When the feed line goes directly to the
shack (and equipment), I don't want such an antenna.

When you are working NVIS on 75/80m, you don't want the vertical
component as this leads to radiation under low elevation, hence
stronger reception of ground based interference.

In case of DX, the vertical component may help you as this may result
in lower elevation of main lobe; over here we have much soil with
better then average conductivity. If I would like vertical
polarization, I prefer 100% of that, so no windom or OCF dipoles for
me.

Depending on the design, allowing vertically polarized radiation may
result in worse or better VSWR.

Regarding the color, many straight people wear it over here
(especially in summer days), so you can't judge on color only....

Regarding the balun/transformer, you need a very good one with OCF
dipoles as common mode voltage at feed point can be in the 300V range
with 100W input. just some pF *stray capacitance in a transformer will
provoke feed line radiation.

Best regards,

Wim
PA3DJSwww.tetech.nl
without abc in the address, PM will reach me.- Ocultar texto de la cita -

- Mostrar texto de la cita -

Hello boys, good day for you

Is it Carolina Windom a balanced load to justify the name "balun"? We
could think in a device to transform Z and another device to block
feed line current. What do you think about it?

Miguel

Hello Miguel,

I didn't follow this topic for some days.

The two-step approach will work and you are right, "balun" is not a
good word for an OCF dipole as a "balun" can also be a center-tapped
transformer where the center is connected to the ground of the
unbalanced side (voltage type balun). This one will not suppress
common mode current in an OCF application.

What you need is a "device" that does the required impedance
transformation and accepts large common mode voltage at the high
impedance side without introducing common mode current in the feed
line.

Regarding the two-step approach, I have a simple "device" for
reception. It consists of a 1:3 (1:9 impedance ratio) ferrite auto-
transformer (no galvanic insulation). The 50 Ohms side (coaxial)
contains a three section common mode choke to avoid common mode
current in the 50 Ohms feed line.

Best regards,


Wim
PA3DJS
www.tetech.nl
remove abc from the address before hitting the send button.

In message , John Smith
writes
On 9/12/2010 9:45 AM, lu6etj wrote:

...
Although this is a more important issue, I insist in my original
point, is it "licit" to call "balun" a device connected to two
unbalanced circuits (line and antenna)?, Is it Carolina windom a
balanced antenna?
Here most of hams tend to call balun any toroidal transformer, with TL
or traditional windings connected to any circuit! :)

What you say? Thank for your interest and answers. Best regards to you
and all friends.

Miguel LU6ETJ

Actually, balun = "balanced-to-unbalanced", and unun =
"unbalanced-to-unbalanced." I believe that is correct.

And, I am in agreement, I see isolation RF transformers, RF
auto-transformers and transmission-line-transformers and UNUNs' all
grouped together under "balun." It would be nice to have standardized
terminology and everyone is encouraged to use it ...

Other than that, the rest of your post is sure to fire debate, assuming
that everyone even recognizes the above ...


I think that the simple explanation why 'ununs' get misnamed as baluns'
is that, in their wound transformer form, they often look very similar.
It doesn't help that, depending on how it is wound and connected, one
transformer can sometimes be connected to serve either as a balun or an
unun - and, in many cases, also an impedance transformer.

As far as I'm concerned, while I've known the term 'balun' essentially
'for ever', I had never come across the newly-coined 'unun' until fairly
recently. It was probably simply known by its function, ie an 'RF
transformer'. I have to confess that I don't know why 'unun' has become
popular. It's a rather 'ugly' word, and is somewhat difficult to say
clearly. Maybe that's why they get mis-called 'baluns'!

There is absolutely no reason why there should be any real confusion
between a 'balun' and an 'unun' (other than carelessness, or ignorance
of their function). If you want to group them together, they should
probably come under a general heading of "RF Transformers, and RF
Matching and Other RF Interface Devices" (or maybe something even more
long-winded).
--
Ian

On 14 sep, 01:10, Cecil Moore wrote:
On Sep 13, 5:19 pm, Owen Duffy wrote:

The NEC model I posted
shows that a 1k isolator (common mode choke) is not effective for that
purpose.

Here's a model of a Carolina Windom on 20m with a 2k choke (isolator)
20 feet down the coax from the antenna feedpoint at a height of 50
feet. The maximum current on the coax braid above the isolator is 0.72
amps. The maximum current on the coax braid below the isolator is 0.14
amps. The radiation pattern is close to the advertised one for 20m.

http://www.w5dxp.com/carwin20.JPG
--
73, Cecil, w5dxp.com

Hello boys (greteengs Wimpi, how are you?

For monoband applications we can get more Z from a coaxial choke
making the winding for autorresonance. K1TTT have a good data table.

Time ago I want test differents antenna to lift with a kite and I
found =
http://www.io.com/~n5fc/rfd.htm, the idea seems to me interesting
enough to make some test that are descibed here =

http://www.solred.com.ar/lu6etj/tecn...evisada-en.htm

from here I think of another use of de "coaxial trap" to get more Z
from coaxial winding specially in monoband antennas, I named de
critter "The Trap balun" =

http://www.solred.com.ar/lu6etj/tecn...a_balun-en.htm

4NEC2 simulations and real field test show me both approachs works
fine :)

Miguel Ghezzi LU6ETJ