On Mon, 1 Sep 2008 09:26:26 -0700 (PDT), wrote:

In a perfect situation, with a balanced feedline, the only kind of
current and voltage you have IS common mode!

This statement above contains a serious error of perception while
trying to inhabit the debate over BalUns - and it probably corrupts
that topic too.

First - a circuit has at a minimum two conductors extending from a
source. A circuit by its nature is circular: for every charge carrier
that enters it, one must exit it. Continuity is a necessary condition
for a circuit. No continuity, no conduction, hence an "Open Circuit."

Second - those two conductors, if viewed at a remote point where they
are joined, have equal and opposite paths of current conduction - to
and from that point. This is from Kirchoff's law of currents.

Third - this is called Differential Mode current in anticipation of a
common modality.

Fourth - if that remote point of connection is replaced with a load,
there is a voltage across that load characterized by both the
unaltered directions of current, and its now altered magnitude of
current.

Fifth - this is called Differential Mode voltage in anticipation of a
common modality.

This completes the discussion of the Differential Mode.

If we expand upon this simple model of a source, two wires, and a load
and put it into the context of life as we know it; then the circuit
operates in the proximity of ground. By convention, ground is called
Common.

Ground, by convention is an infinite sink of charge of infinite
extent. Hence as a conductor, it is available everywhere - Common.
This ground may have either deliberate or accidental conductive
relationships to the Differential Circuit.

First - the linkage of ground to the differential circuit can be
through an Ohmic path, or by an inductive path, or by a capacitive
path. To support conduction, the circuit must contain two conductive
paths to ground through any combination of these linkages, and that
path must be complete. The apparent source driving conduction through
that path will be a combination of the differential source and the
differential load as each will have some relationship to ground.

Second - those two conductive paths, if viewed at a remote point
where they are joined, have equal and opposite paths of current
conduction - to and from that point. This is from Kirchoff's law of
currents.

Third - this is called Common Mode current.

Fourth - as the differential circuit is original and establishes both
the source and the load; then through the introduction of ground, this
Common Mode current is mixed with the original Differential Current
and analysis must be performed by substitutions to separate them.

Fifth - the apparent source presents the Common Mode voltage.

This completes the discussion of Common Mode.

The applications of a choke to either circuit is commonplace to
control each mode's current. It would appear through the context of
discussion in other threads that there is some confusion in what is
being choked, and how a choke is properly applied is confounded by
that confusion.

It follows that if the transmission line from the source to load
suffers from Common Mode currents, that this must be due to a Common
Mode voltage gradient extending from the source to the load. If
either lead of that transmission line pair were choked, this would
disrupt the Differential Mode. If both leads of the transmission line
pair were independently choked, this would only double the disruption.
However, if both leads were choked in parallel (both lines either
coiled as a pair rather than individually, or both lines penetrate a
lossy core) then their fields would be contained between them in the
Differential Mode, but their Common Mode path (they both share equal
conduction in the same direction due to the Common Mode voltage
gradient) will be snubbed.

Some BalUns employ these techniques - some don't. BalUns fail by the
degree that they don't when Common Mode, as a problem, is injected
into the circuit through imbalances. As balance in the proximity of
earth and many confounding nearby structures is a forgone failure,
choking is a practical necessity for correct BalUn performance. Any
issues of BalUn heatings are proof of this choking necessity, and
further proof of the demand for additional choking at that point (and
frequently elsewhere at wavelength relationships along the affected
line).

73's
Richard Clark, KB7QHC

On Sep 2, 10:43*pm, John Smith wrote:
wrote:
...
I disagree. There is no choking, there is merely a polarity and phase
shift between the "primary" and "secondary" of the 1:1 balun
"transformer".

The best way I can easily express this is to consider a 1:1 240V 60 Hz
isolation transformer (yes, the balun acts theoretically in the same
manner). ...

No. *But you have focused on your error in thinking/logic/function. *An
RF Transformers does what you state, lengths of transmission line
carrying RF behave in a different "mode." (uh, I hate that word ...)

Now, if you do some research, you can correct your error(s) ...

Regards,
JS

--
It is like a nightmare where the public servants are the people which
the police are supposed to protect us from!

A 1:1 balun IS an RF transformer. Lengths of transmission line wound
an air core can function as a 1:1 RF transformer. Does this in any way
show you the error you are making? Transformers operate in the same
way whether at 60Hz or RF. So much for your "No" statement which seems
to demonstrate a certain confidence masked in senility.

On Sep 3, 7:18*am, Cecil Moore wrote:
wrote:
For a balanced transmission line, the characteristic impedance is not
expressed in differential mode terms, it IS common mode so I do
not know why you ask about differential mode characteristic impedance.

Well, there's your problem. In a properly functioning
transmission line, whether balanced or unbalanced, the
currents in the two conductors are differential, not
common-mode. The two currents are equal in magnitude
and 180 degrees out of phase and their fields tend
to cancel which minimizes radiation.

Common-mode currents only occur when the two currents
are not perfectly differential, i.e. not equal amplitudes
and/or not 180 degrees out of phase.
--
73, Cecil *http://www.w5dxp.com

Nope. The CM choke works precisely because the common mode currents
are mirror images, 180 degrees out of phase. If they weren't, the CM
choke could not act to cancel them and you would need differential
mode chokes to get rid of them. On your balanced feedline, the voltage
at any point is delta between the amplitude of line 1 and 2.

On Sep 3, 7:44*am, Cecil Moore wrote:
wrote:
By the way, I have seen so many articles about baluns written by other
hams and they tend to repeat the same mistakes and assumptions. Most
hams do not understand how a balun works.

Your following statement puts you in that category.

Inserting a balun does not "choke" the current in the shield, it
merely shifts the output phases so that the current (voltage) is
directed towards the dipole at all times (see my other post in this
thread).

This applies to a W2DU balun. Why would you want
differential current fields to be introduced into
the #77 ferrite beads? Their entire purpose is to
provide a large choking impedance and dissipate
common-mode power.
--
73, Cecil *http://www.w5dxp.com

OK, next time I specify an EMC filter for a switching power supply, I
will ensure that the CM choke impedance matches the impedances of the
network and the loads so that I can most efficiently conduct RFI from
the source to the power line, from common mode at the load to
unbalanced load of the power line source. This will ensure maximum
interference is imparted on the phase conductor. In fact, I think I
will change my nomenclature by refering to the "choke" as a
"balun" (they are one and the same; the source doesn't know the
difference!) and promptly fail my next FCC submittal. Then I will be
invited to retire and of course I will have much more time to be re-
educated on rec.radio.amareur.antenna.

On Sep 3, 8:04*am, Cecil Moore wrote:
wrote:
Many US amateurs do not understand how a balun works.

Quoting "The ARRL Antenna Book" re a w2du balun:
"Maxwell made a test balun by slipping 300 #73 beads
over a piece of RG-303 coaxial cable. The impedance
of the outer conductor of the cable measured
4500+j3800 at 4.0 MHz."

The differential current emerging from the inside
of the coax braid encounters, e.g. 30 ohms, looking
toward the antenna. It encounters 4500+j3800 = 5890
ohms looking back down the outside of the coax.
Ohm's law does the rest.

Without the beads, that differential current might
see an impedance lower than 30 ohms looking back
down the outside of the coax for certain unfortunate
lengths of coax. The common-mode choking impedance
forces ~equal currents in each dipole leg at the
BALanced antenna to UNbalanced coax junction. That
common-mode choking impedance causes the balun
function to occur.
--
73, Cecil *http://www.w5dxp.com

Because the input and the out windings of the balun must be isolated
at least at RF of interest, OF COURSE there should be a high impedance
between the ballanced current flow and the unbalanced current flow.
However, the impedance of the source looking into the impedance from
the souurce should match source impedance and the impedance of the
load looking in the output winding of the balun should match the load
impedance (say 70 ohms, or 600 ohms or whatever your antenna or
trnasmission line impedance is. The impedence at frequency of interest
between input winding and output winding should be infinity for
isolation purposes (obviously you do not want to mix the unbalanced
input and balanced output currents.

On Sep 3, 2:10*pm, Cecil Moore wrote:
Richard Clark wrote:
wrote:
Many US amateurs do not understand how a balun works.

How true - not even fundamental terminology.

http://en.wikipedia.org/wiki/Balun(see 1st photo)
"This is a simple RF *choke* which works as a *balun* by
preventing signals passing along the outside of the braid."

*From "The IEEE Dictionary":
"balun (1) A network for the transformation from an
unbalanced line or system to a balanced line or system,
or vice versa."

*From an Unabridged Webster's:
"balun - a device for converting a balanced line into
an unbalanced line and vice versa."

10 PRINT "A W2DU balun is both a choke and a balun!"
20 Goto 10
--
73, Cecil *http://www.w5dxp.com

I agree that a balun operating at 14 MHz would be a choke when
operating at 70MHz.

wrote:
Nope. The CM choke works precisely because the common mode currents
are mirror images, 180 degrees out of phase.

You are 100% wrong. From "The IEEE Dictionary":
"common-mode (1)(general) The instantaneous algebraic
average of two signals applied to a balanced circuit,
both signals referred to a common reference."

The "instantaneous algebraic average of two signals"
180 degrees out of phase is ZERO.
--
73, Cecil http://www.w5dxp.com

On Sep 3, 3:59*pm, Richard Clark wrote:
On Mon, 1 Sep 2008 09:26:26 -0700 (PDT), wrote:
In a perfect situation, with a balanced feedline, the only kind of
current and voltage you have IS common mode!

This statement above contains a serious error of perception while
trying to inhabit the debate over BalUns - and it probably corrupts
that topic too.

First - a circuit has at a minimum two conductors extending from a
source. *A circuit by its nature is circular: for every charge carrier
that enters it, one must exit it. *Continuity is a necessary condition
for a circuit. *No continuity, no conduction, hence an "Open Circuit."

Second - those two conductors, if viewed at a remote point where they
are joined, have equal and opposite paths of current conduction - to
and from that point. *This is from Kirchoff's law of currents.

Third - this is called Differential Mode current in anticipation of a
common modality.

Fourth - if that remote point of connection is replaced with a load,
there is a voltage across that load characterized by both the
unaltered directions of current, and its now altered magnitude of
current.

Fifth - this is called Differential Mode voltage in anticipation of a
common modality.

This completes the discussion of the Differential Mode.

If we expand upon this simple model of a source, two wires, and a load
and put it into the context of life as we know it; then the circuit
operates in the proximity of ground. *By convention, ground is called
Common.

Ground, by convention is an infinite sink of charge of infinite
extent. *Hence as a conductor, it is available everywhere - Common.
This ground may have either deliberate or accidental conductive
relationships to the Differential Circuit.

First - the linkage of ground to the differential circuit can be
through an Ohmic path, or by an inductive path, or by a capacitive
path. *To support conduction, the circuit must contain two conductive
paths to ground through any combination of these linkages, and that
path must be complete. *The apparent source driving conduction through
that path will be a combination of the differential source and the
differential load as each will have some relationship to ground. *

Second - *those two conductive paths, if viewed at a remote point
where they are joined, have equal and opposite paths of current
conduction - to and from that point. *This is from Kirchoff's law of
currents. *

Third - this is called Common Mode current.

Fourth - as the differential circuit is original and establishes both
the source and the load; then through the introduction of ground, this
Common Mode current is mixed with the original Differential Current
and analysis must be performed by substitutions to separate them.

Fifth - the apparent source presents the Common Mode voltage.

This completes the discussion of Common Mode.

The applications of a choke to either circuit is commonplace to
control each mode's current. *It would appear through the context of
discussion in other threads that there is some confusion in what is
being choked, and how a choke is properly applied is confounded by
that confusion.

It follows that if the transmission line from the source to load
suffers from Common Mode currents, that this must be due to a Common
Mode voltage gradient extending from the source to the load. *If
either lead of that transmission line pair were choked, this would
disrupt the Differential Mode. *If both leads of the transmission line
pair were independently choked, this would only double the disruption.
However, if both leads were choked in parallel (both lines either
coiled as a pair rather than individually, or both lines penetrate a
lossy core) then their fields would be contained between them in the
Differential Mode, but their Common Mode path (they both share equal
conduction in the same direction due to the Common Mode voltage
gradient) will be snubbed.

Some BalUns employ these techniques - some don't. *BalUns fail by the
degree that they don't when Common Mode, as a problem, is injected
into the circuit through imbalances. *As balance in the proximity of
earth and many confounding nearby structures is a forgone failure,
choking is a practical necessity for correct BalUn performance. *Any
issues of BalUn heatings are proof of this choking necessity, and
further proof of the demand for additional choking at that point (and
frequently elsewhere at wavelength relationships along the affected
line).

73's
Richard Clark, KB7QHC

Let me put it this way (again very simplifed): How do you explain a
residential 208V power source where you have 120 V from line 1 and
line 2 to ground but 240V with respect to each other. You 240V
household appliances operate this way. Ecept for the fact that the
lines are 120 degrees out of phase phase (insread of 180 because we
use a delta system instead of Y, but this is not that important for
this discussion) this is nearly a BALANCED feed, where lines 1 and 2
degrees out of phase at 60 Hz and the voltage of interest is the
summation of the two lines. Nearly every home in the USA operates this
way. In Europe, 240 V is usually obtained by the voltage difference
between line 1 (240V) and earth (0V). That is an unbalanced feed. You
can insert a 1:1 isolation transformer using the European system at
the input and create the balanced USA system at the output by drawing
+120 and -120 at from the output windings assigning imaginary isolated
earth at centertap. The isolated ground CANNOT conduct tio real ground
if the winding to winding impedance is infinity. Basically, hams' 1:1
baluns do much the same thing: They isolate the real ground as such
and prevent currents from flowing down the input ground shield. On
this ng in a short space I cannot think of a simpler way to express
this although I expect to see many statements (you can't equate 60Hz
to RF!). Yes you can; a transformer operates as a transformer in the
same wayat any frequency providing you design it properly for the
frequency of interest. This subject is not nearly so complicated as
some in this group makes it out to be and the topic certainly does not
rate articles in amateur publications any more than basic application
of ohm's law does.

On Sep 3, 7:12*pm, Cecil Moore wrote:
wrote:
Nope. The CM choke works precisely because the common mode currents
are mirror images, 180 degrees out of phase.

You are 100% wrong. From "The IEEE Dictionary":
"common-mode (1)(general) The instantaneous algebraic
average of two signals applied to a balanced circuit,
both signals referred to a common reference."

The "instantaneous algebraic average of two signals"
180 degrees out of phase is ZERO.
--
73, Cecil *http://www.w5dxp.com

So that means I get 0 volts when I touch one side of the 120V in my
electrical service to the 120V other side? I was afraid I might see
240V.

wrote:
I agree that a balun operating at 14 MHz would be a choke when
operating at 70MHz.

You would do well to agree that a well-designed W2DU balun
operating at 14 MHz is choking the heck out of the 14 MHz
common-mode current in order to achieve the balun function.

You seem to have the IEEE definitions of differential
signals and common-mode signals exactly reversed. Because
of that misconception, might you be the one who doesn't
understand how baluns work?
--
73, Cecil http://www.w5dxp.com