Ralph Mowery wrote:

I don't see wasting time or money on a balun for just a simple dipole
. Sure it may make the patern vary from the normal textbook, but who
cares most of the time. Most people have to put the antenna up
wherever they can and lots of time it is not in the desired direction
anyway.

Very often, those are the same people who complain of "poor conditions"
and "noisy bands", and operate in constant fear of causing RFI. Many of
these problems are simply due to common-mode feedline currents bringing
RF back into the shack and coupling into the mains wiring.

In other words, people with limited antenna opportunities are often the
ones who need a balun - or more accurately, a common-mode choke - the
MOST.

The problems of desperate antenna locations cannot be entirely cured,
but they *can* be improved. Almost always, feedline chokes and/or baluns
will have a valuable part to play.

NOw a beam or some other antenna design is differant.

The largest difference is in the attitudes of the users. No matter what
your antenna is, or where you're forced to install it, it all comes down
to one simple question: do you want to give this antenna the best
possible chance to work correctly... or not?



--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Technically I would have to disagree with calling even a 1:1 balun the
same thing as a common mode choke. A CM choke is an EMI prevention
device intended to filter out RF components generated in a circuit,
away from the feed of a power source, usually an electrical mains. A
balun is intended to change the feed from an unbalanced transmission
line to a balanced output, for example, for connection to a balanced
transmission line or to an antenna such as a dipole. With the balun,
we wany NO reduction in RF current flow. I agree that the effect is
the same, semantically, ie one side effect of the use of a balun is
less CM interference from coming down a balanced feedline but it is
there for a different reason.

Dan

On Aug 28, 2:26*am, Ian White GM3SEK wrote:

In other words, people with limited antenna opportunities are often the
ones who need a balun - or more accurately, a common-mode choke - the
MOST.

Dan wrote:
On Aug 28, 2:26*am, Ian White GM3SEK wrote:

In other words, people with limited antenna opportunities are often the
ones who need a balun - or more accurately, a common-mode choke - the
MOST.

Technically I would have to disagree with calling even a 1:1 balun the
same thing as a common mode choke. A CM choke is an EMI prevention
device intended to filter out RF components generated in a circuit,
away from the feed of a power source, usually an electrical mains.

That is too far narrow a definition of a "common mode choke",
especially the reference to electrical mains. The term is widely applied
to transmission line for both digital data and analog RF signals.

A
balun is intended to change the feed from an unbalanced transmission
line to a balanced output, for example, for connection to a balanced
transmission line or to an antenna such as a dipole. With the balun,
we wany NO reduction in RF current flow.

What exactly do you mean by that?

And also, what exactly do you mean by "balanced" in the context of a
feedline?

I agree that the effect is
the same, semantically, ie one side effect of the use of a balun is
less CM interference from coming down a balanced feedline but it is
there for a different reason.

Not in my station. My motivation for using common-mode chokes is
*specifically* to control any incoming and outgoing interference that
may be caused by common-mode currents on the feedline.

When the common-mode component of the feedline is reduced, it will also
be accompanied by an improvement in "balance" on the antenna, because
the two things go together (or at least, they do for some definitions of
that word). But "balance" is never my primary goal because I don't find
the concept helpful, either when deciding what to do next or when
evaluating the results.



--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

On Aug 31, 3:07*pm, Ian White GM3SEK wrote:
Dan wrote:
On Aug 28, 2:26*am, Ian White GM3SEK wrote:

In other words, people with limited antenna opportunities are often the
ones who need a balun - or more accurately, a common-mode choke - the
MOST.
Technically I would have to disagree with calling even a 1:1 balun the
same thing as a common mode choke. *A CM choke is an EMI prevention
device intended to filter out RF components generated in a circuit,
away from the feed of a power source, usually an electrical mains.

That is too far narrow a definition *of a "common mode choke",
especially the reference to electrical mains. The term is widely applied
to transmission line for both digital data and analog RF signals.

A common mode choke is used in RF applications, very true, but it
serves a filtering purpose,
not a conversion of unbalanced to balanced energy transfer or vice
versa. A common mode choke that operates well will turn
unwanted RF into heat or cause it to dissipate in its core or a
resistor etc..


A
balun is intended to change the feed from an unbalanced transmission
line to a balanced output, for example, for connection to a balanced
transmission line or to an antenna such as a dipole. With the balun,
we wany NO reduction in RF current flow.

What exactly do you mean by that?

You do not want the balun to operate hot (ir to dissipate heat as you
do with a CM choke filter). You strive for 100% transfer of energy and
settle for the best
you can get. With a CM choke, you try to filter and dissipate unwanted
back-RF. Any back RF from your balun
should be converted to unbalanced transfer back to the source. You
reduce back-RF by matching impedances (which can also involve baluns
but not the 1:1 application discussed here). If you try to filter it
the unwanted back-RF, you will also end up filtering the forward
energy transfer. Of course, that would be an undersirable situation.


And also, what exactly do you mean by "balanced" in the context of a
feedline?

For a 2 conductor feedline, the V in each conductor is 180 degrees out
of phase with each other. Same with I. One conductor is +90 degrees
and the other is -90 degrees with respect to earth. At any given
instant and location the summation of both conductors with respect to
each other is equal to the magnitude it would be on the inner
conductor on the unbalanced (coax) with respect to ground (shield).
Since magnitude of the V on each conductor of the balanced line are
equal and opposite in phase, the term "balanced" is appropriate. Same
with I.



I agree that the effect is
the same, semantically, ie one side effect of the use of a balun is
less CM interference from coming down a balanced feedline but it is
there for a different reason.

Not in my station. My motivation for using common-mode chokes is
*specifically* to control any incoming and outgoing interference that
may be caused by common-mode currents on the feedline.

Of course. But it is not due to filtering unwanted RF, it is due to
the conversion of balancing your energy so
that the coax properly acts as a shielded unbalanced line with no
energy in the shield and all energy in the inner conductor
(assuming perfect conditions). Your dipole will try to balance when
fed as a dipole directly from a coax.. Without the balun, any
reflected energy will
partially come down the shield to ground causing interference. The
balun simply unbalances the reflected energy, if any, to that it all
returns through
the inner conductor eliminating RFI if the radio and the shield are
properly earthed.


When the common-mode component of the feedline is reduced, it will also
be accompanied by an improvement in "balance" on the antenna, because
the two things go together (or at least, they do for some definitions of
that word).

But think of your dipole as a balanced transmission line. That's what
it is, with a lot of loss (into radiation resistance).
You WANT common mode on THAT that lossy transmission line and you do
not want it filtered away.

But "balance" is never my primary goal because I don't find
the concept helpful, either when deciding what to do next or when
evaluating the results.

I say "balanced" is your primary goal though you do not realize it.
You want to balance the energy propagation in your dipole "lossy
transmission line", when feeding it with an unbalanced coax. The balun
should accomplish that. Anything reflected is not good but at least it
is reflected "unbalanced" inside the grounded shield causing less EMI.

Dan wrote:
On Aug 31, 3:07*pm, Ian White GM3SEK wrote:
Dan wrote:
On Aug 28, 2:26*am, Ian White GM3SEK wrote:

In other words, people with limited antenna opportunities are often the
ones who need a balun - or more accurately, a common-mode choke - the
MOST.
Technically I would have to disagree with calling even a 1:1 balun the
same thing as a common mode choke. *A CM choke is an EMI prevention
device intended to filter out RF components generated in a circuit,
away from the feed of a power source, usually an electrical mains.

That is too far narrow a definition *of a "common mode choke",
especially the reference to electrical mains. The term is widely applied
to transmission line for both digital data and analog RF signals.

A common mode choke is used in RF applications, very true, but it
serves a filtering purpose,
not a conversion of unbalanced to balanced energy transfer or vice
versa. A common mode choke that operates well will turn
unwanted RF into heat or cause it to dissipate in its core or a
resistor etc..


Common-mode chokes, and filters in general, do NOT aim to "turn unwanted
RF into heat"! That is a total misunderstanding of the whole concept.

An ideal common-mode choke would dissipate zero heat energy, and a
successful real-life choke will dissipate only a tiny fraction of the
available RF power.

When you insert a common-mode choke, you are inserting a large impedance
into the pathway of the common-mode current. The RF current
distribution throughout the entire antenna/feedline/ground system will
adjust to take account of this new impedance. As a result, most of the
common-mode current will be DIVERTED away from its former pathway, and
will flow instead in the antenna.

The details are complicated, but the concept that the choke DIVERTS
common-mode current away from the feedline is reasonably accurate. (By
contrast, the concept that it "turns unwanted RF current into heat" is
just plain wrong.)

If the choke is doing its job, the new value of common-mode current
(I_cm) flowing through the choke will be much less than the previous
value. The power dissipation in the choke will then be (I_cm)-squared x
R, where R is the resistive part of the choke's impedance at that
frequency. Note that I_cm is the small amount of common-mode current
that remains *after* having inserted the choke - not the value before!
The practical outcome is that a higher choke impedance will give *lower*
heat dissipation in the choke itself.

If a common-mode choke is getting hot, it isn't working. Unfortunately
there are many chokes that don't have a high enough impedance to handle
the full range of real-life situations. If a choke is not able to
suppress the common-mode current to a low enough value, then in some
situations it will get hot [1, 2]. But PLEASE don't imagine that is
how common-mode chokes are intended to work!

[1] http://www.w8ji.com/Baluns/balun_test.htm

[2] http://audiosystemsgroup.com/NCDXACoaxChokesPPT.pdf

Also see other pages and publications from the same authors.



A
balun is intended to change the feed from an unbalanced transmission
line to a balanced output, for example, for connection to a balanced
transmission line or to an antenna such as a dipole. With the balun,
we wany NO reduction in RF current flow.

What exactly do you mean by that?

You do not want the balun to operate hot (ir to dissipate heat as you
do with a CM choke filter). You strive for 100% transfer of energy and
settle for the best
you can get. With a CM choke, you try to filter and dissipate unwanted
back-RF. Any back RF from your balun
should be converted to unbalanced transfer back to the source. You
reduce back-RF by matching impedances (which can also involve baluns
but not the 1:1 application discussed here). If you try to filter it
the unwanted back-RF, you will also end up filtering the forward
energy transfer. Of course, that would be an undersirable situation.


Sorry, but that is so confused I can't even begin to unpick it... except
by pointing to "you try to filter and dissipate unwanted back-RF". In so
many different ways, that is NOT what we're trying to do. Tug on that
loose strand, and the whole thing unravels.



And also, what exactly do you mean by "balanced" in the context of a
feedline?

For a 2 conductor feedline, the V in each conductor is 180 degrees out
of phase with each other. Same with I.

Yes.

One conductor is +90 degrees
and the other is -90 degrees with respect to earth.

No. Earth and 90 degrees don't come into this at all.

At any given
instant and location the summation of both conductors with respect to
each other is equal to the magnitude it would be on the inner
conductor on the unbalanced (coax) with respect to ground (shield).
Since magnitude of the V on each conductor of the balanced line are
equal and opposite in phase, the term "balanced" is appropriate. Same
with I.

Yes... but this definition of "balanced" also REQUIRES that the
common-mode current is zero. The two are locked together, so if
"balance" is your aim, the practical way to achieve it is to force the
common-mode current to a lower value.

We have some direct leverage on common-mode current, because it's a
real, measurable thing. But "balance" is only a concept, and there isn't
any *direct* leverage that we can apply to it.

So even though a "common-mode choke" and a "current balun" are two
different names for the same physical device, it does make a difference
which name you choose. Think "common-mode choke", and you can see the
levers that will make your antenna/feedline system perform the way you
want it to. Think "balun", and all you see is a label that covers those
levers up.


[...]
But think of your dipole as a balanced transmission line. That's what
it is, with a lot of loss (into radiation resistance).
You WANT common mode on THAT that lossy transmission line and you do
not want it filtered away.

Again, that is all so misconceived - at every turn, it clashes with
obvious, measurable physical reality; or else it contradicts itself.
I'm sorry, but you really do need to do a clean wipe and start again
with a good textbook.


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

On Sep 1, 4:20*am, Ian White GM3SEK wrote:
Dan wrote:
On Aug 31, 3:07*pm, Ian White GM3SEK wrote:
Dan wrote:
On Aug 28, 2:26*am, Ian White GM3SEK wrote:

In other words, people with limited antenna opportunities are often the
ones who need a balun - or more accurately, a common-mode choke - the
MOST.
Technically I would have to disagree with calling even a 1:1 balun the
same thing as a common mode choke. *A CM choke is an EMI prevention
device intended to filter out RF components generated in a circuit,
away from the feed of a power source, usually an electrical mains.

That is too far narrow a definition *of a "common mode choke",
especially the reference to electrical mains. The term is widely applied
to transmission line for both digital data and analog RF signals.

A common mode choke is used in RF applications, very true, but it
serves a filtering purpose,
not a conversion of unbalanced to balanced energy transfer or vice
versa. A common mode choke that operates well will turn
unwanted RF into heat or cause it to dissipate in its core or a
resistor etc..

Common-mode chokes, and filters in general, do NOT aim to "turn unwanted
RF into heat"! That is a total misunderstanding of the whole concept.

A CM choke aims to present a high impedence to unintentional RF. Once
"choked" by the high impedance,
the enrgey must either reflect or be aborbed somewhere in the circuit
or the core as real power. What is it that you cannot
understand about the term "choke"?



An ideal common-mode choke would dissipate zero heat energy, and a
successful real-life choke will dissipate only a tiny fraction of the
available RF power.

CM choke is a filter, not an energy transfer device. Do you have any
formal education in electrical engineering?


When you insert a common-mode choke, you are inserting a large impedance
into the pathway of the common-mode current. *The RF current
distribution throughout the entire antenna/feedline/ground system will
adjust to take account of this new impedance. As a result, most of the
common-mode current will be DIVERTED away from its former pathway, and
will flow instead in the antenna.

Whew. You sort of describe a balun except that the balun is an
impedance matching device, in this discussion 1:1.
What new impedance does your 1:1 balun change you transmission line
and antenna feedpoint to ;-)


The details are complicated, but the concept that the choke DIVERTS
common-mode current away from the feedline is reasonably accurate. (By
contrast, the concept that it "turns unwanted RF current into heat" is
just plain wrong.)

Strawman. I didn't say that! RF current or voltage at the antenna is
not unwanted. You are the one who says you use a common choke choke at
your antenna feedpoint, not I.


If the choke is doing its job, the new value of common-mode current
(I_cm) flowing through the choke will be much less than the previous
value. The power dissipation in the choke will then be (I_cm)-squared x
R, where R is the resistive part of the choke's impedance at that
frequency. Note that I_cm is the small amount of common-mode current
that remains *after* having inserted the choke - not the value before!
The practical outcome is that a higher choke impedance will give *lower*
heat dissipation in the choke itself.

I cannot believe you are serious. You actually insert a choke at your
antenna input? I insert an efficient balun ;-)
Have you ever thought that there might be a reason for people
differentiating the use of a balun by use of the term "balun"?
There is a reason. On paper, it looks the same as a balun. In
operation, the CM choke presents a high impedance to
unwanted RF where the balun presents a MATCHED impedance to
intentional RF.


If a common-mode choke is getting hot, it isn't working.

It is working quite well if the filtered RF is dissipating in the
intentionally lossy core. (Such as powdered iorn).


Unfortunately
there are many chokes that don't have a high enough impedance to handle
the full range of real-life situations. If a choke is not able to
suppress the common-mode current to a low enough value, then in some
situations it will get hot *[1, 2]. *But PLEASE don't imagine that is
how common-mode chokes are intended to work!

[1] *http://www.w8ji.com/Baluns/balun_test.htm

[2]http://audiosystemsgroup.com/NCDXACoaxChokesPPT.pdf

Also see other pages and publications from the same authors.

A
balun is intended to change the feed from an unbalanced transmission
line to a balanced output, for example, for connection to a balanced
transmission line or to an antenna such as a dipole. With the balun,
we wany NO reduction in RF current flow.

What exactly do you mean by that?

Umm, we do not want to reduce power from the transceiver to the
antenna?


You do not want the balun to operate hot (ir to dissipate heat as you
do with a CM choke filter). You strive for 100% transfer of energy and
settle for the best
you can get. With a CM choke, you try to filter and dissipate unwanted
back-RF. Any back RF from your balun
should be converted to unbalanced transfer back to the source. You
reduce back-RF by matching impedances (which can also involve baluns
but not the 1:1 application discussed here). If you try to filter it
the unwanted back-RF, you will also end up filtering the forward
energy transfer. Of course, that would be an undersirable situation.

Sorry, but that is so confused I can't even begin to unpick it...

It sounds like you have reached the plateau of your ability to
understand RF and transmission lines. THAT is the reason for
you confusion. Sorry.


except
by pointing to "you try to filter and dissipate unwanted back-RF". In so
many different ways, that is NOT *what we're trying to do. Tug on that
loose strand, and the whole thing unravels.

Continue the metaphor. Tug on that loose strand and what do you
discover, thus unraveling what?



And also, what exactly do you mean by "balanced" in the context of a
feedline?

For a 2 conductor feedline, the V in each conductor is 180 degrees out
of phase with each other. Same with I.

Yes.

One conductor is +90 degrees
and the other is -90 degrees with respect to earth.

No. Earth and 90 degrees don't come into this at all.

Yes it does! This reveals a large part of your confusion. The shield
on the coax is at earth. Earth is always involved. Do you know that
you could connect an earthing point exactly half way down the
"balanced" winding of the balun and have no effect on the operation of
the balun? There is no reason to do that of course but it illustrates
what the balun does. The center portion of the balanced winding is an
isolated 'earth' connection (that does need to be isolated but it is).
One side is -90, center is 0 (earth) and the other side is +90. On the
unbalanced side, there is no phase shift of course; you only have 0
(shield) and inner conductor voltage/current.

At any given
instant and location the summation of both conductors with respect to
each other is equal to the magnitude it would be *on the inner
conductor on the unbalanced (coax) with respect to ground (shield).
Since magnitude of the V on each conductor of the balanced line are
equal and opposite in phase, the term "balanced" is appropriate. Same
with I.

Yes... but this definition of "balanced" also REQUIRES that the
common-mode current is zero.

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

I give up! You need some education in this area.

My take on CM chokes is that they are best on TV coax to keep energy on the
shield from bringing trouble to the TV chassis. On a transmitting antenna,
the idea is to enforce a high impedance bump somewhere to set the resonant
length other than what it wants to be. That might not contribute to
efficiency even if it prevents the coax from being part of the antenna. If
the antenna is in resonance, there won't be any coax radiation and no Choke
is really needed. My point is, you are best not needing one, but if that is
what you need to put the current out on the wire, or out of the shack. OK.
Of course high gain antennas have a pattern to protect, but does it matter
all that much for anything up to a 3 element yagi? High currents and
voltages on the coax are to be avoided because that is where your loss will
be.

Dan wrote:
On Sep 1, 4:20*am, Ian White GM3SEK wrote:
Dan wrote:
On Aug 31, 3:07*pm, Ian White GM3SEK wrote:
Dan wrote:
On Aug 28, 2:26*am, Ian White GM3SEK wrote:

In other words, people with limited antenna opportunities are often the
ones who need a balun - or more accurately, a common-mode choke - the
MOST.
Technically I would have to disagree with calling even a 1:1 balun the
same thing as a common mode choke. *A CM choke is an EMI prevention
device intended to filter out RF components generated in a circuit,
away from the feed of a power source, usually an electrical mains.

That is too far narrow a definition *of a "common mode choke",
especially the reference to electrical mains. The term is widely applied
to transmission line for both digital data and analog RF signals.

A common mode choke is used in RF applications, very true, but it
serves a filtering purpose,
not a conversion of unbalanced to balanced energy transfer or vice
versa. A common mode choke that operates well will turn
unwanted RF into heat or cause it to dissipate in its core or a
resistor etc..

Common-mode chokes, and filters in general, do NOT aim to "turn unwanted
RF into heat"! That is a total misunderstanding of the whole concept.

A CM choke aims to present a high impedence to unintentional RF. Once
"choked" by the high impedance,
the enrgey must either reflect or be aborbed somewhere in the circuit
or the core as real power. What is it that you cannot
understand about the term "choke"?


I'm slightly encouraged that the key word "reflected" has now crept into
your description. It wasn't there in what you wrote previously.

[Snip similar]

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


What??? You know that statement didn't come out right, so how much of
the rest did you really mean?

I give up! You need some education in this area.


I give up too - at last, something we can agree about.

My main worry is that anyone *else* might have tried to gain some
education from your confused statements on this particular topic.




--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

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

Readers interested in baluns might take a look at "Baluns: What They Do
and How They Do It" in the _ARRL Antenna Compendium_, Vol. 1 or at
http://eznec.com/Amateur/Articles/Baluns.pdf.

Roy Lewallen, W7EL