On Tue, 28 Mar 2006 12:59:52 -0500, John Popelish
wrote:
With this in mind, do we add a characteristic of loss to the
definition? A lossy air core transformer with series driven, bucking
sections.

Air core? It is a ferrite core transformer with two one turn

Hi John,

If there's a transformer in the sense of windings; then it is an air
core, the ferrite is wholly transparent to the transverse currents.
You could remove the ferrite and it wouldn't make a bit of difference
in that sense of transforming.

this current mismatch would cause the transformer to
produce more or less voltage across the windings
In fact, nothing of that sort happens - at least not by your
description. The ferrite is simply bulk resistance inserted into the
common mode path. That is why common mode current is suppressed. The
same thing occurs in the coiled transmission line choke, but the
resistance is replaced by reactance. Again, common mode current is
snubbed by encountering this too.

The transformer property is in the isolation of the balanced circuit
from the unbalanced circuit through this resistive characteristic.

You are missing one path. The two from the source in the form of the
inner shield of the coax, and the center conductor, and the one from
the load in the form of the outer shield of the coax (same shield, but
isolated circuits). Further, there is no flux linkage of the two
conductors coming from the source. Their magnetic lines never break
the cores, whereas the common mode current does break the core which
thus inserts the resistance of the ferrite.

73's
Richard Clark, KB7QHC

On Tue, 28 Mar 2006 17:39:52 -0800, Richard Clark
wrote:

Further, there is no flux linkage of the two
conductors coming from the source.

That was not correctly expressed, the flux between the two are tightly
bound and:
Their magnetic lines never break
the cores, whereas the common mode current does break the core which
thus inserts the resistance of the ferrite.

Richard Clark wrote:
On Tue, 28 Mar 2006 12:59:52 -0500, John Popelish
wrote:

Air core? It is a ferrite core transformer with two one turn

Hi John,

If there's a transformer in the sense of windings; then it is an air
core, the ferrite is wholly transparent to the transverse currents.

I said that. It is a common mode transformer.

You could remove the ferrite and it wouldn't make a bit of difference
in that sense of transforming.

The short length of the two conductors passing through the ferrite is
certainly a poorer transformer (less mutual inductance between them)
if you remove the cores.

this current mismatch would cause the transformer to
produce more or less voltage across the windings

In fact, nothing of that sort happens - at least not by your
description. The ferrite is simply bulk resistance inserted into the
common mode path.

Make that, "impedance (mostly inductive, if the ferrite is well suited
to the frequency)" and I agree.

That is why common mode current is suppressed. The
same thing occurs in the coiled transmission line choke, but the
resistance is replaced by reactance. Again, common mode current is
snubbed by encountering this too.

I agree with this, except that the purpose of the ferrite is to
increase the common mode inductance of the section of coax passing
through it, not add resistance. Some resistance is inevitable,
because no ferrite is lossless, but the intention is for inductance.

The transformer property is in the isolation of the balanced circuit
from the unbalanced circuit through this resistive characteristic.

Try transmitting through such a resistance and you are going to lose a
lot of your power.

You are missing one path. The two from the source in the form of the
inner shield of the coax, and the center conductor, and the one from
the load in the form of the outer shield of the coax (same shield, but
isolated circuits).

I can't parse this. There are two metal conductors entering the
choke, and two exiting it. All currents pass through those 4 conductors.

Further, there is no flux linkage of the two
conductors coming from the source. Their magnetic lines never break
the cores,

I think you mean by this that a normal unbalanced signal in a coax has
no magnetic field external to the shield. It is all between the
center conductor and the shield. And I agree that this is what you
are trying to accomplish by adding this two conductor choke between
the coax and the balanced antenna. Without it, there would be some
magnetic field from a net (uncanceled) current and voltage on the
outside of the shield that would cause the coax to radiate. And the
voltages and currents fed to the balanced antenna would not be equal
and opposite (balanced) but somewhat unbalanced. There would also be
non equal currents in the center conductor and shield. I think we
agree on all that, but have a different picture of how a choke balun
corrects these problems.

whereas the common mode current does break the core which
thus inserts the resistance of the ferrite.

The common mode current causes flux in the core, and the conductors
passing through that flux produce a voltage proportional to the rate
of change of that flux, just as the conductor passing through any
inductor would. The transformer aspect is that since both conductors
pass through the exact same rate of change of flux, there is the same
voltage produced at the ends sticking out of the core, and this
voltage gets algebraically added to what is already there. If the
inductance of each winding is high enough (5 to 10 times the coax
impedance) a very small common mode current is enough to produce a
large enough voltage across the ends to the two conductors to correct
most of the unbalanced to balanced coupling.

Admittedly, there is no need to get this inductance (including mutual
inductance) with the aid of ferrite around the coax. You could just
wind the coax into an air core transformer. But it would be
considerable larger than one made with a high permeability core,
though, probably lower loss.

John Popelish wrote:
Richard Clark wrote:
. . .

In fact, nothing of that sort happens - at least not by your
description. The ferrite is simply bulk resistance inserted into the
common mode path.

Make that, "impedance (mostly inductive, if the ferrite is well suited
to the frequency)" and I agree.

"Low frequency" ferrites are well suited to applications as HF chokes
and broadband transformers. What you don't want to do is use them for a
high Q inductor in a filter, tuned circuit, or similar application.

That is why common mode current is suppressed. The
same thing occurs in the coiled transmission line choke, but the
resistance is replaced by reactance. Again, common mode current is
snubbed by encountering this too.

I agree with this, except that the purpose of the ferrite is to increase
the common mode inductance of the section of coax passing through it,
not add resistance. Some resistance is inevitable, because no ferrite
is lossless, but the intention is for inductance.

Baluns work fine with a resistive impedance, with the exception of
applications involving large power. In fact, resistive impedance is
desirable because the impedance changes little with frequency, and is
relatively free of resonance effects. (More below.)

The transformer property is in the isolation of the balanced circuit
from the unbalanced circuit through this resistive characteristic.

Try transmitting through such a resistance and you are going to lose a
lot of your power.

You're not "transmitting through" a balun's impedance. Only the common
mode current effectively flows through it, and the power dissipated by
the balun is Icm^2 * R, where Icm is the common mode current and R is
the resistive part of the balun's common mode impedance. If R is small,
dissipation is low. But if R is large, that makes Icm small, so
dissipation is also low. It's really an impedance matching problem when
the balun is resistive -- a very low or very high balun R results in low
dissipation. Dissipation is maximum at some intermediate value of R and
decreases on each side.

A typical balun made with "low frequency" ferrite (e.g. Fair-Rite 70
series) and operating at HF or above (and therefore primarily resistive)
having a common mode impedance of 500 ohms or greater generally won't
dissipate any significant fraction of the transmitted power. However, if
you're running high power, even a fraction of a dB dissipated in the
balun will cause it to overheat. Consequently, people running high power
often resort to type 43 ferrite (a Fair-Rite designation; or its
equivalent from other manufacturers), which is less resistive than lower
frequency ferrites. In extreme cases, high frequency (60 series) ferrite
is necessary. The problem is that it's increasingly difficult to get
adequate impedance with the higher frequency ferrites. Type 43 is often
a good compromise, and it's widely available in many core sizes.

. . .
I think you mean by this that a normal unbalanced signal in a coax has
no magnetic field external to the shield. It is all between the center
conductor and the shield. And I agree that this is what you are trying
to accomplish by adding this two conductor choke between the coax and
the balanced antenna. Without it, there would be some magnetic field
from a net (uncanceled) current and voltage on the outside of the shield
that would cause the coax to radiate. And the voltages and currents
fed to the balanced antenna would not be equal and opposite (balanced)
but somewhat unbalanced. There would also be non equal currents in the
center conductor and shield. I think we agree on all that, but have a
different picture of how a choke balun corrects these problems.
. . .

Common and differential mode currents are physically separated in a coax
cable, and so are the fields from the two components, providing that the
shield is at least several skin depths thick. The differential mode
current and its fields are entirely inside the coax, decaying rapidly as
you go outward from the inner boundary of the shield. By the time you
reach the outer boundary of the shield the fields from the differential
current is negligibly small. So any core you put over the coax doesn't
see or interact with the common mode current or its fields at all, and
you can completely ignore it when analyzing balun action. Similarly, you
can ignore the core when analyzing the differential mode properties of
the system. The common mode current resides in a thin layer on the
outside of the shield, it and its fields never reaching the inside. The
balun provides an impedance to this current just as it would to any
current on the outside of a conductor.

When bifilar wound, the fields from the differential mode current are
primarily between the turns, although some relatively small amount
extends beyond to interact with the core. The net result is nearly the same.

. . .

Roy Lewallen, W7EL

Roy Lewallen wrote:
So any core you put over the coax doesn't
see or interact with the common mode current or its fields at all, and
you can completely ignore it when analyzing balun action.

Roy probably meant "differential" above instead of "common".
Cores on coax definitely "interact with the common mode current
or its fields" and that is their purpose.
--
73, Cecil http://www.qsl.net/w5dxp

In article ,
Cecil Moore wrote:

Roy Lewallen wrote:
So any core you put over the coax doesn't
see or interact with the common mode current or its fields at all, and
you can completely ignore it when analyzing balun action.

Roy probably meant "differential" above instead of "common".
Cores on coax definitely "interact with the common mode current
or its fields" and that is their purpose.

ok so after reading all this, wich i enjoyed, confused me a bit.

lets say i operate 10-160m and 6m (all band antenna)
, at max 500wout. (typically 200w)

who makes a good commercial choke balun"" w/so239's at the ends??


make/model/where to buy, ??


i've been using a w2du, lots have told me it's not the 'best' money
isn't the issue i'd just like to get a 'good one' ie efficient


thanks

any tips appreciated

ml wrote:
In article ,
Cecil Moore wrote:

Roy Lewallen wrote:
So any core you put over the coax doesn't
see or interact with the common mode current or its fields at all, and
you can completely ignore it when analyzing balun action.
Roy probably meant "differential" above instead of "common".
Cores on coax definitely "interact with the common mode current
or its fields" and that is their purpose.

Indeed I did. I apologize for the error.

Roy Lewallen, W7EL

On Tue, 28 Mar 2006 22:33:18 -0500, John Popelish
wrote:
this current mismatch would cause the transformer to
produce more or less voltage across the windings

In fact, nothing of that sort happens - at least not by your
description. The ferrite is simply bulk resistance inserted into the
common mode path.

Make that, "impedance (mostly inductive, if the ferrite is well suited
to the frequency)" and I agree.

Hi John,

No, the principle of the impedance is overwhelmingly resistive, not
reactive. One core (#75) that snuggly fits over RG58, at about 10MHz,
exhibits 25 Ohms resistance to common mode current. My BalUn uses 50
such whose combination presents 1250 Ohms resistance. This value
varies over frequency, but easily finds a 1000:50 ratio over the
entire MF/HF Ham spectrum.

I also have two engineering samples boxes full of various material
types and geometries and have measured them all. Some exhibit
reactance, but are vastly overwhelmed by their intrinsic resistance.

That is why common mode current is suppressed. The
same thing occurs in the coiled transmission line choke, but the
resistance is replaced by reactance. Again, common mode current is
snubbed by encountering this too.

I agree with this, except that the purpose of the ferrite is to
increase the common mode inductance of the section of coax passing
through it, not add resistance. Some resistance is inevitable,
because no ferrite is lossless, but the intention is for inductance.

Quite the contrary. Inductance, or more properly to the application,
reactance, may come as a consequence of these cores, but that is
really just a minor component to the vastly greater resistance.

The transformer property is in the isolation of the balanced circuit
from the unbalanced circuit through this resistive characteristic.

Try transmitting through such a resistance and you are going to lose a
lot of your power.

That power, actually current, was forced into a common mode because of
one of several problems:
1. Massive imbalance in the radiator design,
2. Massive catastrophe with the radiator.

If you are destined to "lose a lot of power" into such resistance, you
have far greater problems you are ignoring. However, let's return to
this "loss of a lot of power." You have an antenna with a nominal 50
Ohm load resistance (presumably balanced to the common). You have a
common mode choke with 1000 Ohms resistance in parallel (to the common
of the common mode). Now, why would the power choose the path of 10
to 40 times more resistance to invest its calories in?

I will be generous and pour 1.5KW into a balanced 50 Ohm load to
develop 275V that is also across the 1000 Ohms of the BalUn. 76W into
50 beads. Now this verges on serious power for this load I will
admit, but it also presumes key-down conditions which would only be
found for RTTY or SSTV. By my bench measurements, I figure that the
core's can tolerate as much power as the bulk equivalent carbon
composition resistor - or least this is my rule of thumb. This means
about 1 or 2W per bead to offer enough heat to cause pain, but perhaps
not enough to blister. This is another benchmark from my days in the
Navy.

I once asked an ET Chief how much heat a transistor could tolerate. He
said
"If you can hold onto it and count to 10, it's not too much."

I've been blistered by TO-5 cans with just a casual brush and they
still filled their design mission.

You are missing one path. The two from the source in the form of the
inner shield of the coax, and the center conductor, and the one from
the load in the form of the outer shield of the coax (same shield, but
isolated circuits).

I can't parse this. There are two metal conductors entering the
choke, and two exiting it. All currents pass through those 4 conductors.

Your count is four terminals (not conductors), there are six. You
need to come to terms with this shortfall in your count as it explains
the utility and design of BalUns.

Further, there is no flux linkage of the two
conductors coming from the source. Their magnetic lines never break
the cores,

I think you mean by this that a normal unbalanced signal in a coax has
no magnetic field external to the shield. It is all between the
center conductor and the shield. And I agree that this is what you
are trying to accomplish by adding this two conductor choke between
the coax and the balanced antenna. Without it, there would be some
magnetic field from a net (uncanceled) current and voltage on the
outside of the shield that would cause the coax to radiate. And the
voltages and currents fed to the balanced antenna would not be equal
and opposite (balanced) but somewhat unbalanced. There would also be
non equal currents in the center conductor and shield. I think we
agree on all that, but have a different picture of how a choke balun
corrects these problems.

That is apparent.

whereas the common mode current does break the core which
thus inserts the resistance of the ferrite.

The common mode current causes flux in the core, and the conductors
passing through that flux produce a voltage proportional to the rate
of change of that flux, just as the conductor passing through any
inductor would.

This "rate of change" is spurious, call it frequency dependant, but
then frequency dependency is neither here nor there at this moment.
More to the matter trying to turn this BalUn into a power transformer
is doomed in this analysis as it has absolutely no impact to
correct
most of the unbalanced to balanced coupling.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Tue, 28 Mar 2006 22:33:18 -0500, John Popelish
wrote:
(snip)
Make that, "impedance (mostly inductive, if the ferrite is well suited
to the frequency)" and I agree.


Hi John,

No, the principle of the impedance is overwhelmingly resistive, not
reactive. One core (#75) that snuggly fits over RG58, at about 10MHz,
exhibits 25 Ohms resistance to common mode current.

Yep. Type 75 operated at 10MHz is very lossy.

My BalUn uses 50
such whose combination presents 1250 Ohms resistance. This value
varies over frequency, but easily finds a 1000:50 ratio over the
entire MF/HF Ham spectrum.

Thank you for some specific facts. I had no idea that you were using
a ferrite whose permeability falls to half the low frequency value
(about 5000 at 200kHz) at only 700kHz and is not recommended for flux
coupling applications higher than about 750kHz. It also has a very
low bulk resistivity of 300 ohm cm. At 3 MHz, its permeability is
only about 150 (and plunging).

Type 43 material has a permeability of about 500 at 3 MHz and falling
much more slowly.

I also have two engineering samples boxes full of various material
types and geometries and have measured them all. Some exhibit
reactance, but are vastly overwhelmed by their intrinsic resistance.

(snip)
I agree with this, except that the purpose of the ferrite is to
increase the common mode inductance of the section of coax passing
through it, not add resistance. Some resistance is inevitable,
because no ferrite is lossless, but the intention is for inductance.

Quite the contrary. Inductance, or more properly to the application,
reactance, may come as a consequence of these cores, but that is
really just a minor component to the vastly greater resistance.

If the cores don't have relative hi permeability (causing mutual
inductance in the two conductors passing through) they can't produce
any impedance in series with the common mode current. That is also
transformed over to the two conductors by mutual inductance (as a
loaded secondary reflected to those conductors as a primary).

Try transmitting through such a resistance and you are going to lose a
lot of your power.

That power, actually current, was forced into a common mode because of
one of several problems:
1. Massive imbalance in the radiator design,
2. Massive catastrophe with the radiator.

If you are destined to "lose a lot of power" into such resistance, you
have far greater problems you are ignoring. However, let's return to
this "loss of a lot of power." You have an antenna with a nominal 50
Ohm load resistance (presumably balanced to the common). You have a
common mode choke with 1000 Ohms resistance in parallel (to the common
of the common mode). Now, why would the power choose the path of 10
to 40 times more resistance to invest its calories in?

I will be generous and pour 1.5KW into a balanced 50 Ohm load to
develop 275V that is also across the 1000 Ohms of the BalUn. 76W into
50 beads. Now this verges on serious power for this load I will
admit, but it also presumes key-down conditions which would only be
found for RTTY or SSTV. By my bench measurements, I figure that the
core's can tolerate as much power as the bulk equivalent carbon
composition resistor - or least this is my rule of thumb. This means
about 1 or 2W per bead to offer enough heat to cause pain, but perhaps
not enough to blister. This is another benchmark from my days in the
Navy.

If the radiator is perfectly balanced, the impedance of the ferrite
(transformed to the primary side) sees half of the voltage that is
between the center conductor and the shield. So if the coax carries
275 volts, half of that or about 1378 volts appears across the bead
bead common mode impedance. So a 1000 ohm common mode choke limits
the common mode current to 138/1000 = 138 mA. And if that impedance
is dominated by resistance, the beads will absorb 138*.138=19 watts.
50 beads will stand that indefinitely.

I don't think the O.P.'s balun has 50 beads, though.

You are missing one path. The two from the source in the form of the
inner shield of the coax, and the center conductor, and the one from
the load in the form of the outer shield of the coax (same shield, but
isolated circuits).

I can't parse this. There are two metal conductors entering the
choke, and two exiting it. All currents pass through those 4 conductors.


Your count is four terminals (not conductors), there are six. You
need to come to terms with this shortfall in your count as it explains
the utility and design of BalUns.

If the other two are the ends of the loss resistance, they can be
transformed back to the two conductors.
(snip)

The common mode current causes flux in the core, and the conductors
passing through that flux produce a voltage proportional to the rate
of change of that flux, just as the conductor passing through any
inductor would.


This "rate of change" is spurious, call it frequency dependant, but
then frequency dependency is neither here nor there at this moment.
More to the matter trying to turn this BalUn into a power transformer
is doomed in this analysis as it has absolutely no impact to

It may not be the approach you are familiar with, but I think it is
valid. The transformer just has a lot of core loss, if you use a
ferrite optimized for a much lower frequency. And that loss shows up
as if it were a resistor connected across the ends of the two
windings. If a low loss ferrite (at the operating frequency) is used,
then the impedance across the windings is dominated by inductance, as
one normally expects with a transformer. But the analysis handles the
whole range of cases.

On Wed, 29 Mar 2006 10:45:05 -0500, John Popelish
wrote:

It may not be the approach you are familiar with, but I think it is
valid. The transformer just has a lot of core loss, if you use a
ferrite optimized for a much lower frequency. And that loss shows up
as if it were a resistor connected across the ends of the two
windings. If a low loss ferrite (at the operating frequency) is used,
then the impedance across the windings is dominated by inductance, as
one normally expects with a transformer. But the analysis handles the
whole range of cases.

Hi John,

Through these last comments, and those that go before, you have
entirely missed the boat of both the dynamics involved (this is not a
magnetic circuit being described, and there are NO magnetic lines
broken in a typical circuit in a balanced configuration), and the
topology. Specifically to this last, you still do not seem to
comprehend that a coax has three conductors and is a six terminal
device.

Roy has also commented to these issues and I think you should review
his correspondence and respond to him.

73's
Richard Clark, KB7QHC