To choke balun Gurus.

There is, in fact, a transformer in a choke balun which you have ALL
forgotten about, or never knew it exists.

It has nothing to do with 1-to-1 or any other turns ratio.

It is a transmission line transformer comprised of the short length of
line (coax or just a pair of wires) which passes through the balun. It
is the length of line which is wound on the balun to form the choke.
(All lengths of line behave as transformers.)

This line has an impedance Zo. If it is coax line then its impedance
is usually 50 ohms. If it is a pair of wires laid alongside each
other then its impedance depends on wire diameter, wire spacing and
permittivity of the insulation. If it is similar to twin speaker cable
then it has an impedance of about 130 ohms. The presence of ferrite
has hardly any effect.

When the balun is located between the main transmission line and the
tuner then on the antenna side of it there can be seen, say, 300, 450
or 600 ohms.

This is transformed to another impedance on the tuner side of the
balun.

The transformation depends on line Zo and its length in wavelengths
which depends on frequency. On the 160m band very little happens. The
frequency is too low and the line is too short. It is only a few turns
of wire around the ferrite core.

On the 10 meter band, at the higher frequencies, the winding length on
the balun can approach 1/4-wavelength and the 450 ohm main-line
impedance can be transformed to something considerably different.

But the tuner couldn't care what it is. Its purpose is to transform
whatever it is presented with to 50 ohms. The presence of the balun
merely causes a change in tuner L and C settings. Insofar as the tuner
and operator are concerned the transformer in the balun does not
exist.

When designing a choke balun the number of turns on the choke and the
length of wire involved are best restricted to something less than
1/4-wavelength at the highest frequency of use. 1/8-wavelength is
suitable.

Restricting turns has the effect of reducing choke inductance and the
choking effect at the lowest frequency of use.

But a 2-inch diameter ferrite ring with a modest permeability of 200
or more, wound with 18 awg stranded twin speaker cable, will allow
operation from 1.8 to 30 MHz.

With a balun constructed of a number of ferrite slugs over a coaxial
cable there is no transformer action at any frequency because the
short length of 50-ohm 'transforming' line is terminated at both ends
with a 50-ohm line.
----
Reg, G4FGQ.

Hi, Reg -

I do not understand...

Reg Edwards wrote:
To choke balun Gurus.

There is, in fact, a transformer in a choke balun which you have ALL
forgotten about, or never knew it exists.

It has nothing to do with 1-to-1 or any other turns ratio.

It is a transmission line transformer comprised of the short length of
line (coax or just a pair of wires) which passes through the balun. It
is the length of line which is wound on the balun to form the choke.
(All lengths of line behave as transformers.)

This line has an impedance Zo. If it is coax line then its impedance
is usually 50 ohms. If it is a pair of wires laid alongside each
other then its impedance depends on wire diameter, wire spacing and
permittivity of the insulation. If it is similar to twin speaker cable
then it has an impedance of about 130 ohms. The presence of ferrite
has hardly any effect.


So, then, I would have the same transformer (or balun or whatever) if I used
a wooden or plastic torus to wind the thing?


When the balun is located between the main transmission line and the
tuner then on the antenna side of it there can be seen, say, 300, 450
or 600 ohms.

This is transformed to another impedance on the tuner side of the
balun.

The transformation depends on line Zo and its length in wavelengths
which depends on frequency. On the 160m band very little happens. The
frequency is too low and the line is too short. It is only a few turns
of wire around the ferrite core.


Why do you use the term ferrite if ferrite is not required? Why not use
torus or toroid ring or donut or something similar?


On the 10 meter band, at the higher frequencies, the winding length on
the balun can approach 1/4-wavelength and the 450 ohm main-line
impedance can be transformed to something considerably different.

But the tuner couldn't care what it is. Its purpose is to transform
whatever it is presented with to 50 ohms. The presence of the balun
merely causes a change in tuner L and C settings. Insofar as the tuner
and operator are concerned the transformer in the balun does not
exist.

When designing a choke balun the number of turns on the choke and the
length of wire involved are best restricted to something less than
1/4-wavelength at the highest frequency of use. 1/8-wavelength is
suitable.

Restricting turns has the effect of reducing choke inductance and the
choking effect at the lowest frequency of use.

But a 2-inch diameter ferrite ring with a modest permeability of 200
or more, wound with 18 awg stranded twin speaker cable, will allow
operation from 1.8 to 30 MHz.


But, you said "The presence of ferrite has hardly any effect" above. I
thought the relative permeability without ferrite was 1. (I am assuming you
meant relative permeability since you had no units associated with the
number 200.)

With a balun constructed of a number of ferrite slugs over a coaxial
cable there is no transformer action at any frequency because the
short length of 50-ohm 'transforming' line is terminated at both ends
with a 50-ohm line.
----
Reg, G4FGQ.


Again, you said the ferrite has hardly any effect. Why not put plastic rings
over the coax?

This is so confusing...


Thanks,
John

A choke is supposed to reduce longitudinal currents on the line to
insignificant amounts.

But very often it doesn't. If you have a choke in the line how much
difference does it make if you remove it? If it makes no difference
you might just as well leave it out.

Insertion of a choke does not affect the manner in which the
longitudinal current is induced to flow in the line in the first
place.

The choke may indeed reduce the magnitude of the current at the
location of the choke. But the current always has standing waves and
the choke may merely shift the maximum current of the wave to another
place along the line. The longitudinal current still exists.

Indeed, if a minimum current should exist at the place where the choke
is inserted then the choke may serve no useful purpose and it can be
removed. It could be re-inserted at a place 1/4-wavelength away at a
current maximum where it MIGHT do some good.

All this requires knowledge of where the standing wave resides. But
one never has such knowledge unless one knows the cause. And if one
knows the cause it can be remedied.

The only way to prevent longitudinal currents on feedlines is to
remedy the cause, or to place chokes at every quarterwave interval all
along the line. Shifting the standing wave maximum, however, might be
sufficient to prevent the trouble it may be causing elsewhere in the
system.

The moral is - don't allow large longitudinal currents to be induced
on the feedlines in the first place. It's poor design.

A little bit of the inevitable longitudinal current on the feedline is
harmless.

If it works - don't fix it!
----
Reg, G4FGQ

So, then, I would have the same transformer (or balun or whatever)
if I used
a wooden or plastic torus to wind the thing?

========================================
John, yes you would. But you would not have the choke.
----
Reg.

John, I'm afraid you havn't the foggiest idea about how a choke balun
works. You are being confused by the Gurus' bafflegab.

A choke balun is a device which permits a balanced circuit to be
connected to an unbalanced circuit without interference to the power
flow. In this respect it is NOT a transformer. No ratios are involved.

There are two conductors or wires in a transmission line.

In a choke balun the two wires are TOGETHER wound round a ferrite core
AS ONE WIRE. It is this pair of wires together, as one wire, which
forms the choke using the ferrite core.

The choke has inductance and inductive reactance. The reactance chokes
the current which would flow equally in both wires, in the same
direction in both wires.

Entirely independently, the pair of wires can carry the normal
transmission line currents which flow in oposite directions to each
other. If normal currents in the two wires flow in opposite
directions to each other then there is no flux induced in the ferrite
and the ferrite may just as well not be there.

So the choking action has no effect on normal transmission line
operation along the two wires.

The choke only acts on that current which flows along the line when
both wires in parallel are considered to be ONE wire.

For longitudinal currents the two wires can be considered as being
connected together at both ends. Connected in parallel. It's really a
single wire choke.

It's all very simple really. There are two INDEPENDENT currents
flowing.
----
Reg, G4FGQ

On Fri, 31 Mar 2006 21:15:53 +0100, "Reg Edwards"
wrote:
You are being confused by the Gurus' bafflegab.

Elevating your status today Reggie?

Reg Edwards wrote:
So, then, I would have the same transformer (or balun or whatever)

if I used

a wooden or plastic torus to wind the thing?


========================================
John, yes you would. But you would not have the choke.
----
Reg.


Reg -

You removed the important part of your post. I will quote it. You said:

"The presence of ferrite has hardly any effect."

This is what I do not understand. If the ferrite has hardly any effect, then
explain to me why plastic could not be used as long as the plastic torus is
shaped the same.

Now you say it wouldn't be a choke. Why not? As long as the shape of the
turns of wire are the same without the ferrite, why would it not be a choke
without the ferrite which has "hardly any effect"?

I am not trying to pick an argument. I am trying to understand something
that goes against everything I have been taught.

Thanks,
John

Reg Edwards wrote:
John, I'm afraid you havn't the foggiest idea about how a choke balun
works. You are being confused by the Gurus' bafflegab.

I accept that statement, although I think my idea is somewhat better than a
fog. I do think I understand relative permeability, for example.

A choke balun is a device which permits a balanced circuit to be
connected to an unbalanced circuit without interference to the power
flow. In this respect it is NOT a transformer. No ratios are involved.

There are two conductors or wires in a transmission line.

In a choke balun the two wires are TOGETHER wound round a ferrite core
AS ONE WIRE. It is this pair of wires together, as one wire, which
forms the choke using the ferrite core.


But, you said, "The presence of ferrite has hardly any effect." Why are you
bringing up ferrite again? Why is ferrite used if it has hardly any effect?
Is there not a cheaper material?


The choke has inductance and inductive reactance. The reactance chokes
the current which would flow equally in both wires, in the same
direction in both wires.

Entirely independently, the pair of wires can carry the normal
transmission line currents which flow in oposite directions to each
other. If normal currents in the two wires flow in opposite
directions to each other then there is no flux induced in the ferrite
and the ferrite may just as well not be there.

So the choking action has no effect on normal transmission line
operation along the two wires.

The choke only acts on that current which flows along the line when
both wires in parallel are considered to be ONE wire.

For longitudinal currents the two wires can be considered as being
connected together at both ends. Connected in parallel. It's really a
single wire choke.

It's all very simple really. There are two INDEPENDENT currents
flowing.
----
Reg, G4FGQ


I must be more dense than I realize. I do not see an answer to my question
in your reply. If your answer is there, I would appreciate it if you would
point it out to me.

Thanks,
John

On Sat, 01 Apr 2006 15:45:48 GMT, John - KD5YI
wrote:

Reg Edwards wrote:
John, I'm afraid you havn't the foggiest idea about how a choke balun
works. You are being confused by the Gurus' bafflegab.
....
I must be more dense than I realize. I do not see an answer to my question
in your reply. If your answer is there, I would appreciate it if you would
point it out to me.

Hi John,

No, you are no more dense than the next, and Reggie's bafflegab is no
more distinct than all that which preceded it - once you discard his
pretension.

If you simply want an explanation from him, we can all see how much
desire will be filled from that. On the other hand, there may soon be
an unzipped executable released soon.

If you simply want to know why he uttered
John, yes you would. But you would not have the choke.

The ferrite is wholly transparent to the differential currents (the
balanced and thus equally opposing line currents). Its presence or
absences is immaterial. This is the abstraction of Reggie's bafflegab
for instead simply saying you don't need a choke (the lines' balance
proves that).

Now, if that condition of balance were to ever go away (like we leave
that comfortable illusion and return to reality), then the absence of
the ferrite has also rendered your "choke" chokeless (by the degree of
its contribution because in spite of Reggie's claim, the turns of your
coil remains a choke, if only an inadequate one).

73's
Richard Clark, KB7QHC

Richard Clark wrote:

(snip)

If you simply want to know why he uttered

John, yes you would. But you would not have the choke.


The ferrite is wholly transparent to the differential currents (the
balanced and thus equally opposing line currents). Its presence or
absences is immaterial. This is the abstraction of Reggie's bafflegab
for instead simply saying you don't need a choke (the lines' balance
proves that).

Now, if that condition of balance were to ever go away (like we leave
that comfortable illusion and return to reality), then the absence of
the ferrite has also rendered your "choke" chokeless (by the degree of
its contribution because in spite of Reggie's claim, the turns of your
coil remains a choke, if only an inadequate one).

73's
Richard Clark, KB7QHC


Hi, Richard -

Although your language is a bit formal for me (I lack a formal education), I
think I understand what your are saying. I am aware that the fields caused
by the differential currents cancel (mostly). It makes sense that a magnetic
core is not necessary when the fields cancel. And, I can see where the core
is useful when the fields do not cancel. I just did not interpret Reg's
information as applying to one situation and not the other.

Thank you and 73.

John