Yet another BALUN questions
 

A current balun (as described by W2DU in his book ''Reflexions''), put at
the center of a dipole, prevents HF current from flowing in the outer shield
of the coax. This is due to the high impedance caused by the ferrite rings.
Now, if instead, I put a voltage balun, what should prevent the current from
flowing in the outer shield of the coax? Am I missing something?

Thanks for helping.

Chris

W2DU's device is not a balun. It has no ratio - it is just a choke.
It behaves in the same way as a single bifilar winding on a ferrite
rod, or on a ring.

But a choke does not necessarily prevent longitudinal standing-wave
currents on the line. It merely shifts standing waves to other
positions along the line.

If a choke is located at a current minimum it may serve no useful
purpose at that operating frequency.

A true balun transformer, whatever its ratio, by itself provides no
obstruction to longitudinal currents. There can be a direct connection
between the line and antenna.
----
Reg, G4FGQ.

On Thu, 28 Apr 2005 14:19:18 +0000 (UTC), after apparently consuming a
750 ml bottle of California red, "Reg Edwards"
wrote:

W2DU's device is not a balun. It has no ratio - it is just a choke.
It behaves in the same way as a single bifilar winding on a ferrite
rod, or on a ring.

Wherever did you get the idea that a balun "must have a ratio?"

"Balun" is a contraction of 'Bal'anced to 'Un'balanced. Walt's device
certainly fulfills this function.

[remaining bafflegab snipped]

Balanced to Unbalanced WHAT ?

"Balun" is a contraction of "Balanced to Unbalanced "TRANSFORMER".

What is the transformation ratio of the W2DU "balun" and other devices
which serve a similar purpose? Between which pair of impedances does
it match?

If YOU cannot provide answers then there are many old-wives who can.

There is a program named BALCHOKE available free from my website.

I have no wish to participate in futile arguments about the meaning of
words. They can drive one to drink
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

===================================

"Wes Stewart" wrote:

W2DU's device is not a balun. It has no ratio - it is just a
choke.
It behaves in the same way as a single bifilar winding on a ferrite
rod, or on a ring.

Wherever did you get the idea that a balun "must have a ratio?"

"Balun" is a contraction of 'Bal'anced to 'Un'balanced. Walt's
device
certainly fulfills this function.

[remaining bafflegab snipped]

You are correct on this point, it is actually an "UnUn."
(UNbalanced-to-UNbalanced--don't confuse this with a child's pronouncing of
"onion.") grin

Regards,
John

Reg Edwards wrote:
What is the transformation ratio of the W2DU "balun" and other devices
which serve a similar purpose? Between which pair of impedances does
it match?

Resorting to passive voice - The W2DU choke is considered to
be a 1:1 balun. Each bead is considered to be one turn. If
one mounts the beads on a piece of 50 ohm coax, it becomes
a 50 ohm balanced to 50 ohm unbalanced balun. With 50 ohms
on both sides of the balun, the Z0 of the transmission line
used should be SQRT(50*50)=50 ohms.
--
73, Cecil, http://www.qsl.net/w5dxp


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The difference between a 1:1 current balun and a 1:1 voltage balun is
that the latter has a third (tertiary) winding. I'll assume for a moment
that the baluns are perfect, i.e., have an infinite common mode
impedance. If the load is balanced, that is, if the two load terminals
have equal impedances to the "cold" side of the balun input, the third
winding of the voltage balun carries no current, and there will be no
current on the outside of the coax. Because the third winding has no
current, it can be removed with no effect, so the voltage balun acts
exactly like a current balun when the load is balanced. However, if the
load isn't perfectly balanced relative to the input terminal of the
balun, a current balun will still prevent current from flowing on the
outside of the coax. The voltage balun, however, will force the voltages
at the two output terminals to be equal and opposite relative to the
cold side of the balun input. This will cause unequal currents from the
two terminals. The difference flows along the outside of the coax.

In summary, the best a voltage balun can do in preventing current flow
on the outside of coax is to be as good as a current balun, and this
happens only if the load is balanced. In all other cases, using a
voltage balun will cause current to flow on the outside of the coax
while a current balun will prevent this flow.

For more information, see the article posted at
http://www.eznec.com/Amateur/Articles/Baluns.pdf.

Roy Lewallen, W7EL

C.Aymon wrote:
A current balun (as described by W2DU in his book ''Reflexions''), put at
the center of a dipole, prevents HF current from flowing in the outer shield
of the coax. This is due to the high impedance caused by the ferrite rings.
Now, if instead, I put a voltage balun, what should prevent the current from
flowing in the outer shield of the coax? Am I missing something?

Thanks for helping.

Chris

Wes Stewart wrote:

On Thu, 28 Apr 2005 14:19:18 +0000 (UTC), after apparently consuming a
750 ml bottle of California red, "Reg Edwards"
wrote:



W2DU's device is not a balun. It has no ratio - it is just a choke.
It behaves in the same way as a single bifilar winding on a ferrite
rod, or on a ring.



Wherever did you get the idea that a balun "must have a ratio?"

"Balun" is a contraction of 'Bal'anced to 'Un'balanced. Walt's device
certainly fulfills this function.

[remaining bafflegab snipped]


Does that make it a 1:1 balun? I'm asking serioulsly, I'm not smart
enough to figure these things out. If I can't picture it in my head, I
can't figure it out!

Butch Magee KF5DE

On Thu, 28 Apr 2005 18:03:40 +0000 (UTC), "Reg Edwards"
wrote:

What is the transformation ratio of the W2DU "balun"

1:1

Think, "One-to-one isolation transformer."

Regards,
John

Reg Edwards wrote:

Balanced to Unbalanced WHAT ?

Isn't that rather like asking Modulated to Demodulated WHAT?

ac6xg

but with isolation transformers - the primary and secondary windings are
**not** physically connected (hence 'isolation' transformer). Maybe call it
a 1-to-1 autotransformer. (with a choke). :-)

"John Smith" wrote in message
...
Think, "One-to-one isolation transformer."

Regards,
John

"Reg Edwards" wrote -

Balanced to Unbalanced WHAT ?

"Balun" is a contraction of "Balanced to Unbalanced "TRANSFORMER".

What is the transformation ratio of the W2DU "balun" and other
devices
which serve a similar purpose? Between which pair of impedances
does
it provide a match?

If YOU cannot provide answers then there are many old-wives who can.

There is a program named BALCHOKE available free from my website.

=====================================

To all and sundry,

My prediction about old-wives was correct.

Anybody who provided a transformation ratio or mentioned matched
impedances can consider him or herself to be an Old Wife.

It would be a waste of time for me to explain to Old Wives how the
uncertain impedance and length of line on the choke, combined with the
unknown impedances of its supposed terminations, actually works.

The impedance transformation ratio is entirely INDETERMINATE.

But it doesn't matter two hoots provided the length of line on the
choke is within certain limits. Only the choking action on
longitudinal currents matters.

smile please
----
Reg, G4FGQ

You are thinking power xfrmr, where an isolation xfrmr is isolating from
ground loops, or possibly even dc.
A 1:1 unun is isolating from rf, the "choke" is implied!

Regards,
John

Reg Edwards wrote:
Balanced to Unbalanced WHAT ?

Balanced to unbalanced....Sir? 8^)


- Mike KB3EIA -

Reg Edwards wrote:
"Reg Edwards" wrote -


Balanced to Unbalanced WHAT ?

"Balun" is a contraction of "Balanced to Unbalanced "TRANSFORMER".

What is the transformation ratio of the W2DU "balun" and other

devices

which serve a similar purpose? Between which pair of impedances

does

it provide a match?

If YOU cannot provide answers then there are many old-wives who can.

There is a program named BALCHOKE available free from my website.


=====================================

To all and sundry,

My prediction about old-wives was correct.

Anybody who provided a transformation ratio or mentioned matched
impedances can consider him or herself to be an Old Wife.

It would be a waste of time for me to explain to Old Wives how the
uncertain impedance and length of line on the choke, combined with the
unknown impedances of its supposed terminations, actually works.

The impedance transformation ratio is entirely INDETERMINATE.

But it doesn't matter two hoots provided the length of line on the
choke is within certain limits. Only the choking action on
longitudinal currents matters.

smile please
----
Reg, G4FGQ



What's a "longitudinal current?" Is there a "latitudinal current" for
it to be opposed to?
73,
Tom Donaly, KA6RUH

On Thu, 28 Apr 2005 23:16:33 +0000 (UTC), "Reg Edwards"
wrote:

Anybody who provided a transformation ratio or mentioned matched
impedances can consider him or herself to be an Old Wife.

There is NO REQUIREMENT WHATSOEVER that a balun provide a
transformation ratio.

To say otherwise is an old wive's ass.

Danny

"John Smith" wrote
Think, "One-to-one isolation transformer."

============================

If it was a fixed 1-to-1 transformer and one end was terminated with
Zx, then the input impedance at the other end would also be fixed at
Zx.

But it isn't!

By no stretch of the imagination is it a fixed voltage or current
transformer of any sort.

By the way, a "Longitudinal current" is that which flows along the
feedline when both wires are considered to be one wire. ie., when
the wires are effectively connected in parallel with each other. It
is that current which is measured by a clamp-on ammeter when clamped
around both wires. The two wires can be coaxial or balanced-twin or
open-wires. I've temporarily forgotten what US citizens call it.
----
Reg, G4FGQ.

LOL!!! I will concede to your argument Reg!!!
But, "It sure seems to work like one!!!!" tongue-in-cheek,
and-only-now-and-then-sticking-between-the-lips

grin
Warmest regards,
John

Roy, many thanks for having so exhaustively answered to my question. I have
downloaded, printed and read your article: it was very enlightening.

Chris

Reg Edwards wrote:
If it was a fixed 1-to-1 transformer and one end was terminated with
Zx, then the input impedance at the other end would also be fixed at
Zx. But it isn't!

It is for cases where Zx = Z0. The impedance seen looking
into my no-tuner feedline system is between 32+j0 ohms and
80+j0 ohms on all HF bands. On a couple of HF bands the
measured SWR is 1:1 and of course, under those conditions,
the impedance at both ends of the 1:1 balun/choke is fixed
at Zx = Z0 = 50 ohms.
--
73, Cecil http://www.qsl.net/w5dxp

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On Thu, 28 Apr 2005 18:03:40 +0000 (UTC), our tipsy English cousin,
"Reg Edwards" wrote:

Balanced to Unbalanced WHAT ?

"Balun" is a contraction of "Balanced to Unbalanced "TRANSFORMER".

No, I stand by my definition: BALUN is a contraction of BALanced to
UNbalanced.

If you want to call it an impedance transformer, then call it a "BALUN
impedance transformer." The functions are independent. In fact, many
"broadband transformers" separate the functions into "balun" and
"transformer."

For example in Fig 2 of this reference:

http://www.minicircuits.com/appnote/howxfmerwork.pdf


What is the transformation ratio of the W2DU "balun" and other devices
which serve a similar purpose?

Let the complex line constant of the line comprising the balun be x =
alpha +j Beta .

Then with Zl being the load, the input Zin will be found from:

Zin = Zo * ((Zl + Zo *tanh(x))/(Zo + Zl *tanh(x))

Which of course for a lossless line of Zo and a load of Zl = Zo
reduces to Zin = Zl = 1:1

But you know all of this.

Between which pair of impedances does it match?

It isn't designed to "match" anything. It's designed to suppress
common-mode current. Other than that, it's a length of transmission
line that behaves just like any other transmission line of the same
length, loss and impedance. But you know this too.


If YOU cannot provide answers then there are many old-wives who can.

There is a program named BALCHOKE available free from my website.

I have no wish to participate in futile arguments about the meaning of
words. They can drive one to drink

I believe you have arrived.

Then if I hook up a power transformer off 125V, and the secondary is in a
circuit where there is NO return path to ground (and it is suppling a
push-pull circuit), I must stipulate that it is a "60Hz BALUN????"

Give me a break!!!

Regards,
John

"John Smith" wrote in message
...
You are thinking power xfrmr, where an isolation xfrmr is isolating from
ground loops, or possibly even dc.
A 1:1 unun is isolating from rf, the "choke" is implied!


we-yell ah reckon the only time I ever heard of - or seen one of dem-there
isolation transformers was in the context of power xfmrs. They were usually
shielded as well. The applications were usually 'computer-rooms'.

Wonder if we could use a 240 primary to 120v secondary as a 4-to-1 balun ?

It would be (and was often used to go from unbalanced to balanced,
or vice versa) , if the transformer was say , wound one to one , with
the primary, or secondary center tapped, the center tap connected to
one leg (perferably the "ground" side) of the other side of the
transformer. Could accomplish the same with a 110 volt to 220 volt,
center tapped xfmr, again tyeing the center tap to one side of the
primary (but for connection to your ac outlet, NOT the safest
construction proceedure! This was the tecknique used from 75 ohms
unbalanced to 600 ohm ballanced (tho obviously, the winding ratio
was different)! Jim NN7K



John Smith wrote:
Then if I hook up a power transformer off 125V, and the secondary is in a
circuit where there is NO return path to ground (and it is suppling a
push-pull circuit), I must stipulate that it is a "60Hz BALUN????"

Give me a break!!!

Regards,
John

Hey, you could, but "220v-110v HF power transformers" are rare... unless you
buy "Baluns", or, "RF Auto-Transformers" (I made up that name grin) then
they are plentiful!!!!

Regards,
John