"Bal uhn" or "bayl uhn"?
 

In article , rickman
wrote:

On 7/31/2015 12:19 PM, John S wrote:
On 7/31/2015 1:15 AM, rickman wrote:
On 7/30/2015 10:52 PM, David Ryeburn wrote:
In article , rickman
wrote:

I can't say I agree with your "choking" impedance idea. The coax
connects to the balun in the same way it connects to the antenna.

No, it's really rather different.

You aren't explaining anything.

Now you are being argumentative, Rick. Do you want to continue the
dialog or not?

Worse than argumentative. I DID explain, but I can't read for him.

I give up. Between us, his word is last. Anyone else who wishes to show
me where my argument involving resistors, Kirchhoff's law, fields inside
coaxial cables, etc. is incorrect, I'll be glad to read. I'm always
ready to learn. In the meantime I'll connect my current baluns the way
I described, and they'll work the way I described. He can do what he
wants.

David, VE7EZM (now), AF7BZ (now), and W8EZE (1949-1967)

--
David Ryeburn

To send e-mail, change "netz" to "net"

"Bal uhn" or "bayl uhn"?
 

rickman wrote:
On 7/31/2015 12:19 PM, John S wrote:
On 7/31/2015 1:15 AM, rickman wrote:
On 7/30/2015 10:52 PM, David Ryeburn wrote:
In article , rickman
wrote:

I can't say I agree with your "choking" impedance idea. The coax
connects to the balun in the same way it connects to the antenna.

No, it's really rather different.

You aren't explaining anything.

Now you are being argumentative, Rick. Do you want to continue the
dialog or not?

That is BS. Saying something is "different" with no explanation is not
"discussion" and is not useful to a "dialog". I'm just pointing that out.

It was nothing more than a knee jerk response without regard to everything
that followed.


--
Jim Pennino

"Bal uhn" or "bayl uhn"?
 

rickman wrote:
On 7/30/2015 6:09 PM, wrote:
rickman wrote:
On 7/30/2015 5:46 PM, John S wrote:
On 7/30/2015 4:28 PM, rickman wrote:
On 7/30/2015 2:01 PM, Dave Platt wrote:
In article , rickman
wrote:

Yes, I read that, but it doesn't really explain this current. Later
they make the statement, "the current on the braid outside side is the
sum of currents other than transmission line currents on the entire
coaxial cable structure". This is pretty clear, but still does not
explain the source, or maybe I should say "why" the current flows on
the
braid and not the antenna.

Don't ask "Why does current flow on the braid?". Ask "What would *stop*
current from flowing on the braid?".

Current flows on *all* paths that have less than an infinite
impedance. That's its nature.

Remember, I = E / R (or, for AC/RF, I = E / Z). "I" (current on the
braid) will be nonzero, if the voltage at that point is nonzero (E !=
0) and the impedance down the braid at that point is not infinite.

The effect of a balun is to place a high "choking" impedance in series
with the outside of the feedline braid, thus "choking off" the current
flow.

I can't say I agree with your "choking" impedance idea. The coax
connects to the balun in the same way it connects to the antenna. The
balun can have no effect on the impedance of the coax shield. Just as
you ask, "What would *stop* current from flowing on the braid?" when
connected to the antenna what will stop the current from flowing on the
braid when connected to the balun?

The balun is an impedance that the RF sees as it starts to travel down
the outside of the coax toward the transmitter. But you know about
common mode currents, I think.

There is something fundamentally wrong with our communications. Are you
saying the balun is *part* of the coax? I have seen baluns made by
wrapping the coax around a core. I have been assuming the balun was a
transformer between the feed line and the antenna.

There are two types of baluns; voltage baluns and current baluns.

A voltage balun is usually a transformer and it forces the output
voltage to be equal.

A current balun is something that increases the impedance of the
outside the shield path. The common forms of choke balun are
simply wrapping the coax into a coil, wrapping the coax into a
coil around a ferrite rod, wrapping the coax into a coil on a
ferrite toroid, or large ferrite beads strung on the coax.

See www.eznec.com/Amateur/Articles/Baluns.pdf

Refer to figure 8. The balun is inserted between the feed line and the
antenna. Clearly this example adds no impedance to the shield of the
feed line. Rather it must present a very low impedance to the flow of
current from the shield to the antenna element.

You can also look at the illustrations in Appendix 1, both the voltage
balun and the current balun. In both cases they show transformers which
must present a low impedance path for the Io current as they call it.

The text here does talk about a construction of the current balun from
coax and the high impedance to current flowing on the outside of the
shield *in the balun*. But when considering the feed line, the balun
provides a low impedance to the current flowing from the inside of the
feed line shield (Ii) which means it will not follow any other path.

If you want to argue about it, argue with the author of the article.

There is little that you said that has anything to do with what I said.


--
Jim Pennino

"Bal uhn" or "bayl uhn"?
 

On 7/31/2015 1:55 PM, David Ryeburn wrote:
In article , rickman
wrote:

On 7/31/2015 12:19 PM, John S wrote:
On 7/31/2015 1:15 AM, rickman wrote:
On 7/30/2015 10:52 PM, David Ryeburn wrote:
In article , rickman
wrote:

I can't say I agree with your "choking" impedance idea. The coax
connects to the balun in the same way it connects to the antenna.

No, it's really rather different.

You aren't explaining anything.

Now you are being argumentative, Rick. Do you want to continue the
dialog or not?

Worse than argumentative. I DID explain, but I can't read for him.

I give up. Between us, his word is last. Anyone else who wishes to show
me where my argument involving resistors, Kirchhoff's law, fields inside
coaxial cables, etc. is incorrect, I'll be glad to read. I'm always
ready to learn. In the meantime I'll connect my current baluns the way
I described, and they'll work the way I described. He can do what he
wants.

I replied to your post in detail. The comment above was about the
single line response which was not useful. If you want to take an
attitude fine. But please don't act like I was not communicating. I
explained to you my points and now you choose to complain.

I never said baluns don't work. So your comment about your equipment is
not relevant to the discussion.

--

Rick

"Bal uhn" or "bayl uhn"?
 

On 7/31/2015 12:13 PM, rickman wrote:
On 7/31/2015 12:19 PM, John S wrote:
On 7/31/2015 1:15 AM, rickman wrote:
On 7/30/2015 10:52 PM, David Ryeburn wrote:
In article , rickman
wrote:

I can't say I agree with your "choking" impedance idea. The coax
connects to the balun in the same way it connects to the antenna.

No, it's really rather different.

You aren't explaining anything.

Now you are being argumentative, Rick. Do you want to continue the
dialog or not?

That is BS. Saying something is "different" with no explanation is not
"discussion" and is not useful to a "dialog". I'm just pointing that out.



If you had continued to read the entire post, it may have made more
sense to you. His explanation followed your contentious comment.


In fact, much of what is being said here is talking past the points I
have made. Rather than try to understand what is going on, most here
seem to just repeat the standard explanation without thinking it
through. One of the references discusses the case of a balun made by
wrapping the coax around a core, but when discussing a separate balun
made of wires they say, "When constructed of twisted-pair line, the
effect on imbalance current is the same and for the same reasons, but
operation is more difficuit to visualize". That is a cop-out. A pair
of wires is very clearly different from a coax.


Then we are all in error concerning the points of your query. You posted
"Perhaps someone can explain the issue of current in the coax shield.
Current gives rise to a magnetic field. But the current in the inner
conductor is opposite and would create a magnetic field that would
cancel the field of the outer conductor, no?
What am I missing?"

Was this resolved? What is it that you want? Please summarize your
point(s) again for those of us who have forgotten them or wish not to
wade back through the posts and ferret them out. Better yet, start a new
thread.


Anytime you don't wish to reply to my posts you are free to refrain.


Of course. You don't need to remind me of my options.

"Bal uhn" or "bayl uhn"?
 

Jeff wrote:

I give up. Between us, his word is last. Anyone else who wishes to show
me where my argument involving resistors, Kirchhoff's law, fields inside
coaxial cables, etc. is incorrect, I'll be glad to read. I'm always
ready to learn. In the meantime I'll connect my current baluns the way
I described, and they'll work the way I described. He can do what he
wants.

Conservation of energy also shows that with a perfectly matched dipole
all of the energy applied to it will be radiated, or lost as heat in the
elements. So by extension there can be no power flowing on the coax outer.

Jeff
So, clearly, the energy supplied from the feeder and conducted down the
coax outer nerver reaches the antenna. Just as two resistors in
parallel share the energy supplied by a voltage applies across them.


--
Roger Hayter

"Bal uhn" or "bayl uhn"?
 

Jeff wrote:

On 01/08/2015 10:54, Roger Hayter wrote:
Jeff wrote:

I give up. Between us, his word is last. Anyone else who wishes to show
me where my argument involving resistors, Kirchhoff's law, fields inside
coaxial cables, etc. is incorrect, I'll be glad to read. I'm always
ready to learn. In the meantime I'll connect my current baluns the way
I described, and they'll work the way I described. He can do what he
wants.

Conservation of energy also shows that with a perfectly matched dipole
all of the energy applied to it will be radiated, or lost as heat in the
elements. So by extension there can be no power flowing on the coax outer.

Jeff
So, clearly, the energy supplied from the feeder and conducted down the
coax outer nerver reaches the antenna. Just as two resistors in
parallel share the energy supplied by a voltage applies across them.



No, there will be no energy "supplied from the feeder and conducted down
the coax outer" as it will all be conducted into the antenna and
radiated if the antenna is perfectly balanced. The power flowing up the
coax, when perfectly matched, will only 'see' the antenna load, not the
coax outer as and element in parallel.

Jeff

If it was perfectly balanced before you connected the feeder, it will no
longer be perfectly balanced once the shunt impedance to earth of the
coax braid is connected to *one* side of it. Dare I say that that is
why you need a balun? This asymmetrical shunt impedance is the source
of the whole question.

--
Roger Hayter

"Bal uhn" or "bayl uhn"?
 

On 8/1/2015 9:09 AM, Roger Hayter wrote:
Jeff wrote:

On 01/08/2015 10:54, Roger Hayter wrote:
Jeff wrote:

Conservation of energy also shows that with a perfectly matched dipole
all of the energy applied to it will be radiated, or lost as heat in the
elements. So by extension there can be no power flowing on the coax outer.

Jeff
So, clearly, the energy supplied from the feeder and conducted down the
coax outer nerver reaches the antenna. Just as two resistors in
parallel share the energy supplied by a voltage applies across them.



No, there will be no energy "supplied from the feeder and conducted down
the coax outer" as it will all be conducted into the antenna and
radiated if the antenna is perfectly balanced. The power flowing up the
coax, when perfectly matched, will only 'see' the antenna load, not the
coax outer as and element in parallel.

Jeff

If it was perfectly balanced before you connected the feeder, it will no
longer be perfectly balanced once the shunt impedance to earth of the
coax braid is connected to *one* side of it. Dare I say that that is
why you need a balun? This asymmetrical shunt impedance is the source
of the whole question.

Not trying to criticize anyone here. I just want to make the
observation that much of the theory that is applied to the systems
discussed here are generalization which only apply under certain
conditions. Often these conditions are "ideal" and even in the best of
circumstances won't match reality perfectly... but are good enough.
Then a discussion starts where something outside the assumptions is
explored and the "ideal" assumptions are forgotten. The discussion goes
in many directions because the general rules are applied when instead,
the topic needs to be considered at a more fundamental level.

So look at the assumptions (or conditions) that exist in this case and
see which ones apply and which don't. I'm pretty sure that the
condition of an impedance match at the feed point does not exist among
others.

That was my point when I suggested that at the junction of the coaxial
feed line and the balun the same condition exists of there being a path
for current on the outside of the shield. This can divert current flow
from the inside of the shield unless... the current path through the
balun from the shield is a very low impedance.

In order to just eliminate any idea of the balun "preventing" an
unbalanced current flow back from the antenna, replace the antenna with
a matched resistor. Then there will be no reflection of any kind at the
load and the only point that needs to be considered is the junction of
the feed line and the balun.

--

Rick

"Bal uhn" or "bayl uhn"?
 

rickman wrote:

On 8/1/2015 9:09 AM, Roger Hayter wrote:
Jeff wrote:

On 01/08/2015 10:54, Roger Hayter wrote:
Jeff wrote:

Conservation of energy also shows that with a perfectly matched
dipole all of the energy applied to it will be radiated, or lost as
heat in the elements. So by extension there can be no power flowing
on the coax outer.

Jeff
So, clearly, the energy supplied from the feeder and conducted down the
coax outer nerver reaches the antenna. Just as two resistors in
parallel share the energy supplied by a voltage applies across them.



No, there will be no energy "supplied from the feeder and conducted down
the coax outer" as it will all be conducted into the antenna and
radiated if the antenna is perfectly balanced. The power flowing up the
coax, when perfectly matched, will only 'see' the antenna load, not the
coax outer as and element in parallel.

Jeff

If it was perfectly balanced before you connected the feeder, it will no
longer be perfectly balanced once the shunt impedance to earth of the
coax braid is connected to *one* side of it. Dare I say that that is
why you need a balun? This asymmetrical shunt impedance is the source
of the whole question.

Not trying to criticize anyone here. I just want to make the
observation that much of the theory that is applied to the systems
discussed here are generalization which only apply under certain
conditions. Often these conditions are "ideal" and even in the best of
circumstances won't match reality perfectly... but are good enough.
Then a discussion starts where something outside the assumptions is
explored and the "ideal" assumptions are forgotten. The discussion goes
in many directions because the general rules are applied when instead,
the topic needs to be considered at a more fundamental level.

So look at the assumptions (or conditions) that exist in this case and
see which ones apply and which don't. I'm pretty sure that the
condition of an impedance match at the feed point does not exist among
others.

That was my point when I suggested that at the junction of the coaxial
feed line and the balun the same condition exists of there being a path
for current on the outside of the shield. This can divert current flow
from the inside of the shield unless... the current path through the
balun from the shield is a very low impedance.

In order to just eliminate any idea of the balun "preventing" an
unbalanced current flow back from the antenna, replace the antenna with
a matched resistor. Then there will be no reflection of any kind at the
load and the only point that needs to be considered is the junction of
the feed line and the balun.

Well I agree with your first point. Not least, the conduction path
along the coax outer is more like a radiating element than a lumped
component, because of its length.

But your second point is unhelpful in some circumstances. For instance,
if the type of balun is the inductive coil of the feeder with or without
ferrites, then there simply *is no* current path down the outside of the
feeder from the junction of the balun and the feeder, Except from the
outer of the cable in the balun coil, and it is this that is decoupled
by the inductance.

Secondly, even if you connect a resistor across the end ot the feeder,
consider that the inner conductor just goes to the resistor, but the
outer conductor sees the resistor and the outer side of the braid in
parallel. So you will get RF (and therefore some radiation) on the
outer of the coax even if you just connect a resistor across the end.
This would actually be quite a simple lab experiment, at UHF or higher.
Compare the amount of RF on the outer with a bare surface mount 50ohm or
with one of the screened 50 ohm terminations (which does not allow any
signal to get to the outer). Or compare the SWR which will be near 1.0
with the screened load and might be very different with the unscreened,
sim,ply because the coax outer is shunting one side of the load.


--
Roger Hayter

"Bal uhn" or "bayl uhn"?
 

On 8/1/2015 1:38 PM, Roger Hayter wrote:

But your second point is unhelpful in some circumstances. For instance,
if the type of balun is the inductive coil of the feeder with or without
ferrites, then there simply *is no* current path down the outside of the
feeder from the junction of the balun and the feeder, Except from the
outer of the cable in the balun coil, and it is this that is decoupled
by the inductance.

Your description is not clear to me.


Secondly, even if you connect a resistor across the end ot the feeder,
consider that the inner conductor just goes to the resistor, but the
outer conductor sees the resistor and the outer side of the braid in
parallel. So you will get RF (and therefore some radiation) on the
outer of the coax even if you just connect a resistor across the end.

Ok, let's discuss this. You are describing a circuit that is just the
coax and a terminating resistor. You seem to be saying that current
will flow on the outer surface of the shield. If that were true, where
does it come from? In this simple circuit the current on the shield
inner surface matches the current on the inner conductor. So there is
no source for current to flow on the shield outer surface.


This would actually be quite a simple lab experiment, at UHF or higher.
Compare the amount of RF on the outer with a bare surface mount 50ohm or
with one of the screened 50 ohm terminations (which does not allow any
signal to get to the outer). Or compare the SWR which will be near 1.0
with the screened load and might be very different with the unscreened,
sim,ply because the coax outer is shunting one side of the load.

Ok, can anyone do this?

--

Rick