"John S" wrote in message ...

On 7/28/2015 12:58 PM, Wayne wrote:

"John S" wrote in message ...

Hey, Wayne -

Do you have or want EZNEC? There is a free (limited) version.

Just curious.

Thanks. I have version 3.0, and it does the job for me.

I got my first copy back in the days when W7EL frequented this group and
knew by call sign who had legal copies

The hidden reason I asked the question is that I think you should model
some antennas and look at the current on the shield of the transmission
line. I have done this, and I don't see major problems if the system
remains balanced just as lore suggests.

This brings up a question of my own. By changing the slope of the coax
shield, I can get increased current in it. The question is, at what point
does it become a problem? As far as the antenna pattern is concerned, I
would not worry. RF in the shack is another matter. In about 1958, my lips
got some RF when they touched the D104 mike. Didn't hurt me, but I didn't
like it. At the time I had no understanding of this phenomenon.

Anyway, it would be nice if we could decide, measure, or simulate how much
feed line current should be allowed. Maybe the answer is to simulate how
much voltage appears in the shack.

Lots of questions. A large area for investigation.

The reason for my balun question (other than to generate meaningful
technical banter on the newsgroup) is that some years ago in the age of
sliderules, a widely known and respected antenna guru told me that a balun
was unnecessary at resonance ( j=0 ).

I lost touch with him and don't know if his views changed over the years.

On 7/29/2015 11:56 AM, Wayne wrote:


"John S" wrote in message ...

On 7/28/2015 12:58 PM, Wayne wrote:

"John S" wrote in message ...

Hey, Wayne -

Do you have or want EZNEC? There is a free (limited) version.

Just curious.

Thanks. I have version 3.0, and it does the job for me.

I got my first copy back in the days when W7EL frequented this group and
knew by call sign who had legal copies

The hidden reason I asked the question is that I think you should
model some antennas and look at the current on the shield of the
transmission line. I have done this, and I don't see major problems if
the system remains balanced just as lore suggests.

This brings up a question of my own. By changing the slope of the coax
shield, I can get increased current in it. The question is, at what
point does it become a problem? As far as the antenna pattern is
concerned, I would not worry. RF in the shack is another matter. In
about 1958, my lips got some RF when they touched the D104 mike.
Didn't hurt me, but I didn't like it. At the time I had no
understanding of this phenomenon.

Anyway, it would be nice if we could decide, measure, or simulate how
much feed line current should be allowed. Maybe the answer is to
simulate how much voltage appears in the shack.

Lots of questions. A large area for investigation.

The reason for my balun question (other than to generate meaningful
technical banter on the newsgroup) is that some years ago in the age of
sliderules, a widely known and respected antenna guru told me that a
balun was unnecessary at resonance ( j=0 ).

I lost touch with him and don't know if his views changed over the years.

I disagree with him.

Please see Roy Lewallen's (W7EL, author of EZNEC) site for some good
reading. He is a superb writer of easy to understand technical tidbits.
He has some balun stuff among other stuff.

http://eznec.com/misc/

On 7/29/2015 1:42 PM, John S wrote:
On 7/29/2015 11:56 AM, Wayne wrote:

Lots of questions. A large area for investigation.

The reason for my balun question (other than to generate meaningful
technical banter on the newsgroup) is that some years ago in the age of
sliderules, a widely known and respected antenna guru told me that a
balun was unnecessary at resonance ( j=0 ).

I lost touch with him and don't know if his views changed over the years.

I disagree with him.

Please see Roy Lewallen's (W7EL, author of EZNEC) site for some good
reading. He is a superb writer of easy to understand technical tidbits.
He has some balun stuff among other stuff.

http://eznec.com/misc/

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?

--

Rick

On 7/29/2015 1:16 PM, rickman wrote:
On 7/29/2015 1:42 PM, John S wrote:
On 7/29/2015 11:56 AM, Wayne wrote:

Lots of questions. A large area for investigation.

The reason for my balun question (other than to generate meaningful
technical banter on the newsgroup) is that some years ago in the age of
sliderules, a widely known and respected antenna guru told me that a
balun was unnecessary at resonance ( j=0 ).

I lost touch with him and don't know if his views changed over the
years.

I disagree with him.

Please see Roy Lewallen's (W7EL, author of EZNEC) site for some good
reading. He is a superb writer of easy to understand technical tidbits.
He has some balun stuff among other stuff.

http://eznec.com/misc/

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?


Skin effect. The currents on the inside of the shield and on the outside
of the shield see different things. They each have no idea what the
other is doing.

As for magnetic field, I must step aside. I can only report what the
gurus say (nothing that I've found).

On 7/29/2015 2:32 PM, John S wrote:
On 7/29/2015 1:16 PM, rickman wrote:
On 7/29/2015 1:42 PM, John S wrote:
On 7/29/2015 11:56 AM, Wayne wrote:

Lots of questions. A large area for investigation.

The reason for my balun question (other than to generate meaningful
technical banter on the newsgroup) is that some years ago in the age of
sliderules, a widely known and respected antenna guru told me that a
balun was unnecessary at resonance ( j=0 ).

I lost touch with him and don't know if his views changed over the
years.

I disagree with him.

Please see Roy Lewallen's (W7EL, author of EZNEC) site for some good
reading. He is a superb writer of easy to understand technical tidbits.
He has some balun stuff among other stuff.

http://eznec.com/misc/

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?


Skin effect. The currents on the inside of the shield and on the outside
of the shield see different things. They each have no idea what the
other is doing.

As for magnetic field, I must step aside. I can only report what the
gurus say (nothing that I've found).

I don't follow what skin effect has to do with the issue. The current
flowing on the outside of the shield is the only current flowing in the
shield. What's your point?

--

Rick

"rickman" wrote in message ...

On 7/29/2015 2:32 PM, John S wrote:
On 7/29/2015 1:16 PM, rickman wrote:
On 7/29/2015 1:42 PM, John S wrote:
On 7/29/2015 11:56 AM, Wayne wrote:

Lots of questions. A large area for investigation.

The reason for my balun question (other than to generate meaningful
technical banter on the newsgroup) is that some years ago in the age of
sliderules, a widely known and respected antenna guru told me that a
balun was unnecessary at resonance ( j=0 ).

I lost touch with him and don't know if his views changed over the
years.

I disagree with him.

Please see Roy Lewallen's (W7EL, author of EZNEC) site for some good
reading. He is a superb writer of easy to understand technical tidbits.
He has some balun stuff among other stuff.

http://eznec.com/misc/

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?


Skin effect. The currents on the inside of the shield and on the outside
of the shield see different things. They each have no idea what the
other is doing.

As for magnetic field, I must step aside. I can only report what the
gurus say (nothing that I've found).

I don't follow what skin effect has to do with the issue. The current
flowing on the outside of the shield is the only current flowing in the
shield. What's your point?

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

At RF, the current flows almost entirely at the surface of the conductors
Since the shield has a discrete thickness, it can carry two unrelated
currents, one around the outer surface of the shield and a simultaneous one
within the inner surface of the shield. The current along the inner
circumference of the shield is approximately the equal of the current in the
center conductor, while the current on the outside of the shield represents
a portion of the current at the feed point that is not delivered to the load
because the outer part of the shield represents a parallel path for the
flow.

"Sal"

On 8/11/2015 1:27 AM, Sal M. O'Nella wrote:


"rickman" wrote in message ...

On 7/29/2015 2:32 PM, John S wrote:
On 7/29/2015 1:16 PM, rickman wrote:
On 7/29/2015 1:42 PM, John S wrote:
On 7/29/2015 11:56 AM, Wayne wrote:

Lots of questions. A large area for investigation.

The reason for my balun question (other than to generate meaningful
technical banter on the newsgroup) is that some years ago in the
age of
sliderules, a widely known and respected antenna guru told me that a
balun was unnecessary at resonance ( j=0 ).

I lost touch with him and don't know if his views changed over the
years.

I disagree with him.

Please see Roy Lewallen's (W7EL, author of EZNEC) site for some good
reading. He is a superb writer of easy to understand technical tidbits.
He has some balun stuff among other stuff.

http://eznec.com/misc/

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?


Skin effect. The currents on the inside of the shield and on the outside
of the shield see different things. They each have no idea what the
other is doing.

As for magnetic field, I must step aside. I can only report what the
gurus say (nothing that I've found).

I don't follow what skin effect has to do with the issue. The current
flowing on the outside of the shield is the only current flowing in the
shield. What's your point?

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

At RF, the current flows almost entirely at the surface of the
conductors Since the shield has a discrete thickness, it can carry two
unrelated currents, one around the outer surface of the shield and a
simultaneous one within the inner surface of the shield. The current
along the inner circumference of the shield is approximately the equal
of the current in the center conductor, while the current on the outside
of the shield represents a portion of the current at the feed point that
is not delivered to the load because the outer part of the shield
represents a parallel path for the flow.

"Sal"

You posted two seemingly contradictory paragraphs separated by a line.
I am confused about what you are trying to say.

--

Rick

In message , John S
writes
On 7/29/2015 1:16 PM, rickman wrote:
On 7/29/2015 1:42 PM, John S wrote:
On 7/29/2015 11:56 AM, Wayne wrote:

Lots of questions. A large area for investigation.

The reason for my balun question (other than to generate meaningful
technical banter on the newsgroup) is that some years ago in the age of
sliderules, a widely known and respected antenna guru told me that a
balun was unnecessary at resonance ( j=0 ).

I lost touch with him and don't know if his views changed over the
years.

I disagree with him.

Please see Roy Lewallen's (W7EL, author of EZNEC) site for some good
reading. He is a superb writer of easy to understand technical tidbits.
He has some balun stuff among other stuff.

http://eznec.com/misc/

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?


Skin effect. The currents on the inside of the shield and on the
outside of the shield see different things. They each have no idea what
the other is doing.

As for magnetic field, I must step aside. I can only report what the
gurus say (nothing that I've found).

Even though the coax shield is grounded at the shack end, both halves of
the antenna get fed push-pull (in anti-phase) with the RF signal flowing
on the outer skin of the inner conductor and the inner skin of the
shield.

However, at the antenna end, the returning RF on the shield side of the
antenna doesn't know that it should stay on the inside of the shield.
Because of the skin effect, it happily makes for the outside, whence it
flows back to shack, and through the shack grounding connections.

If the shack ground connections are not very short - or imperfect - the
supposedly grounded equipment is hot RF-wise. Furthermore, on
transmission the shield outer current radiates, and if it is in close
proximity to any susceptible domestic equipment, it can cause
interference problems to it. And because things will be reciprocal on
receive, the shield won't act too well as a shield to nasty RF
interference being emitted my nearby domestic equipment.
--
Ian

On 7/29/2015 3:14 PM, Ian Jackson wrote:
In message , John S
writes
On 7/29/2015 1:16 PM, rickman wrote:

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?


Skin effect. The currents on the inside of the shield and on the
outside of the shield see different things. They each have no idea
what the other is doing.

As for magnetic field, I must step aside. I can only report what the
gurus say (nothing that I've found).

Even though the coax shield is grounded at the shack end, both halves of
the antenna get fed push-pull (in anti-phase) with the RF signal flowing
on the outer skin of the inner conductor and the inner skin of the shield.

However, at the antenna end, the returning RF on the shield side of the
antenna doesn't know that it should stay on the inside of the shield.
Because of the skin effect, it happily makes for the outside, whence it
flows back to shack, and through the shack grounding connections.

I am having trouble forming an image of this. What exactly is the
source of the "returning RF"? Is this reflected RF at the impedance
mismatch at the feedpoint? If so, the situation being discussed has no
impedance mismatch, so no returning RF. Is the returning RF from the
signal being radiated from the antenna inducing current in the shield?
If so, doesn't the inner conductor also pick up the radiated signal?

--

Rick

In message , rickman
writes
On 7/29/2015 3:14 PM, Ian Jackson wrote:
In message , John S
writes
On 7/29/2015 1:16 PM, rickman wrote:

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?


Skin effect. The currents on the inside of the shield and on the
outside of the shield see different things. They each have no idea
what the other is doing.

As for magnetic field, I must step aside. I can only report what the
gurus say (nothing that I've found).

Even though the coax shield is grounded at the shack end, both halves of
the antenna get fed push-pull (in anti-phase) with the RF signal flowing
on the outer skin of the inner conductor and the inner skin of the shield.

However, at the antenna end, the returning RF on the shield side of the
antenna doesn't know that it should stay on the inside of the shield.
Because of the skin effect, it happily makes for the outside, whence it
flows back to shack, and through the shack grounding connections.

I am having trouble forming an image of this. What exactly is the
source of the "returning RF"? Is this reflected RF at the impedance
mismatch at the feedpoint? If so, the situation being discussed has no
impedance mismatch, so no returning RF. Is the returning RF from the
signal being radiated from the antenna inducing current in the shield?
If so, doesn't the inner conductor also pick up the radiated signal?

The RF (which is, of course, an AC signal) doesn't just flow out of the
top end of the coax and into the two halves of the antenna. The fact
that the antenna has a standing wave on it means that some RF is
bouncing off the far ends of the antenna, and back to (and into) the top
end of the coax.

There is no reason why the returning RF current on the shield leg of the
antenna should want to flow back on the inside of the shield - in fact,
a combination of the Faraday shield effect and the skin effect
encourages it to take the easy route on outside of the shield.
--
Ian