"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"