On 8/1/2015 11:34 AM, Wayne wrote:


"John S" wrote in message ...

Consider a center-fed dipole. The generator is at the center.

----------GEN-----------

A balanced antenna. Familiar, yes?

Now consider attaching a feed line to it. JUST the shield!


----------GEN-----------
|
|
| - line shield
|


What happens? Well, there is one radiating element on one side and two
radiating elements on the other side (element + shield). Not balanced
now, right?

The current divides on the right side such that the current on the
left side is equal to the sum of the currents on the right side. This
is the message David was trying to get across, I think.

So, okay, what are the currents in the two elements on the right side?
Without further knowledge, dunno. BUT note that there will be a
current on the outside of the shield according to its characteristic
impedance (skin effect separates current flow on the inside of the
shield from the current on the outside of the shield).

Well, the outside current we don't really want, so how do we stop it?
What if we install a large impedance just below the GEN that runs down?


----------GEN-----------
Z
|
| - line shield
|

This is the purpose of providing a device (Z) that impedes the current
flowing down the line. There are several ways this can be
accomplished. One way is to run several turns of the coax through a
toroid core so that the impedance reduces the current.

Again, I am no expert on this. I'm just trying to generate discussion
and learn.

John

This is similar to the way I always viewed the current.

In summary, at the balanced antenna, the center conductor path is
straightforward.
However on the shield half, the current has two possible paths: the
antenna half connected to the shield and the outside of the shield.

This would cause half of the dipole to radiate less, with the remainder
being radiated by the outer shield.

The proportion of the current flowing down the outer side of the shield
seems easier to stop than to calculate

flame shields up!

Give the man a cigar! I think your entire post is correct.