Jack originally wrote:

In the real antenna, the feedpoint is connected to a
length of coax such that the center of the coax is electrically
connected to the western half of the antenna and the shield of the
coax is electrically connected to the eastern half.

Cecil wrote to you:

Connect the two sides of the antenna together with a wire and install
a source in the middle of that wire. Forget the coax for now. You can
expand on the model later. Something like this:

---------------------+--S--+-----------------------
| |
-----------+ +------------

I would just add that the coax can be modeled as shown
below:

---------------------+--S--+-----------------------
| |
-----------+ +------------
| (shield)
|
|
|
|
|
|
|
|
|
|
|
--------
-----
---

Jim, K7JEB