On Tue, 28 Sep 2004 13:52:05 GMT, "John Smith"
wrote:

So, I should use 300 Ohm coax?

Hi John,

No such thing, or it would be quite expensive (amounting to no such
thing).

Suppose I construct the antenna as shown except put a Tee at the bottom for
convenience. What will be the impedance at that point? After all, that would
now be the feed point, yes?

No. The feed point is at the inner conductor connection to the outer
conductor. The bend in the line (where you would put the tee) is
merely a bend in the line. You could choose any point in the line,
would that qualify it as a feed point? No. Your eye is merely drawn
to it through the magic of an illustration's symmetry. As a practical
matter, yes you could insert a tee there (provided you open one leg,
you see? even here we have to maintain the continuity out to the true
feed point).

I must add that my analysis on the Z transformation may be at fault.
Again, my focus is in larger antennas where these kind of machinations
would be prohibitive. Others should have chimed in by now, but they
seem transfixed with my postings on politics or bored altogether. It
seems to me that you already have the text description before you.
Certainly in a 800+ page tome Kraus isn't mute on the subject?

On the other hand, you have the instrumentation and the scale of
construction is not so demanding that you couldn't resolve this
yourself at the bench in an evening. We have too many dream weavers
here already and I have pleaded with them to perform simple tests that
apparently befuddle them. Imagine me posing the task of taking
several SWR measurements being responded to with 100 posting threads
of confusion as to how!

I would use solid coax simply because I have several hundred feet of
precision material. It was what we used for 900 MHz spread spectrum
so 400 MHz is no great shakes.

73's
Richard Clark, KB7QHC