"Richard Clark" wrote in message
...
On Sun, 02 Nov 2008 14:00:40 GMT, "Jerry"
wrote:

Hi Owen

Another way of avoiding the math is to use both a Smith Chart and an
overlay of a Z Theta Chart. The problem of choosing line lengths and
their
Zo them becomes intuitive. But any "perfect match" does depend heavily
on
knowing impedance rather than VSWR, as you know.
The load impedance ploted on the Smith Chart can be assummed to
translate
to any impedance on the circle of constant VSWR for any load impedance.
The impedance moves along the line of constant "Theta" on the Z Theta
Chart
for a change of Chart Z.
With the overlay of the two charts, it is fairly easy to see what
lengths
and Zo will produce the best match.

Jerry KD6JDJ

Hi Jerry,

Your solution is rather exotic for this group, but I have encountered
it in my Metrology days as part of the HP legacy. The method you
described is missing from this article, but it gives the group a
picture of the chart, none-the-less:
http://www.hpl.hp.com/hpjournal/pdfs...Fs/1950-04.pdf

73's
Richard Clark, KB7QHC

Hi Richard

As you know, I have been far away from the antenna design community for
such a long time that I feel like a beginner today. So, I wouldnt have
considered anything i know to be "exotic".
For those who havent used the Z Theta Chart, it is identical to the Smith
Chart, but expressed in polar coordinates ( Impedance magnitude with its
angle).
With both a Smith Chart and a Z Theta Chart of equal radius and overlayed,
a pin hole thru both will identify any impedance with real Resistance. The
value identified on the Smith Chart is given as R+/- jX.. The value
identified on the Z Theta Chart is given as Z Angle Theta.

The use of both charts together is a great tool for impedance matching
with transmission line sections. It is quick and simple yet it is quite
accurate. An impedance, plotted on the Z Theta Chart moves along the lines
of constant angle when the chart Impedance is changed. That lets the
designer plot any impedance on the Z Theta Chart with, for instance 50 ohms
as its center, then immediately see where the impedance will move if the
Chart impedance is changed to the value of the new transmission line
impedance chosen for the transformer, for instance 70 ohms.

Jerry