Pat Barthelow wrote:
>I think I am understanding well the measured SWR vs impedance along the
>line question.
>
>My next question is: Given, say, a 100 ohm resistive antenna impedance
>(at the antenna terminals) connected to (assumed lossless) 50 ohm coax
>line, of multiple wavelengths, (producing a 2:1 SWR) What is the most
>extreme feed point impedance swing in the line and how far down the line
>is it? And how can one compute this mathematically, if one does not have
>access to a smith chart?
How can one calculate it mathematically? Gee, that's tough! Use a
computer! :-)
What do you mean by most "extreme" impedance?
OK, with a normal Smitch Chart NORMALIZED to 50 Ohms:
100 Ohms is on the real axis. It would be at the constant impedance
circle labled "2". As you move toward the exciter, the antenna will
begin to look capacitive, then you'll reach a point of pure capacitance
at 1/8 wavelength. As you keep going it will look less capacitive and
finally reach 25 Ohms real impedance at a 1/4 wavelength. Keep going and
at 3/8 wavelength, the antenna will look purely inductive. At a half
wavelength, you'll be back to 100 Ohms and this will repeat over and over
every half wavelength.
Now do you want to know what the values are for the points of maximum
capacitance or maximum inductance or what? When we say the impedance
changes, it doesn't become something like 10,000 Ohms In fact, you will
never have a real part of the resistance greater than 100 Ohms.
73,
Jon
KE9NA
-------------------------------------
Jon Ogden
KE9NA
http://www.qsl.net/ke9na <--- CHECK IT OUT! It's been updated!!!!!
"A life lived in fear is a life half lived."
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