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Old August 13th 06, 08:28 PM posted to rec.radio.amateur.antenna
Cecil Moore Cecil Moore is offline
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First recorded activity by RadioBanter: Jul 2006
Posts: 1,614
Default Frequency Sensitivity of mobile HF vertical antennas.

Dave Oldridge wrote:
My question is one of Physics.


Lest anyone think I have invented something new, I'm sure
Walter Maxwell was doing these sorts of Smith Chart
calculations while I was in high school.

Given the following 1/4WL resonant stub with Z01 = 600
ohms and Z02 = 4000 ohms:

Source----Z01A----x----Z02----y----Z01B----open

Boundary conditions a The feedlines are lossless. The
source sees zero ohms. The Z01A length is 45 degrees. The
Z02 length is 45 degrees. How long is the Z01B length?

This is a problem easily solved by using the outside circles
of two Smith Charts, one normalized for 600 ohms and the
other normalized for 4000 ohms. The procedure is:

Assuming the source is seeing zero ohms, calculate the
impedance at 'x'. Plot that impedance on a Z02 Smith Chart.
Calculate the impedance at point 'y' of the Z02 length. Plot
that impedance on the first Smith Chart and see how long
Z01B needs to be to reach to infinity.
--
73, Cecil http://www.qsl.net/w5dxp