"Will" wrote:

How do you figure the lower "coaxial sleave" dimentions.

It's usually 1/4WL long. The theory is to turn that 1/4WL of
feedline into a transmission line where the currents on the
outside of the original shield are balanced by the inside
shield on the sleeve which balances the antenna currents.
It functions over a certain single bandwidth.
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73, Cecil http://www.qsl.net/w5dxp