pezSV7BAXdag wrote:
The limit for Z does not exist
or is (in general) the complex infinity.

As the length of a dipole is increased, for the same
power input, more energy is radiated during the first
transcient cycle and less is available for reflection
from the ends of the dipole. Reflected energy is what
is causing the feedpoint impedance to change. As the
length of the dipole is incrementally increased, the
magnitude of the reflected energy is incrementally
decreased. I believe Balanis alludes to this characteristic
of standing-wave antennas.

The feedpoint impedance is Zfp = (Vfor+Vref)/(Ifor+Iref)
using phasor addition.

The limit of that equation as Vref and Iref go to zero
is Vfor/Ifor. That's what happens for an infinitely
long dipole. That's also what happens during the transient
phase of a finite dipole. Thus, Vfor/Ifor can be thought
of as the characteristic impedance of the dipole. Seems
to me, Vfor/Ifor could actually be measured during the
transient phase of a long finite dipole. Will a TDR
report the ratio of V/I for an RF pulse?
--
73, Cecil http://www.qsl.net/w5dxp

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