Richard Harrison wrote:
Keith wrote:
"Why the resistance to explaining this case?"
Because it should be obvious to anyone who knows enough to ask the
question.
Nevertheless, I assume the questioner is sincere so here is a simple
answer. It`s in Terman if you want more details.
The question was, indeed, sincere.
Zo = sq rt Z/Y
Z = R + j omega L = line series impedance per unit length, ohms.
Y = G + j omega C = line shunt admittance per unit length, ohms.
For r-f in good lines, this reduces to:
Zo = sq rt L/C
For d-c, this reduces to:
Zo = sq rt R/G
But we were discussing ideal lines, for which, if I recall correctly,
R and G are both 0.
This leaves us with Z0 = jwL/jwC (w being my font challenged excuse
for Omega)
which should, in the limit as w approaches 0, leave us with the same
answer as for RF. Or have I forgotten how to do math (which is quite
possible).
In any case, a slight modification to the experiment can get around
this difficulty. We'll just perform the experiment at a frequency
sufficiently low as to be indistinguishable from 0 given the duration
of the experiment.
Obviously line immpedance at d-c is likely quite different from line
impedance at r-f.
This would certainly be true for real world lines where the luxury of
R=G=0 does not exist.
....Keith
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