wrote:

Cecil Moore wrote:

All (rho = -1) requires is a
short at the end of a transmission line as explained in _Transmission_
Lines_and_Networks_, by Walter C. Johnson when he was chairman of the
Princeton EE Dept. Here's how he calculated rho for a short:

rho = (Z1-Z0)/(Z1+Z0) = (0-Z0)/(0+Z0) = -Z0/Z0 = -1

So your argument is with Dr. Johnson whom I am merely quoting. The
(rho = -1) simply indicates a 180 degree phase shift in the reflected
voltage at the short.

Quite false. Negation is not simply a 180 degree phase shift.

Yes, it is, in the reflected voltage. A short has a voltage rho of -1
indicating a 180 degree phase shift between the incident voltage and
the reflected voltage. An open has a voltage rho of +1 indicating no
phase shift between the incident voltage and reflected voltage. The
rho for current has the opposite sign from the rho for voltage at a
short and open. And sure enough, the reflected current is 180 degrees
out of phase with the reflected voltage.

And let's see about a few values. How about?

0.5 + j0.5 Vs -(0.5 + j0.5) or -0.5 + j0.5 Vs 0.5 - j0.5

Sure enough. The first value is at 45 degrees and the second value
is at 180+45 degrees. The third value is at 135 degrees and the
fourth value is at 180+135 degrees.

And if Walter C. Johnson is worthy of the respect he receives
here, he has certainly never said it is.

Refer to Fig. 1.13 on page 20. The voltage reflection coefficient
at the open end is +1. The current reflection coefficient at the
open end is -1.
--
73, Cecil http://www.qsl.net/w5dxp



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