Dave Shrader wrote:
My understanding is that the phase of the forward and reflected waves
varies along the transmission line. One 'rotates clockwise' the other
'rotates counterclockwise'. In the case of 'perfect reflection', a
mathematical study condition, the sum of these two waves varies along
the transmission line. The resultant sum produces the minimum and
maximum voltage we observe in a slotted line. It is to be noted that the
phase shifts at the all half wave points from the load, by convention,
rotate from the 'positive' two quadrants to the negative two quadrants.
Therefore, a polarity change exists.

If a current is 0 + j1.0 amps, exactly where is that one amp of current
located? The real component of phasor current always lies along the 'x'
real axis. A change from +0.001 amp at zero degrees through a zero magnitude
to -0.001 amp at 180 degrees is a 180 degree phase shift in *real* current
that exists in the real world. Imaginary current is, well, imaginary, and
is an artifact of the phasor math model. Has anyone ever measured j1.0 amps
of current at a point where the real current is zero?

Is this the 180 degree phase shift being discussed?

Originally, the 180 degrees phase shift being discussed was concerning
a current standing wave in a thin wire where the forward current and
reflected current are equal in magnitude. The phase of the net current
is 0 degrees for awhile and then shifts abruptly to 180 degrees according
to Kraus.

There are only two directions in a wire. For an AC signal, the current
is flowing one direction for 1/2 cycle and the other direction for the
other 1/2 cycle. The *real* magnitude of the current varies with physical
length (sin kL) and can be analyzed without any reference to phase.
--
73, Cecil http://www.qsl.net/w5dxp



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