John Popelish wrote:
Roy Lewallen wrote:
John Popelish wrote:

A point of clarification to John's posting:

When a standing wave exists on a transmission line, the phase of the
voltage or current is fixed (other than periodic phase reversals) with
position only if the end of the line is open or short circuited.
Otherwise, the phase of voltage and current will change with position.

Is that because the result is not a pure standing wave (superposition of
two equal and oppositely traveling waves), but a superposition of a pair
of traveling oppositely traveling waves of different amplitudes?

Yes, but I wouldn't put it quite that way. I prefer to say that this is
simply a special case of the more general result you get when you sum
forward and reverse waves. Nothing magical or abrupt happens when the
two traveling waves are equal in amplitude -- if they're slightly
different, you get a little phase shift of the total current with
position along the wire, the current minima aren't quite zero, and the
spatial shape of the amplitude of the total current -- that is, the
shape of the standing wave -- isn't quite sinusoidal. Making the
amplitudes more and more different smoothly transitions the nature of
the total current until in the special case of the reverse traveling
wave being zero you have the distribution of a pure traveling wave.

Roy Lewallen, W7EL