Gene Fuller wrote:
Cecil Moore wrote:

If the wave reflects from a short circuit, the voltage reverses
phase by 180 degrees such that Vf+Vr=0. The current does not
reverse phase so If+Ir=2If=2Ir.

Incidentally, this is a different convention from the field
of optics.

Cecil,

That is a rather curious comment. Why do you say the convention is
different for optics? There are no commonly used "voltage" or "current"
descriptions in optics, so analysis is done using E-fields and H-fields.
Otherwise there is no difference in convention between optical and RF.

In any case this reversal or non-reversal is not a "convention". It is
the mathematical result that comes out of a proper solution to the
boundary value problem. The "convention" exists only if one considers
Maxwell equations to be a "convention".

I'm not seeing Cecil's comments in context, so this might be irrelevant,
but there is a convention involved with the direction of
reverse-traveling current waves. The common convention used in
transmission line analysis is that the positive direction of both
forward and reverse current is from the generator toward the load end of
the line. The consequences of this is that the current reverses sign --
really meaning only that it reverses direction -- upon reflection from
an open circuit (+1 voltage reflection coefficient), and it allows
calculation of the total current as the sum of the forward and reflected
currents. An equally valid convention is to define the positive
direction of both forward and reflected currents to be the direction of
travel. If this convention is used, then the current undergoes no change
in sign upon reflection. But the total current then equals the forward
current minus the reverse current. Either convention will produce
correct results, of course, as long as it's carefully and consistently
applied.

Roy Lewallen, W7EL