Cecil Moore wrote:
John Popelish wrote:

Cecil Moore wrote:

Compared to zero amps of standing wave current when the forward current
phasor and the reflected current phasor are 180 degrees out of phase,
just how much effect can capacitance have?


A standing wave voltage passes exactly as much (AC RMS) current
through a capacitance as a traveling wave voltage does.


But the two waves are different as can be seen from their
equations.

That difference is a difference in the pattern (distribution) of
voltage and current along the line, as well as a possible difference
in amplitude and phase at any given point. But at any point that is
not a node in the standing wave pattern, there will be an ordinary AC
voltage or current at some amplitude between double the traveling wave
amplitude and zero amplitude, and one of two phases (that switch each
time you pass a node).

A traveling wave transfers net energy along a
transmission line or antenna wire. A standing wave transfers
zero net energy along a transmission line or antenna wire.

No argument. But a standing wave still represents storage of energy
in the line, as with any resonant structure, and that stored energy
shows up as magnetic fields and electric fields along the line. The
big difference is that the magnetic fields bob up and down at some
areas and the electric fields bob up and down half way in between
those areas. At any given moment, there is a fixed total energy in
the combination of all the magnetic and electric fields.

In the areas where the electric field is bobbing up and down, there
must be capacitive current caused by that variation in electric field.

From "Fields and Waves in Modern Radio", by Ramo & Whinnery,
2nd edition, page 43: "The total energy in any length of line
a multiple of a quarterwavelength long is constant, merely
interchanging between energy in the electric field of the
voltages and energy in the magnetic field of the currents."

Exactly. How can you write this, but deny the capacitive current that
delivers this electric field energy twice every cycle to all
capacitance feeling this voltage swing?

Hecht says it best in "Optics" concerning standing waves:

"The composite disturbance is then:

E = Eo[sin(kx+wt) + sin(kx-wt)]

Applying the identity:

sin A + sin B = 2 sin 1/2(A+B)*cos 1/2(A-B)

yields:

E(x,t) = 2*Eo*sin(kx)*cos(wt)"

cos(wt) is the AC swing that drives the capacitive current. sin(kx)
is the positional variation of that AC voltage along the line. I have
absolutely no argument with the expression, only with your
understanding of what it says.

"This is the equation for a STANDING or STATIONARY WAVE, as opposed
to a traveling wave. Its profile does not move through space; it is
clearly not of the form Func(x +/- vt)."

Profiles do not charge capacitance, instantaneous rate of change of
voltage drives current through capacitance. cos(wt) describes a
sinusoidal variation of voltage over time (you couldn't have an RMS
value of voltage at a point or an RMS value of current past a point,
without it.

[Standing wave phase] "doesn't rotate at all, and the resultant
wave it represents doesn't progress through space - its a standing
wave."

I suggest you drop talking about phasors, till you understand what
cos(wt).

Speaking of "... net transfer of energy, for the pure standing
wave there is none."

But it does represent net storage of energy. The total stored energy
is the sum of energies in the two traveling waves over the length. A
standing wave does not violate conservation of energy.

Storage that must continuously be swapping back and forth from
magnetic field energy to electric field energy. When the energy
storage is all electric, that implies charges capacitance.

Don't give up, the light may be just about to come on.