John - KD5YI wrote:
I thought there were two traveling waves, forward and reverse, with the
reverse wave being a reflection of the forward wave from the end of the
antenna. I thought that the total current was the sum of the two waves,
could be measured with an ammeter, and that it could be referred to as
the standing wave.

If the antenna were lossless, that would be true. However, the
antenna loses RF energy to radiation, ground, I^2*R, etc. Since
the same thing is true of a transmission line, let's first look
at a transmission line.

Let's say we measure (at the tuner)
a forward power of 100 watts and a reflected
power of 80 watts. We can assume that the losses in the line
and the power delivered to the load add up to 20 watts. The
20 watts can be associated with a pure forward traveling wave.
The other 80 watts of the forward power and the 80 watts of
reflected power can be associated with a pure standing wave.
The equations for such would look something like this.

Itot = Ifor*cos(kx+wt) + Iref*cos(kx-wt) =

Itot = I1*cos(kx+wt) + I2*cos(kx)*cos(wt)

I1 would be considered to be the part of the traveling wave that
is delivering net power to the load. I2 would be considered to be
the standing wave current delivering no net power to the load.
It's just another way of mathematically partitioning the currents.

Let's assume for the sake of discussion that the forward wave at
the antenna feedpoint is 100 watts and the reflected wave at the
antenna feedpoint is 80 watts. That means there are 20 watts of
total losses. We can partition the currents in the same way that
we did in the transmission line.

Incidentally, if we assume the antenna is 1/2 wavelength with a
Z0 of 600 ohms, we can calculate the feedpoint impedance just as
if it were a piece of transmission line with a resistive termination.
Anybody want to try that exercise? What impedance is seen looking
into a 600 ohm 1/4WL open stub when the forward power is 100 watts
and the reflected power is 80 watts?

Are you now saying that the standing wave and the reverse wave are the
same wave?

The reverse wave is half of the standing wave. The other half of
the standing wave is part of the forward wave. One might say that
the energy in the reverse wave neutralizes the ability of the
forward wave to deliver that same amount of energy to the load.
And indeed, we know the power delivered to the load is the forward
power minus the reflected power.
--
73, Cecil http://www.qsl.net/w5dxp