Roy Lewallen wrote:
I think it might be useful to say a little more about standing waves.

Imagine a single lossless transmission line with a sine wave source at
one end and a load at the other. Begin with a load equal to the line's
Z0. Make a graph of the magnitude of the current or voltage as a
function of distance from the source. With the Z0 load, the magnitude
will be the same all along the line so your graph will be a straight
line. This is a "flat" line, with no standing wave. A probe sitting at
one spot would show the instantaneous voltage or current amplitude going
up and down in a sinusoidal manner. A probe a bit farther down the line
would look the same, but delayed; there's a phase difference between the
voltages or currents at the two points. The phase difference is equal to
the line's physical length in degrees divided by the velocity factor.

I've done exactly that with current using EZNEC. The traveling wave
graph is on the left at http://www.w5dxp.com/travstnd.gif

The standing wave current graph described in Roy's next quoted
paragraph below is on the right. The tabulated data provided by
EZNEC is at the bottom.

If standing-wave current is all that exists, EZNEC faithfully
reports the amplitude and phase of the standing-wave current.

If traveling-wave current is all that exists, EZNEC faithfully
reports the amplitude and phase of the traveling-wave current.

At the most extreme case of mismatch -- an open, short, or purely
reactive load, resulting in an infinite SWR -- the amplitude of the
standing wave along the line goes from zero to twice the value it had
when the line was flat. And a really interesting thing happens to the
phase of the voltages and currents on the line. Remember how as the
mismatch got worse, the voltage and current phase difference between two
points got farther and farther away from the electrical line length
between them? Well, when the SWR is infinite, it's gotten to the point
where the voltage or current phase remains the same for a distance of a
half electrical wavelength, then abruptly changes 180 degrees, repeating
every half electrical wavelength. Some antennas behave in some (and only
some) ways like transmission lines, and you'll find that modeling
programs report just this behavior of the phase of the current along a
straight wire antenna.

The question is, Roy, since as you say, "the current phase remains
the same for a distance of a half electrical wavelength", how can
you possibly use that same current to measure the phase shift
through a coil and convert your reading to a delay through the
coil? If the phase of the current doesn't change over the entire
1/2 wavelength, it certainly doesn't change through the coil. What
you have proven above is that your and W8JI's previously reported
coil measurements are meaningless and that the only valid way to
measure the delay through a coil is to use the traveling wave
current described in your first paragraph above.

What you are saying in the above paragraph is that the current in
a high-SWR environment carries virtually no phase information. So
the question remains:

WHY DO YOU THINK THAT PHASE MEASUREMENTS OF STANDING WAVE CURRENT,
GIVEN ITS VIRTUALLY UNCHANGING PHASE, WILL YIELD ANY USEFUL
INFORMATION ABOUT THE DELAY THROUGH A LOADING COIL?

You did measure the phase shift through the coil but the
measurement was meaningless and the conclusions invalid.
We already knew it would be close to zero and bear no
relationship to the delay through the loading coil -
BECAUSE THERE IS VIRTUALLY NO PHASE INFORMATION IN THE
PHASE OF STANDING WAVES.

The phase information in standing waves is in the amplitude
but you obviously don't realize that fact since you continue
to talk about the current "drop" through the coil being due
to losses, radiation, and leakage to the environment. If there
were zero losses, zero radiation, and zero leakage, the current
"drop" would still be there as a result of nothing more than
the superposition of the forward and reflected waves.

I hope this helps in clarifying the meanings of traveling and standing
waves, voltage and current along a transmission line.

I agree with what you have said in this posting. Unfortunately
for you, what you said in this posting contradicts and invalidates
the conclusions that you and W8JI drew from your phase
measurements of current through a loading coil in a standing-
wave antenna.

Out of one side of you mouth, you tell us that the standing-
wave current phase is unchanging over 1/2 wavelength. Out of
the other side of you mouth, you tell us that same current can
be used to measure the delay through a loading coil. Please
pick one side or the other - they cannot both be right.
--
73, Cecil http://www.w5dxp.com