On Sat, 05 Jun 2004 13:05:18 -0500, Cecil Moore wrote:

Cecil Moore wrote:

Walter Maxwell wrote:
But Cecil, take another look at Fig 6 on page 23-5 to note that those
two waves arrive 180 out of phase at point A, which means only that
the E and H fields cancel in the rearward direction only, resulting
in a Zo match to the source.

Yes, and that is exactly my point. EXACTLY the same thing happens to the
E-fields and H-fields. That means exactly the same thing that happens to
the rearward-traveling voltages also happens to the rearward-traveling
currents.

In my class in secondary school counseling, I learned a technique that
might be helpful here. It's called, "Be the thing." Whatever it is that
you are trying to understand, mentally become that thing. In other words,
assume that you are the reflected current to find out what you
would experience. Obviously, it is just a mental exercise, but one
that I have found quite useful throughout the years.

First, assume that you are the reflected voltage from a mismatched load.
What do you encounter back at the match point? You encounter another
reflected voltage with equal magnitude and opposite phase traveling in
the same rearward direction. What happens to you? Your momentum in the
rearward direction is reversed and your energy starts flowing toward the
load. As a reflected voltage, based on your necessarily limited knowledge,
you assume that you must have encountered a virtual short circuit.

Second, assume that you are the reflected current from a mismatched load.
What do you encounter back at the match point? You encounter another
reflected current with equal magnitude and opposite phase traveling in
the same rearward direction. What happens to you? Your momentum in the
rearward direction is reversed and your energy starts flowing toward the
load. As a reflected current, based on your necessarily limited knowledge,
you assume that you must have encountered a virtual open circuit.

There exists an apparent contradiction. A match point cannot simultaneously
be a virtual short and a virtual open. How is the apparent contradiction
resolved? Is there anything else in physics that can cause a total reflection
of energy besides a short, open, or pure reactance? The answer is, "yes", and
it happens all the time in the field of optics. In a system with only two
directions of energy travel available, total destructive interference in one
direction has to result in total constructive interference in the other
direction. That's the way perfect non-glare thin-film coated glass works in
the presence of a coherent single-frequency laser beam.

Yes, Cecil, I understand. However I don't particularly like the notion of saying
both fields go to zero, or both fields go to zero in the rearward direction.
Confusing. Remember, weeks ago I swore that both fields could never go to zero
simultaneously? The reason I disagreed with you is that you didn't mention the
'direction'. The reason I dislike hearing that both fields go to zero is that
it's really not true. Like I've said many times, on encountering a short,circuit
voltage and the E field go to zero and the current and H field doubles AND
REVERSES DIRECTION. To me, Reversing direction is more meaningful and less
confusing than both going to zero, and it still says there is no energy
propagating rearward of the match point.

Going now to the cancellation process when the voltages and currents of both
waves are mutually out of phase. You say that voltages 180 out yields a short
(agreed) and that currents 180 out yields an open. Sounds good, and I mistakenly
agreed a coupla days ago. But I don' think so. I believe voltage 180 out defines
a short--period. Look at it this way. Take a zip cord and put male plugs on both
ends. Plug one end into an outlet, say the top one, and then plug the other end
into the bottom outlet with the polarities reversed. With respect to voltage we
have a 'circuit breaker' short circuit, because the voltages entering the zip
cord at each end were 180 out. But so were the currents initially. Then why the
short circuit current flow? Certainly not because the circuit is open to
current.

Another scenario with the same initial conditions and results: Take two
identical generators delivering the same level of harmonically related output
voltages. Connect their terminals in phase.Voltages in phase--currents in phase.
Result? No current flow. Why? Zero voltage differential. Open circuit to
voltage--open circuit to current.

Now reconnect their terminals in the opposite manner. Voltages 180 out--currents
180 out. Do we have current flow? You bet--dead short! Because current results
from voltage, if voltages are 180 out of phase we have a short to both voltage
and curent. No open circuit to current.

Cecil, I hope we're both still on the same page on this one;

Walt