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.
--
73, Cecil http://www.qsl.net/w5dxp



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