"Cecil Moore" wrote in message
et...
Richard Harrison wrote:
Why is a principle so trivial as superposition worth a thread in this
newsgroup?

Because most of the posters to this newsgroup do not
know what happens to the energy in the waves during
superposition inside a transmission line. They seem
to understand superposition in free space but not
inside a transmission line. Maxwell's laws are the
same for EM waves in free space and inside a
transmission line.
--
73, Cecil http://www.w5dxp.com

"Sal M. Onella" wrote in message
...

"Cecil Moore" wrote in message
et...
Richard Harrison wrote:
Why is a principle so trivial as superposition worth a thread in this
newsgroup?

Because most of the posters to this newsgroup do not
know what happens to the energy in the waves during
superposition inside a transmission line. They seem
to understand superposition in free space but not
inside a transmission line. Maxwell's laws are the
same for EM waves in free space and inside a
transmission line.
--
73, Cecil http://www.w5dxp.com



Sorry for the blank post, above, -- double-click-itis set in.

I like 90% of these technical discussions. I'm a curious person by nature
but I don't always know what doors to pull open, so it's nice when a good
door is held open for me.

73
"Sal"
(KD6VKW)

Sal M. Onella wrote:
I like 90% of these technical discussions. I'm a curious person by nature
but I don't always know what doors to pull open, so it's nice when a good
door is held open for me.

It stands to reason that if interference is associated
with a redistribution of EM wave energy in free space,
essentially the same thing could happen in a transmission
line. Incidentally, interference is also associated with
the feedpoint impedance of a standing wave antenna. If
the feedpoint impedance of a dipole is 50 ohms, that's
a Z0 match to 50 ohm coax for an antenna supporting an
SWR far in excess of 1:1.
--
73, Cecil http://www.w5dxp.com

On Nov 18, 7:40 am, Cecil Moore wrote:
Just as constructive interference functions to
increase antenna gain in one direction while
destructive interference functions to decrease
antenna gain in another direction, in a transmission
line at a Z0-match point, constructive interference
functions to increase the energy flow toward the
load while destructive interference functions to
decrease the energy flow toward the source.

Correction. The Z matching device functions to increase the energy
flow toward the load and decreases the energy flow toward the source.
Interference is just the mathematical description of the resulting
spacial distribution.

73, ac6xg

Jim Kelley wrote:
Correction. The Z matching device functions to increase the energy
flow toward the load and decreases the energy flow toward the source.
Interference is just the mathematical description of the resulting
spacial distribution.

The decrease to zero in reflected energy flow toward the source
is known as "total destructive interference" in the noun version
of the word as used by Hecht. The increase in energy flow
toward the load is known as constructive interference. One need
not refer to superposition as the cause of interference since
the interference *event* implies superposition of two (or more)
coherent waves as the *cause* of the interference *process*.

I am using "interference" as a noun synonymous
with an "interference process" event, not as in "interference
rings". The Z0-matching event cannot occur without an interference
process (event). "Total destructive interference" as defined
by Hecht is *necessary and sufficient* for a Z0-match to occur,
i.e. if total destructive interference exists toward the source,
a Z0-match has been achieved.

From Websters: "interference - n. the *process* in which
two coherent EM waves combine to reinforce or cancel each
other." The reinforcing or canceling can be partial or total.
Thus, I am using Hecht's noun definition of "interference"
which "yields a resultant irradiance that deviates from the
sum of the component irradiances". Reinforcement or cancellation
is the *result* of that *process*. Superposition is the *cause*
of that *process*.

The *result* of the interference *process* is sometimes wave
cancellation if the appropriate conditions exist. That's
what happens at a Z0-match.

The interference pattern of an antenna is the *result*
of the interference *process*. Hecht says interference
"corresponds" to the "interaction" of two or more
coherent EM waves "yielding a result ...". He clearly
considers interference to be in the cause and effect
chain of events, as do I.
--
73, Cecil http://www.w5dxp.com

"Antonio Vernucci" wrote in message
...
................
If you instead put your receiver/antenna in a point where the two waves
have equal amplitude and same phase, your receiver will measure 200
joules/s (i.e. four times the power produced by each wave alone, not just
two times).
.....................
73

Tony I0JX

You know that can't be right, because combining two antennas gives 3 db
gain. For example, if you connect them in series, you will get twice the
voltage, but the impedance also doubles.

Tam

Richard Clark wrote:
On Sat, 17 Nov 2007 17:16:11 -0500, "Stefan Wolfe"
wrote:

snip


Then I am sure you will agree that using terms like "taking Cecil's sucker
bait" is not the type of "strict language" and "solid logic" appropriate in
a technical forum.

In fact, it is in the strictest language par excellence! Strict
allows for no wiggle room, nothing nebulous. You completely
understood what it meant and technical forums are assaulted with a lot
of bankrupt theories- sometimes innocently offered, but not in this
case. You might complain of style, but not substance.

That made me think of a paper that I read a few years ago that summarized:

"There would appear to be the possibility of a potential correlation..."


Talk about going out on a limb!

- 73 de Mike N3LI -

Tam/WB2TT wrote:
"Antonio Vernucci" wrote in message
...
...............
If you instead put your receiver/antenna in a point where the two waves
have equal amplitude and same phase, your receiver will measure 200
joules/s (i.e. four times the power produced by each wave alone, not just
two times).

You know that can't be right, because combining two antennas gives 3 db
gain. For example, if you connect them in series, you will get twice the
voltage, but the impedance also doubles.

The constructive interference in free space occurs before
the antennas, not after them. Such is the nature of
constructive interference which very few posters fully
understand. My original posting was designed to expose
the beauty of constructive interference. Instead, I
was accused of diverting the issue or worse.

But it's simply a fact of physics - total constructive
interference between two equal amplitude waves results
in four times the amplitude of each wave. Of course, the
result somewhere else is total destructive interference,
i.e. complete absence of energy.

No one can fully understand what happens at a Z0-match
point without an understanding of interference.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Jim Kelley wrote:
Correction. The Z matching device functions to increase the energy
flow toward the load and decreases the energy flow toward the source.
Interference is just the mathematical description of the resulting
spacial distribution.

The decrease to zero in reflected energy flow toward the source
is known as "total destructive interference" in the noun version
of the word as used by Hecht. The increase in energy flow
toward the load is known as constructive interference. One need
not refer to superposition as the cause of interference since
the interference *event* implies superposition of two (or more)
coherent waves as the *cause* of the interference *process*.

I am using "interference" as a noun synonymous
with an "interference process" event, not as in "interference
rings". The Z0-matching event cannot occur without an interference
process (event). "Total destructive interference" as defined
by Hecht is *necessary and sufficient* for a Z0-match to occur,
i.e. if total destructive interference exists toward the source,
a Z0-match has been achieved.

From Websters: "interference - n. the *process* in which
two coherent EM waves combine to reinforce or cancel each
other." The reinforcing or canceling can be partial or total.
Thus, I am using Hecht's noun definition of "interference"
which "yields a resultant irradiance that deviates from the
sum of the component irradiances". Reinforcement or cancellation
is the *result* of that *process*. Superposition is the *cause*
of that *process*.

The *result* of the interference *process* is sometimes wave
cancellation if the appropriate conditions exist. That's
what happens at a Z0-match.

The interference pattern of an antenna is the *result*
of the interference *process*. Hecht says interference
"corresponds" to the "interaction" of two or more
coherent EM waves "yielding a result ...". He clearly
considers interference to be in the cause and effect
chain of events, as do I.

Cecil,

You are waaay too concerned with philosophical words like *cause*,
*process*, *result*, and *event*.

There is no justification for saying that interference causes
superposition or that superposition causes interference or any such
combinations. Causality is a very important concept in physics, but it
has no useful meaning in this situation.

The way a physicist solves problems like this is to set up the equations
in terms of generic sinusoidal functions with variable parameters. Then
the boundary conditions of the problem are applied to determine
precisely what the parameters must be. That's it. No worries about *why*
something is happening or what is causing what. Those items are
impossible to define in any case.

If you were to read Born and Wolf you would find that they deal with the
multiple interference problem (antireflective glass) in exactly the same
manner. They never even mention constructive or destructive interference.

There is a reason physicists use this type of problem solving method. It
works for a entire range of boundary conditions. Try using your
constructive/destructive interference technique when the problem is not
quite so simple. For example, 3D problems when the incidence angles are
not so tidy, materials with absorption, or multiple films such as those
used in *real* AR coatings. You might muddle through with some generic
concept of constructive/destructive interference, but you won't be able
to get a quantitatively useful answer.

By the way, Born and Wolf must have been pretty well connected. It
appears that they copied the multiple reflection lattice diagram from
your web page. 8-)

73,
Gene
W4SZ

Tam/WB2TT wrote:
"Antonio Vernucci" wrote in message
...
...............
If you instead put your receiver/antenna in a point where the two waves
have equal amplitude and same phase, your receiver will measure 200
joules/s (i.e. four times the power produced by each wave alone, not just
two times).
.....................
73

Tony I0JX

You know that can't be right, because combining two antennas gives 3 db
gain. For example, if you connect them in series, you will get twice the
voltage, but the impedance also doubles.

If you supply your power to two identical antennas instead of one, each
antenna gets half the power. If there's no mutual coupling between the
antennas (seldom actually true), then each then produces 0.7071 times
the field strength that the original antenna did, because each is
getting half the original power. At the points where the fields from the
two antennas completely reinforce, the sum of the fields is 0.7071 +
0.7071 = 1.4142 times the field produced by the original antenna. This
is a field strength gain of 3 dB compared to the original antenna, and
it's a field strength gain, as Antonio says, of 2 (6 dB) compared to the
field produced by each of the two antennas.

Your comments about impedance and voltage makes me wonder if maybe
you're confusing feedpoint voltage with field strength. If you connect
two antennas in series and supply the same total power as you did with
one, both the current and the voltage of each will be 0.7071 times the
values the single antenna had. Again, though, all this assumes no mutual
coupling between the antennas, which is seldom true.

Roy Lewallen, W7EL