Constructive interference in radiowave propagation
 

Richard Harrison wrote:
Owen Duffy wrote:
"In the same vein, I saw an assertion without sufficient qualification
that in a transmission line, 50% of the energy is stored/contained in
the electric field and 50% in the magnetic field. Again, general
statements from specified cases."

Now we accept that energy travels a guided path as an EM wave. The
electric and magnetic fields of a wave alternately contain the energy of
the wave. When the electric-field is at its maximum, the magnetic-field
is at its minimum, and vice versa.

In addition:
Assuming ideal TEM waves, the B-field (magnetic) is always
orthogonal to the E-field (electric) and both are orthogonal
to the direction of travel. The power associated with the
ideal TEM wave is ExB in watts (no vars). A TEM wave travels
at the c' = c(VF) speed of light and cannot travel at any other
speed. If it slows down or stops, it is not longer a TEM wave
and has necessarily been converted to some other form of energy.
Energy "sloshing" back and forth between reactances is NOT TEM
energy.

The principle of superposition gives us permission to treat
the forward traveling wave and reverse traveling wave separately
and superpose the results. Superposing the results does NOT
change the nature of the TEM waves. The fact that the net total
fields are no longer orthogonal gives the illusion that there
exist vars in the circuit but they are only virtual vars based
on virtual voltages and virtual currents. There are no vars in
ideal TEM waves in ideal lossless purely resistive Z0 transmission
lines. The forward traveling wave TEM fields have no effect on
the reverse traveling wave TEM fields as long as a physical
impedance discontinuity is not encountered.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

On Sun, 08 Apr 2007 20:26:41 GMT, Owen Duffy wrote:
Owen, the following is a copy of your post of 4-8-07, and my response 0n 4-12-07 to which you haven't
responded. Perhaps you haven't seen my response, or perhaps you chose not to respond, which is ok either way.


Walter Maxwell wrote in
:

Walt, I can see that you have taken my comment as personal criticism. That
was not intended, and to the extent that I may have caused that, I
apologise. In that context, it is better that I refrain from further
comment.

Regards
Owen

Hi Owen,

Please excuse the long delay in responding to your post of 4-8-07, 4:26 pm EDT. I have been away from the
computer since then, attending to personal chores that took priority over rraa.

I'm sure your comments weren't meant as a personal attack, and I accept your apology.

However, your consideration of statements appearing in Reflections as flawed on the assumption that the
concepts presented there concerning impedance matching apply only to lossless and distortionless lines, IMHO
is unfair, because it is not true.

For readers of your post who now may be questioning the reliability of statements appearing in Reflections,
I'm working on a more detailed discussion of the issue for clarification that I will enter on the rraa as a
new thread.

Walt

Constructive interference in radiowave propagation
 

Owen Duffy wrote:
"Richard "over a prolonged period" is a qualification, and still doesn`t
sufficiently qualify the statement to be true."

Maybe not the best words, but they are true in the practical case. In an
EM-wave, energy is being passed back and forth netween the electric and
magnetic fields on a periodic basis. At any given instant most of the
wave`s energy may reside mostly in one field or the other at a given
point. Half a cycle nas no practical significance among a million or
more.

Best regards, Richard Harrison, KB5WZI

Constructive interference in radiowave propagation
 

Walter Maxwell wrote:
On Sun, 08 Apr 2007 20:26:41 GMT, Owen Duffy wrote:
Owen, the following is a copy of your post of 4-8-07, and my response 0n 4-12-07 to which you haven't
responded. Perhaps you haven't seen my response, or perhaps you chose not to respond, which is ok either way.

Perhaps instead of asking Owen to point out what is wrong with
your writings, he would be more comfortable discussing his
theory, given the Vr and Ir terms that he uses, of how the
energy associated with that Vr and Ir wave gets its direction
and momentum changed at a Z0-match when Vr and Ir are
canceled/re-reflected/redistributed.
--
73, Cecil, w5dxp.com

Constructive interference in radiowave propagation
 

Owen Duffy wrote:
If the distributed network model you favour is the S paramater model,
properly applied, it is in fact entirely consistent with the distributed
impedance line model because the parameters are derived from the solution
to the distributed impedance line model.

Given that the S-Parameter analysis is valid as explained in
HP's Ap Note 95-1 available from:

http://www.tm.agilent.com/data/stati...-1/an-95-1.pdf

--------Z01--------+--------Z02--------
a1-- b2--
--b1 --a2

where a1, a2, b1, and b2 are normalized voltages.

The equation for b1 is b1 = s11(a1) + s12(a2)

Given that a1 and a2 are in phase and that b1 = 0
then s11(a1) and s12(a2) would have to be of equal
magnitude and opposite phase thus making the reflected
power |b1|^2 equal to zero. s11(a1) and s12(a2) cancel
each other out. (What happens to the energy in the
canceled waves?)

What do you get when you square both sides of the equation:?

b1 = s11(a1) + s12(a2) = 0 reflected voltage

Since the square of any of those terms yields watts,
If we simplify by replacing complicated terms with symbols:

|s11*a1|^2 = P1 and |s12*a2|^2 = P2 we get:

|b1|^2 = 0 = P1 + P2 - 2*SQRT(P1*P2) = 0 reflected power

These squared (power) terms are all explained in Ap Note 95-1.
The intensity-irradiance-Poynting vector equation can be
derived from the S-Parameter equations. Good thing the S-Parameter
analysis is consistent with Hecht and Born & Wolf, huh?
--
73, Cecil, w5dxp.com

Constructive interference in radiowave propagation
 

Cecil Moore wrote:

Perhaps instead of asking Owen to point out what is wrong with
your writings, he would be more comfortable discussing his
theory, given the Vr and Ir terms that he uses, of how the
energy associated with that Vr and Ir wave gets its direction
and momentum changed at a Z0-match when Vr and Ir are
canceled/re-reflected/redistributed.
--
73, Cecil, w5dxp.com

You seem to be implying that there's something different about how
these electromagnetic waves change direction compared to other
electromagnetic waves. Why is that?

73, ac6xg

Constructive interference in radiowave propagation
 

Cecil Moore wrote:

"Powers, treated as scalars, are incapable of
interference."

And when powers sic are not treated as scalers, then sometimes it's
ok to use power in interference equations, but other times it's not -
pretty much just depending on whether or not you get the answer you
want. And sometimes you have to either add or subtract the amount of
power that isn't somewhere else, or else average with zero in order to
get the right answer.

All this and more, this week on r.r.a.a.

:-)

AC6XG

Constructive interference in radiowave propagation
 

Jim Kelley wrote:
You seem to be implying that there's something different about how these
electromagnetic waves change direction compared to other electromagnetic
waves. Why is that?

There is something different but not unusual. We don't
often observe wave cancellation of visible light waves
because of the problem of getting coherent beams of light
perfectly aligned. Yet, we experience RF wave cancellation
every time we adjust our antenna tuners for a Z0-match
because the perfect alignment of coherent RF waves inside
a piece of coax is an automatic given.

Here's a very simple example. The measured forward
and reflected powers are given. The source and load
impedances are irrelevant and the length of the Z01
and Z02 lines are irrelevant. Any one of these
measured values could be unknown and solved for by
calculations based on the conservation of energy
principle.

------Z01------+------Z02------
Pfor1=100w-- Pfor2=200w--
--Pref1=0w --Pref2=100w

We have 100 joules/sec incident upon the Z0-match
point from the direction of the source. We have 100
joules/sec incident upon the Z0-match point from
the direction of the load. Those waves combine
to obtain 200 joules/sec toward the load. It is
obvious that Pref2 has to change direction and
momentum for that condition to exist.

The power reflection coefficient, rho^2, is obviously
0.5 so the voltage reflection coefficient, rho, is
just as obviously +/- 0.707, depending upon whether
[Z02 Z01] or [Z02 Z01}.

The direction and momentum of the Pref2 reflected wave
obviously reverses at the Z0-match point '+'. Exactly
how does the direction and momentum of the Pref2 wave
get reversed? Where are the physics equations for that
process that we hams label "re-reflection"? You and others
have been strangely silent on that subject preferring to
kibitz rather than provide any technical insight.

An exact duplicate of the above conditions would exist
with a 100w laser beam traveling through 1/2WL of thin
film with an index of refraction of 5.83.

A B
i=1.0 | i=5.83 | i=1.0
100w laser---air---|--1/2WL thin-film--|---air---...
--Pref1=0w | --Pref2=100w | --Pref3=0w
Pfor1=100w | Pfor2=200w-- | Pfor3=100w--

What happens to reverse the direction and momentum of
the internal reflection in the thin film? Hint: Both
Hecht and Born & Wolf give the equations for what happens
at plane A. And yes, the S-Parameter equations agree 100%
with them.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Jim Kelley wrote:

Cecil Moore wrote:
"Powers, treated as scalars, are incapable of
interference."

And when powers sic are not treated as scalers, ...

There you go again, Jim, trying to set up a straw man.
I do NOT treat powers as anything except scalars. Any
phase angle that enters into the calculation is the
phase angle between the two voltages associated with
those powers. They are copied directly from Hecht, Born
& Wolf, and the S-Parameter analysis.

Why not, instead of your underhanded, unethical
kibitzing, present your own set of equations that govern
the process that we hams call "re-reflection"?
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Cecil Moore wrote:

What happens to reverse the direction and momentum of
the internal reflection in the thin film?

That's what I was asking you. You seem to be hinting at something,
but not actually saying it. What, other than reflection, are you
suggesting causes electromagnetic waves to reverse their direction of
propagation in the system you describe?

Thank you,

AC6XG