Constructive interference in radiowave propagation
 

Jim Kelley wrote:

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?

I have published my take on that reflection. It is a two
step process involving:

1. A normal reflection from a physical impedance discontinuity
that doesn't account for all the reflected energy since the
physical reflection coefficient is not 1.0.

2. Wave cancellation between two reflected wave components
in the direction of the source results in a redistribution
of that energy in the direction of the load. This accounts
for the rest of the reflected wave energy.

You have objected to step 2 as invalid so the onus is upon
you to provide an alternate explanation. Please post the
governing equations. So far you have refused to do anything
except harp, nit-pick, and kibitz while wildly engaging in
hand-waving. Time to put up or shut up. Please explain the
process of 100% re-reflection of the internal reflected wave.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Cecil Moore wrote:

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.

It was curious that someone would qualify his statement that way to
begin with - "treated as scalars". What's that supposed to imply if
not that there are other ways to treat "powers" sic.

Is there, or is there NOT a cosine term in the interference equation?
How can a scalar have a PHASE ANGLE, and how can the cosine term
possibly apply to anything OTHER than the terms used IN THE EQUATION?!!

I wonder if you'd care to comment on the other mathematical techniques
you introduced to the group this week:

Subtracting power that isn't somewhere else from a number that's
apparently higher than it should be in order to get the right answer,
and averaging power with zero as a means for reducing an excessively
large number by a factor of two in order for the answer to come out
right. I'm still trying to parse how neglecting units makes it ok to
use equations as you see fit. $100 + $100 + 2*SQRT($100*$100) = $400
(The third term represents the amount of money that isn't somewhere
else and should therefore be mine.) ;-)

73, Jim AC6XG

Constructive interference in radiowave propagation
 

Cecil Moore wrote:

I have published my take on that reflection. It is a two
step process involving:

1. A normal reflection from a physical impedance discontinuity
that doesn't account for all the reflected energy since the
physical reflection coefficient is not 1.0.

2. Wave cancellation between two reflected wave components
in the direction of the source results in a redistribution
of that energy in the direction of the load. This accounts
for the rest of the reflected wave energy.

Right. But the question still remains, what is your claim regarding
the exact nature of the "redistribution" if NOT reflection from a
partially reflective surface?

73, Jim AC6XG

Constructive interference in radiowave propagation
 

On Fri, 13 Apr 2007 12:55:46 -0700, Jim Kelley
wrote:

$100 + $100 + 2*SQRT($100*$100) = $400
(The third term represents the amount of money that isn't somewhere
else and should therefore be mine.) ;-)

Hi Jim,

By substitution, EVERYONE knows TIME is money:
24Hrs + 24Hrs + 2*SQRT(24Hrs*24Hrs) = a work week

Hmmm, does time superpose? Can we find two coherent generators of
time? We can certainly find two generators of money like Ron Popiel's
vegamatic or George Forman's diet grill and as anyone can tell they
superpose with a veggie-burger.

73's
Richard Clark, KB7QHC

Constructive interference in radiowave propagation
 

Constructive interference in radiowave propagation
 

Jim Kelley wrote:
It was curious that someone would qualify his statement that way to
begin with - "treated as scalars". What's that supposed to imply if not
that there are other ways to treat "powers" sic.

You falsely accused me of treating powers other than
as scalars. Now you are trying to twist my denial into
something untoward. Just how low are you willing to
stoop to discredit Hecht, Born & Wolf, and Dr. Best?

Is there, or is there NOT a cosine term in the interference equation?

Yes, there is. Look in Born and Wolf and Hecht's "Optics".
There it is. I didn't put it there. The cosine term is
the angle between the two interfering voltages. All three
authorities, Hecht, Born, and Wolf, present the same
watts/unit-area equation with a term that they call the
interference term. Your argument is with them, not with me.
Watts/unit-area is certainly a scalar, yet all the experts
insert a cosine term into the scalar equation. That you don't
comprehend is somewhat ironic, wouldn't you say?

I wonder if you'd care to comment on the other mathematical techniques
you introduced to the group this week:

Subtracting power that isn't somewhere else from a number that's
apparently higher than it should be in order to get the right answer,
and averaging power with zero as a means for reducing an excessively
large number by a factor of two in order for the answer to come out
right.

Please don't blame me. Hecht says in "Optics" that destructive
interference somewhere else allows the constructive interference
that we are experiencing. I didn't invent the concept. It was
invented by optical physicists before I was born. That you
are completely ignorant of the concept is downright appalling.
It just goes to show that people who believe they know everything
rarely know anything.

I'm still trying to parse how neglecting units makes it ok to
use equations as you see fit. $100 + $100 + 2*SQRT($100*$100) = $400
(The third term represents the amount of money that isn't somewhere else
and should therefore be mine.) ;-)

Here's equation (15) on page 259 of Born and Wolf's, "Principles
of Optics". Intensity is certainly a scalar value in watts/unit-area.
Why do you think Born and Wolf would put a cosine function into a
scalar equation? Up until you discovered them doing such a
dastardly thing, they were your heroes.

Imax = I1 + I2 + 2*SQRT(I1*I2)*cos(A) (15)

Does watts/unit-area have a phase angle? No. But there is a
phase angle associated with the corresponding two E-fields.

As far as I know, a money equation doesn't possess an interference
term but intensity equations, irradiance equations, and Poynting
vector equations do indeed possess an inteference term. Here's
what Hecht says in "Optics". " Briefly then, optical interference
corresponds to the interaction of two or more lightwaves yielding
a resultant irradiance that DEVIATES FROM THE SUM OF THE COMPONENT
IRRADIANCES." You are objecting to the deviation from the sum of
the component power densities. Please take that up with Hecht.

Maybe the head of your department could explain the interference
term in the irradiance-intensity-Poynting vector equation to you.
But if I were you, I wouldn't expose your gross ignorance to him.

All anyone reading this posting has to do to see just how confused
Jim really is, is to read a copy of "Optics" by Hecht, or a copy
of "Principles of Optics", by Born and Wolf.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Jim Kelley wrote:
Right. But the question still remains, what is your claim regarding the
exact nature of the "redistribution" if NOT reflection from a partially
reflective surface?

It is impossible for a "partially reflective surface"
to reflect 100% of the intensity. My two step process
explains 100% reflection. Walt's virtual short explains
100% reflection. How do *you* explain 100% reflection
from a partially reflective surface? Time to cease the
mealy-mouthing and hand-waving and give us some facts.

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--

The intensity reflection coefficient seen by the internal
reflected wave is 0.5 yet the net reflection is 100%. I
have explained how that is possible through wave cancellation.
You have not explained how that is possible without wave
cancellation. Time to put up or shut up.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Cecil Moore wrote:

It just goes to show that people who believe they know everything
rarely know anything.

That's probably a bit of an overstatement. But they certainly can be
annoying.

ac6xg

Constructive interference in radiowave propagation
 

Richard Clark wrote:

Hi Jim,

By substitution, EVERYONE knows TIME is money:
24Hrs + 24Hrs + 2*SQRT(24Hrs*24Hrs) = a work week

Heaven help us if the unions ever find out about it.

Hmmm, does time superpose?

Interesting point, Richard. Evidently that doesn't actually matter as
long the answer comes out as desired.

73, ac6xg

Constructive interference in radiowave propagation
 

Cecil Moore wrote:
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.

[Example snipped]

Cecil,

This is a rather curious notion. Where did you get the idea that waves
must be perfectly aligned to "cancel"?

Suppose I set up an experiment in which two coherent laser beams are
misaligned by, say, one picoradian. The phases are adjusted so that the
waves "cancel" in the region of overlap. This is much the same as the
Java picture you like to reference from the FSU Magnet Lab. Any
measurement that might be made in the overlap region would show the
destructive interference, or "cancellation" if you wish. However, the
beams are not perfectly aligned, so eventually the overlap ceases, and
the individual beams proceed on toward infinity. I believe most people
would agree that those exiting beams would not be altered by any
interaction or interference that might have occurred in the lengthy
overlap region. (That is a very easy experiment that can be conducted in
any elementary optics lab.)

OK, so now we fine tune the illuminating mechanism so that the two beams
are perfectly aligned. Are you saying that there is now some fundamental
physical difference, and that the beams indeed cancel?

What is the equation that provides such a dramatic change resulting from
an adjustment of one picoradian? What reference is there for this
dramatic change mechanism?

73,
Gene
W4SZ