Constructive interference in radiowave propagation
 

Roy Lewallen, W7EL wrote:
"No, the Bird wattmeter measures only the average power and only at one
point."

True. The Bird wattmeter measures average power, the same as any a-c
wattmeter, and only at the point of measurement. If the line is lossy,
the numbers are higher near the generator, and difference between
forward numbers, for example, is an indication of loss between insertion
points.

Best regards, Richard Harrison, KB5WZI

Constructive interference in radiowave propagation
 

Constructive interference in radiowave propagation
 

Roy Lewallen wrote:
You're sadly mistaken if you think
you're getting this information from your Bird wattmeter.

Richard seems to be getting all the information from
the Bird that he needs. However, your psychological
compulsion to measure something besides average power
is a perplexing need indeed.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Cecil Moore wrote:

...
Richard seems to be getting all the information from
the Bird that he needs. ...

Better to get 'yer information from the bird, then to be given the bird.
Seems to be more than one bird "flying" around here! chuckle

Regards,
JS

Constructive interference in radiowave propagation
 

On Apr 11, 1:06 pm, Cecil Moore wrote:
Keith Dysart wrote:
So it is settled then. There is no NEED for a forward OR reverse
travelling wave. Differential equations rule.

Yes, it is settled in your own mind. In my mind,
there is certainly a need for forward and reverse
traveling waves without which standing-waves would
not be possible. If you want to deny the existence
of the cause of standing-waves, there is nothing
I can to stop you.

My mistake. But it is difficult to know your position when
you don't indicate clearly that you disagree, so I thought
that with your reply you were agreeing. Apologies.

Well, except for the inability to explain where the "reflected
power" goes in the transmitter. Of course this is not an issue
for carefully selected examples where no "reflected power" reaches
the transmitter. A more general analysis technique would not
require such careful selection of examples.

The more general analysis technique tells us that
the moon is 1000 miles away from the earth. I don't
know how far away the moon is but I know it is not
1000 miles away.

This is a bit of a non sequitur. So what is it that you really
disagree with in the analyses performed by myself and others?

Just for clarity, an example problem that has been previously
analysed is the following:
A generator with a 450 Ohm source impedance drives a 450 Ohm
ideal transmission line terminated in 75 Ohms. What is the
magnitude of the re-reflected wave at the generator?

I think you object to computing the amount of the reverse wave
that is reflected at the generator by using the source impedance.
More specifically you do not agree that the reflection
coefficient at the generator can be derived using
RC = (Zsource - Zline)/(Zsource + Zline).
Also, you do not agree that superposition applies at the source.

Given this, you then do not agree with the computations of the
quantity of the reverse wave that is reflected at the source which
then invalidates any further analysis.

Have I managed to capture the essence of your disagreement with
my and others analyses?

Note that these analyses have been performed without the use of
powers or interference so these side issues are not part of this
question.

....Keith

Constructive interference in radiowave propagation
 

Keith Dysart wrote:
My mistake. But it is difficult to know your position when
you don't indicate clearly that you disagree, so I thought
that with your reply you were agreeing. Apologies.

I don't disagree with anyone's metaphysics. What
you do inside your own mind is none of my business.
(In my mind, I can still dunk a basketball.)

This is a bit of a non sequitur. So what is it that you really
disagree with in the analyses performed by myself and others?

I have told you many times. Bench test measurements
performed over the past 20 years or so prove that it
works only in your mind, not in reality. The source
impedance of a typical ham transmitter remains somewhat
of a mystery during actual operation. The arguments
continue to rage after decades of bench test experiments
and measurements. The pages of QEX are filled with those
arguments.

A generator with a 450 Ohm source impedance ...

False assumption. That transmitters's source impedance
changes away from 450 ohms just as soon as the reflections
arrive incident upon the source, i.e. the source impedance
is a *variable* that depends upon the magnitude and phase
of the reflected wave. If your source impedance is constant,
it doesn't match real-world conditions.

I think you object to computing the amount of the reverse wave
that is reflected at the generator by using the source impedance.

I certainly don't object to your computations but the
results of those computations have been disproved on
the bench using real world ham transmitters over the
past 20 years or so. Your simple mental model doesn't
correspond to reality unless you take some extraordinary
steps which deviate from real-world ham transmitters.
Have you taken the time to review those experiments?
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Jim Kelley wrote:
Hint:
people who write physics books know that power does not interfere.

Jim, I'll make the same deal with you that I have offered
to others with, so far, no takers. If you can prove that
I said that powers interfere, I will send you $100. If
you cannot prove that, you send me $100, and cease your
unfair straw man argument methods.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

On Apr 12, 3:35 am, "Keith Dysart" wrote:


Just for clarity, an example problem that has been previously
analysed is the following:
A generator with a 450 Ohm source impedance drives a 450 Ohm
ideal transmission line terminated in 75 Ohms. What is the
magnitude of the re-reflected wave at the generator?

Interesting to me that CM railed at me for complaining that his
trivial trumped-up non-real-world example wasn't worth considering,
and now he's unwilling to accept an example that IS quite realizable.
I can EASILY do it on my bench, though I'd prefer to use a 50 ohm
generator and 50 ohm line, and a 300 ohm load at the end of the line.
It's certainly no more difficult to get a known output source
impedance than it is to get a lossless transmission line, but we talk
about lossless lines all the time, to remove an unnecessary
complication from our discussions. Since we have to test our
generators to insure that they really are 50 ohm sources, I feel quite
confident that their source impedance doesn't depend on the load you
put on them.

With respect to the output impedance of a transmitter, it may indeed
depend on the tuning/loading of the transmitter's PA, likely even the
power level it's running, and _maybe_ even on the load impedance you
put on the transmitter's output terminals. But what I do doubt is
that it _changes_ for a given setup including a given load impedance,
and in steady state, for sure the load impedance isn't changing. So
in steady state, can we determine if there are or are not reflections
on a transmission line connected to the transmitter, at that
interface? If you can't, how much do you have to disturb steady state
to make that measurement?

If battles have raged on for years about the output source impedance
of a transmitter, I submit that the people making the measurements
either (a) don't understand what they are doing, or (b) have not fully
specified the conditions under which they made the measurement, or
both. I assume they would't battle if they agreed they measured
different values, but that the conditions were also different, but
that may not be a valid assumption--some are known to battle
regardless.

As I mentioned, we have to be very careful about input and output port
impedances in measurement equipment. It's not necessarily an easy
thing to get "right," but I'm confident that we've been doing it
right, and probably for longer than the "debate" over transmitter
output source impedance has been going on.

If you don't believe there's a solution to the example Keith posted,
you have no right to believe in the results of a measurement with a
vector network analyzer, and you should certainly not trust the
indicated output level of any signal generator.

Cheers,
Tom

Constructive interference in radiowave propagation
 

On Apr 12, 8:15 am, Cecil Moore wrote:
I have told you many times. Bench test measurements
performed over the past 20 years or so prove that it
works only in your mind, not in reality. The source
impedance of a typical ham transmitter remains somewhat
of a mystery during actual operation. The arguments
continue to rage after decades of bench test experiments
and measurements. The pages of QEX are filled with those
arguments.

So your only beef with my examples is that they do not
accurately model a "typical ham transmitter"?

A generator with a 450 Ohm source impedance ...

False assumption. That transmitters's source impedance
changes away from 450 ohms just as soon as the reflections
arrive incident upon the source, i.e. the source impedance
is a *variable* that depends upon the magnitude and phase
of the reflected wave.

When you say that source impedance is a "variable", do you
mean this for a "typical ham transmitter", or do you assert
that it applies to every generator, even those which can be
accurately modelled with a Thevenin equivalent circuit (as
many signal generators, even TVSGs can)?

I think you object to computing the amount of the reverse wave
that is reflected at the generator by using the source impedance.

I certainly don't object to your computations but the
results of those computations have been disproved on
the bench using real world ham transmitters over the
past 20 years or so.

Which results have been disproved on the bench?

Your simple mental model doesn't
correspond to reality unless you take some extraordinary
steps which deviate from real-world ham transmitters.
Have you taken the time to review those experiments?

Are the experiments documented in Reflections chapter 19 and
19a representative examples?

My read of these chapters is that they offer compelling
argument and evidence (at least for the tube style
transmitters examined) that ham transmitters are linear*,
at least over their normal region of operation.

Is it your assertion that these claims are incorrect?

....Keith

* Don't confuse this use of linear, which is that the
output stage is linear, with whether the input to output
transfer function of the transmitter is linear. The transfer
function may be non-linear even though the output stage is.

Constructive interference in radiowave propagation
 

K7ITM wrote:
If you don't believe there's a solution to the example Keith posted,
you have no right to believe in the results of a measurement with a
vector network analyzer, and you should certainly not trust the
indicated output level of any signal generator.

Methinks you have missed the context of the discussion.
If the model doesn't work for an IC-706 it is not much
use to amateur radio operators. I have already said that
a valid model can be had for a signal generator equipped
with a circulator load. Now do it for an IC-706.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

On Sun, 08 Apr 2007 20:26:41 GMT, Owen Duffy wrote:

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
 

Keith Dysart wrote:
So your only beef with my examples is that they do not
accurately model a "typical ham transmitter"?

Yes, I have said so about a half-dozen times now.

When you say that source impedance is a "variable", do you
mean this for a "typical ham transmitter", ...

Yes, the discussion is about typical ham
transmitters - nothing else matters to typical
hams.

Which results have been disproved on the bench?

Please research the grand argument between Warren
Bruene, w5oly, and Walter Maxwell, w2du.

Are the experiments documented in Reflections chapter 19 and
19a representative examples?

As far as I know, the Bruene/Maxwell argument first saw
light in a QST article in the early '90s and has been
raging ever since.

My read of these chapters is that they offer compelling
argument and evidence (at least for the tube style
transmitters examined) that ham transmitters are linear*,
at least over their normal region of operation.

Linear is not the requirement for your source impedance.
Constant, fixed, and linear is the requirement for your
source impedance. Nothing you have presented had the
source impedance as a linear variable.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Cecil Moore wrote:
Jim Kelley wrote:

Hint: people who write physics books know that power does not interfere.


Jim, I'll make the same deal with you that I have offered
to others with, so far, no takers. If you can prove that
I said that powers interfere, I will send you $100. If
you cannot prove that, you send me $100, and cease your
unfair straw man argument methods.

Please don't take this the wrong way, Cecil, but after seeing this
response to a fairly inert remark, I'm not feeling comfortable enough
to take you entirely at your word.

Perhaps we just misunderstand each other, but I don't know of another
way to interpret what you have written. If you don't believe that
power interferes, then why else would you continually write
interference equations in terms of power? You can't just arbitrarily
throw quantities with any units you like into equations, and then
claim authoritative references as your source, Cecil. Is it your
contention that interference is not a validating pre-requisite for use
in an interference equation?

I'm pretty sure somebody using the name Cecil Moore posted Ptot = P1 +
P2 +2*SQRT(P1*P2), and used the equation to show how two 100 watt
generators generate 400 watts. Help me out. Where did I mess up here?

73, Jim AC6XG

Constructive interference in radiowave propagation
 

Jim Kelley wrote:
Perhaps we just misunderstand each other, but I don't know of another
way to interpret what you have written.

Yes, you do, Jim. You know that I agree with you on almost
every technical point yet you incessantly try to erect
straw men so you can knock them down. You are almost
always trying to discredit someone who agrees with you.
To that unfair tactic my response is:

From: "An Energy Analysis at an Impedance Discontinuity in
an RF Transmission Line", by W5DXP, WorldRadio, Oct. 2005

"Single-source RF energy in a transmission line and laser
light are both coherent electromagnetic energy waves that
obey the laws of superposition, interference, conservation
of energy, and conservation of momentum."

"The term 'power flow' has been avoided in favor of 'energy
flow'. Power is a measure of that energy flow per unit time
through a plane. Likewise, the EM fields in the waves do the
interfering. Powers, treated as scalars, are incapable of
interference. Any sign associated with a power in this paper
is the sign of the cosine of the phase angle between two
voltage phasors."

If you don't believe that power
interferes, then why else would you continually write interference
equations in terms of power?

Because that's what Dr. Best, Hecht, and Born and Wolf do.
Intensity, irradiance, and Poynting vectors are *power*
densities. Multiply the following intensity-irradiance
equation by unit-area and what do you get? Why, you get
WATTS of power!

Itot = I1 + I2 + 2*SQRT(I1*I2)cos(A) in watts/unit-area

Multiplying both sides of the equation by unit-area

Ptot = P1 + P2 + 2*SQRT(P1*P2)cos(A) in watts

I assume that's how Dr. Best came up with the equation.

Or don't even multiply by unit area - just use Poynting
vectors instead where each P above is a Poynting vector.
The dimensions of a Poynting vector are identical to
the dimensions of irradiance and intensity.

You can't just arbitrarily throw
quantities with any units you like into equations, and then claim
authoritative references as your source, Cecil.

I have not done that, Jim. The Poynting vector has exactly
the same units as intensity and irradiance. Multiply both
sides of the equation by unit-area and the result is WATTS,
the unit of power and that's fully consistent with the
rules of mathematics.

Is it your contention
that interference is not a validating pre-requisite for use in an
interference equation?

The question appears to have a trivial answer so it must
be just another straw man. Yes, interference exists if
interference exists and interference doesn't exist if
interference doesn't exist. Satisfied?

I'm pretty sure somebody using the name Cecil Moore posted Ptot = P1 +
P2 +2*SQRT(P1*P2), and used the equation to show how two 100 watt
generators generate 400 watts. Help me out. Where did I mess up here?

False so just another straw man. I said two 100 watt generators
do *NOT* generate 400 watts because there is no interference
between the generators. Maybe you need your glasses changed?
I did follow that posting up showing how two 100 watt *waves*
can engage in total constructive interference and obtain a total
of 400 watts.

Even you should be able to figure out how two 100 watt generators
can be made to produce a forward power of 400 watts in a
transmission line with an SWR of 5.83:1 and that is perfectly
consistent with Hecht, and Born & Wolf's intensity equations.

************************************************** ****************
HECHT AND BORN & WOLF'S TOTAL CONSTRUCTIVE INTERFERENCE EQUATIONS
ASSUME THERE IS AN EQUAL MAGNITUDE OF TOTAL DESTRUCTIVE INTERFERENCE
OCCURRING SOMEWHERE ELSE TO SATISFY THE REQUIREMENTS OF THE
CONSERVATION OF ENERGY PRINCIPLE. For every total constructive
interference equation I1 + I2 + 2*SQRT(I1*I2), there exists a
total destructive interference equation I1 + I2 - 2*SQRT(I1*I2)
The destructive interference and constructive interference
always sum to a net power density of ZERO such that the AVERAGE
power always remains the same.
************************************************** ****************

Let's say we have two light waves of 100 watts/cm^2 intensity
and we cause them to interfere constructively. Here's the
intensity equation for total constructive interference.

I1 + I2 + 2*SQRT(I1*I2) = 100 + 100 + 2*SQRT(100*100) = 400 watts/cm^2

Multiply both sides of the equation by cm^2 and you get
400 watts of power and indeed that square cm would be
getting very warm. Somewhere else exists a square cm
with zero intensity.

That is Born and Wolf's equation (16a) on page 259 of the 4th
edition of "Principles of Optics). The equation is correct
and the dimensions are correct. It is also Hecht's equation (9.15)
on page 388 of the 4th edition of "Optics". Those authors all label
the 2*SQRT(I1*I2) term as the *interference term*.

Let's say we have two RF waves or 100 watts/cm^2 intensity and
we cause them to interfere constructively in a coax transmission
line with a cross sectional area of one square cm.

P1 + P2 + 2*SQRT(P1*P2) = 100 + 100 + 2*SQRT(100*100) = 400 watts/cm^2.

With those dimensions, the intensity equation and the Poynting
vector equation are EXACTLY the same. This is equation 12 from
Dr. Best's QEX article, "Wave Mechanics of Transmission Lines,
Part 3: ..." in the Nov/Dec 2001 edition. The fixed cross sectional
area of the coax is redundant and we can choose to deal entirely
with watts.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Jim Kelley wrote:
I'm pretty sure somebody using the name Cecil Moore posted Ptot = P1 +
P2 +2*SQRT(P1*P2), and used the equation to show how two 100 watt
generators generate 400 watts. Help me out. Where did I mess up here?

Jim, you asked me not to tell you what you said but instead
to furnish the quote showing what you said. Above you are
violating the rules you asked me to abide by. Produce that
quote and I will explain it.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

On Apr 12, 3:23 pm, Cecil Moore wrote:
K7ITM wrote:
If you don't believe there's a solution to the example Keith posted,
you have no right to believe in the results of a measurement with a
vector network analyzer, and you should certainly not trust the
indicated output level of any signal generator.

Methinks you have missed the context of the discussion.
If the model doesn't work for an IC-706 it is not much
use to amateur radio operators. I have already said that
a valid model can be had for a signal generator equipped
with a circulator load.

The only problem with this statement is the assumption that
the result can only be achieved with a circulator. It only
takes a 10 cent resistor. You really should put down your
optics books for a few hours and crack open a basic circuit
theory or transmission line text. Or google, "'lattice
diagrams' reflection". For matching at the source,
only 10 cent resistors are used.

....Keith

Constructive interference in radiowave propagation
 

On Apr 12, 3:37 pm, Cecil Moore wrote:
Keith Dysart wrote:
So your only beef with my examples is that they do not
accurately model a "typical ham transmitter"?

Yes, I have said so about a half-dozen times now.

When you say that source impedance is a "variable", do you
mean this for a "typical ham transmitter", ...

Yes, the discussion is about typical ham
transmitters - nothing else matters to typical
hams.

So when a poster presents a problem in a context other "typical
ham transmitters", why do you dispute the answers. If you can't
discuss the problem in the context presented by the poster, why
not have the courtesy to stay out. Others may be interested in
learning about how things relate in contexts other than "typical
ham transmitters". Why sabotage the discussions by arguing and
arguing and then saying "Oh, I only meant my comments in the
context of "typical ham transmitters" WHICH WAS NOT THE CONTEXT
OF THE PROBLEM STATEMENT. And kindly stop using the Texas A&M
example of TVSG and 1000 feet of line. It is clearly out of
your context of "typical ham transmitters".

Perhaps, in your dissertations on optics, it would be valuable
to state that they apply only in the context of "typical ham
transmitters". This might make it clear to the reader that
your suggestions are not generally applicable and could reduce
the wasted bits.

Which results have been disproved on the bench?

Please research the grand argument between Warren
Bruene, w5oly, and Walter Maxwell, w2du.

Are the experiments documented in Reflections chapter 19 and
19a representative examples?

As far as I know, the Bruene/Maxwell argument first saw
light in a QST article in the early '90s and has been
raging ever since.

My read of these chapters is that they offer compelling
argument and evidence (at least for the tube style
transmitters examined) that ham transmitters are linear*,
at least over their normal region of operation.

Linear is not the requirement for your source impedance.
Constant, fixed, and linear is the requirement for your
source impedance. Nothing you have presented had the
source impedance as a linear variable.

No indeed, the source impedance was a constant and resistive
in all my examples. That meets the needs for linear analysis.
Remember f(a+b) = f(a) + f(b)?

You are claiming that for "typical ham transmitters" the
source impedance is undefinable. This is quite at odds with
the exposition in Reflections chapters 19 and 19a. Or maybe not,
after all, Reflections is quite precise and claims only for a
specific class of ham transmitters, which, I suppose, may not
be typical. Though they look so to me.

So I take it that you no longer agree with the analysis presented
in Reflections 19 and 19a. I am pretty sure that you have stated
agreement in the past.

It would be valuable if you were to expand on the reasons for your
change of thought. What convinced you that "typical ham transmitters"
could not have their source impedance measured?

....Keith

Constructive interference in radiowave propagation
 

Owen Duffy wrote:
Cecil, you have conveniently clipped the context (as you do), the
relevant context being the line-load interface and source-line interface.

Following published usenet rules, I trim the part to which
I am not replying.

Statements in some explanations (by others) like "This clearly proves
that reflected power and forward power in a transmission line are both
real power, and that no fictitious power, or reactive volt-amperes,
exists in either one." seem incompatible with the basic AC circuit theory
explanation of a reactive load which must exchange reactive energy with
the transmission line over a complete cycle (and the same effect at the
source end).

Those statements are generally about lossless lines where the
Z0 is purely resistive. In the lossless wave reflection model,
there is no reactive energy in the transmission line. The forward
voltage is in phase with the forward current and the reflected
voltage is 180 degrees out of phase with the reflected current.
Both V*I*cos(theta) terms are in watts with zero vars. Of course,
real world transmission lines have (hopefully negligible) vars.

BTW, I am not surprised at your dissertation apparently dismissing the
distributed impedance model of a line, because after all it is the
solution of that model that gives us the classic transmission line
equations that you seem to not want to use.

It is NOT the distributed impedance model to which I object. It is
the lumped circuit model which assumes the speed of light is infinite
and 75m loading coils don't occupy any space. Here's a quote from an
IEEE white paper at: http://www.ttr.com/TELSIKS2001-MASTER-1.pdf

"Consequently, lumped element circuit theory does not (and cannot)
accurately embody a world of second order partial differential
equations in space and time."
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Keith Dysart wrote:
The only problem with this statement is the assumption that
the result can only be achieved with a circulator.

Please stop putting words into my mouth. I said it could
be achieved with a circulator. I did *NOT* say it could
*only* be achieved with a circulator.

It only takes a 10 cent resistor.

That is naive in the extreme and makes you sound about
ten years old. If a 10 cent resistor would accomplish
that in the real world, nobody would ever buy a
circulator.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

On Apr 12, 8:06 pm, Cecil Moore wrote:
Owen Duffy wrote:
Cecil, you have conveniently clipped the context (as you do), the
relevant context being the line-load interface and source-line interface.

Following published usenet rules, I trim the part to which
I am not replying.

Statements in some explanations (by others) like "This clearly proves
that reflected power and forward power in a transmission line are both
real power, and that no fictitious power, or reactive volt-amperes,
exists in either one." seem incompatible with the basic AC circuit theory
explanation of a reactive load which must exchange reactive energy with
the transmission line over a complete cycle (and the same effect at the
source end).

Those statements are generally about lossless lines where the
Z0 is purely resistive. In the lossless wave reflection model,
there is no reactive energy in the transmission line. The forward
voltage is in phase with the forward current and the reflected
voltage is 180 degrees out of phase with the reflected current.
Both V*I*cos(theta) terms are in watts with zero vars. Of course,
real world transmission lines have (hopefully negligible) vars.

There are two models that can accurately describe the same
phenomenon: the power folk like VAs, Watts and VARs; the RF folk
like forward and reverse travelling waves. But the phenomenon
is the same. One can indeed describe what happens on a transmission
line in terms of VAs, Watts, and VARs and any line that has a
reverse wave will be found to have VARs. The different terms apply
to different models, not to different situations.

Just another reason why you have to be careful when you think
that the forward and reverse waves necessarily represent real
power. Trust the power folk on this one; they know what represents
real power, they are billing for it. And its Watts. Net. They
only power that counts is the power you can bill for.

....Keith

Constructive interference in radiowave propagation
 

Keith Dysart wrote:
So when a poster presents a problem in a context other "typical
ham transmitters", why do you dispute the answers.

Uhhhhhh Keith, because you presented the problem to me,
not someone else. You asked me what was wrong with your
examples. I obliged you. If you don't want me to answer,
don't ask me to respond.

Perhaps, in your dissertations on optics, it would be valuable
to state that they apply only in the context of "typical ham
transmitters". This might make it clear to the reader that
your suggestions are not generally applicable and could reduce
the wasted bits.

Perhaps, you should learn to recognize the common misleading
logical diversions, including your reductio ad absurdum assertion
above, and avoid them in the future.

No indeed, the source impedance was a constant and resistive
in all my examples.

Did you bench test it or just dream it up and wave your hands?
Maybe your ten cent resistor can resolve the war in Iraq - in
your mind.

So I take it that you no longer agree with the analysis presented
in Reflections 19 and 19a. I am pretty sure that you have stated
agreement in the past.

Please stop putting words in my mouth. I have never stated
agreement or disagreement. It is just one possibility out
of many that have been presented over the years. The fact
that there are so many theories is proof that it has not
been settled. Why don't you whip out an article that settles
everything and see what QEX thinks about it?

It would be valuable if you were to expand on the reasons for your
change of thought.

Since I haven't changed my thought, that would be difficult.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Keith Dysart wrote:
Just another reason why you have to be careful when you think
that the forward and reverse waves necessarily represent real
power. Trust the power folk on this one; they know what represents
real power, they are billing for it. And its Watts. Net. They
only power that counts is the power you can bill for.

:-) :-) :-) Uhhhhhh Keith, the power company does NOT bill
you for "Watts. Net." They bill you for the number of joules
(KWH) that you convert from 60 Hz AC to heat. Where the heck
did you learn your physics?

Last month I converted 3,452,400,000 joules to heat here
at my QTH. That's 0.000002442 cents per joule.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

On Apr 12, 8:20 pm, Cecil Moore wrote:
Keith Dysart wrote:
The only problem with this statement is the assumption that
the result can only be achieved with a circulator.

Please stop putting words into my mouth. I said it could
be achieved with a circulator. I did *NOT* say it could
*only* be achieved with a circulator.

Do you have a list of possible approaches?

Is there any environment in which a 10 cent resistor is the
optimal solution?

It only takes a 10 cent resistor.

That is naive in the extreme and makes you sound about
ten years old. If a 10 cent resistor would accomplish
that in the real world, nobody would ever buy a
circulator.

In my world, the solution is optimized for the problem at
hand: sometimes a circulator, sometimes a resistor,
sometimes feedback and sometimes we just don't care about
matching the source so nothing at all is needed.

....Keith

Constructive interference in radiowave propagation
 

Keith Dysart wrote:
Do you have a list of possible approaches?

I only use one - I don't allow reflected energy
to become incident upon my IC-706 and IC-756PRO.
That is, by far, the most common configuration
in amateur radio.

Is there any environment in which a 10 cent resistor is the
optimal solution?

To the best of my knowledge, not on the output
of any 100 watt amateur radio transmitter.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

"Keith Dysart" wrote in
ups.com:

....
Just another reason why you have to be careful when you think
that the forward and reverse waves necessarily represent real
power. Trust the power folk on this one; they know what represents

Keith, that was indeed my point, that talking of the forward and
reflected waves as power waves (or whatever non-phasor term is being used
today) and the assertion that those "power" waves are entirely real power
(for whatever reasons), and the talk of superposition of these waves
(where the examples seem to deal with power algebraicly with sometimes a
fudge for phase correction) cannot explain the role of a transmission
line as an energy store at any instant, nor the exchange of reactive
energy at source and load over time.

If that seems a jumble, it is because this stuff is bandied around
without much discipline.

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 specific cases.

It isn't the special case of a lossless line the causes this, it is the
conclusions that are incorrectly drawn from the lossless line or
incorrectly applied that are the problem.

Owen

Constructive interference in radiowave propagation
 

Owen Duffy wrote:
Keith, that was indeed my point, that talking of the forward and
reflected waves as power waves ...

If you are trying to quote me, Owen, you are misquoting me.
Exactly what is it about the following excerpts from my
2005 energy article with which you disagree?

From: "An Energy Analysis at an Impedance Discontinuity in
an RF Transmission Line", by W5DXP, WorldRadio, Oct. 2005

"Single-source RF energy in a transmission line and laser
light are both coherent electromagnetic energy waves that
obey the laws of superposition, interference, conservation
of energy, and conservation of momentum."

"The term "power flow" has been avoided in favor of 'energy
flow'. Power is a measure of that energy flow per unit time
through a plane. Likewise, the EM fields in the waves do the
interfering. Powers, treated as scalars, are incapable of
interference."
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

On Apr 12, 4:50 pm, "Keith Dysart" wrote:
On Apr 12, 3:23 pm, Cecil Moore wrote:

K7ITM wrote:
If you don't believe there's a solution to the example Keith posted,
you have no right to believe in the results of a measurement with a
vector network analyzer, and you should certainly not trust the
indicated output level of any signal generator.

Methinks you have missed the context of the discussion.
If the model doesn't work for an IC-706 it is not much
use to amateur radio operators. I have already said that
a valid model can be had for a signal generator equipped
with a circulator load.

The only problem with this statement is the assumption that
the result can only be achieved with a circulator. It only
takes a 10 cent resistor. You really should put down your
optics books for a few hours and crack open a basic circuit
theory or transmission line text. Or google, "'lattice
diagrams' reflection". For matching at the source,
only 10 cent resistors are used.

...Keith

Well, I'm not sure that's the ONLY problem with it, Keith! ;-)

Whether the model works for me with an IC-706 will have to wait till
someone sends me an operating IC-706 to test. (They should not expect
its return...) But I can assure you that whether it does or not, it's
a VERY useful model to me, and I am an amateur radio operator. I
certainly do NOT accept that the context of this thread is amateur
transmitters--there's been so much basenote drift by this time that
practically anything relating to vector addition of signals seems fair
game.

Cheers,
Tom

PS--know any circulators that work over a range from 10kHz to 6GHz??
Know any that work at 10kHz even?

Constructive interference in radiowave propagation
 

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.

The change in one field induces the other field and vice versa. Thus it
is the same energy which is being passed back and forth between both
fields. Therefore, over a prolonged period, 50% resides in each field.

Best regards, Richard Harrison, KB5WZI

Constructive interference in radiowave propagation
 

Constructive interference in radiowave propagation
 

K7ITM wrote:
I certainly do NOT accept that the context of this
thread is amateur transmitters--

Granted, the thread drifted away from the subject line
which has little to do with transmitters, but amateur
transmitters are what the entire Maxwell-Bruene
brouhaha is all about.

We already have a special case where a signal generator
plus circulator yields everything we need to know. One
more special case doesn't add much even if it works
which is questionable.

We do not have a valid generalized case that covers
amateur radio transmitters. IMO, that's what the
brouhaha is all about.
--
73, Cecil http://www.w5dxp.com

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