Constructive interference in radiowave propagation
 

Owen Duffy wrote:
If in fact the power delivered by the "100 watt IC706" radio was indeed
100W, and some directional wattmeter correctly indicated 200W forward, it
must indicate 200W-100W reflected which is indicative of a VSWR of 5.8,
which should have reduced power output from the IC706 markedly.

Did you make this example up on the fly, or is it the result of actual
observation on one or many occasions?

I made it up but let's take the actual example of
my 33' rotatable dipole on 20m.

IC-706---1WL 300 ohm twinlead---51.5 ohm antenna

The IC-706 is delivering 100 watts. The forward power
is 200 watts. The reflected power is 100 watts. Why
in the world would a VSWR of 5.8:1 on the 300 ohm
twinlead "reduce the output from the IC706 markedly"
when the IC-706 is perfectly matched to a 51.5 ohm
virtual impedance?
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

On Apr 9, 5:48 am, Cecil Moore wrote:
Roy Lewallen wrote:
Next, do the same for a transmission line. Show how two coherent
traveling waves can be produced which will propagate together in the
same direction but out of phase with each other, resulting in a net zero
field at all points beyond some summing point.

Roy, it is done all the time represented by the
S-Parameter equation for the reflected wave
toward the source. Assuming an impedance discontinuity
in a transmission line:

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

If b1=0, then s11(a1) and s12(a2) are indeed two coherent
traveling waves propagating together in the same direction
but out of phase with each other. The net reflected wave
field is zero.
--
73, Cecil http://www.w5dxp.com


So what? Roy didn't say that was difficult at all. Now answer the
REST of Roy's parapgraph which you so conveniently failed to include
in your quoted material.

Constructive interference in radiowave propagation
 

Jim Kelley wrote:

Cecil Moore wrote:
Of course, I regularly obtain 200 watts of forward
power from my 100 watt IC-706. It's all due to
constructive interference.

Nice try, but you're kidding yourself if you think you're getting 200
watts out of an IC706.

As anyone can readily see, I did NOT say I was "getting
200 watts out of my IC706" so your attempt at obfuscation
is obvious. I said "I regularly obtain 200 watts of forward power
from my 100 watt IC-706". Here is my exact configuration
for my 33' rotatable dipole based on actual measurements
on 20m.

100W IC-706--choke--1 WL 300 ohm twinlead---51.5 ohm antenna
Pfor=200W--
--Pref=100W

The forward power is indeed 200 watts. I have measured it
with my 300 ohm SWR meter.

Heck, on 17m, I regularly obtain 350 watts of forward power
using a 100W IC-706 as the source.

Back to the laser example, the answer you can't seem to get right is
that, recombing the split beam back into one beam will at best recover 1
watt of laser power. That's the limit allowed by conservation of energy
as it happens.

That's true for average power, Jim, and I have never said otherwise.
But if we observe interference rings, the bright rings can contain
all the power while the dark rings contain none. Thus, the bright
rings represent *double the average power* just as Born and Wolf report.

Shirley, that is not beyond your comprehension. If there is zero
intensity in the dark rings, there must be double the average
intensity in the bright rings to keep from violating the
conservation of energy principle.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

K7ITM wrote:
Let's see... 600 ohm line feeding a nominally 60 ohm dipole. (It's
not very high above the ground.) 600 ohm line is 1/2 wave long, and
essentially lossless. I feed 60 watts in, the 60 ohm dipole absorbs
60 watts. I suppose the forward power on the line is a bit more than
60 watts. My transmitter doesn't seem to have too much trouble with
the 60 ohm load, though a balun between the unbalanced transmitter
output and the balanced line is nice.

The SWR is 10:1 making rho = 9/11 = 0.818 and rho^2 = 0.67
So the SWR is close to 10:1 and the forward power with a
100 watt IC-706 source is about 303 watts. Such is the
nature of constructive interference.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

K7ITM wrote:

So what? Roy didn't say that was difficult at all. Now answer the
REST of Roy's parapgraph which you so conveniently failed to include
in your quoted material.

Thanks, but I'm not interested in Cecil's response, since I know for
certain that he'll never directly answer the question. Evasion, subject
changing, diversion, misquoting, and anything else but solid reasoning
or direct confrontation of a problem is all you'll ever get, as each new
batch of people joining this group sadly discover sooner or later. I
won't see his imaginative but evasive responses anyway unless quoted by
someone, since he's one of the four people in my kill file. ("Jesus" is
another of the four. I haven't seen any postings by him for quite some
time, but there's no harm in leaving him listed in case he's resurrected
someday.)

But I'd really like to hear from anyone else who's subscribed to Cecil's
unique views of superposition, wave interaction, and bouncing waves of
average power (although admittedly these views seem to rapidly morph as
necessary to avoid any direct confrontation with rational thought). Or
even anyone who believes (as I think you've said you do, Walt) that
traveling waves can and do affect each other under any circumstances in
a linear medium. Show me how waves can modify each other simply by
passing, and any circumstance under which they do. And I'll show you how
exactly the same result can be explained without this supposed interaction.

Roy Lewallen, W7EL

Constructive interference in radiowave propagation
 

K7ITM wrote:
So what? Roy didn't say that was difficult at all. Now answer the
REST of Roy's parapgraph which you so conveniently failed to include
in your quoted material.

I will be glad to if you will tell me specifically what
"REST of Roy's paragraph" you are talking about.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Roy Lewallen wrote:
Show me how waves can modify each other simply by
passing, and any circumstance under which they do.

STRAW MAN ALERT! Nobody has said that passing waves
can modify each other. The requirements for wave
modification are very well defined. The two waves
must be coherent and traveling in the same direction
in the same path. Under those circumstances wave
modification is impossible to avoid. When the reflected
waves are canceled in the direction of the source by
an antenna tuner or other matching means, those waves
permanently disappear in the direction of the source.
Seems permanent disappearance meets the definition
of being modified.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

On Apr 9, 8:31 am, Cecil Moore wrote:
Keith Dysart wrote:
The junk science is often presented with very rational sounding
arguments and it can be difficult to detect the flaws. This example
was a case for me and you expose the flaw nicely.

Hint to omniscient gurus: One cannot use ignorance
for exposing flaws. Roy says in his Food for Thought
article:

I personally don't have a compulsion to understand where this power "goes".

Seemingly, that feeling of his is supposed to be enough
incentive to discourage the rest of us to give up on our
quest for tracking the energy through the system.

Roy has ploinked me for disagreeing with him. What
does that say about his inability to technically
defend his concepts?

The S-Parameter equations completely debunk what Roy
posted.

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

|b1|^2, the reflected power, equals zero because
of wave cancellation involving those components
of a1 (forward normalized voltage) and a2 (reflected
normalized voltage).

If s11, a1, s12, and a2 are all non-zero, then wave
cancellation has occurred between s11(a1) and s12(a2)
proving Roy's statements to be false. The above wave
cancellation happens every time a ham adjusts his
antenna tuner for zero reflected power.
--
73, Cecil http://www.w5dxp.com


So, for example, if I send 50 watts of a sinusoid down a 50 ohm line,
and there's a transition to a 291.4 ohm line that's half a wave long
at the sinusoid's frequency, terminated in 50 ohms, there's no
reflected power on the 50 ohm line. Cool. I knew that. In re-
reading what Roy wrote, I see NO disagreement with that. But in the
291.4 ohm line, there's 100 watts forward and 50 watts reverse. At
the interface between the two lines, there's a total of 100 watts
coming in: 50 from the 50 ohm line and 50 from the 291 ohm line. And
wonder of wonder, there's 100 watts going out; it happens to all be in
the 291 ohm line.

If you go back to Roy's posting in this thread and look at the WHOLE
paragraph where he issued the challenge (if you want to call it a
challenge), you'll see that you have to come up with an example where
there's a node with different power coming out than going in, to be
disagreein' with him.

Constructive interference in radiowave propagation
 

Roy Lewallen wrote in
:

Owen Duffy wrote:

If in fact the power delivered by the "100 watt IC706" radio was
indeed 100W, and some directional wattmeter correctly indicated 200W
forward, it must indicate 200W-100W reflected which is indicative of
a VSWR of 5.8, which should have reduced power output from the IC706
markedly.
. . .

Nah, no problem.

Connect your rig through a half wavelength of 250 ohm ladder line to a
50 ohm load. Presto, 200 watts "forward power" and 5:1 SWR on the
line, and the poor ignorant Icom doesn't have any hint that all those
waves of power or energy or whatever are bouncing around on the line,
trying desperately but unsuccessfully to overheat the final or
whatever they're supposed to do.

Of course, it would take a 250 ohm directional wattmeter to read that
"forward power" or SWR. But we don' need no steenkin' meter -- we know
it's there, don't we?

Roy Lewallen, W7EL

Roy, I was assuming that the instrument was a nominal 50 ohm instrument
measuring conditions adjacent to the transmitter.

Your workup is correct enough for the case you describe (though for
Pf/Pref=2, VSWR=5.8).

Of course, if you had a coaxial reflectometer calibrated (nulled) for 8.6
ohms or 290 ohms then you would get the same indications on a 50 ohm
load, you don't actually need the 8.6 ohm or 290 ohm transmission line.

These are just examples that question the reality of these "component
powers" when you can change their magnitude by choosing the reference
impedance for measurement or calculation. They reinforce the view that
whilst Pf-Pr has meaning (irrespective of Z), Pf and Pr each alone have
no meaning.

Owen

Constructive interference in radiowave propagation
 

"K7ITM" wrote in
oups.com:

On Apr 9, 4:59 pm, Owen Duffy wrote:
Cecil Moore wrote
. net:

Jim Kelley wrote:
And so that's your explanation for how 2 Joules per second can be
obtained from a source which is in fact producing only 1 Joule per
second.

Of course, I regularly obtain 200 watts of forward
power from my 100 watt IC-706. It's all due to
constructive interference.

If in fact the power delivered by the "100 watt IC706" radio was
indeed 100W, and some directional wattmeter correctly indicated 200W
forward, it must indicate 200W-100W reflected which is indicative of
a VSWR of 5.8, which should have reduced power output from the IC706
markedly.

Taking another view, if the IC706 will tolerate VSWR of 2 before
reducing power (ie and still deliver exactly 100W), then the forward
power would be just 113W.

More likely, the IC706 levels its power output on the forward
detector, and runs 100W "forward" until the reflected power reaches
about 12W whereupon it reduces drive so maintain maximum reflected
power =12W.

Did you make this example up on the fly, or is it the result of
actual observation on one or many occasions?

Owen

Let's see... 600 ohm line feeding a nominally 60 ohm dipole. (It's
not very high above the ground.) 600 ohm line is 1/2 wave long, and
essentially lossless. I feed 60 watts in, the 60 ohm dipole absorbs
60 watts. I suppose the forward power on the line is a bit more than
60 watts. My transmitter doesn't seem to have too much trouble with
the 60 ohm load, though a balun between the unbalanced transmitter
output and the balanced line is nice.


Tom, as I noted in another response, I assumed that the observation was
based on measurement with a nominal 50 ohm instrument adjacent to the
transmitter.

You can of course re-evaluate the forward and reflected power components
in a 50 ohm load by changing the reference impedance, and so make them
anything you want. Cecil didn't suggest a specific reference impedance,
so knowing that the IC706 is designed for a nominal 50 ohm load, it
seemed reasonable to make the assumptions that I did.

Owen