Constructive interference in radiowave propagation
 

Jim Kelley wrote:
So do you get the point, or not?

I've always gotten the point. The question is since
you seem to have blown the dust off of Born and Wolf,
do you get the point? Born and Wolf agrees in every
way with Hecht. Total constructive interference yields
an intensity four times the intensity of one individual
wave.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Mike Lucas wrote:
Keith, I really like when junk science gurus exibit
constructive interference, the bafflegab sums to
four times the normal power!

Exactly in accordance with Born and Wolf's equation
(17) in their chapter on "Interference and
Interferometers". Quoting:

"In the special case where I1 = I2, (15) reduces to
I = 4*I1" [for in phase waves].

I'm sorry if you disagree with the laws of physics.
You are not alone in being ignorant of what occurs
when two coherent waves are superposed in phase.
The kicker is that we cannot have two coherent
waves superposed in phase at one location without
having two coherent waves superposed out of phase
somewhere else (assuming no local source).
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Cecil Moore wrote:

Jim Kelley wrote:

So according to your theory I can take a 1 watt laser, split the beam
into two coherent beams, recombine the beams in-phase together along
the same path thus creating constructive interference, and obtain 2
watts of laser power. Or would it be 4 watts?


If it were total constructive interference, two 1/2W
beams would yield an intensity of 2 watts. Of course,
at another location, total destructive interference
would have to occur where the intensity was zero.

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.

As I said before, this ain't rocket science.

That is for damn sure. :-)

Jim AC6XG

Constructive interference in radiowave propagation
 

"Cecil Moore"
The kicker is that we cannot have two coherent
waves superposed in phase at one location without
having two coherent waves superposed out of phase
somewhere else (assuming no local source).
_____________

As shown by the real-world result for the combined r-f system configuration
I posted earlier (and which result I, and many others have measured in real
hardware systems) -- one output port of the 3 dB hybrid combiner when
powers there are equal and in phase (ie, fully coherent) contains twice the
average output power of either tx alone, while the other output port has
zero power. These are exactly the conditions in your quote above.

The conflict here occurs because of your belief that the combined, average
power in this scenario is not 2X, but 4X that of the individual
transmitters.

Or have you changed your mind from what you first posted?

RF

Constructive interference in radiowave propagation
 

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 you have a bright ring exhibiting 2 joules/sec/unit-area
and a dark ring exhibiting zero joules/sec/unit-area,
don't you see how that averages out to the average
source power of one joule/sec?

As I said before, this ain't rocket science.

That is for damn sure. :-)

Glad you (finally after all these years) agree.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Richard Fry wrote:
The conflict here occurs because of your belief that the combined,
average power in this scenario is not 2X, but 4X that of the individual
transmitters.

No, no, no! The combined average power is 2X. The point
of total constructive interference is 4X. The point of
total destructive interference is 0X. The average of
the total constructive interference and the total
destructive interference is 2X. Seems to me that you
have not been reading and understanding my postings.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Cecil Moore wrote in
t:

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

Constructive interference in radiowave propagation
 

Cecil Moore wrote:

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.

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

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.

73, ac6xg

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.
. . .

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

Constructive interference in radiowave propagation
 

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.

Cheers,
Tom