On Jan 23, 8:35*am, Cecil Moore wrote:
Yes, signals traveling in opposite directions don't interfere.
Call this assertion A.

Consider two antennas several wavelengths apart and driven with
the same frequency. Exploring the field strength far from the
antennas we find regions with zero field strength (nulls) and
regions with increased field strength. This variation in field
strength is usually ascribed to interference and the pattern
of variation is often called an interference pattern.

Similar results can be observed with light (google "two slit
experiment").

Locate one of these nulls far from the antennas and follow it
back towards the antennas. Eventually you will be on a line
between the two antennas.

From assertion A above, is it your contention that far from
the antennas it is "interference" that causes the variation
in field strength, but that on the line drawn between the two
antennas some other mechanism is responsible?

If so, what is the other mechanism? And does it only work
exactly on the line, or does it start working when you get
close to the line? How close?

Now I suggest that interference works just as well on the
line drawn between the antennas as it does every where
else and the conditions along that line are not a special
case.

That said, when we look at the two slit experiment, it is
generally agreed that the photons are redistributed such
that there are no photons in dark regions and more photons
in the bright regions.

On the line drawn between the two antennas, there are dark
regions and bright regions (the standing wave). By analogy,
there are no photons in the dark regions and more in the
bright regions. But the photons from the two sources were
travelling towards each other. What is the mechanism that
redistributes the photons such that there are none in the
dark regions? Do the photons stop and not enter the dark
region? Or do they turn into 'dark photons' as they
transit the dark regions? What are 'dark photons'?

...Keith

Keith Dysart wrote:
From assertion A above, is it your contention that far from
the antennas it is "interference" that causes the variation
in field strength, but that on the line drawn between the two
antennas some other mechanism is responsible?

Of course not - please don't be ridiculous. If the two
antenna elements were isotropic point sources, on a
line drawn between them, there could be no interference
and there would be only standing waves in free space
along that line assuming no reflections from nearby
objects, etc.

Everywhere else there are components of waves traveling
in the same direction so interference is possible anywhere
except on that line between the point sources. When the
sources are not a point, seems to me, interference could
occur at any and all points in space.

My "assertion A above" was about transmission lines,
an essentially one-dimensional context. Two waves in
a transmission line are either traveling in opposite
directions or in the same direction.

Incidentally, I came across another interesting quote
from one of my college textbooks, "Electrical Communication",
by Albert. "Such a plot of voltage is usually referred to
as a *voltage standing wave* or as a *stationary wave*. Neither
of these terms is particularly descriptive of the phenomenon.
A *plot* of the effective values of voltage ... is *not a wave*
in the usual sense. However, the term "standing wave" is in
wide-spread use." [Emphasis is the author's]
--
73, Cecil http://www.w5dxp.com

On Jan 23, 1:12*pm, Cecil Moore wrote:
Keith Dysart wrote:
From assertion A above, is it your contention that far from
the antennas it is "interference" that causes the variation
in field strength, but that on the line drawn between the two
antennas some other mechanism is responsible?

Of course not - please don't be ridiculous. If the two
antenna elements were isotropic point sources, on a
line drawn between them, there could be no interference
and there would be only standing waves in free space
along that line assuming no reflections from nearby
objects, etc.

Everywhere else there are components of waves traveling
in the same direction so interference is possible anywhere
except on that line between the point sources. When the
sources are not a point, seems to me, interference could
occur at any and all points in space.

OK. So it is your contention that "far from the antennas
it is "interference" that causes the variation in field
strength, but that on the line drawn between the two
antennas some other mechanism is responsible".

But why do you say "Of course not" and then proceed to
paraphrase my statement?

When the mechanism abruptly changes from interference
when off the line to "standing wave" when EXACTLY (how
exact?) on the line, is there any discontinuity in
the observed field strengths?

...Keith

Keith Dysart wrote:
OK. So it is your contention that "far from the antennas
it is "interference" that causes the variation in field
strength, but that on the line drawn between the two
antennas some other mechanism is responsible".

It is unethical to bear false witness about what I said.
What I said was:

On a line drawn between two *isotropic point sources*,
when there are no reflections anywhere around, along
that line, interference is impossible. The only thing
existing along that line would be standing waves.
There is no point along that line where the power
density is not equal to the sum of the two sources,
i.e. there is superposition but no interference along
that line.

If the elements are not point sources, interference
is obviously possible at each and every point. I assume
your example elements are not point sources so what you
claimed was my contention was a false statement. If
you can't win the arguments without making false
statements about what I said, you lose anyway.
--
73, Cecil http://www.w5dxp.com

On Jan 23, 1:46*pm, Cecil Moore wrote:
Keith Dysart wrote:
OK. So it is your contention that "far from the antennas
it is "interference" that causes the variation in field
strength, but that on the line drawn between the two
antennas some other mechanism is responsible".

It is unethical to bear false witness about what I said.
What I said was:

On a line drawn between two *isotropic point sources*,
when there are no reflections anywhere around, along
that line, interference is impossible. The only thing
existing along that line would be standing waves.

And you also wrote:
Everywhere else there are components of waves traveling
in the same direction so interference is possible anywhere
except on that line between the point sources.

I am having great difficulty finding any difference
between my writing:

So it is your contention that "far from the antennas
it is "interference" that causes the variation in field
strength, but that on the line drawn between the two
antennas some other mechanism is responsible".

and your paraphrase.

...Keith

Keith Dysart wrote:
I am having great difficulty finding any difference
between my writing:

So it is your contention that "far from the antennas
it is "interference" that causes the variation in field
strength, but that on the line drawn between the two
antennas some other mechanism is responsible".

and your paraphrase.

The difference is that your example contained elements
that are not zero dimensions. My assertions covered only
antenna elements of zero dimensions. I repeat:

On a line drawn between two coherent isotropic radiators,
in the absence of any reflections, interference along
that line is impossible because the average total
power density all along that line is constant.
There is no interference in standing waves given
"interference" as defined by Eugene Hecht in "Optics".
--
73, Cecil http://www.w5dxp.com

On Jan 23, 2:21*pm, Cecil Moore wrote:
Keith Dysart wrote:
I am having great difficulty finding any difference
between my writing:

* So it is your contention that "far from the antennas
* it is "interference" that causes the variation in field
* strength, but that on the line drawn between the two
* antennas some other mechanism is responsible".

and your paraphrase.

The difference is that your example contained elements
that are not zero dimensions. My assertions covered only
antenna elements of zero dimensions. I repeat:

On a line drawn between two coherent isotropic radiators,
in the absence of any reflections, interference along
that line is impossible because the average total
power density all along that line is constant.
There is no interference in standing waves given
"interference" as defined by Eugene Hecht in "Optics".

So then, for "two coherent isotropic radiator",
it is your contention that "far from the antennas
it is "interference" that causes the variation in field
strength, but that on the line drawn between the two
antennas some other mechanism is responsible".

...Keith

"Cecil Moore" wrote
Keith Dysart wrote:
From assertion A above, is it your contention that far from
the antennas it is "interference" that causes the variation
in field strength, but that on the line drawn between the two
antennas some other mechanism is responsible?

Of course not - please don't be ridiculous. If the two
antenna elements were isotropic point sources, on a
line drawn between them, there could be no interference
and there would be only standing waves in free space
along that line assuming no reflections from nearby
objects, etc.
______________

Cecil, hopefully you understand that even isotropic radiators near each
other and excited on the same frequency with the same amount of power will
generate far-field pattern nulls.

Maybe I'm misunderstanding you.

RF

Richard Fry wrote:
Cecil, hopefully you understand that even isotropic radiators near each
other and excited on the same frequency with the same amount of power will
generate far-field pattern nulls.

Maybe I'm misunderstanding you.

I'm trying to understand how a line drawn between two
"isotropic radiators near each other" could ever be
in the far field.
--
73, Cecil http://www.w5dxp.com

"Cecil Moore wrote
Richard Fry wrote:
Cecil, hopefully you understand that even isotropic radiators near each
other and excited on the same frequency with the same amount of power
will generate far-field pattern nulls.

Maybe I'm misunderstanding you.

I'm trying to understand how a line drawn between two
"isotropic radiators near each other" could ever be
in the far field.
_______________

Everywhere it exceeds 2*D^2/lambda in length, where D is the greatest
dimension of the array.

RF