Richard Fry wrote:
It isn't necessary for the radiators to be in each other's far field.

I'm just trying to understand your point. You said there
are nulls in the far field. If the radiators are not in
each other's far fields, how could the line drawn between
them be in the far field?
--
73, Cecil http://www.w5dxp.com

Keith Dysart wrote:
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".

Please define "field strength". The total average
power density along a line drawn between the two
point sources is constant, i.e. the average sum
of the energy in the E-field and H-field is
constant. If you are defining "field strength"
as only the E-field, of course standing waves
are the cause, not interference, as defined by
Hecht in "Optics".
--
73, Cecil http://www.w5dxp.com

"Cecil Moore" wrote
I'm just trying to understand your point. You said there
are nulls in the far field. If the radiators are not in
each other's far fields, how could the line drawn between
them be in the far field?


X Iso source 1

=================== to far field, where nulls will exist

X Iso source 2,
1 lambda from
Iso source 1



RF

Richard Fry wrote:
"Cecil Moore" wrote
I'm just trying to understand your point. You said there
are nulls in the far field. If the radiators are not in
each other's far fields, how could the line drawn between
them be in the far field?


X Iso source 1

=================== to far field, where nulls will exist

X Iso source 2,
1 lambda from
Iso source 1

No, no, no, Richard. The line is drawn from one source to
the other source. Your line is not drawn from either
source to the other source.
--
73, Cecil http://www.w5dxp.com

"Cecil Moore" wrote
No, no, no, Richard. The line is drawn from one source to
the other source. Your line is not drawn from either
source to the other source.
__________

Obviously we are not talking about the same net radiations patterns.

Carry on.

RF

Richard Fry wrote:
"Cecil Moore" wrote
No, no, no, Richard. The line is drawn from one source to
the other source. Your line is not drawn from either
source to the other source.

Obviously we are not talking about the same net radiations patterns.

Sorry about that. English semantics strikes again. Your
line was indeed "between" the two sources but not the
"from - to" line that I had in mind when I said "between". :-)
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Gene Fuller wrote:
Why do you attribute such magic to the word "interference"? Do you
think that Hecht's "interaction" is any different than superposition?

It is not magic. "Interference" and "superposition" simply
have different definitions.

Interference is a subset of superposition, i.e. interference
cannot occur without superposition but superposition can occur
without interference. This subject is covered in every optics
text that I have ever seen, including Born and Wolf. Given two
waves of equal power densities (irradiances) if the resultant
irradiance is not equal to the sum of the two irradiances, then
interference has occurred.

What if the waves are not quite anti-parallel, say at an angle of 179
degrees? Is interference now possible?

Impossible in a transmission line which is the context.
In free space, I would guess that interference is possible
in their common direction of travel.

Suppose the waves are only 1 degree from parallel. Does that negate
the interference?

For coherent waves in free space, that would ensure interference
until the beams diverged. It should result in the usual light
and dark interference rings.

Repeating: This is a distinction with no technical value.

Maybe it would help if you published a video of you waving
your hands as you scream that assertion at the top of your
lungs? :-)

Cecil,

Many people, myself included, treat the term "interference" in a
qualitative manner. The general meaning is that two entities somehow
interact in a noticeable way, and the result has some signature of that
interaction.

You appear to use a very precise, quantitative definition of
"interference." I do not recall ever seeing such a quantitative
definition. Could you please give us a reference or an exact quote from
some reasonably reputable source that defines "interference" in a
quantitative and unambiguous manner?

You imply that some interactions lead to "interference" and some do not.
How can the unwashed among us know when the magic occurs and when it
does not?

73,
Gene
W4SZ

Gene Fuller wrote:

...
You imply that some interactions lead to "interference" and some do not.
How can the unwashed among us know when the magic occurs and when it
does not?

73,
Gene
W4SZ

You mean if I just wash it will increase my ability to understand? D*mn
man, I would NEVER have thought it possible. Indeed, if most were to
suggest that, I would laugh. But, given it is you, ... chuckle

And please, take this as a friendly joke! (albeit a poor one) I tire of
the religiously devout crying "blasphemy" and posting stones and
pitchforks! ROFLOL

Warm regards,
JS

Roy Lewallen wrote:
[... very nice explanation]

Sine waves are another problem -- there, we can easily have
overlapping waves traveling in the same direction, so we'll run into
trouble if we're not careful. I haven't worked the problem yet, but
when I do, the energy will all be accounted for. Either the energy
ends up spread out beyond the overlap region, or the energy lost
during reflections will account for the apparent energy difference
between the sum of the energies and the energy of the sum. You can
count on it!

As always, I appreciate any corrections to either the methodology or
the calculations.

Roy Lewallen, W7EL

How about analyzing a vibrating string? If you play guitar, there's a very
nice note you can make by plucking a high string, then putting your finger
at exactly the correct spot and removing it quickly. The note will jump to
a much higher frequency and give a much purer sound. Clearly, the
mechanical energy has split into two waves that cancel at the node.

In principle, you could show the node is stationary, thus contains no
energy. But there is energy travelling on both sides of the null point -
you can hear it.

You can also create other notes by touching different spots on the
vibrating string. These create standing waves with energy travelling in
both directions, but cancelling at the null points. Very similar to
transmission lines.

Regards,

Mike Monett

Mike Monett wrote:

How about analyzing a vibrating string? If you play guitar, there's a very
nice note you can make by plucking a high string, then putting your finger
at exactly the correct spot and removing it quickly. The note will jump to
a much higher frequency and give a much purer sound. Clearly, the
mechanical energy has split into two waves that cancel at the node.

In principle, you could show the node is stationary, thus contains no
energy. But there is energy travelling on both sides of the null point -
you can hear it.

You can also create other notes by touching different spots on the
vibrating string. These create standing waves with energy travelling in
both directions, but cancelling at the null points. Very similar to
transmission lines.

Regards,

Mike Monett

Sounds like a great idea. I'll look forward to seeing your analysis.

Roy Lewallen, W7EL