Cecil Moore wrote:

Jim Kelley wrote:

I don't think it matters where it is, or how much space is involved.
For a single source to create an interferernce pattern, there must be
a reflector somewhere. An antenna tuner for example. Interference is
the result of the overlap of waves.


Do you consider a dipole in free space to be
a "single source"? There is no reflector yet
there is plenty of interference.

If there is no reflector and no splitter to redirect a portion of the
ratiated energy, but an interference pattern still results, then there
must be more than a single source. It should be fairly obvious that
both parts of the antenna must be present in order to generate the
dipole-type interference pattern.

73, ac6xg

On Oct 31, 12:08 pm, Jim Kelley wrote:
Owen Duffy wrote:
Jim Kelley wrote in
:

Owen Duffy wrote:

Jim Kelley wrote in news:fg8c3e$kbc$1
:

I don't think it matters where it is, or how much space is involved.
For a single source to create an interferernce pattern, there must be
a reflector somewhere. An antenna tuner for example. Interference
is the result of the overlap of waves.

Jim, could a diffractor or refractor provide the physical device that
might lead to interference?

Owen

I am almost certain that you already know the answer to that
question, so I'm left to wonder why you are asking it.

No, I am not certain, and in the interest of learning from you I am
questioning the generality of whether a reflector is the only means of
creating interference from a single source.

Owen

Fair enough, Owen. The easiest way I can think of to demonstate
interference of light is with a laser and a pair of narrow, closely
spaced slits. A diffration grating is essentially an array of
slit-like reflectors that generates a more complex type of
interference pattern. You could use one of the internal surfaces of a
prism (refractor) as a reflector. Partially reflective beam splitters
or mirrors are often used in interfereometers. And there are of
course methods by which to create sonic interference. The simplest
way is to wire a pair of stereo speakers out of phase and observe the
frequency dependent phase cancellation effect by listening to music at
different positions and speaker separations.

There are any number of possible ways to generate interference
phenomena, all of which utilize real physical objects to redirect
radiation. It is the real physical objects used to create the
interference pattern that redirect energy.

73, ac6xg

You can also use pure refraction--for example through multiple prisms
whose output face is not parallel with the input face, to bend the
light around as many total degrees as you wish (barring attenuation in
the prism). You can also bend the light away, and then back, to get a
displacement. But I suppose in all these, the effect depends on waves
coming from what appear to be different points in space.

Of course, it does not require coherent sources to see the effects of
interference. Interference is an instantaneous effect, and you can
take the average over a single cycle to see the power. So even with
sources on slightly different frequencies, it's easy to see the
pattern. However, with different frequencies, the pattern is ever-
changing, repeating when the sources are all back to the starting
phase.

As H.A.S. says, "waves of average nausea" or maybe it's becoming
intense nausea. Are we sea-sick yet? Or just sick and tired of it.

Cheers,
Tom

Jim Kelley wrote:
Do you consider a dipole in free space to be
a "single source"? There is no reflector yet
there is plenty of interference.

If there is no reflector and no splitter to redirect a portion of the
ratiated energy, but an interference pattern still results, then there
must be more than a single source. It should be fairly obvious that
both parts of the antenna must be present in order to generate the
dipole-type interference pattern.

Just trying to understand - are you considering the two
sections of dipole to be two separate sources?
--
73, Cecil http://www.w5dxp.com

K7ITM wrote:
Of course, it does not require coherent sources to see the effects of
interference.

True, but it does require coherent waves to accomplish
the permanent wave cancellation described at:

micro.magnet.fsu.edu/primer/java/scienceopticsu/interference/waveinteractions/index.html

"... when two waves of equal amplitude and wavelength that are
180-degrees ... out of phase with each other meet, they are not actually
annihilated, ... All of the photon energy present in these waves must
somehow be recovered or redistributed in a new direction, according to
the law of energy conservation ... Instead, upon meeting, the photons
are redistributed to regions that permit constructive interference, so
the effect should be considered as a redistribution of light waves and
photon energy rather than the spontaneous construction or destruction of
light."

This is what happens to the reflected waves at a Z0-match
in a transmission line.
--
73, Cecil http://www.w5dxp.com

K7ITM wrote:

On Oct 31, 12:08 pm, Jim Kelley wrote:

Owen Duffy wrote:

Jim Kelley wrote in
:

Owen Duffy wrote:

Jim Kelley wrote in news:fg8c3e$kbc$1
:

I don't think it matters where it is, or how much space is involved.
For a single source to create an interferernce pattern, there must be
a reflector somewhere. An antenna tuner for example. Interference
is the result of the overlap of waves.

Jim, could a diffractor or refractor provide the physical device that
might lead to interference?

Owen

I am almost certain that you already know the answer to that
question, so I'm left to wonder why you are asking it.

No, I am not certain, and in the interest of learning from you I am
questioning the generality of whether a reflector is the only means of
creating interference from a single source.

Owen

Fair enough, Owen. The easiest way I can think of to demonstate
interference of light is with a laser and a pair of narrow, closely
spaced slits. A diffration grating is essentially an array of
slit-like reflectors that generates a more complex type of
interference pattern. You could use one of the internal surfaces of a
prism (refractor) as a reflector. Partially reflective beam splitters
or mirrors are often used in interfereometers. And there are of
course methods by which to create sonic interference. The simplest
way is to wire a pair of stereo speakers out of phase and observe the
frequency dependent phase cancellation effect by listening to music at
different positions and speaker separations.

There are any number of possible ways to generate interference
phenomena, all of which utilize real physical objects to redirect
radiation. It is the real physical objects used to create the
interference pattern that redirect energy.

73, ac6xg


You can also use pure refraction--for example through multiple prisms
whose output face is not parallel with the input face, to bend the
light around as many total degrees as you wish (barring attenuation in
the prism). You can also bend the light away, and then back, to get a
displacement. But I suppose in all these, the effect depends on waves
coming from what appear to be different points in space.

Of course, it does not require coherent sources to see the effects of
interference. Interference is an instantaneous effect, and you can
take the average over a single cycle to see the power. So even with
sources on slightly different frequencies, it's easy to see the
pattern. However, with different frequencies, the pattern is ever-
changing, repeating when the sources are all back to the starting
phase.

As H.A.S. says, "waves of average nausea" or maybe it's becoming
intense nausea. Are we sea-sick yet? Or just sick and tired of it.

Yes, in the future we should try to better refinine our
generalizations to include any means which can be used to redirect one
or more paths of radiated energy (not including particles with rest
mass greater than zero) in such a way as to be coincident at some
point in space. Lest we allow ourselves to stray too far from it, the
only point attempting to be noticed here is that all such means must
be physical objects and not photons, waves, or interference patterns
created by any or all the above. Disclaimer: This is neither a new
nor a unique concept.

73, ac6xg

Jim Kelley wrote:


Cecil Moore wrote:

Jim Kelley wrote:

I don't think it matters where it is, or how much space is involved.
For a single source to create an interferernce pattern, there must be
a reflector somewhere. An antenna tuner for example. Interference
is the result of the overlap of waves.


Do you consider a dipole in free space to be
a "single source"? There is no reflector yet
there is plenty of interference.

If there is no reflector and no splitter to redirect a portion of the
ratiated energy, but an interference pattern still results, then there
must be more than a single source. It should be fairly obvious that
both parts of the antenna must be present in order to generate the
dipole-type interference pattern.

73, ac6xg

A dipole is by no means a single (point) source. Each tiny part of the
dipole creates a field proportional to the current at that tiny part, so
in effect it behaves like an infinite number of sources which are spread
out in space along the dipole conductors. Interference of all those
various fields is what creates the familiar dipole radiation pattern. In
fact, moment method antenna analysis programs such as NEC and EZNEC
break the antenna into a finite number of segments and calculate the
current (magnitude and phase) on each segment. It then calculates the
field produced by each segment according to its length, orientation, and
current. The sum of the fields is shown as the radiation pattern. This
process can be done manually as well.

The hypothetical isotropic radiator is a point source. It has a
perfectly spherical pattern because there's no interference.

Roy Lewallen, W7EL

Cecil Moore wrote:

Jim Kelley wrote:

Do you consider a dipole in free space to be
a "single source"? There is no reflector yet
there is plenty of interference.


If there is no reflector and no splitter to redirect a portion of the
ratiated energy, but an interference pattern still results, then there
must be more than a single source. It should be fairly obvious that
both parts of the antenna must be present in order to generate the
dipole-type interference pattern.


Just trying to understand - are you considering the two
sections of dipole to be two separate sources?

I think I know what you want me to say, but I need you to go first.
How many sources is a monopole? :-)

jk

Cecil Moore wrote:
K7ITM wrote:
Of course, it does not require coherent sources to see the effects of
interference.

True, but it does require coherent waves to accomplish
the permanent wave cancellation described at:

micro.magnet.fsu.edu/primer/java/scienceopticsu/interference/waveinteractions/index.html


"... when two waves of equal amplitude and wavelength that are
180-degrees ... out of phase with each other meet, they are not actually
annihilated, ... All of the photon energy present in these waves must
somehow be recovered or redistributed in a new direction, according to
the law of energy conservation ... Instead, upon meeting, the photons
are redistributed to regions that permit constructive interference, so
the effect should be considered as a redistribution of light waves and
photon energy rather than the spontaneous construction or destruction of
light."

This is what happens to the reflected waves at a Z0-match
in a transmission line.

Cecil,

The FSU website you like to reference is a perfect example of the
problem Jim is describing.

As shown, the FSU demonstration is physically impossible. There is no
way for two plane waves to be trucking along independently and then
suddenly decide to interfere.

There is basically nothing wrong with the demo as far as it goes; it
nicely shows the effects of combined phase and amplitude on the
resulting wave. However, the demo is not rigorous science or
mathematics. It is not suitable as an authoritative reference.

73,
Gene
W4SZ

Jim Kelley wrote:
I think I know what you want me to say, but I need you to go first. How
many sources is a monopole? :-)

As many segments as are specified using EZNEC.
Does that help?
--
73, Cecil http://www.w5dxp.com

Gene Fuller wrote:
As shown, the FSU demonstration is physically impossible. There is no
way for two plane waves to be trucking along independently and then
suddenly decide to interfere.

They do NOT "truck along and then suddenly decide to
interfere". Such nonsense is just a strawman presented
for the purpose of obfuscating the technical facts.

The two independent waves are generated at a physical
impedance discontinuity, the Z0-match point, and are
immediately canceled at that point. The energy in the
canceled waves is redistributed in the only other
direction possible in a one-dimensional transmission
line.

Exactly the same thing happens when the external
reflection is canceled by the internal reflection
at a non-reflective 1/4WL thin-film coating on
glass. Quoting the Melles Groit web page:

"In the absence of absorption or scatter, the principle
of conservation of energy indicates all 'lost' reflected
intensity will appear as enhanced intensity in the
transmitted beam."

i.e. the energy re-reflected at the Z0-match joins the
forward wave toward the load. The conservation of energy
principle will not allow any other result. Dr. Best's
phantom waves continuing to flow toward the source with
zero energy is just a wet dream.
--
73, Cecil http://www.w5dxp.com