On May 9, 2:54 pm, Cecil Moore wrote:

I agree that there is a logical contradiction between standing
waves and electromagnetic waves.

If there is, then there must also be contradiction between traveling
waves and destructive interference, and between two dissonant notes
and the beat they create. They are all simply the result of
superposition. Two things happening at the same time in the same place
with one result. But nothing more.

Take two sound waves of identical frequency and superpose them. The
result is a single waveform. Now decrease the frequency of one just a
bit. They still superpose to create a single waveform but now the net
amplitude varies with time according to the difference in frequency.
Decrease the frequency even more. We still have a single waveform,
and the beat frequency may now be too rapid to easily discern, but now
we can begin to discern two distinct pitches. Look at it on a
spectrum analyzer and we can see each of the two frequencies
individually. Yet all we see on the oscilloscope is one waveform.

Is that the contradiction?

73, Jim AC6XG

"Jim Kelley" wrote in message
ps.com...
On May 9, 2:54 pm, Cecil Moore wrote:

I agree that there is a logical contradiction between standing
waves and electromagnetic waves.

If there is, then there must also be contradiction between traveling
waves and destructive interference, and between two dissonant notes
and the beat they create. They are all simply the result of
superposition. Two things happening at the same time in the same place
with one result. But nothing more.

Take two sound waves of identical frequency and superpose them. The
result is a single waveform. Now decrease the frequency of one just a
bit. They still superpose to create a single waveform but now the net
amplitude varies with time according to the difference in frequency.
Decrease the frequency even more. We still have a single waveform,
and the beat frequency may now be too rapid to easily discern, but now
we can begin to discern two distinct pitches. Look at it on a
spectrum analyzer and we can see each of the two frequencies
individually. Yet all we see on the oscilloscope is one waveform.

Is that the contradiction?

73, Jim AC6XG


No, Its an illusion. The same thing happens when you view an AM signal. On
an oscilloscope the pattern you see may give you the impression that the
carrier is changing in amplitude with the modulation. Perhaps standing waves
are this same type of illusion.

Jimmie

On May 10, 6:29 am, "Jimmie D" wrote:
No, Its an illusion. The same thing happens when you view an AM signal. On
an oscilloscope the pattern you see may give you the impression that the
carrier is changing in amplitude with the modulation. Perhaps standing waves
are this same type of illusion.

I am unsure why you would call this an illusion.

The modulated waveform can be accurately described by
(f(t)+1)*cos(2*pi*fc*t) where f(t) is the modulating signal

from which it is easy to discern that the amplitude is changing
with the modulation.

There is often more than one way to describe an observation and
the existence of this description in no way detracts from the
alternative which has a carrier plus and minus the modulating
signal.

Many of the arguments here do seem to be of the form "You
say tomatoe and I say tomatoe", but the important point is
that the appropriate description be used for the problem at
hand. Filter design is probably better done with the latter,
while modulators and envelope detectors are likely better
analyzed with the former.

But I find no reason to declare one to be less of an illusion than
the other.

You are correct though; this is exactly like the arguments
about "standing waves" and "travelling waves". The mathematical
expressions for each accurately describe the voltage and
current distribution on the line, yet some wish to argue that one
description is more real than the other.

They are equally real and equally illusions. The important point
is to choose the one that best helps solve whatever problem is
at hand and not to get carried away with a belief that one is more
real than the other.

....Keith

Keith Dysart wrote:
On May 10, 6:29 am, "Jimmie D" wrote:
No, Its an illusion. The same thing happens when you view an AM signal. On
an oscilloscope the pattern you see may give you the impression that the
carrier is changing in amplitude with the modulation. Perhaps standing waves
are this same type of illusion.

I am unsure why you would call this an illusion.

The modulated waveform can be accurately described by
(f(t)+1)*cos(2*pi*fc*t) where f(t) is the modulating signal

from which it is easy to discern that the amplitude is changing
with the modulation.

There is often more than one way to describe an observation and
the existence of this description in no way detracts from the
alternative which has a carrier plus and minus the modulating
signal.

Many of the arguments here do seem to be of the form "You
say tomatoe and I say tomatoe", but the important point is
that the appropriate description be used for the problem at
hand. Filter design is probably better done with the latter,
while modulators and envelope detectors are likely better
analyzed with the former.

But I find no reason to declare one to be less of an illusion than
the other.

You are correct though; this is exactly like the arguments
about "standing waves" and "travelling waves". The mathematical
expressions for each accurately describe the voltage and
current distribution on the line, yet some wish to argue that one
description is more real than the other.

They are equally real and equally illusions. The important point
is to choose the one that best helps solve whatever problem is
at hand and not to get carried away with a belief that one is more
real than the other.

...Keith


Thank you for nicely elucidating the
distinctions in emphasis between
"science" and engineering, Keith.

I believe a perfect (just to keep this
at an abstract level) SA reveals the
underlying reality of the modulated AM
carrier.

An oscilloscope displays a waveform that
can be mathematically derived from the
underlying reality. On the scope, it is
produced by electronically combining
three (assumed) sine waves. Without the
mathematical or electronic operations, I
suggest the waveform displayed by the
scope does not exist.

Mathematical equivalence between time
and frequency domains does not
demonstrate (in my humble opinion) a
duality in the underlying reality.

In reality, there are only the original
three frequencies which can be
demonstrated by selective filtering.
Whether the oscilloscope waveform is an
illusion is perhaps a semantic issue
since it is an artifact constructed
from, and convertible at will back into
the three continuously existing sine
waves which never surrender their
independent qualities.

Quite a bit of difference from
transmission line standing waves, no?

My $02.

Chuck


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On May 10, 11:25 am, Chuck wrote:
Thank you for nicely elucidating the
distinctions in emphasis between
"science" and engineering, Keith.

I believe a perfect (just to keep this
at an abstract level) SA reveals the
underlying reality of the modulated AM
carrier.

Let me offer two examples.

I turn on my RF signal generator. I turn up the RF Level,
then I turn it down, then up, then down, ....
I can see this varying RF level on my oscilloscope (slow
sweep), and even on my RF voltmeter.
I know I am varying the level of the RF.
But I also know that I could produce exactly the same
output by adding 3 signals of slightly different frequency
together. I am not at all comfortable with saying the latter
is 'real' while the former isn't. I know I was varying the RF
Level.

Or,
I turn on my RF signal generator with some level for 1
minute. I turn it off for a week. I turn it on for one minute.
I turn it off. I compute the Fourier transform. I can create
exactly the same signal by adding all the Fourier terms,
extending forward and backwards in time, forever.
But is this more real than: I turn it on, then off, then
on, then off?

Using these examples, I can find no reason why the
multiple signal explanation is more real than the
varying amplitude explanation. And I suggest, that for
these two cases, the varying amplitude explanation
is probably more useful.

....Keith

Keith Dysart wrote:
On May 10, 11:25 am, Chuck wrote:
Thank you for nicely elucidating the
distinctions in emphasis between
"science" and engineering, Keith.

I believe a perfect (just to keep this
at an abstract level) SA reveals the
underlying reality of the modulated AM
carrier.

Let me offer two examples.

I turn on my RF signal generator. I turn up the RF Level,
then I turn it down, then up, then down, ....
I can see this varying RF level on my oscilloscope (slow
sweep), and even on my RF voltmeter.
I know I am varying the level of the RF.
But I also know that I could produce exactly the same
output by adding 3 signals of slightly different frequency
together. I am not at all comfortable with saying the latter
is 'real' while the former isn't. I know I was varying the RF
Level.

Or,
I turn on my RF signal generator with some level for 1
minute. I turn it off for a week. I turn it on for one minute.
I turn it off. I compute the Fourier transform. I can create
exactly the same signal by adding all the Fourier terms,
extending forward and backwards in time, forever.
But is this more real than: I turn it on, then off, then
on, then off?

Using these examples, I can find no reason why the
multiple signal explanation is more real than the
varying amplitude explanation. And I suggest, that for
these two cases, the varying amplitude explanation
is probably more useful.

...Keith


Well, if I understand, and I often
don't, you are saying that the spectrum
produced by method 1 is
indistinguishable from the spectrum
produced by method 2 and THEREFORE,
neither spectrum alone can be considered
true reality.

I grant immediately that it doesn't
matter how you produce the spectrum.

What is at issue, if I am not mistaken,
is whether the reality is that which is
observed on the scope, vs. that which is
observed on the SA (in the case of an
amplitude modulated carrier, of course).

Abstracting, there are three (by
assumption) coherent sinusoids in the AM
modulation case. Each can be directly
measured and characterized.

A composite of these sinusoids can be
displayed on a scope. Any number of
mathematical or electronic operations
can be performed on the sinusoids, and
the results displayed on a scope.

Usefulness, like convenience, may share
a bed with veracity, but its intentions
should be suspect.

I guess I can continue to assert that
mathematical equivalence between
frequency and time domains is not
evidence to me of an underlying duality
in reality, and you can continue to
assert that to you, it is. And I guess
we could still be friends. ;-)

73,

Chuck





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Chuck wrote:

Keith Dysart wrote:
Using these examples, I can find no reason why the
multiple signal explanation is more real than the
varying amplitude explanation. And I suggest, that for
these two cases, the varying amplitude explanation
is probably more useful.

...Keith


Well, if I understand, and I often don't, you are saying that the
spectrum produced by method 1 is indistinguishable from the spectrum
produced by method 2 and THEREFORE, neither spectrum alone can be
considered true reality.

What he said is neither case is less real than the other. It's simply
two different ways of describing the same thing. Have a look at a
table of trigonometric identities. It is a list of different ways of
saying the same thing, mathematically. Each is real in one way or
another, but not necessarily in the same way.

I guess I can continue to assert that mathematical equivalence between
frequency and time domains is not evidence to me of an underlying
duality in reality, and you can continue to assert that to you, it is.

I guess that would depend on what underlying duality you are inferring
from the mathematical equivalence. Not that it necessarily applies
here, but one of the problems we frequently face here on the newsgroup
is a direct result of incorrect inference.

And I guess we could still be friends. ;-)

One of the great contributors to the ham radio newsgroups used to
remind us that "a gentleman is a man who can disagree without being
disagreeable". The challenge then is to remain agreeable amidst a
barrage of disagreeable comments.

73, Jim AC6XG

Jim Kelley wrote:
Cecil Moore wrote:
I agree that there is a logical contradiction between standing
waves and electromagnetic waves.

Is that the contradiction?

You obviously misunderstood what I was trying to say
so let me expand my statement:

Since contradictions do not exist in reality, any
apparent contradiction between standing EM waves and
traveling EM waves has to exist only in the human mind.
There is no contradiction in the real world. The photons
in a standing wave are moving at the speed of light,
c*VF, not standing still in the standing wave. Believing
that the component traveling waves cease to exist is
the contradiction and cannot occur in reality.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Jim Kelley wrote:
Cecil Moore wrote:
I agree that there is a logical contradiction between standing
waves and electromagnetic waves.

Is that the contradiction?

You obviously misunderstood what I was trying to say
so let me expand my statement:

Since contradictions do not exist in reality, any
apparent contradiction between standing EM waves and
traveling EM waves has to exist only in the human mind.
There is no contradiction in the real world. The photons
in a standing wave are moving at the speed of light,
c*VF, not standing still in the standing wave. Believing
that the component traveling waves cease to exist is
the contradiction and cannot occur in reality.

Cecil,

Why do you seem to believe that bringing photons into the discussion
adds any light? (pun intended)

Does the word "photon" sound more hifalutin than "wave"?

It is instructive to follow the lead of Kraus. In the second edition of
"Antennas", on page 19, Kraus notes, "In simplest terms an antenna
converts photons to currents or vice versa."

He then goes on to write nearly 900 pages, and it is not apparent that
he ever again mentions "photon". I did not find any cases in a quick review.

Have you ever seen any technical treatment of HF radiation that actually
used photons in the equations?

73,
Gene
W4SZ

Gene Fuller wrote:
Why do you seem to believe that bringing photons into the discussion
adds any light? (pun intended)

Does the word "photon" sound more hifalutin than "wave"?

Using "photons" instead of "EM waves" makes things a little
more obvious. While "standing EM waves" may imply EM waves
that are standing still, "standing photons" are obviously
impossible. Photons cannot stand still. EM waves cannot
stand still for the same reason. A "standing EM wave" is
a human abstraction that doesn't really exist in reality.

The only people with something to gain by objecting to
the use of "EM waves" and "photons" interchangeably are the
people trying to hoodwink the uninitiated into believing
that photons can stand still. :-)
--
73, Cecil, w5dxp.com