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On 19 May 2006 10:14:30 -0700, wrote:
I would like to hear from someone who has actually measured the
linearity of a simple antenna. I have not done this, so would only be
one guy with an opinion. Plenty of us around.

Hi Glenn,

Then you have a point in that regard. Bench work is rarely offered
here and when it is, we are lucky if it is accompanied with the
particulars of measurement so that it could be assessed or
re-performed. It took very many years between cfa antenna claims, and
legitimate field work by cfa proponents to show that their claims were
unsupported.

By 'simple antenna' I mean an antenna such as a wire dipole without
traps, baluns or other things that could degrade linearity. Since the
linearity of antenna systems in general is in question, the simplest
setup that answers the question would be best.

Well, a BalUn is one of those elements that would be welcome so as to
enforce the simplicity you demand, and so as to not disturb what is
being measured. The BalUn (more properly, a choke) for this purpose
would be for isolating the antenna from the transmission line.

In the absence of measurement, can anyone comment on the modelling
software? Does it assume and model a linear system? If so, do we know
of any substantial nonlinear departures from the modelling software?

The modelers using NEC generally obtain results that conform to
observable phenomenon. The modelers are supposed to be neutral
observers. In other words, the non-linearity shown by the lack of
congruence to the Cosine curve is not a presumption of non-linearity
by the modeler; it is merely reporting an analysis. It may be noted
that this analysis has been supported by a combination of bench work
and theory.

All of this is the long way of saying non-linearity has been
demonstrated, that is has been measured, and that it has been long
explained. There are no surprises here.

73's
Richard Clark, KB7QHC

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"Richard Clark" wrote in message
...
On 19 May 2006 03:26:29 -0700, wrote:

I do not agree with you on antenna linearity, but that is another
subject for another rainy weekend, and I'm not the right person to be
discussing that anyway.

Hi Glenn,

By this very post you are discussing it.

Who, in your estimation, does qualify to discuss it? Despite all
outward appearances (and certainly the troll inspired name of the
topic), this is NOT about one-upmanship competition.

73's
Richard Clark, KB7QHC

don't you call me a troll... i just set the stage with an aptly named thread
to get things started for my own amusement... wait a minute, maybe that
does make me a troll! but at least i was open about my motives, and boy am
i enjoying it.... especially since its still raining! maybe you guys can
keep going through this weekend???

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Cecil Moore wrote:

wrote:

By 'simple antenna' I mean an antenna such as a wire dipole without
traps, baluns or other things that could degrade linearity.


Seems the easiest measurement of nonlinearity would be the
harmonics (if any) generated by the antenna that do not
appear in the source signal.

Which wouldn't tell you a single thing about the current
distribution along the length of the dipole.
73,
Tom Donaly, KA6RUH

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Richard Clark wrote:

On Fri, 19 May 2006 15:08:11 GMT, "Tom Donaly"
wrote:


Stokes' law and the Raman effect can be found in
physics texts dealing with quantum mechanics. Georg Joos, in
his book _Theoretical Physics_ deals with such things. The reading
is dense but the underlying concepts aren't too difficult. The
difficulty might lie in understanding how they apply to this
discussion.


Hi Tom,

Certainly Joos would give some entry into the field, but finding work
as accessible outside of a bookstore or library (in other words,
through a search engine) makes for drinking out of a fire hose to
quench a sip's worth of thirst.

Insofar as HOW this applies, I've spoken to that and Tom shows
interest. That alone goes beyond the typical churning that passes for
discussion. The point is that these underlying concepts are fairly
simple as you imply and they are certainly not remote from the usual
topics of consideration here. What they lack is specifics that relate
to our common applications, and there too I've offered discussion.
However, few seem inspired to travel those paths and that fault can
hardly be laid at my doorstep.

73's
Richard Clark, KB7QHC

Hi Richard,
I didn't intend any criticism. People like Cecil, with
home-grown theories, don't ever seem to want things considered in
depth. That's understandable from a psychological standpoint, but
it isn't any help to the rest of us when some of the things the theory
ignores become significant. In the case of antennas, practically
everything is significant.
73,
Tom Donaly, KA6RUH

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Reg,

Thank heavens there is someone here who knows the Queen's English.

Glenn

========================================
The trouble with Richard is that he wraps everything up in
Shakespearian prose, verse and poetry. The sonnets. Queen Elizabeth
the First's language.
----
Reg.

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On Fri, 19 May 2006 19:01:23 GMT, "Tom Donaly"
wrote:

In the case of antennas, practically everything is significant.

Les Mots Juste ;-)

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Richard Clark wrote:

On Fri, 19 May 2006 15:08:11 GMT, "Tom Donaly"
wrote:


Stokes' law and the Raman effect can be found in
physics texts dealing with quantum mechanics. Georg Joos, in
his book _Theoretical Physics_ deals with such things. The reading
is dense but the underlying concepts aren't too difficult. The
difficulty might lie in understanding how they apply to this
discussion.


Hi Tom,

Certainly Joos would give some entry into the field, but finding work
as accessible outside of a bookstore or library (in other words,
through a search engine) makes for drinking out of a fire hose to
quench a sip's worth of thirst.

Insofar as HOW this applies, I've spoken to that and Tom shows
interest. That alone goes beyond the typical churning that passes for
discussion. The point is that these underlying concepts are fairly
simple as you imply and they are certainly not remote from the usual
topics of consideration here. What they lack is specifics that relate
to our common applications, and there too I've offered discussion.
However, few seem inspired to travel those paths and that fault can
hardly be laid at my doorstep.

73's
Richard Clark, KB7QHC

And a web search produced a couple very good links out of the first 20.
One was a great discussion of problems in long optical fibers, and
some relatively simple ways to work around some of them, or at least to
mitigate them.

tom
K0TAR

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On Fri, 19 May 2006 14:24:07 -0500, Tom Ring
wrote:
And a web search produced a couple very good links out of the first 20.
One was a great discussion of problems in long optical fibers, and
some relatively simple ways to work around some of them, or at least to
mitigate them.

Hi Tom,

In my early days in this game (late 80s), I sought to turn lemons into
quantum-aide. That is, I sought erbium doped fiber optics to amplify
nanowatt fluorescence signals with 10 to 50 µS decay times. Not one
of those off-the-shelf commodities, however; so I had to amplify in
the conventional way with an PMT.

For those interested, long haul communications fiber optics
(transoceanic grade) met with the same requirements for amplifiers
placed along the length to maintain S+N/N. Erbium doped fibers were
projected as a solution. You could pulse UV into the fiber to charge
it, and a IR data pulse would be amplified, continuously along its
length. The IR data pulse would be boosted by the previous charge of
energy. This is an example of forward Raman scattering and is called
Raman Amplification (which at the time would have been about 30dB and
10% efficient).

73's
Richard Clark, KB7QHC

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Tom Donaly, KA6RUH wrote:
"Actually, it`s supposed to be impossible to represent the current
distribution along a dipole using simple mathematical formulas because
integral equations have to be solved that are impervious to any solution
other than numerical approximation."

How many places do you attach to pi?

First, what is linearity? It is the absence of nonlinearity.

Millman and Seely wrote on page 525 of the 1951 edition of "Electronics"
(one of my old textbooks):
"Because of this nonlinear characteristic of the dynamic curve over the
operating range, the wave form of the output wave differs slightly from
that of the grid-exciting-voltage waveshape. Distortion of this type is
called "nonlinear" or "amplitude" distortion.."

All of the antennas I`ve worked with had no noticeable amplitude
distortion. They caused no harmonics or mixing products.

On page 235 of Kraus` 1950 edition of "Antennas" he sets out to solve
Hallen`s equation for current distribution. On page 239, Kraus writes:
"It is generally assumed that the current distribution of an
infinitesimally thin antenna is sinusoidal, and that the phase is
constant over a 1/2-wavelength interval, changing abruptly by
180-degrees between intervals."

You can take what Kraus says to the bank.

Best regards, Richard Harrison, KB5WZI