On Fri, 19 May 2006 16:01:53 -0500, (Richard
Harrison) wrote:

"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.."

Hi Richard,

This harkens back to your observation about how many places in Pi.

How much distortion has to exist before you hear it? As this directly
relates to your quoted selection, are we to believe that distortion
does not exist if you cannot perceive it?

This gives a great range of flexibility to the word linear through the
careful selection for tone-deaf judges.

Back in the late 40s, Bell labs experimented with human subjects'
ability to discern distortion. Turns out that they could take quite a
bit (10 to 15%) before they could faithfully call it noticeable. So,
by these stricter standards (Cecil would allow 59% before ringing the
alarm) no distortion exists below 10%.

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

No noticeable "amplitude" distortion? In a world of possible
distortions, does linearity boil down to just one metric? Are you
asking us to believe you anticipated any antenna would be non-linear
and purposely tested them all? Nah, this is wholly unreasonable.

Richard, I frankly doubt you looked for spurs that would have been
70dB down in the worst of circumstances. More overwhelming would be
corroded joints swamping that pursuit.

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.

So is Kraus bankrupt by contrary evidence that presumes he meant his
quote to be taken strictly? Even Kraus hedges with "assumed" and he
does not otherwise force the conclusion, does he? Why indeed would he
for such a trivial topic is the more astute observation.

This entire line of argument (distortion) is wholly specious. This
violates most analysis by demanding that a wavelength sizeable element
conform to lumped expectations. The non-linearity is found along the
entire length of the element, not at a point. The characteristic Z
varies by simple geometrical observation - it doesn't take quantum
mechanics to arrive at this obvious conclusion. The ONLY linear
quarterwave antenna is a biconical dipole - that has been established
since the 40s. Even the Cosine distribution is blatant evidence of
non-linearity (try listening to Mozart with an amp that has a cosine
gain curve). An antenna has to be huge (wavelengths) and close (far
less than a wavelength) to the earth before any linearity begins to
arise - this too is historic.

73's
Richard Clark, KB7QHC

Richard,

Maybe someone can help us here. Linearity is well-defined in
electronics by the law of superposition, and is characterized by
well-known measurements such as harmonic generation, compression point,
and third-order intercept point. I'm assuming antennas must follow the
same law of superposition while transmitting and receiving to be
linear.

It is not clear to me that a nonlinear or even unpredictable current
distribution along a wire antenna produces signals that violate the law
of superposition. Under a strange current distribution the antenna
radiation pattern will certainly distort, but how does that violate the
law of superposition? That is, how can a strong received signal
influence a weak one on an antenna with nonlinear current distribution?

Maybe, like so many other threads in this group, we are discussing
orthogonal concepts.

73,
Glenn AC7ZN

In article .com,
wrote:

Maybe, like so many other threads in this group, we are discussing
orthogonal concepts.

I believe you're correct.

As I see it, in the *general* sense, linearity refers to a
relationship between two variables, where the relationship is one of

OUT = IN * F + C

where F and C are constants (plus a dimensional factor in many cases).
In other words, it's a straight-line relationship (hence, the name)
between two variables of the same or different dimension.

The sort of "linearity" that people usually refer to in electronics,
involves voltages and currents (vs. one another). A theoretically
perfect resistor, capacitor, or inductor is linear, because (e.g.) the
peak current through it has a strictly linear relationship to the peak
voltage across it.

A semiconductor junction is described as nonlinear, because the
current through it is not related to the voltage across it in a
strictly linear relationship.

The sort of "linearity" which Cecil seems to be referring to (if I
understand what he's written correctly) involves a completely
different sort of relationship. It's not current-vs-voltage, or
voltage-vs-current - it's current-vs-distance.

If I recall correctly, an infinitesimally-short "monopole" has a
current-vs-distance relationship which is close to linear. A
half-wave monopole does not.

Nonlinearities of this sort would have entirely different effects on
an antenna system than nonlinearities of the voltage-vs-current sort.

They're two different beasts entirely.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Dave Platt wrote:
The sort of "linearity" which Cecil seems to be referring to (if I
understand what he's written correctly) involves a completely
different sort of relationship. It's not current-vs-voltage, or
voltage-vs-current - it's current-vs-distance.

Assuming thin constant diameter wires with a constant Z0 and VF.

If the diameter of the wire changes, or Z0 changes, or VF changes,
the 'K' term in the cos(KX) expression changes. A change in a
constant does NOT produce non-linearity in a linear system. Just
because a wave slows down in a medium with a low VF doesn't mean
that the system has gone non-linear.
--
73, Cecil http://www.qsl.net/w5dxp

On 19 May 2006 17:09:50 -0700, wrote:

Maybe someone can help us here.

Hi Glenn,

In the half dozen postings that followed this, did you find anything
discussed that helped you? Perhaps orthogonal was the wrong word,
transverse concepts?

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On 19 May 2006 17:09:50 -0700, wrote:

Maybe someone can help us here.

Hi Glenn,

In the half dozen postings that followed this, did you find anything
discussed that helped you? Perhaps orthogonal was the wrong word,
transverse concepts?

73's
Richard Clark, KB7QHC

whatever it is, KEEP IT GOING! just got off the tower after pulling up the
lifting rope and caught up while my legs are recovering... boy its chilly up
there, had to wear my winter coat and hat and gloves! but there are more
showers forecast for this afternoon so i'll need some more fresh reading
material! FIGHT! FIGHT! FIGHT!

On Sat, 20 May 2006 12:14:29 -0000, "Dave" wrote:

KEEP IT GOING!

Dave, your trolling effort is rather a poor substitute for the sense
of accomplishment. Too many do it far better, with more flair, and
offer more entertainment than this pallid use of the CAPS KEYS.

"Richard Clark" wrote in message
...
On Sat, 20 May 2006 12:14:29 -0000, "Dave" wrote:

KEEP IT GOING!

Dave, your trolling effort is rather a poor substitute for the sense
of accomplishment. Too many do it far better, with more flair, and
offer more entertainment than this pallid use of the CAPS KEYS.

I'm just cheering you on... besides if I'm going to troll I might as well
abandon some other parts of decency in the process. And it doesn't seem
like anyone cares, even with the obvious thread title it took off all on its
own.

Richard Clark wrote:
How much distortion has to exist before you hear it? As this directly
relates to your quoted selection, are we to believe that distortion
does not exist if you cannot perceive it?

How about: Distortion can be measured.
--
73, Cecil http://www.qsl.net/w5dxp