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May 19th 06, 11:08 PM posted to rec.radio.amateur.antenna

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

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