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Richard Clark · June 17th 08, 11:47 PM posted to rec.radio.amateur.antenna

On Tue, 17 Jun 2008 17:08:12 -0500, (Richard
Harrison) wrote:

Owen has it wrong. The final amplifier is linear because its output is
an exact replica of its input except for amplitude, or close enough so.

Hi Richard,

This is a presumption that is either not in evidence, or it is forced
by the necessity of your argument. Consider:

When the waveshape of the output signal from an amplifier varies in any
respect other than amplitude from the waveshape of the signal feeding
the amplifier, the amplifier is distorting the signal.

The presumption (forced, or otherwise) is that the input is
sinusoidal. In fact, the cathode current of the amplifier proves
quite positively that only a pulse in, 120 degrees of the sinewave, or
even less, is sufficient to generate a remarkably clean sinewave at
the final's output.

Simply put, a pulse with a 33% duty cycle, and having sufficient
amplitude (and steep skirts) would present an output that was wholly
non-linear in relation to the pulse excitation. Looking only at the
output, you couldn't possibly say if the input was a complete 360
degrees of sine wave, or 33% DC of a rectangular wave. Not unless new
constraints are added that push the argument away from current issues.

To extend an analogy, the circular motion of the car's wheels prove
there is a non-linear relationship to the explosion of the gas mixture
in the compression cylinder.

Or to further decimate the argument, an oscillator produces as pure a
signal to no input at all (barring the excitation of noise that
engenders a selectively reinforced oscillation).

But the debate over linearity is window dressing to answering the
practical question:
What is the source resistance of any power amplifier?

I am not interested in the values that are NOT the source resistance.
I am content that those who have not responded to this specific and
observable characteristic don't know. However, given the thrashing of
this topic, someone (besides me) should.

73's
Richard Clark, KB7QHC