...I would rather be clean & linear right up
to the overload point. I usually use some form of negative cycle
attenuation
(not loading) to keep the carrier power above zero though.
"Ultra Modulation" is nothing more than a form of controlled carrier with
some even-harmonic distortion thrown in. The increase in carrier level is
accomplished by increasing the average DC plate voltage to the final. Where
does this increased voltage come from? From rectifying some of the audio
output from the modulator. The ultramodulation process attenuates the
negative half of the audio cycle using a voltage divider. This modification
of the sine waveform results in substantial even harmonic distortion. The
plate current meter will show an increase under modulation, and if you put a
DC voltmeter on the B+ line to the final, you would see that the DC plate
voltage increases, too. When I tried ultramodualtion, making an A-B
comparison with conventional audio, the reports I got were that
ultramodualtion made the audio sound a little raspy, but was not really any
louder. I suspect the distortion leaves the false impression that the audio
has more "punch"... the audiophools love it.
Using the same modulator minus the ultramodulation circuitry, one can
achieve the same positive peak percentage of modulation by taking advantage
of the natural asymmetry of the human voice. Just make sure the polarity of
the audio feed is correct, and that every stage of the audio chain is
capable of handling the audio peaks generated by your voice. Of course, as
with ultramodualtion, the modulator must be capable of the peak audio output
power capability necessary to modulate in excess of 100% in the positive
direction. Otherwise, you just get flat-topping on the positive peaks
resulting in splatter and distortion.
Don K4KYV
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