[AMRadio] Schematic Needed

[Donald Chester]

>...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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