[ARC5] AM modulating an "ARC-5" transmitter...

[Richard Knoppow]

    Supermodulation AKA Taylor modulation had a spurt of popularity in 
the late 1940s.  You are correct that many transmitters are capable of 
higher than 100% upward modulation and, I think the phase flopper in the 
old CBS Volumax (or maybe Audimax) was designed for achiving this 
consistently on speech which is generally non-symmetrical.  However, one 
can not do it without producing distortion. In fact, it is a form of 
partial carrier suppression and will increase distortion at the receiver 
unless used with some form of product detector or synchronous detector. 
There was a thorough analysis of its use in ham radio in _QST_ December 
1950, p.33
_"Supermodulation"-- An Evaluation and Explanation_  Oswald G. Villard 
jr.  This is worth reading and is available for ARRL members via the QST 
web site

On 10/10/2015 4:10 PM, Kenneth G. Gordon wrote:
> On 11 Oct 2015 at 11:44, AKLDGUY . wrote:
>
>> Surely the peak power is the absolute limit for 100% modulation.
> Hmmm....I think I would say, rather, the peak-power-capability of the output
> device. Then I would say, "Yes".
>
>> It doesn't matter whether the modulating waveform is a sine wave,
>> speech, square wave, or anything else. Cross that 100% line and
>> you're overmodulating and into the realm of distortion.
> Generally correct,  but always so in the negative direction.
>
> There are common ways of increasing "positive" modulation to well above
> the 100% level, but there is no way to do so in the negative "direction". Even
> with greater than 100% modulation in the positive direction, one must be very
> careful not to exceed the capability of the modulated stage or serious
> distortion will result.
>
> BC stations routinely use up to 125% positive modulation. In fact, the FCC
> specifies this as a certain "limit".  But no one can modulate more than 100%
> in the negative direction. The stage cuts off, and very serious distortion
> results.
>
> Years ago, before SSB, I did some serious study of "SuperModulation"
> methods. Some were quite ingenious. The broadcast industry uses modifed
> versions of some of those methods.
>
>> It's average power, not peak power, that is determined by the
>> modulating waveform.
> Well, I would say both are affected by the modulating wave form. To me,
> peak power is more a function of the capability of the amplifier in question,
> along with its power supply. One can achieve a certain peak power with any
> mode, even CW, and that peak power is a function of what I stated above,
> and includes drive level, amplifier capability, etc.
>
> Total average power is most definitely and primarily a function of waveform.
>
> We may be talking about the same things here, using different viewpoints
> and differing language, but even so, I think I know what you mean. I think we
> are agreed.
>
> Ken W7EKB
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL