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

[Kenneth G. Gordon]

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