[AMRadio] Side band power with increased carrier/was clipperton on AM

[Geoff Edmonson]

On 04/13/2011 08:01 PM, Gary Schafer wrote:
> If you read Johns article carefully and reread what I wrote you will see
> that when he uses 660 watts carrier and 1500 watts PEP with his 2:1
> asymmetrical modulation,

you mean 3:1 SR, right?

> that is very close to what I describe using 750
> watts. Although I used a symmetrical sin wave and found the power in each
> side band to be around 40 watts with 750 watts of carrier and 1500 watts
> PEP.
>
> If you look at the top of the waveform on John's picture of the inverted
> modulation you will see that the average modulation power is only on the
> very top of the waveform. Also doing the calculations there it would also
> give modulation power of around 40 watts in each side band.
>
> With his signal not inverted and running 165 watts carrier in order to
> accommodate the 2:1

3:1

> wave form, modulation power in each side band and also
> hit 1500 watts PEP that would also be around 40 watts in each side band
> modulation power.
>
> By the way his SR index of 3 is the same as a 2:1 ratio.

Negative.  The definition of SR *is* the Symmetry Ratio.  In Johns case, 
his asymmetrical audio (and thus the reason for his building up four 
813's in push-pull parallel) is *3*.   That means, that setting the 
carrier envelope on the scope to consume 2 divisions on the graticule, 
you'll see the positive peaks reach a peak of 6 divisions, and not go 
beyond the base-line negative.

6:2 reduces to 3:1

As an aside, *my* voice is more peaked than John's.    With a Sure 55-S 
microphone, a 31-band equalizer, a modified 100w Bogen audio amp, the 
solid-state Class-B driver, 60Hy of Modulation Reactor with audio 
coupled with 9uF @ 5,000VDC of coupling capacitance, I see on my scope 
an SR of 4.

My rig is plate modulated, running a pair of 250TH's in the final, and 
another pair of 250TH's in the modulator.  I typically don't run more 
than 150w of carrier, and if I -really- wanted to pour the coals to the 
audio, I'll run double the voltage on the modulators.  That's somewhere 
in the neighborhood of 1500vDC on the final, and 3kV on the modulators.  
Generally, I run 1500v on both, and 0v bias at 1500v on 250TH's in Class 
B draws around 220mA of current.  That's 330w of Power in the modulator, 
-at rest-

With an SR of 4 (with the B+ high on the modulators) 100w carrier will 
modulate to 1600w PEP.

Then again, the definition of Peak-Envelope-Power is:

      Peak envelope power is the /average power/ supplied to the
      antenna transmission line by a transmitter during one radio
      frequency cycle at the crest of the modulation envelope,
      under normal operating conditions.


>> *Here's the math:
>> PEP = ((peak-to-peak modulated RF voltage / un-modulated carrier
>> voltage) squared) * un-modulated carrier power *
>>
>> *    This large PEP can occur without negative over modulation, if the
>> modulating audio is acquired by a voice from a microphone. Microphone
>> audio is generally asymmetrical. *
>>
>> *    To help me understand and explain the relationship between audio
>> and purity of modulation, I've defined a function, which I call Symmetry
>> Ratio (SR). *
>>
>> *Symmetry Ratio (SR) defined: *
>>
>> *SR = (Peak-to-Peak audio voltage) / (lesser of the two Peak Audio
>> Voltages above or below the quiescent line)
>> SR = 2 if the signal is a Pure Sine Wave
>> SR cannot be less than 2 *
>> _______________________________________
>>
>> This, as a result of John's discovery that his natural voice, as viewed
>> on a scope, is asymmetrical, by an SR of 3.
>>
>> Voice patterns are complex waveforms, very dissimilar to a single tone.
>>
>> An analogy could be drawn from watching the ripples in a pond of water,
>> after a rock is thrown into the center of it.  Further away from the
>> point of impact, the waves are symmetrical.  However, at the point of
>> impact, the water is -very- asymmetrical.  Quite disturbed.  Voice waves
>> hitting a microphone diaphragm act the same way.
>>
>> The whole explanation, with drawings and diagrams, is available at
>> http://www.qsl.net/wa5bxo/asyam/aam3.html

73 = Best Regards,
-Geoff/W5OMR