[AMRadio] Dentron Clipperton on am?..

Tue Apr 12 11:28:55 EDT 2011

With the magic 375 watts of carrier you don't gain a thing by inverting the
audio phase.

If you have unsymmetrical audio with positive peaks higher than negative
peaks here's what happens. 

With 375 watts carrier, with positive peaks hitting 100% positive
modulation, this will yield 1500 watts PEP, the legal limit. You will not be
hitting 100% modulation on negative peaks.

If you invert the phase with the same unsymmetrical audio and same 375 watts
of carrier you will hit 100% modulation on negative peaks, the most that you
can go, before you will hit 1500 watts PEP with the positive peaks.

Either way you have the same amount of modulation density (same audio
power).

100% modulation occurs when the modulation voltage is equal to the modulated
stage plate voltage. This is true for both positive and negative modulation
peaks.

You could lower the carrier power and increase the modulation to over 100%
on the positive peaks (while still staying below the 1500 watt PEP limit)
provided the negative audio peaks were lower and didn't cause over
modulation on negative peaks.

If you increase the amount of carrier you could increase the modulation on
negative peaks and not over modulate on negative peaks, but you would have
to decrease the positive peaks in order to stay under the 1500 watt PEP
limit.

Increasing or decreasing the amount of carrier (from 375 watts) will only
lessen the amount of power in the side bands, provided that you still stay
under the 1500 watt PEP limit and do not over modulate on the negative
peaks.

It would seem that aiming for symmetrical audio would have the most benefit.
This would give the highest percentage of modulation in both positive and
negative direction giving the most power in the side bands.

For those that wonder how PEP is found, you do so by adding voltages in the
carrier with the voltage in the applied audio. Since 100% modulation is the
doubling of the plate supply voltage which causes the plate current to also
double (2x2=4) this is where the 4 times PEP comes from.

73
Gary  K4FMX

> -----Original Message-----
> From: amradio-bounces at mailman.qth.net [mailto:amradio-
> bounces at mailman.qth.net] On Behalf Of Kim Elmore
> Sent: Tuesday, April 12, 2011 8:41 AM
> To: Discussion of AM Radio in the Amateur Service
> Subject: Re: [AMRadio] Dentron Clipperton on am?..
> 
> Thanks, Geoff!
> 
> Yes, it is interesting.
> 
> What I'm looking for amounts to a rigorous Fourier analysis of some
> of the things I see discussed. For example, does inverting the phase
> of the audio really change the power in the side bands? If so, by how
> much?
> 
> It's been awhile since I took time series analysis, but I think that
> all inverting the audio phase is multiply the entire Fourier series
> by -1. The signs are arbitrary, though, as long as the relative signs
> remain unchanged. So, because the power density is given by the
> square root of the sum of the squares (a Minkowski L2 norm for those
> so inclined) the power distribution across the spectrum remains
> unchanged.
> 
> I am quite ready to be shown my error, though. I'll try to make time
> to pull out my time series notes to check what I've written though.
> Again, I'm pulling it all out of rather dusty memory...
> 
> 73,
> 
> Kim N5OP (still working on getting the Globe Champ airworthy)
> 
> At 05:53 AM 4/12/2011, you wrote:
> >On 04/11/2011 08:42 PM, Kim Elmore wrote:
> > > Discussions like this are interesting and I hope not to open a can
> of
> > > worms, but I think the proof of any assertion like this lies within
> > > some estimate of the actual power in the side bands. That's where
> any
> > > signal that we want lies and it's what is detected. Has anyone done
> > > an analysis to show that more power is in the side bands one way
> than
> > > another? Any spectrum analysis or spectrum analyzer displays?
> > >
> >
> >There's some good discussion on this, Kim, at
> >http://www.qsl.net/wa5bxo/all-about-modulation.htm and at
> >http://www.qsl.net/wa5bxo/amtech.html
> >
> >Very interesting reading.
> >
> >73 = Best Regards,
> >-Geoff/W5OMR
> >
> >
> >
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