[AMRadio] Dentron Clipperton on am?..

[Gary Schafer]

Hi John,

If you have a 375 watt carrier and symmetrical audio, both positive and
negative peaks equal, then you should reach 100% modulation on the negative
peaks at the same level as you reach 100% modulation on the positive peaks
and also reach the 1500 watt PEP legal limit.

If you start out with the carrier at 375 watts and your audio is
unsymmetrical, positive peaks greater than the negative peaks. If you were
to modulate 100% in the negative direction, just reaching carrier level,
then you would be modulating greater than 100% in the positive direction and
your Peak Envelope Power (PEP) would be greater than the 1500 watt limit.

If you then reversed the phase of the audio so that the negative peaks were
greater than the positive peaks and increased the carrier so that those
negative peaks did not cause greater than 100% negative modulation you would
be ok there. But as you increased your carrier power that would also add to
the PEP on the positive side. 

PEP is the sum of the carrier voltage and the audio voltage. 

If you want to maintain legal limit and not over modulate, you have a brick
wall at the top (PEP limit) and a brick wall at the bottom (over modulation
on negative peaks).

But my point is that with 375 watts of carrier and maintaining legal limit
on the positive side and not over modulating on the negative side, you will
come out with the same amount of audio if you have higher negative peaks or
higher positive peaks. At legal limit you gain nothing by increasing or
decreasing the carrier. Your best bet is to run 375 watts of carrier.

73
Gary  K4FMX


> -----Original Message-----
> From: amradio-bounces at mailman.qth.net [mailto:amradio-
> bounces at mailman.qth.net] On Behalf Of John Coleman
> Sent: Tuesday, April 12, 2011 3:15 PM
> To: 'Discussion of AM Radio in the Amateur Service'
> Subject: Re: [AMRadio] Dentron Clipperton on am?..
> 
> I agree with you Jim on the 375 watt output is safe in just about all
> cases.
> 
> To answer someone else's question about SB power of AM when an
> asymmetrical
> modulation envelope is inverted.
> 
> 	It is easy to understand in a high-level modulated rig.
> If you look at the plate voltage while it is modulated you can see what
> is
> happening.
> IF the modulation level, audio drive, modulator output power, whatever
> you
> want to call it, is the same in either case, and you don't over modulate
> (send the plate voltage negative on a spike),then the sideband power is
> the
> same. The asymmetrical wave of audio is short time on the spikes and
> long
> time on the lower level stuff. So even though the tall spike is a high
> peak
> power its average power is the same as the lower level part of the wave.
> The lower level part of the wave has a lower voltage but is there for a
> longer time so over the whole wave envelope it makes no difference as to
> whether the wave is inverted or not, it still has the same average power
> of
> audio and side band power
> 
> 	But here is the difference.  If the audio is asymmetrical and you
> are modulating a rig at the 100% level on the wide troughs of the audio
> wave
> almost pinching the carrier, and perhaps tripling the voltage on the
> spikes
> peak, and then you invert the audio you will clip the carrier
> (overmodulate).  This is easily compensated for by raising the plate
> voltage
> on the final amp until the now downward going spike is no long over
> modulating.  You will be increasing the carrier level while keeping the
> audio level the same.  The carrier power will go up but the sideband
> power
> RF will still be at the same level that it was before inversion. And the
> PEP
> power of the rig will still be the same even though the carrier power is
> greater.
>