[AMRadio] AM power

[Gary Schafer]

Sorry for the misspelled name Geoff. 

It sounds like you have your transmitter set up to never reach 100%
modulation on positive or negative peaks. That's ok too.

But there are two different 100% areas to be concerned with. The positive
and the negative. If your transmitter output voltage doubles on positive
peaks, that is 100% positive modulation and is what you are concerned about
for measuring peak envelope power. It does not matter that your negative
peaks never hit 100% on the negative side. You still calculate PEP with
positive modulation  peaks.

If you do not hit 100% modulation on positive peaks you still calculate PEP
by the sum of the carrier voltage and the audio voltage. Yes you can run a
higher carrier power with lower audio power and still stay under the 1500
watt PEP limit. But the most effective level is 375 watts of carrier. Not
higher and not lower.

If your audio is unsymmetrical then you are being penalized by not being
able to run as much audio power as you could if it was symmetrical. 

It would probably help to run a processor that turned your audio into a more
symmetrical form.

73
Gary  K4FMX

> -----Original Message-----
> From: amradio-bounces at mailman.qth.net [mailto:amradio-
> bounces at mailman.qth.net] On Behalf Of Geoff Edmonson
> Sent: Saturday, June 18, 2011 11:08 PM
> To: Discussion of AM Radio in the Amateur Service
> Subject: Re: [AMRadio] AM power
> 
> On 06/18/2011 09:55 PM, Gary Schafer wrote:
> > Jeff,
> 
> My name is Geoff.  With a G e o f f.
> 
> > An easy way to prove this to yourself: set your scope on the output of
> your
> > transmitter for say 2 divisions of carrier.
> 
> Seems I'm the one that told you I -did- this.  That's why I KNOW I've
> got a voice with an SR of 4, when there's proper voltage on the
> modulators.
> 250TH's, in Class B,  like ~3000VDC.  I run about half that and 0 bias.
> At that level, there's 220mA of resting current.  There's not enough
> voltage to properly modulate the final - the positive peaks are kinda
> rounded off, they don't reach, but with an SR down to 3 (instead of 4) I
> can run the carrier up to around 200w.
> 
> 
> > Then modulate it with a single
> > tone until the voltage on the scope doubles (4 divisions). That is
> 100%
> > modulation I am sure that you would agree.
> >
> > Now remove the single tone and modulate with your voice until the
> voice
> > peaks hit the same 4 divisions on the scope. You are now modulating
> 100%
> 
> what you're not getting, Gary, with the proper voltage and everything
> running the way it should on my rig, when I DO hit the same point on
> positive voice peaks as the single-tone, the negative peaks aren't
> anywhere -near- the baseline of the carrier.  That is -not- 100%
> modulation.
> 
> 
> 
> 
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