[AMRadio] AM power

[Gary Schafer]

Hi Geoff,

You are doing exactly what I have been describing. 
You are reducing your carrier power down to the point where the sum of your
positive audio peaks and the carrier equal 1500 watts PEP. (1600 in your
case).

But in doing so you are running less carrier power AND less average audio
power so you have less average power in the side bands than you would if you
got rid of those high asymmetrical peaks. Then you could run the carrier
power and average audio power up and still stay under the 1500 watt PEP
limit. 

And guess what? With symmetrical audio you could run 375 watts of carrier
and fully modulate 100% on positive and negative peaks and not exceed the
1500 watt PEP limit.

73
Gary  K4FMX

> -----Original Message-----
> From: Geoff Edmonson [mailto:w5omr at att.net]
> Sent: Sunday, June 19, 2011 6:26 AM
> To: garyschafer at comcast.net; Discussion of AM Radio in the Amateur
> Service
> Subject: Re: [AMRadio] AM power
> 
> On 06/18/2011 10:29 PM, Gary Schafer wrote:
> > 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.
> 
> No.. that's an incorrect statement.  I can crank the gain up and have
> the transmitter look like a CB radio with a pre-amplified mic and a
> leen-yer, with spikes on the positive side, and gaps in the base line
> where the negative peaks have extended far beyond the baseline.
> 
> > But there are two different 100% areas to be concerned with. The
> positive
> > and the negative.
> 
> Right.  Maintaining just slightly less than 100% negative will keep the
> carrier and audio clean.
> 
> Let the positive peaks reach up to wherever they want.
> 
> > 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.
> 
> A 375w carrier is a myth, for obtaining 1500w PEP output.
> 
> > 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.
> 
> The opposite is true, Gary.  I can run 100w of Carrier with full voltage
> on the modulators, see a 4:1 ratio between positive and negative peaks.
> Let me say this again;
> a ratio of 2:1, with a 100w carrier, will produce a PEP level of 400w.
> a ratio of 3:1, with a 100w carrier, will produce a PEP level of 800w
> a ratio of 4:1, with a 100w carrier, will produce a PEP level of 1600w
> 
> 
> 
> > It would probably help to run a processor that turned your audio into
> a more
> > symmetrical form.
> >
> 
> Why would I want to limit the effect of 'loudness' of my audio, while
> maintaining the cleanness of my carrier?