FW: [AMRadio] Ranger... good news, bad news


Jack Schmidling jack at schmidling.com
Wed Nov 8 23:05:50 EST 2006


Gary Schafer wrote:

> The peak envelope power of an AM signal increases by 4 times over the
> carrier power with 100% modulation.

We speak of peak envelop POWER but a scope is actually displaying peak 
voltage.  How do we relate this to 4 times carrier on a scope?

> The linear amplifier must be tuned at the peak envelope power level or the
> peaks will never reach full power, the amplifier will flat top and splatter
> and you will not sound good.

I still do not understand.  The final is tuned with a tank capacitor and 
a loading cap.  On my amp, the optimal positions of these knobs only 
change with the frequency is changed.  Changing the input level does not 
effect this tuning in any way that I can see.

> How much drive power did you have when tuning up the amp?

Anywhere from 15 to 80.

> Were you using a rice box to tune the amp or the ranger?

Either... both.

> If you don't see the scope voltage double with modulation you haven't tuned
> up right. If you adjust the scope to say 2 centimeters with carrier then the
> modulation peaks should hit 4 centimeters.

Ok... that answers the first question.

However, today I changed the rf pickup from a loop on top of the tuner 
to a wire just running off away from the rig.

Bottom line is, that it now looks like 100% modulation.

js
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