Hello Gary,
Isn't that 50% difference only true because we cause it to be tuned that
way? We could tune it to be more or less different between carrier and pep
but we cause it to be 50% for the sake of AM linearity.
If we didn't cause the 50% difference in class A or any case, wouldn't that
mean the AM signal was not amplified linearly? Not that it would
necessarily be a bad signal. In fact, we can affect modulation percentage
through the amplifier if other limitations are observed.
This class A RF thinking is different.
Jeff/KA5MIR
> Using a class A amp as an AM linear I don't think the 50% efficiency
> change rule applies as it does with a class B linear amplifier. With a
> class B amplifier the efficiency difference between maximum peak envelope
> power output and carrier output is right at 50% difference.
> In other words if the efficiency of the class B amp is 70% at maximum PEP
> then it will be 35% efficient at carrier power level of the AM signal.
> (carrier at 1/4 power of PEP)
>
> With class A amplifiers I think it is stated that the efficiency must not
> exceed 50% of full output efficiency but it can be less, and by looking at
> the fact that plate input power does not change at all from zero power out
> to maximum power out on a class A amp the efficiency would not be a 50%
> change but something greater.
>
> In the original example of 25% efficiency at full output (maximum PEP)
> then carrier output efficiency would be 6.25% with the class A amplifier.
> It would also seem that that % would change with a class A2 amplifier
> slightly because grid current would only flow on modulation peaks.
>
> 73
> Gary K4FMX
>
>
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