> It doesn't matter what the amplifier efficiency is. The
> carrier efficiency
> for good linear AM, carrier efficiency will be exactly 1/2
> of the PEP
> efficiency if the amp is set up properly to just handle
> 100% modulation
> peaks. To handle greater than 100% peaks carrier
> efficiency has to be less
> than 1/2 of PEP efficiency.
> Carrier output power will be 1/4 of PEP output power when
> set up for 100%
> modulation peaks.
Why not measure the efficiency of a few class AB amplifiers
when peaked at some maximum envelope power and then again
with drive reduced to 1/4 output power.
I think you will change the word "exact" to "around".
It's certainly very close to half in a class B stage, and in
the ideal theoretical case it is half, but it is an
imperfect world. As a matter of fact the PA can be very
non-linear so far as transfer characteristics and not have
prohibitive distortion, or one with more linearity in
transfer characteristics might have more objectionable
It's all about the shape of the slope in this imperfect
world, and even the class of the amplifier.
For example, I can have a class A amplifier and the input
power won't change a bit between carrier and modulation
peaks. A pure ideal class B will behave as you suggest. A
class AB amp can be anywhere in between, and in the real
world we might have to even overload the amp a bit to
The rule efficiency doubles is generally a good guideline,
but it isn't an *exact* rule any more than we can say any
gain compression or operation where non-linearity occurs
always produces objectionable distortion. Our amps are
between class A and B, and they don't have perfect transfer
characteristics. They also, especially on six meters with
big tubes, can have pretty lossy tanks.
It's like saying the tank Q has to be 12.
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