> > As I understand it, Mr. Maxwell asserts that linear amplifiers are
> > conjugately matched. If this is true, the efficiency could not
> > exceed 50%.
>
> OK. You are correct Rich. If conjugate match occurs, then an equal
> amount of power is absorbed by both source and load - hence the 50%
> efficiency.
That is not correct, although it has crept into recent texts. I think
that concept comes from taking a Thevenin model literally, as an
actual circuit with a dissipative resistance in series with a source.
It's unfortunate that electrical engineers used the same term
(resistance) to describe the ratio of across-to-through vectors as
we use to describe the characteristics of a resistor.
Even more unfortunate, we now are assuming a Thevenin model is
actually the real world system with a dissipative resistance.
I did load pulls on class C PA's with more than 70% efficiency, and
the load-pull indicated a conjugate match (50 ohm source) when
efficiency was maximum. There is nothing that says PA's must be
operated at a conjugate match, just like there is nothing that says
efficiency is only 50% when the PA is conjugately matched.
It isn't that difficult to measure a PA and prove this, yet most
people spend far more time arguing than measuring.
73, Tom W8JI
W8JI@contesting.com
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