> What Jeff recommends is adjusting the
> impedance matching
> device and/or the power setting so as to optimize the
> efficiency. In other
> words, get more power to the antenna and reduce the amount of internal
> heating. It may turn out that the point of optimum efficiency
> is not at the
> rated power output setting.
That's kinda what I was saying. You'll always be able to tune the Z-matcher
to find the load Z that yields the best efficiency *at whatever power level
you're targetting* (assuming the Z-matcher is able to yield that optimum Z),
but what that efficiency is (as a ratio of RF out to DC in) is going to
change depending on what power level you're targetting..
In the purest sense, if I'm understanding what Eric is saying, there will be
some power level at which the true maximum efficiency of the amplifier can
be found. That power level isn't necessarily (or likely) the power level
you're planning to operate it at. The PA may be 30% efficient at 50 watts
when the Z-matcher is optimized at that power level, 35% efficient at 75
watts when matched at that level, 40% efficient at 100 watts, etc. Chances
are you'll find the maximum efficiency lies close to, or possibly a bit
above, the rated output level. But that doesn't mean that the *dissipation*
is lowest at the power level that yields the best efficiency! It just means
that the ratio of RF out to DC in is at its peak efficiency, not that the
dissipation is at its minimum.
Did that make sense, or just confuse things?
--- Jeff
