That's not necessarily the case.. if the amplifier has variable bias and
drain voltages that adjust to what's needed for the match, you can
optimize the efficiency at all powers. A simple design with fixed
Vdd/Vcc, yes, you'll have a bigger power supply and efficiency will be bad.
That scheme works if the load is resistive and other than 50 ohms, like
100 ohms or 25 ohms. Unfortunately, it doesn't work if load is
partially reactive, like 50 + j50 ohms. That is a power factor problem
and there is simply no way to get good efficiency other than tuning out
the reactance AFAIK. One could imagine a hybrid
system where there was a rudimentary tuner that only tuned out the
reactive component, and then the scheme you suggested dealt with
the resistive component not being 50 ohms. By the time you jump
through all those hoops, again, it appears to make more sense to
have an amplifier that just amplifies and a power supply that just
puts out 48V and a tuner that just tunes.
If you have something better in mind, please educate us.
Rick N6RK
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