Antonio Vernucci wrote:
Usually, when a transmitter is tuned for maximum output power,
efficiency results to be higher than 50% (typically 60% for class-B,
70% for class-C). This would seem to contradict the above cited fact
that, under maximum power transfer condition, efficiency is 50%.

The maximum power transfer theorem only applies to
linear sources. What is the linear source impedance
of a class-C amp?
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73, Cecil http://www.w5dxp.com