John wrote:
Interesting idea, Johan, but I believe you'll find that if you drive the
amplifiers with a sinewave, there is an efficiency penalty; whereas, if you
drive them with a square wave, you actually have made a PWM modulator.
Yes and yes.
I meant square wave drive (class D).
My idea was to combine the modulator and the P.A. in the same stage.
This would eliminate the need for a separate PWM modulator in the
P.A. power supply.
The switching waveform will look a bit "spikey" at low output power. Worst case
is when the output power is close to zero, the signal will look like a train of
impulses
with alternating polarity. I guess the spectrum will then contain all odd
harmonics
at the same amplitude as the fundamental, limited only by the switching times.
Assuming a Q of 6 in the series resonant output circuit (typical value, I
think), this
circuit alone would attenuate the 3f component by 24dB. Not too bad.
73
Johan SM6LKM
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