Dear Stefan,
thanks very much for sharing this very useful
design!
Just in case you would like to extend this to
linear modulation: The H-bridge topology
naturally lends itself to the Outphasing technique (aka "Chireix" modulation",
"Ampliphase", "LINC"), which was invented in the 1930ies to increase
AM transmitter efficiency. The idea is to drive the two half-bridges separately
with a variable phase difference: 180° gives full power, 90° gives -3
dB, and 0° gives no differential output across the load.
Instead of generating the two carriers by
special envelope-driven phaseshifter hardware, you could
also take a software approach through the two outputs of a stereo
soundcard. It may then be best to feed the PA
drivers directly, avoiding the dividers which can introduce an unwanted 180° ambiguity.
If you feel like trying this concept, I could be
persuaded to adapt the Chirped Hell software for this purpose. What day is
your birthday? ;-))
Best regards,
Markus (DF6NM)
PS: In case you decide to use small audio
transformers at the input, make sure their insulation can safely withstand the
line voltage!
