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!
