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!
