Paul Burridge wrote in message . ..
....
What leads you to believe I have enough 5th harmonic in *my*
particular case?

The trace on the web site you provided a link to. The fact that
you're using HC logic (which has inherent rise and fall times rather
faster than the square wave source I used in my experiment). Your
avering that the duty cycle is very nearly 50%. That's not to say you
aren't doing something to kill it, but it's NOT difficult to extract
it. Note that the subject you put on this thread really nails it:
all you need to do is extract (and possibly amplify, depending on the
final power level you need) what's already there. Now go do it. But
feeding the whole square wave to the amplifier stage is a BAD idea
because you can inadventently change the duty cycle (as seen at that
amplifier's output) to one where the fifth is nulled. If you only
need a few milliwatts, you can get that from the square wave directly,
if the source impedance is low enough, simply by using the proper
filter.