On Sat, 13 Mar 2004 12:50:42 -0600, John Fields
wrote:

That's close enough to 50% that you should have no problem generating
and extracting a fifth harmonic.

Thanks, John. I'd have been surprised if having tweaked it for maximum
50:50 this still wasn't good enough (it's only a tiny bit out now).

If you've got the cap and resistor in series with the base, and no other
circuitry in there, then what you're doing is half-wave rectifying the
square wave in the base-to-emitter diode, and that's what you're seeing,
along with what looks like some AC at the fundamental riding on the
falling peaks and rising valleys of the square wave. The reason you
can't see the fifth harmonic is because it's far enough down that
everything else is so much higher in voltage that it's essentially down
in the mud. If you want the fifth out, you'll have to extract it using
a filter of some sort, the easiest being a series tuned trap or a
parallel tuned tank.

I've lashed up a 17.2Mhz BPF that should do the trick just fine. It'll
be a bit of a fiddle trying to hook it into the existing circuit but
I'll do my best.

Why don't you post your schematic so we can see exactly what you're
doing?

Will do....
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