On Sat, 13 Mar 2004 16:26:10 +0000, Paul Burridge
wrote:

On Sat, 13 Mar 2004 10:00:52 +1000, Tony wrote:

The 5th harmonic should be only 14dB below the fundamental, although it will
drop fairly quickly as the sides of the input square wave deviate from vertical.

Does the 3.44MHz have a 50% duty cycle?

Okay, I've now tweaked the osc. to get as near to 50% as possible.
Alas, still no sign of any 5th present in the multiplier's output.
Here's a shot of the (fundamental) output from the inverters. I can't
see any real problem with why it shouldn't be good for a reasonable
comb of harmonics, but our experts may know better. BTW, settings were
2V/div. and 0.1uS/div.

http://www.burridge8333.fsbusiness.co.uk/trace.gif

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

This other trace was snapped at the base of the transistor stage that
does the multiplying. All there is (circuitry-wise) between this trace
and the last one is a 330 ohm series resistor and a 47pF cap. I'd have
expected to see some clamping action due to the b/e junction, but the
waveshape seems very odd - but does concur with the Spice simulation.
Is there anything amiss, here? (Setting here is 0.5V/div)

http://www.burridge8333.fsbusiness.co.uk/trace2.gif

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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.

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

Still not a sniff of a fifth! :-(
Currently building Reg's 17.2Mhz BPF to see if that can expose it.

---
That'll probably do it, but it needs to go on the output of the
multiplier, not between the square wave generator and the input, I
think.

Again, why don't you post a schematic of what you're up to? Please?-)

--
John Fields